Lane M. Smith, Arthur G. Appel, and Gary J. Keever

AAES researchers have found that traditional pest control methods targeted against smokybrown cockroaches can greatly increase abundance of other nuisance insects. Furthermore, traditional treatments can also reduce populations of beneficial insects that prey on pests.

Smokybrown cockroaches are the main outdoor-nuisance pests around Alabama homes. Traditional efforts to control cockroaches were shown to significantly increase populations of other pests, such as Argentine ants, fire ants, acrobat ants, and small black ants. In addition, these pesticide treatments reduce numbers of beneficial predators - such as jumping spiders and ground beetles - which are natural enemies of pests that feed on grass, bushes, and trees.

However, an AAES-developed integrated pest management (IPM) program for smokybrown cockroaches only slightly increased abundance of some pests, while also slightly increasing abundance of some beneficial insects. The IPM treatment includes strategic applications of gel and pellet baits to mulch, wood piles, aluminum sheds, crawl space gratings, and other outside spots where cockroaches are likely to hide and eat. Previous research showed that the IPM system is not only more effective than the traditional pesticide sprays applied in a perimeter around the house, but it also reduces the amount of pesticide needed by up to 10%.

At 107 houses in Lee County, researchers compared the IPM treatment to no control and to the perimeter spray cockroach treatment, which is applied in a 10-foot swathe around the house. Special baited traps were used to capture cockroaches in order to gain information about changes in cockroach numbers. These traps also collected about 30 different types of other insects or spiders. Insects were sampled six times from July through September. Researchers compared the numbers of insects and spiders captured at homes receiving the various treatments.

IPM and perimeter treatments reduced the abundance of smokybrown cockroaches, as well as some other pests, such as camel crickets (see table). But American cockroaches and native woods cockroaches were not controlled, Homeowners cannot expect to control all pests by applying methods designed for use against smoky brown cockroaches, Abundance of the beneficial daddy-long-legs was reduced by both treatments, but the beneficial crab spider was unaffected by either.

Several house-infesting insects were more abundant at homes where cockroach control treatments were used, Numbers of Argentine ants, fire ants, acrobat ants, and small black ants increased, compared to homes where no pesticides were applied. This response by ants may result from the scavenging of dead insects left after application of the two treatment methods. Nevertheless, increased ant activity near homes might lead to greater human contact with these pests and greater perceived problems.

When viewed in terms of species composition (see figure), homes treated with perimeter sprays had a greater relative percentage of Argentine ants, fire ants, and field and house crickets. While IPM-treated homes also had more ants, these pests were much more abundant at homes treated with perimeter sprays. Jumping spiders and ground beetles were reduced at homes receiving the perimeter spray, but IPM-treated homes had a much greater relative abundance of these beneficial predators.

Points in the diagram show the average relative change in abundance of pests and beneficials caused by each treatment. The perimeter spray had a much higher relative abundance of pests than the IPM or no control treatments. The IPM treatment had a higher relative abundance of beneficials than no control, and the perimeter spray treatment had fewer beneficials than the no control treatment.

Even if the population of a given insect or spider increases, that does not necessarily mean they will increase to problem levels. The actual size of a decrease or increase of beneficials or pests caused by treatment depends on the abundance of insects present before treatment. Homes with initially low pest abundance would not experience as big an increase as houses with initially high pest abundance.

A problem with assessing the treatments is that some insects prefer certain environments, and thus are more likely to be found at some homes, regardless of whether any cockroach treatment methods are used. For example, Argentine ants appear to prefer open lots without trees, whereas native woods cockroaches prefer wooded lots. Lots with a few trees have different insects associated with them. Researchers accounted for these differences by statistically factoring out the effect of tree abundance. Trees are not the only environmental factor around homes, but the AAES analysis showed they do provide an explanation for the distribution of some insects and spiders. Even after correcting for this environmental difference, researchers still detected the differences in relative abundance of pests and beneficials between the two treatment methods and no control.

Perimeter sprays reduced the abundance of some pests by 10-30%, compared to 75-95% for smokybrown cockroaches, Unfortunately, they also increased the abundance of some pests 10-30%. Perimeter sprays have the potential for increasing other pest problems by reducing the abundance of beneficial insects and spiders. These studies show that besides using less pesticide, and providing good control, IPM has less impact on other pests and beneficials in the urban environment.

Smith is a Post-Doctoral Fellow and Appel is a Professor of Entomology. Keever is a Professor of Horticulture.