Genetic sexing for a mosquito sterile-male release

Two strains of Anopheles culicifacies have been synthesized in which the dieldrin resistance locus on chromosome 3 has been translocated to the Y chromosome. Both strains appear sufficiently stable for the preferential recovery of males for mass production of mosquitoes for field releases.

Biological control of the snail intermediate hosts of human Schistosoma spp.: a review of its present status and future prospects

The biological control of freshwater snail hosts of schistosome parasites has attracted much attention in recent years, but the efficiency of such bio-control agents has rarely been tested outside laboratory conditions. The present paper attempts to summarize the present status of biological control of snails intermediate hosts, to indicate some major gaps in our knowledge of this subject, especially those of a practical kind and, not least, to identify studies and activities which apparently merit priority for further sponsorship and support.

The use of dragonfly nymphs in the control of Aedes aegypti

The predatory rates of the dragonfly nymphs on Aedes aegypti were studied in the laboratory and under field conditons. Labellulid nymphs were found to predate on Ae. aegypti larvae and pupae readily. The rate of consumption was found to be 133 +/- 21 all stages of larvae per medium size nymph per 24 hours. In container habitats complete elimination of all larvae and pupae were achieved between day 4 and 9 depending on density of aquatic stages. The dragonfly nymphs as predators could be used in biological control of Aedes mosquitoes.

Laboratory infection of blackflies (Simuliidae) and midges (Chironomidae) by the mosquito mermithid, Romanomermis culicivorax

Penetrating infective juveniles of Romanomermis culicivorax usually killed first-stage larvae of Chironomus maturus Johann., Chironomus sp., Simulium damnosum Theo., and S. venustum Say. Nematodes were melanized and died after they entered fourth stage larvae of 2 chironomid species, but no host reaction was evident after entry into fourth-stage blackfly larvae. In contrast, the nematodes initiated development in the latter hosts, which died before the nematodes completed their development.

Toxicity of parasporal crystals of Bacillus thuringiensis to the Indian meal moth, Plodia interpunctella

Toxicity of Bacillus thuringiensis parasporal crystals to the Indian meal moth, Plodia interpunctella, is described. The numbers of insects killed were in relation to crystal dry weight. Mortality was determined by comparing adult emergence in diets treated with crystals to emergence in untreated diets. There was only a 30% survival at an application of 0.414 microgram/cm2, and the mean 50% lethal concentration value was found to be 0.299 microgram/cm2. The use of emergence data has provided a reliable and reproducible bioassay for comparing relative toxicities of crystals, spores, and other cellular components to this economically important insect.

A review of helisoma duryi in biological control

Biological control of schistosomiasis by means of introduction of the north American planorbid snail, Helisoma duryi, as a competitor of the intermediate host snails has been proposed. The systematics of the genus Helisoma and the geographic distribution of the different species is described. Papers dealing with laboratory experiments or field observations on the competition between H. duryi and different intermediate host snails have been reviewed. The status of H. duryi as intermediate host of trematodes has been evaluated by searching the literature for all the trematode species that are recorded from the genus Helisoma. The list does not include trematodes of medical or veterinary importance and despite many attempts it has not been possible to infect H. duryi with Schistosoma mansoni and S. haematobium. Finally this paper makes a few comments on the experiments that should be performed in the laboratory, under semifield conditions and and field conditions before H. duryi should be actively dispersed in Africa. The aspects to be considered include the nature of the competitive interactions, the relation between H. duryi and different medical and veterinary important trematodes and the effect of H. duryi on the biotope.

[Control of vectors of human onchocerciasis in intertropical Africa (author's transl)]

First the authors make short comments on the two Simuliidae species complexes vectors of African human onchocerciasis (S. damnosum s.l. and S. neavei), as well as on the reasons for renewed interest in the control of those vectors; then they review the various possible methods of control (ecological, biological, genetical and chemical methods) and they finally detail the methodology of anti-S. damnosum chemical larviciding which is the only kind or large scale control presently used against onchocerciasis vectors. The experiences and results of the previous campaigns resulted in the large Onchocerciasis Control Programme in Volta River Basin (O.C.P.) which now appears as a model for present and future control measures against S. damnosum. This Programme is briefly described, together with its results, problems (reinvasion) and orientations. As a conclusion, the excellent level of control of the vectors and onchocerciasis transmission which is obtained is emphasized and it is expected that in the future new large scale campaigns using O.C.P. experience may be initiated.

[Genetic means for control of insect vectors of human diseases (author's transl)]

We divide genetical control methods in two major groups:--mechanisms operating between different species and an example is the attempt of control of A. gambiae in West Africa,--mechanisms operating in a single species with: gamma rays and chemical treatment for sterilisation, cytoplasmic incompatibility (ex.: C. pipiens). Genetical control also suppose the knowledge of biology and ecology of the target insect. This paper does not want to be an exhaustive review of this problem. Its only ambition is to try and expose the possible applications of genetics in the control of vectors.

[Biological control of vectors of human and tropical diseases. Present means and prospects (author's transl)]

Biological control is "direct or indirect use of natural enemies of the injurious species to increase its mortality" (W.H.O., 1963). The more and more frequent apparition of resistant insects populations, the fears as regards the environment, the increase cost of hydrocarbur products and also some technic and operational difficulties to stop transmission by the use of only insecticide pulvérisation, impose this process. Nevertheless, practic use of natural enemies of vectors is yet unusual in spite of important research. (Identification problems, dynamic of species, insufficiency of ethology knowledge particulary of the host specificity, difficulties of application on the vectors which are the most usually widely scattered). For control of insects of medical importance (mosquitoes, black flies, tse-tse flies) it has been used either pathogen agents such as virus bacteria, microsporida or parasit agents such as fungi, mermithid nematods or at last, predators, essentially larvivorus fish. Actually, no biological agent is able to take the place of chemical and physical "traditional" means. In case of mosquito control which is more advanced, the only biological mean which is operational is the use of larvivorus fish and specially Gambusia.

Schistosoma mansoni: identification of chemicals that attract or trap its snail vector, Biomphalaria glabrata

A new bioassay for chemical attractants of aquatic snails demonstrated that Biomphalaria glabrata could be attracted to or trapped in the vicinity of homogenates of lettuce. Fractionation of homogenates revealed the amino acids glutamate and proline and the primary attractants. Attraction was specific for the L form of glutamate. Proline appeared to stimulate reproductive activity. Glutathione, gamma-aminobutyric acid, and a number of other compounds had no effect. Extracts of lyophilized snail tissue also attracted other snails and may thus contain pheromones. These results permit formulation and testing of controlled-release attractants designed to overcome the repellant effects of slow-release molluscicides, as well as the design of stimulants to be used with no-release poisons.

Current problems in the control of mosquitoes

Since the incidence of mosquito-borne disease was drastically reduced by the use of DDT in the 1950s, the problem has again worsened and no single method of eradication seems likely to achieve lasting success. It now seems that the best hope lies in the combination of various methods of chemical control and perhaps genetic control to rid the Third World of its most important disease sector.

Genetic method for the preferential elimination of females of anopheles albimanus

Recent field experiments demonstrated the possibility of using the sterile male method for the control of Anopheles albimanus Wiedemann, the most important vector of human malaria in Central America. Until now there was no practical method for excluding females from the releases of sterile males. A genetic method was developed for the preferential elimination of females during any of the four life stages. This genetic sexing system utilizes propoxur (o-isopropoxyphenyl methyl-carbamate) susceptibility as a recessive conditional lethal a T(Y:2R) translocation, and an In(2R)inversion. The propoxur resistance allele (dominant) was linked to the Y chromosome via a radiation-induced translocation, and genetic recombination was suppressed by inversions. In one of the strains produced, 99.7 percent of the females are eliminated when treated with propoxur, without male loss.

Characteristics of successful natural enemies in models of biological control of insect pests

Biological control of insect pests is characterised by a persistent, strong reduction in the pest population following the introduction of a natural enemy. Analysis of mathematical models suggests that differential exploitation of patches of the pest in a spatially heterogeneous environment provides the most likely mechanism to account for known successes.

North American egg parasite successfully controls a different host genus in South America

Telenomus alsophilae, a parasite of the eggs of the geometrid Alsophila pometaria in North America, was introduced into Columbia, South America, for the biological control of a pest host in another genus, Oxydia trychiata. Successful results were obtained with this unorthodox procedure to control a forest insect.

A field trial of suppression of Aedes aegypti population by releasing sterile males into a domestic population

After release of an average of 1260 sterile male each day for a period of sixty two days, the average fertility of Aedas aegypti population remained above 50% in Ererwani village. It is concluded that the irradiated sterile males may not be suitable as a control measure, despite the fact that irradiation was carried out in nitrogen atmosphere.

Action of Bacillus thuringiensis preparation against larch bud moth, Zeiraphera diniana (Gn.), enhanced by beta-exotoxin and DDT

Addition of either DDT or the supernatant of a centrifuged liquid culture of Bacillus thuringiensis, serotype H1, containing beta-exotoxin, enhanced the action of the bacterial preparation Thuricide 90 T against larvae of the larch pest Zeiraphera diniana, increasing mortality from 53% to more than 80%. Since DDT alone produced 57% mortality, its combined action corresponds to independent action. The preparation of beta-exotoxin, on the other hand, had only little effect alone but synergized the action of the bacterial preparation considerably.

Sporeless mutants of Bacillus thuringiensis. II. mutants derived from var. thuringiensis and var. sotto

Three sporeless mutants of Bacillus thuringiensis, 2 derived from var. thuringiensis and 1 from var. sotto were selected after mutagenic treatment. They were completely lacking in ability to form spores, yet maintained intact insecticidal activity.

[Some problems in the study of mermitids for the purpose of the biological control of midges]

The method of "flooding" with mermitids, which was successfully used against mosquitoes, is unreal for biological control of black flies because of difficulties and unprofitableness of their laboratory maintenance and reproduction. A more probable way of solving the problem is the untroduction of effective forms of parasites. In perspective the cultivation of the adipose tissue of the host and biochemical overcoming of its protective reactions are necessary.

[Predation of Lymnaea (Galba) truncatula Müller by Zonitoides nitidus Müller (Mollusca Gastropoda Pulmonata) (author's transl)]

Zonitoides nitidus is omnivorous with carnivorous tendancies: the presence of food coming from snails is required for growth of this predator. This snail is not selective for the choice of its preys. Zonitoides cannot be taken for an absolute predator for all growing periods of Lymnaea truncatula: eggs and large snails are not eaten. This species can be cannibal.

Development of morphogenetic agents in insect control

Chemicals which interfere with the growth and development of insects (morphogenetic agents) have been receiving major attention as potential means of selective insect control. Major advances in this field resulted from the identification of Juvenile Hormones -1, -2, and -3, and the discovery that various terpenoid and sesquiterpenoid derivatives were more potent morphogenetic agents than the three known Juvenile Hormones. Several highly active compounds have emerged from these research programs. Their field performance, problems, and prospects in selective insect control are considered here.

Entomopathogens as insecticides

Entomopathogens, diseases of insects, are suggested as a possible new generation of safe, selective insecticides. Over a thousand pathogens have been isolated from insects. Many of these, associated with major insect pests, are potential candidates for development into microbial insecticides. Phases in the development of a microbial insecticide are discussed as well as factors (production, safety, efficacy, registration, non-technical) which may influence this development.

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.

Manipulating sex pheromones for insect suppression

A review is given of different methods of using sex pheromones in pest control programs. Survey and monitoring traps have been used extensively for determining the presence and abundance of pest populations are commercially available. Pheromone trapping studies for insect suppression have shown success with some species and could be a useful tool in some situations. The technique of attracting insects to the host for insect removal or exposure to insecticide has also proved to be useful in some programs. Mating disruption studies using widely-separated pheromone evaporators or encapsulated pheromone distributed throughout an area have indicated a great potential for this technique in insect suppression programs.

Control Methods for Snail-Borne Zoonoses

All trematodes which cause infections and diseases in humans (zoonoses) require snails for their first intermediate host. Some have additional intermediate hosts such as crustaceans, fishes and frogs. In this paper I have discussed the use of various procedures for controlling snail populations thereby reducing the population of trematodes whose cercariae penetrate the skin of man, or which are acquired by eating raw aquatic vegetation such as watercress, or which cause pathology in fish. Biological, chemical, and physical snail control techniques are discussed. The most promising molluscucides are copper compounds, Bayluscide, biocidal rubber and molluscicidal bait.