RESISTANCE OF BT TRANSGENIC MAIZE TO LESSER CORNSTALK BORER (LEPIDOPTERA: PYRALIDAE)

Abstract

The lesser cornstalk borer, Elasmopalpus lignosellus (Zeller) (Lepidoptera: Pyralidae), maize causes the symptom known as “dead heart” to maize. The objective of this research was to evaluate if Bt maize would protect seedlings against lesser cornstalk borer damage and whether different temperatures affect the insect-plant interaction. Two experiments were conducted. Seeds from Pioneer Bt maize hybrids P33G27, P34R07, P34G82, P33A14, and P34D34, expressing the toxin Cry1A(b) were obtained from the market. Seeds from the hybrids Mycogen (experimental) and Garst 8539 expressing, respectively, the toxin Cry1F and Cry9C as well as the control Garst 8539 (non-Bt) were obtained from the seed producers. Lesser cornstalk borer for artificial infestation were obtained from a colony maintained by USDA-ARS-CPMRU, in Tifton, GA. The first experiment included 7 maize hybrids tested at two plant growth stages (3 and 4 leaf) at a constant temperature of 27 ± 0.7 ° C and photophase of 14 h light: 10 h darkness. The experimental unit was 9 seedlings infested with 2 second/third instars per plant and replicated 3 times. One week after infestation, the experiment was evaluated by weighing and counting the number of surviving larvae and the number of undamaged plants. A damage score (0-no damage, 10-dead plant) was used. There was a significant difference between the Bt and the non-Bt hybrids regarding the damage score and the number of dead plants (Table 1). However, there was no significant difference among the Bt hybrids regarding those variables. The degree of plant damage and number of dead plants/plot were highly correlated (r = 0.998). Fewer numbers of lesser cornstalk borer larvae survived on Bt than non-Bt maize. In addition, larvae surviving on Bt maize weighed less than those surviving on non-Bt maize (Table 1). There was a high correlation (r = 0.991) between the number and weight of surviving larvae. A significant reduction on the number of survivors, caused by Bt toxin, was reported to lesser cornstalk borer on transgenic sugarcane (Fitch et al. 1996).