Learning Behavior of <i>Sclerodermus sichuanensis</i> Xiao: Habitual Responses and Cumulative Effects

Abstract

Sclerodermus sichuanensisXiao is an important natural enemy of forest boring pests. We used a two-way selection test to investigate the behavioral mechanisms used by S. sichuanensis when searching for hosts. Y-tube olfactometers and electroantennogram recordings were used to study learning by S. sichuanensis exposed continuously or discontinuously to a mixture of longhorn beetle (Anoplophora chinensis Forster) fecula and wood meal, and to mixtures of A. chinensis fecula and wood meal from different trees, either successively or simultaneously. Following exposure of 4-day-old adult S. sichuanensis to a mixture of A. chinensis fecula and wood meal for 3 d, tropism toward this odor did not improve significantly. After discontinuous exposure to a mixture of A. chinensis fecula and wood meal, adult S. sichuanensis exhibited a habitual response and its tropism to this odor decreased markedly. Five-day-old female S. sichuanensis that previously experienced a mixture of A. chinensis fecula and wood meal from two different host trees (willows, Salix sp., and oriental parasol, Platanus orientalis) or a mixture of A. chinensis fecula and wood meal (willows) during the eclosion period and were then stimulated by the mixture of A. chinensis fecula and wood meal (oriental parasol) at 4 days old exhibited a relatively strong behavioral reaction to mixed stimulation by the two types of substrate information. These observations suggest that the learning behavior of S. sichuanensis is cumulative. The parasitoid can differentiate between two kinds of chemical information experienced simultaneously and recognize the two odors when they are experienced successively. This discovery is important for elucidating the behavioral mechanisms of learning in parasitoids and for the development and application of natural enemy insects for pest control.