Oviposition-Deterring Pheromone(ODP) Originated From Larval Frass Of Cotton Bollworm, Helicoverpa Armigera (Lepidoptera: Noctuidae)

The cotton bollworm (CBW), Helicoverpa armigera (Hubner) (Lepidoptera:Noctuidae) is a major pest of cotton in China, The larvae feed on cotton leaves, young buds, flowers and bolls, resulting in a huge yield reduction in northern China since 1990's. There remains a need, therefore, to develop alternative control strategies. Oviposition-deterring pheromones (ODPs) can deter oviposition by intra- and interspecific females, elicit defense by host plant and attract natural enemies. Therefore, ODPs have some potential field applications. Here we investigate oviposition-deterring pheromone originated from larval frass of cotton bollworm.1. The chemical identification of the ODPs from larval frassOviposition-deterring pheromone in the frass of cotton bollworm, Helicoverpa armigera larvae fed on an artificial diet (FA) and on cotton Gossypium hirsutum leaves (FC) were investigated by behavioral bioassays in laboratory. It was found that a water suspension or a hexane extract of the frass FA or FC, in contrast to the corresponding foods, significantly deterred oviposition of conspecifics. When hexane extracts of the frass FA and FC were further partitioned into polar and neutral lipid fractions, two polar fractions and the neutral fraction from frass FC significantly reduced oviposition. The polar lipid fractions of two frass extracts contained several fatty acids and their corresponding methyl esters, mainly palmitic and oleic acid at the ratio nearly 1:1. The artificial diet and cotton leaves also had these fatty acids, but the total amount was about 1/7-1/9 of those in corresponding frass. These results demonstrate that oviposition-deterring compounds are greatly concentrated in the larval gut, thereby reaching a threshold concentration and thus gaining oviposition-deterring activity.2. EAG response to the larval frass extractsFemale electroantennography (EAG) responses to two frass extracts (FA, FC) and several authentic fatty acids were tested. It was found that all test materials elicited significant EAG responses above solvent and background when applied in an amount equivalent to 2.5 μg fatty acids per filter paper strip. Among five fatty acids, palmitic acid...