Joint Toxicity of Insecticides and some Entomopathogenic Nematode Species against Rhynchophorus ferrugineus (Olivier) Insect In Vitro

Abstract

Efficacy of imported and local entomopathogenic nematodes (EPNs) alone or in combinations with the insecticides, imidacloprid, zeta-cypermethrin, profenfos and emmectin benzoate against red palm weevil (RPW), Rhynchophorus ferrugineus differed greatly according to nematode species and instar larvae under laboratory conditions.Both Heterorhabditis bacteriophora (HP88 strain) and local species H.bacteriophora (Ar-4 strain) showed promising results by killing 92.20 and 82.13 % of the 4th instar larvae after 9 days of exposure, respectively. Whereas, S. feltiae and H. bacteriophora (Ht strain) showed less insecticidal activity against 4th, 9th and 11th instar larvae. On the other hand, Egyptian H. bacteriophora (Ar-4 strain) was more effective than H.bacteriophora (Ht strain). Adults of R. ferrugineus were less susceptible to nematode infection than instar larvae. According to LD 50 with LT 50 values, H. bacteriophora (HP88 strain) was more aggressive killer to RPW than native strains and LT50 values were 5.693, 4.319 and 2.943 days at concentrations of 500, 1500 and 2500IJs/ml, respectively. At the LC50 and LC90 values, imidacloprid was the most toxic for 9th and 11th Instars of R. ferrugineus, whereas, profenfos was the least effective one after 24 hr of exposure. The joint action of chemical pesticides with IJs of EPNs in controlling the 9th and 11th instar larvae of R. ferrugineus showed an additive or potentiation reaction with no evidence of antagonistic action.Overall, results indicate the feasibility of an integrated use of these nematode species and chemical pesticides in controlling red palm weevil under field conditions.