Abstract Background The growing insecticidal resistance in vector mosquitoes is alarming and calls for an alternative, safe, and eco-friendly control strategy. As an alternative, entomopathogenic fungi (EPF) have gained attention. Hence, the present study evaluated different solid substrates to understand the nutrient requirements of EPF for conidial production and their infectivity against the vector mosquito. Methods Eleven solid substrates were tested for the conidial production of PDBC-Bb5a. The conidial load per gram of substrate was calculated using the spread plate technique. The conidial germination rate at 8, 16, and 24 h after incubation was recorded. The conidial infectivity against Anopheles stephensi was assessed with the WHO cone bioassay tests, exposing mosquitoes to PDBC-Bb5a (1 × 10 7 conidia/mL) treated cement and mud panels for 30 min. Four replicates, each containing 20 mosquitoes, were maintained for each substrate and the control group. Mosquito mortality was recorded over 10 days. ANOVA was performed to examine the difference between conidia produced on different solid substrates, and the Wilcoxon signed-rank test was used to compare germination rates at 8 versus 16 h of incubation. The Kaplan–Meier test was undertaken to represent the survival function. Results The highest number of PDBC-Bb5a conidia was produced on white rice (6.8 × 10 5 CFU g −1 ), followed by sorghum and broken wheat ( p < 0.05). Further, the highest germination rate was achieved from conidia produced on white rice (37%) and broken wheat (56%) at 8 and 16 h of incubation, respectively. An increase in germination rate overtime was observed on white rice (37.0 to 54.3% at 8 and 16 h) and broken wheat (36.3% at 8 h and 56.0% at 16 h), yet there was no significant difference among the substrates. The conidia produced on white rice recorded 90% and 86.25% of mortality with 5 (χ2 = 200.32; df = 5; p < 0.01) and 7 (χ2 = 200.32; df = 5; p < 0.01) median survival times of An. stephensi on cement and mud panels, respectively. However, barley observed 51.25 and 47.50% mortality with 10 days of median survival time on cement and mud panels, respectively. Conclusion The study proved that white rice was a better substrate for the production of B. bassiana. Further multicentric studies are needed to test in different eco-geographical areas to assess the efficacy and persistence in varied environmental conditions before considering it in vector control programs.
Siddaramegowda et al. (Sat,) studied this question.