Effects of entomopathogenic nematodes and/or fungus on the red palm weevil, Rhynchophorus ferrugineus (Curculionidae: Coleoptera)

Abstract

Summary The invasive red palm weevil (RPW) (Rhynchophorus ferrugineus) (Coleoptera: Curculionidae) is one of the most destructive palm pests in the world. More options are needed for its management, including optimised use of microbial entomopathogens (EP). The sub-lethal effects of an entomopathogenic fungus (EPF) Beauveria bassiana (isolate WG-11) (Ascomycota: Hypocreales) (at 1 × 104 spores ml−1) and two entomopathogenic nematode (EPN) species, Heterorhabditis bacteriophora (at 100 infective juveniles (IJ) ml−1) and Steinernema carpocapsae (at 50 IJ ml−1) were evaluated in various combinations against laboratory-reared 3rd, 5th and 8th instar larvae of RPW in bioassays. Individual and combined effects of both EP were observed after the pre-application of B. bassiana fungus at 0-, 1- and 2-week intervals. Combined treatments were tested for antagonistic, additive and synergistic effects. Additive and synergistic effects were observed in B. bassiana/S. carpocapsae and in B. bassiana/H. bacteriophora combined treatments. Early instar larvae of RPW were more susceptible than older instars. Sole and combined EP treatments decreased pupation, subsequent emergence of RPW adults and hatching. Sub-lethal effects of EP were observed in R. ferrugineus following application at the above-mentioned rates to 3rd, 5th and 8th instar larvae, including reduced larval weights, increased larval, pre-pupal and pupal durations, reduced adult weights and life spans. Simultaneous combined applications of B. bassiana/S. carpocapsae and B. bassiana/H. bacteriophora at the above-mentioned rates against last instar (9th) larvae of R. ferrugineus reduced food consumption, frass production and affected weight gains.