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 soils1

摘要

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 from salt marsh substrates. Three types of samples (seeded withknown numbers of larvae, homogenized field samples with approximately equal numbers of imma-tures, and regular field samples with an unknown number of immatures) were evaluated. Two substrate sample sizes were used (100 ml and 1000 ml). Agar extractionwas 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 percent 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 about twice more immatures than the CSFE, but on a mean numberof immatures recovered per ml basis, CSFE recovered 5.2 times more than AE1000. Similarly, for the regular field samples, on a per sample basis the AE1000 method recovered ca. 1.5 times more immature stages than samples processed by CSFE, but on the immatures per ml of substrate basis the CSFE method recovered ca. 6.6 times 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 greaternumbers 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 thespatial 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.