It's been a busy week for music - my jazz band performed three times in eight days. One tune especially satisfied the requirements of this blog quite nicely: "Inchworm." Jazz aficionados will recognize this tune as a Coltrane standard.

But I never liked the fact that Coltrane only played one of the two counter-melodies in the song, which originated from the movie musical "Hans Christian Anderson," starring Danny Kaye. The song starts as children in a school house chant addition in a rather haunting melody, which Kaye then sings against as he watches a caterpillar crawling on a plant. (See the scene on YouTube here, and the more complete version of the song with the muppets - including muppet inchworm - here.)

So, I did a new jazz arrangement that includes both melodies. In addition to the sung counter-melodies, there is a third counter-melody in the strings that I decided to add to the jazz version as well. Thus, with three saxes and two vocalists, we covered it all.

"Inchworm", by the way, is the common name for moths in the family Geometridae, of which some in Hawaii are sit-and-wait predators. But the family is cosmopolitan, and recognizable in the caterpillar because unlike other families they only have prolegs at the back end of their abdomen, resulting in their distinctive inching walk. Many species are also known as "loopers" for the same reason.

Labels: cool bugs, insects, jazz, music

The mountain pine beetle (Dendroctonus ponderosae, Coleoptera: Scolytidae) is native to western North America. A finer resolution of its range, however, reveals that it is historically native to some parts of the West, but not others. Specifically, it has generally had a limited presence in Canada, primarily due to very low winter temperatures. Although the pine beetle's cold tolerance is incredibly high because they have the anti-freeze compound glycerol in their bodies, generally sustained (5 or more days) temperatures below -30F kill most of them off. This has reduced the likelihood of mountain pine beetle outbreaks in Alberta, and thus susceptible trees there have historically been protected, but are now exposed and being attacked (Rice et al., 2007).

In the last 5-10 years, however, conditions in the West, including Alberta, have changed. Rising temperatures have meant that for several winters in a row, the northern Rockies have not reached low enough temperatures to kill off the mountain pine beetles infesting the trees there. Even in the U.S., the historical trend was that every few years most of the beetles are killed due to cold, and thus the outbreaks were knocked back. So the pine beetles, which are a native species, have begun behaving like an invasive one: they are multiplying rapidly without a natural check, and expanding their range, attacking populations of trees that are not adapted to them.

Compounding this problem is the recent history of fire suppression in the West. One of mountain pine beetle's favorite hosts, lodgepole pine (Pinus contorta) is a fire-adapted species; it is common for lodgepole stands left undisturbed to burn once or twice a century, and be replaced by seeds from serotinous cones (cones in which the seeds are sealed unless they reach the high temperatures of a fire). Lodgepole stands are striking in that usually all the trees are the same age and size due to the burn regimen. Mountain pine beetles prefer older, larger trees. The larger the tree, the more food available for the developing beetle larvae, and the larger the increase in population the next year, if there is not a sustained hard freeze. By suppressing natural fires in lodgepole habitat, we may have enhanced the long term outbreak we are seeing now.

But here's the flip side: mountain pine beetle outbreaks make lodgepole pine stands more susceptible to fire down the road (Page and Jenkins, 2007). For instance, the 1988 Yellowstone National Park fires were highly correlated spatially with trees affected by a mountain pine beetle outbreak about fifteen years before (Lynch et al., 2006). What we may be experiencing now is a mega-outbreak, due to warming and fire suppression, which will eventually contribute to massive forest fires throughout the West in the future (also increasing of course from drier weather), which may have the benefit of being a different kind of check on mountain pine beetle populations. But instead of the historical ecology, in which mountain pine beetle outbreaks occurred for maybe 3-4 years, decades apart, a whole new, different ecology driven by constant high beetle populations decimating the forest, which as a result may burn more often, will remake the landscape in ways that we cannot yet imagine.

Of course there are those who believe that we can replicate the ecological benefits of fire, while keeping the timber available for human use. However, thinning trees mechanically is a blunt instrument that does not mimic the effects of fire at all in the case of lodgepole (Sibold et al., 2007). In fact, there is the danger of unintentionally increasing the density of trees (and necessitating, further, constant thinning effort) if enough of the canopy is opened to encourage new seeds to germinate and grow. There are those who believe humans are all powerful and can easily control insect outbreaks and fires through management if only the wicked, meddling environmentalists would let them (never mind that somehow the forests managed themselves just fine for millennia). In fact, many species are adapted to respond to biotic (e.g. herbivory pressure) and abiotic (e.g. weather) influences in ways we don't even understand. Global climate change is now accepted by anyone rational to be at least partly enhanced by the massive release of carbon dioxide into the atmosphere by industrial humans that would not have occurred otherwise. Fire suppression is an active (and expensive) choice that trades short-term convenience for long-term ecological disruption, whose consequences we are barely beginning to understand. Those who blame "environmentalists" for the hundreds of acres of brown pines they see spreading like a cancer in the West, would find that ecologists (pretty much environmentalists by default) only wish they had such god-like power to affect the ecology of our forests, so they could save them from 150 years of disastrous "management."


References

Lynch, H.J., Renkin, R.A., Crabtree, R.L. & Moorcroft, P.R. (2006) The influence of previous mountain pine beetle (Dendroctonus ponderosae) activity on the 1988 Yellowstone fires. Ecosystems, 9:1318-1327.

Ono, H. (2003) Mountain Pine Beetle Symposium: Challenges and Solutions. Kelowna, British Columbia. T.L. Shore, J.E. Brooks, and J.E. Stone (editors). Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Information Report BC-X-399, Victoria, BC. 298 p.

Page, W.G. & Jenkins, M.J. (2007) Mountain pine beetle-induced changes to selected lodgepole pine fuel complexes within the intermountain region. Forest Science, 53:507-518.

Rice, A.V., Thormann, M.N. & Langor, D.W. (2007) Mountain pine beetle associated blue-stain fungi cause lesions on jack pine, lodgepole pine, and lodgepole x jack pine hybrids in Alberta. Canadian Journal of Botany-Revue Canadienne de Botanique, 85:307-315.

Sibold, J.S., Veblen, T.T., Chipko, K., Lawson, L., Mathis, E. & Scott, J. (2007) Influences of secondary disturbances on lodgepole pine stand development in rocky mountain national park. Ecological Applications, 17:1638-1655.


Thanks to T. Etienne for initial information on mountain pine beetle

Labels: ecology, environment, forests, insects, invasive species

Certain institutions exist in order to have a place to put those people who one way, or another, are on the fringes of society. For example, the NBA and WNBA provides a community where otherwise freakishly tall people fit right in. Academia provides a community where people missing some normally important life skills can find a comfortable home. There is one important difference between these examples, though; when a basketball player retires, he (or she) can do so with a decent amount of money and the continuing worship of adoring fans. When a professor retires, he (or she) actually doesn't, really, because he doesn't have any money. That's usually OK, though, because he gets to continue his life's passion, research on a field so narrow, he is the world's only expert.

The problems start when retired professors attempt new life pursuits after retirement. Evert Schlinger, a retired professor of entomology, made the mistake of trying a second career managing a foundation, with disastrous results.

Although it may seem hard to believe to those living in the real world, it is probable that Dr. Schlinger was foolish and naive rather than deliberately engaging in fraud that ended up losing nearly all of his foundation's money. Although he is implicated in a pyramid scheme, it is quite possible that he had no idea what a pyramid scheme was at the time. It sounds like he was an easy mark for crooks who wanted to make off with the foundation's money, and leave him holding the bag (one of his financial "advisors" is filed under "whereabouts currently unknown").

There is a reason that certain people become entomologists and others become kingpins of the financial world. Entomologists are at their best tramping through jungles looking for tiny creatures. Insects are elegant beasts, thrilling to watch and holding keys to many of the mysteries of life. They are not out to get us (despite what the layperson might believe). In contrast, the world of finance is not only complex but bewildering at times, and if you are lucky enough to have the millions to start a foundation, there will be people waiting in line to try and take your money away. The world of insects has nothing to do with money (apart from the funding needed to seek them out). It is a world of interlacing webs of ecological interactions that no matter how much we discover, will always hold more mysteries for the human mind to delve into. Entomologists will never be burned by entering the world of the insect, only fascinated and delighted over and over again.

So do not condemn Dr. Schlinger as a shyster or a fool. In his world, he is king. We need to remember that some of us need protection from some of the harder realities of human interaction, because we are focused instead on the interactions among a multitude of species that are simply far more interesting. If Dr. Schlinger was able to transmit his enthusiasm for his world to some students who will also see beyond the minutiae of day-to-day maneuvering, then he has done more than his job.

Labels: insects

Acacia ants, in the genus Pseudomyrmex, and their acacia tree hosts, are a terrific example of coevolution between plants and insects. While yellow flowers and many species demonstrate a loose form of the coevolution between generalized pollinators and a large range of plants, the coevolution in this case is very specific, although there are other examples of Acacias with ants that have a looser association.

The species depicted here are likely Acacia cornigera and Pseudomyrmex ferruginea, native to Mexico and Central America. These photos were taken at Palo Verde National Park in Costa Rica.

While some instances of coevolution may be hard to demonstrate for certain, this case is definitive. First, a common name of this acacia species, bullhorn acacia, refers to the extremely large, swollen thorns shown here. The horns also happen to be hollow, and provide perfect chambers for nesting ants. (An ant on the left thorn can be seen entering a hole in it.)

Next, the tree provides food for the ants in two forms. The first is nectar, but this is not the generalized nectar production of flowers attracting pollinators. The acacia nectar is provided from extrafloral nectaries, found actually on the leaf petioles, as shown here (slightly out of focus). Because of the location and size of these nectaries, it is clear that the trees are obtaining a benefit apart from pollination.

Second, the tree also produces a unique protein source for the ants called Beltian bodies (after the naturalist Thomas Belt). These extraordinary structures are produced as part of new developing leaves. When the new leaves unfold and expand, there is a Beltian body on the tip of each leaflet. These are harvested by the acacia ants and provide most of their protein. Between the nectar and the Beltian bodies, and the housing provided by the thorns, the tree provides all an ant colony's needs.

What does the tree get in return? It gets extremely aggressive defense from herbivores, both large and small. Pseudomyrmex have one of the nastier stings in the world of Hymenoptera (the order comprising ants, bees and wasps). Any insect that alights on the tree is instantly driven away or killed, and the ants are quite effective against potential vertebrate herbivores as well -- to which I can attest first hand when I made the mistake of brushing against a branch while taking these pictures.

The ants are so aggressive that they also take care of potential plant competitors, by cutting down any seedlings that sprout in the vicinity of the tree. In this photo it should be clear that the acacia in the center is sitting in a circle of bare dirt, courtesy of its ant colony.

The relationship between the acacia tree and Pseudomyrmex ants is thus a true mutualism, in which both species have a large benefit from the association.

Labels: cool bugs, ecology, evolution, insects

The 22nd edition of the Circus of the Spineless is now online at Burning Silo. Check it out for some beautiful photos and accounts of our invertebrate friends.

Labels: biodiversity, carnivals, insects

Eupithecia is a large, worldwide genus of inchworms (moths in the family Geometridae). The Eupithecia in Hawaii are unique because of the particular ecological niche they fill - they are predators, while nearly all other known caterpillars are plant feeders only.

Here is the abstract of the original paper describing carnivorous Eupithecia (Montgomery, S. L., 1983. Carnivorous caterpillars: the behavior, biogeography and conservation of Eupithecia (Lepidoptera: Geometridae) in the Hawaiian Islands. GeoJournal 7:549-556.):

A completely new feeding pattern has been found among caterpillars native to Hawaii: certain geometrid larvae (commonly called inchworms) consume no leaves or other plant matter. Instead, they perch inconspicuously along leaf edges and stems to seize insects that touch their posterior body section. By bending the front of their body backwards in a very rapid strike, the caterpillars opportunistically capture their prey with elongated, spiny legs and 900 larvae and eggs of these moths have been collected from native forests of all the main islands and reared in the laboratory. All are species of Eupithecia, a worldwide group of over 1000 members that had been reported to feed only on plant matter such as flowers, leaves or seeds. At least 6 of Hawaii's described Eupithecia species are raptorially carnivorous, only 2 are known to feed predominantly on plant material, especially Metrosideros flowers. A diet including protein-rich flower pollen and a defensive behavior of snapping may have preadapted Hawaii's ancestral Eupithecia for a shift to predation. Severe barriers to dispersal of mantids and other continental insect predators into Hawaii resulted in an environment favoring behavioral and consequent morphological adaptations that produced these singular insects, which can be commonly called the grappling inchworms.

When insects colonized the remote Hawaiian Islands over millions of years, the results were remarkable because the chances of them getting there were so slim. This meant that a species that managed to be blown out over vast distances of ocean and land on one of the islands faced little competition or predation pressure. They then diversified into ecological niches that would not have been possible for their mainland relatives. Because there were fewer predators in the islands than the mainland from which the colonizing Eupithecia originated, there was wide-open opportunity in predation and Eupithecia had the right biological tools to grab it, despite its evolutionary history as an eater of plant parts. Interestingly, people collected these caterpillars for years without recognizing them as predators, because it was assumed that all caterpillars must be plant feeders. The story is that they always died in the lab until a fly inadvertantly got into a rearing cage, and the caterpillar was observed eating it. In the clarity of hindsight, it is interesting that it did not occur to people that these were predators, because they have quite distinct morphology and behavior. They have raptorial claws adapted for grabbing struggling prey, and long thin appendages on the tip of their abdomens which probably work somewhat like the trigger hairs in venus fly-traps. They are sit-and-wait predators, disguising their long bodies along the edge of a leaf -- behavior that makes no sense for an herbivore caterpillar which must move around a lot to feed on the plant. When an insect touches the Eupithecia while crawling up a leaf edge, it whips its head around and captures it.

Nearly all the 22 known Hawaiian species of Eupithecia behave as described in the paper. Interestingly, some are host plant specific, even though they do not eat the plant, because they look so much like that particular plant and it gives them a great advantage in disguise. Some are even specific to the part of the plant on which they rest. One Eupithecia is specific to the green, living fronds of the native Hawaiian fern known as uluhe, and it is the perfect green to match their color. Another dark brown species is always found on the mats of dead fronds underlying the green, living part of the plant.

One exception to the sit-and-wait behavior of most Hawaiian Eupithecia is the species E. monticolans (above), which appears to behave much more like a plant-feeding inchworm. It does not have the raptorial claws or the trigger hairs on the abdomen, and does not sit along leaf edges as its congeners do. When I first collected it, its food was not known, but assumed to be flowers on the `ohi`a tree (as mentioned in the above abstract). I suspected this was not necessarily the case because I collected many from trees that were not in flower. I was not successful in rearing E. monticolans caterpillars for over a year, until I inadvertantly provided one with leaves that were loaded with galls made by small insects related to aphids, in the family Psyllidae. Within a day the leaves looked like swiss cheese, with all the galls eaten out of the leaves. From then on, I always provided this species with leaves covered with galls and I never again had problems rearing them to adulthood. So while E. monticolans was thought to be a "missing link" from pollen-eating to predatory behavior, they are in fact predators, but without the morphology to make a quick strike, they must rely on eating sessile insects that cannot escape or defend themselves from a slow-moving caterpillar.

Almost no parasitoids have been reared from Eupithecia caterpillars. It certainly seems likely that Eupithecia may be rarely parasitized because it is difficult for a parasitic wasp to sneak up on it and lay an egg without being caught. Here is a brief video showing lightning-fast E. orichloris capturing a parasitic wasp (and releasing it - apparently they are not very tasty).



Listen to the jazz tune "Inchworm" here...

Labels: cool bugs, ecology, Hawaii, insects

The pipevine swallowtail is Battus philenor. In the U.S., it occurs roughly in the southern half of the country, east to west.
The caterpillars of B. philenor (below) feed exclusively on plants in the genus Aristolochia (pipevine). These plants are loaded with toxic compounds called aristolochic acids, which would kill, and thus deter, most herbivores. The pipevine swallowtail, however, is not harmed by aristolochic acids, and instead it sequesters them in its own body to use as a defense against predators. These butterflies are a classic example of aposematism, which means they advertise the fact that they taste bad to predators.
If an insect is black, red, yellow, orange, or any combination of those colors, it is likely to be distasteful. If an insect is green or brown and seems to blend into foliage, it likely tastes good to potential predators, and because of that it is hiding. Aposematic insects do not want to hide, they want to make it clear to the predators out there that they are no good to eat. This is because they are relying on learning by those predators (in the case of butterflies, often birds) learning to associate those colors with bad food. Another better known distasteful butterfly is the monarch, which feeds on milkweed, another plant with nasty chemicals.

Some butterflies which have aposematic coloring do not sequester nasty chemicals. Instead, they use a strategy of mimicry, and rely on the likelihood that predators will mistake them for bad food and avoid them as well. This of course only works if most of the aposematic butterflies do actually taste bad, because if a bird eats a black butterfly and it tastes good, it will not learn to avoid black butterflies, but to eat them. So generally in a population there is a stable balance of truly distasteful butterflies and mimics.
The caterpillars of B. philenor can either be black or red, and this is entirely due to the temperature at which they develop (Nice and Fordyce, 2006). When the temperature is over 30°C, A black caterpillar will overheat, so they become red instead, which keeps them cooler (black absorbs sunlight, and thus heat, much more readily than red). Interestingly, aposematism in B. philenor caterpillars seems to serve a dual function: in addition to deterring predators, the contrasting black or red color also deters a B. philenor adult female from laying more eggs on the same plant already occupied by larvae of the same species (Papaj and Newsom, 2005). This ensures that her offspring will have adequate food left for development.

Adult females lay their eggs preferentially on young foliage. This is probably because younger leaves are more tender and easy to eat by early stage caterpillars. Females determine the suitability of the foliage via chemical receptors (taste buds) on their feet. I established this in an unpublished study in which I stimulated oviposition by females on filter paper using organic extracts of young vs. old Aristolochia foliage (above); they much preferred to oviposit on extracts from young foliage. High pressure liquid chromatographic analysis revealed higher levels of several sugar alcohols in the younger foliage, so the butterflies may use that information to choose oviposition sites. At the time, however, we were unable to measure levels of aristolochic acids in young vs. old foliage, so that may also be a cue instead of or in addition to sugar alcohol levels.

These butterflies can be reared in the laboratory, but not easily. Getting butterflies to mate in a lab is challenging, but B. philenor was often quite accommodating. One could manipulate the genitalia of a male and female into contact, and sometimes get them to hold on and complete the mating (and thus get fertilized eggs in the female). Interestingly, what mattered in lab mating success often was the individual male - certain males could not be induced to mate, while with others we had success with several females.

These insects have been of interest to scientists not only because of their chemical relationship with their host plant, but because of their behavior as well. Many people assume that insects behave only according to instinct, but in fact many species have shown quite good learning ability. Parasitic wasps are often studied for their odor and sometimes visual learning skills, and butterflies as well are good learners. Mainly visual cues, e.g. color and shape, have been shown to be learned by B. philenor. For example, in parts of their range there are multiple species of Aristolochia upon which they feed, and females learn the leaf shape of the dominant species (Papaj 1986). This saves time for females searching for host plants, because ovipositing (egg laying) females can visually scan for potential host plants, and then test leaves of the correct shape for the compounds in Aristolochia, after which they confirm or reject it as a host plant.

A female B. philenor can also simultaneously learn one color associated with egg laying, and another color associated with nectar sources for food (Weiss and Papaj 2003). Similar ability has been found in some parasitic wasps. It actually should not be surprising that insects are good at learning. If your brain is tiny, you have fewer neurons to hardwire different behaviors, so it pays to be flexible anyway.


References

Nice, C.C. & Fordyce, J.A. (2006) How caterpillars avoid overheating: behavioral and phenotypic plasticity of pipevine swallowtail larvae. Oecologia, 146, 541-548.

Papaj, D.R. (1986) Conditioning of leaf-shape discrimination by chemical cues in the butterfly, Battus philenor. Animal Behaviour, 34, 1281-1288.

Papaj, D.R. & Newsom, G.M. (2005) A within-species warning function for an aposematic signal. Proceedings of the Royal Society B-Biological Sciences, 272, 2519-2523.

Weiss, M.R. & Papaj, D.R. (2003) Colour learning in two behavioural contexts: how much can a butterfly keep in mind? Animal Behaviour, 65, 425-434.

Labels: biodiversity, cool bugs, ecology, insects

Trap-jaw ants are the venus fly traps of ants, in the tropical/subtropical genus Odontomachus. They are some of the most incredible animals on earth, because of the speed at which they can snap their jaws together to snatch their prey. The species at left, O. clarus, is one I encountered in Arizona. Like many desert animals, these ants like to hunt at night, and it was common to see them milling about on the University of Arizona campus in the glow of the street lights. The workers are striking to see because they walk about with their huge jaws in the open position. In the picture you can barely see tiny trigger hairs, which are similar to trigger hairs in venus fly traps. Because this is an animal, though, there are large jaw muscles which contract like coiled springs to hold the jaws open. When there is pressure on a trigger hair, the effect is like unhooking a latch (think of a mousetrap), and the jaws explosively close on their prey, at a nearly unimaginable speed:

"Biologists clocked the speed at which the trap-jaw ant, Odontomachus bauri [at right], closes its mandibles at 35 to 64 meters per second, or 78 to 145 miles per hour - an action they say is the fastest self-powered predatory strike in the animal kingdom. The average duration of a strike was a mere 0.13 milliseconds, or 2,300 times faster than the blink of an eye."

To record the entire motion requires filming the ants at 50,000 frames per second, rather than the usual 24.

In their paper published last August (Patek, S.N., J.E. Baio, B.L. Fisher, and A.V. Suarez, 2006. Multifunctionality and mechanical origins: Ballistic jaw propulsion in trap-jaw ants. Proceedings of the National Academy of Sciences 103: 12787-12792), researchers added to this incredible story by discovering an additional purpose of the trap jaws. They first calculated the force of the mandibles: "...a single mandible could potentially generate a force that is 371-504 times the ant's body weight." Then they documented a previously unknown use for this force in O. bauri: self-propulsion.

You must watch these videos to fully appreciate this behavior. But, to summarize, by snapping their jaws against a hard surface, O. bauri achieves "heights up to 8.3 centimeters and horizontal distances up to 39.6 centimeters. That roughly translates, for a 5-foot-6-inch tall human, into a height of 44 feet and a horizontal distance of 132 feet." Of course, whenever comparisons are made between insects and humans, the former come out looking like Schwarzeneggers to the hundredth power. This is because such comparisons do not take into account the effects of scaling. The insect world, with the same gravity and atmosphere as we have, but with exoskeletons and light weight, is a very different place (which is a topic for a later time). Everyone knows you can drop an insect from great height and it will emerge unscathed. This is very useful if your escape route is flying eight times your body length straight up into the air.

To see some amazing biodiversity in action, watch the videos.


More incredible ant pictures are posted at myrmecos.net!

Labels: ants, behavior, biodiversity, cool bugs, ecology, insects

The Belostomatidae is a family of giant water bugs (Order Hemiptera) that has been fairly extensively studied because of the various species' unusual reproductive systems. In short, this is one of the few groups of animals that exhibit paternal care of offspring.


Probably the most well known animals with paternal care is the sea horse, who carries its mate's eggs in a brood pouch until they hatch. Belostomatids are similar because the male also takes care of the eggs, although he does it in two different ways between the two subfamilies, Lethocerinae and Belostomatinae. Above is a giant water bug in the genus Lethocerus. They are sit-and-wait aquatic predators, hanging head down on sticks or reeds underwater. An appendage extending from their abdomens remains above water and allows them to breathe. They are quite large, and much of their prey consists of tadpoles and small fish.


They have a somewhat painful bite, because they have a sharp beak with which they inject a neurotoxin which helps them control their prey. However, if one holds them just behind the head as shown it is safe to pick them up. (I was holding this particular specimen (from Costa Rica) that another student and I were studying; we were doing measurements to look for morphometric differences between males and females, and I had to do all the measuring because he was too afraid to pick one up.)

The Lethocerines are thought to be the more ancestral lineage in the family, based partly on the way they brood their young. Females lay eggs along the top of a stem sticking out of the water, but the eggs will dry out and die without care. The male stays as a sentry on that stem, periodically carrying water up to moisten the eggs and oxygenate them.


The Belostomatines are considered more derived evolutionarily, because the brooding behavior seems to be more efficient. Females lay their eggs directly on the back of the male, who must swim around with them until they hatch to keep them properly oxygenated. The picture at left shows a male with eggs.

Scientists like to study "reverse mating-system" species such as these because it gives us clues about what governs decision-making in animals. In the case of mating behavior, in nearly all animals known, females are choosy about their male mates, who often have elaborate physical features or behavior designed to attract the attention of females (or fight off other males). This is why in many species of birds, the males are more brightly colored than the females. The reverse mating-system species allow us to ask questions like, are females always the choosy ones, because they invest more resources in their gametes (eggs are a lot bigger and fewer than sperm), or is the parent with the largest investment overall the choosy one? Gamete size is an important measure of investment, but time and energy invested in a single mate are important too. In most animal species, a male has the sperm and the time to mate with many females, so he tends not to be choosy. A female not only has fewer gametes but usually invests more time in rearing the offspring than the male, so it's more important that she choose a mate with good qualities (for that species).

It has been found that in reverse mating-system species, the males actually tend to be the choosy ones - so there's nothing about being female per se that makes one choosy. Parental care of offspring is a huge investment, so when it switches to the males, they become the choosy ones. In the case of giant water bugs, a female may have enough eggs to mate with several males, and as soon as she lays them she can move on and find another mate. The male is the parent stuck taking care of the eggs for a couple weeks and thus loses opportunities for more matings in that time. Thus, accordingly, belostomatids and sea horses tend to have choosy males rather than females.

Labels: cool bugs, ecology, evolution, insects, sex

Diachasmimorpha juglandis is a parasitoid wasp in the family Braconidae. Like other braconids, it is relatively large; while most parasitic wasps are probably less than 5 mm long, D. juglandis can get nearly up to 1 cm.

This species is categorized as a "solitary larval-pupal endoparasitoid," meaning that an egg is laid inside the host - in this case a larva (or close relative) of the walnut fly Rhagoletis juglandis, and a single adult wasp emerges from the pupal stage of the fly, having devoured it from within.


D. juglandis females, shown in these pictures, have to find their hosts without ever making visual or physical contact with them, because they are feeding within the husks of walnut fruits. Once a wasp has landed on the fruit, she walks around its surface, pausing every few seconds to feel for vibrations beneath her, caused by moving fly larvae. When she has located one, she inserts her long ovipositor through the husk (above right), and hopefully, into the body of the fly larva, where she lays a single egg.

The tiny wasp soon hatches, and bides its time as a first stage larva, cruising through the bodily fluids of its host, sustaining itself on stored fat. Interestingly, the length of the first stage is variable, depending on what stage the fly was at when parasitized; the wasp needs to wait for the fly to begin its pupation (which it does after dropping out of the walnut and digging down into the soil). At this point, the wasp molts into the next stage and begins devouring the entire body of the fly, a task made especially easy because the fly tissues have begun breaking down on their own in preparation for reassembling as an adult fly.

Notice that in the picture above and at the left, of a recently hatched wasp larva, it has a rather large sclerotized head, somewhat like a helmet with jaws. This structure is present only in the first stage; after the first molt, the wasp larva looks like an amorphous white blob.

The reason for the sclerotized head and jaws has to do with the fact that these wasps are solitary - it is only possible for one wasp to emerge from a single host. It is possible for two wasps parasitize to the same host, so that there are two first-stage larvae present at the same time. Because the host only provides enough food for one, these wasp larvae must fight to the death within the host - which all the while continues on its merry way in the walnut, eating fruit until it is full grown and ready to pupate, oblivious to the battles occuring within its body. The jaws on the wasp allow it to easily attack and kill a rival wasp in the fly.

Which wasp wins? This is a fascinating question that has been studied in several solitary parasitic wasp species. In most cases, the one that got there first has the advantage, because it has had time to feed and grow a bit, making it stronger than any subsequent intruder. But back in the early part of the last century, some biologists studying these interactions in a related Diachasmimorpha species in Hawaii (imported there for biological control of medfly and oriental fruit fly) came to a fascinating conclusion following their dissection of hundreds of parasitized flies. They found that they could distinguish how old a first-stage wasp larva was by how fat it was - newly hatched larvae were skinny, but a wasp that had been in the host for a few days had begun to get tanked up on all the fat it was feeding on in the host. When they found two wasps in a death struggle, the skinny one had killed the fat one.

So apparently, when a wasp first hatches, it swims around the host before it tanks up, perhaps looking for any other wasp larvae. When it encounters a fat larva that has been there alone for a few days, it is an easy task for the skinny and much more maneuverable wasp to pop the older one with its jaws like a balloon (upper inset on photo above right).

By the time the fly begins to pupate, it is in the soil and will not be parasitized by another wasp; at this point there is only one wasp survivor inside of it. The sclerotized head of the first stage wasp larva is no longer necessary, and when it molts to the second instar upon fly pupation, the helmet is gone.

Both the host, and thus by necessity, the parasitoid, have just one generation a year. There are a few short weeks as adults for them when the flies emerge from the soil and oviposit in ripe walnut fruits, and then the emerging adult wasps try to find them and parasitize as many as possible. Flies and wasps then diapause (a type of insect hibernation) in the soil for nearly a year until ripe walnut fruits are available again.

Labels: cool bugs, ecology, flies, insects, wasps

I thought about doing a post on all the wasp mimics out there, but within the flies (Diptera) there are plenty, and it clearly evolved multiple times - in most cases, not all the species within the following family are mimics. Obviously it would be some benefit for any insect to be thought a wasp by a vertebrate predator. Flies cannot sting for defense, so some of them just look a lot like wasps so predators will think they can sting. The ways in which they mimic wasps are fascinating.

The following families include wasp mimics: Micropezidae, Conopidae, Mydidae and Syrphidae. I'm surely missing some - don't be shy about pointing it out, all you Dipterists out there.

There is a whole family of bee mimics as well, the Bombylidae (the bumblebee genus is Bombus). They are big fuzzy things (below right), but if you look closely, you will see only two wings, which gives away their lineage - all bees and wasps (and all orders of insects except for the flies) have four wings.

But I'm more interested in the wasp mimics here. I'll start with my favorite, a Micropezid I caught in Costa Rica, at the La Selva research station. These are fantastic mimics, and a still photo just doesn't do them justice because their behavior is an important part of the package. You can see the fly has a pointy abdomen, which helps, and when grabbed, it pokes its abdomen into the grabber's skin repeatedly as if to sting. (Kinda cute, since it's completely harmless.) The other important combination of morphology and behavior has to do with the long forelegs, which end in white tips (which you should be able to see in the photo, along the edge of my thumbnail). In the tropics especially, the long antennae of stinging wasps have white or yellow tips. Flies, as a group, have very small antennae, but this family of flies has long legs. It was a quicker evolutionary step for the mimic species to use its forelegs to mimic antennae, than to develop long antennae itself. So you will see this fly walking rapidly along leaves in the manner of wasps, tapping its forelegs in front of it just as wasps use their antennae. It's really amazing to watch. (Although this fly family is more ubiquitous in the tropics, there are North American species and I have seen them in central Virginia.)

Conopids have a generally different look, mimicking thread-waisted wasps (Sphecidae) rather specifically. A common wasp-mimic morphology is to have a somewhat constricted abdomen, because a distinguishing character of the Hymenoptera (ants, bees, wasps) is a distinct constriction in the first few abdomenal segments, which means that hymenopterans are more or less restricted to liquefied foods, but also allows flexible reach for the abdomen when stinging prey or for defense. The conopids combine this with the elongated abdomen characteristic of sphecid (digger) wasps. I'm not aware of any specific behaviors that help promote their ruse.

Some Mydidae (mydas flies) apparently go for the pompilid (spider wasp) look. According to the source for this photo of Mydas clavatus, Tom Murray, it is mimicking spider wasps in a particular genus, Anoplius. Pompilids have a quite characteristic look of a black body and darkly pigmented wings. The photo on the right is Anoplius.

The syrphids (hoverflies) are not so precise in their mimicry. Here are two, with one clearly mimicking a bumble bee, and the other just looking generally wasp-like with its black and yellow markings. Their behavior does not necessarily contribute to the show; as their common name suggests, syrphids spend a lot of time hovering, which is generally unwasplike.








Thus mimicry takes many forms. It is interesting that some mimics seem to be modeling specific insects while others just seem to have the general look of wasps or bees. Does the selection pressure differ for these mimics, and why? Perhaps the generalist mimics live where there are a big enough variety of stinging Hymenoptera that they don't need to get specific. Why do some converge on specific families? Is there a dominant model present in those habitats? I'll admit up front that I have not done a literature search, so I don't know what is known specifically about the evolution of mimicry in these groups. I just like them because they are so cool.

The only picture of mine above is the worst one by far, of the micropezid. The syrphids and Anoplius come from Forestry Images, a wonderful image database, and the rest are by Tom Murray, and used with his permission. See many wonderful fly images of his here.

Labels: bees, biodiversity, cool bugs, ecology, evolution, flies, insects, wasps

What do you think this sound is? Continue reading for the answer...

Since it's been two weeks since my last "cool bug" post, I thought I had better change the name of the series... we'll see where it goes from here.

Today's subject is a fruit fly, Rhagoletis juglandis. This is not related to the fruit fly of genetics fame, Drosophila melanogaster, which is in a different family. Nearly all drosophilids only eat fruit once it is rotting; flies in the family Tephritidae, including the genus Rhagoletis, feed on ripe fruit and thus are known to entomologists as the "true" fruit flies.



I will admit up front that these flies are mainly of interest to me as larvae (at the left), because they serve as hosts for one of my favorite parasitic wasps, Diachasmimorpha juglandis, below. R. juglandis larvae feed on and live in the fruit of the Arizona walnut (Julglans major) (i.e., the husk surrounding the actual nut), and D. juglandis females parasitize them through the walnut fruit skin.


The fly larvae live in groups in the walnut husk, sometimes by the dozens. All the larvae in a fruit may or may not have the same parents, if there have been multiple ovipositions in the fruit.




In the picture to the right is a mating pair of R. juglandis adults on a plastic walnut model. Males and females mate multiply, with several individuals if given the opportunity.





There are territorial contests by the males on the ripe walnuts while they are still hanging in the tree. This behavior is known as "boxing." The males stand on their hind legs and bat their forelegs and wings together. (In the picture to the left, the wings are only a blur.) The idea is that the winners of these contests have access to more females, who will come to the walnut to mate and lay eggs. Some poor females are forced to mate as they extrude their ovipositors to dig a hole in the husk in which to lay eggs; the males will grab them from behind and mate with them before they have a chance to oviposit. Sometimes, though, males are so intent on fighting with each other that they don't seem to notice a third male that is mating with the female on the fruit while they are going after each other.


While males are duking it out, mated females also get the opportunity to finally oviposit without harassment (left). A female drills a hole in the husk with the tip of her ovipositor (which eventually shows signs of wear) and deposits several eggs in a cavity just beneath the surface of the husk. These grow and feed inside the husk until they are ready to pupate, when they exit the fruit and burrow into the soil. Sometimes there are so many larvae within the husk of a walnut that their feeding is audible. Click here to listen to the sounds of feeding fly larvae in a walnut.

Unfortunately for the larvae, the racket they make chowing down on the walnut is their undoing... as will be revealed in the next Cool Bug of the Fortnight!

Here are references for more information on Rhagoletis juglandis:

Papaj, D.R., 1994. OVIPOSITION SITE GUARDING BY MALE WALNUT FLIES AND ITS POSSIBLE CONSEQUENCES FOR MATING SUCCESS. BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY 34 (3): 187-195.

Henneman, M.L. and Papaj, D.R., 1999. Role of host fruit color in the behavior of Rhagoletis juglandis (Diptera: Tephritidae). Entomologia Experimentalis et Applicata 93:247-256.

Nufio CR, Papaj DR, Alonso-Pimentel H, 2000. Host utilization by the walnut fly, Rhagoletis juglandis (Diptera : Tephritidae). ENVIRONMENTAL ENTOMOLOGY 29 (5): 994-1001.

Labels: biodiversity, cool bugs, ecology, evolution, flies, insects

I decided a good weekly column would be a post about one of the cool insects I have known during my career.

My first featured bug will be a species of honeypot ant from the southwestern deserts, Myrmecocystus mexicanus.

This is a fun species to mess with because they are the most nocturnal ants I've ever seen. Some other species are nocturnal, but you sometimes see them during the day; others you find at night but they can be easily observed with a flashlight. M. mexicanus, however, is completely anti-phototaxic - the second a light is shone on workers, they run away from it. This provides a cool effect when you go out at night an locate a nest, which is very distinctive. When you shine a flashlight on the nest, you see a lot of ants hanging around on the surface that immediately go down the hole, as if they were being slowly sucked. Turn off the light a minute, then turn it back on, and you can repeat the process. Kinda mean to do over and over, I guess, but this is serious minutes of entertainment.

I got to know these ants while working as a field assistant on a grad student's project. The grad and I mused that it would be great fun to design different types of ant furniture, including an M. mexicanus lamp. The colony could be contained in a hollow lamp, which they could crawl around on but not off (there are handy materials for keeping ants contained). When you turned on the light at night, they would all quietly slip back into the lamp, which would then be ant-free in a couple seconds. Hmm, maybe not a huge money-maker, but it could definitely be marketed to entomologists...

The cool thing about honeypot ants in general (i.e., several species in the genus Myrmecocystus) is that they use some workers, called replete workers, as storage vessels. This is a great way to get through the dry season in a desert. They in turn become famine food for larger animals, including humans - the abdomens are quite sweet and tasty. Some people with captive colonies feed the ants specific foods to get a good flavor in the replete workers. Molasses is supposed to be a good one.

There are several more pictures of the M. mexicanus here.

Labels: ants, biodiversity, cool bugs, ecology, insects