The Joint Action of Entomopathogenic Nematodes Mixtures and Chemical Pesticides on Controlling Helicoverpa armigera (Hübner)

Abstract

Chemical pesticides are characterized by the rapid impact effect in reducing pest population, while, microbial pesticides need along the latent period to cause a limited reduction of the pest population. Low efficiency of biocides may be due to low compatibility with agrochemicals or poor application of biocide, so, the study carried out to evaluate the possibility of mixing five common chemical insecticides and nematicides with five compatible entomopathogenic nematodes (EPNs). For the control of tomato fruit borer (Helicoverpaarmigera),bioassay revealed that pesticide chlorpyrifos (Pestban 48% EC), chlorpyrifos (Tafaban 48% EC) and flubendiamide (Takumi 20% WG) were applied at the recommended dose.  Flubendiamide was less toxic to EPNs infective juveniles compared to fenamiphos (Dento 40% EC). Moreover, steinernematid species were more sensitive than heterorhabditid species to pesticides recording 49.45% and 43.76%, respectively, after 7 days of exposure. The joint action of tested chemical pesticides with IJs of EPNs in controlling the 5th instar larvae of tomato fruit wormshowed an additive or antagonistic reaction with no evidence of synergistic action. Antagonism reaction was recorded with all fenamiphos combinations;the combination ofabamectin and S. feltiae as well as H. bacteriophora (Ba-1), in addition to, flubendiamide combinations with S. feltiae and H. bacteriophora (Ba-1). While, an additive effect was observed in flubendiamide combinations with S. glaseri, S. carpocapsae and H. bacteriophora (HP 88). In the greenhouse experiment, the application of EPNs alone caused mortality ranged from 28 to 36% for 5th instar larvae. Whereas, the highest larval mortality was observed in descending order for combinations between H. bacteriophora (HP88 strain) with fenamiphos (64.0%), chlorpyrifos (54%) and abamectin (54.0%), while, local isolate, H. bacteriophora (Ba-1 strain) achieved mortality ranged from 40 to 50 % with the tested pesticides. Overall, results indicate the feasibility of the integrated use of these nematode species and chemical pesticides in crop protection.