Pest Management with Insect Sex Attractants

In 1964, Wright (1) suggested that multicomponent pheromones would be widely used because they could convey more information than a single compound; evolutionary selectivity would favor the organisms that had the better communication systems. Wright had little compunction in overriding the evidence reported prior to 1964 for single compounds in two moth species (the silkworm moth and the gypsy moth). But, in general, this proposal was ignored, and throughout the 1960s, a number of moths were reported to use single component pheromones.

What happened to lead so many investigators astray? Why was the "magic bullet" concept -- one insect, one specific compound -- so firmly implanted?

The story goes back to the heroic achievement by Butenandt's group, reported in 1959 (2): the isolation and identification of the chemical compound that elicited the sexual excitation response from the male silkworm moth; the work was done without benefit of modern instrumentation --

Abstract

In 1969, four terpenoid compounds were demonstrated by identification and synthesis to comprise the boll weevil pheromone. Since then the pheromone has been utilized successfully for monitoring and population reduction and has been a component in several integrated pest management and elimination programs. In the course of these tests, it was necessary to develop a long-lasting formulation, to determine the best ratio of components, to improve the methods of syntheses to reduce costs, to commence registration with EPA, and to develop efficient traps and trapping procedures. The pheromone was effectively utilized in the recent South Mississippi tests to monitor and reduce the insect population. Plans for future tests are discussed. Recent studies showed that gut microflora, deficient diets, and sterilization decrease pheromone biosynthesis.

An important advantage of pheromones for insect control is their specificity for the target species. In some cases several closely related species may respond to the same compound and, through its use the environmental pollution, ecological disruption, and the destruction of beneficial insects brought about by the use of insecticides may be avoided. Unfortunately, we seldom find a situation wherein only one economically important insect pest occurs in a particular crop or area. Thus, for practical pest management purposes, this specificity of pheromones could be almost as great a disadvantage as an advantage.

In survey programs the specificity of pheromones is an obvious advantage, and traps baited with synthetic pheromones have been used extensively to monitor for insect pests. Monitoring of specific pest populations is now incorporated into several pest management programs to allow more timely application of insecticides (1,2,3).

Mass trapping, wherein a sufficient number of traps are deployed

Abstract

Females of the pink bollworm release gossyplure, a mixture of the cis,cis- and cis,trans-isomers of 7,11-hexadecadienyl acetate, to attract males for mating. Hexalure, cis-7-hexadecenyl acetate, although not a natural pheromone of this species, is also attractive to the male moths. The atmosphere above extensive acreages of cotton was continuously permeated with gossyplure or hexalure for periods up to 20 weeks. The resulting disruption of premating communication between males and females provided ca 75% reduction in the numbers of pink bollworm larvae infesting cotton bolls, compared with larval infestations in untreated cotton fields. An intimate knowledge of the normal premating behavior of the moths is essential to the intelligent development of this technique for disruption of communication.

The numerous species of insects and mites that feed on apple trees in New York represent one of the most formidable pest complexes affecting any cultivated crop. The high quality insect-free fruit desired by the consumer has necessitated the use of a preventive chemical pesticide program that blankets the growing season from bud break in April practically until the fruit is harvested in the fall. The divergent concerns of economics, ecology and pesticide resistance, however, have increased pressure for the implementation of pest management programs that integrate a variety of techniques. The development of pheromone lures for the major lepidopterous pests has provided the capability of monitoring for the presence of these species for more accurate timing of insecticide sprays. A pest management research project in New York (1) has relied heavily on the use of pheromone monitoring traps for most of the species listed in Table I. The change

Summary

This paper attempts to answer the question "why have no pheromones been registered for use in crop protection?" from an economic viewpoint. Based on the assumption that pheromones can be used to disrupt insect communication to prevent mating and larval damage, the various components of research and development needed to achieve registration for practical use are listed and their costs are estimated. For economic analysis, a specific case of codling moth control is used to estimate the acreage involved, the cost per season and the expense of developing and introducing a pheromonal method of pest control to derive the internal rate of return on the research and development investment. Assuming commercialization of the product, it appears from the calculated cash flow that the project could not break even on annual basis before the fourth year. Using discounted cash flow analysis, the internal rate of return is found to be

Although insecticides continue to be our major means of defense against insects that attack our food, fiber, and other agricultural products, difficulties related to the use of insecticides have generated a sustained search for alternative means of insect control, or at least some means of reducing the use of insecticides required for pest management. In this regard, the behavior-controlling chemicals, and insect sex attractants in particular, have received considerable attention during the past several years.

The present paper describes some of the recent research conducted by the USDA and cooperators with behavior-controlling chemicals. Work with the sex pheromone of the gypsy moth (Porthetria dispar (L.)) will be used to illustrate this research for the most part because of the author's major involvement and familiarity with this project.

Insect Sex Attractant Pheromones

Insect sex attractant pheromones are chemicals emitted by one member of a species to call a mate to it

Parasites and predators have been used successfully to control insect pests. However, efforts to control insect pests with parasites, especially the release of parasites, have often failed. These failures occurred because of a number of factors, most of which could be corrected if more information was available concerning the host-parasite relationship. Information concerning the roles of chemicals (kairomones) in this relationship has recently appeared. These chemicals play a major role in the host selection sequence of the parasite and can be used to manage parasites to make them more effective as a pest control measure.

The following discussion will be limited to insect parasites, but most of the principles are applicable to predators as well.

Host Selection

An understanding of the host-selection phase of the host-parasite relationship is a prerequisite to a study of the role of kairomones.

Salt (1) and Flanders (2) divided the host-selection processes into four phases.

For those of you who do not know, I regretfully report that Dr. Len Axelrod suffered a fatal heart attack a few weeks ago, and needless to say, I feel very humble standing here in his place.

During the few years in which I had the distinct pleasure of associating with Len, he always received my deepest respect, not only as a scientist, but as a humanitarian who was greatly concerned with the welfare and survival of man and his environment.

So, without any further adieu, I would like to dedicate this presentation to Dr. Leonard R. Axelrod.

During the past year, Criteria and Evaluation Division has worked closely on a contract with the Zoecon Corporation. The purpose of this contract was to provide scientific and technical data to enable the Environmental Protection Agency to develop guidelines for the registration of pheromones and insect growth regulators. Part of what

To be of practical value in insect control, a chemical or combination of chemicals that affects insect behavior should evoke an approaching or departing response or nullify one of these responses. Furthermore, the action should be demonstrable in the normal habitat of the insect. The more compelling the response to the chemical, the greater will be its potential as an insect control agent.

A compilation of such "insect-behavior" chemicals is given in Table I. Many of the compounds have been identified as pheromonal components, but many found active in field trials are not known to be present in the responding insect. Footnotes in the table indicate whether a compound is produced by males (g) or females (h), or derived from mixed sexes (q). Compounds not known to be present in the insect are also designated by a footnote (d); this broad category includes compounds foreign to the insect as well