Behavioral responses of riptortus pedestris to volatile organic compounds of the major host plant, glycine max

Abstract

The bean bug, Riptortus pedestris, is a polyphagous insect that feeds primarily on leguminous plants, especially soybean (Glycine max). Although the bean bug is an economically important pest of soybean, little is known about how the insect locates soybean fields. In this dissertation, literature on plant-insect interactions focusing on the behavioral responses of insects to plant semiochemicals were reviewed, highlighting different theories on how insect perceive host odors, procedures of the studies and application of these knowledge to solve real-world problems. In order to understand behavioral responses of the bean bugs to soybean semiochemicals, behavioral responses of adult bean bugs to soybean odor was monitored. R. pedestris adults were attracted more to their host-plant soybean, even when physical contact was absent, than to air or to a non-host plant. Accordingly, we hypothesized that R. pedestris can recognize soybean through a plant’s volatile organic compounds (VOCs). After collection of soybean VOCs via dynamic headspace collection method followed by gas chromatography-mass spectrometry (GC-MS), five VOCs were identified and quantified from intact soybean plants at the vegetative stage including (Z)-3-hexen-1-ol, (Z)-3-hexenyl acetate, 4-ethylbenzaldehyde, α-farnesene, and methyl salicylate. We then examined the electroantennogram responses of R. pedestris to soybean volatiles. Response spectra of the antennae to these volatiles clearly showed that both male and female R. pedestris can detect all of identified soybean volatiles. The adult bean bugs did not show behavioral orientation to any individual compounds, but showed significant orientation to a particular blend of synthetic soybean volatiles when tested under the laboratory conditions. In the field, this soybean volatile blend did not significantly attract the bean bugs, but it did interact synergistically with the aggregation pheromone to attract the bean bugs. These results highlight the role of host plant volatiles in the sensory ecology of R. pedestris and help explain colonization pattern of the bean bugs in soybean fields. We also identified a semiochemical blend that repels the bean bug strongly in the laboratory setup. We tested the efficacy of this blend as a tentative repellent in combination with tactical deployment of the blend of soybean volatiles and the bean bug aggregation pheromone in soybean field. As a result, we could observe significantly less number of bean bugs attracted to soybean plot treated with both repellent and attractant (push-pull treatment), compared to the plot where only attractant was treated (pull treatment). Overall, the findings of this dissertation can contribute to a development of cost-effective and environmentally friendly push-pull strategy as a part of integrated pest management in soybean agriculture against the bean bug.