Disease Research

Understanding Disease and Mosquito Impacts

Mosquito and Disease Research

MFBRP has been conducting research on avian disease and mosquitoes in the wild. 

Mosquito-borne diseases, particularly avian malaria (Plasmodium relictum), are considered the most widespread and devastating factor contributing to the decline of Hawaiian honeycreeper populations. Introduced disease has restricted native forest bird populations to elevations above those at which both the introduced parasite (Plasmodium relictum) and vector, the Southern House Mosquito (Culex quinquefasciatus), cannot consistently survive and reproduce. Due to climate change, disease and mosquito abundance is changing the disease landscape, increasing disease transmission risk at higher elevations. In some areas, malaria is already reaching the highest elevation forests leaving the remaining honeycreepers little to no disease-free habitat.

See Mosquito ControlAvian Disease, and Birds, Not Mosquitoes.

Mosquito and Disease Prevalence

Research is taking place throughout Hawaiʻi to better understand the distribution and population dynamics of C. quinquefasciatus and P. relictum. Much of this research is being used to inform effective implementation of landscape-scale mosquito control efforts utilizing the Incompatible Insect Technique (IIT) via Wolbachia incompatibility. Planning for this technique requires understanding of distribution, dispersal, and abundance of mosquitoes across the region. 

To understand more about the disease prevalence in bird population, mist nets are used to catch birds temporarily to obtain blood samples to test for avian malaria. All work is conducted through State and Federal permit and under the guidance of the Institutional Animal Care and Use Committee (IACUC) through the University of Hawai’i.

To understand more about the distribution of mosquito populations, we set out different types of mosquito traps to collect adult mosquitoes and egg rafts. We also survey areas for mosquito larvae and egg rafts. Adult mosquitoes are also tested for avian malaria.

Samples are analyzed using Polymerase chain reaction (PCR), a technique used to amplify copies of a section of DNA. Both mosquitoes and blood samples are analyzed to determine whether PCR detects the parasite (positive) or does not detect (negative). This method determines if a particular mosquito or bird ever carried the malaria parasite. 

Prevalence, or the percentage of positive outcomes of birds or mosquitoes, at each site is then calculated, allowing us to estimate baseline information prior to implementation of mosquito control, and also determine areas and species with positive samples.

Examples of mosquitoes traps: Modified Centers for Disease Control and Prevention (CDC) light traps with CO2 cylinder (left) and Reiter-Cummings Modified Gravid Trap (right).

Adults Mosquito Control Efficacy

Prior to implementing Wolbachia Incompatible Insect Technique (ITT) to reduce C. quinquefasciatus mosquito populations for the benefit of native birds across the landscape, we are conducting trials to understand the efficacy of the control and how we may improve protocols. This involves helicopter release drops of IIT male mosquitoes. We then monitor the distribution of these mosquitoes and the prevalence of mosquitoes within sites by conducting mosquito trapping techniques. We also collect egg rafts and larvae to look at the percentage of viable offspring hatched in the trial sites.

Mosquito Larvae Control

Our team has been assisting with an additional method of mosquito control – Bacillus thuringiensis israelensis, better known as BTI. BTI is a naturally occurring group of bacteria that when used as a larvicide targets mosquito larvae and prevents their development. This does not harm native species or water systems. Through repeated applications to an area, BTI can reduce the number of adult mosquitoes potentially spreading disease. To do this, we utilize helicopters with special rigging to spray the larvicide. Prior to starting the application, our team conducted mosquito trapping within the spray area and will be conducting trapping again during the spraying and after to see if there are any immediate impacts that can be detected. We are targeting a region known for having the most endangered birds and is not receiving any other mosquito control. Trials were conducted prior to these efforts and have been published here.

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