Effects of single and combined applications of entomopathogenic fungi and nematodes against Rhynchophorus ferrugineus (Olivier)

Authors: WAKIL, WAQAS - Non ARS Employee; YASIN, MUHAMMAD - Bahauddin Zakariya University; Shapiro Ilan, David

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2017
Publication Date: 7/20/2017
Citation: Wakil, W., Yasin, M., Shapiro Ilan, D.I. 2017. Effects of single and combined applications of entomopathogenic fungi and nematodes against Rhynchophorus ferrugineus (Olivier). Scientific Reports. 7:5971. https://doi.org/10.1038/s41598-017-05615-3.
DOI: https://doi.org/10.1038/s41598-017-05615-3

Interpretive Summary: Broad spectrum chemical insecticides can harm humans and other non-target organisms. Therefore, environmentally sound alternatives to broad spectrum chemicals must be sought. Certain fungi and nematodes (small round worms) are natural-occurring biological insecticides. These fungi and nematodes are safe to humans and other mammals. The fungi and nematodes are sold commercially to control a variety of economically important insect pests. However, in some cases the level of efficacy (how many pests are killed) is not sufficient. Therefore, methods to improve insect control using fungal and nematode insecticides are needed. In this study, we investigated the potential to combine nematode bio-insecticides with fungal bio-insecticides. As a model insect, we used an important insect pest, the red palm weevil. We discovered that combining fungal and nematode bio-pesticides is highly beneficial because the level of insect mortality observed was synergistic (greater than the sum of the two treatments when applied alone). Therefore, this research indicates potential to improve natural insect pest control by combining nematode and fungal bio-insecticides for control of red palm weevil and other pests.

Technical Abstract: This study was carried out to investigate the insecticidal properties of Beauveria bassiana and Metarhizium anisopliae, and Heterorhabditis bacteriophora Poinar for their virulence against 2nd, 4th and 6th instar larvae of Rhynchophorus ferrugineus (Olivier). Both fungi were either applied alone or in combination, with H. bacteriophora simultaneously or 1 and 2 weeks after fungal application; EPN were also applied alone for comparison. Moreover, assessment of host development, diet consumption, frass production and weight gain were observed at sub-lethal dose rates. In combined treatments, additive and synergistic interactions were observed. Synergism was observed more frequently in H. bacteriophora+B. bassiana combinations than in H. bacteriophora+M. anisopliae combinations. In 2nd and 4th instars, synergy was noted in H. bacteriophora+B. bassiana combinations at 0, 7 and 14 d intervals and in 6th instar synergy was observed only in H. bacteriophora+B. bassiana combinations (at 0 and 7 d intervals). A decrease in pupation, adult emergence and egg hatching was enhanced in the combined treatments. Furthermore, reduced weights and variation in duration of insect developmental stages were observed among entomopathogens and enhanced in H. bacteriophora + B. bassiana combinations. Larvae treated with sub-lethal concentrations exhibited reductions in food consumption, growth and frass production and weight gain.