Side effects of kaolin on natural enemies found on olive crops.

Abstract

Protected barriers of kaolin, a natural clay mineral, were tested against olive pests in the last few years with good results on Bactrocera oleae, the most serious pest of olive groves. Good control of the carpophagous generation of Prays oleae, as well as a minor presence of Saissetia oleae, were also reported. Adults of Psyttalia concolor (parasitoid of B. oleae), Chrysoperla carnea (oophagous predator of P. oleae), Chilocorus nigritus (predator of diaspidid scales) used in this work as representative of Chilocorus bipustulatus and Anthocoris nemoralis (predator of Euphyllura olivina and Liothrips oleae) were selected to be exposed to an inert surface treated with kaolin at the maximum field rate used against B. oleae. Dimethoate was used as reference compound. Mortality was recorded at 24, 48 and 72 h. Sublethal effects, as life span in C. nigritus and reproductive parameters (fecundity and fertility in case of C. carnea and A. nemoralis, beneficial capacity in P. concolor) were also assessed. Kaolin was classified as harmless (1) to adults of C. nigritus. There were no effects on mortality on C. carnea and P. concolor, although C. carnea fecundity and P. concolor progeny were slightly reduced (2). A. nemoralis was the most sensitive of the four insect tested, with 44% mortality and 66.6% reduction of eggs production. Dimethoate was very toxic with 100% mortality for each test species after only 24h of exposure. Compared to classical insecticide commonly used in olive crops as dimethoate, Kaolin seems to be a promising compound because of its selectivity. However, because of its uncommon mode of action, other modes of exposure than contact with a treated surface need to be tested to confirm or infirm the apparent harmlessness of this product