Куликоиды имикола: Распространение, экология и роль в переносе вирусов.

Species of fly

Culicoides imicola (Culicoides imicola Kieffer, former name C. pallidipennis Carter) is a species of Ceratopogonidae that transmits the bluetongue virus (BTV) and the African horse sickness virus. This particular species has been recorded in Africa, Asia and Europe. However, variation is significant, as their quantity has been recorded to range from 8 to 145 spicules. Spicules are needle like projections from the genitalia.

Historically, Culicoides imicola has been found in Africa and southwestern Asia, but their distribution has been increasing, as human activity has catalyzed this spread. Because of the connection between cattle and C. imicola, C. imicola can be found where cattle are densely populated. Coupled with irrigation in farms which provides damper more habitable soil, C. imicola population has been able to rise.

Unlike other species of Culicoides, C. imicola has been shown to prefer drier environments in multiple studies. A likely reason is that C. imicola pupa are especially prone to drowning, so their eggs are often laid in surfaces free of running water. However, the larvae need moist soil, so there tends to be a trade off between dry and wet areas.

In a study done in Sicily, C. imicola do not inhabit undulating or high altitude areas. They instead prefer lower altitude flattish regions at around 200 meters. This is because in steeply undulating topographic areas, rapid desiccation leads to drying of soil, which prevents proper larval development. Further examination has shown that the biggest determining factor in their distribution is not altitude but a suitable climate and nutritious soil.

Culicoides bolitinos, once thought to be the same species as C. imicola, has now been recognized as a separate but closely related species. In laboratory tested flies, it was found that at 20 °C it takes up to 2 months to go from egg laying to adulthood, up to 21 days at 25 °C, and up to 16 days at 28 °C. However, at higher temperatures there were fewer hatchings and higher variability in fecundity. It is also interesting to note that more males emerge from pupae than females, although the exact reasons are unknown. Some possible explanations are that the female larvae have higher mortality rates, or that the sex ratio is temperature dependent.

Culicoides imicola, like most other biting midges, feed on animal blood. In Africa, C. imicola is known to feed on horse, cattle, and sheep. Nonetheless, their feeding preferences haven't been studied extensively in Europe but should be similar to those in Africa.

Culicoides species vary significantly in their activities in different contexts. In a study done in Kenya, Culicoides imicola effectively ceases all activity at wind speeds above three meters per second. And, like most Culicoides, Culicoides imicola is also known to be nocturnal and tend to be more active during cooler temperatures.

Culicoides imicola and humans usually do not interact directly, but they do so through their capabilities as disease vectors for many farm animals such as cows, horses, and sheep. In the past, AHS has only occurred periodically, no more than two years at a time. However, there has been occasions where it has persisted for over 5 years. The year round presence of C. imicola in the face of climate change has been identified as the possible source of longer durations of AHS.

Traditionally, Culicoides imicola has been found in subtropical Asia and Africa. However, due to climate change, they have spread all the way to Europe and as far as Sweden. Without a significant improvement in epidemiological control measures, what is currently considered a once in 20 years outbreak of bluetongue would occur as frequently as once in five or seven years by midcentury under all but the most optimistic climate change scenario.

The expansion of C. imicola out of its traditional Old World region of Africa and Asia may be a risk for significant spread orbivirus in the near future. Already, it is well distributed in Spain, Portugal, and several Greek islands; all of these area tend to be much warmer than their northern European counterparts. If temperatures continue to increase or stay roughly the same, the spread of these viral vectors will need to be properly prepared for and countered. Other species affecting Europe include C. obsoletus, C. pulicaris, C. nubeculosus and C. schultzei.

Culicoides imicola acclimated to different temperatures were found to have different survival capabilities in low temperatures but were about the same at high temperatures. Flies acclimated at 24 °C survived better at lower temperatures ( 6 °C) while those at 29 °C did not get past 3 °C. However, there was no significant difference at higher temperature because once 42 °C was reached there was near total fatality. Due to the profound survival effect attributed to temperature, climate change altered the distribution and abundance of C. imicola.

Much is left to be understood about C. imicola. Because of the many closely related species in the family, it is important to properly identify each individually as to prevent confounding different species together. Their thermal limits in larvae stages is also of interest, as that could further explain their distribution across the world. Additionally, because of the difficulty in laboratory conditions in matching field conditions, more research is needed to study how their life cycle plays out.