Big or small, mosquitoes are pesky. But it's the little ones that you really need to watch out for, a new study finds.

Scientists measured mosquitoes' wings, then fed them blood that packed the dengue virus (which causes dengue fever, a disease found in the tropics and Africa). The smaller bugs were more likely to become infected and therefore more likely to transmit disease.

The study, led by Barry Alto of the Illinois Natural History Survey, a division of the University of Illinois Institute for Natural Resource Sustainability, is detailed in the November issue of the American Journal of Tropical Medicine and Hygiene.

The tests were done on both Asian tiger mosquitoes and yellow fever mosquitoes. Both pests are found in the United States and throughout the world and are the two main transmitters of dengue virus. The size factor held up for both.

"Only slight differences in the body sizes of these mosquitoes drastically alter their potential to transmit viruses causing human disease," the researchers said in a statement today.

The finding may prove fortuitous: Larvacides that aim to kill mosquito larvae don't always kill them all, but they result in less competition among those that remain, meaning bigger mosquitoes, which may be less able to transmit infections.