The Effect of Seston on Mortality of Simulium vittatum (Diptera: Simuliidae) From Insecticidal Proteins Produced by Bacillus thuringiensis subsp. israelensis

Abstract

Water was collected from a site on the Susquehanna River in eastern Pennsylvania, where less-than-optimal black fly larval mortality had been occasionally observed after treatment with Bacillus thuringiensis subsp. israelensis de Barjac insecticidal crystalline proteins (Bti ICPs). A series of experiments was conducted with Simulium vittatum Zetterstedt larvae to determine the water related factors responsible for the impaired response to Bti ICPs (Vectobac 12S, strain AM 65-52). Seston in the water impaired the effectiveness of the ICPs, whereas the dissolved substances had no impact on larval mortality. Individual components of the seston then were exposed to the larvae followed by exposure to Bti ICPs. Exposure of larvae to selected minerals and nutritive organic material before ICP exposure resulted in no significant decrease in mortality. Exposure of larvae to silicon dioxide, cellulose, viable diatoms, and purified diatom frustules before Bti ICP exposure resulted in significant reductions in mortality. Exposure of larvae to purified diatom frustules from Cyclotella meneghiniana Kützing resulted in the most severe impairment of mortality after Bti ICP exposure. It is postulated that frustule-induced impairment of feeding behavior is responsible for the impairment of larval mortality.

Mortality Patterns ofSimulium vittatumLarvae (Diptera: simuliidae) Following Exposure to Insecticidal Proteins Produced byBacillus thuringiensisVar.israelensis

“…Kaolinite clay is naturally occurring in many waterways. Iburg et al (2011) found that larval susceptibility to Bti ICPs was not significantly influenced by the presence of clay in the larval medium. Gray et al (2012) also found that larval susceptibility Fig.…”

“…Pesticide applicators are instructed on the product label to apply the larvicide when the turbidity in a river is low. While this may increase efficacy in some cases, results from Experiment 2 and observations made by Iburg et al (2011) suggest that the components of the seston affect larvicide efficacy more than the turbidity of the water.…”

“…Back et al (1985) found that the majority of larval mortality occurred within the 1st 3 h after exposure to a high label rate of ICPs, and that the final mortality could take over 24 h. Gaugler and Molloy (1980) evaluated larval mortality following exposure to ICPs for 4 days and found that 95% of the mortality occurred within the first 24 h. Studies looking at the effects of Bti ICPs on larvae have evaluated mortality at 24 h (Lacoursiere and Charpentier 1988, Boisvert et al 2002), 9 h (Car and De Moor 1984, and 6 h (Wilson et al 2005). Iburg et al (2011) andOvermyer et al (2006) evaluated larval mortality after 5 h. These studies utilized various formulations containing Bti ICPs both in the field and in the laboratory. A more thorough understanding of larval mortality following exposure to Bti ICPs is necessary to standardize the time at which larval mortality is assessed.…”

“…An additional experiment was performed to determine the effects that the presence of clay or cellulose would have on larval mortality from ICPs. Clay material was used because Iburg et al (2011) and Gray et al (2012) found that clay material had no significant effect on larval mortality following exposure to Bti ICPs. Cellulose material was used because previous studies have demonstrated that this material can cause significant reductions in larval susceptibility to ICPs (Iburg et al 2011).…”

“…Clay material was used because Iburg et al (2011) and Gray et al (2012) found that clay material had no significant effect on larval mortality following exposure to Bti ICPs. Cellulose material was used because previous studies have demonstrated that this material can cause significant reductions in larval susceptibility to ICPs (Iburg et al 2011). This material is not naturally occurring; however, the fibers are released as effluent by some paper mills and Illesova (1988) found that the effluent can alter the feeding behavior of black fly larvae.…”