Reduction of insect cold-hardiness using ice-nucleating active fungi and surfactants

The supercooling point (SCP) of an insect model, the lady beetle Hippodamia convergens Guerin-Meneville (Coleoptera, Coccinellidae) was markedly eleva ted by treatment with aqueous suspensions of the filamentous, ice nucleatio n active (INA) fungi Fusarium avenaceum and slightly elevated by Fusarium a cuminatum. Addition of the surfactant Tween 80 to the fungal suspensions fu rther reduced the supercooling capacity of adult beetles. When used alone t he surfactant Triton X-100 produced a greater SCP elevation than Tween 20 o r Tween 80. The emulsifier gum arabic was ineffective in elevating beetle S CPs when applied alone and when added to INA fungal preparations it decreas ed their efficacy. Aqueous suspensions of both viable sporulating and viabl e pleomorphic (a permanent, degenerative, nonsporulating cultural state) fo rms of both fungal species were more effective in elevating the SCP than ki lled preparations except for the pleomorphic F acuminatum suspension in whi ch the killed form was slightly more active. Application of INA fungi appli ed in combination with surfactants may be useful in the development of meth ods for the biological control of overwintering freeze-susceptible insect p ests by decreasing their capacity to avoid lethal freezing by supercooling.