Combination of azadirachtin and entomopathogenic fungus as a better control agent against Riptortus pedestris...

Riptortus pedestris (Fabricius) (Hemiptera: Alydidae) is a major soybean pest controlled mostly with synthetic insecticides, but environmentally friendly alternatives are needed. To develop a better microbial control option using the entomopathogenic fungus Beauveria bassiana ARP14 (ARP14), we evaluated whether azadirachtin (AZA) enhances its effectiveness in topical bioassays on eggs and second‑instar nymphs. At 10 d, the hatching rates for the AZA and the AZA + ARP14 mixture were all lower (33%) than those for the synthetic insecticide λ‑cyhalothrin (83%), ARP14 (73%) or no treatment control (100%). Similarly, in the assay of second instars in the absence of food sources, the ST50 values for AZA and the AZA + ARP14 mixture were almost 1.8 times lower than that for singly applied ARP14. Also, in the presence of food sources, earlier mortality of the 2nd and 3rd instars was observed in the treatment of the AZA + ARP14 mixture compared to agents applied singly from daily observation after treatment. Mycosis was up to 3.5 times higher at 10 d when the AZA + ARP14 mixture was applied to second‑instar nymphs compared to a single application of ARP14. Nevertheless, the developmental time became shorter only in the single treatment of ARP14 than in the control, whether applied to eggs or to second-instar nymphs. These results suggest that the combined application of AZA and ARP14 provides improved efficacy compared to single treatments against second instars of R. pedestris. Thus, the AZA + ARP14 mixture can be a potential control agent to replace synthetic chemical insecticides used against R. pedestris.