Better prediction of tiny bloodsuckers to protect livestock

Most South Africans love eating meat, but animal diseases regularly threaten a constant, affordable supply.

Bluetongue, epizootic haemorrhagic disease, and Rift Valley fever lead to sickness and death in our cattle, sheep and goats, and are all spread by insects called blood-feeding midges. These tiny insects, a little bigger than a grain of sugar, are extremely abundant in rural areas and can carry and transmit the viruses causing livestock diseases when they feed on animal blood.

A team comprising Dr Heike Lutermann, Prof Kerstin Krüger and Prof Chris Weldon from the Department of Zoology and Entomology and their colleagues at the Agricultural Research Council are working to find better ways to predict the transmission of disease by blood-feeding midges. “The results to date suggest the value of using an existing surveillance network for other small insect pests and weather records to warn farmers when to protect their livestock,” explained Dr Lutermann.

The researchers sorted through the catch of insects by traps in an existing nationwide network of Rothamsted-type suction traps for blood-feeding midges in the genus Culicoides. “These blood-feeding midges, particularly C. leucostictus and C. pycnostictus, are associated with the transmission of viruses to cattle and sheep. The suction traps are generally used for early detection of aphids that transmit plant viruses to wheat and potatoes but also catch a wide range of other small flying insects within a diameter of 100 m. The suction trap catch was compared with captures of light traps usually used to monitor Culicoides but are difficult to service, have a limited attractive radius and are biased towards species that respond to light. The suction traps caught fewer Culicoides species and individuals but provided an unbiased representation of the dominant species, including C. leucostictus and C. pycnostictus.”

The team explored how the suction trap captures Culicoides changes in response to earlier weather conditions. They found that Culicoides abundance increased if weekly minimum and maximum temperatures, and rainfall, were higher than average 3-4 weeks before the midges were trapped. “This is likely due to the stimulation of reproduction by warm temperatures coupled with an abundance of moist breeding sites. If relative humidity was high or wind speed was low just before the trapping, there was also an increase in the number of Culicoides caught by the suction traps.”

According to Dr Lutermann, this study highlights the currently underutilised potential of an existing network of Rothamsted-type suction traps to assist red meat farmers in protecting their animals’ health and productivity. In addition, the predictive potential of weather variables for Culicoides abundance could also help define time windows for farmers to prevent their cattle from falling victim to these bloodsuckers.

Researchers

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  Professor Chris Weldon

  Professor Christopher Weldon is an Associate Professor in Applied Entomology at the University of Pretoria (UP). He completed his undergraduate studies at the University of Newcastle in Australia, graduating with a Bachelor of Environmental Science (honours) and the Dean’s Medal. He has been pursuing research at UP since he was appointed as a lecturer in Applied Entomology in 2012.
  
  Prof Weldon says his field of research would contribute to the betterment of the world because human health and livelihoods often intersect with the activities of insects. Using a foundation in insect behaviour, ecology and physiology, his research aims to address these interactions, whether negative or beneficial, with a focus on flies but also insect pests of horticulture. Results from these studies inform sustainable management practices that can reduce reliance on pesticides but may also facilitate the beneficial use of flies.
  
  He leads a research group of postgraduate students at honours, master’s and PhD level. “We pursue projects on the traits that make fruit flies destructive and invasive pests; the behaviour and movement of fruit flies that damage our fruit for consumption and exports; the biology and management of mosquitoes and other blood-feeding flies that affect human and animal health; and the use of flies for bioconversion of organic waste to promote a sustainable, circular economy,” Prof Weldon explains.
  New research that the professor and his research group have been working on over the past 18 months has been the practical interventions that can be used by hotels to reduce mosquito abundance, the nuisance of mosquito bites and the potential spread of diseases. Such practical interventions will improve the experience of hotel guests and encourage tourism.
  
  Prof Weldon and his group have also done research on how body condition and environment affect fruit fly attraction to lures and movement in the field; the diversity, abundance, and damage caused by thrips in avocado and macadamia orchards; and how to improve surveillance of invasive pests of citrus. All this work is being done in partnership with South African horticulture industries as well as international organisations to improve the productivity and competitiveness of South African horticulture.
  His advice to school learners or undergraduates who are interested in his field is to read widely about the diversity and importance of insects. There are plenty of interesting and reputable sites featuring that kind of content, Prof Weldon says, such as Entomology Today, as well as great books on insects in southern Africa. He also suggests they join a society like the Entomological Society of Southern Africa or the Lepidopterists’ Society of Africa to learn more about insects from experts and have opportunities to work with them. “Register for an undergraduate degree programme in Entomology like UP’s BSc Entomology, he adds, “and be sure to take the right subjects in school to be admitted.”
  

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