Severe drought in the Midwest could send insect and spider populations skyrocketing, adding insult to injury for farmers already facing billions of dollars in crop losses, entomologists and other experts said this week.
"These insects are favored by hotter, drier weather," said Sue Blodgett, the Entomology Department chairwoman at Iowa State University. "They're feeding on agronomically important crops. They're damaging and compromising the plant and impacting yield."
The extreme weather is especially beneficial for spider mites, which infect corn and soybean crops, destroying foliage and reducing harvest size. This year's mild winter and warm spring gave the arachnids ample opportunity to multiply. One of the most common responses is to apply pesticides to the outer rows of a field, where spider mites tend to congregate.
"We have some people who are spraying insecticides for these pests," Blodgett said. "Spraying insecticides costs money."
The sudden population increase is one that many insects experience during periods of extended warming.
"What you have to understand about insects is they're all coldblooded, so they rely on the environment to tell them what their body should be doing," said Missy Henriksen, a spokeswoman for the National Pest Management Association. "When the temperatures warm, their bodies warm, and everything goes much quicker."
That means everything in an insect's life cycle, from maturation to reproduction, is fast-forwarded. For corn, it's a vicious feedback loop. Drought conditions cause a breakdown in the plant's ability to process nutrients such as amino acids, a mite's favorite food. The acids build up in the corn stem, providing easy access for mites and causing a population explosion. More mites put more stress on the corn, which increases the amount of amino acids in its stem, and the cycle continues.
Ticks, spiders seek shelter and moisture
Of course, not all insects and spiders enjoy the heat. The National Pest Management Association released a report last week warning homeowners of "accidental invaders" -- pests that fight their way inside as a last-ditch effort to survive.
"They're coming indoors in search of moisture," Henriksen said. "They're not finding the moisture that they need in their natural environment."
The result is an increase in ticks, brown recluse spiders and black widow spiders, all serious health hazards for both pets and humans, she added.
For pests that don't generally migrate indoors, the heat wave can also reduce their effect on a crop. Many insect populations are just as water-dependant as their plant hosts, said Christian Krupke, an associate professor of entomology at Purdue University. Sightings of the corn rootworm, a pest that feeds on corn roots, and the Japanese beetle, an insect that can destroy corn tassels, have actually decreased, he added.
"It's pretty slim pickings for insects right now," Krupke said. "They're not immune to the same laws of biology that the plants are succumbing to."
The insects that rely on water to reproduce aren't going to fare well, either, he said. Thus, the Midwest can also expect to see a decrease in mosquito populations, which carry disease like West Nile virus.
Crop loss devastation
Yet a major die-off of any insect population isn't necessarily a good thing. Ecosystems rely on a host of organisms in order to function. Despite the stigma attached to bugs, many of them perform services necessary for a productive ecological community.
High temperatures are detrimental to predatory insects that aid farmers, protecting crops from pest invasions, said Bradford Hawkins, a professor with the Department of Ecology and Evolutionary Biology at the University of California, Irvine. These insects can even reduce the need for a farmer to use pesticides, saving the industry time and money, he added.