Posts Tagged: mite
Revisiting 'The 13 Bugs of Christmas'
Back in 2010, UC Cooperative Extension apiculturist Eric Mussen (1944-2022) of the UC...
A golden honey bee, a Cordovan, nectaring in a Vacaville, Calif., garden. (Photo by Kathy Keatley Garvey)
A varroa mite attached to a foraging bee in a Vacaville, Calif. garden. (Photo by Kathy Keatley Garvey)
UC Davis Scientist Will Discuss Disarming Defenses of the Varroa Mite
Honey bee scientists, beekeepers and other bee enthusiasts are especially looking...
A varroa mite on a foraging honey bee. (Photo by Kathy Keatley Garvey)
What’s with all of the trash bugs this season?
I have received a handful of calls this season with concerns about “trash bugs,” a catch all term for various soil invertebrates. These soil invertebrates include root maggots, springtails, bulb mites, and symphylans, all which will happily feed on decomposing plant debris, i.e., trash. If given the opportunity, trash bugs will feed on seedlings and transplants, but high pressure can usually be avoided by allowing plant debris to fully breakdown before planting the next crop. A long enough pause between plant debris and seedlings acts as a sort of field-level host-free period, allowing trash bug populations to drop before planting.
Why does it feel like we have more trash bugs this season?
We had an unseasonably cool, wet spring. Under these conditions, crop debris from the fall was breaking down much slower than usual. With the compressed start to the season, folks have been eager to plant into fields as soon as possible, so many were likely planting into fields with higher-than-optimal plant debris.
By mid-April, daily temperatures were starting to get more back to normal, so why are we still dealing with more trash bugs? From talking with a handful of growers and PCAs, the slow start to the season has set back the whole planting schedule. To try and bring things back to schedule as close as possible, folks are still pushing the limit on how quickly they turn around fields for the next crop. A perfect storm for trash bug pressure.
Which trash bug am I dealing with?
A diverse group of pests can cause stunting and stand loss, so accurate pest ID is critical for successful management.
Root Maggots (seedcorn maggots or cabbage maggots, Delia spp.)
Root maggots are the larvae of small grey flies. The adult flies are commonly caught on sticky cards that are deployed for monitoring thrips and aphids.
Seedcorn maggot, Delia platura, seems to be the primary culprit that I have come across that is stunting brassicas. Seedcorn maggots tend to hit fields within a week or two after planting, causing patchy stands and stunted seedlings. Closely related cabbage maggots tend to hit fields a few weeks after planting and can continue to cause damage as plants mature.
To scout for root maggots, pull up stunted plants (see picture #1 below) and check roots for small, yellowish-white maggots (less than ¼ of an inch long). They can be easy to miss when they're all tangled up in the roots (picture #2). If scouting is delayed, you may also find the brown pupa (picture #3). With seedcorn maggots, timing a reactive control (i.e., insecticide application) can be tricky since the damage may go unnoticed until the maggots have already pupated and left the field.
From left to right: #1 broccoli stunting caused by root maggot feeding; #2 maggot tangled up in the roots of a broccoli plant; #3 root maggot pupa found next to a stunted broccoli plant. |
Springtails and soil mites
Pest springtails and soil mites are trickier to identify, since non-pest species are common in healthy soils. The one species of springtail that has been identified as an occasional pest of lettuce and brassicas is Protaphorura fimata, while the main pest mites are bulb mites (Rhizoglyphus spp., Tyrophagus spp.). Both P. fimata and bulb mites are small and whiteish while non-pest species are often larger and more colorful.
Clockwise from top left; Protaphorura fimata, the springtail species that can be a pest (Photo Credit: Shimat Joseph, previous UC IPM Advisor); non-pest springtails (note that these springtails are more colorful and have long antennae); a predatory soil mite (not a pest); and two bulb mites (Photo Credit: Jack Kelly Clark, UC IPM). |
Symphylans
Symphylans look like small (less than ½ an inch), white centipedes. Since symphylans are fast and mobile, you will be more likely to catch symphylans in action if you dig around stunted plants that are near healthy looking plants. If you readily find symphylans just by digging, the symphylan pressure is probably high enough to cause economic damage.
Lower symphylan densities can be harder to observe, so you may want to try bait-trapping with potato or beet wedges if you suspect symphylans but cannot find any by digging around stunted plants. The bait-trapping method can also be used to scout for springtails.
For more on the identification, scouting, and management of these pests, be sure to reference the UC IPM Pest Management Guidelines:
https://ipm.ucanr.edu/agriculture/cole-crops/
https://ipm.ucanr.edu/agriculture/lettuce/
Related blog posts from past entomology advisors:
Root maggots:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=9804
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4301
Symphylans:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=18819
Springtails:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=16769
Bulb Mites:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=13271
/table>If Honey Bees Fascinate You, Think About Becoming a CAMBP Certified Apprentice Assistant
If honey bees fascinate you, you might want to take the first step toward becoming affiliated with...
Can you find the queen bee? (Photo by Kathy Keatley Garvey)
Can you find the varroa mite on this worker bee? She is nectaring on lavender. (Photo by Kathy Keatley Garvey)
Honey bee heading toward lavender. (Photo by Kathy Keatley Garvey)
Fungus Helps a Honeybee
New fungus strain could provide a chemical-free method to help honey bees
Jennifer Han
jennifer.o.han@wsu.edu
PULLMAN, Wash. -- A new fungus strain could provide a chemical-free method for eradicating mites that kill honey bees, according to a study published this month in Scientific Reports.
A team led by Washington State University entomologists bred a strain of Metarhizium, a common fungus found in soils around the world, to work as a control agent against varroa mites. Unlike other strains of Metarhizium, the one created by the WSU research team can survive in the warm environments common in honey bee hives, which typically have a temperature of around 35 Celsius (or 95 F).
"We've known that metarhizium could kill mites, but it was expensive and didn't last long because the fungi died in the hive heat," said Steve Sheppard, professor in WSU's Department of Entomology and corresponding author on the paper. "Our team used directed evolution to develop a strain that survives at the higher temperatures. Plus, Jennifer took fungal spores from dead mites, selecting for virulence against varroa."
Jennifer Han, a post-doctoral researcher at WSU, led the breeding program along with WSU assistant research professors Nicholas Naeger and Brandon Hopkins. Paul Stamets, co-owner and founder of Olympia-based business Fungi Perfecti, also contributed to the paper. Stamets is a fungi expert, well-known for using several species in applications ranging from medicine to biocontrol.
Varroa destructor mites, small parasites that live on honey bees and suck their "blood," play a large role in Colony Collapse Disorder, which causes beekeepers to lose 30-50% of their hives each year. The mites feed on bees, weakening their immune systems and making them more susceptible to viruses.
The main tools beekeepers use to fight varroa are chemicals, such as miticides, but the tiny pests are starting to develop resistance to those treatments, Naeger said.
Metarhizium is like a mold, not a mushroom. When spores land on a varroa mite, they germinate, drill into the mite, and proliferate, killing it from the inside out. Bees have high immunity against the spores, making it a safe option for beekeepers.
Stamets, who did some of the initial testing with Metarhizium that showed the fungus couldn't survive hive temperatures, was impressed by the work done by the WSU researchers.
"Science progresses through trial and error, and my technique wasn't economical because of the hive heat," he said. "But Jennifer did enormous amounts of culture work to break through that thermal barrier with this new strain. It's difficult to really appreciate the Herculean effort it took to get this."
Han and Naeger screened more than 27,000 mites for levels of infection to get the new strain.
"It was two solid years of work, plus some preliminary effort," Han said. "We did real-world testing to make sure it would work in the field, not just in a lab."
This is the second major finding to come from WSU's research partnership with Stamets involving bees and fungi. The first involved using mycelium extract that reduced virus levels in honey bees.
"It's providing a real one-two punch, using two different fungi to help bees fight varroa," Stamets said. "The extracts help bee immune systems reduce virus counts while the Metarhizium is a potentially great mite biocontrol agent."
The next step is to seek approval from the Environmental Protection Agency to use Metarhizium on hives used in agriculture. The team must also finalize delivery methods for beekeepers to apply the fungus in hives.
"We hope in 10 years that, rather than chemical miticides, Metarhizium is widely used to control Varroa mites," Sheppard said. "And that the mite problem for beekeepers has been significantly reduced."
The team thinks the methods they developed to evolve Metarhizium for varroa control could be used to improve biocontrol agents in other crop systems as well.
A female Varroa destructor Anderson & Trueman, feeds on the hemolymph of a worker bee. The mite is the oval, orange spot on the bee's abdomen. Photograph by James Castner, University of Florida.