Biological Control

By   October 8, 2015

Given enough time, nature usually finds a balance through biological control. There’s a famous quote from Jonathan Swift:
Big bugs have little bugs
Upon their backs to bite them.
Little bugs have littler bugs.
And so, ad infinitum.
Modern plant science has found a way to put this saying to work with several instances of “littler” bugs that attack the bigger bugs that harm grass. Biological control is a growth area in plant science now, and many of these biologicals are still new or in the testing stage.

Some bacteria cause disease in insects, call it biological warfare among bugs. The most common bacterium used against turf insects in Bacillus thuringiensis, often called Bt. Bt works by producing a toxin which paralyzes the insects gut, so the insect stops feeding right away and later dies. New Englanders are familiar with Bt for its effectiveness against Gypsy Months. It’s also effective against other types of caterpillars, but it doesn’t affect anything else. A new strain is currently being tested against white grubs and appears to be effective.

Another species of bacterium causes a disease in Japanese beetle grubs. Bacillus popilliae, sometimes called Milky Spore, causes “milky disease” in the grubs. Infected grubs take on a very milky appearance and are very flaccid. It’s action is very slow though and sometimes takes years to build up effectiveness. Milky Spore disease is available now and, although somewhat expensive, offers good value because of it’s long lasting effectiveness.

Neither of these bacteria are 100%, but can reduce the population enough so that it’s target bugs are no longer a problem.
Similar to bacteria, some fungi can cause disease in or in insects. It’s almost like a terminal case of athlete’s foot. Several of these fungi already exist naturally, others have been identified and need to be adapted for use here. One of the “native” fungi is Beauveria bassiana, which attacks chinchbugs and billbugs. Especially in cool, wet springs these insects may be found covered with tiny strands of materials that looks like cotton candy. These strands are mycelia of the fungus, which has invaded the insect body and attacked the internal tissue.

Another fungus, Metarhizium anisopliae, appears to be quite effective against white grubs in the soil. Researchers are commercializing this now and have hopes for its success.

Insect Growth Regulators, known as IGRs, are naturally occurring hormones that confuse the insect’s development. and prevent it from reaching adulthood. Several IGRs have been developed for such insects as whiteflies and mosquitoes, and at least one is being tested for white grubs. With my collection of pets at home, I’m a frequent user of Precor, an IGR that prevents fleas from maturing. The idea is that only adult fleas bite and reproduce, and preventing them from reaching adulthood ends the cycle.

 Nematodes

Nematodes are small parasitic worms that can carry bacteria inside their body, so when the nematode penetrates an insect victim, it releases bacteria, which break down the internal tissues of the target insect, resulting in death by infection. As the insect dies, the nematodes reproduce within the cadaver, and the juvenile nematodes pick up some of the bacteria and move on to new insects.
These are called Entomopathogenic Nematodes (“entomo” = insect; “pathogenic” = causes disease) and are already effective against several turf insects. The big prize will be when they finish development of nematodes that attack white grubs. Researchers are getting close.

Endophytes will be covered more in the grass seed section. Some species of grasses contain endophytes, which are fungi which produce substances which are toxic to certain insects. Endophytes occur in some perennial ryegrasses and fescues and have been incorporated into some commercial cultivars. They are effective in the suppression of chinchbugs and billbug populations and are active against cutworms and webworms as well.