[Experimental study of larval efficiency of Gambusia affinis holbrooki (GIRARD, 1859) (fish-Poecilidae)]

Experimental study of efficiency of Gambusia affinis holbrooki (GIRARD, 1859) (Fish-Poecilidae). Gambusia affinis is a culiciphage fish which was introduced in Tunisia in 1929 to control mosquito larvae. In the present study, we confirm, under laboratory conditions, the good efficacy of Gambusia affinis against mosquito larvae. The consumption of larvae decreases with the evolution of larvae instars and increases, for the same instar, in relation with the fish size. In fact, the size of the prey is related to the predator's size: fish belonging to the length class [20-24 mm] prefer IIIrd instar, fish from class length [25-29 mm] prefer pupae and IVth instar. The trophic test shows that G. affinis has a clear preference for Culicidae larvae, except fish belonging to the 2 length classes [35-39 mm] and [40-44 mm] for which Culicidae and Ephemeroptera have similar preference. In addition, at high temperature (30 degrees C), Gambusia affinis has a higher efficiency.

Similarity in moth-fly specific larvicidal activity between two serologically unrelated Bacillus thuringiensis strains

Parasporal inclusions of a Bacillus thuringiensis isolate designated 92-KU-105-9 (H14/19) exhibited unusual larvicidal activity, specific for the moth-fly, Telmatoscopus albipunctatus (Diptera: Psychodidae), similar to that of a previously reported B. thuringiensis serovar leesis (H33) strain. The LC50 value of the purified inclusions was 4.92 micrograms ml-1 for the moth-fly larvae, while no mortality was shown in the mosquitoes Culex pipiens molestus and Anopheles stephensi, at protein concentrations up to 10 mg ml-1. Morphologically, the inclusion was a homogeneous globular body surrounded by an electron-dense, thick envelope. Multilamellar inner structure was evident between envelope membrane and inclusion matrix. SDS-PAGE revealed that the inclusions consist of five proteins with molecular masses of 72, 70, 68, 56 and 30 kDa. These proteins cross-reacted with the antibodies against inclusion proteins of the serovar leesis strain. High homologies existed in N-terminal amino acid sequences between the three major proteins (72, 70 and 68 kDa) and the two established protein classes, Cry4A and Cry10A.

Biological control of Haemonchus contortus infective larvae in ovine faeces by administering an oral suspension of Duddingtonia flagrans chlamydospores to sheep

A single oral dose of an aqueous suspension containing 11,350,000 chlamydospores of a Mexican isolate of Duddingtonia flagrans (FTHO-8) given to sheep, resulted in a maximum reduction of 88% (range 86.7-90.4%) of the population of Haemonchus contortus infective larvae in the faeces. The effect of this treatment continued for 4-5 days after administration of the suspension. The possible use of this treatment as a method of control of ovine haemonchosis is discussed.

Population dynamics of and larval trematode interactions with Lymnaea tomentosa and the potential for biological control of schistosome dermatitis in Bremner Bay, Lake Wanaka, New Zealand

Lymnaea tomentosa, the intermediate host of a schistosome which causes schistosome dermatitis in Lake Wanaka, was found to depths of 16 m. The snail recruits in January, lives for up to 21 months, is associated with all water plant species and is found in areas devoid of macroscopic plants. It is host to several trematode species. Avian schistosome infections appear in the spring when echinostome prevalence is low, and a decrease in schistosome prevalence may be correlated with an increase in echinostome prevalence during the summer. A multiple-kind lottery model analysis of parasite species richness implies that interspecific interactions may be occurring in the host snail during the months of December and January.

[The efficacy of Salmocumarín rodenticide in livestock-raising and urban sites]

The activity in burrows at four different sites was calculated, and it went from 80 to 98% during pretreatment. For the first time in our country, average values of days/deaths of synanthropic rodents in natural conditions were obtained, and the reached values were between 16.50 and 19.06 after applying the biorodenticide. In the statistical analysis, a significant difference was found in the set of objectives related with days/deaths averages (H = 8.60*; p < 0.05). Moreover, no significant differences were found in percentages of residual activity in burrows (G = 8,27; p < 0.05). Results obtained show that Salmocumarín biorodenticide is much more effective in places where great populations of this species of cosmopolitan rodents exist.

A method for studying the population dynamics of Candida oleophila on oranges in the grove, using a selective isolation medium and PCR technique

Populations of the biological control agent Candida oleophila on fruit in an orange grove were monitored by plating fruit washes and peel homogenates on a selective medium, followed by PCR analysis of DNA from yeast colonies resembling C. oleophila. The C. oleophila transformant ADGus-10 formed colonies on a selective medium that suppressed the development of 99% of the filamentous fungi and the indigenous yeasts, Aureobasium (a yeast-like fungus) and Rhodotorula. Only 6-8 indigenous yeasts/cm2 fruit surface gave rise to colonies that resembled C. oleophila on the selective medium. The identity of the C. oleophila transformant colonies was verified by PCR analysis of yeast DNA. The presence of a 599-bp band in the PCR product primed by beta-glucuronidase gene primers, confirmed the identity of C. oleophila transformant ADGus-10. Colony-forming units of C. oleophila were recovered efficiently from fortified washes of the fruit surface and from homogenates of wounds excised from fruit sprayed in the grove with C. oleophila.

[Importance of Tarebia granifera in the control of a population of Biomphalaria peregrina introduced in Cuba]

It was observed that the Tarebia granifera plays a significant role in the control of a Biomphalaria peregrina population introduced in a permanent water body. The densities of this planorbid, which had reached high levels, were notably reduced by two important events: an increase of the water level due to heavy rains, and the introduction of the competitor, whose effectiveness had been tested in a different habitat. Knowledge on the ecology and biology of the competitor and the host in permanent water bodies helped to elaborate the measures of control which led to the reduction of the host densities while those of the competitor increased.

Biophysical properties of the surface of desiccation-tolerant mutants and parental strain of the entomopathogenic nematode Heterorhabditis megidis (strain UK211)

Entomopathogenic nematodes (EPN) are useful biological control agents of insect pests. However, the infective juvenile (IJ) stage which is the only stage to occur outside the host is susceptible to environmental extremes such as desiccation. We have isolated desiccation-tolerant strains of the EPN Heterorhabditis megidis. In this paper we describe the surface properties of these desiccation-tolerant mutants. Heterorhabditid IJs retain the sheath of the previous larval stage. The mutant lines possess alterations in the surface properties of the sheath. Differences were observed in fluorescent lipid analogue insertion into the surface of the sheath. Furthermore, cationized ferritin-binding studies demonstrated that the mutant lines possessed an increase in net negative surface charge. Removal of the surface layer of the sheath resulted in the loss of the mutant phenotype and in a reduction in the desiccation tolerance of the parental strain. Therefore, the negatively charged 'surface coat' appears to play an important role in the desiccation tolerance of Heterorhabditis species.

Comparison of the trapping ability of Arthrobotrys robusta and Monacrosporium gephyropagum on infective larvae of Strongyloides papillosus

In an in vitro trial, the trapping ability of Arthrobotrys robusta and Monacrosporium gephyropagum against Strongyloides papillosus infective larvae on corn meal agar plates, was evaluated after seven days of interaction at 25 degrees C. Monacrosporium gephyropagum trapped 93.1% of the larvae whereas A. robusta trapped only 32.3%. Variability in the capture of S. papillosus infective larvae by both trapping fungi is discussed.

Field evaluation of Mesocyclops longisetus (Copepoda: Cyclopoidea) for the control of larval Aedes aegypti (Diptera Culicidae) in northeastern Mexico

Field trials of the predacious copepod Mesocyclops longisetus Thiubaud were conducted in northeastern Mexico to determine the effectiveness of this species to control larval Aedes aegypti (L.) populations and to survive and reproduce in nature. Groups of 200, 50, and 50 ovigerous M. longisetus females were inoculated into 200-liter metal drums, discarded tires, and cemetery flower vases, respectively, which are 3 of the more important Aedes breeding sites in this area. Larvae were sampled at 15-d intervals, and total surviving cyclops were collected at the end of the study, 120 d later. Community participation was solicited through a simple training program on copepod rescue before drum cleaning and facilitated by the addition of a drum marker to remind residents of copepod presence. Results showed good cooperation and after 4 mo all peridomestic drums, still supported variable numbers of cyclopoids. Average of larvae reduction was 37.5% for drums, 67.5% for flower vases, and 40.9% for tires. This study shows difficulties of using cyclopoids for tires and vases in areas where prolonged dry seasons desiccated these habitats and reduced copepod survival.

Mortality of horn fly (Diptera: Muscidae) larvae in bovine dung supplemented with loline alkaloids from tall fescue

Larvae of arthropod ectoparasites of livestock, such as the horn fly, Haematobia irritans (L.), may be exposed to acyl-loline alkaloids in dung of ruminant livestock ingesting herbage of the tall fescue (Festuca arundinacea Schreb.)-endophyte association [Neotyphodium coenophialum (Morgan-Jones & W. Gams) Glenn, Bacon & Hanlin comb. nov.]. Biological activity of alkaloid-supplemented bovine dung was assayed by growth, development, and survival of 1st instars of horn fly. An extract from tall fescue seed, containing N-formyl loline (NFL), N-acetyl loline (NAL), and loline (59:21:20 by mass, respectively) caused 100% mortality of horn fly larvae when dung was supplemented at > or = 100 micrograms/g. Probit analysis of data corrected for natural mortality indicated a LD50 of 30 micrograms/g (95% fidicial limits: 20-49 micrograms/g). When horn fly larvae were introduced to dung supplemented with up to 50 microM of acyl-loline derivatives, mortality of larvae varied significantly between alkaloids (P < 0.0001). Probit analysis indicated that NFL [LD50: 34 microM (95% fidicial limits: 3-53 microM)] was more toxic than NAL [LD50: 46 microM (0-83 microM)], and that loline hydrochloride was not toxic.

Entomopathogenic nematodes as a potential biological control method for ticks

Entomopathogenic nematodes have been used for biological control of certain insect pests. In these studies the nematodes were tested as a possible biological control agent for engorged female ticks. Five species of infective juveniles (IJs) were tested initially for their ability to penetrate and kill ticks, including Steinernema glaseri (SG), S. riobravus (SR), S. carpocapsae (DT), S. feltiae (SF) and Heterorhabiditis bacteriophora (HP88). Infective juveniles (IJs) of SRs and SFs appeared to be the most effective in killing ticks and invaded and killed 30 to 100% of replete females. These two nematode species were tested on several tick species including Amblyomma americanum, A. cajennense, A. maculatum, Dermacentor variabilis and Rhipicephalus sanguineus. Although the killing rate of each tick species varied, the nematodes did not appear to be host specific and were able to kill ticks of all species tested. Egg mass weights of exposed ticks of each species were significantly lower than those of the controls. Ticks were examined with microscopy to determine whether nematodes entered and multiplied inside ticks. Partially fed female Amblyomma americanum and Dermacentor variabilis exposed to 5000 IJs in petri dishes were collected at 8, 24, 48 and 96 hrs (Trial 1) and 1, 2, 3, 4, 7 and 9 days (Trial 2) post-exposure, and fixed, processed and embedded in resin for microscopy studies. Only a few nematodes were seen in the hemocoel and tissues and they were surrounded by a clear space. Bacteria, released from the nematodes, were present in the exposed ticks and appeared to increase daily causing a generalized infection. Degeneration of tick tissues and death of the ticks appeared to result from bacterial proliferation. Nematodes did not multiply within ticks as they do in insect larvae. In these controlled laboratory studies, exposure of ticks to nematodes resulted in tick mortality and reduced egg production. Entomopathogenic nematodes appear to have potential as a biological control agent of ticks, but future studies will be required to determine whether nematode/tick interactions will occur in the field.

Laboratory and field evaluation of efficacy of VectoBac 12AS against Culex sitiens (Diptera: Culicidae) larvae

Laboratory bioassay studies of the efficacy of VectoBac 12AS (active ingredient: 1,200 International Toxic Units [ITU]/mg Bacillus thuringiensis var. israelensis) against field-collected late 3rd/early 4th-instar larvae of Culex sitiens indicated excellent control potential. A 95% lethal concentration (LC95) value of 1.381 x 10(7) ITU was calculated, which equated to a dosage of 0.011 liters/ha. This dosage represented 1.8% of the recommended lowest dosage rate for the product. A field trial of VectoBac 12AS against late 3rd/early 4th-instar field specimens of Cx. sitiens in floating mesh cylinders was then conducted in salt-marsh pools near Coomera Marina, southeast Queensland, Australia. At a rate of 0.5 liters/ha, 100% mortality of Cx. sitiens larvae was recorded at 24 h posttreatment.

Occurrence of digestive cysteine proteases in Perillus bioculatus, a natural predator of the Colorado potato beetle

Oryzacystatins (OCs) are protease inhibitors (PIs) that inhibit Colorado potato beetle (CPB) digestive proteases, and transgenic potato plants containing these PIs are currently under test. However, OCs could interfere with the digestive system of beneficial insects. Protease activity and susceptibility to class-specific protease inhibitors were studied in protein extracts of Perillus bioculatus, a stinkbug predator that has shown potential for biological control of the CPB. At physiological pH, the analysis of protease activity showed that up to 90% of P. bioculatus protease activity is of the cysteine type. All active life stages of the predator were tested, and electrophoretic characterization detected no major qualitative variation in protease pattern between stages. Protease activity in extracts of P. bioculatus nymphs was significantly reduced, up to 70%, by the two recombinant cystatins from rice (OCI and OCII), and by stefin A, a PI encoded by a human gene. These results clearly indicate that cysteine PIs are active not only against the CPB digestive protease complex, but also against proteases of one of its most important natural predators.

The initial impact of rabbit hemorrhagic disease on European rabbit populations in South Australia

The calicivirus agent for rabbit hemorrhagic disease (RHD) escaped from an island quarantine station to the Australian mainland in October 1995. Within 2 wk it was detected at an established field study site where wild European rabbits (Oryctolagus cuniculus) were being monitored in the Flinders Ranges National Park (South Australia, Australia). During November 1995, RHD reduced the rabbit numbers on the site by 95%. Approximately 3% of the population survived challenge by RHD and developed antibodies. Most of the antibody-positive survivors were 3- to 7-wk-old when challenged. Many rabbits died underground, but counts of rabbit carcasses found on the surface indicated that approximately 1 million rabbits had died above ground in the National Park, and that > 30 million rabbits may have died in adjacent areas during the November epidemic.

Impact of treatments with Bacillus sphaericus on Anopheles populations and the transmission of malaria in Maroua, a large city in a savannah region of Cameroon

Simultaneously with a control of breeding sites primarily for Culex quinquefasciatus and secondarily for anophelines with Bacillus sphaericus in the town of Maroua (120,000 inhabitants) in North Cameroon, a survey of anopheline populations and of transmission rates of malaria was performed. Monthly night catches in 8 districts of the town emphasized the relation between the biting rate by Anopheles in the districts and two main factors. One factor was the distance of a district from the breeding sites, i.e., natural flooded areas along the periphery of the town or artificial breeding sites (ditches, puddles) filled with rain water during the rainy season and with water from the water network throughout the year. The second factor was the density of the habitation that reduced dispersal of female mosquitoes from the breeding sites and the risk for inhabitants to be injected because of scattered bites. The treatment with B. sphaericus was followed by a delay (2 months) in the beginning of the transmission period and a decrease in the incidence of malaria cases studied in a health facility of the town. It thus seems to be possible to reduce malaria transmission by applying B. sphaericus to the breeding sites, but this requires a good knowledge of the location and dynamics of breeding sites and an improved formulation of the pesticide.

Experimental control of the schistosome-transmitting snail Biomphalaria pfeifferi by the ampullariid snail Pila ovata

Adults of the African ampullariid snail Pila ovata were examined for their ability to control laboratory populations of the pulmonate snail Biomphalaria pfeifferi, a widespread, intermediate host of the human pathogen Schistosoma mansoni in sub-Saharan Africa. In a 6-week experiment conducted in large (100 x 60 x 60 cm) outdoor tanks containing floating macrophytes (Nymphaea caerula) and initially set up with one adult ampullariid for every three adult pulmonates, the numbers of B. pfeifferi egg masses were always about half those in similar tanks without P. ovata. Although, by week 6, the numbers of B. pfeifferi in the control tanks (without ampullariids) had increased 5-fold, from an initial mean of 30 snails/tank, there was no significant increase in the numbers of B. pfeifferi in the experimental tanks (containing ampullariids). Results of experiments conducted in indoor glass aquaria indicated that adult P. ovata rapidly attacked egg masses or neonates (< 2.5 mm shell diameter) of B. pfeifferi but had no effect on the adults. The adult ampullariids also significantly decreased cover by floating macrophytes over a 6-week period compared with that in similar but ampullariid-free aquaria. This decrease in plant cover is relevant to biological control of the schistosome vectors as macrophytes serve as food, shelter and oviposition sites for pulmonate snails. The present result indicate the ability of P. ovata to inhibit multiplication of B. pfeifferi populations, at least under laboratory conditions, both directly, through predation, and indirectly, by competition for resources. Pila ovata may therefore prove useful in the biological control of medically important, pulmonate snails.

Bacterial symbiosis in arthropods and the control of disease transmission

Bacterial symbionts may be used as vehicles for expressing foreign genes in arthropods. Expression of selected genes can render an arthropod incapable of transmitting a second microorganism that is pathogenic for humans and is an alternative approach to the control of arthropod-borne diseases. We discuss the rationale for this alternative approach, its potential applications and limitations, and the regulatory concerns that may arise from its use in interrupting disease transmission in humans and animals.

Biology and applications of mycorrhizal fungi

Mycorrhizae have been shown to increase growth and yield of plants. They have been identified with both nutrient mobilization and nutrient cycling. Arbuscular (or endo-) mycorrhizae play a significant role in agriculture and most natural ecosystems, whereas ectomycorrhizae have a great potential in forestry and wasteland regeneration. The use of mycorrhizal fungi would reduce dependence on chemical fertilizers besides minimizing environmental pollution. The present review addresses the progress that there has been in the area of the ecto- and endomycorrhizae. It also examines the potential of field applications of mycorrhizal biotechnology in agriculture and forestry.

Field trials of VectoLex CG, a Bacillus sphaericus larvicide, in Illinois waste tires and catch basins

The susceptibilities of Aedes triseriatus (Say), Anopheles punctipennis (Say), Culex restuans (Theobald), and Culex pipiens (L.) larvae to VectoLex CG were determined. VectoLex, formulated on corncob granules (10-14 mesh) was applied to 2 tire dumps and numerous catch basins located in east-central Illinois. VectoLex, formulated as effervescent tablets, was also applied to catch basins. In a sunlit dump, there was a 99.6% reduction in Ae. triseriatus, Cx. restuans, and Cx. pipiens larvae as long as 32 days after treatment, and no pupae were recovered during this interval. There was still a 71.6% larval reduction 74 days after treatment. There was an overall reduction of 22% for An. punctipennis larvae. In a shaded dump, no larval Ae. triseriatus, Cx. restuans, or Cx. pipiens were recovered for 25 days after treatment, and no pupae were recovered 25-67 days after treatment. There was still a 68.7% larval reduction 74 days after treatment. An. punctipennis was unaffected. In one catch basin study, VectoLex was comparable to Altosid (average of 46 days vs. 50 days until larvae were recovered from catch basins). As the summer progressed, the duration of VectoLex control was reduced to 30 days. VectoLex effervescent tablets (evaluated mid-August through September) gave 18-day control. VectoLex was effective against Ae. triseriatus, Cx. restuans, and Cx. pipiens, but was not effective against An. punctipennis in waste tires. VectoLex was effective against Cx. restuans and Cx. pipiens in catch basins.

Laboratory assessment of the molluscicidal and cercaricidal activities of the Egyptian weed, Solanum nigrum L

The molluscicidal properties of Solanum nigrum L. were tested against three Egyptian snail species (Biomphalaria alexandrina, Bulinus truncatus and Lymnaea natalensis), each an intermediate host of parasites causing human schistosomiasis or fascioliasis. The plant was collected in two regions within Egypt: Fayium and Giza. Snails were exposed for 24 and 48 h, to the dry powdered fruits and leaves or to crude water extracts of the powders, and mortality was recorded. The water extract of the leaves collected in Fayium (FLWE) had the highest molluscicidal activity, with median lethal concentrations (LC50) of 18.6 mg/litre for Bi. alexandrina, 14.5 mg/litre for Bu. truncatus and 17.7 mg/litre for L. natalensis. When Bi. alexandrina infected with Schistosoma mansoni were exposed to FLWE (20 or 25 mg/litre), they shed significantly fewer cercariae than unexposed snails (P < 0.02). The cercaricidal properties of FLWE were directly tested against S. haematobium, S. mansoni and Fasciola gigantica cercariae and a time-concentration relationship was observed; the concentrations needed to kill all cercariae (LC100) within 30 min of exposure were 30 mg/litre for both S. haematobium and S. mansoni and 40 mg/litre for F. gigantica.

The Mossie-Buster: a hose-driven insecticide delivery tool for the control of container-breeding mosquitoes

A novel insecticide delivery tool, the Mossie-Buster, was recently developed to control larval populations from urban breeding sites in Townsville, Australia. This functional and user-friendly control device directly targets the main breeding sites of Aedes aegypti (L.) with a focused delivery of insecticides. The Mossie-Buster comprises a commercially available device and attachments that mix an insecticide solution into the flow of water emitted from a hose. Attached to the device is a trigger for controlled insecticide release. Preliminary laboratory and field trials demonstrated the tool to be effective in eliminating all Ae. aegypti present in various typical breeding containers in different environmental conditions for a minimum of 2 wk in exposed areas to 3 months in an unexposed area.

Field trials with Bacillus sphaericus formulations against polluted water mosquitoes in a suburban area of Bangkok, Thailand

Two newly developed Bacillus sphaericus larvicidal formulations, VectoLex CG (corncob granules) and VectoLex WDG (water dispersible granules), were tested against Culex quinquefasciatus larvae in 4 highly polluted breeding sites in Thailand. VectoLex CG, applied at rates of 0.5-2 g/m2, gave satisfactory to complete control of late-instar larvae and pupae for up to 4 wk after treatment. The VectoLex WDG, which had higher potency and was applied at rates of 0.1-0.5 g/m2, gave satisfactory control for 1-4 wk after treatment. Among the factors influencing longevity of control were dosage of a given formulation, precipitation, and flooding of the treated sites; the latter had the greatest impact. Presence of larvivorous fish did not seem to influence larval populations because there were heavy populations of mosquito larvae present in the test sites in the presence of moderate numbers of fish before the application of B. sphaericus treatments.

Field evaluation of Vectobac G, Vectobac 12AS and Bactimos WP against the dengue vector Aedes albopictus in tires

The efficacy of three formulations of Bacillus thuringiensis var. israelensis was studied against Aedes albopictus in discarded tires. The formulations were: Vectobac G (corn cob formulation), Vectobac 12AS (aqueous suspension), and Bactimos WP (wettable powder formulation). Both Vectobac G and Vectobac 12AS were effective for 24 hr with more than 80% mortality. Both Vectobac formulations were significantly more effective than Bactimos WP for 24 hr after treatment (P < 0.0005). A week after treatment, Vectobac 12AS was significantly different than Bactimos WP (P < 0.05). However, Vectobac G did not differ significantly from Bactimos WP (P > 0.05); two weeks after spraying there was no significant difference among the various formulations (P > 0.05).

Biological control of gastro-intestinal nematodes--facts, future, or fiction?

The potential of using fungi to prevent nematodosis caused by parasites with free-living larval stages is well documented today. In this respect Duddingtonia flagrans, a net-trapping, nematode-destroying fungus, appears to be the most promising candidate. Laboratory experiments and in-vivo studies, where fungal spores have survived passage through the gastro-intestinal tract of cattle and horses, plus field studies with cattle, horses and pigs, demonstrate significant reduction in the number of infective larvae that develop in the faecal environment. In field trials this reduction subsequently leads to reduced infectivity of herbage and also reduced worm burdens in grazing animals. A status of the present situation, primarily based upon work performed in Denmark within the last 6-8 years, plus an outlook for practical implementation of an integrated control strategy including the use of nematode-destroying fungi in the future is discussed.

Dispersal and parasitizing abilities of Eupelmus vuilleti (Hymenoptera: Eupelmidae) within a column of cowpea seeds

Eupelmus vuilleti (Crawford) is an ectoparasitoid of the seed-eating beetle Bruchidius atrolineatus (Pic), which is an important pest of stored cowpea, Vigna unguiculata Walp, seeds in West Africa. Herein, we investigated the dispersal abilities of females within columns of seeds to assess the potential of E. vuilleti as a biological control agent of bruchids in cowpea granaries. The influence of host presence together with the 2 abiotic factors light and gravity on parasitoid movement and parasitization efficiency were analyzed. E. vuilleti females were able to travel through large seed masses and parasitize hosts located at the end of the seed column opposed to their introduction zone. Parasitoid movement was stimulated by light. E. vuilleti females exhibited a negative geotropism. Females introduced at the bottom of the seed column dispersed more and parasitized more hosts than females introduced at the top. Host presence had some influence on the dispersal of the parasitoids within the seed column at a host density of 10 infested seeds for 16,000-18,000 uninfested seeds. This depended on female introduction zone because gravity was the major factor influencing dispersal. The possible applications of these results for biological control of bruchids in cowpea granaries are discussed.

Control of Culex quinquefasciatus (Diptera: Culicidae) with Bacillus sphaericus in Maroua, Cameroon

Two strategies were tested to control Culex quinquefasciatus with Bacillus sphaericus in Maroua (population 130,000), Cameroon. The treatment of all potential breeding sites (27,000) with B. sphaericus during the dry season caused up to a 90% reduction in the adult biting rate. Because of the short persistence of B. sphaericus and the occurrence of new breeding sites, unacceptable levels of adult biting rates were reached again in 5 months. In the second strategy, two treatments per year of the most productive breeding sites (10,000) stopped the biting rate increase during the rainy season. The results were only partially successful because of variations in B. sphaericus toxicity. The first treatment required 1,200 man-days of work vs. 200 for the simplified treatments. The density of breeding sites depends on the rainfall and the presence of a tap-water network. A sustained control program of Cx. quinquefasciatus will depend upon the dynamics of the principal breeding sites and an improved formulation of B. sphaericus.

A new approach to insect-pest control--combination of neurotoxins interacting with voltage sensitive sodium channels to increase selectivity and specificity

Voltage-sensitive sodium channels are responsible for the generation of electrical signals in most excitable tissues and serve as specific targets for many neurotoxins. At least seven distinct classes of neurotoxins have been designated on the basis of physiological activity and competitive binding studies. Although the characterization of the neurotoxin receptor sites was predominantly performed using vertebrate excitable preparations, insect neuronal membranes were shown to possess similar receptor sites. We have demonstrated that the two mutually competing anti-insect excitatory and depressant scorpion toxins, previously suggested to occupy the same receptor site, bind to two distinct receptors on insect sodium channels. The latter provides a new approach to their combined use in insect control strategy. Although the sodium channel receptor sites are topologically separated, there are strong allosteric interactions among them. We have shown that the lipid-soluble sodium channel activators, veratridine and brevetoxin, reveal divergent allosteric modulation on scorpion alpha-toxins binding at homologous receptor sites on mammalian and insect sodium channels. The differences suggest a functionally important structural distinction between these channel subtypes. The differential allosteric modulation may provide a new approach to increase selective activity of pesticides on target organisms by simultaneous application of allosterically interacting drugs, designed on the basis of the selective toxins. Thus, a comparative study of neurotoxin receptor sites on mammalian and invertebrate sodium channels may elucidate the structural features involved in the binding and activity of the various neurotoxins, and may offer new targets and approaches to the development of highly selective pesticides.

Differential induction of systemic resistance in Arabidopsis by biocontrol bacteria

Selected nonpathogenic, root-colonizing bacteria are able to elicit induced systemic resistance (ISR) in plants. To elucidate the molecular mechanisms underlying this type of systemic resistance, an Arabidopsis-based model system was developed in which Pseudomonas syringae pv. tomato and Fusarium oxysporum f. sp. raphani were used as challenging pathogens. In Arabidopsis thaliana ecotypes Columbia and Landsberg erecta, colonization of the rhizosphere by P. fluorescens strain WCS417r induced systemic resistance against both pathogens. In contrast, ecotype RLD did not respond to WCS417r treatment, whereas all three ecotypes expressed systemic acquired resistance upon treatment with salicylic acid (SA). P. fluorescens strain WCS374r, previously shown to induce ISR in radish, did not elicit ISR in Arabidopsis. The opposite was found for P. putida strain WCS358r, which induced ISR in Arabidopsis but not in radish. These results demonstrate that rhizosphere pseudomonads are differentially active in eliciting ISR in related plant species. The outer membrane lipopolysaccharide (LPS) of WCS417r is the main ISR-inducing determinant in radish and carnation, and LPS-containing cell walls also elicit ISR in Arabidopsis. However, mutant WCS417rOA-, lacking the O-antigenic side chain of the LPS, induced levels of protection similar to those induced by wild-type WCS417r. This indicates that ISR-inducing bacteria produce more than a single factor that trigger ISR in Arabidopsis. Furthermore, WCS417r and WCS358r induced protection in both wild-type Arabidopsis and SA-nonaccumulating NahG plants without activating pathogenesis-related gene expression. This suggests that elicitation of an SA-independent signaling pathway is a characteristic feature of ISR-inducing biocontrol bacteria.

Effects on white Leghorn hens of constant exposure to ultraviolet light from insect traps

Constant exposure of Hy-Line W-36 White Leghorn hens to ultraviolet light from insect traps resulted in no significant differences in egg production, fertility, hatchability of fertile eggs, or total hatchability. Also, there were no apparent effects on the eyes of the birds. Results were the same when either blacklight or blacklight blue tubes were used. The need for additional testing of light traps for nuisance fly control in commercial caged layer houses is discussed.

Field trial of Bacillus sphaericus strain B-101 (serotype H5a, 5b) against filariasis and Japanese encephalitis vectors in India

A large-scale operational field trial was conducted from June 1993 to October 1994 to evaluate the efficacy of Bacillus sphaericus (strain B-101, serotype H5a,5b) for control of the vectors of filariasis (Culex quinquefasciatus) and Japanese encephalitis (Cx. tritaeniorhynchus and Cx. vishnui) in Rourkela city. Application of B. sphaericus, when sprayed at 1 g/m2 in storm drains, wastewater pools, abandoned masonry tanks, peripheral paddy fields, ditches, and other small water collections and at 4 g/m2 in domestic septic tanks, significantly reduced larval and pupal counts (P < 0.0001) and significantly reduced the percentage of habitats containing larvae (3rd-4th instars) (P < 0.0001) as compared with routine antilarval measures. This in turn resulted in a reduction in the indoor density of disease vectors in particular and a reduction in mosquito nuisance in general. The trial demonstrated that B. sphaericus has good potential for use against disease vectors and mosquito breeding in polluted as well as clean waters.

Importance of Hydrilla verticillata (hydrocharitaceae) as habitat for immature mosquitoes at the Ross River reservoir, Australia

From November 1990 to November 1992, immature mosquitoes were sampled from the shoreline and from emergent beds of the submerged aquatic plant Hydrilla verticillata at the Ross River reservoir, northern Australia. Aerial mapping of Hydrilla beds was done in conjunction with sampling to estimate total immature mosquito numbers. Larvae of 7 species were found. Culex annulirostris. Anopheles annulipes s.l., and Anopheles amictus comprised 80.4% of the total. Peak larval densities occurred in the late wet season period in both habitat types (March to May) but Hydrilla generally supported higher densities, particularly of An. annulipes s.l. (43.7% of the total sample), than the shoreline habitats. Anopheles annulipes replaced Cx. annulirostris as the predominant taxon when 1990-92 data were compared with data for 1985-86. The Hydrilla beds supported on the order of 5.6 x 10(9) immatures during the period of peak density. This suggests that where human exposure is of concern, mosquito control in habitats such as Hydrilla is warranted.

Use of Bactimos briquets (B.t.i. formulation) combined with the backswimmer Notonecta irrorata (Hemiptera:Notonectidae) for control of mosquito larvae

The efficacies of Bacillus thuringiensis var. israelensis (Bactimos briquets) and the backswimmer Notonecta irrorata were evaluated both individually and in combination to control mosquito larvae in plastic containers in Monterrey, Mexico. The combined strategy proved to be the most effective one.

Evaluation of Caribbean strains of Macrocyclops and Mesocyclops (Cyclopoida:Cyclopidae) as biological control tools for the dengue vector Aedes aegypti

Fifteen Caribbean strains of copepods were assessed for their predation ability against mosquito larvae. Macrocyclops albidus from Nariva. Mesocyclops aspericornis from Oropouche, and Mesocyclops longisetus from E1 Socorro, Trinidad, were most effective against Aedes aegypti but not against Culex quinquefasciatus. Mesocyclops longisetus and Me. aspericornis prevented any mosquito survival over 25 wk of observation despite weekly challenges with Ae. aegypti. The copepods were tolerant to dosages of the insecticide temephos that are usually toxic to mosquito larvae. This indicated that copepods could be incorporated into an integrated control system. To determine whether pathogenic microbes might be introduced with copepods into drinking water, microbial studies were done on the copepods. These showed the presence of only Aeromonas sobria, Pseudomonas sp., Alcalignes sp., and gram-positive bacilli. Although none of these are highly pathogenic to humans, the application of these copepods has not yet been recommended for use in drinking water.

Effects of two insect growth regulators on the susceptibility of Aedes aegypti (Diptera:Culicidae) to Molinema dessetae (Nematoda:Filarioidea)

The effects of 2 growth regulators, diflubenzuron (DFB) and OMS 2017, on the ability of females Aedes aegypti to become infected with Molinema dessetae was studied under laboratory conditions. OMS 2017 and DFB had no effect on either the amount of blood ingested or the microfilarial load. The infective potential of females that survived DFB treatment was significantly greater than untreated females, but there was no difference between OMS 2017-treated and control females. The percentage of infective larvae in the head after OMS 2017 and DFB treatments was significantly greater than for control females. Insect growth regulators appear to affect the vectorial competence of mosquitoes, and these results indicate the need for preliminary studies before these compounds are used in large-scale control programs.

The impact of Ixodiphagus hookeri, a tick parasitoid, on Amblyomma variegatum (Acari: Ixodidae) in a field trial in Kenya

In an experiment to investigate the effect of the tick parasitoid, Ixodiphagus hookeri, on tick numbers on cattle, 150000 parasitoids were released over a period of 1 year in a field where ten cattle infested with multiple tick species were kept. Amblyomma variegatum was reduced from 44 to two ticks per animal while Rhipicephalus appendiculatus increased over the time of parasitoid release. During the time of release 51% of the nymphs of A. variegatum collected from the animals were parasitized. The recovery of the parasitoids after the releases were stopped was only 9%. The total numbers of A. variegatum remained low up to 1 year after the parasitoid release was stopped. This study gives an insight into how I. hookeri could be used strategically for the management of A. variegatum on small-scale farms.

Control of pest blackflies (Diptera:Simuliidae) along the Orange River, South Africa: 1990-1995

The efficacy of Bacillus thuringiensis var. israelensis (B.t.i.) and temephos in controlling the pest blackfly Simulium chutteri Lewis along the middle Orange River between 1990 and 1995, was assessed. Larvicides were applied by helicopter to rapids and riffles between Hopetown and Onseepkans, a river distance of 807 km. Larvicidal efficacy was based on the change in larval abundance at selected sites before and after each treatment. The success of the control programme was assessed independently by local farmers, who ranked adult blackfly annoyance on a 4-point scale. Before treatment, blackfly annoyance showed consistent peaks in spring, and sometimes in autumn, and levels were unacceptably high for between 17 and 36 weeks of the year. After treatment started, blackfly annoyance levels were reduced significantly. The number of annual treatments necessary to reduce blackfly annoyance to acceptable levels was highly variable (3-13), and depended on river conditions, as well as the efficacy and timing of each treatment. During low-flow conditions (< 50 m3/s), applications became increasingly difficult in braided sections of the river, and dosage calculations were inaccurate because of local abstraction and return flows. Both larvicides worked well in winter (water temperature 11-13 degrees C). Control of the spring outbreak can be planned well in advance, with the first treatment starting in mid July. A flexible protocol is required to control outbreaks at other times of the year. We recommended the use of B.t.i. for most applications, with increased dosages during algal blooms (> 1500 cells/ml). The use of temphos in the Orange River should be considered only during algal blooms or when flows exceed 300 m3/s. We conclude that helicopter application of larvicides is an effective method or controlling blackflies, along the middle Orange River.

Synergistic activity of a Bacillus thuringiensis delta-endotoxin and a bacterial endochitinase against Spodoptera littoralis larvae

In an attempt to increase the insecticidal effect of the delta-endotoxin crystal protein CryIC on the relatively Cry-insensitive larvae of Spodoptera littoralis, a combination of CryIC and endochitinase was used. CryIC comprising the first 756 amino acids from Bacillus thuringiensis K26-21 and endochitinase ChiAII encoded by Serratia marcescens were separately produced in Escherichia coli carrying the genes in overexpression vectors. The endochitinase on its own, even at very low concentrations (0.1 microgram/ml), perforated the larval midgut peritrophic membrane. When applied together with low concentrations of CryIC, a synergistic toxic effect was obtained. In the absence of chitinase, about 20 micrograms of CryIC per ml was required to obtain maximal reduction in larval weight, while only 3.0 micrograms of CryIC per ml caused a similar toxic effect in the presence of endochitinase. Thus, a combination of the Cry protein and an endochitinase could result in effective insect control in transgenic systems in which the Cry protein is not expressed in a crystalline form.

The biology and predatory potential of notonectid bug, Enithares indica (Fabr) against mosquito larvae

The biology of a notonectid bug Enithares indica against immatures of Anopheline, Culicine and Aedine mosquitos was studied in the laboratory. The life cycle of the bug consists of the egg and five nymphal stages and takes about 64 +/- 1.54 days for completion. All stages of E. indica have good predatory potential. It can be used as a biological control agent in an integrated disease vector control program.

Efficacy of Bacillus sphaericus in different breeding habitats of Culex quinquefasciatus

'Spherifix', an alginate based slow release formulation of Bacillus sphaericus was field tested in different types of breeding habitats of Culex quinquefasciatus at the dose of 15 kg ai/ha at bimonthly interval. The efficacy of the formulation was higher in most of the months except in rainy and post-rainy months. The mean percentage reduction +/-SD during the treatment phase of one year was 31.2 +/- 17.9, 50 +/- 29.4, 28.3 +/- 17.6, 30.3 +/- 21.1, 66 +/- 22.5 and 53 +/- 20.4 in larval density and 49 +/- 20.8, 65.1 +/- 26.1, 30.3 +/- 21.9, 59.8 +/- 22.6, 63.1 +/- 21.9 and 47.7 +/- 24.2 in pupal density respectively in cement tanks, cesspools, cesspits, disused wells, unlined drains and cement lined drains. The reduction in immature density was relatively higher in undisturbed, debris free and shallow habitats such as cesspools, unlined drains and cement lined drains. After withdrawal of treatment, the effect of the formulation could be seen for a period of four months.

Efficiency of Altosid (S-methoprene) liquid larvicide formulated on Biodac (granular carrier) against spring Aedes species in flooded woodlots

Exposure of spring Aedes larvae to Altosid Liquid Larvicide formulated on the granular carrier Biodac under field conditions was evaluated. Both aerial and hand-applied treatments were monitored. Mosquitoes collected from aerially treated sites (9 kg/ha) showed an average 80% mortality. In hand-treated sites excellent control was achieved at label rates of 11.3-14.7 kg/ha (10-13 lb/acre); at dosages less than recommended rates, control was unsatisfactory.

Effects of sublethal dosages of methoprene on Anopheles dirus species A and B

Anopheles dirus species A and B individuals were exposed as 4th-stage larvae to sublethal concentrations of methoprene. Median lethal concentrations were 0.21 ppb for species A and 0.17 ppb for species B. When exposed to 0.10 ppb methoprene the sex ratio of species. A changed from fewer males to more males; no effect was observed in the sex ratio of species B. Exposure to methoprene had no effect on wing length and survival of either species. Results indicate that exposure to methoprene significantly affected fecundity of both species of An. dirus.

Microdroplet application of mosquitocidal Bacillus thuringiensis using ultra-low-volume generator for the control of mosquitos

In an effort to develop a more effective technique in dispersing a microbial control agent, Bacillus thuringiensis (Bt), a truck-mounted ultra low volume (ULV) generator (Scorpion) was used to disperse B. thuringiensis israelensis (Bti) and Bti with malathion. Complete larval and adult mortalities for all tested mosquito species within the first 70-80 feet from the ULV generator were achieved. Beyond that distance less than 50% mortality was achieved as insufficient sprayed particles reached the area. A minimum of 10(3) Bti colony forming units per ml is required to cause 100% larval mortality. The sprayed Bti larvicidal toxins were persistent in the test water 7 days post ULV. The effectiveness of B. thuringiensis jegathesan (Btj), a new mosquitocidal Bt serotype was also evaluated. Similar mortality results as Bti were achieved except that the Btj toxins underwent degradation in the test water, since less than 50% less in larval mortality was observed in 7 days post ULV samples. This ULV method has the potential to disperse Bt and malathion effectively for a simultaneous control of mosquito adults and larvae.

Control of Oesophagostomum dentatum and Hyostrongylus rubidus in outdoor-reared pigs by daily feeding with the microfungus Duddingtonia flagrans

An investigation of pasture-reared pigs experimentally infected with Oesophagostomum dentatum and Hyostrongylus rubidus showed that daily doses in the feed with the microfungus Duddingtonia flagrans over a 2-month period led to lowered herbage larval infectivity of both species. This was further substantiated by low worm recoveries in initially parasite-naive tracer pigs that were later introduced to the pasture plot. The control setup comprised the release of similarly infected but nondosed pigs on a plot of the same area, followed by a group of tracer pigs. This paper discusses the potentials for using this biological control principle in the pig industry and emphasizes the research required, primarily regarding production technology and elaboration of feasible epidemiology-based dosing regimens, before such control can be implemented in practice.

Effect of plumbagin on gonadotrophic cycle of the housefly, Musca domestica L

Topical treatment of the phytochemical plumbagin in doses ranging 0.005-5 micrograms prevented oocyte development and affected fecundity and fertility in M. domestica. The treatment to wandering larvae was less effective as the compound could only effect the fertility to a significant level whereas the fecundity was not significantly reduced. The effect of the compound was more pronounced in adult treatments where both fecundity and fertility reduced drastically. The compound also effected the oocyte maturation as it arrested the development of vitellogenic oocyte at stage six. As the juvenile hormone analogue methoprene and moulting hormone 20-hydroxyecdysone or the mixture of these hormones could not restore the development of the oocyte in ovaries of plumbagin treated flies, it is concluded that the compound does not effect the female houseflies through hormonal pathways, instead in all probability it acts like a cytotoxic compound.