Reports of bollworm, Helicoverpa zea (Boddie), larvae feeding in white flowers of Bollgard ^® cotton have been relatively common each year since its commercialization. Currently, no information is available explaining the mechanisms that lead to bollworm infestations in white flowers. Field studies were conducted in northeast Louisiana to determine if differences in bollworm larval behavior occur on conventional (cv. Deltapine 5415) and Bollgard ^® (cv. NuCOTN 33B) cottons. Larvae were placed in the terminals of either single cotton plants or on all plants within 1-m row micro-plots. On non-flowering cotton plants, significantly more bollworms moved from the site of infestation (terminal) on Bollgard plants compared to that on non-Bollgard plants. On individual flowering plants, the number of nodes larvae moved from the terminal and number of infested bolls were greater on Bollgard cotton plants. Similar differences between Bollgard and non-Bollgard plants in the percentage of infested terminals and squares were observed at 48-h after infestation when 1-m rows were infested. These data will be used to refine scouting protocols for bollworm larvae on Bollgard ^® cotton.

Bollgard breeding lines. Parker and Luttrell (1998) found no differences in tobacco budworm egg density on Bollgard cottons compared with the non-Bollgard parental cottons. Also, the vertical distribution of eggs on plants was not different between Bollgard and non-Bollgard plants (Parker and Luttrell 1998). In Louisiana, no differences were observed in the number of soybean looper, Pseudoplusia includens (Walker), eggs recovered from a Bollgard cultivar and a non-Bollgard cotton cultivar (Hall 2000).

An alternative theory is that early instar larval dispersal is different on Bollgard cotton plants compared to non-Bollgard cotton plants. Tobacco budworm larval movement has been observed to be different on Bollgard cotton plants compared to non-Bollgard plants in field and greenhouse studies (Benedict et al. 1993, Parker and Luttrell 1999). In both of these studies, tobacco budworm larvae moved from Bollgard plant terminals faster than on non-Bollgard plants. These authors did not report on the fate of larvae after leaving the terminals. Larvae are the developmental stage controlled by the Cry1Ac protein in Bollgard cotton, and differences in larval behavior could result in feeding preferences on specific plant parts. Therefore, studies were conducted in Louisiana to determine if differences in bollworm larval behavior occur on Bollgard cotton plants compared to non-Bollgard plants. This study consisted of one experiment during vegetative plant development and two experiments during reproductive plant development.