Prospects of fungal endophytes in the control of Liriomyza leafminer flies (Diptera: Agromyzidae) in common bean Phaseolus vulgaris Linnaeus (Fabales: Fabaceae) under field conditions

Liriomyza leafminers species are exotic pests of horticultural crops in Africa. The most economically important species include Liriomyza sativae (Blanchard), L. trifolii (Burgess) and L. huidobrensis (Blanchard) (Diptera: Agromyzidae) which are major pests of many vegetables and ornamental crops worldwide. In Kenya, production of horticultural crops is severely constrained by infestation of Liriomyza leafminer flies (LMF). As a result, farmers increasingly use synthetic chemical insecticides and spray more frequently in response to damage by key pests such as LMF which has led to development of pests’ resistance to synthetic pesticides, elimination of natural enemies, environmental contamination, and health risks due to pesticide residues and increased costs of production costs. These challenges have stimulated an increased interest in the use of biological control strategies. Parasitoids and fungal entomopathogens are being considered as part of an integrated strategy for leafminer management in Kenya. The objective of this study was to evaluate the prospects of endophyte isolates of Beauveria bassiana (Balsamo) Vuillemin G1LU3 and Hypocrea lixii Patouillard F3ST1 for the control of Liriomyza leafminer in common bean Phaseolus vulgaris (Linnaeus) (Fabales: Fabaceae) crops through seeds inoculation under field conditions. Autodissemination device (AD) treated with conidia of Metarhizium anisopliae (Metschnikoff) Sorokin ICIPE 20 was also added as a treatment. Leafminer flies infestation was not significantly different during the long rains season (season 1) but was higher in the controls than in endophtyte treatments at both sites during the short rains season (season 2). Three key Liriomyza species [(L. huidobrensis Blanchard, L. sativae Blanchard and L. trifolii (Burgess)] and six parasitoid species [(Opius dissitus Muesebeck, Phaedrotoma scabriventris Nixon, Diglyphus isaea Walker, Neochrysocharis formosa Westwood, Hemiptarsenus varicornis Girault and Halticoptera arduine (Walker)] were identified during the trials. The effects of endophytes on leafminer infestation, number of pupae, leafminer flies and parasitoids emergence and yield were the parameters evaluated. The experiments were conducted in the laboratory and field. Field trials were carried out for two seasons (long and short rains seasons) in two sites (Sagana and Naromoru, Central province of Kenya). Both isolates successfully colonized different parts of P. vulgaris plants, although the colonization was higher with H. lixii F3ST1 than B. bassiana G1LU3 at both sites. The mean number of xv pupae from the infested leaves varied between 141-252 and 331-416 in endophyte and control treatments, respectively, during the long rains season (season 1) and from 110-223 and 366-523, respectively, in endophyte and control treatments during the short rains season (season 2). There were no significant differences among the treatments in the number of parasitoids that emerged from pupae. Higher yield of P. vulgaris seeds was obtained in endophyte treatments than in control treatments. The inclusion of AD treatment did not have significant effect on all the parameters evaluated, except yield. Results of the present study suggest that both fungal isolates hold potential for pest management and could be considered for the control of leafminer flies. Improvement of the autodissemination device traps is necessary by using materials which could withstand harsh environment conditions in the field. Further work should be done to establish colonization of P. vulgaris plants in the subsequent generations.