Counting Mosquitoes

Summer interns Kathleen Connolly, left, and Christina Mangan pose with some of their finds.

Since October 2011, we have been monitoring disease vectors in the Safari Park Biodiversity Preserve (aka The Back 900). Here, the valuable coastal sage scrub habitat has been undergoing cactus restoration as well as monitoring of one of its important inhabitants, the cactus wren (see post Cactus Wrens Rise from the Ashes). Our goals are to monitor the presence and activity of mosquitoes and midges, two important disease vectors, and test them for West Nile virus and blood parasites, including plasmodium, the cause of avian malaria, in and around this reserve. From this data, we will be able to look at the occurrence of these disease agents in insects within the cactus wren habitat and which mosquito or midge species act as likely vectors.

Another interesting aspect of this study is analyzing what hosts these insects have been feeding on by evaluating their blood meals. Only females feed on blood; the male mosquitoes and midges feed on nectar. So for this study we are only concerned with the female insects. DNA is extracted from the blood meal, and a barcoding PCR is performed. The PCR product sequences are then compared to published sequences in the Barcode of Life database, which contains DNA sequence information for a large number of animals. Finding a match between the DNA sequence extracted from the blood meal and a known DNA sequence will enable us to determine which animals these insects have been feeding on. Mosquitoes and midges within the Safari Park have been found to feed upon various local creatures, including mallards, desert cottontail rabbits, mule deer, humans, and an occasional collection animal.

So, how do we convince the insects to be tested? Once every other week, our summer interns and I go out into the field, setting up UV traps and CO2 traps to attract and capture mosquitoes and midges. While out in the field, it can be quite an adventure, from the bumpy roads and rolling hills to the occasional visit from a resident mule deer or a speeding roadrunner. It is often enjoyable to get out of the laboratory and into the field and observe virtually undisturbed habitat right in our own Park’s backyard.

The UV traps attract the mosquitoes by emitting a UV light of about 350 to 400 nanometers; this acts as a visual stimuli for the mosquitoes and midges. The CO2 trap contains dry ice that emits CO2 to mimic the respiration of an animal and works as a chemical attractant for the insects. After anesthetizing the insects back at our Wildlife Diseases Laboratory, the students then have the arduous task of tediously counting and identifying the various species of mosquitoes and midges. Later, they extract the DNA and RNA from these insects and utilize it for the PCR testings.

This project has given our interns the opportunity to gain experience in the laboratory and in the field!

Jennifer Burchell is a research coordinator for the San Diego Zoo Institute for Conservation Research. Read her previous post, Invisible Clues.

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