Tag: beneficials

Underrated Beneficial Arthropods Part 2: Natural Enemies

Continuing with the theme of Underrated Beneficial Arthropods that I brought up in my December post about Underrated Pollinators– I will be focusing on the next category of what I consider the trio of beneficial arthropods (which includes pollinators, natural enemies, and nutrient cyclers).

Natural Enemies

Natural enemies are comprised of predatory and parasitic arthropods, in which one or more life stages of the arthropod feed on other organisms, such as garden pests, thereby killing them. Many gardeners are familiar with this group which includes some of our most ‘famous’ predatory arthropods such as mantids, lady beetles, lacewings, etc. This category, however, contains a plethora of beneficials that you may not always think about because most of what they do often occurs behind the scenes.

This is also a very broad category so this post will not be a comprehensive collection of all the natural enemies out there (because there are literally countless) but will have a variety of some of the most abundant, important, and unique. Like the last post it will be grouped by order or major category of Arthropod, where I will go into examples of the rockstars within that category. I will also include several resources at the end which I used to compile this information and encourage those of you who want to dig deeper into the world of natural enemies to take a look.

Flies

Flies (order: Diptera) are an incredibly diverse group of insects which provide a wide variety of different ecosystem services. They undergo complete metamorphosis (which basically means that they have 4 growth stages starting as an egg, and a major transition from their larval form of maggots that turn into pupae, and then into the adults that we recognize as flies). As such, flies also inhabit countless different ecosystems (including terrestrial and aquatic) and can be found on every continent including Antarctica. We learned about pollinating flies in the Underrated Pollinators blog post but, like many of the arthropods that we are going to cover, flies span all 3 of the major categories of beneficial arthropods. We will discuss them a bit more in-depth in the nutrient cycler category, but for this post I wanted to highlight some examples of the cool predatory and parasitic flies that we can find in our yards and gardens.

Tachinid flies [Tachinidae] are dark-colored medium-sized flies that are recognized by the dark bristles covering the body of the adults (which look similar to house flies). This family contains over 8000 described species and can be found on nearly every continent. The cool thing about this group is that every single species of Tachinids has a parasitic larval stage and many are continually utilized as natural enemies of many common pest species. As such, these flies have also been intentionally imported into various locations for biocontrol purposes. The targets of tachinids include a variety of different arthropods including caterpillars, sawflies, grubs, adult beetles, and many more! To learn more about this awesome group of parasitic flies, check out this excellent article on Tachinids written by Susan Mahr of University of Wisconsin-Madison.

Adult Tachinid fly. Photo: David Cappaert, Bugwood.org

Hover flies [Syrphidae] also known as flower flies or ‘Syrphids’ are another awesome group (you might recognize them from their shout-out as pollinators in their bee-resembling adult stage). Larval syrphids can be terrestrial or aquatic. You may recognize the term “rat-tailed maggots” which refers to the aquatic larval syrphids that have a breathing tube resembling a ‘tail’ at the end of their body. They are used in biocontrol of a variety of soft-bodied arthropods including aphids, mealybugs, thrips, mites, and more. To learn more about hover flies, check out this excellent resource about their use as a biocontrol agent from Cornell University. 

Syrphid larva feeding on oleander aphid. Photo: David Cappaert, Bugwood.org

True Bugs

True bugs (Hemiptera and Homoptera) contain a variety of easily recognizable garden inhabitants that can be characterized by their piercing/sucking mouthparts. Although there are many plant feeders and common pests in this category (including aphids, cicadas, mealybugs, leafhoppers, scale insects, stink bugs, etc.) there are also some excellent natural enemies that don’t always get the spotlight. Often referred to as ‘Predatory Bugs’, this fierce category of insects includes assassin bugs [Reduviidae], big-eyed bugs [Geocoridae], minute pirate bugs [Anthocoridae], damsel bugs [Nabidae], and predatory stink bugs [Pentatomidae]. They vary in shape and size, but feed in the same way: by piercing their prey with their mouthparts and sucking out the fluids. Many are, therefore, excellent biocontrol agents in our yard and garden landscapes. Some are even commercially available for use in greenhouses and hoop houses/high tunnels to suppress populations of common soft bodied insect and mite pests. To learn more about them, check out this great article on Predatory Bugs from Colorado State University.

Assassin bug feeding on elm leafminer. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Wasps

Wasps (order: Hymenoptera) often strike fear in many people who are unaware of the sheer diversity and complexity of this group of insects. You learned about the pollinating wasps in my last Blog post, but there are also several groups of predatory and parasitoid wasps that are commonly found in our landscapes. Predatory wasps include many different species including the commonly known social wasp species (such as yellow jackets, hornets, and paper wasps) but also include countless other predatory species. One group of these common predators includes the striking family of thread-waisted wasps [Sphecidae]. This family includes spider-hunting wasps, cricket-hunter wasps, and katydid wasps. Another common family includes the cicada-killers [Crabronidae] which are a large and intimidating-looking wasp species that are actually harmless to humans. Both of these groups of solitary wasps work similarly by paralyzing their prey (often characterized by their common names) and then bringing their live bodies back to their underground nests for their larvae to feed on.

Cicada killer wasp carrying a paralyzed cicada back to her nest. Photo: Ronald F. Billings, Texas A&M Forest Service , Bugwood.org

Parasitoid wasps are an incredibly large group of wasps which include many species varying greatly in size and shape. If you’ve seen the movie ‘Alien’ you have an idea of what the life cycle of these wasps is like. The mother lays her eggs in a living host (which spans countless species of insects), and her larvae feed on the host from within, until they emerge as adults. This includes groups such as braconid wasps [Braconidae], ichneumon wasps [Ichneumonidae], and families such as Aphelinidae, Scelionidae, Eulophidae, and Trichogrammatidae. Each species of parasitoid wasp needs another species of host insect in which to complete its life cycle, and entomologists estimate that there may be hundreds of thousands of species of these incredible organisms!  Many parasitoid wasp species are important biocontrol agents for some very famous insect pests (including the Emerald Ash Borer, which those of us in North America are very familiar with). You can even purchase some commercially available species of these parasitoids to manage certain pests in your gardens and greenhouses. There are even hyperparasitoids which are parasitoid wasps that specifically use other parasitic wasps as hosts. To learn more about the incredible world of wasps, check out this great article by Marissa Schuh from University of Minnesota.

A tomato hornworm caterpillar parasitized by braconid wasps that have emerged from internally feeding on the caterpillar, and exited their white silken pupae as adults. Photo: Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Beetles

Beetles (order: Coleoptera) are one of the most diverse groups of insects and include groups that fall into each of the three categories of beneficial arthropods. Although some are pests in their larval and/or adult stages (example: Japanese beetles) and feed on a variety of different plant structures including leaves, stems/trunks, fruit, flowers, seeds, and roots. We are also familiar with some of these predatory beetles (with many shining a spotlight on the easily recognizable and lovable lady beetles). That being said, there are countless other groups of predatory and parasitic beetles that can have a significant beneficial impact on our landscapes.

A violet ground beetle (Carabus violaceus) which is a nocturnal hunter of slugs. Photo: Mary C Legg, Mary C Legg, Bugwood.org

One example of a large group of these are the predatory ground beetles [Carabidae]. This dark and iridescent family of beetles can vary in size and shape. They have distinct and powerful chewing mouthparts (mandibles) which enable them to be excellent generalist predators and scavengers. The more than 40,000 species (spanning every continent except Antarctica) are common garden-inhabitants and perform invaluable services of biocontrol in agricultural, horticultural, and home garden settings.  

In addition to feeding on many insect and mollusc pests, certain host-specific groups of plant-feeding beetles are also used in the biological control of weed species (including many noxious weeds) and reared by insectaries for distribution.

Neuroptera

Neuroptera (derived from the Greek words meaning “nerve” and “wing”) is an entire order consisting only of predatory insects! The most famous of this group are the lacewings [Chrysopidae] (which many gardeners recognize as an awesome predator of many soft-bodied garden pests). This order also includes other incredible species such as antlions or “doodle-bugs” [Myrmeleontidae], dobsonflies [Corydalidae], mantidflies or mantid lacewings [Mantispidae], snakeflies [Raphidiidae], and more.

Lacewing larva feeding on potato psyllid. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Mites

Mites (subclass: Acari) are another often misunderstood group of arthropods. These are arachnids (characterized by 4 pairs of legs and two body segments). Mites feed on countless living and decaying organisms including plants, animals, fungi, yeasts, algae, mosses, and even bacteria. They range in size, though most are tiny and many are even microscopic soil-dwelling organisms. The sheer diversity of mite species (due to their very broad range of ecological roles) indicates that there may be over a million species that have yet to be described.

Packet of predatory mites, to be released in a nursery. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Many gardeners recognize some common mite pests (such as the two-spotted spider mite), but there are countless predatory mite species as well. Predatory mites [Phytoseiidae] are slightly larger than spider mites, and excellent predators of spider mites and eriophyid mites which are common plant-gall causing mites. There are several species used in biocontrol of soft-bodied insect and mite pests as well as commercially available ones that you can purchase.

Spiders

I am sure that no one reading this post would be surprised to find these amazing arachnids on this list. Although some species are dangerous to humans, most species of spiders will leave you alone, and are incredible predators of lots of indoor and outdoor insect pests. Many humans dislike these 8-legged organisms, though most are still understanding of the important role that they play. Spiders can be strikingly beautiful, colorful, and variable in size and shape. Although some build webs to capture prey, others are active hunters or trappers that capture other organisms on which to feed. Some are even kept as pests (I had 4 tarantulas of my own at one point, and I thoroughly enjoyed observing them daily, and handling the more mild-mannered ones). There is so much that can be said about the incredible role of spiders in our homes, gardens, and natural ecosystems that it would be difficult to condense into a short summary (and may therefore be a separate Blog post in the future since this one is getting pretty lengthy).  

Jumping spider. Photo: Joseph Berger, Bugwood.org

Centipedes

Centipedes span 4 different orders including soil centipedes [Geophiulomorpha], garden/rock centipedes [Lithobiomorpha], giant centipedes [Scolopendromorpha], and house centipedes [Scutigeromorpha] all of which are carnivorous. This group of arthropods is characterized by many body segments, venomous fangs, and 1 pair of legs per segment. Although many people are creeped out by these ferocious many-legged beasts, they stay out of the way and eat many common pests in home and garden landscapes.

Stone centipede. Photo: Joseph Berger, Bugwood.org

I hope that you enjoyed reading about some of your gardening companions, and if nothing else: I hope that it broadened your perspective of all the different critters that share your landscape with you. Stay tuned for my next post in June, which will cover the third and final category of beneficial arthropods: the nutrient cyclers.

Resources

Natural Enemies of Pests. (Colorado State University).
https://agsci.colostate.edu/agbio/ipm/natural-enemies-of-pests/

Tachinid Flies. (University of Wisconsin-Madison).
https://hort.extension.wisc.edu/articles/tachinid-flies/

Syrphid Flies. (University of Minnesota Extension).
https://extension.umn.edu/beneficial-insects/syrphid-flies

Hover Flies. (Cornell University).
https://cals.cornell.edu/new-york-state-integrated-pest-management/outreach-education/fact-sheets/hover-fly-biocontrol-fact-sheet

Wasps are a gardener’s friend. (University of Minnesota Extension). https://extension.umn.edu/yard-and-garden-news/wasps-are-gardeners-friend

Cicada Killer Wasps. (University of Kentucky).
https://entomology.ca.uky.edu/ef004

Parasitoid Wasps. (University of Minnesota).
https://extension.umn.edu/beneficial-insects/parasitoid-wasps

Hyperparasitoid Wasps. (North Carolina State University).
https://entomology.ces.ncsu.edu/biological-control-information-center/beneficial-parasitoids/hyperparasitoids/

Predatory Ground Beetles. (Colorado State University).
https://agsci.colostate.edu/agbio/ipm-pests/ground-beetles/

Biological Control of Weeds. (Washington State University).
http://invasives.wsu.edu/biological/index.htm

Digging these wasps!

After writing about the unusually bad scourge of Japanese Beetles earlier in the month, I thought I’d continue on down the “garden bugs” path. The Japanese Beetles have died down, but now we have oodles of these pretty black and yellow-spotted waspy things around. They’re everywhere, and in large numbers. I planted some buckwheat over our potato garden bed, and it is covered up with them. The point of the buckwheat was as a primo late-season nectar source for our honeybee hives as they prepare for winter. Blooming for the last week or two, I kept checking it expecting to see happy bees, feasting away. Nada. Just the wasps.

Intriguing. A brief googling revealed the wasp to be Scolia dubia, one of the “digger wasps.” They rarely sting, and better yet -their larvae are parasites of Japanese Beetles! All that swooping around over our so-called lawn is apparently the mating dance, then the female digs into the soil to find the grubs. After stinging the grub, she lays an egg…and you see where this is going. Cozy winter grub cocoon for the pupating larvae!

Blue Wing Digging Wasp on buckwheat.
Blue Wing Digging Wasp on buckwheat.

Back to the bed of gourmet buckwheat. I’m thrilled to see all those wasps feeding on the nectar. Eat, dig, and be merry, ladies! But what about the honeybees – seemingly ignoring this glorious patch of buckwheat planted just for them? I don’t need any more picky eaters…aren’t our two dinner-snubbing dogs enough? So I asked Dr. Richard Fell, legendary Apiculture faculty here at Virginia Tech, about this mystery. “Honeybees only work buckwheat in the morning” sayeth Rick. Went out this morning and observed that buckwheat is indeed the breakfast of champions. The entire patch was literally humming with multiple species, including loads of honeybees. I’d only been checking in the evening.

Addendum:
So my post apparently isn’t breaking news. Just came across this as I checked my Scolia spelling. Sounds like they had beetles galore in Maryland as well this summer.
If you’re not familiar with Dr. Michael Raupp, Entomologist and Extension Specialist at University of Maryland, he’s awesome, and his “Bug of the Week” blog is a must. His September 1 post reviews the digger wasp/japanese beetle relationship as well, with more factoids and a lovely video featuring writhing grubs. http://bugoftheweek.com/blog/2014/9/1/white-grubs-beware-the-blue-winged-digger-wasp-iscolia-dubiai-has-arrived

Mortal Kombat – garden version

Soil solarization is regarded as an environmentally friendly alternative to pesticides for controlling nematodes, weeds and disease.  Sheets of plastic (generally clear) are spread over the ground and solar energy heats the soil underneath to temperatures as high as 55C (or 131F).  Since the soil environment is usually insulated from temperature extremes, the organisms that live there are unlikely to be resistant to heat stress.

This is a practice best suited to agricultural production, where monocultures of plants have attracted their specific diseases and pests.  Decades of research have shown success in controlling pests in greenhouses, nurseries, and fields.  But there’s a down side to this chemical-free means of pest control.

It shouldn’t be surprising that beneficial soil organisms, in addition to pests and pathogens, are killed by solarization.  Studies have found that soil solarization wipes out native mycorrhizal fungi and nitrogen-fixing bacteria.  One expects that other beneficial microbes, predacious insects, and parasitoids living in the soil (but so far unstudied) would be eliminated as well.

This may be an acceptable loss to those who are producing crops; soil can be reinoculated with mycorrhizal fungi, for example.  But for those of us caring for our own gardens and landscapes, this is literally overkill.  (And consider that most of us probably have trees and shrubs whose fine roots extend over our entire property.)

So this spring, instead of solarizing your soil, consider some less drastic measures of pest and disease control. Minimize soil disruption to preserve populations of desirable microbes. Plant polycultures (more than one species) in your vegetable garden, or at least practice crop rotation.  Protect and nourish vegetable gardens with compost.  Use coarse organic mulches, which provide habitat for beneficial insects and spiders, in landscaped areas.  Above all, try to treat your soil as the living ecosystem it is, rather than a war zone.

Are Fertilizer and Insecticide Spikes a Good Idea?

One of the products that I often hear gardeners raving about are their fertilizer / pesticide combination spikes which are supposed to not only feed your plants, but also kill all of the insects which attack them.  I, personally, have not used these products, but I’m generally the kind of person who says “If it works for you then keep using it”.  Still, these spikes bug me a little.  Here’s why.

First of all I should point out that I’m not opposed to fertilizer spikes by themselves.  I’m a little concerned that fertilizer should be spread out instead of concentrated in one place, but still, I don’t consider them that bad.  The insecticides used for these spikes is where I have the problem.  Once upon a time these spikes were made with a chemical called disulfoton (aka disyston) which is bad news.  It’s a water soluble chemical which is highly toxic to people.  If you have an old package of fertilizer / insecticide spikes around there’s a good chance they were made with this chemical.  Do yourself a favor and get rid of them.  This stuff is really toxic and not to be messed with.  On the other hand, if you’ve purchased fertilizer / insecticide spikes recently, then the active insecticide in those spikes is probably imidacloprid.  Imidacloprid is a mixed bag when it comes to safety.  It’s not nealy as toxic as disulfoton, but it’s not non-toxic.  It has been banned in Europe for a variety of reasons, the most important of which seems to be that it was implicated in the collapse of bee hives (imidacloprid is systemic insecticide so it will get into a plants pollen where honey bees could eat it).  At this point it hasn’t been ruled out as having something to do with hive collapse here in the states — though if it does have a role it does not seem to act alone.  It can also affect other beneficial insects who feed on pollen.  Additionally, it has been known to control some pests while allowing mites to go crazy — in fact, it may even increase the rate of mite egg laying.

But imidacloprid is an effective insecticide which works against a wide range of insects which you that you might find on your plants.  It is much safer than many of the older systemic insecticides, and it isn’t readily translocated to fruits (a problem that many people are concerned about with systemic insecticides is the movement of these insecticides into the fruit itself where it can’t be washed off — Imidacloprid is translocated to fruits –just not that much — it moves in the xylem and fruit takes up mostly phloem).

So these spikes are one of those things that I’m wary of.  Not to say you shouldn’t use them, but be aware of what they are and what they could do before you buy them.