Bioefficacy of entomopathogenic Aspergillus strains against the melon fly, Bactrocera cucurbitae (Diptera: Tephritidae)

Abstract

Three Aspergillus strains were isolated from naturally diseased adults of the melon fly Bactrocera cucurbitae Coquillett (Diptera: Tephritidae) collected from Hainan Province, China. Then laboratory bioassays were carried with A. flavus (BC-22 and BC-D-1) and A. tamarii strains (BC-212) against B. cucurbitae. The results indicated that conidial suspensions (1 × 108 conidia/ml) of the three strains exhibited high toxicity against the adults of B. cucurbitae and low insecticidal activity to the eggs, larvae and pupae. Furthermore, the virulence of three strains (BC-22, BC-D-1 and BC-212) for the adults was compared; the LT50 values were 6.05, 5.81 and 4.91 days with 1 × 108 conidia/ml, respectively. After 8 days after inoculation, the LC50 values were 12.00 × 105, 1.15 × 105 and 0.28 × 105 conidia/ml, respectively. Undiluted culture supernatant of the three strains had less bioefficacy to B. cucurbita compared to use of the conidia suspension. The three strains, especially BC-212, showed a faster colony growth, higher germination rate and sporulation. These results indicated that the A. tamarii BC-212 strain was the better one to consider for the control of melon flies. In conclusion, Aspergillus species could be candidates for fly control as pest control agents. To our knowledge, this is the first report on A. flavus and A. tamarii strains pathogenic to B. cucurbitae.