Robert T. Staten

Field Performance of a Genetically Engineered Strain of Pink Bollworm

Pest insects harm crops, livestock and human health, either directly or by acting as vectors of disease. The Sterile Insect Technique (SIT) – mass-release of sterile insects to mate with, and thereby control, their wild counterparts – has been used successfully for decades to control several pest species, including pink bollworm, a lepidopteran pest of cotton. Although it has been suggested that genetic engineering of pest insects provides potential improvements, there is uncertainty regarding its impact on their field performance. Discrimination between released and wild moths caught in monitoring traps is essential for estimating wild population levels. To address concerns about the reliability of current marking methods, we developed a genetically engineered strain of pink bollworm with a heritable fluorescent marker, to improve discrimination of sterile from wild moths. Here, we report the results of field trials showing that this engineered strain performed well under field conditions. Our data show that attributes critical to SIT in the field – ability to find a mate and to initiate copulation, as well as dispersal and persistence in the release area – were comparable between the genetically engineered strain and a standard strain. To our knowledge, these represent the first open-field experiments with a genetically engineered insect. The results described here provide encouragement for the genetic control of insect pests.

Sustained susceptibility of pink bollworm to Bt cotton in the United States

Evolution of resistance by pests can reduce the benefits of transgenic crops that produce toxins from Bacillus thuringiensis (Bt) for insect control. One of the worlds most important cotton pests, pink bollworm (Pectinophora gossypiella), has been targeted for control by transgenic cotton producing Bt toxin Cry1Ac in several countries for more than a decade. In China, the frequency of resistance to Cry1Ac has increased, but control failures have not been reported. In western India, pink bollworm resistance to Cry1Ac has caused widespread control failures of Bt cotton. By contrast, in the state of Arizona in the southwestern United States, monitoring data from bioassays and DNA screening demonstrate sustained susceptibility to Cry1Ac for 16 y. From 1996-2005, the main factors that delayed resistance in Arizona appear to be abundant refuges of non-Bt cotton, recessive inheritance of resistance, fitness costs associated with resistance and incomplete resistance. From 2006-2011, refuge abundance was greatly reduced in Arizona, while mass releases of sterile pink bollworm moths were made to delay resistance as part of a multi-tactic eradication program. Sustained susceptibility of pink bollworm to Bt cotton in Arizona has provided a cornerstone for the pink bollworm eradication program and for integrated pest management in cotton. Reduced insecticide use against pink bollworm and other cotton pests has yielded economic benefits for growers, as well as broad environmental and health benefits. We encourage increased efforts to combine Bt crops with other tactics in integrated pest management programs.

Successful Area-Wide Program to Control Pink Bollworm by Mating Disruption

This review deals with the pragmatic aspects of pheromone use for the control of the pink bollworm (PBW), Pectinophora gossypiella. FSFS FS We will provide a brief historical summary of the principal pheromone formulations used in the United States, defining them within two categories based largely on amounts of active ingredient used. We will summarize results from two area-wide management programs. Within these programs, population suppression has been maximized It has exceeded the degree of suppression obtained when pheromone has been used on limited numbers of fields within a large geographically defined growing area. We will then briefly speculate on long-term implication of these programs and where they fit within the overall theory and practice of integrated pest management.

Engineered Repressible Lethality for Controlling the Pink Bollworm, a Lepidopteran Pest of Cotton

The sterile insect technique (SIT) is an environmentally friendly method of pest control in which insects are mass-produced, irradiated and released to mate with wild counterparts. SIT has been used to control major pest insects including the pink bollworm (Pectinophora gossypiella Saunders), a global pest of cotton. Transgenic technology has the potential to overcome disadvantages associated with the SIT, such as the damaging effects of radiation on released insects. A method called RIDL (Release of Insects carrying a Dominant Lethal) is designed to circumvent the need to irradiate insects before release. Premature death of insects’ progeny can be engineered to provide an equivalent to sterilisation. Moreover, this trait can be suppressed by the provision of a dietary antidote. In the pink bollworm, we generated transformed strains using different DNA constructs, which showed moderate-to-100% engineered mortality. In permissive conditions, this effect was largely suppressed. Survival data on cotton in field cages indicated that field conditions increase the lethal effect. One strain, called OX3402C, showed highly penetrant and highly repressible lethality, and was tested on host plants where its larvae caused minimal damage before death. These results highlight a potentially valuable insecticide-free tool against pink bollworm, and indicate its potential for development in other lepidopteran pests.

Measuring Pheromone Concentrations in Cotton Fields with the EAG Method

Mating disruption has proved to be an important method of pest control for many cropping systems. However, there seems to remain a large potential for improvement and optimization of the method. For example, there are different types of formulations available, but there is very little data about their actual performance in the field: What level of pheromone concentration can each formulation maintain, and for how long? Apart from the performance of the pheromone sources, other questions arise. How homogeneous is pheromone distribution? How far does pheromone drift into adjacent fields? Do the plants’ leaves interact with pheromone?

Measurement by electroantennogram of airborne pheromone in cotton treated for mating disruption of Pectinophora gossypiella following removal of pheromone dispensers

The presence of pheromone in cotton foliage after removal of pheromone dispensers was assessed by measuring the airborne pheromone concentration with an electroantennogram device. Plots of 0.4 ha in isolated cotton fields were treated with Shin‐Etsu PBW‐Rope® pheromone dispensers for mating disruption of Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae). The dispensers contained (Z,Z)‐ and (Z,E)‐7,11‐hexadecadienyl acetates (gossyplure) in a 49:51 ratio and were applied at a density of 1 000/ha. The 400 pheromone dispensers were removed 1–12 days later. In four experiments involving canopy heights from 30–150 cm, the decay of the pheromone concentration was recorded repeatedly in short intervals for up to 7 h. Decay to undetectable concentrations generally occurred within 1–10 h, depending on plant size and wind conditions. In all four experiments, pheromone concentration 24 h after removal was found to be near or below detection threshold of the electroantennogram. The presence of pheromone within and above the cotton after dispenser removal would be due to re‐entrainment of pheromone that had been adsorbed on cotton foliage or possibly some residual airborne pheromone.