Cotton Boll Abscission and Yield Losses Associated with First-Instar Bollworm (Lepidoptera: Noctuidae) Injury to Nontransgenic and Transgenic Bt Cotton

Abstract

Field tests were conducted in northeastern Louisiana to determine the effects of infestations by Helicoverpa zea (Boddie) on cotton bolls of varying ages. First instars were caged on bolls of nontransgenic ('Deltapine 5415') or transgenic Bacillus thuringiensis Berliner variety kurstaki (Bt) ('NuCOTN 33B') cotton from 29 June to 11 August during 1997 and 1998. Deltapine 5415 bolls that accumulated 179 (7.2 d), 281 (11.2 d), and 253 (10.1 d) heat units beyond anthesis were safe from bollworm-induced abscission at 72 h after infestation, 7 d after infestation, and at the time of harvest, respectively. NuCOTN 33B bolls that accumulated 157 (6.3 d), 185 (7.4 d), and 180 (7.2 d) heat units beyond anthesis were safe from bollworm-induced abscission at 72 h after infestation, 7 d after infestation, and at the time of harvest, respectively. Bollworm larvae reduced seedcotton weights of Deltapine 5415 bolls that accumulated between 58.5 (2.3 d) and 350.5 (14.0 d) heat units beyond anthesis. Seedcotton weights of NuCOTN 33B bolls that accumulated between 0 and 281 (11.2 d) heat units beyond anthesis were reduced by bollworm injury. Deltapine 5415 and NuCOTN 33B bolls that accumulated 426.5 (17.1 d) and 299.5 (12.0 d) heat units beyond anthesis, respectively, before infestation were not injured by first-instar bollworm larvae. These data provide information about late-season insecticide termination strategies for bollworms on nontransgenic and transgenic Bt-cotton. This, in turn, will help pest managers determine when insecticides are no longer economical during the late season.

Volatiles released from cotton plants in response to Helicoverpa zea feeding damage on cotton flower buds

“…This may be explained by an abscission of squares in response to 72 h feeding which may be preceded by a reduced volatile production. Abscission of squares (Holman and Oosterhuis 1999) and of bolls (Gore et al 2000) in response to larval feeding has been described. The abscission of bolls 7 days after anthesis of up to 50% by 72 h after infestation with H. zea (Gore et al 2000) is lower compared to 88% abscission of squares after 72 h of H. zea feeding in our experiments.…”

“…Abscission of squares (Holman and Oosterhuis 1999) and of bolls (Gore et al 2000) in response to larval feeding has been described. The abscission of bolls 7 days after anthesis of up to 50% by 72 h after infestation with H. zea (Gore et al 2000) is lower compared to 88% abscission of squares after 72 h of H. zea feeding in our experiments. The abscission of squares may be the most efficient way for the plant to prevent further investment of resources in a flower tissue that can no longer be functional in reproduction after severe damage.…”

Bollworm (Lepidoptera: Noctuidae) Survival on ‘Bollgard’ and ‘Bollgard II’ Cotton Flower Bud and Flower Components

“…White ßowers of Bollgard cotton appear to be the plant structures most susceptible to bollworm feeding. Gore et al (2000) infested white ßowers and various aged bolls with Þrst instar bollworm larvae. Abscission rates of Bollgard bolls that were infested as white ßowers were higher compared with bolls that were infested during later stages of development.…”

Transgenic Bt Cotton: Effects on Target and Non-Target Insect Diversity

“…Among the chewing insect pests, cotton bollworm complex (Helicoverpa armigera (Hubner), Pectinophora gossypiella (Saunders) and Earias Spp.) are the most destructive ones in Pakistan and causes 30-40% yield reduction [63], because of damage to flowers, squares and bolls [64,65]. Among sucking insect pests i.e., whitefly, jassid, thrips, aphid and cotton mealy bug are important [66,67].…”