Contact and Gastric Effect of Peppermint Oil on Selected Pests and Aphid Predator Harmonia axyridis Pallas

Peppermint essential oil (EO) has been extensively tested to date in reducing stored-product insects and insects of public health concern with very promising results, while only a few studies target important crop pests. There is also very little information on the effects of peppermint EO on non-target organisms, especially concerning contact and gastric effects at the same time. The goal of the investigation was the determination of the effect of peppermint EO on the mortality of Aphis fabae Scop.; the feeding intensity and weight gain of Leptinotarsa decemlineata Say. larvae; and the mortality and voracity of non-target organism Harmonia axyridis Pallas larvae. Our research indicates promising use for the M. piperita EO against aphids and young larvae (second instars) of the Colorado potato beetle. M. piperita EO showed good insecticidal efficacy against A. fabae with LC(50) = 0.5442% for nymphs and 0.3768% for wingless females after 6 h. Over time, the LC(50) value decreased. For the second instar larvae of L. decemlineata, the LC(50) values were 0.6278%, 0.3449%, and 0.2020% after 1, 2, and 3 days of the experiment, respectively. On the other hand, older larvae (fourth instar) were characterized by significant resistance to the tested oil concentrations with LC(50) value = 0.7289% after 96 h. M. piperita oil (contact and gastric effects) at a concentration of 0.5% was found to be toxic to young larvae (2 and 5 days old) of H. axyridis, while EO at a concentration of 1% was toxic to 8-day-old larvae. Thus, for the sake of ladybug safety, it would be advisable to use EO from M. piperita against aphids at concentrations lower than 0.5%.