How do herbivorous insects cope with noxious secondary plant compounds in their diet?

Abstract

Herbivorous insects use a variety of physiological mechanisms to cope with noxious (i.e., unpalatable and/or toxic) compounds in their food plants. Here, I review what is known about this coping process, focusing on one species of caterpillar, the tobacco hornworm (Manduca sexta). Herbivorous insects possess both preingestive (i.e., chemosensory) and postingestive response mechanisms for detecting plant secondary compounds. Stimulation of either class of detection mechanism inhibits feeding rapidly by reducing biting rate and/or bite size. This aversive response is highly adaptive during encounters with secondary plant compounds that are toxic. The insect's dilemma is that many harmless or mildly toxic compounds also activate the aversive response. To overcome this dilemma, herbivorous insects employ at least three mechanisms for selectively deactivating their aversive response to relatively harmless secondary plant compounds: (1) the presence of carbohydrates can mask the unpalatable taste of some secondary plant compounds; (2) prolonged dietary exposure to some unpalatable secondary plant compounds can initiate long-term adaptation mechanisms in the peripheral and central gustatory system; and (3) dietary exposure to toxic compounds can induce production of P450 detoxication enzymes. Thus, herbivorous insects utilize an integrated suite of physiological mechanisms to detect potentially toxic compounds in foods, and then selectively adapt to those that do not pose a serious threat to their growth and survivorship.

Honeybees and nectar nicotine: Deterrence and reduced survival versus potential health benefits

“…Sweetness may likewise mask the bitter taste of alkaloids in caterpillars, in which simple carbohydrates such as myo-inositol can interfere with the response to caffeine (Glendinning, 2002), and the deterrent effect of a given quinine concentration on feeding in blowflies depends on the sucrose concentration in the mixture (Moss and Dethier, 1983). We observed an increase in uptake of concentrated sugar diets, which is expected for honeybees as these diets are more profitable (Roubik and Buchmann, 1984).…”

The effect of varying alkaloid concentrations on the feeding behavior of gypsy moth larvae, Lymantria dispar (L.) (Lepidoptera: Lymantriidae)

“…We have evaluated the deterrency of these alkaloids without addressing their neural modes of action. It was not possible to address this question with our experimental design, since the feeding behavioral bioassays extended over several hours and we could not rule out that several mechanisms, including gustation, olfaction, somatosensory, and viscerosensory (e.g., habituation, pre-and post-ingestive feedback mechanisms, and/or toxicity) could have been responsible for the feeding deterrency, as suggested in other studies (e.g., Glendinning et al, 2001;Wheeler et al, 2001;Glendinning, 2002). Determining the underlying neural mechanisms of alkaloid feeding deterrency will be a challenging, but rewarding aim of future studies.…”

Attraction of Spodoptera frugiperda Larvae to Volatiles from Herbivore-Damaged Maize Seedlings

“…However, linalool is unlikely to be the only volatile from maize seedlings that could evoke behavioral responses in sixth instar FAW, due in part to the role of feeding experience in orientation behaviors of generalist noctuid larvae. Olfactory preferences of polyphagous noctuids, such as FAW, are strongly influenced by exposure to odors during feeding (Anderson et al, 1995;Carlsson et al, 1999;Glendinning, 2002). Experience-based preferences are thought to confer a certain degree of behavioral plasticity on the development of host location Fig.…”