IRSPAS 2018
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Item Effect of aqueous extracts of Annona glabra plant and extracellular metabolites of two Trichoderma species on the survival of larval Culex quinquefasciatus and eggs of Aedes aegypti(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Aberathna, A. A. A. U.; Ranasinghe, H. A. K.; Rajapaksha, R. D. T.; Amarasinghe, L. D.Phytochemicals constitute a rich source of bioactive chemicals and some microbial products carry selective toxicity to many insect species, hence those are considered as alternatives to chemical insecticides. This study aimed to determine the potential of concentration gradient of Annona glabra aqueous leaf and fruit extracts for the mortality of third instar larvae of Culex quinquefasciatus; and to determine the ovicidal activity of extracellular metabolites of Trichoderma harzianum and Trichoderma viride at concentration gradient of 100, 200, 300, 400, 500 g/L on field collected eggs of Aedes aegypti with four replicates including controls for all bioassays. For the bioassays, aqueous crude extraction of plant materials was done by overnight shaking and extraction of extracellular metabolites of T . harzianum and T . viride was done using Richard ’ s broth . Study revealed that LC50 for A . glabra aqueous leaf extract for third instar larvae of Cu . quinquefasciatus was 16.26 g/L and 8.29 g/L in 24 hr and 48 hr exposure respectively (Minitab 14, Probit analysis). LC50 for A . glabra aqueous fruit extract, for third instar larvae of Cu . quinquefasciatus were higher than the LC50 for A . glabra leaf extract; 422.54 g/L and 114.01 g/L in 24 hr and 48 hr exposure respectively. 100% mortality was observed in mosquito larvae under 69.86 g/L of leaf and 1000g/L of fruit extract treatments after 24 hours of exposure. Mosquito larvae mortality compared to those in the control group reveals that the mortality of mosquito larvae may be due to the toxic compounds found in the plant. Although literature has shown that most Trichoderma strains produce volatiles and non-volatile toxic metabolites, significant ovicidal activity of extracellular metabolites of T . harzianum and T . viride on field collected eggs of Ae . aegypti was not observed (One-Way ANOVA; P>0.05) after 24 hr of exposure. The results of the study revealed that, both A . glabra fruit and leaf extracts are potential mosquito larvicides for Cu . quinquefasciatus. This may contribute to the formulation of an environmentally friendly measure to control Cu . quinquefasciatus vector mosquito species, which is a vital need to overcome the use of synthetic insecticides.Item Prevalence of micro-fauna associated in rice field habitats in Kurunegala district in Sri Lanka and potential mosquito larvicidal effect of Vorticella microstoma(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Ranasinghe, H. A. K.; Amarasinghe, L. D.Micro-fauna are associated with most of the mosquito larval breeding habitats in tropical climate. There may be parasitic, pathogenic or even predatory species among these biota to mosquito larvae and their potential use against mosquitoes is a new avenue of study in vector control. Rice fields are common breeding sites for certain vector mosquito species in Sri Lanka. The objective of the present study was to find the prevalence of micro-fauna in order to search for potential parasitic or pathogenic taxa/ species associated with mosquito larvae inhabiting rice field breeding habitats and to carry out bioassays for potential taxa. Sampling was done from paddy fields (n=12) in Kurunegala district using a metal larval scooper and the samples were preserved using Rose Bengal solution. Twelve micro-fauna species were recorded; the highest abundance was recorded from Vorticella microstoma (62.68%). Other micro-fauna species recorded were Zoothamnium sp., Diurella stylata, Keratella valga, Lecane luna, Monostyla bulla, Philodina citrina, Acanthocystis aculeata, Canthocamptus staphylinus, Daphnia longis, Notholca acuminata, Arcella arenaria . Also, 98 . 60 % of mosquito larvae which were collected from rice fields belonged to the genus Culex . Culex gelidus and Culex tritaeniorynchus represented the majority of samples (76.26%) and the highest abundance was recorded from Cu . gelidus . Study revealed that Vorticella microstoma trophont stage was lethal to Cu . tritaeniorynchus and Cu . quinquefasciatus larvae. Bioassay resulted that, 32.14% of Cu . quinquefasciatus died 05 days after infection with lab maintained V . microstoma cultures . Pupation was also delayed compared to the duration of normal life-cycle and only 10.71% of population emerged as adults. 100% mortality was recorded from Cu . quinquefasciatus in 2 days of infection with V . microstoma. The mean mortality percentage of two mosquito species studied were significantly different from each other (IBM SPSS Software, One-Way ANOVA: P<0.05). Trophonts of V . microstoma were infected to thorax, abdominal segments and anal papillae regions of larvae. The results of study revealed that Vorticella microstoma could be used as killing agent of mosquito larvae in future studies and would be a new avenue to work on environmentally agreeable manner in reducing the Culex spp . mosquito populations .