Sand fly colony crash tentatively attributed to nematode infestation

Authors: Temeyer, Kevin

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary: Laboratory colonies of pest organisms greatly facilitate research investigations of pest biology and development of potential pest control technologies. However, maintenance within a densely populated environment can lead to rapid spread of pathogens throughout the colony population, decimating colony numbers and productivity. A laboratory colony of sand flies used for research directed to identify novel insecticides and repellents was maintained for several years without any notable difficulties until suddenly, a precipitous drop in the numbers of newly emerging sand flies was noted. Colony productivity dropped from over 10,000 flies/week to less than 100 flies/week. Although mites had been regularly observed in the sand fly larval medium, they did not appear to cause any severe productivity issues, however, tiny threadlike worms were observed in the larval medium that had not previously been seen. DNA was isolated from nematode worms collected from the larval medium, and specific universal primers for ribosomal DNA genes were used to amplify and sequence the nematode ribosomal DNA. Computer searches through ribosomal DNA sequence databases gave a tentative match for a novel nematode that had been previously described only once. Nematode worms were collected and sent to Dr. Ernest Bernard at the University of Tennessee for expert identification, who identified the nematodes as Tricephalobus steineri, based on morphological characteristics of the nematode esophagus and male copulatory apparatus. We hypothesized that the nematodes had contaminated rabbit dung used to prepare the sand fly larval medium. Replacement of rabbit dung from a new, clean source restored sand fly colony productivity within 2 generations.

Technical Abstract: Maintenance of laboratory colonies of insects and other arthropod pests offers significant research advantages. The availability, age, sex, housing conditions, nutrition, and relative uniformity over time of biological material for research facilitates comparison of results between experiments that would otherwise be difficult or impossible. A laboratory research colony of Phlebotomus papatasi (Scopoli), old world sand flies, was maintained with high colony productivity for a number of years, but within a relatively short (4-6 months) time period, colony productivity declined from over 10,000 flies/week to less than 100/week. Mites and nematodes were both visible in the larval medium, however, the mites had been present throughout high productivity periods, therefore it seemed reasonable to investigate the nematodes. PCR amplification of 18S rRNA yielded a clean cDNA sequence identified by BLAST search as Procephalobus sp. 1 WB-2008 small subunit ribosomal RNA gene, GenBank Accession EU543179.1, with 475/477 nucleotide identities. Nematode samples were collected and identified as Tricephalobus steineri, based on morphological characteristics of the esophagus and the male copulatory apparatus. Mites (Tyrophagus putrescentiae) may have played an additional predatory role in the loss of sand fly colony productivity. We hypothesized that the origin of the nematode infestation was rabbit dung from a local rabbitry used in preparation of the larval medium. Colony productivity was fully restored within 3 months (2 sand fly generational periods) by replacement of the rabbit dung from a clean source for use to prepare sand fly larval medium.