Effects of pyriproxyfen and imidacloprid on mortality and reproduction of Menochilus sexmaculatus (Coleoptera: Coccinellidae), predator of Agonoscena pistaciae

Abstract

The effect of two insecticides, imidacloprid and pyriproxyfen, were investigated on some biological parameters of ladybird beetle Menochilus sexmaculatus (F.) (Coleoptera: Coccinellidae) under laboratory condition. The ladybird beetle were exposed to insecticides by ingestion of the common pistachio psylla, Agonoscena pistaciae Burckhardt and Lauterer (Hemiptera: Psyllidae) (prey). For imidacloprid, maximum field recommended concentration (MFRC) (1/1 MFRC = 140 ppm), 1/2 and 1/4 MFRC were tested. For pyriproxyfen dilutions of 1/1 MFRC (50 ppm), 2/1 and 1/2 MFRC were used after 24 h. The 100% mortality was observed with imidacloprid in all tested concentrations, whereas no mortality was observed by pyriproxyfen even at the highest concentration (2/1 MFRC). Because of the high mortality observed with imidacloprid, lower concentrations of 1/10, 1/20 and 1/40 MFRC were tested and all predators were killed 3, 7 and 10 days after treatment, respectively. At 1/100 MFRC, no eggs were laid but prey consumption was continued for two weeks. At 1/1 and 2/1 MFRC of pyriproxyfen, ingestion of prey was reduced by 18% and 23%, respectively. At 1/1 and 1/2 MFRC of pyriproxyfen, fecundity and fertility of the coccinellid predator was decreased to 43% and 24.5%, respectively. Imidacloprid at 1/100 MFRC caused significant reduction on fecundity but had no detrimental effect on fertility of the produced eggs. Therefore, unlike the pyriproxyfen that had not acute toxicity, the imidacloprid was extremely toxic to coccinellid at MFRC. However, pyriproxyfen was able to affect on feeding ratio and reproduction of M. sexmaculatus.