Feeding by lepidopteran larvae is dangerous

ecoent0042

Ecological Entomology (1997) 22, 121–123

S H O R T C O M M U N I C AT I O N

Feeding by lepidopteran larvae is dangerous
E . A . B E R N AY S
Department of Entomology and Centre for Insect Science, University of Arizona, U.S.A.

Key words. Predation, feeding, Manduca sexta, Uresiphita reversalis, caterpillars, wasps, bugs.

Introduction It is difficult to obtain direct measures of predation on small animals such as insect herbivores. Instead, disappearance has sometimes been used as a rough measure of predation, or, more reliably, populations of insects inside and outside exclosures may be compared over time. In this way, many studies have deduced the importance of predation as a mortality factor for insect herbivores such as lepidopteran larvae. For example, Feeny et al. (1985) showed that predation was the largest source of mortality of Papilio polyxenes larvae. Invertebrates were most important for smaller larvae while vertebrates became important for larger ones. Much can also be deduced after natural selection has operated, about the evolutionary importance of predators by the avoidance strategies employed by caterpillars (Heinrich, 1993) However important predation of lepidopterans may be, relatively few people have spent time observing larvae for long enough to see many predation events, except where populations of both herbivores and predators were unusually large. Examples of data that demonstrate the danger of movement include the finding that movement increased the risk of ant predation on a geometrid caterpillar (Bergelson & Lawton, 1988). Similarly, caterpillar movement was shown to increase predation by a pentatomid bug (Marston et al., 1978) and a crab spider (den Boer, 1971). So, while it may be assumed that movement is generally dangerous, less is known about the risk of actually feeding. This study is a quantification of the risk of predation by two predators, posed by feeding in two caterpillar species. Methods and Results