Field appraisal of entomopathogenic fungi horizontal transmission device for entomo-vectoring of Beauveria bassiana and Metarhizium anisopliae in bitter gourd field against Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae)

Abstract Background Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) infestation poses a serious risk to bitter gourd cultivation. Traditionally, B. cucurbitae has been controlled using synthetic pesticides, which have drawbacks such as non-target toxicity and pest resistance. Entomopathogenic fungi (EPF) provide concentrated ecological alternatives, which support ongoing pest reduction and sustainable agriculture by adhering to Integrated Pest Management principles. Therefore, EPF provides a viable alternative for chemical control of B. cucurbitae, addressing its shortcomings and promoting environmentally friendly pest control technology. This study evaluated the effectiveness of entomo-vectored horizontal transmission devices (EV-HTD) against B. cucurbitae in bitter gourd fields, focusing on GF-120 and Butanone acetate. Assessment parameters include converting fruit infestation data into yield loss per plant, marketable fruit yield per plant, marketable yield per hectare, and yield loss per hectare. Results The highest mean percentage of entomo-vectored B. cucurbitae (70.50%) was found in plots treated with Butanone acetate + B. bassiana-based EV-HTD. This was followed by GF-120 + B. bassiana-based EV-HTD (66.18%), Butanone acetate + M. anisopliae-based EV-HTD (58.95%), and GF-120 + M. anisopliae-based EV-HTD (54.78%). The Butanone acetate + B. bassiana-based EV-HTD produced the highest mean number of spores per B. cucurbitae (7.80 spores/cm2), while the other treatments produced low spore counts. Plots treated with Butanone acetate + B. bassiana-based EV-HTD had the highest percentage mortality of B. cucurbitae (81.20%). The percentage of fruit infestation varied between 9.00 and 34.00%, with the least amount of infestation seen in plots treated with B. bassiana + Butanone acetate. There were minimal yield losses in Butanone acetate. The Butanone acetate + B. bassiana-based EV-HTD showed the lowest yield losses (66.66 g/plant), while the other treatments showed high losses. Plots treated with Butanone acetate + B. bassiana-based EV-HTD had the highest marketable yield per plant (673.87 g/plant), while yields in control treatments were low. Plots treated with Butanone acetate + B. bassiana-based EV-HTD had the highest marketable yield (2217.85 kg/ha). Lastly, plots treated with Butanone acetate + B. bassiana-based EV-HTD (219.40 kg/ha) showed the lowest yield losses per hectare. Conclusions According to the study’s findings, Butanone acetate-based EV-HTD was more successful than GF-120. Furthermore, B. bassiana was more effective at controlling B. cucurbitae than M. anisopliae. With a maximum cost–benefit ratio of 14.99, the treatment Butanone acetate + B. bassiana was shown to be the most advantageous economically, suggesting its potential for use in practical pest management techniques.