What Does This Warm Winter Mean for Insects?

Published: March 1, 2012

This winter has been one of the warmest on record in many areas of the US including Missouri. According to Dr. Pat Guinan, State Climatologist for the Univ. of Missouri Extension, regionally, February temperatures averaged between 34-37°F over northern sections, 38-41°F across central MO and 40-43°F in the southern third of the state. Most days averaged above normal during the month with only 5-7 days recording below normal temperatures. Seasonally, about 70% of the days, from December through February, averaged above normal, and will rank the winter of 2011-12 in the "Top 5" mildest winters for MO, and the warmest since the winter of 1991-92.

Average Temperature (°F), February 1, 2012 - February 29, 2012

Source: Midwestern Regional Climate Center, Illinois State Water Survey, Prairie Research Institute, University of Illinois at Urbana-Champaign

What does this mean in terms of insect's ability to survive and timing of appearance in the farms? That question has been asked repeatedly but unfortunately the answer isn't clear. One may think that relatively warm weather may favor insect survival. However, many factors contribute to insect population dynamics. Spring and summer weather patterns, abundance of the insects' natural enemies, and crop growth and development are as big of influence on insect populations as winter weather. Mortality could actually be increased for insects that over-winter above ground due to a lack of snow cover, which can expose insects to days with below-freezing temperatures compared to years with adequate insulating snow cover. Mortality could actually be increased for insects that overwinter above ground due to a lack of snow cover, which can expose insects to days with below-freezing temperatures compared to years with adequate insulating snow cover.

In contrast, for insects that overwinter below ground (e.g., Japanese beetle grubs which can overwinter up to 10 inches deep into the soil) they will not likely be affected by a mild winter because soil temperatures are more constant. Another aspect that we need to consider regarding insect overwintering is that all insects develop based on ambient temperature. A warm winter day could cause some insects (e.g., woolly bear caterpillars) to become active when they normally should be dormant. This activity uses up stored fats they depend on to survive until the spring. And, without access to food, these active insects could starve to death before food becomes available.

Whether insect pest will be a problem this year in vegetable farms is therefore uncertain. For example, high populations of overwintering insect pests may cause little if any economic problems if spring weather isn't favorable, if natural enemy populations are high or if crop growth isn't favorable. Likewise, low overwintering populations may cause damage if conditions are good. Therefore, careful crop scouting for the insect, their damage and natural enemies is necessary and will remain an important component of an IPM program. In 2011, preliminary monitoring of cucumber beetles indicated that a wave of striped cucumber beetles and a few spotted cucumber beetles appeared on one farm located in St. Charles, MO, on May 4, 2011. In 2012 we will be monitoring the timing of appearance of key insect pests of vegetables such as cucumber beetles, squash bugs, Japanese beetles, stink bugs, and tomato pinworm in various locations: St. Charles, Jefferson City, and Southwest MO. Updates on the observed timing of appearance in farms will be provided through this IPM Newsletter.