Insects in winter

Looking out towards a snow-covered parking lot and hearing the forecast of 3 to 5 inches of snow for tonight, and minimum temperatures in the teens in (can you believe it?) Virginia Beach for the next several nights, I am simply overwhelmed by the contrast between this winter and the past couple of winters.
It leaves me wondering what the insects are doing to cope with this weather, and if they are as shocked as we are.
Let’s start at the bottom (figuratively) and work our way up. Soil dwellers, either full or part-time, will simply move down a few more inches to escape the frozen soil. Last year’s overwintering generation did not experience frozen ground in eastern Virginia, but this is another year, and the success of insects is in their ability to adapt. Such larvae as Japanese beetles and related scarabs will simply go deeper “under the covers.”
Predicting Japanese beetle populations is shaky, but out of a very recent discussion with colleagues has come some interesting observations. One predictor that has been discussed is that the climate during June of the previous year foretells adult beetle populations. June is the period of oviposition, and newly hatched larvae are the most susceptible to environmental conditions. If the June temperatures are very hot and the soil is hardened to near brick consistency with compounded dry weather, larval mortality will be high. Lower larval hatch results in lower adult emergence the following year. I’ll hedge a little here, because we all know golf courses, nursery plots and suburban areas are aerated and irrigated. In studies conducted and published by Dr. Daniel Potter, University of Kentucky, irrigated plots had significantly higher levels of Japanese beetle grubs than non-irrigated plots. So we will have a trend with lower overall populations, but one could still experience high populations in or near irrigated areas.
Insects in the leaf litter in uncultivated areas would follow the lead of their soil dwelling neighbors and just burrow a little deeper. Thus box elder bugs, two-spotted spider mites and their many friends that prefer the safe haven of leaf litter will still be healthy survivors in the upcoming year. In the case of mites, they do not like rainy weather, and populations can crash quickly after heavy rains.
Insects that overwinter on twigs and branches are feeling the full effects of the cold winter temperatures. Their survival depends on their ability to withstand the ambient temperatures, as they are usually immobile (at least in that life stage). Each species will have a different threshold temperature, one at which they are unable to survive.
The mild winters the past few years have extended the distribution of wax scale much farther north than previously recorded. Twenty years ago, its northern limit was coastal Virginia, with populations disappearing every few years following cold winters. Urban heat islands extended its range into the Richmond and Washington, D.C., metropolitan areas.
I don’t know how wax scale gets distributed, but the likely sources are by the movement of plant material and wind. I do know that blueberry bushes in my yard have for the first time 10 to 15 overwintering wax scale on the twigs. With temperatures near 20 degrees a few nights ago, and colder temperatures expected, I am quite sure all wax scale will be dead. Outwardly, mortality is difficult to assess, but flicking the scale over will expose the red female (males are not known from North America). If females are bright red, they are alive; but if they are dull red to nearly black, they have perished. I would look for wax scale to be a rarity in the Mid-Atlantic states for several years, with the lowest levels this spring.
At recent horticulture conferences, the question of the Asian ambrosia beetles came up frequently. The spring of 2002 produced a severe outbreak in areas not known for the insect to be a pest of nursery-grown shade trees. Could this have been the outcome of a series of mild winters that let the insect expand its range without winter mortality? Or did the crazy January weather with its 70-degree days that pushed the sap flow followed by a frost predispose nursery stock to attack?
All insect populations go through peaks and valleys, with the highest peaks often followed by a population crash. Many a graduate student has been the victim of having his test insect disappear in the final year of field research. After eight years of trapping, I can predict that the peak flight will occur the first warm days in spring (10 to 15 degrees above normal). Those are the days the buds swell on the cherries and tent caterpillars hatch. Treatment at that time may be justified if there is a history of attack on the property. Adult beetles can be killed by trunk applications immediately upon detection of the toothpick-like projections. Astro is registered and effective.
I have seen a number of trees survive beetle attack, particularly larger trees. However, the adult or the entry hole could be a source of entry for a tree pathogen, which may lead to mortality. After the initial flight, subsequent beetle activity is minimal by comparison; thus late season pesticide applications would be of little benefit.
One additional factor affecting insect pest outbreaks in the upcoming year is already on your property. Temperatures in those overwintering structures are not nearly as extreme, and those plants could provide harborage for pests with a broad host range. Ideally, those plants were scouted before the plants were tightly packed and the coverings were applied.
So be vigilant in scouting plant material for evidence of insects and mites, especially plants newly purchased from warmer climates and those that had overwintering protection. The harsh winter should have helped you with some, but not all, pests.