Do colour and surface area of ovitrap influence the oviposition behaviour of Aedes aegypti, the vector of dengue and DHF?

A newly developed ovitrap made from a fiberglass tray (FGTO) was compared with conventionally used black jar ovitrap (BJO) in field condition in terms of number of eggs received. The number of eggs laid in FGTO was consistently higher than in BJO. The number of eggs collected in FGTO was significantly higher and it was 5-94 times more than that of BJO (t =9.45; p<0.0001). This finding has implication in designing lethal ovitraps for the control of dengue vectors.

Population interactions between Culex vishnui mosquitoes and their natural enemies in Pondicherry, India.

Population interactions among mosquitoes in the Culex vishnui subgroup, which are vectors of Japanese Encephalitis, and their natural enemies were studied in Pondicherry, India. We tested the hypothesis that the breakdown of interactions between the larvae and their natural enemies due to drought followed by rain was responsible for the sudden increase in the vector population above the threshold for disease transmission during the heavy rainy period. We randomly sampled mosquito larvae and their predators in different breeding habitats and subjected the mean densities of prey, predator, and mosquito larvae infected with parasites/pathogens to covariate analysis to understand the interaction between prey and their natural enemies in relation to environmental factors. In rice fields, neither prey nor predator showed any positive correlation with temperature, RH, or the number of rainy days. However, the pathogen/parasite of mosquito immatures showed a positive correlation with RH. Among the mosquito predators, notonectids exhibited a significant positive correlation with Cx. vishnui larvae. The parasitic Romanomermis iyengari and pathogenic Coelomomyces anopheliscus also showed positive correlations with immatures. No parasites and pathogens of mosquito larvae were recorded in shallow water pools (SWP) or cement tanks (CT) during the study period. Important predators recorded in SWP were notonectids, damselfly nymphs, Diplonychus indicus, and hydrophilids. Dragonfly nymphs, gerrids, and tadpole shrimps were recorded in CT. In CT, prey and their predators were positively correlated with RH and rainy days. In SWP, there was a highly significant correlation between prey, predators and environmental factors. We conclude that rice fields are a stable ecosystem where regular interaction occurs between larvae and their natural enemies and a sudden increase in mosquito populations is uncommon. In transient habitats, no such stability is present and they become more important as breeding habitats in terms of seasonality and number. Shallow water pools should be seriously considered for the control of these vectors.

Utility of expanded polystyrene (EPS) beads in the control of vector-borne diseases.

The use of chemicals or bio-larvicides for the control of Culex quinquefasciatus and Anopheles stephensi breeding in pit latrines and overhead tanks (OHT) respectively is discouraged owing to many undesirable impacts in the environment. Due to faecal contamination and poor survival, use of predatory fish in OHTs is not feasible. The use of expanded polystyrene (EPS) beads is a potential alternative in these habitats. EPS beads not only prevent oviposition but also kill the immature by forming a thick blanket on the water surface. A thick layer of 2 cm with beads of 2 mm is sufficient to suppress and prevent mosquito breeding. These are cheap, environmentally safe and do not need frequent application since they remain on the surface for quiet a long time. Successful trials against C. quinquefasciatus breeding in pit latrines, soakage pits, septic tanks, etc., have been carried out in Kenya, Zimbabwe and Tanzania. Certain trials with EPS indicated reduction in microfilaria (mf) rate besides decline in biting density. In India, EPS beads have also been used on small scale for the control of A. stephensi and A. culicifacies breeding in OHTs and unused wells respectively. The polystyrene beads have also been reported to be effective in the control of mosquito breeding in biogas plants and other industrial situations. The practical utility of EPS beads in the control of vector-borne diseases has been discussed in the present review.

Efficacy of two organophosphorus insecticides, Reldan & Dursban against the larvae of Culex quinquefasciatus.

BACKGROUND & OBJECTIVES: The resistance in vectors to conventional insecticides warrants development of newer insecticides for mosquito control besides use of other counter-measures. The present study was undertaken to test the efficacy of a new and toxicologically safe organophosphorus compound, Reldan (chlorpyrifos-methyl) and compare its efficacy with Dursban (chlorphyrifos-ethyl) against larvae of different mosquito vectors under laboratory conditions and against Culex quinquefasciatus in three larval habitats. METHODS: The susceptibility of larvae of mosquito vector species to Reldan and Dursban was determined by following the standard procedure and the LC50 in mg/l values were calculated by probit analysis. The insecticides were evaluated in the larval habitats of C. quinquefasciatus in and around Pondicherry. The percentage reduction in larval density was calculated using Mulla's formula and duration showing more than 80 per cent reduction was calculated by annotating the graph obtained by plotting percentage reduction in larval density against days of post-treatment. RESULTS: Dursban and Reldan were effective against Anopheles fluviatilis larvae at lower LC50 of 5.90 x 10(-7) and 1.07 x 10(-9) mg/l respectively compared to other species of mosquitoes. Dursban and Reldan were equally effective against Aedes aegypti, An. stephensi and An. culicifacies. Reldan was about nine times more effective than Dursban against C. quinquefasciatus with respective LC50 of 1.17 x 10(-4) and 1.34 x 10(-3) mg/l. Field evaluation of these insecticides against C. quinquefasciatus showed that Reldan and Dursban at the application rate of 500 g (ai)/ha reduced immature density by more than 80 per cent for a mean duration of 4.0 and 4.5 days and 4.6 and 3.7 days in cesspits and cement tanks respectively. In U-drains, at 500 g (ai)/ha, Reldan was effective for a period of 3.6 days whereas, Dursban was not effective. It was effective for 4.0 days only at 1000 g(ai)/ha. There was no significant increase in the residual activity of both Dursban and Reldan with increase in application rates. INTERPRETATION & CONCLUSION: In view of the lack of sustained control with the applications, it is inferred that these insecticides will be of limited use as larvicides against C. quinquefasciatus breeding in polluted habitats.

Efficacy of insect parasitoid Dirhinus himalayanus (Hymenoptera: Chalcididae) & insect growth regulator, triflumuron against house fly, Musca domestica (Diptera: Muscidae).

BACKGROUND & OBJECTIVES: In fly management programme chemicals are extensively used. Combined use of insect growth regulator (IGR) and parasitoids would yield a better reduction in fly density, as exposure of fly larvae to sub lethal dose of IGR enhances pupal duration and thereby increases the exposure time for parasitism. The objective of the present study was to explore the additive effect of both Dirhinus himalayanus, an insect parasitoid and triflumuron, an IGR in controlling house fly, Musca domestica. METHODS: In the field trial the study sites were allocated based on two-way ANOVA performed on one year pre-treatment survey. Parasitoid release and IGR treatment were initiated when the growth rate (lambda) of M. domestica was in an increasing trend. Parasitoids were released at a rate of 6 number/m2 for three months (February-April 2000), whereas IGR was applied at a dose of 10 mg/m2 at fortnightly interval from February to December 2000. Control efficacy was assessed using Mulla's formula. RESULTS: Reduction in puparia density was 59.29, 48.67 and 69.08 per cent respectively in areas, where parasitoids, ICR and combination of both IGR and parasitoids were used. Corresponding figures for adult population were 55.69, 49.71 and 77.14 per cent respectively. The per cent reduction in puparia and adult density was significantly (P<0.05) higher in the experimental areas than in the check. When the per cent reduction in adult and puparia density among different experimental areas was compared, it was observed that the reduction in fly density was significantly higher in the areas, where the combination of both parasitoid-IGR (P=0.00102) and IGR (P=0.03175) were used, while in areas where parasitoid (P=0.06191) were released the reduction in fly density was not significant. Similarly, there was a significant reduction in puparia density in areas where both parasitoid-IGR combination (P=0.0001) or IGR (P=0.002) were used, whereas in parasitoid (P=0.0612) released areas it was not significant. INTERPRETATION & CONCLUSION: The results show that the combined use of parasitoid and IGR is effective in reducing puparia and fly density. Therefore, for sustenance of an effective fly control programme, both parasitoid and IGR may be used.