Insects and plants co-evolved because insects are the marital aids of flowers. Magnolias entice beetles, apple blossoms seduce their bees, and orchids go to elaborate lengths to draw in horny wasps. But sometimes sex toys go bad and take eating out (nudge, nudge, wink, wink, know what I mean, say no more!) to an extreme. For example, check out these gaudily striped, ribbed-for-her pleaure dildoscerpillars.
Here's a dude munching away lustily. His little claws give that extra stimulation.
A double headed toy for fast action:
And here's the orgy shot. That parsley plant didn't have a chance.
These caterpillars are the larval stage of the Eastern black swallowtail butterfly, Papilio polyxenes Fabricius. They feed almost exclusively on plants in the Apiaceae family which includes parsley, carrot, celery, Queen Annes lace, the noisome wild parsnip and the highly toxic poison hemlock. All contain a class of secondary compounds called furanocoumarins. These compounds serve as a defense mechanism (antifeedant) for the plants. Plants of the Rutacea (citrus) family also contain furanocoumarins.
The black swallowtail caterpillars are able to consume massive quantities of Apiaceae, including the more toxic species, because of their ability to detoxify furanocoumarins using the cytochrome P450 enzyme, CYP6B1. Other species of insects have co-evolved with Apiaceae by exploiting variants of CYP6B1. May Berenbaum and her lab crew at the University of Illinois-Urbana have studied the co-evolution of insects with furanocoumarin-containing plants and published some nice studies.
As an aside, the furanocoumarins 6,7-dihydroxybergamottin and bergamottin are the problematic players in grapefruit juice. These are potent inhibitors of the cytochrome P450 CYP3A4 in the human liver. This is the CYP which clears a lot of drugs from the human system. Inhibition of the enzyme thus raises concentrations of the meds to potentially hazardous levels.
Back to the sex toys...
These caterpillars are colorful buggers. A question - is there any correspondence between coloration on the larva and the wings of the adult? My guess is "no,' but I'm just a biochemist, so what would I know from segmentation and pigmentation and degeneration?
Pant-hoots of gratitude and vigorous back scratching go to K. Ferrell for granting permission to publish her photos in the Chimp Refuge. Ferrell passes along the news that a number of the caterpillars became the main course of a very happy bird's buffet.
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Although I no longer have access to this journal, perhaps the following article may be of interest...although it seems to be discussing only the adult coloration. My guess is, however, that the references section may have some good leads.
Koch PB, Behnecke B, ffrench-Constant RH, 2000. The molecular basis of melanism and mimicry in a swallowtail butterfly. Curr Biol. 10(10):591-4.
From the abstract: "Nowhere is butterfly melanism more striking than in the Eastern Tiger Swallowtail (Papilio glaucus) of North America [3] [4] [5]. In this species, females can be either yellow (wild type) or black (melanic). The melanic form is a Batesian mimic of the distasteful Pipevine Swallowtail (Battus philenor), which is also black in overall color. Melanism in P. glaucus is controlled by a single Y-linked (female) black gene [6]. Melanic females, therefore, always have melanic daughters. Black melanin replaces the background yellow in melanic females. Here, we show that the key enzyme involved is N-beta-alanyl-dopamine-synthase (BAS), which shunts dopamine from the melanin pathway into the production of the yellow color pigment papiliochrome and also provides products for cuticle sclerotization. In melanic females, this enzyme is suppressed, leading to abnormal melanization of a formerly yellow area, and wing scale maturation is also delayed in the same area. This raises the possibility that either reduced BAS activity itself is preventing scale sclerotization (maturation) or, in contrast, that the delay in scale maturation precludes expression of BAS at the correct stage. Together, these data show how changes in expression of a single gene product could result in multiple wing color phenotypes. The implications for the genetic control of mimicry in other Lepidoptera are discussed."