Mating Success, Longevity, and Fertility of Diabrotica virgifera virgifera LeConte (Chrysomelidae: Coleoptera) in Relation to Body Size and Cry3Bb1-Resistant and Cry3Bb1-Susceptible Genotypes

Abstract

Insect resistance to population control methodologies is a widespread problem. The development of effective resistance management programs is often dependent on detailed knowledge regarding the biology of individual species and changes in that biology associated with resistance evolution. This study examined the reproductive behavior and biology of western corn rootworm beetles of known body size from lines resistant and susceptible to the Cry3Bb1 protein toxin expressed in transgenic Bacillus thuringiensis maize. In crosses between, and within, the resistant and susceptible genotypes, no differences occurred in mating frequency, copulation duration, courtship duration, or fertility; however, females mated with resistant males showed reduced longevity. Body size did not vary with genotype. Larger males and females were not more likely to mate than smaller males and females, but larger females laid more eggs. Moderately strong, positive correlation occurred between the body sizes of successfully mated males and females; however, weak correlation also existed for pairs that did not mate. Our study provided only limited evidence for fitness costs associated with the Cry3Bb1-resistant genotype that might reduce the persistence in populations of the resistant genotype but provided additional evidence for size-based, assortative mating, which could favor the persistence of resistant genotypes affecting body size.

Restoration of susceptibility following removal of selection for Cry34/35Ab1 resistance documents fitness costs in resistant population of western corn rootworm, Diabrotica virgifera virgifera

“…However, previously documented resistance for WCR exist largely without apparent fitness costs, and remains highly stable in the absence of selection pressures ( i.e . insecticides, Cry3 toxins, crop rotation) 15,31,42,49 . Yet in other insect systems, fitness costs of resistance appear quite frequently 46 .…”

Inheritance and Fitness Costs of Cry3Bb1 Resistance in Diapausing Field Strains of Western Corn Rootworm (Coleoptera: Chrysomelidae)

“…Similarly, in studies of laboratory strains with field-evolved Cry3Bb1 resistance, fitness costs were absent for two strains (Hopkinton and Monona) but were present in two other strains (Cresco and Elma) ( Ingber and Gassmann 2015 , Paolino and Gassmann 2017 ). The fitness cost affecting size in this study may translate to differences in fecundity because larger females rootworm tend to have higher fecundity ( French et al 2015 ). To the extent that fitness costs of Cry3Bb1 resistance may be present, it appears that the effect of fitness costs on delaying resistance was outweighed by factors favoring the evolution of resistance including non-resessive inheritance of resistance, wide-spread planting of Bt crops, and a lack of compliance in planting of refuges ( Gassmann et al 2011 , Dunbar et al 2016 ).…”