Beta-ionone is a functional plant volatile that attracts the parasitic wasp, Microplitis pallidipes

The effects of plant volatiles on parasitoids are important with regards to the tri-trophic interactions among host plants, insect herbivores, and their natural enemies. However, the effects of plant volatiles on the important parasitoid ( Microplitis pallidipes Szépligeti; Hymenoptera: Braconidae) of noctuids have not been determined at the molecular, laboratory, and outdoor scales with complementary approaches. The odorant binding protein 8 of M. pallidipes (MpOBP8) with an open reading frame of 459 bp was cloned and successfully expressed in Escherichia coli (Eubacteriales: Enterobacteriaceae). The purified protein MpOBP8 had a relatively high binding capacity to the plant volatile β- ionone (Ki value was 28.86 μM) in the fluorescence competitive binding assay. Meanwhile, Y-tube olfactometer experiments indicated that β- ionone selectively attracts the parasitic wasp as the ratio of M. pallidipes selecting β- ionone vs. control was 2:1. Likewise, field screenhouse experiments verified the above results as the ratio of M. pallidipes selecting β- ionone vs. control was close to 2:1. This study suggested that β- ionone is a plant volatile that attracts the parasitoid M. pallidipes , and MpOBP8 may play a key role in the discrimination of M. pallidipes in searching for hosts via β- ionone. In general our results suggest that β- ionone has the potential to enhance the biocontrol effect of parasitoids on insect herbivores.