Over-informed on IPM - Episode 005: Intro to IPM - What is a pest?

Show Notes

Some Super Cool Links 

Can earwigs be beneficial in some orchards? – Video

Monitoring and Conserving Earwigs in Washington State Apple Orchards

Field evidence and grower perceptions on the roles of an omnivore, European earwig, in apple orchards

Transcript

From UNH Cooperative Extension, this is Over-Informed on IPM

I got my start in entomology down in Virginia where, like in most of the country, agriculture means corn and soybeans. Because corn and soybeans are rotated, every once in a while, an errant corn plant will grow in a soybean field. I guess you could call a corn plant in a soybean field a weed? Its unwanted…but corn isn’t a pest organism so the term weed seems inappropriate. But of course biologists came up with a term for this errant corn growing in a soybean field. We just love coming up with terminology but I find this one particularly charming…they’re called volunteers. I just think that’s so lovely – the imagery of a talk corn stalk standing, dare I say it, proudly, in the middle of a soybean field. Charming!

But back to the topic of this week’s episode – what is a pest? By definition, a pest is any organism detrimental to humans, including invertebrate and vertebrate animals, pathogens, and weeds. So a pest could be emotionally detrimental, like the organisms that torment us personally. In agriculture, we kind of divide things up into economic and nuisance pests. Economic pests cause damage that effects your bottom line, like crop yield or quality. Nuisance pests are normally considered emotionally detrimental but in some circumstances they can have serious impacts on your bottom line. The first thing that comes to mind is wasps in pick-your-own fruit. They’re generalist predators that might eat a little bit of fruit, not enough to hurt your yield, but who wants to pick fruit in a field full of wasps! These insect swap from from one side of the good guy continuum to the other pretty fast.

But today we’re going to get over-informed on an insect group that you might be surprised lays anywhere else on the good guy bad guy continuum other than pest and that’s earwigs. Bare with me as I read a section from the 1941 USDA Technical Bulletin on the European earwig:

“The European earwig has come into prominence largely as a nuisance in and about human habitations rather than as an economic pest. A furtive insect with foul odor and formidable-appearing forceps, the earwig seems to have a proclivity for creating annoying situations – scuttling out from among the bed linens, lurking among foodstuffs, dropping upon the table from among cut flowers, marring choice ornamental plants, and falling in large numbers when an outer door is opened in the morning. Such occurrences drive the tidy householder to war of extermination, entered into with a zeal out of all proportion to the actual damage for which the earwig is responsible.”

Well if the writer of this bulletin is experiencing all of these things, I don’t know if any level of zeal would be out of proportion. That sounds like a pretty bad infestation. But they do end up in human habitations from time to time and they are creepy  but not at all dangerous. They are omnivorous so they’ll eat just about anything, including other insects, plants and decaying organic matter – like the wood surrounding a plumbing leak in your house. If you find earwigs in your house, you are much more likely to need a plumber than a pest management specialist. Earwigs are nocturnal so any time you encounter them, you’re likely rousing them from sleep – startling both of you. And they are pretty startling as they can pinch with chewing mouthparts on the front end and a pair of forceps on the back end. These are bigger and scarier on males.

Despite all of this, this group is pretty interesting from an ecological perspective. Several species in this insect order take part in some level of maternal care. These mothers guarding their offspring from predators and will clean eggs of pathogens using their mouthparts. This is very rare among insects. In agricultural settings, earwigs are thought of as both pest and beneficial predator of pests, depending on the system. To understand more of this story in tree fruit I called a buddy out in Washington State:

Rebecca Schmidt-Jeffries, USDA-ARS: So earwigs are really a mixed bag. Sometimes they’re a pest and sometimes they’re not. It really just depends on whether or not they can damage the fruit. In pome fruit, apples and pears, earwigs are really only beneficial. A recent graduate from Washington State, Robert Orpet, did a study where he removed earwigs and added earwigs to orchards and found that, where he added them, wooly apple aphid biocontrol was improved and there was no difference in fruit damage. So for the past ten years or so a lot of growers had thought that earwigs were a pest, but what Robert found was that earwigs were really only found in split fruit, fruit that was mechanically damaged and would be culled anyway. The earwig is not causing damage in those situations.

The other end of the spectrum is in soft fruit, they’ll chew on cherry. Organic nectarine and apricot orchards will see problems with earwigs.

So Robert showed that earwig biocontrol worked in apple in an experimental setting. We want to see if it works in a commercial setting. We want to see if they work in pear because they eat pear psylla, codling moth, and some other aphid species. We’re also interested to see if there’s any benefit to moving them from crops where earwigs are a pest.

Anna: Do you have a feeling of whether or not people are convinced?

It really seems to be leaning that way. Part of Robert’s study was to survey field managers feelings on earwigs. For the most part they were confident that earwigs weren’t pests in apple but they weren’t too sure whether or not they make for good biological control. As humans we tend to believe what we see with our own eyeballs. Managers are used to seeing wooly apple aphid mummies, lacewing larvae eating aphids, they can see predatory mites with a hand lens, but they don’t get to see predatory earwigs doing their thing because they hunt at night time – they’re nocturnal tree foragers that hunt and night and hide during the day – so there’s a little ways to go but I think we’re getting there that earwigs are good in pome fruits.

Anna: So what makes a good biocontrol?

Oh man – that’s a tough question. This is something I go through when people are learning what biocontrol is. So you give them an idea of what a specialist predator is and you give them an idea of what a generalist predator is, and then you ask them the pros and cons of using those for biocontrol. So obviously specialists would be really good at attacking the pest you want them to attack, but if your pest isn’t there your specialist is either going to die or leave. Generalists, like earwigs, are going to eat a bunch of things, maybe they’ll control more than one pest. That also means they won’t necessarily focus on what you want them to eat. If you do gut content analysis of earwigs you may find they’ve been eating lady beetles for example.

So love them or hate them, earwigs are a pretty interesting group. When they come into your house they may be firmly planted in the bad guy column for most people, but I feel pretty confident about putting them in the good guy column out in the apple orchards.

That’s all for this weeks episode. Thanks to Dr. Schmidt-Jeffries from USDA-ARS in Wapato, WA. And special thanks to Brentwood’s favorite son, Jason Lightbown who wrote and performed out theme music.