Recent published research shows that pollen from most Bt hybrids rarely if ever affects monarch larvae, but pollen from event 176 hybrids, which are being phased out, could have negative effects. Although Bt corn pollen does not appear to pose a risk to monarch larvae, questions have been raised concerning other plant tissues, primarily anthers. In 2001, field studies were conducted using naturally occurring milkweed plants to determine the frequency and distribution of anthers on milkweeds inside cornfields. In 2002, this study was expanded to observe how far anthers traveled outside cornfields. Also in 2002, studies were conducted to determine if Bt-corn anthers had adverse effects on monarch larvae. Laboratory bioassays and field studies consisted of three treatments, Bt anthers, non-Bt anthers, and no anthers. In the lab, a Petri-dish bioassay was used to expose larvae to a constant density of anthers through their development. The amount of leaf feeding at 48 and 96 hours and a 4- and 9-day larval weight were compared. In the field, cages were placed around individually-potted common milkweed plants that were then placed in a section of detassled corn, ten replications of each treatment. Five neonates were placed on each common milkweed plant and exposed to a constant known density of anthers through their development. Larval survival and a 4- and 9-day larval weight were compared. These data in combination with studies on larval behavior will be important in assessing if Bt anthers are a potential hazard to monarch larvae.
Species 1: Lepidoptera Danaidae Danaus plexippus (Monarch Butterfly)
Keywords: risk assessment, non-target species
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