Occurrence of five distinct clades of mermithid nematodes (Nematoda: Mermithidae) infecting black fly larvae (Diptera: Simuliidae) in tropical streams in Malaysia.

Mermithids are the most common parasites of black flies and are associated with host feminization and sterilization in infected hosts. However, information on the species / lineage of black fly mermithids in Southeast Asia, including Malaysia requires further elucidation. In this study, mermithids were obtained from black fly larvae collected from 138 freshwater stream sites across East and West Malaysia. A molecular approach based on nuclear-encoded 18S ribosomal RNA (18S rRNA) gene was used to identify the species identity / lineage of 77 nematodes successfully extracted and sequenced from the specimens collected. Maximum likelihood and neighbor-joining phylogenetic analyses demonstrated five distinct mermithid lineages. Four species delimitation analyses: automated simultaneous analysis phylogenetics (ASAP), maximum likelihood Poisson tree processes with Bayesian inferences (bPTP_ML), generalized mixed yule coalescent (GMYC) and single rate Poisson tree processes (PTP) were applied to delimit the species boundaries of mermithid lineages in this data set along with genetic distance analysis. Data analysis supports five distinct lineages or operational taxonomic units for mermithids in the present study, with two requiring further investigation as they may represent intraspecific variation or closely related taxa. One mermithid lineage was similar to that previously observed in Simulium nigrogilvum from Thailand. Co-infection with two mermithids of different lineages was observed in one larva of Simulium trangense. This study represents an important first step towards exploring other aspects of host - parasite interactions in black fly mermithids.

Natural infections and distributions of parasitic mermithids (Nematoda: Mermithidae) infecting larval black flies (Diptera: Simuliidae) in tropical streams of Malaysia.

Mermithids are parasites of black flies that cause host mortality along with physical and behavioural changes in infected hosts. However, there is a lack of knowledge on the distribution of mermithids infecting black fly larvae and the factors that influence these distributions in Asia, including Malaysia. A total of 13,116 mid- to late-instar black fly larvae belonging to 42 species were collected from 138 streams across East and West Malaysia and screened for the presence of mermithid parasites. Overall, 121 mermithids were obtained from 107 (0.82%) larvae of nine (21.4%) black fly species. The average number of mermithids per black fly host was 1.10 ± 0.04 (SE), ranging from one to three mermithids per host. Mermithid infection was highest in Simulium trangense, with a frequency of occurrence of 6.5%, followed by S. cheongi (5.8%) and S. angulistylum complex (2.9%). Infection was lowest in S. brevipar and S. tahanense, with a frequency of occurrence of 0.7% each. Regression analysis indicated that mermithid infections in larval black flies were significantly associated with cooler and shallower streams with more canopy cover, dense riparian vegetation, high dissolved oxygen, and lower conductivity and complete pH. Forward logistic regression further indicated that infections in S. cheongi were associated with shaded, cooler, slightly acidic streams with higher conductivity and dissolved oxygen. These findings suggest that mermithid infections in larval black flies in Malaysia are not randomly distributed and are influenced by the breeding habitat of their hosts.

Microfungi Associated with Pteroptyx bearni (Coleoptera: Lampyridae) Eggs and Larvae from Kawang River, Sabah (Northern Borneo).

Overlooking the importance of insect disease can have disastrous effects on insect conservation. This study reported the microfungi that infect Pteroptyx bearni eggs and larvae during ex-situ rearing project. Two different species of microfungi that infected the firefly's immature life stages were isolated and identified. Penicillium citrinum infected the firefly's eggs while Trichoderma harzianum infected the firefly during the larval stage. Both microfungi species caused absolute mortality once infection was observed; out of 244 individual eggs collected, 75 eggs (32.5%) were infected by Penicillium citrinum. All 13 larvae that hatched from the uninfected eggs were infected by Trichoderma harzianum. This study was the first to document the infection of Pteroptyx bearni's eggs and larvae by Penicillium citrinum and Trichoderma harzianum.