Feeding behaviour of young larvae of Pieris rapae crucivora (Lepidoptera: Pieridae) and its effect on parasitism by Cotesia glomerata (Hymenoptera: Braconidae)

Aya Nakayama,Jun Tagawa,Keiji Nakamura

doi:10.14411/eje.2018.038

Abstract

We investigated the effect of the feeding behaviour of young larvae of Pieris rapae crucivora Boisduval (Pieridae) on parasitism by the parasitoid wasp, Cotesia glomerata (L.) (Braconidae). Young, 1st-3rd instar larvae used approximately three sites for feeding each day. When not feeding, they moved a short distance away from the feeding sites (= feeding marks) and rested. For first, second and third instar larvae, the distances from the new mark, made within 24 h, to larva at rest were, respectively, about 3.5 mm, 5 mm and more than 10 mm. To resume feeding, they moved back to one of the former feeding sites or a new site. The percentage of the feeding marks older than 24 h that attracted parasitoids was less than 50%. Time spent searching for hosts by a parasitoid was short. Larvae placed 5 mm or more from a feeding mark were less parasitized than the larvae placed near a mark. The number of feeding marks affected parasitism. When comparing single-marked and triple-marked leaves, the percentage parasitism of the larvae on the latter was significantly lower than that of the larvae on the former. On triple-marked leaves, parasitoids visited each mark unevenly. Accordingly, the time spent searching each mark differed significantly among the marks. Because of this confusing effect, hosts are considered to be reducing the risk of parasitism. Our results demonstrate that the feeding habits of young larvae of P. rapae crucivora are adaptive in terms of reducing the risk of parasitism by C. glomerata.

Highlights

Many insects have evolved various types of defensive behaviour to counter attacks by parasitoids
Feeding behaviour of host The larvae of P. rapae crucivora moulted to the third instar 5–6 days after hatching when kept at room temperature
Distance to a fresh mark from the previous mark increased with larval development, not significantly between the second and third instar larvae

Summary

Introduction

Many insects have evolved various types of defensive behaviour to counter attacks by parasitoids. Pieris rapae crucivora Boisduval (Lepidoptera: Pieridae) is a well-known, small white butterfly in Japan. It is likely that large larvae are at a greater risk of being attacked by predators than small larvae. Small larvae are more likely to be vulnerable to parasitoids than large larvae (Slansky, 1986; Van Driesche, 1988; Reavey, 1993). The gregarious parasitoid wasp Cotesia glomerata (L.) (Hymenoptera: Braconidae) attacks young Pieris larvae and strongly affects the population dynamics of P. rapae crucivora (Matsuzawa, 1958; Ohsaki & Sato, 1990). Percentage parasitism of P. rapae crucivora by C. glomerata are high in Japan. It is likely that cabbageworms have evolved methods for reducing the risk of parasitism.

Methods

Results

Conclusion