Variation in the Susceptibility of the Forest Tent Caterpillar (Lepidoptera: Lasiocampidae) to <I>Bacillus thuringiensis</I> variety kurstaki HD-1: Effect of the Host Plant

Abstract

Host-mediated effect on the efficacy of Bacillus thuringiensis Berliner against larvae of the forest tent caterpillar. Malacosoma disstria Hübner, was investigated under controlled conditions. Host plants used in this study were quaking aspen, Populus tremuloides Michx., a preferred host, and sugar maple, Acer saccharum Marsh., a secondary host. Larvae were reared in the laboratory on leaves of these hosts, and upon reaching the third, fourth, and fifth instar, they were fed leaves treated with one of a range of concentrations of B. thuringiensis variety kurstaki HD-1 suspensions. Larvae were tested on the host on which they were feeding before the 4-d bioassays. The estimated LC50s were 100-fold greater on quaking aspen than on sugar maple. Also, there was a decrease in efficacy over the whole ranges of concentrations with larval age on both hosts. LC50s varied approximately two-fold between third and fifth instar. These results indicate that host-mediated effects on B. thuringiensis efficacy warrant more interest. In particular, they strongly indicate that the host plant modifies the interaction between B. thuringiensis and a target insect, and offer the opportunity to investigate the mechanism(s) that may be involved in the enhancement of B. thuringiensis toxicity.

Midgut juice components affect pore formation by the Bacillus thuringiensis insecticidal toxin Cry9Ca

“…Despite several reports demonstrating that midgut microenvironmental factors can greatly affect toxin activity (Pang and Gringorten, 1998;Shao et al, 1998;Tran et al, 2001;Fortier et al, 2005Fortier et al, , 2007Vachon et al, 2006), this aspect of their mode of action has been largely overlooked. Nevertheless, because at least some of these factors are likely to vary in function of the physiological state of the insect, they could contribute to the still poorly understood mechanisms by which the efficacy of B. thuringiensis crystal toxins often depends on biological factors such as larval instar (Wierenga et al, 1996;van Frankenhuyzen et al, 1997) and nutrition (Bauer, 1992;Meade and Hare, 1993;Appel and Schultz, 1994;Moldenke et al, 1994;Farrar et al, 1996;Beveridge and Elek, 2001;Kouassi et al, 2001).…”

Effect of Insect Larval Midgut Proteases on the Activity of Bacillus thuringiensis Cry Toxins

“…These differences could possibly result, at least in part, from the fact that the brush border membrane vesicles (17,36) and midgut juice were isolated from fifth-instar larvae, the electrophysiological experiments were carried with midguts isolated from thirdinstar larvae, and in vivo toxicity data were obtained using neonate larvae. Numerous authors have reported differential effects of the larval instar on the potency of B. thuringiensis toxins (2,3,9,12,18,19,21,24,31,39,42). For example, Gilliland et al (12) observed that M. sexta third-instar larvae had significantly fewer binding sites for Cry1Ac than neonates while no significant changes were observed for Cry1Ca.…”

Biosafety in Populus spp. and other forest trees: from non-native species to taxa derived from traditional breeding and genetic engineering

“…Release of these living bacteria may represent a similar or probably higher risk than GM plants (Brimner and Boland 2003;Boland and Brimner 2004). However, they have not been questioned as Bt toxin carrying transgenic plants (Bt trees), are freely available in many countries and have being used in forest protection against lepidopteran defoliators for many years (Bauce et al 2004;Kouassi et al 2001;Cadogan and Scharbach 2003).…”