Optimal concentration of Beauveria bassiana vectored by bumble bees in relation to pest and bee mortality in greenhouse tomato and sweet pepper.

Kapongo, J.-P., Shipp, J.L., Kevan, P.G., and Broadbent, A.B. (2008). "Optimal concentration of Beauveria bassiana vectored by bumble bees in relation to pest and bee mortality in greenhouse tomato and sweet pepper.", BioControl, 53(5), pp. 797-812. doi : 10.1007/s10526-007-9142-9

Abstract

Greenhouse cage trials were conducted to determine the optimal concentration of Beauveria bassiana (Balsamo) Vuillemin (Ascomycota: Hypocreales) (BotaniGard 22WP(r) formulation) as vectored by the bumble bee, Bombus impatiens (Cresson) (Hymenoptera: Apidae) pollinator for control of greenhouse whitefly, Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) on greenhouse tomato, tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae) and green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae) on greenhouse sweet pepper. Three inoculum concentrations of B. bassiana: low, 9 × 10⁹; middle, 6.24 × 10¹⁰; and high, 2 × 10¹¹ conidia g 1 of inoculum and two controls (one with bees and heat-inactivated inoculum, and the other which contained only the host plants and pest species) were tested in a completely randomized block design. Beauveria bassiana killed 18, 54 and 56% of the adult T. vaporariorum and 33, 70 and 67% of the adult L. lineolaris, respectively, at the low, middle and high concentrations; but no infection from B. bassiana occurred in each of the control treatments. Internal infection rates after surface sterilization of the pest insects were 11, 34 and 35% for adult T. vaporariorum, 29, 54 and 58% for adult L. lineolaris, 22, 34 and 30% for nymphal M. persicae and 17, 29 and 32% for nymphal T. vaporariorum, respectively, at the low, middle and high concentrations. Significantly more bumble bees died at the high concentration of B. bassiana (42-45%) than at the other concentrations (9-15%) and the controls (5-7%). Spores of B. bassiana were collected throughout the plant canopy with the greatest numbers sampled from the top third of the canopy [ca. 1,200 colony forming units (CFU) per cm²]. The middle concentration was selected as the optimal concentration because it provided the best pest control with the least impact on the bees.