Field evaluation of the biolarvicide, spinosad 20 per cent emulsifiable concentrate in comparison to its 12 per cent suspension concentrate formulation against Culex quinquefasciatus, the vector of bancroftian filariasis in India

Background & objectives: Biolarvicides may offer alternatives to chemical larvicides as these are known to be safe to environment and selective against the target species. However, only a limited number of biolarvicides have been approved for mosquito larval control. In the current study, a new formulation of spinosad, 20 per cent emulsifiable concentrate (EC) was tested for its efficacy against Culex quinquefasciatus, in comparison to its 12 per cent suspension concentrate (SC). Methods: Spinosad 20 per cent EC was tested against Cx. quinquefasciatus immature at 25, 50, 100 and 150 mg active ingredient (ai)/m[2] in cesspits, drains and abandoned wells in comparison with spinosad 12 per cent SC at the optimum field application dosage of 50 mg ai/m[2]. Results: The 20 per cent EC caused 90-100 per cent reduction of pupal density for 7-14 days in cesspits, 10-17 days in drains and 14-30 days in abandoned wells at all dosages tested. At lower dosages of 25 and 50 mg ai/m[2], >90 per cent reduction of pupal density was observed for one week in cesspits and street drains and for two weeks in abandoned wells. The effective duration of control provided by the higher dosages, 100 and 150 mg ai/m[2] was 1.4 to 2 times greater than the lower dosages, 25 and 50 mg ai/m[2]. Interpretation & conclusions: The findings showed that the spinosad 20 per cent EC can be used for larval control against Cx. quinquefasciatus, at the dosage of 25 mg ai/m[2] at weekly interval in cesspits and drains and at fortnightly interval in abandoned wells. Spinosad 20 per cent EC could be one of the options to be considered for larval control under integrated vector management.

Efficacy of three formulations of diflubenzuron, an insect growth regulator, against Culex quinquefasciatus Say, the vector of Bancroftian filariasis in India.

Background & objectives: Insect growth regulators (IGRs) offer alternatives to conventional chemical larvicides that pose problem of resistance and environmental safety. However, only a limited number of IGRs have been approved for use in mosquito control. In the present study, two new formulations of the IGR diflubenzuron, 2 per cent granular (GR) and 2 per cent tablet (DT) were tested for its efficacy against Culex quinquefasciatus, in comparison to its 25 per cent wettable powder (WP) formulation. Methods: The WP, GR and DT formulations were tested in cesspits, street drains and abandoned wells each at four dosages, 25, 50, 75 and 100 g ai/ha. Additionally, the DT formulation was tested at a higher dosage of 1 tablet/m2 (equal to 400 g ai/ha). Results: The WP and GR formulations yielded >80 per cent inhibition of adult emergence (IE) for 7-10 days in cesspits, 4-7 days in street drains and 7-21 days in abandoned wells at all dosages tested. The DT formulation was effective only at higher dosage 100 g ai/ha and or 1 tablet/m2 for 7-15 days at all habitats. Interpretation & conclusions: The trial showed that the dosage 25 g ai/ha of 25 per cent WP could be the field dosage for cesspits and wells, and 50 g ai/ha for drains, to be applied at weekly intervals. The dosages 25, 50 and 100 g ai/ha of 2 per cent GR could be the field dosages for application in cesspits at weekly intervals, in abandoned wells every three weeks and in drains at weekly intervals, respectively. Diflubenzuron 25 per cent WP and 2 per cent GR could be used for larval control of Cx. quinquefasciatus under integrated vector management programme.

Laboratory & field evaluation of controlled release formulation of the insect repellents N,N-diethyl-m-toluamide (DEET) & N,N-diethyl phenylacetamide (DEPA) against mosquito vectors.

BACKGROUND & OBJECTIVES: Repellents can play a useful role in reducing the man-vector contact and help in interrupting disease transmission. Newer formulations are necessary to improve the efficacy of the repellent on the treated sites for enhanced protection. METHODS: To determine the comparative efficacy, 20 per cent liposphere lotion formulation and 20 per cent alcohol solution of two insect repellents DEET and DEPA were evaluated for the extent of protection on rabbits against Aedes aegypti during the day in the laboratory and on human volunteers during the night against Culex quinquefasciatus in the urban areas of Pondicherry, India. RESULTS: In the laboratory, the lotion formulations of DEPA and DEET were found to enhance the repellency by 1.5 (4.00 to 6.00 h) and 1.25 (4.00 to 5.00 h) times respectively compared to the alcohol solution of the repellents against Ae. aegypti at the application rate of 0.5 mg/cm2. In the field, the lotion formulation of DEPA at 0.3 mg/cm2 could increase the protection time from 6.30 to 8.36 h (1.3 times) whereas the lotion formulation of DEET at 0.3 mg/cm2 could increase the protection time from 6.54 to 8.42 h (1.2 times). INTERPRETATION & CONCLUSION: In laboratory and field tests, the lotion formulations of both repellents were found to give a higher protection compared to alcohol solution. The lotion formulations of DEET and DEPA were found to be equally effective.

Observations on nocturnal activity and man biting habits of malaria vectors, Anopheles fluviatilis, An. annularis and An. culicifacies in the hill tracts of Koraput District, Orissa, India.

Biting and feeding behavior of malaria vectors were studied in nine villages (5 from Jeypore zone and 4 from Malkangiri zone) of Koraput District. Man biting catches comprised of 16 anopheline species including the incriminated vectors of this area: An. fluviatilis, An. annularis and An. culicifacies. An. fluviatilis was predominant and biting of this species recorded indoors throughout the year in both the zones. The period, during which the biting activity peaked, was different between the two zones and consequently the time of peak transmission was also different between the zones. The biting activity was at its peak between 21.00 and 03.00 hours in both the zones. However, in cold season the biting activity peaked in the first quarter of the night in Jeypore zone. The anthropophilic index (AI) of An. fluviatilis was 26.2% in Jeypore and 83.7% in Malkangiri and of An. culicifacies the AI was 0.4% in Jeypore and 7% in Malkangiri. Analysis of gonotrophic stages of night resting females indicated that in Jeypore zone, the majority of An. fluviatilis female left indoors for outdoor resting before the completion of gonotrophic cycle, but in Malkangiri, the females remained indoors till the end of the gonotrophic cycle. The presence of full-fed females in night resting catches in Jeypore village further suggested that the females do not leave the house immediately after taking blood meal but rest for some time.

Studies on dispersal of malaria vectors in a hilly tract of Koraput District, Orissa State, India.

Dispersal of malaria vectors was studied in a hilltop village in Koraput, a highly malarious district of Orissa. Immatures from terraced stream beds and day-time resting adults from artificially dug pit shelters, distributed centrifugally at different distances from the village were sampled. Breeding of Anopheles fluviatilis, An. annularis and An. culicifacies was found up to a distance of 1,700 m. Immature density of An. fluviatilis and An. culicifacies showed a negative correlation with the distance, but they were not statistically significant. The maximum distance at which An. fluviatilis adult females collected was 1,500 m. A significantly negative correlation was observed between An. fluviatilis resting females and distance. An. culicifacies adults were collected in low numbers even in the nearest pit shelters. No An. annularis was recorded from the pit shelters. The present record on the dispersal range of An. fluviatilis is estimated to be higher than that reported elswhere in India.

A note on the impact of mud plastering on the efficacy of DDT residual spraying in tribal villages of Koraput District, Orissa State.

A field trial was undertaken to study the impact of mud plastering on the efficacy of DDT spraying in two villages in Koraput district. In Maliguda village, where 95 per cent spray coverage was achieved and the spray surfaces were retained without mud plastering up to 29 and 60 days in first and second round of the spray respectively, malaria cases reduced by 72 per cent after spray for a period of two months. In Dandabedha village with 85 per cent coverage and immediate mud plastering, the malaria cases reduced by 49 per cent. It is concluded that even though mud plastering reduces the effectiveness of the residual spraying to a certain extent, timely spray and better coverage with correct dosage can still effectively reduce the malaria incidence.

Pattern of rice cultivation and anopheline breeding in Koraput district of Orissa state.

The potentiality of rice fields in anopheline vector breeding in Koraput district was studied in two agricultural seasons--rubi and kharif. Altogether, 17 species were recorded from the rice fields. The terraced stream bed paddy-fields with a perceptible water flow in top-hill areas support heavy breeding of the principal vector A. fluviatilis at all stages of paddy growth. A. culicifacies and A. annularis breeding became scarce when the paddy plants reached a height of 80 cm. Vector species formed 2 per cent in rabi and 32 per cent in kharif of the anopheline fauna from the paddy fields and the maximum production was during early stage of paddy growth or after harvesting.

Anopheline fauna of Koraput district, Orissa state, with particular reference to transmission of malaria.

The anopheline fauna was surveyed in Koraput district of Orissa, which is highly malarious. A total of 62,086 anophelines belonging to 22 species and two varieties were collected, including eight species of anophelines which are recognized malarial vectors in India. Anopheles sergenti, A. pulcherrimus, A. jeyporiensis var candidiensis and A. annularis var adiei was recorded for the first time in this area. A total of 24154 mosquitoes were dissected and 18 mosquitoes belonging to four species, A. fluviatilis. A. annularis, A. culicifacies and A. aconitus were found with the gut/gland infection.

Prevalence of bancroftian filariasis & its control by single course of diethyl carbamazine in a rural area in Tamil Nadu.

The prevalence of microfilaraemia, clinical spectrum of bancroftian filariasis and vector potential were studied in Vettavalam village in North Arcot district of Tamil Nadu. The effectiveness of selective therapy with diethyl carbamazine (DEC) in controlling filariasis in rural areas was also evaluated. The prevalence of microfilaraemia (mf rate) and disease (disease rate) was found to be 11.7 and 11.09 per cent respectively. Hydrocele was the dominant clinical sign in males and lymphoedema in females. The density of the vector Culex quinquefasciatus was 25.44 females/man-hour, and the infection and infectivity rates were 18.16 and 1.09 per cent respectively. All mf carriers detected after the mass blood survey were given a single course of DEC at the dosage of 6 mg/kg of body wt/day for 12 days. Only 61.6 per cent of them took the full course of DEC treatment. DEC therapy brought down the mf rate from 11.7 to 5.84 per cent after one month. In the absence of further treatment, there was no significant change in mf prevalence after one year.