การคัดเลือกชื้อ Streptomyces spp. ที่มีคุณสมบัติในการฆ่าแมลงและทางการควบคุม แมลงวันผลไม้ Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

Abstract

The screening insecticidal activity of 52 isolates of Streptomyces spp. by brine shrimp bioassay were investigated. Ten isolates (K4H-9, K4H-10, K5-4, KSH-10, K6-5, K8-4, K8-10, NRST9, NRST15 and NRST17) showed insecticidal activity with percentage cumulative mortality of brine shrimp more than 90% at 24 hours and significantly different from other isolates and control (P<0.05). The most screened isolates of Streptomyces spp. showed chitinase and protease activities. The cultivation time of Streptomyces spp. for produce secondary metabolite were tested. Isolates K5-4, K8-4, NRST9, NRST15 and NRST17 were suitable at 1 week, isolates K8-10 was suitable at 2 weeks and isolates K4H-9, K4H-10 and K5H-10 were suitable at 3 weeks, respectively. The preliminary screening effects of Streptomyces spp. on Bactrocera dorsalis were studied. Three isolates of Streptomyces spp. i.e. K8-10, NRST15 and NRST17 had an effects on survival rate of B. dorsalis with 60.38, 73.33 and 77.50%, respectively. Three selected isolates were studied on morphological and molecular identifications. Isolate K8-10 was similar to bacterial species S. hygroscopicus and isolates NRST15 and NRST 17 were similar to bacterial species S. albidoflavus. The crude extract of secondary metabolite of Streptomyces sp. isolated K8-10 were investigated by LCMS analysis. Five molecules were found ie. 609.3740 m/z, 700.4400 m/z, 729.4539 m/z, 591.3637 m/z and 761.4827 m/z and peak similar to allosamidin, moxidectin, avermectin, spinosyn A and spinosyn Q respectively. The crude extract of Streptomyces sp. isolate K8-10 at concentration 50 mg/ml showed negative effect on egg, larval and adult stages of B. dorsalis, except on the pupal stage. The treated egg had 53.00% of hatching and 36.17% of survival to adult stage, the treated larvae had 68.00% of mortality and 19.33% of survival to adult stage, the treated adult had percentage mortality 28.33%, respectively, this concentration significantly different from other concentrations and control (P<0.05). The Streptomyces sp. isolates K8-10 had the potential for use in biological control and management of insect pests in future.