Efficacy of diatomaceous earth, and entomopathogenic fungi, Beauveria bassiana, and Trichoderma asperellum in combination and separately, against Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae)

Abstract

Abstract Background Callosobruchus maculatus (F.) (Coleoptera: Chrysomelidae) is one of the most significant pests infesting leguminous crops since it is found in tropical and subtropical climates, as well as in Turkey. The most often utilized methods of managing these insects are fumigants and synthetic insecticides. However, chemical pesticides lead to increased risks for human health, chemical residues, insect resistance, and environmental contamination. Therefore, the present study aimed to determine the effectiveness of entomopathogenic fungi [Beauveria bassiana (Bb) and Trichoderma asperellum (Ta)] individually or in combination with diatomaceous earth (DE) against C. maculatus. The fungi Bb and Ta were applied at 1 × 104, 1 × 106 and 1 × 108 spores/kg of chickpea seeds and mixed with 200, 400, 800 mg/kg of DE. Additionally, the progeny production of the insect on chickpea in the different treatments was evaluated after 40 days of exposure. Results In all individual treatments, total adult mortality of the insect was accomplished solely by using the highest DE treatment rate (800 mg/kg) after 7 days. The most effective combination that was a mixture at highest application rate of DE/Bb (800 mg/kg of DE + 1 × 108 spores/kg of Bb) caused 100% mortality after 6 days of exposure and had the lowest LT50 (2.97) and LT90 (5.46) values (days). Although other DE/Bb binary combinations caused 100% mortality of C. maculatus 6 days after treatment, their LT50 and LT90 values were lower. Insect mortalities were 100% in all DE/Ta binary combinations on days 7 and 8, and the highest application rate (800 mg/kg of DE + 1 × 108 spores/kg of Ta) of this combination had the lowest LT50 (4.14) and LT90 (6.17) values (days). Individual treatments of DE, Bb, Ta and their binary combinations caused significant reduction in progeny production after 40 days of treatment compared with progeny production in the control of C. maculatus. The highest progeny production (88.9%) was observed at the highest treatment rate of DE/Bb combinations (800 mg/kg of DE + 1 × 108 spores/kg of BB). Conclusions The treatments used in combination of Bb or Ta with DE resulted in increased insecticidal effectiveness against C. maculatus. These natural agents caused considerable decreasing of progeny production of the pest. Even with reduced application rates, the agents with a promising potential against the pest showed acceptable results in binary combinations.