Laboratory survival and blood feeding response of wild-caught Culicoides obsoletus Complex (Diptera: Ceratopogonidae) through natural and artificial membranes.

In late summer 2002, live wild-caught midges of the Obsoletus Complex were collected using blacklight traps placed at a horse stable in Teramo (Abruzzo, Italy). For the survival study under laboratory conditions, 1,500 Obsoletus Complex midges were kept at 17 degrees C-25 degrees C and provided only with a sucrose solution. Of these, 150 (10%) survived for at least 40 days and 3 midges were still alive after 92 days. In addition, 10 midges survived 10 days at 4 degrees C. For the feeding trials, 40 blood-meals (9,440 midges) were administered, 27 of which were successful (67.5%); the feeding rate ranged from 0.3% to 16.7%, with a total of 592 engorged midges. Similar feeding rates (U Mann-Whitney test=129.5 p>0.05) were obtained when natural (day-old chicken skin) and artificial (stretched parafilm) membranes were used. To infect the insects, a field strain of bluetongue (BT) virus (BTV) serotype 2 isolated from the spleen of a sheep during the 2000 Italian outbreak was added to the blood-meal. Two different viral solutions, with titres of 10(6)TCID(50)/ml and 10(7)TCID(50)/ml, were prepared. Uninfected blood was significantly more appetising (U Mann-Whitney test=88.5 p<0.05) than the infected meal and the midges preferred (U Mann-Whitney test=48 p<0.05) to feed on blood containing BTV-2 at a lower titre. A total of 251 midges were fed on BTV-2 infected blood and were then incubated at 23 degrees C-25 degrees C and fed with a sucrose solution for 10 days. During the incubation period, the dead insects were collected daily and analysed for evidence of virus infection. Of the 251 engorged midges, 54 (21.5%) died in the feeding chambers or during sorting on the chill table, 136 died within the first 10 days and 61 survived longer. BTV was isolated only from those which died just after feeding (52.6%; 10/19) or 24 h later (47.8%; 11/23). Considering the small number of midges tested after 10 days of incubation, the prevalence of infection detected in this study (95% probability) would have been higher than 4.74%. These preliminary results appear very promising as this is the first time that midges of the Obsoletus Complex have been successfully fed under laboratory conditions.