The Romanomermis iyengari parasite for Anopheles pseudopunctipennis suppression in natural habitats in Oaxaca State, Mexico.

In September and November 1996 Romanomermis iyengari Welch, a parasite of larval mosquitoes, was released in 44 natural larval habitat sites of Anopheles pseudopunctipennis Theobald in an attempt to reduce the larval populations of this important malaria vector. The selected treatment sites ranged in size from 5 to 500 m2. The study was carried out in Pochutla District of Oaxaca State, on the Pacific coast of Mexico. Chemical pesticides to reduce vector populations have been the principal tool in malaria suppression campaigns. However, the excessive use of these chemicals has created pesticide resistance and other serious collateral problems. Therefore, a biological control project using agents that are pathogens of Anopheles larvae was initiated in 1996. The principal objective was to establish mass rearing capacities for R. iyengari. Detailed methodology for rearing and introducing these nematodes into mosquito larval habitats was established at the National Polytechnic Institute of Oaxaca State. Before application of the parasites to larval habitats, site characteristics were determined, including size, depth, aquatic vegetation, salinity, pH, conductivity, temperature, and pretreatment larval density. With a compressed air sprayer, infective mermithid parasites were released at rates of either 2,000 or 3,000/m2, and the parasites produced high levels of infection. Anopheles populations were sampled 72 h posttreatment, and the larvae obtained were taken to the laboratory and examined through microscopic dissection to determine infection levels and mean parasitism. Nematode parasitism ranged from 85 to 100% at all the treatment sites, even though no previous information concerning field parasitism of An. pseudopunctipennis by R. iyengari has been reported. In addition, a significant reduction of mosquito larval density at the treatment sites was found five days after the nematode application. Levels of parasitism were indicative of the number of mosquito larvae killed by the treatment since infected larvae never progressed to the pupal stage. Results from sampling nine of the sites 2 months after the initial application of nematodes indicated that a high number of mosquito larvae were infected by parasites that had emerged from eggs previously deposited in the stratum. This work suggests the potential of this mermithid to reduce An. pseudopunctipennis populations in Oaxaca State.

Role of adrenal androgens in prostate regression in rats treated with an antiandrogen and an LHRH agonist.

Histrelin, a potent luteinizing hormone releasing hormone (LHRH) agonist, and flutamide, an antiandrogen, were administered to intact and adrenalectomized rats to determine the role of adrenal androgens in the additive effects of the two drugs on prostate regression. Each compound, given separately, was effective in decreasing prostate weights in intact rats. When given together, additive effects were demonstrated by even greater atrophy of the prostates. It has previously been proposed that this additive effect may be primarily attributed to the ability of the antiandrogen to block the action of adrenal androgens. However, in adrenalectomized rats, the combination of histrelin and flutamide still produced a greater reduction in prostate weights than did either drug alone, indicating that the role of adrenal androgens in this effect is negligible. This experiment also was repeated with castrate, androgen-supplemented rats, and the additive effects previously described were not observed. In a final experiment, prostatic atrophy in castrate rats was not enhanced by either adrenalectomy or flutamide treatment. Thus, the additive effects of histrelin and flutamide appear to focus on testicular rather than adrenal androgens.