Submitted to: Russian Entomology Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2008
Publication Date: 8/30/2008
Citation: Kline, D.L. 2008. A comparison of a new centrifuge sugar flotation technique with the agar method for the extraction of immature Culicoides (Diptera: Ceratopogonidae) life stages from salt marsh soils. Russian Entomological Journal. 17(1):75-80.
Interpretive Summary: A major emphasis of research by scientists in the Mosquito and Fly Research Unit at the Center for Medical, Agricultural and Veterinary Entomology (CMAVE), Gainesville, FL, is the development of surveillance technologies for mosquitoes and other biting flies. Culicoides biting midges are severe nuisance pests of humans and livestock. The immature stages are difficult to detect and sample because they are found in several inches deep in semiaquatic habitats such as salt marsh substrates. This study was conducted to develop a new method to remove biting midge immature stages from salt marsh substrates. A comparison was made between a traditional agar extraction method and a new centrifuge flotation developed at CMAVE. The CSFE technique proved to be advantageous because greater numbers of immatures were collected with less substrate. As a result this technique allowed more samples to be taken over a larger area with less effort.
Technical Abstract: Two sampling techniques, agar extraction (AE) and centrifuge sugar flotation extraction (CSFE) were compared to determine their relative efficacy to recover immature stages of Culicoides spp from salt marsh substrates. Three types of samples (seeded with known numbers of larvae, homogenized field samples with approximately equal numbers of immatures and regular field samples with an unknown number of immatures) were evaluated. Two substrate sample sizes were used (100 ml and 1000 ml). Agar extraction was used with both sample sizes, but CSFE was only used with the 100 ml size. The seeded samples were inoculated with 3rd-4th instar larvae at 5 levels (0, 25, 50, 100 and 200 larvae/sample). Mean per cent recovery was similar at all inoculation rates within each extraction technique, but the CSFE recovered 95.7% compared to 35.3% for AE1000 and 16.7% for AE100. For the homogenized samples, on a per sample basis, the AE1000 method recovered ca. 2X more immatures than the CSFE, but on a mean number of immatures recovered/ml basis, CSFE recovered 5.2X more than AE1000. Similarly, for the regular field samples, on a per sample basis the AE1000 method recovered ca. 1.5X more immature stages than samples processed by CSFE, but on the immatures/ml of substrate basis the CSFE method recovered ca. 6.6X more than AE1000. Overall, on a per ml basis the AE100 and AE1000 recovered an approximately equal number of immatures. The CSFE technique proved to be advantageous because greater numbers of immatures were collected with less substrate. As a result this technique allowed more samples to be taken over a larger area with less effort. Also larvae were recovered from the samples in hours instead of days. Thus, more information on the spatial dynamics of Culicoides immature populations may be obtained in less time using the CSFE technique. A major disadvantage of this method is that a fairly expensive centrifuge is required for processing samples.