Oviposition attractancy of an infusion from a wood inhabiting fungus for vector mosquitoes.

BACKGROUND & OBJECTIVES: Review of literature indicates that none of the chemicals so far studied for oviposition attractancy was found to be promising for operational use. Efforts are being made to find an effective substance to corner a large number of ovipositing females to selective breeding sites for ease of control operation. This will reduce insecticidal consumption and will be cost-effective. This study is aimed to evaluate the oviposition attractancy of aqueous infusion from a wood inhabiting fungus (Polyporus spp.) for vector mosquitoes both in the laboratory and under field conditions. METHODS: An aqueous infusion (10%) was prepared by soaking 10 g of fungal powder in 100 ml of chlorine-free tap water. The mixture was shaken thoroughly and filtered through Whatman No. 1 filter paper. The filtered infusion was tested for oviposition attractancy against vector mosquitoes both in the laboratory and under field conditions. RESULTS: The laboratory study on the dose-effect relationship indicated that at an optimum concentration of 4 ppm, maximum attractancy was observed. Water treated with aqueous fungal infusion (AFI) at 4 ppm received significantly more egg rafts/eggs of vector mosquitoes than other substrates like rearing water, natural breeding water and tap water. Trials conducted in the field showed that mud pots treated with AFI placed in both indoor and outdoor locations received significantly more Aedes aegypti eggs than the control. Similarly, treated pots placed in paddy fields attracted significantly more gravid Anopheles subpictus for oviposition than untreated pots. In contrast, the number of egg rafts of Culex quinquefasciatus laid in AFI treated pots was significantly less than in the control ones owing to strong natural olfactory factors associated with the breeding habitat. INTERPRETATION & CONCLUSION: The results indicated that there is scope for developing a trap incorporating this oviposition attractant along with insect growth regulator(s) (IGR) for surveillance and/or control of Ae. aegypti and other vector mosquitoes breeding in paddy fields.

Field evaluation of Spicbiomoss, a biolarvicidal formulation of Bacillus sphaericus against immatures of Culex quinquefasciatus & Anopheles species.

Spicbiomoss, an aqueous suspension formulation of Bacillus sphaericus was evaluated for its efficacy against immatures of Culex quinquefasciatus at the application rate of 120 l/ha in cement tanks, cesspits and drains in Pondicherry and in drains in Kochi, Kerala. The formulation was also tested against anophelines (Anopheles fluviatilis and An. culicifacies) breeding in stream pools in Malkangiri district, Orissa. In cement tanks and cesspits more than 80 per cent reduction in immature density was observed for a period of 6-13 days (mean 9.8 +/- 1.25 days) and 3-8 days (mean 5.2 +/- 0.7 days) respectively. The same level of reduction was found to last for 1-4 days (mean 2.2 +/- 0.52 days) in drains in Pondicherry and 2-9 days (mean 4.8 +/- 1.17 days) in Kochi. In bunded stream pools 40-79 per cent reduction in immature density of Anopheles was obtained for an average period of 1-7 (mean 3.83 +/- 0.98) days. There was no improvement in the efficacy of the formulation against anophelines even at the higher application rate (240 l/ha). Thus, Spicbiomoss can be used against Cx. quinquefasciatus in an integrated vector management programme.

Susceptibility of Phlebotomus argentipes and P. papatasi (Diptera: Psychodidae) to insecticides.

Field collected fully fed adults of Phlebotomus argentipes and P. papatasi were screened in the laboratory for susceptibility to DDT, BHC, malathion, deltamethrin, permethrin, lambdacyhalothrin and bendiocarb. Pondichery strain of P. papatasi and P. argentipes showed variations in their susceptibility to insecticides. Both the species were resistant to permethrin but tolerant to DDT and malathion with LD99.99 values of 13.88, 1.92, 1.08 and 34.63, 4.69, 16.32 times more than the deterministic doses respectively. However, they were susceptible to bendiocarb with LD99.99 7.6 and 1.6 times lower than the deterministic doses. While P. papatasi was susceptible to BHC, P. argentipes showed tolerance (1.6 times). The former showed tolerance to deltamethrin and the latter exhibited resistance (34 times). It was reverse in case of lamdacyhalothrin. High susceptibility of the vector sandflies to bendiocarb suggests that this insecticide could be used effectively against OP and pyrethroid resistant populations for Kalaazar control.

Biological control of malaria vectors.

A comprehensive review is presented of the potentiality of biocontrol agents viz. entomophagus bacteria (Bacillus thuringiensis var. israelensis and Bacillus sphaericus), fungi, microsporidians, predators and parasites against malaria vectors in the field condition. Unlike insecticides, these control agents are host specific and safer to the environment. However, barring fishes which are being used in certain situations, other biocontrol agents have not yet reached the operational stage. Two spore forming bacteria B. thuringiensis var. israelensis and B. sphaericus have been extensively tested against malaria vectors in the field. Though they are effective in suppressing anopheline larval population, their recycling capacity and availability of toxin hearing spores on the water surface are limited. Therefore, there is a need for developing improved formulations through bio-engineering techniques for enhancing their residual activity and availability of spores for anopheline larvae which feed mostly on the water surface. The biocontrol potentiality of other agents in the field condition is yet to be explored fully. The use of biocontrol agents for malaria control also poses certain operational constraints in view of the vastness of the anopheline breeding habitats and less acceptance for their use in domestic environments. However, there is a scope for using these biocontrol agents in conjunction with other control methods in integrated control programmes.

Breeding habitats of vector sandflies and their control in India.

In India Phlebotomus argentipes and Phlebotomus papatasi are the proven and suspected vectors of visceral leishmaniasis respectively. In the past, only a few samples from the field yielded sandfly immatures though there were many adults in the vicinity. This might be because of dearth of information on the various factors influencing the oviposition of the gravid females as well as survival and development of immatures. Therefore, available information on these aspects has been reviewed so as to highlight the imperative of undertaking further studies on the ecology of immatures in field conditions.

Insecticide impregnated cotton fabrics of different hydrophobicity against Aedes aegypti (Diptera:Culicidae).

Residual efficacy of synthetic pyrethroids, viz, permethrin, deltamethrin, lambdacyhalothrin and an insect repellent DEPA in cotton fabrics of different hydrophobicity was tested against Aedes aegypti. Amino silicone was used for enhancing the hydrophobicity of the fabrics. The results showed that there was an increasing trend in repellency/feeding deterrency with the increase in hydrophobicity up to 17.5 weeks at an optimum level of 30g/l. The adulticidal effect lasted for 1 to 4 weeks and this lower residual activity was attributed to the repellency of the treated fabrics. The results indicated that the residual efficacy of cotton fabrics could be enhanced by treating with an hydrophobic agent that increases the availability of the insecticide on the surface.

Bioefficacy of mosquito mat, coil and dispenser formulations containing allethrin group of synthetic pyrethroids against mosquito vectors.

The bioefficacy of mats, coils and dispensers containing allethrin group of synthetic pyrethroids was studied against laboratory strains of Culex quinquefasciatus, Aedes aegypti and Anopheles stephensi. Except esbiothrin in the mat formulation which was 100 and 178 times more effective against Cx. quinquefasciatus than against Ae. aegypti and An. stephensi with KT50 of 0.005, 0.5 and 0.89 min. respectively, all the three allethrins in mat or coil formulations were equally effective against the three vector mosquitoes. When compared to mat formulations of d-allethrin and bioallethrin, mat formulation of esbiothrin was 156 and 144 times more effective against Cx. quinquefasciatus. It was 162 times more effective against Cx. quinquefasciatus than in the coil formulation. Dispenser containing d-allethrin was the least effective against Cx. quinquefasciatus (KT50: 2.65 min.) and Ae. aegypti (KT50: 4.68 min.) but as effective as coil against An. stephensi. When mat and dispenser heated or coil burnt continuously for 10 hours the knockdown was consistently above 60% in all the three vector species but mortality was not consistently > 60% in Ae. aegypti. Repellent effect of the formulations ranged from 0.0 to 80.3%, 0 to 57.3% and 59.2 to 78.3% against Cx. quinquefasciatus Ae. aegypti and An. stephensi respectively. Repellency was more against An. stephensi than against the other two species. Mats and coils deterred > 50% of the mosquitoes from feeding on the chicken (range: 50 to 99.52%) but in case of dispenser the effect was only 14.72 to 65.01%. The use of these formulations as a control tools in reducing man-vector contact is discussed.

Toxicity of insecticides to Toxorhynchites splendens and three vector mosquitos and their sublethal effect on biocontrol potential of the predator.

Toxicity of six larvicides ie fenthion, temephos, malathion, deltamethrin, alphamethrin (Fendona), OMS 3031 and five adulticides ie malathion, fenitrothion, propoxur, deltamethrin, permethrin to Aedes aegypti, Culex quiquefasciatus, Anopheles stephensi and the predator, Toxorhynchites splendens was studied for evaluating safety margin. Concentrations of alphamethrin that killed 50% larvae of T. splendens were 53 and 12 times more than that which killed Cx. quinquefasciatus and Ae. aegypti. In case of deltamethrin, concentrations required to kill 50% larvae of T. splendens were 14 and 5 times more than that required against other two species. Other larvicides tested were equally toxic to both T. splendens and vector mosquitos. There was no significant difference in the toxicity of larvicides to T. splendens and An. stephensi. Deltamethrin was 25-132 times less toxic to adults of T. splendens in comparison to vector mosquitos. For other adulticides the range was 1-10. Immature developmental time of T. splendens was not affected by any of the insecticides tested. However, predation rate was lowered when larvae of Ae. aegypti previously exposed to fenthion and temephos were offered. Whereas, alphamethrin and OMS 3031 did not affect the feeding rate of the predator. There was a significant reduction in the pupal weight and pupation as a result of the predator feeding on the insecticide treated prey. There was a significant negative relationship between rate of pupation and dosage. The present study indicates that synthetic pyrethroids owing to their higher safety margin can be used in an integrated vector management program.

Insecticidal activity of some new synthetic compounds against different mosquito species.

Insecticidal activity of an organosilane (HOE 84498, OMS 3055), Organophosphorous (MAT 9460, OMS 3052) and a synthetic pyrethroid compound (Trebon, OMS 3002) was evaluated against adult and larval stages of eight species of mosquitoes. Insecticidal activity of these compounds was limited to larval stages only. Highest activity of HOE 84498 was found against both Cx. tritaeniorhynchus and Anopheles culicifacies (LC50-0.0065 mg/I), MAT 9460 against Armigeres subalbatus (LC50-0.00043 mg/I) and Trebon against Cx. quinuefasciatus (LC50-0.00579 mg/I). Adulticidal effect was observed at higher dosages of 25-100 ug/cm2 of MAT 9460 and HOE 84498 against all the species with LT50 ranging from 22.15-33.76 min. No appreciable residual effect was evident for the three compounds on the surfaces treated at the rate of 1-100 mg/m2 against any mosquito species.

Population interaction of Toxorhynchites splendens and Aedes aegypti (Diptera: Culicidae) in the laboratory.

Population interaction of Toxorhynchites splendens and Aedes aegypti in relation to the complexity of the breeding habitats and their initial number was studied in the laboratory. The predator and the prey were introduced in different ratios in the colony cages (1 m3) with different oviposition structures. Predator-prey interaction lasted for 5-9 weeks without structural complexity of the oviposition containers. When there was a structural complexity, their interaction lasted for 18 weeks. During the interaction period, Ae. aegypti number was at a lower level. Therefore, both structural complexities of the breeding sites and initial predator and prey number play a crucial role in establishing stable interaction between them at a lower threshold level for a longer period.

Cannibalism and carnivory in Toxorhynchites splendens (Diptera: Culicidae).

Laboratory reared larvae of Toxorhynchites splendens, which were previously starved for 24 hours, cannibalized eggs of their own kind or preyed upon the eggs of other species (Aedes aegypti and Anopheles stephensi) present on the surface of water in small containers. Second and third instars consumed eggs faster than first and fourth instars. The first instar consumed larvae of its own kind faster than the other instars, in the absence of other prey. However, when prey larvae were provided, there was a significant fall in the rate of cannibalism.

Evaluation of EMD vaporizers and bioallethrin vaporizing mats against mosquito vectors.

Different Electric-Mat-Device (EMD) vaporizers and bioallethrin impregnated mats were evaluated for the knockdown and mortality in the adults of Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti. Percentage knockdown of 80-100 was recorded throughout the test period of 11 hours. However, the percentage mortality observed was not appreciable in all types of EMD vaporizers. Device "A" was found to be effective only against Ae. aegypti. Devices "C" and "D" showed moderate effects against An. stephensi and Ae. aegypti. Only device "B" was found to give appreciable mortality in all three vector mosquito species compared to other devices which may be attributed to the uniform release rate (2 mg/hour) of bioallethrin.