Lethal and oxidative stress side effects of organic and synthetic pesticides on the insect scale predator Rhyzobius lophanthae

Although pesticides are the most widely used method for the control of agricultural pests, natural insect enemies can successfully suppress pest populations. However, side effects of pesticides can have strongly deleterious impacts on these biocontrol agents. In this context, lethal (mortality over time) and sublethal (oxidative stress) effects of organic and synthetic pesticides (seven of each) on the insect scale predator Rhyzobius lophanthae Blaisdell (Coleoptera: Coccinellidae) were evaluated. Adults of R. lophanthae were exposed to pesticide residues every seven days over a period of 49 days following pesticide application. Oxidative stress was measured only in the insects surviving the first day of pesticide application. We found that most organic pesticides were harmless, causing less than 30% mortality in R. lophanthae, whereas the majority of the tested synthetic pesticides led to 100% mortality, which was persistent over time. Some organic pesticides, however, caused significant oxidative stress in R. lophanthae. Overall, the results showed that organic pesticides were less harmful than synthetics, resulting in low mortality over time in R. lophanthae, although some may result in sublethal effects in biological control agents. Our findings offer useful insights into general impacts of organic versus synthetic pesticides on beneficial insects, suggesting that they could provide a safer and effective alternative to synthetics for the control of agricultural pests.