Low doses of entomopathogens matter hugely, gateway to resistance development and retarded growth in Helicoverpa armigera

• Published in: Journal of plant diseases and protection (2006) 2024-10, Vol.131 (5), p.1573-1581
• Main Authors: Qayyum, Mirza Abdul, Zhihang, Zhuo, Wakil, Waqas, Ali, Habib, Ali, Abid, Ghazanfar, Muhammad Usman, Yasin, Muhammad, Danping, Xu, Almoallim, Hasham S., Ansari, Mohammad Javed, Tahir, Muhammad, Ali, Kashif, Chaudhry, Muhammad Asrar
• Format: Article
• Language: English
• Subjects: Biomedical and Life Sciences; Life Sciences; Original Article; Plant Pathology; Plant Physiology; Plant Sciences
• ISSN: 1861-3829; 1861-3837
• DOI: 10.1007/s41348-024-00981-3

This study investigates the insecticidal efficacy of low doses of Beauveria bassiana and Bacillus thuringiensis on second and fourth instar Helicoverpa armigera larvae, encompassing various facets of toxicity, developmental impacts, diet consumption, frass production, weight gain, and foliar persistence. Bt and Bb were evaluated for insecticidal properties against the 2nd and 4th instar of H. armigera . To each larvae, a Bt-treated diet (1 ml) was provided to feed for 72 h. For the application of Bb, larvae were dipped in spore suspension (1 × 10 6 and 1 × 10 7 conidia ml −1 ) for 10 s. For combined application of Bb and Bt, larvae were first dipped in fungal suspension and then allowed to feed on Bt-treated diet in rearing vials (7 × 3 cm). The research reveals concentration-dependent responses, wherein increased mortality, reduced pupation, adult emergence, and egg hatching are observed. Notably, second instar larvae exhibit higher susceptibility, demonstrating a linear correlation between mortality and developmental stage. A synergistic effect (Co-toxicity Factor CTF ≥ 20) is observed when larvae are simultaneously exposed to higher concentrations of B. bassiana (1 × 10 7 conidia ml −1 ) and B. thuringiensis isolates (Bt-a1 and Bt-s1), both for second and fourth instar H. armigera larvae. Lower concentrations of B. bassiana (1 × 10 −6 conidia ml −1 ) yield an additive effect in combination with Bt. Pupation, adult emergence, and egg eclosion from surviving individuals show an inverse correlation with the toxic level of microbial agents. Growth and development are adversely affected when treated with B. bassiana and fed on B. thuringiensis -mixed diets, resulting in significant variations in larval and pupal duration, pupal weight, and adult longevity. The study results highlight an increase in larval and pupal duration, alongside a decrease in pupal weight and adult longevity, corresponding to the lethal action of the applied agents. Additionally, microbial agents impact weight gain, frass production, and diet consumption. Larvae treated with lower concentrations of B. bassiana (1 × 10 6 conidia ml −1 ) and B. thuringiensis demonstrate higher weight gain compared to higher application rates (1 × 10 7 conidia ml −1 ) or combined applications. The initial weight of larvae influences weight gain and diet consumption, aligning with the pathogenicity of the applied agents. In conclusion, this study underscores the substantial influence of microbial agents on