Abandoned boats contribute to spread of Aedes and Culex vector mosquitoes in coastal belt, Galle District, Southern Sri Lanka

Background & objectives: Although, the number of considerable cases of dengue and lymphatic filariasis have been reported from Galle District, Sri Lanka in the past several years, contribution of abandoned boats to spread vector mosquitoes of Aedes and Culex in the coast is not well studied. Our aim was to assess the positive composition of different types of abandoned boats by larval vector mosquitoes to investigate their occurrence and habitat preference, and the monsoonal and co-existence variation of Aedes mosquitoes. Methods: The 4th instar larvae of Aedes and Culex species from three different abandoned boat types in nine subsampling sites at three municipal areas in Galle District were collected during 2017–2019. In total, 15 sampling rounds were conducted in each site for three years duration as five sample rounds per year. Larval collections and identifications were carried out using standard techniques and identification keys according to WHO guidelines. The occurrence of mosquito larvae was analysed by boat type, locations within area and year. Further, the average infestation variation of Aedes mosquitoes were compared with monsoonal and co-existence changers. Results: Out of the total abandoned boats, majority (51%) were engine boats and, 32.7%, 16.35% were troller boats and canoe boats, respectively. Troller boats were highly infested boat type for vector mosquitoes. Aedes albopictus was the dominant vector in abandoned boats other than recorded Ae. aegypti and Culex quinquefasciatus. Culex quinquefasciatus showed comparatively low infestation percentages. The average infestation of Ae. albopictus showed a consistent pattern with monsoon variation. A competitive rapid invasion of Aedes aegypti was observed with the suppressing Ae. albopictus in abandoned boats after 2018. Interpretation & conclusion: Abandoned boats contribute noteworthy to spread of Aedes and Culex vector mosquitoes in coastal belt, Galle District. These study findings would be helpful for researchers and health authorities to design appropriate vector control measures and to mitigate future dengue and filariasis outbreaks

Avaliação comparativa da eficiência de armadilhas para a captura e coleta de Aedes aegypti em condições de campo / Comparative evaluation of trap efficiency for the capture and collection of Aedes aegypti under field conditions

Resumo Introdução Estudos que aperfeiçoam e/ou aferem a capacidade de armadilhas na detecção de vetores auxiliam sobremaneira o processo de controle das doenças causadas por eles. Objetivo Objetivou-se comparar quatro tipos de armadilhas para captura/coleta de A. aegypti em condições de campo e avaliar a influência da temperatura e precipitação na eficiência destas armadilhas. Método Armadilhas ovitrampas (papel-filtro e paleta), mosquitéricas e MosquiTRAP ® foram instaladas em 10 quarteirões, que recebiam, em cada uma de suas faces, um tipo destas armadilhas. Foram calculados índices entomológicos qualitativos e quantitativos para todas as armadilhas. Resultados A armadilha mosquitérica apresentou o menor índice de positividade (3%). Apenas os índices IPAaegypti e IDAaegypti demonstraram relação positiva com a temperatura e a precipitação, respectivamente. As armadilhas ovitrampas tiveram até 6,6 vezes maiores chances de positividade para A. aegypti quando comparadas com as MosquiTRAP ®, sem diferença significante entre os substratos papel-filtro e paleta. Conclusão As armadilhas ovitrampas apresentaram os melhores índices para serem utilizadas na vigilância do A. aegypti. É recomendado de forma imperativa o uso do papel-filtro como substrato para oviposição, pelo seu menor custo, maior facilidade de confecção, transporte e armazenamento, além da melhor visibilidade dos ovos depositados.

Abstract Background Studies that improve and/or assess the ability of traps in vector detection, facilitate the control of diseases caused by these vectors. Objective The objective of this study was to compare four types of traps for A. aegypti capture and collection under field conditions, and to evaluate the influences of temperature and precipitation on the efficiency of these traps. Method Ovitraps (filter paper and palette), "mosquitéricas" and MosquiTRAP® were installed in 10 city blocks, which received on each face, one type of trap. Qualitative and quantitative entomological indices were calculated for all traps. Results The "mosquitéricas" trap had the lowest positivity index (3%). Only the IPAaegypti and IDAaegypti indices showed a positive relationship with temperature and precipitation, respectively. The ovitraps had up to 6.6 times more chances of positivity for A. aegypti when compared to MosquiTRAP®, with no significant difference between the filter paper and the palette substrates. Conclusion The ovitraps presented the best indices to be used in the surveillance of A. aegypti . The recommendation to use filter paper as a substrate for oviposition is imperative because of its lower cost, easier manufacturing, transport and storage, as well as better visibility of the deposited eggs.

Laboratory observations on the larvicidal efficacy of three plant species against mosquito vectors of malaria, Dengue/Dengue Hemorrhagic Fever (DF/DHF) and lymphatic filariasis in the semi-arid desert.

Comparative larvicidal efficacy of aqueous and organic solvent extracts from seeds, leaves and flowers of three desert plants viz. Calotropis procera (Aiton), Tephrosia purpurea (L.) Pers. and Prosopis juliflora (Sw.) DC. was evaluated against Anopheles stephensi (Liston), Aedes aegypti (Linnaeus) and Culex quinquefasciatus (Say). For this purpose larvae of all the three mosquito species were reared in the laboratory and studies carried out on late 3rd or early 4th instars using standard WHO technique. Based on concentration mortality data 24 and 48 hr LC50 and LC90 values along with their 95% fiducial limits, regression equation, chi-square (c2)/ heterogeneity of the response were determined by log probit regression analysis. Experiments were carried out with different solvent extracts of seeds of C. procera which revealed that methanol (24 hr LC50: 127.2, 194.8, 361.0) and acetone (229.9, 368.1, 193.0 mg l-1) extracts were more effective with the three mosquito species, respectively. Petroleum ether extract was effective only on An. stephensi while aqueous extracts were not effective at all with any of the mosquito species (mortality <10-30%). Tests carried out with methanol extracts of fresh leaves (24 hr LC50: 89.2, 171.2, 369.7) and flowers (24 hr LC50: 94.7,617.3, 1384.0 mg l-1) of Calotropis showed that preparations from fresh parts were 2-3 times more effective as compared to the stored plant parts. Efficacy was less than 10-30% with both An. aegypti and Cx. quinquefasciatus while An. stephensi was still susceptible to extracts from both leaves and flowers even after two years of storage. The 24 hr LC50 values as observed for methanol extracts of seeds of T. purpurea and leaves of P. juliflora were 74.9, 63.2 and 47.0 and 96.2, 128.1 and 118.8 mg l-1 for the above three mosquito species, respectively. Experiments carried out up to 500 mg l-1 with leaves (T. purpurea) and seeds (P. juliflora) extracts show only up to 10-30% mortality indicating that active larvicidal principle may be present only in the seeds of Tephrosia and leaves of Prosopis. In general, anophelines were found more susceptible than the culicines to the plant derived derivatives. More studies are being carried out on some other desert plants found in this arid region. The study would be of great importance while formulating vector control strategy based on alternative plant based insecticides in this semi-arid region.

Evaluation of larvicidal efficacy of Solanum xanthocarpum storage against vector mosquitoes in north - western Rajasthan.

Efficacy of the methanol extracts from fruits without seeds, whole yellow ripe fruits and seeds of the plant Solanum xanthocarpum was evaluated against larvae of Anopheles culicifacies, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important vector mosquitoes prevalent in the arid region. Experiments were carried out on late 3rd or early 4th instar larvae of these mosquitoes using standard WHO technique. 24 and 48 hr LC50 and LC90 values along with their fiducial limits, regression equation, chi-square (x2)/ heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for fruit without seeds, whole fruits and seeds after six months were 79.6, 91.7 and 131.7; 131.4, 186.9 and 195.6; 273.4, 290.9 and 377.6 and 384.9, 450.6 and 520.0 mgl-1 for An. culicifacies, An. stephensi, Ae. aegypti and Cx. quinquefasciatus respectively. However, the 24 hr LC50 values for fresh yellow ripe fruits and seeds determined previously were 51.6 and 66.9; 52.2 and 73.7; 118.3 and 123.8 and 157.1 and 154.9 mgl-1 for the above four vector species respectively showing that the efficacy was decreased two to three times more after six months of storage. The 24 hr LC50 values were also determined after one year of storage for fruit without seeds, whole fruits and seeds. The values were 103.3, 120.1 and 195.7; 146.3, 224.3 and 251.2; 316.9, 336.5 and 426.2 and 393.0, 500.3 and 656.7 mgl-1 as compared to the 24 hr LC50 values of 47.4,51.6 and 66.9; 52.3,52.2 and 73.7; 108.0,118.3 and 123.8 and 141.1, 157.1 and 154.9 mgl-1 of all the three fresh preparations for the above four vector species respectively showing that the efficacy was further decreased after one year of storage. Further the extracts should be used when they have been prepared from the fresh plant parts instead of the old stored parts. Larvae of anophelines were found more susceptible as compared to culicine. HPLC and IR studies showed that active component might be present in the fruits and seeds of this plant species. The study would be of great importance while planning vector control strategy based on alternative plant derived insecticides.

Larvicidal activity of the extracts from different parts of the plant Solanum xanthocarpum against important mosquito vectors in the arid region.

Larvicidal efficacy of the aqueous and methanol extracts from green unripe and yellow ripe fruits, seeds, leaves and roots of the plant Solanum xanthocarpum was evaluated against Anopheles culicifacies, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus, the important mosquito vectors prevalent in the arid region. Studies were carried out on late 3rd or early 4th instar larvae of these species using standard WHO technique. Based on concentration mortality data LC50 and LC90 values along with their fiducial limits, regression equation, chisquare (l2)/ heterogeneity of the response have been determined by log probit regression analysis. The 24 hr LC50 values as observed for aqueous extracts for green unripe and yellow ripe fruits were 112.7, 498.2 and 846.3 mgl-1 and 104.7, 267.7 and 832.2 mg l-1 for Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus respectively. However, the 24 hr LC50 values for methanol extracts of yellow ripe fruits and seeds were 51.6, 52.2, 118.3 and 157.1 mg l-1 and 66.9, 73.7, 123.8 and 154.9 mg l-1 for the above four vector species respectively. The results showed that larvae of anophelines were much more susceptible as compared to culicines to both the aqueous and methanol extracts from fruits and seeds of the plant tested. The methanol extracts were found 2-5 times more effective as compared to the aqueous extracts. The chi-square values calculated during the analysis did not show any heterogeneity of the response. Experiments conducted with aqueous and methanol extracts from leaves and roots of this plant species didn’t show any larvicidal activity against any of the mosquito species tested. The study would be of great importance while formulating vector control strategy based on alternative plant based insecticides.