A tiny wasp with enormous numbers of descendants - Polyembrionic Copidosom sp.

I am still trying to keep my basil plant alive, through short days and some freezing nights. But most of the larger leaves are falling off anyway. So now several dry, rolled up ones became very obvious. Each contained a cocoon - similar to that of the green noctuid moth caterpillars that sometimes compete with me for the basil leaves.
But the cocoons were quite thin, likely unfinished, and inside was a rather repulsive looking, thick sausage with no recognizable organisation. 

Cocoons of noctuid moth caterpillars on basil. The caterpillars were killed by parasites

The casing was stretched thin enough to be transparent, so I could see that it was stuffed full of little grains, like rice, but each only less than 0.5mm long.

Under magnification, little eyes became visible on those white grains. So probably really parasites. Larval (or pupal) wasps rather than flies, because those eyed creatures did not look like headless maggots. 

Copidosoma spp, Pupae

But so many? I had never seen anything like it. So I posted them on BugGuide.net and my Facebook Group SW US Arthropods. 
Charles Melton and Dennis Haines had the answer quickly: 

Copidosoma spp, adult female

A Chalcid wasp in the genus Copidosoma (Pentalitomastix) was behind this amazing find.
The tiny, 1.5mm long wasp female produced just a few eggs, and probably even spread those among the three affected caterpillars that I found.  But she did not actually attack the grown caterpillar, she had laid her eggs early, right when a moth female deposited her eggs on my basil plant.
The wasp eggs multiplied then by cloning into as many as a few thousand (polyembryony). The larvae didn't begin growing until the caterpillar has reached a certain size. So they all uniformly ended up killing their caterpillar just as it was about to spin a cocoon and pupate. 
I collected two of the cocoons to see what will emerge. Dennis Haines remarked that these wasps are obviously interesting for researchers working on biological control, but they are difficult to raise in captivity. 
The sex of the larvae seems to be determined by temperature ... just one more fascinating aspect.

12 days after I discovered the caterpillar full of pupae, tiny wasps are hatching. This one is sitting next to some writing in font size 12, so you see that they are barely 1mm long.

A day later, the container was alive with thousands of little wasps, and some were already mating. So I quickly released them on my lattice plants that often get eaten by noctuid caterpillars. I wish the little wasp females luck in finding any moth eggs in the middle of winter!

Better here: https://flic.kr/p/QKNxHH

PS: there is already another generation pupating in another noctuid cat, again on basil. This is now happening in February, while we actually had a very rare snow fall righr here. Picture Rocks, Pima Co, AZ elev ca 2500 feet. 

It always pays to watch the competition

Yesterday, when I arrived for the weekly nature walk of the Friends of Sabino Canyon the temperature was in the fifties. Much too cold for mid-April morning in Tucson and too cold for most insects and lizards that I wanted to see. In addition, a fierce wind was howling down into the canyon from the Catalinas. The other naturalists decided to look mostly at plants, I guess because those can't hide from the elements. Two saguaros, one with an imposing crest, looked indeed positively defiant.

Eastern Collared Lizard, who stayed hidden yesterday (Photo Ned Harris, April 2012)

But I don't get to Sabino often enough, so I was going to give Esperero Trail a try because that's where I had seen the beautiful Eastern Collared Lizards last year. The trail leaves the main canyon and winds up the mountain side with full exposure to the western wind gusts. It seemed like a dumb idea but I am stubborn and in Arizona the sun usually breaks through eventually.

View into Sabino Canyon from Esperero Trail

 Well, it didn't and there seemed to be very few living things willing to share the exposed mountain side with me. Until I came to some part of the trail that rose somewhat over its surroundings resulting in a low but pronounced hill top.

Ash-throated Flycatcher, who was out and about

 There was a big Ash-throated Flycatcher busily swooping from his perch as if catching - flies? Sure enough, even in this abysmal weather some Bee Flies, Tachinids, Robber Flies  and even some butterflies (Tiny Checker Spots, Marine Blues) were hill-topping, a behavior that is typical for many flying day active insects.

Some of the hill-topping flies and butterflies

 Males had staked out little territories, patrolling back and forth, chasing everything that flew by, driving off other males and trying to mate with passing females. I think I understand why the big collared lizards and the flycatcher seem to prefer this exact area. It's the place where they can be sure to find enough prey. Of course the ectotherm lizards had the luxury to take the cold day off while the endotherm bird had to keep working, especially as he was feeding nestlings that I could hear keening in a Saguaro hole. I followed the bird to an especially exposed area with some bare boulders where he seemed to concentrate his efforts.

 At first I payed little attention to a big black fly that landed as if to bask in one of the sparse sunny spots because I mistook it for a Mexican Cactus Fly, a common syrphid. But then I heard a very deep basso buzz when the fly changed to another boulder, only about 5 m from the first. That sound is one of the loudest and deepest flight noises I've ever heard here in Arizona - not easy to forget. Through my new little Papillon binoculars I could also verify that the fly was not all black but had silvery grey flanks - a bot fly in the genus Cuterebra. (Later identified by Jeff Boettner as C. austeni)

Rodent Bot Fly, Cuterebra austeni, Esperero Trail, Sabino Canyon, Pima County Arizona, April 2013 

This is only the third time that I encountered these big, fascinating insects. Some people may feel that the live history of bot flies seems like an episode from the X Files or the movie Aliens. I think, however, that the film makers borrowed their ideas from the biology of these flies whose larvae are mammalian parasites.

Deer Bot Fly, Cephenemyia jellisoni infects the alimentary tract of ungulates like white-tailed deer, mule deer, moose or elk. Photo by Philip Kline Pusch Peak,  Catalina Mountains, Pima County, Arizona, March 2009

 While some bot fly larvae develop in the alimentary tract of mammals, the big black and grey Cuterebra that I was watching yesterday belonged to the group that develops subcutaneously in mammals. Luckily they are quite species specific in their host choices so I knew that I wasn't the target - the host would most likely be a rabbit or a pack rat.

Pack rat with 2 nearly grown Cuterebra larvae Photo Jan Emmings

 The female fly will lay hundreds of eggs in rat runways. Only a few of the larvae will actually find their way into a passing rodent.There it will develop rather quickly feeding on the body fluids of the rat that this irritation draws. Inflammation and pain are controlled by the larva and the wound heals very quickly as soon as the guest drops out of the host to pupate.

Cuterebra sp. larva ready to pupate found crossing Sabino Canyon Rd. on Feb. 22, 2011. Photo by Fred Heath

Rodent Bot Fly, Cuterebra sp., Pima Canyon, Catalina Mts. Pima County, Arizona, September 2009

 The only bot flies likely to infest humans do not occur north of Southern Mexico. As I mentioned, the deep characteristic buzz of the big flies is rather recognizable and would probably warn the victim of an intended egg drop. To give their larva a chance to find their way into the body of a wary primate, female bot flies in the genus  Dermatobia  have an amazing strategy. They capture another insect like a mosquito, horsefly or tick that is drawn to warm blooded mammals for its own reasons and attach a load of their eggs to this carrier. When the released  mosquito later lands on a primate for a blood meal, the bot fly eggs hatch and the young larvae bore into the warm skin of the doubly victimized monkey or human.

 While feeding from the host subcutaneously for several weeks the larvae have to behave reasonably well. They seem to prevent inflammation even though they need to keep a hole in the host's skin open to be able to breath periodically. They probably have anti inflammatory and antibiotic capacities. I have two good friends who both got parasitized in Central America, are now in their eighties, and live and love to tell about it. If not removed prematurely, the larvae will eventually leave the host, drop to the ground and pupate. In time a new generation of mature adults will hatch. These big flies are born without mouth parts. From their time as maggots in the flesh, they are provisioned with enough energy reserves to survive for about 10 days, time enough to start the cycle again.

Catching the redeye to Amhesrt, MA 

Yesterday's bot fly, however, is not going to propagate his genes this way. Instead he is contributing them to conservation biologist Jeff Boettner's research project at UMASS - Amherst. There are many open questions concerning host relationships and phylogeny of the group. As specimens are difficult to obtain, Jeff would be grateful for specimens and info about lek sites. Here is a link to his info pamphlet.
Here is a link to photos of the removal of a human bot fly larva (Peruvian Amazon)
Classification:
Arthropoda (Arthropods) » Insecta (Insects) » Diptera (Flies) » Calyptratae » Oestroidea » Oestridae (Bot Flies) » Cuterebrinae (New World Skin Bot Flies) » Cuterebra (Rodent and Lagomorph Bot Flies)

Tent Caterpillar Nests and Surprises

Noel McFarland and David Wagner

 This spring the author of several great books on caterpillars, David Wagner, visited us at the University of Arizona Insect Collection. Working out of the University of Connecticut, he had concentrated mostly on eastern species (Caterpillars of Eastern North America, Princeton University Press, 2005) but now he's progressed to the real thing, working on a guide to Arizona, or better southwestern caterpillars.

Caterpillars and provisions ready for over-night shipping across the US

Inspired by him, I have been looking at caterpillars with renewed interest. Most specimens that I found were shipped as quickly as possible to Connecticut to (in)star in the new book.

This year we had  an impressive outbreak of Tent-Caterpillars of the genus Malacosoma on Mount Lemmon in the Catalina Mts. One of my collecting trips in mid May was mostly devoted to these guys.

Western Tent Caterpillars Malacosoma californicum on aspen, left, Sonoran Tent Caterpillar, Malacosoma tigris, on Silverleaf Oak, right

 Different host plants yielded at least two different species: The caterpillars on oaks were probably Malacosoma tigris, the Sonoran Tent Caterpillar.

 Of the oak feeders, I only found early instar caterpillars in very rudimentary nests, all the larger caterpillars were by themselves. I learned later that this solitary life style is typical for the species.

 The oak feeders spin flocculent cocoons under and between oak leaves to pupate.

 The caterpillars on Cherry, Aspen, and Willows at Marshall Gulch are probably M. californicum, the Western Tent Caterpillar.  The final word (from Dave Wagner) on these ids will come when the adult moths hatch. He confirmed it later.

Western Tent Caterpillar nest on Cherry

The Western Tent Caterpillars on aspen, cherry and high-elevation willow spin communal nests between branches of their food plant. When they leave the nest to forage they seem to follow scouts and leaders, and around the nests I found silky threads marking their highways. After feeding, the caterpillars return to the safety  (and warmth) of their nest to digest their food. The protection of these communal nests is profound. In Greece I once tried to open an empty nest of the related Procession Spinner. The urticating hairs left in the old nest caused my hands to blister so badly that it nearly spoiled the whole trip.

On Mt Lemmon I also found big gatherings of the aspen feeders resting out in the open on tree trunks and fence posts.

One of the caterpillars spun its cocoon on the way home from the mountain - anchoring it to a plastic bag instead of leaves of the food plant.  Note the infusion with a yellowish powder, typical for some Malacosoma species.

Pupa and adult tachinid flies in the genera Exorista and Lespesia that hatched from Malacosoma pupae

Although several of my Malacosoma caterpillars eventually  wove their silky cocoons and pupated inside, I have not yet seen any adult moths. Instead, I soon found a big hole in each cocoon, and next to it a smaller pupa in the barrel shape characteristic for a dipteran (fly) cocoon. Over the last few days several adult Tachinid Flies of different genera, but no adult moths, eclosed.  I hope David has more luck with the caterpillars I sent him. Parasitism of caterpillars is common. As a child in Germany I wanted to raise our beautiful Peacock Butterfly, Inachis io. Instead I got a whole row of little wasp cocoons (Ichneumonid) attached to an empty,  hollowed out caterpillar skin.. The experience shocked me so much that I didn't try to raise any more caterpillars until I had to do it in a developmental physiology course during my biology studies. We worked with wax moths and repeated Kopec's ligation experiments - so again, I was deprived of any inspiringly beautiful results.

But - the limited success of this generation of tent caterpillars will probably save some aspen trees on Mt Lemmon from death by defoliation next year. And I am sure Nature will strike a balance in a way that will eventually allow me to see an adult Tent Caterpillar Moth.

June 17, 2012
 A moth eclosed from a pupa that I collected from Gambel's Oak at Summerhaven, behind the Community Center

David Wagner answered in three consecutive e mails::

* Malacosoma tigris is scarcely distinguishable from the others based on its phenotype and/or genitalia.   It is closest to constrictum, which, mercifully, is found only in California.

* adults of tigris, incurvum, and californicum are very close and in some cases indistinguishable

* adults of incurvum and californicum are especially close and no genital characters are known that distinguish them.

* Stehr's (and all subsequent) taxonomy is based larval phenotypes (and hosts).

* I plan to call Stehr tonight.

* the good news: there are only four species in the Southwest.

Called Fred.  He says egg color is definitive.  If you can find any of the old egg clusters on the cherry trees that had tents in April, Fred says we can get a definitive ID.  Incurvum eggs are white; californicum eggs are grayish white.

Also, which seems important: incurvum and californiucm are only marginally distinct as species....and could be lumped by some...or at least would still be expected to be in some genetic contact.

I am sticking with my original thoughts:  Malacosoma tigris for your oak-feeders and M. incurvum for all others on Mount Lemmon.  

 I have enough reared adults and larval images to feel that this is the best we can do until we see egg clusters.  These dets are consistent with the larval images recently sent to me by Terry Fitzgerald, a social caterpillar guy at SNY Cortland. Anyway, that's my story and I am sticking to it. 

 No M. californicum until you prove it! (Usually, and only usually, californicum caterpillars have a pale middorsal stripe.)

Dave Wagner