Toxicological studies of certain insecticides on peach fruit fly, Bactrocera zonata (Saunders) (Diptera: Tephritidae) in Sohag governorate, Egypt

Peach fruit fly, Bactrocera zonata (Saunders) (Diptera: Tephritidae), considered a serious pest in the last decade which attacking a wide range of fruits in Egypt. Control strategies for B. zonata in Egypt are mainly based on the use of conventional chemical pesticides. The aim of this study is to evaluate the efficiency of five pesticides i.e., malathion, methomyl, lambodcyhalothrin, imidacloprid, and spinosad against the three field strains of B. zonata, in addition to susceptible strain. The results showed that, the tested insecticides against the adult stage of susceptible strain of B. zonata arranged descendingly according to LC50 values as followed: λ-cyhalothrin, imidacloprid, methomyl, malathion and spinosad and the corresponding LC50 values were 0.5, 0.5, 0.76, 1.04, and 1.09 ppm, respectively. While when evaluating the same pesticides on the three field strains from three different locations in Sohag governorate (Maragah, Tahta and Shatwra), the results showed that,in Maragah strain was more susceptible than other strains to pesticides λ-cyhalothrin,  imidacloprid, and malathion with LC50 values, 15.22, 31,40, and 30,49 ppm, respectively. While Shatwra strain was the most susceptible to spinosad and Tahta strain to the methomyl pesticide. Likewise, results indicated that the order of the tested field strains of malathion, λ-cyhalothrin and imidacloprid based on the degree of resistance was in descendingly arranged as followed: Tahta, Shatwra, and Maragah, respectively, whereas the corresponding resistance degrees were as follows; (76.95, 51.62, and 29.38)., (84.53, 64.23., and 30.28)., and (241.17, 101.68, and 62.45) – fold.  On the other hand, for methomyl and spinosad, the arrangement differed, as the three field strains were arranged according to their degree of resistance to methomyl as follows: in Shatwra was (462.09 fold), Maragah was (307.94 fold) and Tahta was (178.95 fold), respectively, while for spinosad it was in  Tahta (27.08), Maragah (26.16) and Shatwra (19.88) - fold. The development of resistance to spinosad was observed for the peach fruit fly, thus, we recommended looking for other alternative insecticides in integrated pest management programs.