Colorado potato beetle (Leptinotarsa decemlineata)(Say) dispersal and reproduction as potential factors in the development of resistance to Bacillus thuringiensis subsp. tenebrionis Cry3A toxin
Dispersal and reproduction of the Colorado potato beetle, Leptinotarsa decemlineata (Say), with and without Bacillus thuringiensis subsp. tenebrionis Cry3 A δ-endotoxin in the environment were investigated through a series of field and laboratory studies. Possible implications for resistance management are discussed.
Mating behavior of post-diapause beetles was observed. The influence of spring mating on beetle flight was investigated using a flight mill system. The beetles mated at the overwintering site, as well as in the potato field, and in the fields rotated out of potatoes. Mating status did not affect beetle flight, while absence of food encouraged flying over long distances.
Dispersal of the summer-generation beetles was studied using a mark-recapture method. Effect of female age at the time of mating on the production of viable offspring was tested in the laboratory. Flight behavior of mated and unmated beetles was quantified on a flight mill. About 25% of the beetles remained close to the site of their pupation when they reached sexual maturity. Beetles produced viable offspring only if they accumulated at least 34 DD before mating. The largest number of flights was recorded for the unmated females.
Use of phosphoglucomutase allozymes separated by cellulose acetate gel electrophoresis as genetic markers showed that sperm precedence in the Colorado potato beetle was incomplete, with about 72% of the larvae fathered by males at the second mating.
A flight mill system was used to determine the effect of feeding on transgenic potato foliage, potato foliage treated with δ-endotoxin, and regular potato foliage on the flight of full-sib beetle families. Feeding on transgenic foliage had a strong negative effect on beetle flight. The beetles from the families that performed the longest flights when fed on regular foliage performed the shortest flights when fed on transgenic foliage.
Laboratory experiments were conducted to compare relative fitness of beetle strains resistant and susceptible to δ-endotoxin. Net replacement rate, intrinsic rate of population increase, overwintering survivorship, and male mating capability were reduced for the resistant strain. Mortality, fecundity, and flight of the same strains were tested under laboratory conditions after beetles were fed on transgenic potato foliage, regular potato foliage, and regular potato foliage followed by transgenic foliage. Both strain and treatment had pronounced effects on the tested parameters, values for which decreased when the beetles were allowed to feed on regular foliage prior to a toxin ingestion.