Helisoma duryi: its present range of distribution and implications with schistosomiasis snails in Egypt

The range of distribution of Helisoma duryi, a potential competitor to schistosomiasis snail vectors in Egypt, was determined in the south of Nile Delta. Results show that H. duryi was found in the River Nile, Geziret El Kerateyeen banks, Damietta and Rosetta Branches, Tawfiky and Menoufy Canals and their branches and Bassoussiya, Bahadiya and Sheshaa canals and their branches. Helisoma was found in all categories of canals and drains co-existing in various degrees with other snail species including schistosomiasis vectors (Bulinus truncatus and Biomphalaria alexandrina). The population density of H. duryi and associated B. truncatus, B. alexandrina and Physa acuta were studied for one year in three channels. Statistical analysis of results show that Helisoma has a significantly negative correlation with schistosomiasis vectors in these channels. Helisoma population showed a major peak in the warmest months of the year (July-August) thus showing recovery in population after "Winter Closure" later than Bulinus, Biomphalaria and Physa. Helisoma proved to be free of any natural trematode infection.

Factors affecting the acquisition of Plagiorchis noblei (Trematoda: Plagiorchiidae) cercariae by black fly (Diptera: Simuliidae) larvae and the effect of metacercariae on host survival

Larvae of 4 species of black flies, Prosimulium mixtum, Simulium vittatum, S. decorum and Stegopterna mutata, were exposed in the laboratory to cercariae of the digenean Plagiorchis noblei in flowing water. Prevalence and intensity of infection of all species varied directly with exposure intensity and decreased with increasing water velocity; prevalence increased with larval size. Infection levels for P. mixtum were higher than for the 3 other species. Mortality among infected larvae of all species was 3 times that of controls. Exposure of black fly larvae to P. noblei cercariae may adversely affect their survival.

Reducing the overwintering ability of Aedes albopictus by male release

Eggs of temperate Aedes albopictus populations are cold hardy and can diapause, but tropical populations are not cold hardy and cannot diapause. Heterozygotes possess intermediate diapause and cold hardiness. Males of a tropical strain from Malaysia with a distinctive genetic marker were released into an existing temperate population in East St. Louis, Illinois. Subsequent egg samples from the release site had genetic marker frequency of up to 24%. Reduced cold hardiness and decreased diapause incidence were also observed in the release site population. No such changes occurred at a nearby control site. The rank order of overwintering survival of eggs at the release site was: Aedes triseriatus > temperate Ae. albopictus > hybrid temperate/tropical Ae. albopictus > tropical Ae. albopictus. Eggs collected from the release population the next summer showed total absence of the genetic marker; presumably carriers were removed by the winter.

[Campaign against Culex quinquefasciatus using Bacillus sphaericus: results of a pilot project in a large urban area of equatorial Africa]

Culex quinquefasciatus, which is sometimes the vector of Bancroft's filariasis, is a harmful mosquito, the immature stages of which live in collections of waste water resulting from human activity. Larval control, the most appropriate method, is at present carried out with chemical insecticides. But the toxicity of these compounds, together with phenomena of resistance, and the cost of substitute insecticides have turned research towards products of biological origin, and one of the most promising is a liquid concentrate of Bacillus sphaericus strain 2362. This was applied experimentally over an area of 200 hectares in a large city in the south of Cameroon, characterized by a short dry season during which mosquito density is at its highest. Spraying was carried out every three months for a year in a concentration of 10 g/m2 and its efficacy evaluated at the level of adult mosquitos through an indirect system of capture on human baits. The results of this study show, in essence, a reduction by 52.7% in the number of females captured in the overall study area treated, and that the impact of treatment is greater during the period of high mosquito density (55.1%) than in the low density period (40.7%). After analysis of the full set of results, the authors conclude that the pattern of rainfall, the conditions in which the insecticide is applied and reinvasions of mosquitos from untreated areas were the principal factors limiting the efficacy of this control campaign.(ABSTRACT TRUNCATED AT 250 WORDS)

Insecticidal properties of genetically engineered baculoviruses expressing an insect juvenile hormone esterase gene

Exploring the possibility of enhancing the properties of baculoviruses as biological control agents of insect pests, we tested the effect of expressing an insect gene (jhe) encoding juvenile hormone esterase. Juvenile hormone esterase inactivates juvenile hormone, which regulates the outcome of an insect molt. A cDNA encoding the juvenile hormone esterase of Heliothis virescens was inserted into the genome of Autographa californica nuclear polyhedrosis virus such that the gene was expressed under the control of a strong, modified viral promoter. This virus, however, naturally encodes an ecdysteroid UDP-glucosyltransferase which inactivates ecdysone, the hormone which initiates molting. Since ecdysteroid UDP-glucosyltransferase could mask the effects of jhe expression by blocking molting entirely, jhe-expressing viruses in which the ecdysteroid UDP-glucosyltransferase gene was deleted or disrupted were constructed. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of proteins from infected cells revealed several intracellular proteins and two major secreted proteins which reacted with antibodies to authentic juvenile hormone esterase. Western blot analysis coupled with tunicamycin treatment indicated that differential glycosylation was responsible for the multiple products. Hemolymph of recombinant virus-infected fourth-instar Trichoplusia ni larvae contained levels of juvenile hormone esterase activity 40-fold higher than maximal levels found in uninfected larvae. However, little or no difference in developmental characteristics, weight gain, or time of mortality was observed between insects infected with the jhe-expressing viruses and control viruses.

New plasmid vector and host system for genetic engineering in Bacillus sphaericus

A new plasmid, pNQ116, was constructed in Bacillus sphaericus by cloning a promoter fragment from B. sphaericus Ts-1 into pNQ112. The plasmid (CmrKmr, 5.23 kb) contains a restriction endonuclease polylinker used for cloning foreign genes, and its cat-86 gene is expressed at high levels from the Ts-1 promoter. This plasmid vector has been transformed into B. sphaericus AS 1.270, AS 1.465, AS 1.469, and 2362, at frequencies of 10(2)-10(3) transformants per microgram of DNA, and is maintained stably under nonselective conditions in these host strains. The presence of pNQ116 in B. sphaericus 2362 does ot interfere with the mosquito larvicidal activity of the organism.

Population biology and biological control of nematodes

We studied the population biology of the nematophagous fungus Hirsutella rhossiliensis to understand its potential as a biological control agent. Because the fungus is an infectious and transmissible parasite, we framed our study within an epidemiological context. Field observations, theory, and experiments demonstrated that (i) parasitism of nematodes by H. rhossiliensis is dependent on nematode density, (ii) local populations of the fungus will go extinct unless supplied with some minimum number of nematodes (the host threshold density), and (iii) natural epidemics of this fungus in populations of nematodes develop slowly and only after long periods of high host density. Additional in-depth research on population biology is needed to explain other biological control systems and to guide future research. The most effective research will combine field observation, theory, and experimentation.

Synthesis and toxicity of full-length and truncated bacterial CryIVD mosquitocidal proteins expressed in lepidopteran cells using a baculovirus vector

Full-length (72K) and truncated (61K) CryIVD mosquitocidal proteins of Bacillus thuringiensis (Bt) were expressed in Spodoptera frugiperda cells and larvae of Trichoplusia ni using a baculovirus vector to investigate the role of CryIVD peptides in toxicity as well as to evaluate further the baculovirus/lepidopteran system for expressing Bt proteins. The cryIVD genes were inserted into the Autographa californica multinucleocapsid nuclear polyhedrosis virus (AcMNPV) under control of the polyhedrin promoter by recombination in S. frugiperda cells between a transfer vector carrying the Bt genes and vDA26Z, a recombinant AcMNPV carrying the Escherichia coli beta-galactosidase gene under control of the DA26 promoter. Recombinant AcMNPVs carrying the genes were detected as blue occlusion body-negative plaques in monolayers of S. frugiperda cells grown in the presence of X-Gal. Infection of S. frugiperda cells and T. ni larvae with plaque-purified recombinant virus, expressing either the full-length or truncated CryIVD protein, resulted in the synthesis of proteins of the expected size, as confirmed by immunoblot analyses, and their crystallization into cuboidal inclusions in the cytoplasm. Infected cells and purified inclusions from the virus (AcCryIVD) expressing the full-length protein were highly toxic to mosquito larvae, but similar preparations from the virus (AcCryIVD-C) expressing the truncated protein with a 9.6K deletion at the N terminus were non-toxic. Proteolysis with trypsin of CryIVD proteins produced by Bt and the recombinant AcMNPVs yielded peptides corresponding in size, showing that synthesis of mosquitocidal Bt proteins in lepidopteran cells occurred. The lack of toxicity of the truncated CryIVD protein, which like the toxic full-length protein yielded a 34K protein on proteolysis that has been implicated in toxicity, indicates that by itself this protein is non-toxic. These results demonstrate the utility of the baculovirus system for expression of mosquitocidal Bt proteins and for investigation of their mode of action.

Astronotus ocellatus (Cichlidae:Pisces) and Macropodus opercularis (Anabatidae:Pisces) as predators of immature Aedes fluviatilis (Diptera:Culicidae) and Biomphalaria glabrata (Mollusca:Planorbidae)

Two fish species, Astronotus ocellatus (Cichlidae) and Macropodus opercularis (Anabatidae) were tested for predacious behavior toward immature mosquitoes (Aedes fluviatilis, Diptera:Culicidae) and schistosomiasis snail hosts (Biomphalaria glabrata, Mollusca:Planorbidae), in the presence or absence of non-living food and in laboratory conditions. A. ocellatus, a species indigenous to Brazil, was a very efficient predator of both organisms (alpha = 0.05); M. opercularis, an exotic species, preyed well on immature mosquitoes, but small snails and snail egg-masses were ingested only irregularly. Both fish species seemed to prefer live to non-living food.

Toxicity of Bacillus sphaericus strain 2362 on Mansonia spp. larvae

The efficiency of Bacillus sphaericus strain 2362 (Vectolex) as larvicide against Mansonia spp. was studied. Bioassay studies showed that the toxicity of B. sphaericus on both age groups (I-II instar and III-IV instar) of Mansonia spp. larvae occurred within 24 hours. Probit analysis revealed that LC100 (one hundred per cent lethal concentration) for both age groups of M. boneae were higher than those of M. dives. Small scale field trials were done at Kreng Village, Cha-uat District, Nakhon Si Thammarat Province, one of the most serious filarial infected areas. It was indicated that 100% kill of Mansonia spp. larvae in the field occurred within 9 days after the larvicide application. When a dose of 5 times of LC100 value was used, 100% control was achieved up to about one month.

Laboratory evaluation of Bacillus thuringiensis H-14 against Aedes aegypti larvae in the northeast region of Thailand

Laboratory bioassays using a preparation of Bacillus thuringiensis H-14 (Bt.H-14), namely Skeetal were conducted to determine their effectiveness against late 3rd/early 4th instar larvae of Aedes aegypti. The larvae were collected from municipal areas in 7 provinces, namely Burirum, Roi-Et, Khon Kaen, Ubol Ratchatani, Nakorn Phanom, Surin and Nakorn Ratchasima, in the Northeast of Thailand. It was found that for Skeetal, LC50 ranged from 128 to 151 nl/l (average 143) and LC90 ranged from 254 to 289 nl/l (average 275). The mortality rate of Ae. aegypti larvae in the 7 provinces did not differ significantly (p greater than 0.05) at a concentration of 300 nl/l. The result of the bioassays show that the preparation of Bt.H-14 is very effective against Ae. aegypti larvae in Northeast of Thailand and the mosquito larvae in the various areas were nearly equal in susceptibility to Bt.H-14.

The advantages of mosquito biocontrol by stocking edible fish in rice paddies

Edible fish stocked in rice fields at a density of 600-800 fry per mu (1 mu = 1/15 hectare) for 150-170 days may act as an effective mosquito biocontrol agent. Common carp (Cyprinus carpio), grass carp Ctenopharyngodon idella) and Tilopia spp. killed late stage larvae and pupae of Anopheles sinensis and Culex tritaeniorrhyncus in laboratory and field trials. Stocking of fish in experimental rice fields decreased larval numbers significantly in comparison with control areas. Expansion of fish stocking in rice fields on a large scale over several years correlated with a marked decrease in malaria transmission. The addition of fish to the rice fields also resulted in increased yields. A ditch-ridge system of field arrangements is described for optimization of fish handling. Preliminary cost-benefit analysis indicates that this approach to mosquito control conveys considerable economic advantage and thus provides incentive to the community to participate in vector control programs. Farmers' experience in Guangxi over a number of years indicates that the use of edible fish for this purpose can be carried on a large, commercially viable scale.

Shade as a means of ecological control of Biomphalaria pfeifferi

Species of Biomphalaria are attracted to light and negatively affected by darkness. Artificial shading of a breeding-site eliminated a population of B. pfeifferi within six weeks. The site was recolonized by eight weeks after the shade was removed. The time taken for recolonization suggests that shade acts not only by affecting snail behaviour but also indirectly by removing the diatoms which are food for the snails. The use of natural shade for ecological control of some snail vectors of schistosomiasis deserves, at least, careful consideration.

Isolation and identification of Bacillus sphaericus strains pathogenic for mosquito larvae

Three selective media for the isolation of Bacillus sphaericus have been compared. BATS medium and a formulation employing adenosine as the principal carbon source were the most effective for the recovery of spores of strain 1593. Anthranilic acid as the principal carbon source was less efficient. Eighty-four strains were isolated from mud samples using these media and were identified by computer. Identifications were confirmed for representative strains using DNA sequence homology. Most were B. sphaericus sensu stricto or members of an unnamed group. However, one strain (BSE 18) was identified as the DNA homology group IIB and this organism was found to be highly toxic toward larvae of Culex pipiens. Southern hybridization of BSE 18 DNA to a probe prepared from the cloned toxin gene from strain 1593 revealed that BSE 18 contained a typical gene for the 41.9-kDa toxin.

Role of Azolla in controlling mosquito breeding in Ghaziabad district villages (U.P.)

A survey was carried out during post-monsoon period (1988-89) in villages of Dhaulana Primary Health Centre, Distt. Ghaziabad (U.P.) to evaluate the utility of Azolla pinnata for the control of mosquito breeding in different habitats. Results of the survey revealed that pools, ponds, wells, rice fields and drains were infested with Azolla. Infestation rate and intensity of infestation varied from habitat to habitat. Maximum infestation (36.5%) was observed in pools and minimum (3.7%) in rice fields. Anopheline breeding was almost completely suppressed (0-1.6/dip) in pools, wells and ponds completely covered with Azolla. The breeding of Culex spp. was not completely inhibited in any habitat, though reduction in immature density was observed in comparison to control. The role of Azolla in controlling mosquito breeding and its association with the blue green algae which fixes nitrogen is discussed.

Fermentation of a Malaysian Bacillus thuringiensis serotype H-14 isolate, a mosquito microbial control agent utilizing local wastes

A screening program searching for indigenous microbial control agents of mosquitos in Malaysia is initiated since 1987 and to date at least 20 isolates of mosquitocidal Bacillus thuringiensis serotypes have been obtained. Preliminary field evaluation of several isolates indicated that they are highly effective in the control of medically important mosquito species. For operational purposes, there is an urgent need to produce this agent utilizing cheap and locally available wastes through fermentation biotechnology. Fermentation studies in shake-flasks containing standard nutrient broth and soya bean waste, respectively, indicate that it takes about 37 hours for a Malaysian isolate of B. thuringiensis serotype H-14 to mature. In the grated coconut waste, fishmeal and rice bran, the bacteria took 28 hours, 26 hours and 126 hours respectively to mature. The endotoxin was harvested from the standard nutrient broth at 55 hours and at 50 hours from soybean, grated coconut waste and fishmeal. The endotoxin could only be harvested 150 hours after inoculation from rice bran medium. However, no bacterial growth was detected in palm oil effluent. In terms of endotoxin and biomass production, fishmeal appears to be a suitable medium. Variations in the pH of the fermenting media were also noted.

Insect resistant cotton plants

We have expressed truncated forms of the insect control protein genes of Bacillus thuringiensis var. kurstaki HD-1(cryIA(b) and HD-73 (cryIA(c) in cotton plants at levels that provided effective control of agronomically important lepidopteran insect pests. Total protection from insect damage of leaf tissue from these plants was observed in laboratory assays when tested with two lepidopteran insects, an insect relatively sensitive to the B.t.k. insect control protein, Trichoplusia ni (cabbage looper) and an insect that is 100 fold less sensitive, Spodoptera exigua (beet armyworm). Whole plants, assayed under conditions of high insect pressure with Heliothis zea (cotton bollworm) showed effective square and boll protection. Immunological analysis of the cotton plants indicated that the insect control protein represented 0.05% to 0.1% of the total soluble protein. We view these results as a major step towards the agricultural use of genetically modified plants with insect resistance in this valuable, high acreage crop.

A host-host-pathogen model with free-living infective stages, applicable to microbial pest control

A model has been investigated of the dynamics of the interaction between two hosts which are both attacked by a common pathogen, where the pathogen has free-living infective stages the population size of which must itself be modelled explicitly, and where the host species do not interact with one another except through their shared pathogen. If either host interacted with the pathogen alone, three broad classes of dynamics would be possible: host regulation, pathogen persistence and pathogen extinction. Here, all possible types of combinations of hosts are examined: regulation-regulation (both hosts would be regulated if they interacted with the pathogen alone), regulation-persistence, regulation-extinction, persistence-persistence persistence-extinction and extinction-extinction. A wide range of dynamics is generated, including a number of patterns quite unlike those found in the one-host pathogen case (e.g. persistence in one host, elimination of the other host) and behaviour contingent on initial densities in the system. For clarity and pertinence, attention is focused on the case where one host is a pest, the pathogen is a potential microbial control agent, and the other host is a non-target species which it is undesirable to harm. The model suggests, broadly, that non-targets are unlikely to be seriously threatened in such cases, and also that non-targets, far from undermining pest control, are quite likely to contribute to its efficacy.

The New World screw-worm fly in north Africa

The course of the North African outbreak of New World screw-worm myiasis (Cochliomyia hominivorax) since its discovery in 1988 is described. Chemical and biological control measures are reviewed, including the current progress of the 'sterile male' (SIT) eradication programme.

Control of Culex quinquefasciatus in Myanmar (Burma) and India: 1960-1990

During the past 30 years three major programmes of research have been carried out in Myanmar (Burma) and India on the ecology and control of Culex quinquefasciatus. To differing degrees the programmes have employed environmental, chemical, biological and genetic control strategies, but none has been an unqualified success. Results have been good when well-trained staff with substantial resources were employed, but much poorer when less-well-equipped general health workers took over the programmes. Overall, it would seem most cost-effective for health workers to concentrate their efforts on the elimination of the limited number of larval habitat categories which commonly contribute a large fraction of the adult population. Insecticides and biological control agents should serve as supplements, not as alternatives, to environmental management. Genetic control strategies have currently no place in C. quinquefasciatus programmes.

The Tsetse Research Laboratory

The Tsetse Research Laboratory in Bristol was opened in December 1962, with the initial objective of developing techniques for rearing tsetse flies on a large scale outside Africa. Its work has, however, extended greatly since then. This article highlights the research undertaken at the Laboratory, not only on the breeding of tsetse flies but also on various aspects of their biology and control.

[The biological control of Fossaria cubensis, the intermediate host of Fasciola hepatica, in 2 localities with different control agents]

A control was carried out on Fossaria cubensis, intermediate host of Fasciola hepatica, in two localities, by means of 2 different control agents. In one of them Helisoma duryi was used due to its ecological advantages as compared with the intermediate host (higher growth rhythm and lower generational time), and in the other Tarebia granifera was used, which has biological and ecological advantages upon most mollusks (ovoviviparous, parthenogenetic, longer life cycle and higher growth rhythm). In both localities an effective control was seen with the remarkable decrease of the host density after the introduction of the competitive agent.

Isolation of indigenous larvicidal microbial control agents of mosquitos: the Malaysian experience

A nationwide screening program searching for microbial control agents of mosquitos was initiated in Malaysia in 1986. A total of 725 samples were collected and 2,394 bacterial colonies were isolated and screened for larvicidal activity. From such screening, 20 Bacillus thuringiensis, 6 B. sphaericus, 1 Clostridium bifermentans and 2 Pseudomonas pseudomallei larvicidal isolates were obtained. Of these, a new B. thuringiensis named as subspecies malaysianensis was found, while the C. bifermentans was also a new anaerobe individualized as serovar malaysia. It was concluded that this screening program was highly successful.

The prehatch period and larval survival of Boophilus decoloratus (Koch, 1844) (Acarina: Ixodidae) under natural conditions in the Transvaal, South Africa

Studies were made on the duration of the prehatch period of Boophilus decoloratus and on the subsequent survival and viability of larvae under natural conditions. The length of the prehatch and larval survival periods was found to be inversely dependent on increased temperature. A high initial temperature at the time of female drop decreased the prehatch period further, resulting in synchronous hatching of eggs laid at different times. Oviposition occurred but no eggs hatched during mid-winter months with mean temperatures below 10 degrees C. Eggs laid after mid-winter hatched because of the higher temperatures during subsequent months. Diapause occurs at the egg stage in areas with mean winter temperatures below 10 degrees C. Larvae survived for 10-35 weeks during periods of high and low seasonal temperatures respectively. Larval viability decreased concomitantly with larval survival. The results suggest that pasture spelling alone would be impractical as a control measure for this tick species.

[Control of Simuliidae with an emulsifiable concentrate of Bacillus thuringiensis]

The effects of the three flowable concentrate formulations of Bacillus thuringiensis var. israelensis (H-14): Teknar (Zoecon, Sandoz Inc.), Vectobac (Abbott Labs.), and Bactimos (Biochem, Solvay Labs.) against Simulium pertinax were evaluated in 24 streams in the North Littoral Zone of São Paulo State, Brazil. There was no significant difference in effective carry (80% or more mortality) among the formulations when applied at the rate of 10 mg/liter for one minute. There was a strong correlation between stream discharge and effective carry of the formulations, except in the case of Teknar, possibly due to the influence of the physical characteristics of the streams where evaluation was conducted.

[Trials to introduce Romanomermis culicivorax (Nematoda: Mermithidae), mosquito larva parasites, into the reservoirs of Voronezh and Moscow Province]

Possibility of using Romanomermis culicivorax for mosquito control in the town of Voronezh and Moscow Province has been assessed. The infection rate of mosquito larvae didn't exceed 26% when preparasitic juveniles were released into water bodies at a ratio of 1-3 thousand per 1 m2 and temperature 18-25 degrees C. There were no evidences of mermithid settlement and hibernation in the water bodies of Voronezh. High efficacy of using R. culicivorax in mosquito larvae control can only be expected in these regions under hot summer conditions.

A genetic sexing system to improve the sterile insect technique against the Mediterranean fruit fly

The autosomal recessive allele v wing (v) in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), produces flies that when reared at 30 degrees C have stubby wings. The mutant was used to construct a translocation-based genetic sexing system in an attempt to improve the efficiency and effectiveness of the sterile insect release method for field control.

[An evaluation of the possibility of using Romanomermis iyengari Welch mermithids for mosquito control in Uzbekistan]

Mermithid nematodes Romanomermis iyengari were released into 13 natural water bodies of various types at a ratio of 300-8000 invasive preparasites per 1 m2 of water surface in Tashkent region of Uzbekistan. Infected larvae of Anopheles martinius, An. hyrcanus, Culex modestus were found in 6 water bodies with low content of dissolved salts (Ca2+ + + Mg2(+)-3.8-6.7 mg equivalent/l, Cl(-)-38.3-160.2 mg/l). The infection rates of mosquito larvae were 9-67%. In laboratory tests mermithids infected up to 100% of mosquito larvae of the above-mentioned species as well as An. superpictus and Cx. pipiens from natural populations. Aedes caspius were resistant to mermithid infection. It is expected that in Tashkent region these mermithids can be used only in water bodies with low salt content.

Long residual activity of Bacillus sphaericus 1593 against Culex quinquefasciatus larvae in artificial pools

The microbial larvicide, Bacillus sphaericus 1593, was evaluated against Culex quinquefasciatus larvae in artificial pools at Huay Kwang area in Bangkok between March and October 1985. This study was aimed at determining the residual activity of B. sphaericus 1593 in waste water under field conditions. The larvicidal activity of B. sphaericus 1593 was found to persist for at least 5 months in artificial pools containing waste water. The populations of B. sphaericus 1593 in the test water fluctuated, decreasing by approximately 4.25 and 3.47 log10 colony forming unit (cfu)/ml from the original concentrations in 60 and 80 days after application and then increasing approximately 2.92 and 2.77 log10 cfu/ml in 92 and 72 days for pools No. 1 and No. 2, respectively. This evidence indicates that B. sphaericus 1593 can recycle in such conditions.

[Beetles as biological agents in fly control]

309 beetles of 11 species were collected in Apsheron and other regions of Azerbaijan on sites polluted by animal and human feces to study the feasibility of using them as biological agents for flies' control. Two beetle species--S. planus and B. lethifers pterotapha belonging to the Carabidae and Tenebrionidae families--turned out to be predators which could destroy the larva of L. sericata flies under experimental conditions.

Models to assess the potential of Capillaria hepatica to control population outbreaks of house mice

Population outbreaks of house mice (Mus domesticus) occur periodically in the wheatlands of southeastern Australia. This paper uses mathematical models to assist in the evaluation of the potential of a nematode, Capillaria hepatica, as a biological control agent to reduce the severity of these 'plagues'. C. hepatica is unique amongst helminths of mammals in that its eggs are released only upon the death of an infected host. The major goal of the modelling in this paper is to determine the impact of this feature on the population dynamics of the host-parasite interaction. Simple differential equation models are used to examine the general properties of the system and determine which population parameters are most crucial to the outcome of the interaction. These models are supplemented by age-structured models which investigate the initial behaviour of the system after introduction of the parasite. The necessity of host death for transmission is a strongly destabilizing factor, suggesting that C. hepatica cannot regulate most populations stably in the absence of strong resource limitation, although it has the potential to depress mouse populations below infection-free levels. Although C. hepatica influences mouse fecundity at lower burdens than it affects mortality, the age-structured models show that parasite-induced host death cannot be neglected. Because transmission requires host death, the parasite life-cycle operates on a time-scale similar to that of the hosts, and introduction of the parasite as early as possible in the development period of an outbreak will therefore be necessary to achieve substantial reductions in plague intensity.

Larvicidal properties of water bug Diplonychus indicus Venkatesan & Rao and its use in mosquito control

Males, females and egg carrying males of water bug D. indicus were collected at different sites from Chetpet pond, Madras, India. The bugs showed differences in their predatory efficiencies in relation to density, size and type of prey. The bug showed a typical predatory response in relation to hunger level.

Nematophagous fungi: strategies for nematode exploitation and for survival

The nematode-nematophagous fungus system offers excellent models for studies of interaction mechanisms between two groups of organism. Sufficient laboratory and field data are now available from studies at the physiological, biochemical, molecular and/or ecological levels to present a unified view of these diverse fungi, their survival strategies and their potential as regulators of nematode populations.

[Malaria in the Republic of Djibouti. Strategy for control using a biological antilarval campaign: indigenous larvivorous fishes (Aphanius dispar) and bacterial toxins]

The authors take stock of the present situation of malaria in the Republic of Djibouti which, after several decades of silence, seems to have been reintroduced at the beginning of the seventies. Actually it is hypo-endemic malaria with Plasmodium falciparum of which the only vector seems to be Anopheles arabiensis, gambiae complex. The specificity of the larvae nests allows a control strategy based on the only treatment of larvae sites by biological control: larvivorous fishes (Aphanius Dispar) and in addition the pin-point use of bacterial toxins as a complementary measure. The first results obtained in the rural zones around the capital are encouraging and permit to envisage the extensions of such a strategy to the whole of the territory of the Republic.