Volatile and non-volatile organic compounds stimulate oviposition by aphidophagous predators

Authors: Riddick, Eric

Submitted to: Insects
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2020
Publication Date: 10/10/2020
Citation: Riddick, E.W. 2020. Volatile and non-volatile organic compounds stimulate oviposition by aphidophagous predators. Insects. 11:1-11. https://doi.org/10.3390/insects11100683.
DOI: https://doi.org/10.3390/insects11100683

Interpretive Summary: In pesticide-free growing systems, predatory insects are important natural enemies of crop pests such as aphids. Developing techniques to stimulate egg production by predators will ensure a ready supply of individuals for release into growing systems for aphid control. Volatile and non-volatile organic compounds can play a role in stimulating predators to lay their eggs, i.e., oviposit. This study compiled all available records of compounds stimulating oviposition by aphid predators, calculated an egg production ratio (EPR), and correlated EPR to vapor pressure and molecuar weight of active compounds. The results indicated that volatile organic compounds and non-volatile ones stimulated lady beetles (coccinellids) and hoverflies (syrphids) to produce eggs. Only volatile organic compounds stimulated oviposition by lacewings (chrysopids). Molecular weight and vapor pressure of these compounds were correlated with EPR. EPR was negatively correlated with molecular weight, but positively correlated with vapor pressure. In summary, this study suggests that the most effective oviposition stimulants (for aphid predators) will be low-to-moderate molecular weight compounds with moderate-to-high vapor pressures.

Technical Abstract: Introduction: Evidence that volatile organic compounds (VOCs) and non-VOCs stimulate oviposition by aphidophagous predators is scattered throughout the literature. The objectives of this review were to (1) compile records indicating that VOCs and non-VOCs were responsible for oviposition stimulation, (2) calculate an egg production ratio (EPR) for stimulated predators, and (3) determine if EPR was correlated with vapor pressure and molecular weight of active compounds. Methods: The USDA, National Agricultural Library, online digital catalog system was used to retrieve abstracts, then the full text of manuscripts on oviposition stimulants for predators. Oviposition-stimulating VOCs and non-VOCS were tabulated with molecular weights and vapor pressure estimates. EPRs were calculated for stimulated coccinellids, syrphids, and chrysopids. Results: Both VOCs and non-VOCs stimulated oviposition behavior by coccinellids and syrphids, but not chrysopids. EPR was greatest for syrphids. Two VOCs, (E)-ß-farnesene and 3-methyl-2-butenal, stimulated very high EPR values by the syrphid Episyrphus balteatus. Regardless of predator taxa, EPR was negatively and positively correlated with molecular weight and vapor pressure, respectively. Conclusions: Syrphids (rather than coccinellids or chrysopids) produce more eggs in response to VOCs. Organic compounds with low-to-moderate molecular weights and moderate-to-high vapor pressures might be most effective oviposition stimulants for aphidophagous predators.