LAST OCCURRENCE AND SURVIVAL DURING WINTER OF THE ARBOVIRUS VECTOR CULICOIDES-BREVITARSIS AT THE SOUTHERN LIMITS OF ITS DISTRIBUTION

Linear regression analysis was used to describe the decline in numbers of Culicoides brevitarsis Kieffer into winter with monthly maximum, average and minimum temperatures at the southern limits to its distribution in New South Wales. From this, low temperature thresholds were derived when C brevitarsis would be absent from the field. The low minimum threshold +/- 2 SE (95% Confidence Interval) of 8.1 +/- 0.3-degrees-C was used with historical temperature data to estimate the last month that the species should occur (March to June) and the mean number of months (2 to 6.5) below the threshold at 17 selected sites. Probability for survival during winter at these sites was estimated from years when the number of consecutive months below the threshold was less-than-or-equal-to 2 months. This varied from zero to 51% depending on the location of the site. Last occurrence was 0.7 months later on average and absolute probabilities for survival ranged from zero to 100% when the temperatures were increased by an arbitrary 2-degrees-C.