Ovipositional Behavior of the Alfalfa Seed Chalcid (Hymenoptera: Eurytomidae) in Response to Volatile Components of Alfalfa 1

Abstract

Behavior of the alfalfa seed chalcid, Bruchophagus roddi (Gussakovsky), during site selection and oviposition is described. Seed development and morphological changes in seed are also described for the period that seeds are susceptible to oviposition by chalcids. Females laid significantly more eggs when exposed to myrcene, hexyl acetate, (Z)-3-hexenyl acetate, caryophyllene, octan-3-one, and β-farnesene. Fewer eggs were laid when females were exposed to octan-3-ol, γ-muurolene, and 2-phenylethanol. Based on observations with pin-pricked pods, a high rate of evaporation of these compounds via physical wounds in the pod (e.g., oviposition wounds) may warn females to avoid the area for oviposition so that two eggs are not laid in the same seed. Since octan-3-ol, γ-muurolene, 2-phenylethanol, and β-farnesene are concentrated in seed pods, the lower rate of emanation of these compounds from undamaged pods may also provide chemical stimuli that help females distinguish seed pods from other parts of the plant. Volatile components in alfalfa that had an effect on oviposition varied substantially in concentration among plant parts; none occurred only in pods.