Insects caterpillars

Figure 5.8c. Example of a displaced insect caterpillar of a European butterfly feeding on a bitter American lupine plant in the lupine collection in Poznan, Poland.

Some insects can protect themselves against the toxins present in their food plants by storing them. One example is the monarch butterfly, the caterpillars of which store potentially toxic cardiac glycosides obtained from a food plant, the milkweed (see Harborne 1993). Subsequently, the stored glycosides have a deterrent effect upon blue jays that feed upon them. 

Caterpillars and other moulting insects excrete the hormone a-ecdysone which at moulting time becomes hydroxylated to 20-hydroxyecdysone (20-E), which in turn triggers the moulting process enabling the insect to shed its exoskeleton and resume feeding. Rohm and Hass have developed a novel insecticide, tebufenozide (Formula 9.5) which mimics 20-E, binding to the same site. The consequence of this is that the insect stops... 

Not all caterpillars achieve this comfortable lifestyle. Enjoying the ants hospitality depends on being taken home by the right kind of ants. The caterpillars have no control over this crucial matter, because the first Myrmica ant to notice a caterpillar takes it off to its own nest. Although each Myrmica species can distinguish its own larvae from those of related species, all local Myrmica ants accept the caterpillars as their own. How this comes about is unclear. Like other insect larvae living openly in ant nests, the caterpillars presumably carry the odor of ant larvae. Perhaps they smell enough... 

Caterpillars and grasshoppers cause localized damage to banana foliage. Bordeaux coverage of the banana leaf surfaces, however, acts as a partial repellent to these insects. 

The relationship between milkweeds and the monarch butterfly demonstrates a synergistic relationship between a plant and an insect (Harborne, 1993). The larvae of the monarch butterfly feed on milkweeds and accumulate cardenolides. Birds feeding on the caterpillars, pupae, or adults, will vomit and subsequently become averted and thus avoid the monarch butterflies. Interestingly, other butterflies, such as viceroy, which do not feed on milkweed, have evolved with nearly identical color pattern (mimicry), so birds avoid these nontoxic insects as well. 

The insects attracted by flowers, and especially their eggs, grubs, and caterpillars, will in turn become food for birds, predatory beetles, parasitic wasps, voles, and amphibians. Many creatures regarded as garden pests are actually a valuable food source for other creatures. 

Insects such as blister beetles and some caterpillars can sting or bum when they are touched. Wear gloves or leam to identify common garden insects. 

Most insect herbivores appear to be rather effectively repelled by furanocoumarin-containing plants (21-24). A notable exception to this generalization occurs among some butterflies of the family Paplllonldae, whose caterpillars are adapted to feed successfully and in fact preferentially on plants that contain linear, but not angular, furanocoumarlns (22). These circumstances prompted us to undertake studies with the black swallowtail butterfly (Papilio polyxenes) and radiolabeled furanocoumarlns in attempts to elucidate the nature of the Insect/furanocoumarln Interactions Involved. 

The disposition patterns of psoralen and Isopsoralen in polyxenes under the parameters studied were not dramatically different. As Indicated in Table III, there were no appreciable differences in the rate of excretion of radioactivity by caterpillars treated with the two compounds. In body tissues, however, levels of total radioactivity in Isopsoralen-treated caterpillars were consistently about twice those observed in psoralen-treated insects (Table IV). Further, levels of unmetabolized parent compounds retained in body tissues (where toxic effects would be expressed) were on the order of 3 times as high in caterpillars treated with the angular furanocoumarin, isopsoralen (Table V). 

Our studies with polyxenes caterpillars and radiolabeled furanocoumarins have provided what appears to be a definitive explanation of the apparent total Insensitivity of these insects to the toxic effects of linear furanocoumarins present in their... 

Microbial chitinase has been proposed as a syngergist for Bt (71). Its role would be to digest holes in the insect gut wall and facilitate penetration of Bt toxin. However, unless the caterpillar s gut pH can be manipulated (71), this is unlikely to be effective with Bt, but might be feasible with NPV (Figure 4). 

But why would a caterpillar not feed for up to 12 hours If suitable food is widely scattered and risks of movement eunong feeding sites are high (above), many insects may be forced to feed only at night (29,54). In north temperate forests, such an insect will "starve" for from 8 to 14 hours. One consequence of this tactic may be that the first meal of the evening may be very risky. 

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