Sublethal effects of Bacillus thuringiensis on the spruce budworm, Choristoneura fumiferana

Abstract

Exposing larvae of the spruce budworm, Choristoneura fumiferana (Clemens), to sublethal (≤ 50% lethal dose) levels of Bacillus thuringiensis subsp. kurstaki at various stages of their development significantly increased development time to the pupal stage and reduced pupal size and number of eggs laid per female, but did not affect the proportion of embryonated eggs. The changes in larval development time, pupal weight and fecundity depended on the larval stage that was treated. Exposure of fourth instars delayed larval development and reduced only male pupal weights with no effects on fecundity. Exposure of sixth instars delayed larval development to a lesser extent than exposure of fourth instars but had a pronounced effect on weight of both male and female pupae. The effect on pupal weight was sex dependent, as males tended to be more affected than females. The reduction in male pupal weight did not appear to influence fecundity, because the effect of exposure was explained by the change in female pupal weight. Effects on larval growth and pupal weight were proportional to the dose that was ingested during exposure, and were observed at doses as low as one‐tenth of the LD50. Ingestion of an LD50 caused a 29 or 45% delay in development of, respectively, female or male larvae when exposed as fourth instars and a 30% reduction in female pupal weight when larvae were exposed as sixth instars.

Virulence, horizontal transmission, and sublethal reproductive effects of Metarhizium anisopliae (Anamorphic fungi) on the German cockroach (Blattodea: Blattellidae)

“…Adult females of Colorado potato beetle surviving exposure to delta-endotoxin of B. thuringiensis tended to produce around 45% fewer eggs (Costa et al, 2000). Similarly, adult females of spruce budworm Choristoneura fumiferana Clemens coming from larvae surviving delta-endotoxin treatments laid a lower number of eggs even if egg fertility was not affected (Pedersen et al, 1997). In contrast, B. thuringiensis b-exotoxin seems to cause no negative effects on fecundity and fertility of survivors (Toledo et al, 1999).…”

Fitness costs of sublethal exposure toBacillus thuringiensisinHelicoverpa armigera: a carryover study on offspring

“…While many studies have proved the adverse effect of Btk on pupal weight of insect pests (Alford and Holmes ; van Frankenhuyzen and Nystrom ; Pedersen et al. ; Erb et al. ), Khalique and Ahmed () and Aly et al.…”

“…; Pedersen et al. ). Environmental factors such as rainfall, sunlight or temperature are major determinants of the residual life of Bt (Frye et al.…”

Sublethal Acute and Chronic Exposure of Colorado Potato Beetle (Coleoptera: Chrysomelidae) to the δ-Endotoxin of <I>Bacillus thuringiensis</I>

“…Bacillus thuringiensis-induced reductions in fecundity after sublethal exposure of immature stages have been noted in a number of species: Heliothis virescens (F.) (Dulmage andMartinez 1973, Gould andAnderson 1991), Anagasta kuehniella (Zell) (AfÞfy and Matter 1969), Agrotis ypsilon (Hufnagel) (Salama and Sharaby 1988), Culex quinquefasciatus Say (Lavina et al 1996), and Choristoneura fumiferana (Clemens) (Pedersen et al 1997). There were often reductions in pupal or adult weight concomitant with the reductions in fecundity, as noted in the current study.…”