P&PDL Picture of the Week for
March 8, 2004

Insects and Winter

Tim Gibb, Insect Diagnostician, Department of Entomology, Purdue University

Many ask how cold winters affect insect populations the following spring and summer. While there is undoubtedly some mortality caused by severely cold temperatures, for the most part insects are protected from these extremes. This is accomplished in many different ways. Some insects migrate southward, others move deep into the soil or into protected structures to avoid the harsh winter temperatures. Some insect populations pass the winter in the egg stage, which is inherently less susceptible to temperature fluctuations. Other insects can pass the winter in the adult stage because the physiological processes of the insect metabolism have nearly shut down and the insect has produced a material in its blood that is very much like the ethylene glycol (antifreeze) that we put into our cars to prevent the radiator water from freezing. These and other strategies help insects to ensure survival until spring.

The northern house mosquito that is responsible for the spread of west niles virus overwinters as an adult. Spring will begin with gravid (pregnant), infected females that are able to spread the virus shortly after emergence. In addition, recent research indicates that the virus can be transmitted from adult female to eggs and into a second generation without having to become re-infected by biting host birds. These facts suggest that we should prepare now and Adult females overwinter Use DEET, wear long sleeves and expect populations of house mosquitoes in 2004 to carry west niles virus. Plans to protect ourselves include; monitoring the populations, wearing protection such as DEET and long sleeves and pants and reducing evening outdoor activities when necessary. Sanitation efforts such as eliminating old tires, cleaning gutters, correcting filth pools, etc. will also help. Chemical controls such as treating standing water with methoprene products, or BTI can help if done correctly. Fogging for adult control is not generally useful.

Educating ourselves now and planning for mosquito populations in the spring is a better winter time activity than hoping that the cold will kill all mosquitoes.

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Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service