Novel approaches to assess lethal and sublethal effects when evaluating risks of biopesticides toward beneficial arthropod

Biopesticides are defined as substances derived from naturally occurring materials (i.e., plants, microorganisms and minerals) characterized by low environmental effects, rapid degradation, and low toxicity for humans and beneficial insects. However, the assumption of safety for beneficials is generally solely based on the evaluation of acute mortality upon exposure, overlooking possible underhanded sublethal effects.

We selected the parasitoid Leptomastix dactylopii Howard (Hymenoptera: Encyrtidae) attacking the mealybug pest Planococcus citri Risso (Hemiptera: Pseudococcidae) as case study to investigate whether the exposure to four biopesticides authorized in organic citrus orchards in the EU, in addition to a Clitoria ternatea (Fabales: Fabaceae) extract, causes significant alterations in the parasitoid physiology and behavior. Classical ecotoxicological tests aimed at evaluating survival rate, parasitization rate, emergence rate and sex-ratio, have been combined with olfactometry to assess deviation in the dynamics of the orientation toward the host, and with a novel optical oxygen respirometry technique to observe possible alterations in oxygen consumption.

All the tested compounds except spinosad were found to not harm L. dactylopii, causing neither lethal nor significant sublethal effects in the exposed parasitoids compared to the control.

In conclusion, all the tested biopesticides showed compatibility within biological control strategies in a field scenario (i.e., organic orange orchards). Moreover, the screening protocols described in the present manuscript, integrating classical ecotoxicological tests and novel approaches targeting specific behavioral and physiological toxicant-induced alterations, allowed to shed light on the multifaceted impact of biopesticides on natural enemies.