Clover mites: The other spider mites

A typical individual of the genus Bryobia, often called a "clover mite". Photo by Scott Justis.

Most gardeners and plant-keepers are familiar with spider mites, including well known pests like two-spotted spider mites (Tetranychus urticae), boxwood spider mites (Eurytetranychus buxi), and spruce spider mites (Oligonychus ununguis). However, some people each spring or fall become VERY familiar with another group of spider mites: so-called "clover mites" in the genus Bryobia.

Clover mites can become a nuisance when they invade homes in large numbers. This spring we have seen a  number of samples submitted to the clinic already. But first, a little bit about these mites.

What are they?

Clover mites are arachnids and true members of the mite family Tetranychidae (spider mites). All members of this family feed on plants throughout their life. Typical spider mites mentioned above are in the subfamily Tetranychinae - these are the most commonly encountered pest species. Clover mites belong to the other less common subfamily: Bryobiinae. Within this subfamily are several genera including a few that are also pests of plants. One of the more well known, for example, is the brown wheat mite (Petrobia latens (Müller)) a pest of wheat and barley that is also known to transmit barley yellow streak mosaic virus. Members of this subfamily do not spin silk as is common in Tetranychinae.

How do you identify these mites?

As is typical for many mites, clover mites are small. Adults are around 1 mm in length and the young are smaller.

A dried clover mite specimen on a US penny. Photo by Matt Bertone.

If you can observe them up close there are several characteristics that can help identify them as clover mites (or at least members of the genus Bryobia). They are typically green or brown (sometimes grayish) with red or orange legs. Their first pair of walking legs is elongate compared to the other legs. They also have a wrinkly body, appearing as if it was made by a fingerprint. One feature that seems fairly distinct for the genus is a four-pronged tip of the snout (above the mouthparts), each "tine" tipped with a flattened scale-like seta. Scale-like setae are also present on the body. Other that these traits, specimens need to be mounted on slides and viewed under a compound microscope to see the small structures.

High magnification photo of clover mite specimens showing traits of the group. Photo by Pia Scanlon DAFWA

What do they do?

Clover mites will feed on a variety of different plant types. In fact, the different feeding forms have long been considered different species in a species complex (often commonly referred to by the scientific name "Bryobia praetiosa"). A few of the variants mentioned by Jeppson et al. (1975) are as follows: (1) those that feed on fruit trees, are multivoltine (many generations per year) and overwinter as eggs; (2) those that feed on a wide range of herbaceous hosts, univoltine (one generation per year) or multivoltine, and overwinter at various stages; (3) those that are specific to English ivy, multivoltine, and overwinter at various stages; and (4) those that infest gooseberry, are univoltine, and overwinter as eggs.

A group of clover mites on grass. Photo by Whitney Cranshaw

Injury to plants is typical of other spider mites, showing a general linear or random stipple pattern:

Clover mite damage on impatiens. Photo by Rayanne Lehman

Clover mites are rarely an important pest of plants. They are most active in cooler weather - thus this post may already be a tad late. The following is a nice phenogram from Jeppson et al. (1975) showing when certain mite stages are present in Canada:

One of the main issues with clover mites - and the reason I mentioned for writing this post - is that high populations often hatch or become active in the vegetation around the foundations of human structures. This usually happens in the spring and fall. Despite only feeding on plants, they can travel into houses in huge numbers and worry homeowners. They are especially worrisome when the residents squish the mites, causing a red smear. Although it's the mite's blood, people mistake it for theirs and think they are dealing with a blood-feeding organism (which they are not). Although the stains can persist, the mites themselves very quickly dry out and die inside. Thus, no chemical control is recommended for inside the home; one can simply wait for them to die or vacuum up the mites. Insecticides can be used on the vegetation and foundation within 18" of the structure, but is rarely needed unless the mites have been an issue. Many general, over-the-counter insecticides used for various arthropod pests will work, but please heed local application laws and product labels.

References:

Jeppson, L. R., Keifer, H. H., & Baker, E. W. (1975). Mites injurious to economic plants. Univ of California Press.

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P.S. - People often mistake a few common mites that crawl around the foundations of homes for "clover mites" (enough for a future post, perhaps). Here are two common RED mites you might see.

velvet mites (Trombidiidae):

Velvet mites are like small strawberries, but large for mites (typically 4 mm long, but some over a centimeter!). They are parasitic on insects as larvae and predators as adults. They do not bite humans.

concrete mites (Erythraeidae: Balaustium sp.):

Concrete mites are smaller than velvet mites but larger than clover mites. They are often abundant on concrete (hence the name) where they scavenges food. In some situations they have been known to bite people, but do not suck our blood. These situations are rare. 

Dickeya dianthicola in the production of herbaceous ornamentals

During the month of March several producers submitted samples to the PDIC that turned out to be infected by the bacterium Dickeya dianthicola. See our full write-up on the Plant Pathology Extension Portal.

Plant Diagnostic Workshop Set for October 7, 2016

The Plant Disease and Insect Clinic (PDIC) will conduct a hands-on workshop in plant disease diagnosis for NCCE Area Specialized Agents and County Agents. 

Date: Friday, October 7, 2016

Time: 8:45 a.m. to 3:15 p.m. 

Place: 1418 Gardner Hall, and the Plant Disease and Insect Clinic, NCSU campus

Instructors: PDIC staff

Participants will learn approaches and techniques that they can use to diagnose plant diseases and disorders. They will examine live material in the classroom and in campus landscapes. Participants will use the skills and knowledge gained from the workshop to “walk through” the process of diagnosing a clinic sample. 

For more information email barbara_shew@ncsu.edu

Seating is limited to 20 Participants

NCCE Area Specialized Agents and recently hired County Agents receive priority

June Beetle Time!

It happened. As I was walking back from lunch my friend and I saw them, buzzing around like little fighter jets. These insects were not wasps, or flies, or dragonflies, but green June beetles (Cotinis nitida (L.)). You'll probably see them too, soon. Then in a few weeks they'll be gone. Well, at least the adults will be.

An adult green June beetle (Cotinis nitida)

Several scarab beetles are called "June beetles" or "Junebugs". Some are more properly referred to as May beetles* such as the brown or reddish-brown Phyllophaga and some Serica species (both in the subfamily Melolonthinae). Other beetles typically called June beetles include the lined June beetles in the genus Polyphylla which are also members of the Melolonthinae.

Green June beetles, however, are members of the beautiful and diverse subfamily Cetoniinae, or flower chafers. This group is typically distinguished by a flat appearance, antennal attachments that can be seen from above, and, in some groups, distinct "shoulders" (humeri - seen as little triangles in the front corner of each wing cover in the photo above). Many members of the group are vividly colored and some are enormous - in fact among the largest insects in the world are the aptly named Goliath beetles (Goliathus spp.).

The species itself is a beautiful emerald green with hues of bronze and tan. Some areas of the body are shiny while others are more flat. It's head looks like it's been hammered out of metal, complete with a horn and a ridge:

Close up of a green June beetle head

These beetles measure about an inch long and, thus, are quite noticeable. There are several species in the genus Cotinis, but the only one in North Carolina is C. nitida. Another local relative, Euphoria fulgida, is similarly colored, but has a triangular scutellum in between the wing covers.

Green June beetles are among the fastest flying beetles around**. It takes a second to determine that they are in fact a beetle and not some large bee or wasp - this can create some momentary terror for those afraid of stinging insects when they are buzzing around. Their rapid flight is aided by the fact that, unlike most other beetles, their wing covers (elytra) remain closed during flight. In fact they are fused and the wings slide out the sides when in use. This makes them particularly streamlined and agile, rather than exhibiting the clumsy flight of other beetles. Although they may come to lights, these beetles are most active during the day.

The western species Cotinis mutabilis in flight. Note how the wing covers are closed during flight, unlike most other beetles. Photo by Dennis Ancinec

So where are they going so quickly? Well, adults (like most adult animals) are interested in two things: mating and eating.

Upon emerging from the ground (more on the life cycle below) the beetles are eager to mate. Females generally stay on the ground and produce a pheromone which attracts numerous suitors. After mating multiple times, the takes off along the ground to find a suitable spot to lay her eggs.

On the food side, green June beetles are known to be pests of soft-skinned fruits and vegetables. This is where their other names come from: fig-eaters or fig beetles. Although not exclusive to figs, these beetles will also attack peaches and other stone fruits, pears, apples, grapes, bramble fruits, tomatoes and corn, among others. They typically attack ripe or over-ripe fruits that are easier to break open and produce early fermentation chemicals we can't detect with our nose. Once at the fruit, the beetles emit a chemical that brings others to the food source, causing a snowball effect which can spill over to other fruits. The physical damage along with fecal matter from the beetles fouls the fruit making it inedible. The feeding, however, increases the reproductive potential of the beetles.

A group of green June beetles attacking a ripe pear. The fruit will be ruined for consumption. Photo by J. Reynolds

Females look for soil that has a high organic matter content, preferring areas with decaying vegetable matter and dung on which the larvae feed. Digging into the ground with their strong, rake-like forelegs and horn, the female lays from 10-30 eggs in a ball of soil and organic matter. She will continue to feed, mate and lay eggs several times.

Larvae go through three instars in the ground. In addition to feeding on organic matter, larvae sometimes cause damage to plants by eating roots. Their digging may also disrupt the root system, especially on turfgrass. Thus both adults and larvae are economically important (though only in some situations). Larvae often live in pastures and fields, but have also been found in leafcutter ant mounds in TX. They can be seen crawling on their back after rains flush them out of the ground; they also travel this way in the soil. This back-crawling behavior is unique and an easy way to quickly identify larvae.

This larva is just the way it likes to be: larval green June beetles are typical white grubs, but atypical in that they travel on their back when moving on the ground or quickly through the soil.

Green June beetles go through one generation per year. The larvae that hatch in the summer from eggs feed until the cooler months when they await the next year's warming spring season. They resume activity for a short time and then spend a few weeks as a pupa, before emerging again in the summer as an adult.

As far as pest status and control, green June beetles are most often an issue in and around pastures. Damage by larvae is characterized by patches of loose turf caused by destruction of roots. As described above, the adults often attack various fruits, but fields and orchards around grassy areas that apply manure or have livestock may be at highest risk for attack by adult beetles. Several types of chemicals are available to apply for control of larvae, and should be treated soon after the larvae hatch in late summer, after breeding season. As far as adults, monitoring using fruit baits near the edges of fields containing fruit crops can help identify the timing and density of the beetles. However, note that like Japanese beetle traps, these bait stations may actually draw beetles nearer to fields. Knowing the local history of outbreaks can also aid in predicting risk.

Colored SEM of a green June beetle by Daniel Kariko 

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* these names are generally based on the timing of usual emergence, despite changes in climate likely affecting this window
** you get interesting results when searching for Cotinis + flight

Mosquitoes in Winter

A female Culex tarsalis, a species that overwinters as a diapausing adult.

The following is a guest post from our mosquito ecologist Michael Reiskind. You can find more of his work here.

Well, we finally have winter like weather here in NC. I saw a flying, adult Aedes vexans on December 23rd, but the hard freezes over the last couple of days should eliminate those guys.

Early in my academic career, I remember seeing a talk by a “freelance” mosquito control professional who provided service to New York City during the initial outbreak of West Nile virus, in 1999. I remember him noting the dramatic decline in Culex pipiens the two weeks after he sprayed between October 8-15th. Of course, that may have coincided with the onset of cold weather. As most even casual observers would agree there are no mosquitoes in winter. Right?

Of course, it is not that mosquitoes disappear in winter; just the life stage we love (to hate): biting adults. Just as we don’t see annual plants (say, tomatoes), mosquitoes are still there. But where? And how?

The avoidance of unproductive (and inhospitable) times is widespread among life. Many animals can go into a low metabolism period: hibernation for mammals, and diapause in insects. Insects prepare for this by building up resources, and then by lowering their energy demands to as low as possible.

One of the most fascinating things about diapause in insects, and even in the family of mosquitoes, is the diversity of life-history stages that can diapause. Some mosquitoes diapause as eggs, some as larvae, and some as adults. This suggests a degree of evolutionary flexibility between species, although diapause stage is usually conserved within a species (that is, it is canalized).

One of the other interesting things about diapause are changes in behavior leading up to shutting down for the winter. These include endophily (coming inside buildings), changes in food preferences (for nectar instead of blood), and changes in oviposition behavior. Pretty neat stuff. But also adaptive to the fluctuating conditions mosquitoes encounter across seasons.

Here in North Carolina you won’t find any mosquitoes flying on a cold winter day, but rest assured, they are here, waiting, as eggs in birdbaths, as adults in basements, or as larvae in wet tree holes.

References:
Armbruster, P. and Denlinger, D. Mosquito Diapause. Annual Review of Entomology 59: 73-93.

We're back! And a cold weather reminder

Happy New Year! The PDIC staff hope you and your plants thrive in good health in 2016.

Now that cold weather has arrived, this is a reminder that samples shipped during the winter can suffer cold damage in transit. Consider shipping your sample in an inexpensive foam cooler to protect it from cold. All but the sturdiest coolers should then be placed inside a cardboard box before shipping.

PDIC Holiday Closing Information

The Plant Disease and Insect Clinic will be closed for North Carolina State University Holidays. We will close at noon on December 23, 2015 and reopen on January 4, 2016. Samples with suspected disease problems should be submitted by Friday, December 18 to allow time for culturing organisms if necessary for diagnosis. However, samples will be accepted until we close on December 23.

Our best wishes for a joyous holiday season and for a happy, healthy New Year for you and your plants!

Matt Bertone, Entomologist
Shawn Butler, Diagnostician, vegetables, home landscapes and gardens
Lee Butler, Diagnostician, turf
Charles Hodges, Professor Emeritus and Diagnostician trees, grapes, and brambles
Mike Munster, Diagnostician, commercial ornamentals
Emma Lookabaugh, Graduate student, tomato diagnostician
April Varner, Student lab support
Barbara Shew, Director

Tales of the Turkey Tail

Thanks to very successful conservation efforts, you may be lucky enough to see a wild turkey if you take a walk in the woods after your Thanksgiving dinner. But it would not take much luck at all to encounter the turkey tail fungus, Trametes versicolor on your walk. This subtly beautiful fungus probably is the most common wood rotting fungus on dead hardwoods throughout North America (Gilbertson & Ryvarden, North American Polypores, 1987). In fact, you may not need to leave your neighborhood to see turkey tails on old stumps like these flowering cherries we removed a couple of years ago.

New fruiting bodies of the turkey tail fungus Trametes versicolor on a flowing cherry stump

The common name of the turkey tail fungus refers to the semicircular rosettes of varying colors in the fruiting bodies (the spore producing part) of this fungus. The species name versicolor describes both the multicolored bands seen at different times within an individual specimen and the color variations seen among different specimens.

Bands of color variations in an old fruiting body

  T. versicolor can be distinguished from similar species by the tiny pores visible on the underside of the fruiting bodies. Like mushrooms, this fungus belongs to the basidiomycetes, but unlike the button mushrooms you may have had with your Thanksgiving dinner, T. versicolor is a polypore, a basidiomycete that produces spores within pores rather than on gills. Also unlike many mushrooms, the fruiting body is somewhat leathery (not fleshy) and long lived. The fruiting bodies first appeared on our cherry stumps in September and have been expanding and changing color since then.

Small pores covering the lower side of the fruiting body

                             

 Trametes versicolor is one of the white rot fungi, indicating that the fungus can decay lignin, which along with cellulose, is a main component of wood. White rot fungi such as T. versicolor break down the dark lignin in wood, leaving the lighter colored cellulose behind. Other so-called brown rot fungi break down cellulose, leaving behind dark lignin. Many species of both white rot and brown rot fungi cause rots in living trees, but T. versicolor is not a pathogen and decays only nonliving materials. When you gather up piles of leaves and fallen sticks and branches in the fall, you can begin to appreciate that decay organisms such as T. versicolor perform a very necessary function in nature. Without them, we’d soon be inundated with layers and layers of plant debris. In fact, a recent theory proposes that the evolution of white rot fungi brought about the end of the massive accumulation of plant materials characteristic of the coal age.

As you might guess, T. versicolor has been studied for its potential to remove lignin in various industrial processes. It also is has been studied for medicinal purposes and is used in traditional Chinese medicine. Not surprisingly, the dried fruiting bodies have been used as dyes of protein based fibers like wool and silk (Binion et al, Macrofungi Associated with oaks of Eastern North America, 2008). The turkey tail fungus is commonly sold in craft stores for use in seasonal floral arrangements, and if you would like to add a touch of turkey to your Thanksgiving decor, the source may be as close as your own backyard.