Targeted insect control

Behavior modifying chemicals, pheromones in particular, offer one of the potential alternatives for future control and management of forest Lepidoptera. These semiochemicals are generally non-toxic and highly specific for target insects, but their use in forest ecosystems is not without problems and possible limitations. 

The other long understood and, indeed, fundamental function of insect cuticular lipids is to restrict water loss to prevent a lethal rate of desiccation (Hadley, 1984 Noble-Nesbitt, 1991 Nelson and Blomquist, 1995). Conservation of water is a primary challenge faced by terrestrial animals with high surface area to volume ratio such as insects. The anti-desiccatory function of the cuticular waxes is crucial in meeting this need, and makes them a focused target for insect control. 

The peripheral pheromone olfactory system in insects targets for species-selective insect control agents... 

Insects have evolved resistance to Bt toxins in the laboratory, yet only one crop pest, the diamondback moth (Plutella xylostella), has evolved resistance to Bt toxins under open field conditions (Tabashnik et al. 2003). But this resistance was not caused by Bt crops, rather it occurred in response to repeated foliar sprays of Bt toxins to control this pest on conventional (non-GE) vegetable crops (Tabashnik 1994). Based partly on the experience with diamondback moth and because Bt crops cause season-long exposure of target insects to Bt toxins, some scientists predicted that pest resistance to Bt crops would occur in a few years. 

One of the major reasons for the interest in insect pheromones is their potential for use to control pests. In one method a large number of traps, baited with small amounts of the sex attractant of the female insect, are used to trap enough males that the breeding of the insects is decreased. In another method that requires fewer traps, a small number of traps are used to monitor the population of the target insect. The best time to apply pesticides can be determined by monitoring these traps. In one case, 10 to 15 applications of a pesticide to control the pink bollworm still resulted in damage to 30% of a cotton crop. This was decreased to almost no damage with only one to two pesticide applications when the ideal times for these applications were determined by the use of traps. 

Tissue deposits are less available to bark beetle predators and parasites searching the bark surface for their host. Therefore, they offer more specificity toward the target insect. Further, tissue deposits may be easier to reproduce consistently. Unless we acquire better understanding of the factors that control crystallization, we will find it difficult to control the character of surface deposits obtained from solution. On the other hand, the character of wettable powder deposits seems to be more easily controlled (particle size, density). 

An intense interest in insect pheromones has been generated around the world in the past few years as applications have been developed to use these biologically active compounds to detect, survey, monitor populations and, in some cases, to control the target insects. Pheromones have been identified for ca. 250 insect species ( 1) most of which are Lepidoptera. Many of these compounds or blends of compounds have been used as baits in survey or monitoring traps to detect or estimate insect populations some have also been successfully applied for mass trapping of males and as mating disruptants in insect control programs. 

For controlled-release formulations to be effective and economical, they must release most of their pheromone during the flight season of the target insect. Too rapid a release would necessitate costly retreatment, and too slow a release would be wasteful of expensive pheromone by leaving a significant amount... 

The emission of a pheromone from a controlled-release formulation can depend on the diffusion through holes in the matrix or on the penetration of the compound through a wall or membrane by absorption, solution and diffusion (8). Thus variation in the parameters of the formulations, such as film thickness, particle size, solvent, pore dimensions, etc., alters the release rate. The design of the formulation must therefore take into account the effect of each variable on the emission rate in order to develop a system that is effective during the appropriate cycle of the target insect. 

In addition to their well established role in catalyzing the metabolism of a wide variety of naturally occurring and synthetic xenobiotics, cytochrome P-450-mediated mixed-function oxidases are of critical Importance in the biosynthesis and regulation of the major hormones (ecdysteroids and juvenile hormone) that control insect growth and development. The characteristics of the mixed-function oxidases involved in the synthesis of insect hormones are described and the possibility that the enzymes might represent potential targets for insect control is discussed. 

Pesticide is used to control pests of different kinds, such as target insects, vegetation, and fungi. Pesticides are known poisons used specifically for the control of crop pests and rodents. Some are very poisonous, or toxic, and may seriously injure or even kill humans. Others are relatively nontoxic. Pesticides can irritate the skin, eyes, nose, or mouth. The health effects of pesticides depend on the type of pesticide. The organophosphate and carbamate pesticides affect the nervous system. Others cause irritation to the skin, eyes, and mucous membranes. Several pesticides are carcinogens and some others cause disturbances to the hormone or endocrine system in the body. 

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