- (Focus Area) Environment
- Author: Maria Murrietta
- Contributor: Dr. David Headrick
We're now seeing the aftermath of this long rainy season. The heavier than normal rain has given us velvety green hills carpeted with an abundance of wildflowers. But we cannot overlook the other less pretty things that benefit from a wet winter – lots of weeds and insects.
For now, we'll focus on insects. They're already showing up in a news-worthy fashion. KSBY did a feature story on whiteflies and spoke with UC Master Gardener Cathryn Howarth.
This story has been posted on various social media pages and people are wondering if this whitefly is a new pest, where it came from and what can be done about it. I wanted to follow up to fill in some of the gaps in information. So, I went to Cal Poly entomology professor, Dr. David Headrick who has done quite a bit of research on whiteflies over the course of his career.
Here's what he had to say after watching the news story.
"The whitefly pictured on hibiscus (in the news story) is giant whitefly which came to California from Mexico. It was first noticed in San Diego County in the early 1990s. Hibiscus is a favored host plant, but they also are seen on citrus, but more commonly on the landscape plant Xylosma. In the mid-1990s, a biological control program began with researchers at the University of California, Riverside. They successfully imported two beneficial species of tiny stingless wasps that feed exclusively on giant whitefly and achieved excellent control of giant whitefly."
"Giant whitefly and the two beneficial wasps (pictured above) all occur in San Luis Obispo County and normally the populations are all under good control. When the giant whitefly first invaded SLO county in the early 2000s, the populations were enormous and made the news then also. But the wasps soon brought whitefly numbers under control. However, in some years since then, environmental conditions have favored the giant whitefly and allowed them to outpace their natural enemies. Eventually, the wasps will catch up and population balance will be restored."
"There are many species of whitefly, most are native species that cause no serious harm to their host plants. The whiteflies that you see on broccoli, citrus, oaks, and poinsettias are all different species. Some of the invasive species of whiteflies, like giant whitefly, can indeed kill their host plants."
"As for management, spraying plants with the garden hose is a good approach when numbers are low."
Thank you, Dr. Headrick, for your insights.
UC Master Gardeners always recommend monitoring your plants regularly to catch pest populations before they become a problem. Whiteflies can be observed any time of day. Remember to flip over the leaves to look for evidence of nymphs and the waxy coating as pictured below. Insecticides, such as horticultural oils may provide some relief. However, direct contact with the insect is necessary to smother and kill them which is difficult to achieve, particularly for whiteflies that congregate under the waxy coating on the underside of leaves.
If you have questions about plant or pest issues, call the Master Gardener Helpline
Arroyo Grande: 805-473-7190
SLO Office: 805-781-5939
Templeton: 805-434-4105
Or email us at anrmgslo@ucanr.edu
Looking for more?
- Visit UC IPM for more photos and information: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html
- For more information about the early biological control program and findings -
UC Riverside research paper - http://www.nhm.ac.uk/resources/research-curation/projects/chalcidoids/pdf_X/BellowMe2000b.pdf
Cal AG article - http://calag.ucanr.edu/Archive/?article=ca.v051n06p5
- And if you really want o geek out, like I sometimes do, check out this catalog of introduced species - https://bugwoodcloud.org/resource/pdf/FHAAST-2018-09_Arthropod_Biological_Control.pdf
- Author: Maria Murrietta
- Contributor: Kim Corella
Beetle borers. They are very small and they cause a lot of damage to trees, including death.
These insects have not been found yet in our County but they are very close and we are especially concerned about the ISHB which can attack over 110 tree species. Many of these are native riparian species such as Sycamore, Cottonwood, Alder, Willows, Box Elders and this insect also attacks coast live oak and valley oaks.
Cal Fire, the City of San Luis Obispo and UC Ag and Natural Resources are offering a workshop to educate the public about these two serious pests. Early efforts and education are key in preventing an attack on a wide range of tree species in San Luis Obispo County.
Here is a message from Kim Corella of Cal Fire:
I am excited to announce that we are having an invasive shot hole borer (ISHB) and goldspotted oak borer (GSOB) workshop here in San Luis Obispo on May 9th from 9:30-2:30.
This workshop will address biology, identification, surveillance, and management of infested trees, downed wood, and firewood. We'll cover these topics in the classroom, then have a hands-on lab to learn how to identify signs of shot hole borer damage, set up a monitoring program, and sample trees.
$30.00 registration fee includes lunch, a ISHB Field Guide, and ISHB Demonstration Kit. Pre-registration is required. Click here to register.
We have applied for CEU's from the Department of Pesticide Regulation and the International Society for Arboriculture.
For more information on the training and to register, visit www.pshb.org.
Kim Corella, Forest Pest Specialist, Cal Fire
Thank you, Kim, for keeping us well-informed!
- Author: Norman Smith
Norman Knows...
Horntailed Wasps
In keeping with wood damaging insects, we turn to an unusual group of insects - the wood wasps, also known as horntails. These primitive wasps actually bore in and feed on wood. They are large, almost two inches in length, with a long ovipositor on the female. Males look much like the females, but are usually smaller, and do not have an ovipositor (note photograph). Despite their ability to bore through wood and other tough substances, and their impressive looking “stinger”, they do not bite or sting humans. They have typical wasp coloration, red and black or yellow and black, which gives them some protection from predators.
The larval stage, the stage that bores in the wood, does most of the damage, but never enough to warrant treatment or wood replacement. So what's the problem? It's actually the adult habit of boring through dry wall, hard wood, or wooden flooring that is the main problem. They leave rather large holes in these surfaces, sometimes requiring cosmetic repair. How does this happen you may wonder? These wasps are attracted to dying or recently dead trees, and are often the first wood boring insect into a recently burned forest. In fact, the adults are attracted to smoke. I have spoken with forest fire fighters who have seen them ovipositing into still smoldering trees or logs. It is almost impossible for a logging company to get into a burned forest and salvage the less damaged trees for future lumber, before the wood wasps infest it. During the milling process, without a doubt, many of the developing wood wasp larvae are cut in half, but many are not, and they will continue their development in the 2x4 or 2x6 stud. And, of course, if that stud is used in your new home, eventually that maturing larva is going to emerge as an adult. Some emerge directly from the stud through the drywall, and often the adults are found with dry wall dust on them. If the adult emerges from the stud into a dark space (inside the wall) it will eventually find a place to chew through into the light.
Anywhere from one to a dozen or more can emerge into a home. Often times all the emergence holes will be limited to one room, or even one area on one wall - the one stud that was infested that was built into the home. I even found one that had emerged into my first home in the valley. When I saw the hole in the drywall in our utility room I knew what had done it, and after a short search, I found a dead male in an upturned chandelier light. Most folks will often find them in window sills where they were trying to get outside. Adults do not re-infest into wood from the home. They must have bark on the tree to initiate oviposition - smooth, milled wood is not an attraction. That is why it is not recommended to treat a home that has had wood wasps emerging from some of the studs. Once they are out, they are done. The only problem is that perhaps one or two adults may not emerge in the same year as all the rest, perhaps emerging the following year. But the integrity of the structure has still not been compromised.
I did have one customer though, who was not satisfied with any of my reassurances that her house was not in danger of falling apart and that it was likely no more would emerge into her son's bedroom. Evidently, the emerging wasp frightened the young boy and unfortunately the parents too. They felt they had bought a contaminated home and would not be happy until they got a new one - provided at no extra cost by the contractor of course. Unfortunately, neither I nor the contractor could guarantee that no wasps would emerge from the studs in that home too. I never did find out what happened. Wood wasps can be a nuisance, albeit a short but relatively harmless one. If you ever find one in your new home, please retain it for me. They aren't all that common.
Norman Smith was the Fresno County Entomologist for 30 years. He fielded calls from the general public, pest control companies, farmers, PCA's, etc.; ran the insect trapping program, and gave presentations on insects to many different groups, including lots of schools. Norman has developed a 100,000 insect specimen collection for the county over the 30 year career. Norman earned a Ph.D. in Entomology at UC Davis in 1979.
Norman says...I now enjoy working in my garden, traveling with my wife, golfing and bowling, taking insect collecting trips in the US and overseas in the tropics, and working on some personal research of some small wasps. I also enjoy working with and for the Master Gardener program in SLO.
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![Horntail wasp3 Horntail wasp3](https://ucanr.edu/blogs/slomggarden/blogfiles/51452.jpg)
- Author: Norman Smith
Norm Knows...
Western Subterranean Termites
Western Subterranean Termites have a winter time activity period, but are year-round pests of wooden structures and dead trees. The winter activity is associated with their swarming habit. The winged adults are black/dark brown with opaque gray wings. King and queen adults will swarm the first warm day after the years first major rain fall. Some of you may have seen the winged adults emerging from a hole in the soil, one after the other, and flying off, but maybe you weren't sure what you were observing. Mating is this activity that allows the termites to spread to other favorable habits.
Kings and queens will pair up, then look for a moist soil situation with wood present, such as 2 X 4's laying on the ground next to the wall of a home, a dead tree trunk and buttress in the garden, or even decorative bark in landscape areas.These can all get a colony started, but the worker termites are seldom satisfied with their initial discovery, and will almost always send out exploratory trails and tunnels to look for other sources of wood. Unfortunately, the wood framing of your nearby house is one of their favorite habitats.
The major portion of the colony and the queen and king are in the soil. Workers must foray back to the soil each 24-hour period, to pick up dirt and certain bacteria, but will then head back up into the above ground structure. Their tunnels in the wood are always lined with dirt from the garden or below the house. The habit of the queen termite residing in the soil and not in the wood source is the main reason that fumigation is not effective for this kind of termite. Fumigation may kill some of the foraging adults in the wood foundation of the home, but not the one termite that can keep the colony going with more eggs and immatures. Termite pest control companies try to put up a toxic barrier between the nest in the soil and the wood source, hoping that as the workers pass through the barrier, they come in contact with the toxin and die. Another control method is to place some poisoned bait wood traps around the home and hope that the foraging workers will discover it and transport the poison wood to the queen.
Termite inspectors will look for the dirt tunnels plastered to the foundation or rising from the soil beneath the foundation. These tunnels should be destroyed by the inspector at the time of treatment so that if more are seen in the future they will know that they were not successful in eradicating the colony.
I saw a stark reminder of the importance of termite control while residing in Fresno. Some of you may remember the Coalinga earthquake. Some of the homes in that town were snapped off their foundations, offset by a foot in some instances. The reason was that some of the homes had weakened wood framing from termite damage and the sharp jolt from the earthquake just snapped the 2 X 4's at their base. Those homes had to be raised and rebuilt. I hope they had good insurance.
Norman Smith was the Fresno County Entomologist for 30 years. He fielded calls from the general public, pest control companies, farmers, PCA's, etc.; ran the insect trapping program, and gave presentations on insects to many different groups, including lots of schools. Norman has developed a 100,000 insect specimen collection for the county over the 30 year career. Norman earned a Ph.D. in Entomology at UC Davis in 1979.
Norman says...I now enjoy working in my garden, traveling with my wife, golfing and bowling, taking insect collecting trips in the US and overseas in the tropics, and working on some personal research of some small wasps. I also enjoy working with and for the Master Gardener program in SLO.
- Author: Norman Smith
Youdid, Wedid, Medid, Shedid, Hedid, Mydid?
Mydid Flies, genus Mydas – Good bugs or not so good?
Norm Knows.
By Norman Smith, UC Master Gardener
So, are these good bugs or bad bugs? What do you think they are, wasps or flies? Actually they are considered to be of little consequence, neither good nor bad. They are flies in the family Mydidae, genus Midas. They are mimicking wasps, mostly spider wasps of the family Pompilidae. Their larvae are predacious on beetle larvae that are found in rotting wood or decaying soil. They do not sting and I don't think they bite like their relatives, the robber flies, though I don't think I would test one. As you can tell from the fly sitting on the hand, they can be fairly large.
Of course, most folks who saw these in their yard would consider them to be a wasp, and would leave them alone. That is exactly what they want. And their mimicry is not limited to looking like a wasp. They also fly like one as I found out too late one day while collecting along the Colorado River near Blythe in late spring. I had seen what I thought were Pepsis wasps (Tarantula hawks), flying around the willows along the river. I had plenty of Pepsis wasps in my collection so I did not bother collecting any until late in the morning when I decided I should go ahead and get one just for the locality data. I could not believe what I found in my net - not a wasp but one of these Mydid flies. I was incredulous. A mydid fly, not a wasp? I immediately began looking for more to catch as I knew that Mydid flies were quite rare and not often collected. Alas, I did not get any more, as the temperatures were nearing 90 degrees at 11:00am in the morning and their flight time was over. It was embarrassing to think how badly I had been fooled by these flies, that looked and flew so much like a tarantula hawk. I had probably seen 1/2 a dozen throughout the morning.
The idea for writing about these flies came about late last week while going over a Cal Poly student's insect collection. The young man had mislabeled a fly in his collection as a wasp. It was the mydid fly with the orange abdomen - he had been fooled too. Because of their rarity, beauty, and large size (though not all of them are as attractive or large as these pictured), they are prized specimens to have in one's collection. I have never caught one here in San Luis Obispo Co. but I never stop trying. Each collecting season presents new possibilities.
Norman Smith was the Fresno County Entomologist for 30 years. He fielded calls from the general public, pest control companies, farmers, PCA's, etc.; ran their insect trapping program, and gave presentations on insects to many different groups, but especially schools. He developed a 100,000-insect specimen collection for the county over the 30 years that he was there. He received his Ph.D. in Entomology at UC Davis in 1979.
Norman says, "I now enjoy working in my garden, traveling with my wife, golfing and bowling, taking insect collecting trips in the US and overseas in the tropics, and working on some personal research of some small wasps. I also enjoy working with and for the Master Gardener program in SLO."