Background: Drastic increases of dengue fever (DF) over the past few years have prompted studies on the development of resistance to insecticides in the mosquito vector, Aedes aegypti (Linnaeus). In Sri Lanka control of the vector population is essentially achieved using larvicides (temephos) and adulticides (principally pyrethroids). The present study investigates resistance to commonly used insecticides and underlying mechanisms of Ae. aegypti in selected sites in Sri Lanka. Methods: In this study, susceptibility to three commonly used adulticides (malathion, permethrin and deltamethrin) and the larvicide temephos were tested for Ae. aegypti sampled from five localities in Sri Lanka using WHO dose diagnostics tests. In addition, we performed dose-response tests for permethrin to determine lethal concentrations (LCs) with CDC bottle bioassays. An assessment of the activity of metabolic detoxifying enzymes (multifunction oxidases (MFOs), glutathione S-transferases (GSTs) and esterases) and determination of frequency of the kdr mutations (F1534C, V1016G and S989P) were also carried out to ascertain the associated resistance mechanisms. Kdr genotype frequencies were compared with samples collected from the same sites in 2015 to determine the change of allele frequencies over the years. Results: The present study revealed resistance in all Ae. aegypti populations studied, with low mortality percentages for both permethrin (10-89%) and deltamethrin (40-92%). Dose response tests revealed highest resistance ratios (RR) for permethrin and temephos from Colombo district whereas Puttalum district exhibited the lowest. High frequencies of the 1534C allele (0.052-0.802) were found in the study sites in 2017. Comparison with samples collected in 2015 revealed a substantial increase in this allele. The activity of MFOs and p-nitro phenyl-acetate esterase was significantly greater in most Sri Lankan populations in comparison to that of the New Orleans (NO) susceptible strain. In contrast, the activity of α-esterase and β-esterase was similar or lower than that in the NO strain.

Phylogeographic relationships among global collections of the mosquito Aedes aegypti were evaluated using the mitochondrial Cytochrome C Oxidase 1 (CO1) and NADH dehydrogenase subunit 4 (ND4) genes including new sequences from Sri Lanka. Phylogeographic analysis estimated that Ae. aegypti arose as a species~614 thousand years ago (kya) in the late Pleistocene. At 545 kya an "early" East African clade arose that continued to differentiate in East Africa, and eventually gave rise to three lineages one of which is distributed throughout all tropical and subtropical regions, a second that contains Southeast Asian/Sri Lankan mosquitoes and a third that contains mostly New World mosquitoes. West African collections were not represented in this early clade. The late clade continued to differentiate throughout Africa and gave rise to a lineage that spread globally. The most recent branches of the late clade are represented by SouthEast Asia and India/Pakistan collections. Analysis of migration rates suggests abundant gene flow between India/Pakistan and the rest of the world with the exception of Africa.

In Sri Lanka, dengue is the most serious arboviral disease. Recent increases in dengue cases suggest a higher infection rate and spread of the disease to new areas. The present study explores gene flow patterns of Ae. aegypti, the main vector of dengue disease, among 10 collection sites including major ports and inland cities using variations at 11 microsatellite loci. Discriminant analysis of principal components (DAPC) and k-means clustering estimated eight genetic clusters. Analysis of Molecular Variance (AMOVA) estimated equal variances among cities and among collections in Colombo, Sri Lanka. Significant evidence, although weak, was detected for isolation by distance. Analysis of gene flow rates and directions using MIGRATE-n indicated that populations throughout the island served as a source of immigrants for Colombo with abundant gene flow among major commercial cities in Sri Lanka, which appear to receive migrant mosquitoes from throughout Sri Lanka. The observed patterns probably arise through human movement of Ae. aegypti during commerce from throughout Sri Lanka into Colombo increasing the risk of spread. The patterns uncovered in this study are significant for global health as Sri Lanka is situated along a key international shipping route.

Among the cereals, rice is the most important staple food supplying energy requirements for most of the worlds' population. However during storage a loss of about 10-20% rice grains occurs due to stored grain pests. Repellents are considered as the best source of protection against insect attack upon stored products as they have potential for the exclusion of stored product pests from grain, and thereby preventing insect feeding and oviposition on food materials. Various plant materials have been utilized effectively through time as safe and ecofriendly insect pest control measures due to their repellent activity. The aim of the present study was to investigate the potential of powdered leaves and leaf extracts of Olax zeylanica as repellents against the rice weevil, Sitophilus oryzae. All the experiments were carried out under laboratory conditions using 1-7 day old unsexed adults. Four different doses (1.0g, 3.0g, 5.0g and 7.0g).of powdered leaves were tested for fumigant repellency in a dual-choice bio-assay apparatus. Repellent action of leaf extracts was evaluated by means of an area preference test using methanol, ethanol and n-hexane as solvents. Repellent effect of powdered leaves against the adult rice weevils was found to be significantly high (P< 0.05) at all doses. The highest repellent effect was produced by 7.0g of leaf powder resulting in repellency of 97%, while the lowest dose (1.0g) also elicited more than 50% repellency in weevils indicating a very strong repellent action of the powdered leaves. In comparison, methanol extract of leaves produced the highest repellent effect (96%) on weevils whereas n-hexane extract elicited the lowest. Nevertheless, at higher concentrations all three extracts produced more or less significantly similar repellent effect on the weevils. The findings of the present study suggest that certain active materials of Olax zeylanica leaves have potential to act as a grain protectant and may be exploited for the control of Sitophilus oryzae in rice storage in an environment-friendly way.

Parasitism leads to severe economic losses to marine fish exports in Sri Lanka. Swordfish is a seasonal species with high demand both locally and internationally. Presence of a parasite in their flesh confuses the suppliers with zoonotic Anisarkis spp. This study is aimed to identify the plerecercoid parasitic larvae found in swordfish and establish a feasible method of diagnosis at fish processing factories. Parasites buried in frozen swordfish (Xiphias gladius) muscles were isolated and stored in cold sea water. Samples were washed with normal saline water and observed under bright field light microscope at 40x and 100x magnifications, and the parasites were identified based on their morphological features. For further confirmation, confocalmicroscope was used to record scolex parameters. Total length of the parasites was 1.7 cm-3.5 cm (2.27 cm). Presence of the elongated, acraspidote scolex (length 6.23 mm, width at pars bothridialis 2.4 mm) with four tentacular armature and curved, apically inverted, thick edged bothridia confirmed the parasitic larvae belonged to the Order Trypanorhyncha. Corona of falciform hooks in the basal armature and the heteromorphous hooks in a half spiral arrangement at metabasal armature are characteristics of the genus Molicola. This is the first record of the Trypanorhynch plerocercoid larvae (genus:Molicola) isolated in swordfishes from Sri Lanka. This study emphasizes that morphological examination of the parasite scolex using bright field microscopy will be helpful to distinguish the parasitic genera and feasible to use in the fish processing factories.