Steven R. Sims

Selection of tobacco budworm for resistance to a genetically engineered Pseudomonas fluorescens containing the δ-endotoxin of Bacillus thuringiensis subsp. kurstaki

Abstract A diet incorporation technique was employed to study the selection response of Heliothis virescens to a genetically engineered strain of Pseudomonas fluorescens . The Pseudomonas expresses a 130-kDa endotoxin protein of Bacillus thuringiensis subsp. kurstaki strain HD-1. Selection was maintained for 14 generations. By generation 3, differences in susceptibility between selected and control lines were significant at 3-fold. Resistance increased to 24-fold by generation 7, and fluctuated between 13 and 20× thereafter. The selected strain was also approximately 4-fold less susceptible to purified HD-1 endotoxin and Dipel. Injection of larvae with engineered or nonengineered Pseudomonas did not result in a significant difference in survival between the two lines, indicating response to bacterial septicemia is a minor part of the resistance mechanism. An unchallenged selected line (F13) maintained its initial level of resistance over two generations, providing evidence for the stability of the trait. The implications of these findings on the development of pest management strategies are discussed.

Genetic basis of tobacco budworm resistance to an engineered Pseudomonas fluorescens expressing the δ-endotoxin of Bacillus thuringiensis kurstaki

Abstract Inheritance of tobacco budworm (Heliothis virescens) resistance to a recombinant Pseudomonas expressing the 130-kDa δ-endotoxin protein of Bacillus thuringiensis strain HD-1 was studied. The tobacco budworm line used was 12-fold more resistant to the endotoxin (LC50) than the susceptible strain. Resistance was autosomally inherited, incompletely dominant, and controlled by several genetic factors. Genetic control of resistance was unstable. An unchallenged line with an initial resistance of 69-fold that of the susceptible line declined to 13-fold by generation 5 of nonselection.

Field Evaluation of Transgenic Corn Containing a Bacillus thuringiensis Berliner Insecticidal Protein Gene Against Helicoverpa zea (Lepidoptera: Noctuidae)

Twelve independently transformed lines of transgenic corn (Zea mays L.) expressing the CryIA(b) insecticidal protein from Bacillus thuringiensis var. kurstaki were field tested to evaluate their re...

Linear Alcohol Ethoxylates: Insecticidal and Synergistic Effects on German Cockroaches (Blattodea: Blattellidae) and Other Insects

Abstract Sixteen linear ethoxylated alcohol surfactants (AEOs) were studied to determine their contact insecticidal activity to adult German cockroaches,Blattella germanica (L.) (Blattodea: Blattellidae). Within groups of AEOs of equal carbon chain length, insecticidal activity, measured as LT50 values (in minutes) and 24-h mortality after treatment, was inversely related to the amount of ethoxylation. There was a highly significant negative relationship between the hydrophile-lipophile balance (HLB) value of the AEO and contact toxicity. The AEO with the lowest HLB value, Tomadol 23-1 (HLB = 3.7), produced the greatest 24-h cockroach mortality. The contact activity of Tomadol 23-1 was evaluated against a wide range of other insect species. Most species were killed within 24 h by direct exposure (1–4 μl of a 50% ethanol solution) to Tomadol 23-1 or by spray exposure to an aqueous solution. Tomadol 23-1, at a sublethal concentration, was tested in combination with representative members of the carbamate, nicotinoid, organophosphate, pyrethrum, pyrethroid, and pyrrole insecticide classes. Significant synergism was demonstrated in combinations of Tomadol 23-1 and chlorfenapyr, clothianidin, imidacloprid, thiamethoxam, and pyrethrum. Tomadol 23-1 significantly reduced the insecticidal activity of propoxur, suggesting antagonism. The insecticidal activity of Tomadol 23-1 was synergized by coapplication with a sublethal amount of piperonyl butoxide, indicating the involvement of cytochrome P450 microsomal monooxygenases in insect metabolism of AEO surfactants.

Comparative Toxicity and Repellency of Microencapsulated and Other Liquid Insecticide Formulations to the German Cockroach (Dictyoptera: Blattellidae)

ABSTRACT Responses of German cockroaches, Blattella germanica (L.) (Dictyoptera: Blattellidae), to microencapsulated (ME) formulations of six insecticides (bifenthrin, chlorpyrifos, cyfluthrin, deltamethrin, lambda-cyhalothrin, and permethrin) were compared with emulsifiable concentrates (EC) (chlorpyrifos, cyfluthrin, deltamethrin, and permethrin) or ready-to-use (RTU) formulations (bifenthin and lambda-cyhalothrin). Two rates were tested per comparison. Baseline toxicity (LT50 value) was determined by continuous exposure to residual deposits. Repellency, toxicity (LT50), and performance index (PI) values were determined using Ebeling choice boxes. Baseline toxicity of the permethrin formulations was similar, but all other active ingredients had significant toxicity differences at one or both formulation × dose comparisons. Baseline toxicity and repellency were negatively correlated. Choice box LT50 and the time to reach 50% of the maximum PI were positively correlated. The maximum PI was positively correlated (P < 0.06) with baseline LT50 and negatively correlated (P < 0.07) with repellency. Chlorpyrifos had the lowest repellency except for the EC at 0.25%. Bifenthrin ME and lambda-cyhalothrin ME had greater PI values than comparative RTU formulations. Cyfluthrin EC at 0.03% and deltamethrin ME at 0.01% had significantly lower PI values than comparison treatments. Permethrin PI value for the EC at 0.03% exceeded that for the ME, but at 0.05% the ME had a significantly greater PI. These data demonstrate the difficulty in making generalizations about the relative performance of ME compared with EC or RTU formulations. Variable results observed within, and between, formulations may be influenced by application rate, formulation type, other formulation components, and the toxicity—repellency of the active ingredient.

Influence of Soil Type and Rainfall on Pupal Survival and Adult Emergence of the Fall Armyworm (Lepidoptera: Noctuidae) in Southern Florida

Soil and rainfall influences on pupal survival and adult emergence of the fall armyworm, Spodoptera frugiperda (J. E. Smith), were studied in subtropical Florida. Increasing amounts of simulated rainfall, from 0–8 cm, significantly reduced adult emergence, whereas the effect of soil type (limestone and marl) was not significant in a greenhouse test. A field study evaluated the influence of soil type under natural conditions of temperature and rainfall over a 14-month period. Experiment date, soil type, and the date x soil interaction significantly affected adult emergence. Adult emergence was significantly greater in marl soil than limestone soil on 5 of 8 dates. These data indicate that soil type and environmental factors, such as precipitation and temperature, are likely involved in affecting pupal survival and adult emergence of the fall armyworm in southern Florida.