Evaluation of Synergistic Interactions Between the Colorado Potato Beetle (Coleoptera: Chrysomelidae) Pathogen <B> <I>Beauveria bassiana</I> </B> and the Insecticides, Imidacloprid, and Cyromazine

Abstract

Laboratory studies investigated the interaction between the fungal entomopathogen Beauveria bassiana (Balsamo) Vuillemin and sublethal doses of the insecticides imidacloprid and cyromazine when applied to larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say). When second instars were fed potato leaf discs treated with sublethal doses of imidacloprid and a range of doses of B. bassiana, a synergistic action was demonstrated. Similar results were observed when larvae were sprayed directly with B. bassiana conidia and immediately fed leaf discs treated with imidacloprid. No synergistic interaction was detected when larvae were fed leaf discs treated with sublethal doses ofimidacloprid 24 h after application of B. bassiana conidia to larvae. However, a synergistic interaction was detected when larvae were fed leaf discs treated with imidacloprid and sprayed with B. bassiana conidia 24 h later. Although sublethal doses of both imidacloprid and the triazine insect growth regulator (IGR) cyromazine prolonged the duration of the second instar, only imidacloprid interacted with B. bassiana to produce a synergistic response in larval mortality. In leaf consumption studies, the highest dose of B. bassiana tested promoted feeding in inoculated second instars. Feeding was inhibited when larvae were fed foliage treated with sublethal doses of imidacloprid and significantly reduced when fed foliage treated with a sublethal dose of cyromazine. Starvation of larvae for 24 h immediately after B. bassiana treatment produced a similar result to the combined treatment of B. bassiana and imidacloprid and increased the level of mycosis when compared with B. bassiana controls. Imidacloprid treatment affected neither the rate of germination of B. bassiana conidia on the insect cuticle nor the rate at which conidia were removed from the integument after application. The statistical analysis used to detect synergism and the possible role of starvation-induced stress factors underlying the observed synergistic interactions are discussed.

Fungal infection counters insecticide resistance in African malaria mosquitoes

“…Studies on insect hosts other than mosquitoes have indicated that fungal infection can act synergistically with insecticides, increasing the impact of otherwise sublethal insecticide doses (24)(25)(26). Mixtures of M. anisopliae and deltamethrin were shown to enhance virulence of both components when tested against ticks, indicating synergistic effects that would enhance the effectiveness of low fungi and insecticide concentrations (27).…”

Interaction between pesticides and other factors in effects on bees

“…In this case no effects on the rate at which conidia were removed from the cuticle were observed but feeding was inhibited when larvae were fed imidacloprid. Decreased resistance to disease is well established to increase susceptibility to pesticides (Furlong and Groden, 2001). A similar non-synergistic effect of co-exposure to imidacloprid and B. bassiana is reported in whitefly that was suggested to be due to B bassiana reducing feeding and thus intake of imidacloprid (James and Elzen, 2001).…”

Synergism between Metarhizium anisopliae (Deuteromycota: Hyphomycetes) and Boric Acid against the German Cockroach (Dictyoptera: Blattellidae)

“…Several studies have focused on the potential use of entomopathogenic fungi primarily, Beauveria bassiana (Balsamo) Vuillemin and M. anisopliae, in combination with sublethal doses of organic insecticides against various insect pests (Anderson et al, 1989;Moorhouse et al, 1992;Li and Holdom, 1994;McCoy, 1997, 1998;Furlong and Groden, 2001). Most recently, the compatibility (increased mortality and lower LT 50 ) of M. anisopliae was demonstrated with imidacloprid (Kaakeh et al, 1997), chlorpyrifos, prometamphos, and cyfluthrin (Pachamutu et al, 1999;Pachamutu and Kamble, 2000) against the German cockroach.…”