Bacillus thuringiensis as an insecticide

The application of Bt crystal proteins as a biological insecticide was first introduced in 1938 in France. The technology was first used in the U.S. in the 1950’s (Deacon, 2001). There are many advantages to using Bacillus thuringiensis as an insecticide, including few known hazards to humans and animals. Applying insecticidal Bacillus thuringiensis can be done up to harvest, creating a larger application window. Once the biological insecticide has been applied, re-entering the field can be immediate (Willie, 2001).

Bacillus thuringiensis, as a bacterial insecticide, can be applied with conventional spraying equipment. An example of spraying equipment can be seen in Figure 9.

Fig. 9 Shows a sprayer applying chemical across a field. (UNL, 2001)

Since it is required that the ECB ingest the Bt protein to be killed, it is important for the spray equipment to have good coverage over the entire field. Bt must also be applied when the population of larvae is at the highest level since this type of organic chemical will only kill the insect in the larval stage. Also, organic insecticides containing Bacillus thuringiensis are only effective during the first generation of ECB (Wright, et al., 1994). This is due to the coverage of the spray application across the field and how long the insecticide remains active. Some of the most common organic insecticides containing Bt used in Nebraska include, Dipel® and Xentari® Biological insecticides. Both Dipel and Xentari can be used on field corn, sweet corn, and popcorn, but only Dipel can be applied to seed corn fields. Dipel can also be used on cotton, apples, beans, potatoes, soybeans, and peas to name a few. Xentari can be applied to peppers, peas, legumes, potatoes, soybeans, apples, and cotton as well as many others (Kelly, 2004).

The application of Bt cultures as an insecticide has the advantage of safety and organic acceptability. Effective application and timing limits its ability to control economic damage.