Alexej B. Bořkovec

Ecdysteroid titers and molting aberrations in last-stage Oncopeltus nymphs treated with insect growth regulators

Abstract The ecdysteroid titers of insect growth regulator (IGR)-treated and untreated large milkweed bug nymphs, Oncopeltus fasciatus (Dallas) (Heteroptera: Lygaeidae), were determined by radioimmunoassay. All of the IGRs tested affected the ecdysteroid levels and the ecdysis of both sexes in some way. AI3-63604, a juvenile hormone mimic, accelerated ecdysteroid production and its subsequent decline, shortened the stadium, and induced a supernumerary nymphal molt. Diflubenzuron had no effect on the onset of ecdysteroid production but slightly retarded the decline in ecdysteroid titers before adult ecdysis, and the ecdysis was incomplete. Ecdysteroid production was delayed and erratic in nymphs treated with azadirachtin and AI3-63967, but the effect on ecdysis was different for each compound. Azadirachtin caused incomplete adult ecdysis, whereas AI3-63967 completely prevented any attempts at ecdysis. The large peak of exdysteroid activity associated with apolysis was absent in starved insects, and they made no attempt to ecdyse.

Toxicology of hexamethylphosphoric triamide in rats and rabbits

Hexamethylphosphoric triamide (HEMPA), an insect chemosterilant, was tested for acute and chronic toxicity in rats and rabbits. In rabbits, the estimated dermal LD50 was 2600 mg/kg. Clinical signs of systemic toxicity preceding death included alterations of nervous, gastrointestinal, and respiratory systems. Repeated application of HEMPA at 100 or 500 mg/kg to the skin of rabbits caused dose-related weight loss, altered gastrointestinal function and produced apparent nervous system dysfunction. Administration of HEMPA to rats at 50 (oral toxicity study) and 10 (reproductive study) mg/kg resulted in exacerbation of the chronic murine pneumonia complex when compared to lower-dosed and control animals. Morphologic differences in the oral toxicity study included imbibition of minimal amounts of proteinaceous material into renal tubular epithelium and increased splenic extramedullary hematopoietic activity in animals given 50 mg/kg when compared to control, 2 mg/kg and 10 mg/kg treated rats. No other compound-related pathologic or morphologic change was present in other tissues examined including the reproductive organs. No teratologic or unequivocal change that could be attributed directly to the compound was observed in the fertility, gestation, live birth, or lactation indices following administration of HEMPA at 2 or 10 mg/kg/day for a total of 169 days during which time the first (F1A) of 3 filial sets of pups were produced. Also, the reproductive activity and function of the offspring were normal.

Chemosterilant action of anthramycin: A proposed mechanism

The activity of anthramycin and structurally related analogs as chemosterilants of the housefly, Musca domestica L., correlates closely with the action of these compounds as inhibitors of Escherichia coli RNA polymerase. Since inhibition of RNA polymerase by anthramycin reflects binding of this antibiotic to the DNA primer required for enzyme activity, we propose that the interaction of anthramycin with DNA may also account for its action as a chemosterilant.

Insect chemosterilants: Their chemistry and application

Sexual sterilization of insects by ionizing radiation and the practical application of this process to insect control have been adequately reviewed in the literature by Baumhover et al. (1955), Bushland and Hopkins (1951 and 1953), Knipling (1955, 1959, 1960 a, and 1960 b), and Lindquist (1955). It is sufficient here to mention briefly the principles and shortcomings of the radiation-sterilization method which provided the impetus to the search for chemosterilants and thus paved a way for this new and promising insect-control tool.

ALKYLATING AGENTS AS INSECT CHEMOSTERILANTS

Birth control pills are becoming widely accepted as one of the means for regulating human populations. However, the concept of decreasing populations of rapidly reproducing organisms by reducing their birth rates rather than by increasing their death rates found its most striking application in the realm of insect pests (Knipling, 1960). Obviously, the reason was not an effort for a humanitarian treatment of some of our most destructive enemies, but an attempt to strike at the very base of the pest problem: the high reproductive capacity. The principle of population control by sterility is simple. If the ratio of the sterile to fertile organisms is made sufficiently large, matings between fertile males and females will become scarce, and the population will gradually diminish. The most important factor for success of this method is not the actual size of the population, but the ratio of the sterile to fertile individuals. Thus, some of the members of the population can be sterilized directly in their habitats or artificially reared and sterilized organisms can be released in sufficient numbers to establish the desired steri1e:fertile ratio. Sexual sterilization of insects can be accomplished in many ways, but only two methods appear to be practical now irradiation with gamma rays and treatment with chemicals. In distinction to birth control pills, sterilizing chemicals or chemosterilants should have a permanent and irreversible effect, but, like birth control pills, they must not interfere with mating and should have a minimum of side effects. One of the first guidelines in the search for effective chemosterilants was the analogy between carcinostatic and sterilizing effects. There is a certain similarity between tumor cells and germ cells, and it appeared logical that the same compounds might interfere with the propagation of either system. Indeed, the first successful insect chemosterilants were antimetabolites and biological alkylating agents that had been used previously with some success in cancer chemotherapy. The alkylating agents were of particular interest because they usually sterilized both sexes, and an extensive program of synthesis and testing was initiated in 1961 by chemists and entomologists of the U.S. Department of Agriculture. Following the discovery of nonalkylating male-insect sterilants (Chang et al., 19641, the emphasis has shifted toward these less toxic compounds, but the high activity and versatility of alkylating chemosterilants has not yet been surpassed.

Inter-species cross-reactivity of the prothoracicotropic hormone of Manduca sexta and egg-development neurosecretory hormone of Aedes aegypti

Abstract The cross-reactivities of the big and small forms of prothoracicotropic hormone (PTTH) from pupal brains of Manduca sexta and egg-development neurosecretory hormone (EDNH) from heads of adult Aedes aegypti were examined for PTTH by the in vitro Manduca prothoracic gland assay and for EDNH by the in vitro and in vivo Aedes ovary assays. The synthesis of ecdysone by both larval and pupal prothoracic glands of Manduca was increased in a dose-dependent manner by crude extracts of Aedes aegypti heads, reaching a maximum of approx. 3- and 2-fold, respectively. Gel filtration chromatography of the Aedes head extract revealed a peak of EDNH activity with an apparent mol. wt of 11 kD. This partially purified EDNH did not possess prothoracicotropic activity in the in vitro prothoracic gland assay, nor did any other fractions from the gel filtration column. Similarly, partially purified big and small PTTH did not activate Aedes atropalpus ovaries to synthesize ecdysone in vitro , nor did they cause ovarian maturation in vivo . Thus, it appears that the structural differences between PTTH and EDNH are sufficient enough to prevent functional cross-reactivity. The apparent discrepancy in the results obtained with the crude and partially purified EDNH and PTTHs raises questions about the reliability of bioassays for screening the presence and cross-reactivity of peptide neurohormones in crude extracts.

Control of Insects by Sexual Sterilization

The control of insect populations by restricting their birth rate offers several advantages over methods based on increasing the death rate. The sterile-male technique scored practical success in the control of the screwworm, Cochliomyia hominivorax (Coquerel), but more general applications of the sterility procedure may be expected in conjunction with the development of integrated procedures for pest insect management.

New aspects of organophosphorus pesticides. VI. Organophosphorus insect chemosterilants.

Sexual sterilization of insects, and for that matter of any sexually reproducing organisms, is one of the most promising approaches to a preventive control and management of populations (Knipling 1959 and 1966). Since the reproductive potential of a population decreases when the proportion of its sterile members increases, any process that will increase the ratio between the sterile and fertile organisms will reduce the population increment. Ultimately, when the ratio becomes very large, the population will cease to be self-sustaining and will die out.