ABSTRACT
Survival and growth of monarch larvae, Danaus plexippus (L.), after exposure to either Cry1Ab-expressing pollen from three Bacillus thuringiensis (Bt) corn (Zea mays L.) events differing in toxin expression or to the insecticide, lambda-cyhalothrin, were examined in field studies. First instars exposed to low doses ( approximately 22 grains per cm(2)) of event-176 pollen gained 18% less weight than those exposed to Bt11 or Mon810 pollen after a 5-day exposure period. Larvae exposed to 67 pollen grains per cm(2) on milkweed leaves from within an event-176 field exhibited 60% lower survivorship and 42% less weight gain compared with those exposed to leaves from outside the field. In contrast, Bt11 pollen had no effect on growth to adulthood or survival of first or third instars exposed for 5 days to approximately 55 and 97 pollen grains per cm(2), respectively. Similarly, no differences in larval survivorship were observed after a 4-day exposure period to leaves with 504-586 (within fields) or 18-22 (outside the field) pollen grains per cm(2) collected from Bt11 and non-Bt sweet-corn fields. However, survivorship and weight gain were drastically reduced in non-Bt fields treated with lambda-cyhalothrin. The effects of Bt11 and Mon810 pollen on the survivorship of larvae feeding 14 to 22 days on milkweeds in fields were negligible. Further studies should examine the lifetime and reproductive impact of Bt11 and Mon810 pollen on monarchs after long-term exposure to naturally deposited pollen.
Subject(s)
Bacillus thuringiensis , Bacterial Proteins/adverse effects , Bacterial Toxins , Butterflies , Endotoxins/adverse effects , Pest Control, Biological , Zea mays , Animals , Bacillus thuringiensis Toxins , Bacterial Proteins/genetics , Endotoxins/genetics , Gene Expression , Hemolysin Proteins , Iowa , Larva , Maryland , New York , Ontario , Pest Control, Biological/methods , Plants, Genetically Modified , PollenABSTRACT
The impact of a predator on its prey may depend on the presence of other species in the community. In particular, if predators are attracted to areas containing one prey species, another prey species may suffer greater predation if it occurs in the same areas. If the predator is omnivorous, this may occur even if one prey species is an animal and the other is a plant. We investigated the role of local dandelion densities on the impact of the predator Coleomegilla maculata on pea aphids in alfalfa fields. At small spatial scales, increased dandelion densities were associated with high C. maculata densities, presumably because these omnivorous ladybird beetles aggregated to pollen resources. In turn, the high C. maculata densities were associated with low aphid densities, presumably because of increased predation. We used laboratory cages to simulate C. maculata foraging in two adjacent patches of alfalfa, one with dandelions and one without. As in the field, the laboratory experiment showed that C. maculata aggregated to alfalfa interspersed with dandelions, which resulted in increased predation on aphids on alfalfa. This study demonstrates that a pollen-producing plant can indirectly decrease nearby herbivore densities by attracting an omnivorous predator.
