Effect of metarhizium anisopliae and its complementation with phenylacetonitrile pheromone on reproductive potential and mortality of gregarious nymphs of schistocerca gregaria

Abstract

Recent concerns over possible human health problems and environmental damage resulting from large scale application of chemical' pesticides for desert locusts control have led to proposals for alternative control strategies. Biological control based on pathogens formulated as biological pesticides is an alternative that offers more rapid prospects for implementation. This study was conducted to investigate, under laboratory conditions the effect of co-treatment of gregarious desert locust nymphs with phenylacetonitrile and low doses of the fungus, Metarhizium anisopliae isolate ICIPE 21, with the aim of developing a mycopesticide formulation. The specific objectives of this study were: To determine median lethal dose (LD50)) and median lethal time (LT 50) of, Metarhizium anisopliae isolate ICIPE 21; to assess the effect of two different modes of application -of pheromone and fungus on insect mortality; to assess the viability of .conidia in fungus-pheromone cocktail, and to investigate the sublethal effect of the pathogen on reproductive potential of the surviving adults. Conidia of Metarhizium anisopliae were formulated in aqueoussolution of Triton X-IOO or in mineral oil while the pheromone, phenylacetonitrile (P ~N) was applied in mineral oil. Experimental and control insects were maintained at 28 ± 2° C and 50-60 % relative humidity throughout the experiment, Evaluations were carried out and fresh wheat seedlings supplied as food daily. The time required to kill 50% of the nymphs decreased significantly with the inclusion of the pheromone, phenylacetonitrile. For instance, Metarhizium anisopliae alone at a concentration, lxl0s conidia ml', had a median lethal time of9.4 days and upon inclusion of PAN, it dropped to 6.2 days. The median lethal dose (LDso) of Metarhizium anisopliae isolate lCIPE 21 was 6.5xl04 conidia ml'. The LTso values (time taken to attain 50% mortality) for the fungus alone, ranged from 30 days for lx104 conidia mr! to 3 days for the highest dosage of 5xl07 conidia mr! . The fungus -pheromone cocktail did not affect conidia viability as it was maintained at 80% for a period of three weeks. The pathogen had no sub-lethal effects on the reproductive potential of the surviving adults. There was no difference in percentage hatchability of eggs between treated (67%) and untreated (74%) females. The results of this laboratory study demonstrate a complementation interaction between phenylacetonitrile (PAN) pheromone and .low doses of M. anisopliae for control of gregarious nymphs of Schistocerca gregaria. These results are promising since they will lead to development of a fungus-pheromone formulation for biological control of the desert locusts.