Bio-efficacy of Indigenous Bacillus thuringiensis JSd1 against Melon Fly, Zeugodacus cucurbitae (Coq.) (Diptera: Tephritidae: Dacinae)
Md. Abdul Bari, Md Asaduzzaman Shishir, Shakil Ahmed Khan, Shakila Nargis Khan, Md. Mozammel Hoq
A sustainable development of Bacillus thuringiensis based Biopesticideagainst Zeugodacus cucurbitae, a detrimental vegetable pest susceptible to Cry proteins, more lab-scale and field bioassay is required to replace hazardous chemical pesticides. In this concern, 44 indigenous Bt strains harboring different cry genes were assayed in vivo against the 3rd instar larvae of Z. cucurbitae following enhanced expression of Cry proteins in T3 broth.Of the tested isolates, 9 causing more than 70% larval mortality were Bt JSd1 (95%), SaS6 (87%), JDc1 (86%), TaSa4 (82%), NaSc3 (80%), RaSa2 (79%), FhSb3 (77%), Ksa2 (75%) and MuSc2 (72%) respectively. Based on the Lethal concentration (LC50, LC99) (Logarithmic value of spore count) and Lethal time (LT50, LT99) as estimated by Probit analysis, the efficacy of the potential strains were compared. LC50 was determined lowest for JSd1 (0.429) and highest for MuSc2 (0.752) ml/gm whereas the LC99 values as determined lowest for JDc1 (3.792) and highest for MuSc2 (6.546) ml/gm. The LT50, the time required for half of the larvae to be killed, was estimated lowest for Bt JSd1 (54.16 hr) whereas for the LT99, lowest 239.47 hr was required for Bt RaSa2 to cause 99% mortality. Btk HD-73 was used as reference strain in this study. The dose and time response based bioassay thus identify the effective Bt strains viz. Bt JSd1 in controlling Z. cucurbitae larvae with lowest of dose and quickest of time in the laboratory which upon field trial will be suitable for large-scale production and sustainable delivery to the farmers.