When good bugs go bad

Suzanne Wainwright-EvansBeneficial insects, predatory mites and beneficial nematodes are being relied on more these days, whether they are purchased or just naturally occurring. We know their job is to help control the pests that dine on our crops, but sometimes they do not behave as they should, opting to eat other beneficials.

Ladybird: friend or foe
Ladybird beetles are always thought of as friends in the nursery and landscape, but sometimes they are not on their best behavior. One of the more commonly seen ladybird beetles today is the multicolored Asian lady beetle, Harmonia axyridis. It has a voracious appetite for other insects; unfortunately, it’s not always pest insects.

This lady beetle was first release in the United States by the federal government to help control tree pest insects in 1916. This was before we understood the consequences of such an act. Subsequent releases continued throughout the decades with no real signs of establishment.

But in the 1980s there was a population explosion. For farmers and nursery owners this seemed to be a blessing because of this lady beetle’s ability to gobble up many pest insects, especially aphids. An adult can consume between 90 and 270 aphids per day in the larval stage, and while growing into an adult can devour 600 to 1,200 aphids. So you can see why some people want them around.

The problem started when a substantial number of these lady beetles started to overwinter in people’s houses. It’s not that the beetles wanted to hang out with humans, it was that the homes (often light colored) mimicked their native overwintering sites. As they congregate in the autumn, they squeeze into cracks, finding their way indoors. This also sometimes caused health issues; research has shown that their home invasion may trigger seasonal inhalant allergies.

As if these problems were not enough, there was also an ecological issue occurring. Harmonia will feed on other ladybird species and can compete with them for the same food sources. H. axyridis had been blamed for the extinction of the nine-spotted lady beetle (Coccinella novemnotata). Fortunately, this is not true, and thanks to The Lost Ladybug Project (www.lostladybug.org), these native nine-spotted ladybirds have been found again. But in Europe, Harmonia is causing such problems that the scientists from the UK’s Centre for Ecology and Hydrology are looking into possibly using biological control agents to stop it.

H. axyridis, once thought of as a great biological control agent has now turned into a health issue for some, but for nurserymen it’s still a great beneficial to have around.

The “mighty” mites
More and more commercial growers are relying on predatory mites for control of pests. Years ago there were only a few predatory mites available on the market, but today there are many, and the programs using them have become much more complex. These programs consist of using multiple species to target multiple pests, but how do these beneficials interact with each other? A lot of this we are still learning, but some things we do know.

Phytoseiulus persimilis and Amblyseius californicus are the two most popular predatory mites used today for spider mite control. Typically growers use P. persimilis for fast knock-down and solely for spider mite control. A. californicus is used more for the hotter months of the year, when P. persimilis may not work as well. It is not as aggressive of a feeder as P. persimilis, but will alternatively feed on other food sources like pollen, thrips and even P. persimilis. Because of this you have to be very careful when applying these two predatory mites together. You don’t want to have the P. persimilis you just paid good money for eaten up by A. californicus. This is where talking to your biological supplier to get the appropriate rates is so important. When these two mites are used in conjunction, there must be a plan.

Another predatory mite, Amblyseius swirskii, is a relative new-comer and has shown to be very useful in a biological control program. It is typically used to help control whitefly and thrips. Three researchers at the University of Guelph looked closer at this predator to see if it was opting to feed on Amblyseius cucumeris, another predatory mite used for thrips control. They found that A. swirskii like to eat A. cucumeris juveniles instead of thrips. A. cucumeris also fed on A. swirskii, but not at a high level. What does this mean to someone wanting to use these beneficials? Work with a supplier that can help set up a program with the correct rates and properly timed releases.

Green lacewing cannibalism
Cannibalism could be green lacewing (Chrysoperla sp.) larvae’s middle name. Luckily, Mother Nature has developed a way to deter green lacewing young from eating each other by laying eggs on the top of threadlike stalks. Once these eggs are ready to hatch, there is a color change from pale green to brown. Once hatched, the larvae then crawl away not realizing its siblings’ eggs are right above and would have made a good meal. Instead they crawl off looking for other sources of food.

Green lacewings are commercially available in their egg or larva stage. Many growers are using them to help control pests like aphids and other soft-bodied insects. If you apply too many of these guys and there are not enough pests for them to feed on, the larva will eat each other if they cross paths. Luckily, the adult green lacewings feed on pollen and nectar. But if you are applying larvae, make sure you spread them out.

Before starting a biological control program, make sure whatever agents are released are not going to predate each other. Any quality supplier will be able to help you with this information. If you are relying more on naturally occurring beneficials, this is not typically a problem. Just watch any pesticide spray used so you do not upset the balance.