Most of us recall the story of Noah and the Ark: It rained for 40 days and 40 nights. Noah was instructed to take the animals two by two into the ark, thus saving the animals (insects too) from the flood that covered the earth. Just as there have been times when there is more water than we know what to do with, there have been droughts that have ravaged the earth. Despite these extreme conditions, insects and other pests have survived and, in some cases, even flourished.
During the past six months, climatic conditions throughout the United States have been extreme with prolonged periods of high temperatures and drought seen in the South and Southwest and an exceptionally cool and wet summer in the Northeast. Unusual weather conditions result in significant changes in pest problems — particularly their activity, survival and reproduction.
Water is the essential ingredient to insect survival because it accounts for 50 to 90 percent of their body weight. Small changes, e.g., a decrease of 15 percent, in body water can cause death in some insects. Water loss in insects naturally occurs through the cuticle and respiratory and excretory systems, and in most insects loss is accelerated by increased temperatures. Water also affects the availability of other resources, such as food and breeding habitats, which are essential to survival.
INSECT SURVIVAL. To survive, most insects must obtain water from other sources. Water can be obtained through several processes. In some insects, e.g., cockroaches, direct absorption of water occurs through the cuticle. Many insects obtain water from food and the amount of moisture in the food may affect consumption, i.e., more food is consumed if the water content is low. A few insects, e.g., mealworms, regulate their water loss and are able to survive on food with a moisture content around 1 percent.
It is obvious that water is a significant factor in insect survival. It is the most vulnerable resource associated with insect behavior. An insect’s need for water provides us insight into pest behavior and an opportunity to anticipate pest problems. Most importantly, it provides us a tool for dealing with pest problems. Astute pest management professionals (PMPs) will use this information in developing pest management strategies.
It is interesting to read in the trade journals and hear PMPs discuss the most significant pest problems during the year as well as the profitability (or nonprofitability) of business. In this regard, the weather is predictive.
Last summer, I had the opportunity to see the effect of drought and high temperatures on pest activity; this summer, I have observed the other extreme, i.e., cool temperatures and exceptional amounts of water. Pest species and activity differed significantly from one summer to the next.
During the drought of 1999, the most significant pest problems in the District of Columbia area were ants and springtails, whereas other outdoor pests, such as clover mites, lady bird beetles and cluster flies, were rarely a problem. The cool and wet weather this summer has precipitated an unprecedented number of calls regarding earwigs and mosquitoes, but ant calls have been practically nonexistent. In addition, the termite-swarming season stretched from January through June.
While there may be numerous environmental conditions affecting these observations, the following comments focus on issues related to moisture:
Ants: Customers rarely complain about ant problems unless they are found indoors. During dry weather, ants have a much more difficult time obtaining water outdoors due to less availability. In addition, there are fewer aphids producing honeydew and insects commonly eaten by ants are less abundant. Water is readily available in structures, so when it is dry outside, ants are more likely to forage indoors.
Ant baiting strategies should be adjusted according to the weather conditions and the foraging area. During dry weather, ants foraging indoors will be attracted almost exclusively to gel and liquid baits. However, during periods of abundant moisture, ants are rarely found indoors and gel and liquid baits are less desirable. Dry baits typically are more effective when applied outdoors.
Springtails: As a result of their susceptibility to dry conditions, these insects are continuously seeking areas with high moisture content. Their activity is more apparent during dry conditions when they enter structures to seek moisture. I have observed structural invasions when new mulch infested with springtails is spread out and begins to dry.
The need for moisture makes it easy to pinpoint where springtails can be found in structures. Typically, they are found in kitchens and bathrooms, but as with carpenter ants, their presence can be indicative of a structural moisture problem, e.g., leaking roof, pipe or drain.
Clover mites, cluster flies and lady bird beetles: Although this diverse group of pests is not directly affected by the amount of environmental moisture, their food sources are. The abundance and subsequent problems associated with these pests are directly correlated to their food supply, i.e., clover mites: grasses, clover and algae; cluster flies: earthworms; and lady bird beetles: aphids. Dry weather significantly reduces the availability of these food sources as well as the subsequent seasonal abundance of these pests. On the other hand, average rainfall can lead to a proliferation of food sources (and these pests).
Awareness of weather conditions preceding the fall invasion of these overwintering pests can be useful in determining the need for perimeter pesticide applications and for preparing customers for problems associated with these structural invaders.
Earwigs: These occasional invaders have moisture requirements similar to springtails, i.e., they are unable to tolerate dry conditions. They become more apparent during wet and cool weather because their populations increase exponentially, whereas, during drought conditions, their presence typically goes undetected. While they pose no threat to human health, their pincers appear ominous to uninformed customers. This, coupled with massive numbers, precipitates panic calls.
Elimination of moisture conditions around structures and removal of clutter and debris that provides harborage can reduce earwig populations. Perimeter sprays should be used to prevent earwigs from entering structures and to treat localized nesting areas.
Termites: Termites build mud tubes to protect themselves from adverse environmental conditions and the loss of water; they do not forage in the open. Moisture around structures is the most significant factor that attracts termites to structures and is the major cause of termite-control failures with soil-applied termiticides.
Moisture within the structural foundation can lead to the formation of isolated colonies of subterranean termites that no longer maintain contact with the soil. Eliminating the moisture minimizes the termite problem.
CONCLUSION. All pests rely on moisture for survival. By eliminating moisture problems, pest populations become stressed and decline, thus making it much easier to solve the customer’s problem.
The author is technical director of American Pest Management, Takoma Park, Md. He can be reached at 301/891-2600 or rkramer@pctonline.com.
