Binding of Insecticidal Crystal Proteins of Bacillus thuringiensis to the Midgut Brush Border of the Cabbage Looper, Trichoplusia ni (Hübner) (Lepidoptera: Noctuidae), and Selection for Resistance to One of the Crystal Proteins

Abstract

The susceptibility of Trichoplusia ni larvae to several BaciUlus thuringiensis insecticidal crystal proteins (ICPs) was tested. Neonatal larvae proved to be susceptible to solubilized trypsin-treated CryIA(a), CryIA(b), and CryLA(c) (50%Yo lethal concentrations [LCsos], 570, 480, and 320 ng/cm2, respectively) but showed little susceptibility to CryIB and CryID (LC50s, 5,640 and 2,530 ng/cm2, respectively). The toxicity of ICPs was correlated to binding to the epithelial brush border of the midgut, as revealed by immunocytochemical staining with monoclonal antibodies. In vitro binding experiments with iodinated ICPs and brush border membrane vesicles indicated that CryIA(b) and CryLA(c) share the same high-affinity binding site, whereas CryLA(a) binds to a different one. The affinities of CryLA(b) and CryIA(c) for the binding site were similar (Kd = 3.6 and 4.7 nM, respectively), and the mean binding-site concentration was 0.71 pmol/mg of vesicle protein. Selection of a population with increasing concentrations of CryIA(b) produced 31-fold resistance in seven generations. The realized heritability (h2) was 0.19. The increase of homozygosity (for resistance factors) as selection proceeded was reflected in the increase in the slopes of the dose-mortality curves. Resistance was specific for CryIA(b) and did not extend to CryIA(a) or even to CryIA(c). This result was not predicted by the binding-site model, in which CryIA(b) and CryLA(c) bind to the same high-affinity binding site. This result may suggest a more complicated relationship between in vitro binding of ICPs to specific sites in the epithelial membrane of the midgut and the in vivo toxic effect.

Broad‐spectrum cross‐resistance in Spodoptera exigua from selection with a marginally toxic Cry protein

“…After 19 generations of continuous selection with activated Cry1Ab, the resistance ratio increased more than 29‐fold relative to the unselected strain. The resistance ratio obtained in the present work is comparable with that reported by Gould et al 32 with H. virescens selecting with Cry1Ac toxin (50‐fold after 17 generations) or by Estada and Ferré33 selecting a T. ni colony with Cry1Ab (31‐fold in seven generations), although lower than that obtained in other studies 19, 20…”

Different Transcript Patterns in Response to Specialist and Generalist Herbivores in the Wild Arabidopsis Relative Boechera divaricarpa

“…Its broad host range includes tomato, lettuce, potato, beans, maize, cotton, and other plants. This pest is difficult to control in agricultural settings due to population explosions and larval resistance to several insecticides [38] , [39] . Plutella xylostella ( P. xylostella ), a crucifer specialist, is one of the most widespread lepidopteran species, and often seriously damages cruciferous crop plants, especially in the tropics [40] .…”

Cloning and Characterization of Manduca Sexta and Plutella Xylostella Midgut Aminopeptidase N Enzymes Related to Bacillus Thuringiensis Toxin‐Binding Proteins

“…target sites was demonstrated by performing in vitro binding studies with insect midgut brush-border-membrane vesicles (BBMV) and 12'I-labeled [ 1-71, ["S]methionine-labeled IS] or biotinylated ICP [9, lo]. Toxin-binding proteins have also been identified by ligand blotting (toxin overlay assays [I 1 -19]), by incubation of larval midgut histological sections with &endotoxins [6,7, and by binding experiments using the surfaceplasmon-resonance technique [23 -251. In general, the results of these experiments have demonstrated the presence of one or more ICP-binding proteins in the midgut brush-border menibrane of susceptible insect larvae. Different ICP can either compete for the same binding site or recognize distinct sites.…”