Monarchs, Bt Pollen, and Hysteria

May 28, 1999
During the most recent week, we received many e-mails and telephone calls concerning the published report in Nature by Dr. John Losey and colleagues that detailed the potential negative effects of Bt pollen on survival of monarch butterfly caterpillars. The results of their investigation indicated that when monarch larvae consumed Bt pollen on milkweed leaves, they developed more slowly and died more readily than larvae that ate non-Bt pollen or leaves without pollen. The research was conducted at Cornell University in the laboratory. Bt pollen (N4640-Bt corn) was obtained by "gently tapping a spatula of pollen over milkweed (Asclepias curassavica) leaves which had been lightly misted with water." The concentration of pollen (Bt and non-Bt) was adjusted to visually approximate that of milkweed leaves obtained from cornfields. Five monarch larvae (3 days old) were placed on milkweed leaves. Treatments were replicated five times. After 4 days of feeding, monarch larval survival (56 percent) on Bt corn pollen-treated leaves was much less than on the other two treatments in which no mortality occurred. Interestingly, both types of pollen (Bt and non-Bt) lowered the milkweed consumption rates of monarch larvae. However, consumption of milkweed tissue by monarch larvae was twice as great on leaves dusted with non-Bt pollen than on leaves dusted with Bt pollen. On average, monarch larvae that ate Bt pollen weighed less than half that of larvae consuming milkweed leaves with no pollen.

Research that was largely ignored by the media appeared in the Proceedings of the North Central Branch Meeting of the Entomological Society of America held in Des Moines, Iowa, March 28­31, 1999. Laura Hansen and John Obrycki, entomologists with the Department of Entomology at Iowa State University, published an abstract entitled Non-target Effects of Bt Corn Pollen on the Monarch Butterfly (Lepidoptera: Danaidae). (The full abstract may be viewed on the Web at the following address: http://www.ent.iastate.edu/entsoc/ncb99/prog/abs/d81.html.) Researchers from Iowa State University examined the density of Bt pollen on milkweed leaves from plants collected within a cornfield as well as 0, 1, and 3 meters from the edge of the field. Not surprisingly, the highest concentration of Bt pollen was found on leaves from milkweed plants collected from within the cornfield. Likewise, the lowest density of pollen occurred on leaves found on plants 3 meters from the edge of the cornfield. Leaves from milkweed plants within and adjacent to the Bt cornfield were used to expose first-instar monarchs to Bt and non-Bt pollen. Within 48 hours, 19, 0, and 3 percent mortality was observed in the Bt pollen, non-Bt pollen, and no pollen control treatments, respectively. What do the findings from these two preliminary studies suggest?

First of all, more robust field studies are required to examine the potential ecological effects of Bt pollen on monarch populations, as well as on other lepidopteran species. More careful research clearly is warranted. How interested will industry be in supporting more intensive studies that might shed light on this topic? Second, rather than criticize the research reported by scientists from these two universities, industry representatives should concentrate on articulating the many proven economic and environmental benefits of using transgenic insecticidal cultivars for the management of European corn borer. By attacking these new and interesting findings concerning monarch survival, the debate over the wisdom of using genetically modified organisms in pest management programs becomes more politically charged. Ultimately, producers may be the losers in this new high-stakes crop protection arena in which we find ourselves.--Mike Gray, Kevin Steffey

Author: Kevin Steffey Mike Gray