Effects of Bacillus thuringiensisδδ‐endotoxins on food utilization, growth, and survival of selected phytophagous insects

Abstract

Feeding experiments using the Bacillus thuringiensisδ‐endotoxins, CryIA(c) and CryIIIA, were conducted with herbivorous insects from various orders (Lepidoptera, Coleoptera, Homoptera) in the laboratory. The mortality data obtained indicate a species‐specific susceptibility of the insects to the toxins whereby the feeding habits of the given animal seem to play a negligible part. An unexpected, severely damaging effect of CryIIIA on caterpillars was established, for the first time. By computing various development and nutritional indices it could be shown that retarded growth of the insects tested may not only be traced back to reduced feeding but also to a decreased utilization of food containing an endotoxin. The insect gut seems to be the site of operation and of storage or complete degradation of the endotoxins because neither in the faeces nor in the haemolymph and fat body, could the toxins and their degradation products, respectively, be detected hitherto by means of gel electrophoreses. An altering effect of the toxins on the gut‐microflora pattern is indicated from the first examinations but has to be further confirmed. Finally the applicability of these trials in corresponding examinations of transgenic plants producing B. thuringiensis toxin is dicussed.

Effects of Activated Bt Transgene Products (Cry1Ab, Cry3Bb) on Immature Stages of the Ladybird Adalia bipunctata in Laboratory Ecotoxicity Testing

“…While this suggests that sublethal effects do not exist with regard to these parameters, effects on other parameters (e.g., fecundity, longevity) cannot be excluded and should be investigated in additional studies. Although we observed no indication of a feeding deterrent behavior, this aspect should be given attention, as reduced feeding and decreased food utilization could also impose a higher mortality, which has been reported from herbivores (Deml et al 1999;Hussein et al 2005). On the other hand, toxin concentrations should be quantified throughout the course of feeding experiments to ensure that degradation of toxins is not responsible for the lack of mortality in later larval stages.…”

A Review of Perennial Ryegrass Endophytes and Their Potential Use in the Management of African Black Beetle in Perennial Grazing Systems in Australia

“…The insecticidal properties of Bt are associated with Cry proteins (δ-endotoxins) which are synthesized as parasporal crystals during sporulation of the bacteria (Deml et al, 1999, Figure 3). Different varieties of Bt produce different toxins that are specific to targets from Lepidoptera to Diptera and Coleoptera (Cidaria et al, 1991).…”

“…However, there is evidence of cross-order toxicities occurring on target species, for example, Cry1Ab affecting mosquitoes Aedes aegypti (Diptera) (Haider et al, 1986), and CryIIIA having a comparable toxicity to CryIA in a number of caterpillars (Lepidoptera) (Deml et al, 1999). Van Frankenhuyzen (2009) highlighted that cross-order toxicities have been reported for 15 of the 87 insecticidal crystal protein families and that these numbers are likely to increase as testing across orders is expanded.…”

“…Similar to Bt, P. popilliae produces parasporal crystals upon sporulation (Klein and Kaya, 1995; Deml et al, 1999). It has been suggested that parasporal crystal proteins may play a part in the mortality caused by milky disease because of the strong similarities and conservation of the hydrophobicity distribution of Cry proteins from Bt and P. popilliae (Zhang et al, 1997).…”

Transgenic Pesticidal Crops and the Environment: The Case of Bt Maize and Natural Enemies

“…Parasitoid performance can be affected as a result of the Bt toxin reducing host's biomass (Farrar and Ridgeway, 1995;Deml et al, 1998), or changing the host hemolymph-pH, hemolymph ion concentration, and nutrient concentration (Tanada and Kaya, 1993), which in turn can affect the parasitoid larvae living in the hemolymph. Alternatively, parasitoid larvae may be affected by ingesting the Bt toxin present in the hemolymph.…”