Effect of volatile emissions, especially alpha-pinene, from persimmon trees infested by Japanese wax scales or treated with methyl jasmonate on recruitment of ladybeetle predators

Abstract

Persimmon, Diospyros kaki L., is an important fruit tree in northern China. Japanese wax scale, Ceroplastes japonicus Green (Hemiptera: Coccoidea: Coccidae), is the most destructive pest in persimmon orchards and is difficult to control using chemical pesticides. This paper studied the variety of volatile emissions from persimmon trees attacked by wax scale or induced by applications of methyl jasmonate (MeJA), an exogenous signaling material. We also studied the role of volatiles in recruiting the ladybeetle, Chilocorus kuwanae Silvestri (Coleoptera: Coccinellidae), a primary predator of wax scale. The results showed that the ladybeetles displayed strong taxis responses to the odor sources from trees treated with MeJA and wax scale-damaged trees. Within 24 h after the trees were treated with MeJA, the number of ladybeetles responding to the treated trees fluctuated based on the amount of volatiles released over a diel period. Chemical analysis of the volatiles showed that terpenoid compounds, especially alpha-pinene, increased from both the wax scale-damaged and MeJA-treated trees and that this was the reason for the ladybeetle attraction. Therefore, alpha-pinene was used as a single signal source to examine the taxis response of C. kuwanae. The results suggest that alpha-pinene plays a significant role in attracting the ladybeetles. It is therefore concluded that MeJA application might be used to stimulate the defense function of persimmon trees by inducing the release of terpenoids, especially alpha-pinene, and thereby recruiting more ladybeetles to control the scale insects.