Effects of entomopathogenic fungus combination withreduced insecticide doses on potato beetle (lepti̇notarsa decemli ̇neata say., 1824) coleoptera: effects onchrysomelidae)

In this study, the aim was to reduce the intensity of insecticide use against the Colorado potato beetle (Leptinotarsa decemlineata Say.) (Coleoptera: Chrysomelidae), which is a major pest of potatoes and negatively affects production. For this purpose, third instar larvae and adults of L. decemlineata were treated with entomopathogenic fungal isolates propagated in sterile conditions from stock cultures and with registered plant protection products at full, half, and quarter doses (120g/l Spinetoram, 10g/l Azadirachtin, 25g/l Deltamethrin, and 20% Acetamiprid). These treatments were also combined with the entomopathogenic fungi (EPF) Beauveria bassiana and Metarhizium bruneum (BBE2, Sivas10, ORP13, and ORP18) at 1x10⁷ conidiospores ml⁻¹. According to the results, the EPF + Acetamiprid applications showed that full-dose Acetamiprid treatments combined with half doses of Sivas10, ORP13, and ORP18 resulted in 100% mortality on day 7. Compared to half-dose (90%) and quarter-dose (80%) Acetamiprid applications, the BBE2 + Acetamiprid combination achieved 95% mortality on day 7. In larval trials, full-dose Acetamiprid resulted in 90% mortality on day 5, while BBE2, Sivas10, ORP13, and ORP18 achieved 95%, 100%, 100%, and 100% mortality respectively. In Spinetoram applications, combinations of ORP13, ORP18, and BBE2 with half-dose Spinetoram reached 100%, 100%, and 95% mortality respectively by day 7, whereas the full-dose Spinetoram application achieved 90% mortality. In larval trials, combinations of half-dose Spinetoram + BBE2, Sivas10, and ORP13 reached 100% mortality on day 5; similarly, full-dose Spinetoram alone also reached 100% mortality. In adult applications of Azadirachtin, quarter-dose combinations with Sivas10, ORP13, and ORP18 achieved 75%, 75%, and 80% mortality respectively, compared to 55% with Azadirachtin quarter-dose alone. The BBE2 + half-dose Azadirachtin combination achieved 90% mortality, while combinations with Sivas10, ORP13, and ORP18 achieved 100%. In larval applications of Azadirachtin, BBE2 and Sivas10 + half-dose Azadirachtin reached 95% mortality on day 5, while the ORP13 + half-dose Azadirachtin combination reached 100%. In Deltamethrin applications, the ORP13 + half-dose combination (95%) matched the mortality of full-dose Deltamethrin (95%). BBE2 and ORP18 half-dose combinations (90%) surpassed the mortality of Deltamethrin half-dose application (80%). In larval trials, BBE2 and Sivas10 + half-dose Deltamethrin achieved 95% mortality, while ORP13 + half-dose Deltamethrin reached 100%. In conclusion, this study demonstrates that using combinations of reduced-dose insecticides with entomopathogenic fungi can achieve effects comparable to those obtained with recommended full insecticide doses. Keywords: Entomopathogenic Fungus, Colorado Potato Beetle (Leptinotarsa decemlineata), Insecticide Combination Applications, Biological Control.