[Research Update] Bait and Take?

Purdue University researchers have been studying the effects of certain baits on several species of ants and cockroaches. Gary Bennett, professor of entomology for the university’s Center of Urban and Industrial Pest Management, briefed pest management professionals on the results of some of those tests at NPMA PestWorld 2007, held last October, in Orlando.

“In our lab, we studied these insects in their various stages,” he said. “Pharaoh, carpenter, Argentine and odorous house ant stages studied included the larvae, pupae and queens. We also looked at the worker caste, the one causing problems for pest control customers.”

The cockroaches in the tests — German, oriental and brownbanded — were early instar nymphs and adult males and females, he said.

For the ant tests, a variety of the pest control industry’s usual suspects were chosen.

“Pharaoh ants are very common in structures, especially larger buildings, hotels, apartment complexes and hospitals. Carpenter ants tend to be a problem in any type of structure, but especially residential. The Argentine ant is found mainly on the Atlantic and Pacific Coasts, as well as the Gulf Coast. The odorous house ant, which has been a problem in the southern part of the country, is beginning to work its way to the top of the list,” he added. “It’s one ant species you may not recognize when you first encounter it because you haven’t routinely dealt with it over the years.”

ANT BAITS. Bennett and his fellow researchers studied colonies of Pharaoh ants in one test. They placed 250 workers, two queens and about 20 milligrams of brood — the eggs, larvae and pupae of the species — in a nester, a unit that contains all stages of ants in a colony. They were put in a “shoe box” type of test arena — a small plastic container where researchers were able to perform various manipulations of baits and active ingredients. In doing so, they were able to determine how well the ants consumed baits and the mortality associated with the baits, he explained.

“We inserted some of the more popular baits currently on the marketplace in the shoe box. We determined that it does take a while for the active ingredients for those baits that performed well to be distributed throughout the colony and to the queens and the brood, and for worker ant mortality to occur. There was a fairly long period when the workers were collecting the bait and going back to the colony to distribute it. Usually queens and brood are not all killed.”

Purdue tested the following ant baits: Advion Ant Bait Arena (featuring the active ingredient indoxacarb); Maxforce FC Ant Killer Bait Gel Station (featuring the active ingredient fipronil); and the Advance Dual Choice Ant Bait Station (featuring the active ingredient abamectin). All of these baits provided 100 percent worker ant mortality, Bennett said, “but is the colony that sends the workers out going to rebound and provide future problems for your customers? You have to be concerned about this,” Bennett said.

Bennett said lab tests provide an indicator of how well an insecticide will work in the field. “However, it’s not absolute. What occurs sometimes in lab tests is not what you encounter in the field. Once you’ve done field testing and worked with PMPs, then you can determine how well a product will ultimately work.”

COCKROACHES AND BAIT AVERSION. According to Bennett, cockroach gel baits were studied by his team because of bait aversion problems that have arisen recently. “Aversion to insecticide active ingredients isn’t the problem. It’s aversion to the bait, which is an inherited behavioral trait. If cockroaches become overexposed to the components in a food bait, other than the active ingredient, they become averse to it,” he said. “You must keep that in mind and be sure to use your materials wisely to avoid future problems.

“We’ve come up with ways to deal with it, including IPM, which incorporates non-chemical methods, as well as other insecticide formulations, for long-term results,” Bennett said.

Bennett conducted lab tests with baits, including indoxacarb and fipronil, among others. “Over a seven-day period, we lab-tested a highly averse strain of German cockroaches — the ‘Cincinnati strain,’” he said. “The strain had been treated extensively with bait and as a result these cockroaches eventually became averse to eating any of the baits. We put bait in the shoe box containers, which included water, harborage and the normal food they feed on, and evaluated the consumption level as well as the mortality level of the target cockroaches. 

In two tests over several days, Bennett reported that none of the baits tested were totally consumed, but mortality levels with fipronil and indoxacarb were very high. Bennett conducted lab tests on oriental and brownbanded cockroaches as well. “We found that these baits worked pretty well on them, too. It takes time, however, and your customers have to be aware of that fact. The cockroaches have to find the baits, take them back to the nesting or harborage areas and distribute them among the cockroaches.”

Brownbanded cockroaches are a bit more difficult to control with baits, Bennett reported. “These roaches tend to be scattered more throughout a building. They’re not as localized, so getting the bait distributed can be difficult in a large structure. It will take time.

“Over a 14-day test period, we saw some of the baits performing better, but never achieved 100 percent control of these roaches in the lab,” Bennett said.

The author is a Milwaukee-based contributor to PCT.