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ARS Home » Plains Area » Manhattan, Kansas » Center for Grain and Animal Health Research » ABADRU » Research » Research Project #427619

Research Project: The Impact of Insect Immunity on Vector Competence in Changing Environments

Location: Arthropod-borne Animal Diseases Research

Project Number: 3020-32000-010-01-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2014
End Date: Aug 30, 2018

Background: Climate change is likely to alter significantly the landscape of vector-borne diseases, as development of the vector as well as the pathogen is temperature-dependent [1]. In addition, temperature can alter vector competence, the ability of a vector to acquire, maintain and transmit a pathogen [2, 3]. However, the nature of this relationship is poorly understood. The insect immune system is a likely player at the intersection of temperature, insect physiology and vectorial capacity. Not only can the immune system of a given insect species reduce its competence to vector particular pathogens [4, 5]– it also is required for the individual’s survival [6, 7] and influences fitness [8, 9]. The insect immune system is affected by a number of environmental factors including nutrition [10, 11], and temperature [12, 13]. However, surprisingly few studies have explored the consequences of temperature fluctuations and seasonality on the immune system of important insect vector species [14]. Recently, the first mechanistic insight into the impact of temperature on vector competence and was provided by the study of RNAi in the yellow fever mosquito, Ae. aegypti [15]. In contrast to prediction, susceptibility to flavivirus infection was increased at lower larval development temperatures. This project is designed to test (i) if this observed pattern holds true in more distantly related vector species that affect human and animal health and (ii) if it can be extended to other branches of the insect immune system. Objectives: 1. Assess the influence of the innate immune system and temperature on vector competence to viral infection of Culicoides biting midges, important arboviral vectors with great impact on animal health 2. Determine the impact of temperature and seasonal variation on immunity and vector competence in disease-transmitting mosquitoes

Approach: Towards objective 1, we will manipulate the immune system of Culicoides midges using RNA interference to knockdown specific branches of the immune system. Specifically, we will target the siRNA pathway, and actin remodeling and assess their impact on viral infection and dissemination. We have recently established successfully an RNAi protocol to knockdown genes in Culicoides sonorensis, which enables this approach. In parallel, we will determine if larval rearing temperature influences viral infectivity of adult midges. Adults will be switched to a common environment before infections to minimize impact on metabolic rates and extrinsic incubation periods of the virus. If indeed infectivity is altered by larval rearing temperature, we will determine the impact of temperature on distinct branches of the immune system, including but not limited to the siRNA pathway. Towards objective 2, we will determine the impact of seasonal variation of larval developmental conditions including temperature and photoperiod on the mosquito’s ability to overcome infection as adults to a variety of pathogens, including bacteria and fungi. As for Objective 1, infections will be carried out once the adult mosquitoes have been switched to a common environment to minimize impact on pathogen growth and insect metabolic rates. Survival after infection and antimicrobial peptide production will be used to assess potential variation of immune system activation in response to temperature variation