@article{johnson_gould_kennedy_1997, title={Effects of natural enemies on relative fitness of Heliothis virescens genotypes adapted and not adapted to resistant host plants}, volume={82}, ISSN={["0013-8703"]}, DOI={10.1046/j.1570-7458.1997.00133.x}, abstractNote={AbstractWe investigated the potential of two natural enemies of Heliothis virescens (F.) (Noctuidae) to affect its rate of adaptation to tobacco containing Bacillus thuringiensis Berliner toxin. Larval fitness of two laboratory strains of H. virescens, one adapted to B. thuringiensis toxin and one not adapted, was compared on toxic and nontoxic plants, in the presence of the parasitoid Campoletis sonorensis (Cameron) (Ichneumonidae) or the entomopathogenic fungus Nomuraea rileyi (Farlow) Samson. By exposing larvae to plants and enemies for no more than 24 h, we focussed on the behavioral rather than physiological component of their interaction with toxic plants and natural enemies.Parasitism of H. virescens larvae by C. sonorensis during exposure periods of 1–4 h was lower on toxic plants than nontoxic plants and was lower for nonadapted larvae than for toxin‐adapted larvae. Decreased larval feeding damage on toxic versus nontoxic plants, and by nonadapted versus adapted larvae, may explain differences in parasitism, because C. sonorensis locates host larvae using cues from damaged plants. Effects of plant toxicity and larval strain on H. virescens survival were numerically consistent with effects on parasitism, but they were not statistically significant. When mean larval survival is used to estimate fitness of the nonadapted genotype relative to the toxin‐adapted genotype, we find that C. sonorensis is expected to delay adaptation to toxic plants.Percent infection by N. rileyi of H. virescens larvae exposed to fungus‐treated plants for 24 h was greater when plants were toxic, and was greater for nonadapted larvae than toxin‐adapted larvae. There were corresponding decreases in larval survival on toxic compared to nontoxic plants, and of nonadapted compared to adapted larvae. Interaction of effects of plant line and larval strain on survival was significant in the presence of fungus, but not in the absence of fungus, which indicates that the effect of toxic plants on the relative fitness of toxin‐adapted and nonadapted larvae was mediated by fungus. As in the interaction with C. sonorensis, behavior of larvae on plants may explain differences in susceptibility to N. rileyi. Because nonadapted larvae moved more than toxin‐adapted larvae on toxic plants, nonadapted larvae may have been more likely to encounter a lethal dose of conidia. In contrast with C. sonorensis, N. rileyi, which decreased the fitness of the nonadapted genotype relative to the adapted genotype, is expected to accelerate adaptation to toxic plants.}, number={2}, journal={ENTOMOLOGIA EXPERIMENTALIS ET APPLICATA}, author={Johnson, MT and Gould, F and Kennedy, GG}, year={1997}, month={Feb}, pages={219–230} }
 @article{johnson_1997, title={Interaction of resistant plants and wasp parasitoids of tobacco budworm (Lepidoptera: Noctuidae).}, volume={26}, ISSN={["0046-225X"]}, DOI={10.1093/ee/26.2.207}, abstractNote={The interactions of 2 species of parasitoid wasps, their host, Heliothis virescens (F.), and transgenic tobacco producing a low concentration of Bacillus thuringiensis Berliner toxin were investigated in field tests. Campoletis sonorensis (Cameron) and toxic plants each decreased survival of larvae during the first 6 d on plants. C. sonorensis and toxic plants acted synergistically in combination, decreasing larval survival beyond the level expected for an additive interaction. Cardiochiles nigriceps Viereck did not significantly reduce 6-d survival of host larvae and did not interact with plant toxicity. Parasitism of H. virescens exposed for 1 d to natural populations of the same parasitoids was highly variable from day to day, and also varied between years. In 1990, C. sonorensis was the more prevalent species; in 1991, C. nigriceps was dominant. In 1990, single-day parasitism of neonates by C. sonorensis was lower on toxic plants than nontoxic plants. This result, which contradicted previous findings of increased parasitism among larvae exposed for several days on toxic plants, probably was caused by differences in initial behavior of larvae on toxic versus nontoxic plants. In 1991, position of larvae on plants did not affect parasitism by C. sonorensis ; however, parasitism by C. nigriceps was significantly higher among larvae collected from exposed positions on leaves compared with apical buds. Patterns of daily parasitism of 1- to 8-d-old larvae were extremely different for the 2 parasitoids: vulnerability to C. sonorensis among host larvae on nontoxic plants began to decline after 3 d; whereas, parasitism by C. nigriceps increased over the 1st few days and remained high through 8 d.}, number={2}, journal={ENVIRONMENTAL ENTOMOLOGY}, author={Johnson, MT}, year={1997}, month={Apr}, pages={207–214} }
 @article{johnson_gould_1992, title={INTERACTION OF GENETICALLY ENGINEERED HOST PLANT-RESISTANCE AND NATURAL ENEMIES OF HELIOTHIS-VIRESCENS (LEPIDOPTERA, NOCTUIDAE) IN TOBACCO}, volume={21}, ISSN={["0046-225X"]}, DOI={10.1093/ee/21.3.586}, abstractNote={Field experiments were conducted to examine interactions of Heliothis virescens (F.), its natural enemies, and tobacco plants engineered to express low levels of Bacillus thuringiensis Berliner toxin. Survival of H. virescens larvae was measured in response to four treatments: (1) toxin-producing plants exposed to natural enemies, (2) toxin-producing plants caged to exclude enemies, (3) toxin-free plants exposed to enemies, and (4) toxin-free plants caged to exclude enemies. B. thuringiensis toxin mediated resistance caused a significant decrease in first-instar survival, and natural enemies caused a significant decrease in third-instar survival. Survival of uncaged first instars as a proportion of survival of caged first instars was significantly lower on toxic plants than control plants, indicating synergism of resistance and natural enemies. Among collections of artificially infested larvae, parasitism by Campoletis sonorensis (Cameron) was significantly higher on toxic plants than on control plants, another indication of synergism. Among collections of wild larvae and larvae censused in the field, parasitism usually did not differ between plant lines. Larval development of H. virescens was significantly slower on toxic plants than on control plants in two out of five trials. Prolonged vulnerability to natural enemies appeared to provide a mechanism for synergism. However, synergistic increases in mortality and parasitism were detected in two trials when development rates on toxic plants and control plants were equal, indicating existence of another mechanism. B. thuringiensis toxin-mediated partial resistance appeared compatible with natural enemies for control of H. virescens . However, a simulation using a theoretical population genetic model suggested that synergism of the level measured in this study could accelerate pest adaptation to resistant plants.}, number={3}, journal={ENVIRONMENTAL ENTOMOLOGY}, author={JOHNSON, MT and GOULD, F}, year={1992}, month={Jun}, pages={586–597} }