Bt-Corn

Bt-corn and its Effects on Danaus plexippus

Recently, in response to the chronic problem of insects destroying crops and from the known effects of pesticides on humans and on the environment, a new form of insecticide was discovered, particularly for corn. In this new case, the organism itself is genetically modified for protection. This insect-resistant corn is the new Bt-corn and contains genetic material from the donor organism, a bacterium. Bacillus thuringiensis contains a protein that kills the larvae of Ostrinia nubilalis, European corn borers, but is harmless to other insects (Bessin, 1999). When the Bt is consumed by the larvae, toxins paralyze the insectÐ'Ѓfs intestines, eventually causing death (Peairs, 2001). A small material of this genetic material is added to the inserted into the Bt-corn and thus enables the Bt-corn to produce its own insecticide. This Bt-corn has the same nutritional value as non-genetically modified corn but with a tolerance to insects (Bessin, 1999). Although Bt-corn may seem like a picture perfect crop, there are questions about it possible harm, which has been causing controversy.

The greatest scientific controversy regarding this new Bt-corn has been the effects that it has on Danaus plexippus Ð'Ѓ| the Monarch butterflies. The larvae feed primarily on milkweed, and if there is milkweed growing next to Bt-corn farms, the Bt-corn pollen drifts onto the milkweed, affecting the Monarch population. To test the effects of Bt-corn pollen on Monarch butterflies, a research team at Cornell University performed an experiment in a controlled environment, where three groups of larvae fed on milkweed leaves either dusted with Bt-corn pollen, non-Bt-corn pollen, or with no pollen. From this experiment, it showed that slightly less than half of the larvae that fed on the milkweed dusted with Bt-corn pollen did not survive to adulthood. In addition, the larvae that survived were less than half of the size of those larvae that did not come into contact with Bt-corn. Pollen from non-Bt-corn had no effect on the larvae. However, there was a flaw in this experiment. The amount of pollen placed on the milkweed was not calculated nor recorded. Therefore, whether a similar situation could occur in nature or not was questionable (Rice, 1999).

Upon further research, it was determined that the amount of pollen used for the experiment was implausible in nature; not that much pollen would naturally dust the milkweed plants. A 1999 experiment performed by the Agricultural Research Service, U.S. Department of Agriculture determined that monarch larvae had to consume pollen levels greater than 1,000 grains/cm^2 in order for the population to be affected by its toxicity (http://www.ars.usda.gov/is/br/btcorn/index.html#bt1, 2004). On top of this, it was also determined that by the time that the monarch larvae had emerged from their eggs, 80% of the corn had already shed their pollen (Bartholomew and Yeargan, 2001). By this time, the pollen levels on milkweed leaves had averaged out to only be at around 170 grains/cm^2, far from the lethal level (http://www.ars.usda.gov/is/br/btcorn/index.html#bt1, 2004). Thus, such reasoning concluded in the Bt-cornÐ'Ѓfs benefit; from the volumes of pollen consumed by the Monarch larvae, lethality was not possible.

In response to the argument that lethality of the Monarchs from Bt-corn pollen was not possible, a more accurate experiment was performed to try to disprove this notion. This time, milkweed plants near actual Bt-corn farms were fed to the Monarch larvae. The pollen exposure levels of the plant were also recorded, where it ranged from 122 to 188 grains/cm^2. This time, the pollen levels were parallel to those naturally found when Monarch larvae would actually be feeding on the milkweed, of 170 grains/cm^2. It was concluded from this experiment that compared to the larvae that did not come into contact with the Bt-pollen, within 48 hours since starting the experiment, there were about a quarter less survivors with those fed on Bt-contaminated milkweed (Divley, et al. 2004). Therefore, this experiment suggested what the Cornell experiment did, that Bt-corn could affect the Monarchs negatively.

Although this experiment may suggest that the amount of pollen left on the milkweed plants from the Bt-corn Ð'Ѓ| despite if the corn had already shed their pollen by the time the Monarch larvae feed on it Ð'Ѓ| does have a negative effect on the survival rate of the butterflies, the conditions found in nature are far different from those recreated in an enclosed laboratory. In nature, precipitation would rinse off of dilute the pollen levels, wind direction and natural obstructions would affect pollen gathering on the milkweed, and the distance of the milkweed plants from the corn field would also be a variable. Therefore, every milkweed plant around the same Bt-corn field will have a different dusting of the pollen, differing each season. The determination of actual, realistic Bt-corn negativity on Monarch larvae would be very inaccurate in a laboratory setting, where natural forces would not be taken into account.

While Monarch butterflies are being