- Author: Ben Faber
The weather continues to offer new opportunities. Recently there have been reports of Avocado Brown Mite infesting trees. This is a pest (Oligonychus punicae) of dust and disturbance. Normally found along picking roads and up against areas that are dusty. Not a problem. But growers in San Diego and Ventura have both commented on their unusual presents and some cause for concern. It's early appearance in the season when the spider mite destroyer hasn't yet built its population is the most likely reason. But……………
Avocado brown mite is a sporadic pest, mostly in coastal growing areas. Bronzing of leaves, mite cast skins, and partial defoliation of some trees by avocado brown mite is most noticeable from about July to September. Severe infestations tend to occur in border row trees along dirt roads, where road dust is detrimental to mite predators. Ash deposited on leaves from wildfires reportedly also causes brown mite outbreaks.
Avocado brown mite feeds almost entirely on upper leaf surfaces. Bronzing damage is not severe when mite numbers are low to moderate (about 10 to 20 adult females per leaf). If the spider mite destroyer lady beetle (Stethorus picipes) is present and reproducing well at this time, brown mite does not normally become a problem. Damage occurs if avocado brown mite averages about 80 to 100 adult females per leaf (about 200-300 motile stages, adults and nymphs combined). At these higher densities mites also colonize the lower leaf surface and sometimes fruit, and partial defoliation can occur. These higher numbers cause leaf bronzing along the midrib, then along smaller veins, and finally the entire leaf turns brown.
Brown mite is related to Persea Mite (http://ipm.ucanr.edu/PMG/r8400211.html) but rarely causes the damage that its relative can cause. The Persea Mite feeds mainly on the bottom of the leaf and forms web-covered colonies which help to distinguish it from O. punicae (first described in Carthage?).
At this stage, unless there is severe defoliation, it might be best to leave it alone until biocontrol kicks in or we get a hot spell to burn it out. Keep the trees adequately watered and flushing new leaves to outgrow it. Call a PCA if you are worried.
More about the weather:
And whatever happened to the Bagrada Bug?
Photo: Brown mite feeding on top of leaf surface
- Author: Christina Herrick
This article is from Florida Grower News. Thanks for Jim Lloyd-butler for pointing it out.
A sister species of the Varroa destructor mite is developing the ability to parasitize European honeybees, threatening pollinators already hard pressed by pesticides, nutritional deficiencies, and disease, a Purdue University study says.
Researchers found that some populations of Varroa jacobsoni mites are shifting from feeding and reproducing on Asian honeybees, their preferred host, to European honeybees, the primary species used for crop pollination and honey production worldwide. To bee researchers, it's a grimly familiar story: V. destructor made the same host leap at least 60 years ago, spreading rapidly to become the most important global health threat to European honeybees.
While host-switching V. jacobsoni mites have not been found outside of Papua New Guinea, Purdue researchers Gladys Andino and Greg Hunt say vigilance is needed to protect European honeybees worldwide from further risk.
“This could represent a real threat,” said Andino, a bioinformatics specialist with Information Technology at Purdue. “If this mite gets out of control and spreads, we might have another situation like V. destructor.”
Varroa mites are obligate parasites, meaning their lifecycle is inextricably entwined with that of their bee hosts. The mites can do serious damage to their hosts' health due to their relatively large size – “think of a tick as big as your fist,” Hunt said. Mites latch on to bees and feed on their hemolymph, insects' rough equivalent to blood, leaving behind open wounds that are susceptible to infection. They can also transmit diseases such as deformed wing virus and have been linked to colony collapse disorder.
To gain insight into the biology behind V. jacobsoni‘s host switch, Andino and Hunt, professor of behavioral genetics and honeybee specialist, studied the differences in gene expression between V. jacobsoni mites that fed and reproduced on Asian honeybees and those that parasitized European honeybees. Knowing which host cues mites respond to and the genes involved could lead to potential control strategies, the researchers said.
“If we can understand the mechanism, we might be able to disrupt, block, or manipulate that,” Andino said. “But first we have to understand what is happening and which genes are involved in allowing the mites to shift to a new host.”
Andino and Hunt said the mites' leap to European honeybees likely occurred within the last decade. Previously, V. jacobsoni mites were occasionally found on European honeybees but seemed unable to produce healthy offspring, limiting their destructive capacity.
Catching the host transition in its early stages will allow researchers to continue to investigate the complex genetic details behind the shift and monitor infected European honeybees, Hunt said.
“This happened once with one species of mite, and it looks like it's happening again. Maybe if we catch this as it's beginning, we'll be able to figure out why it's happening or, down the road, stop it.”
The paper was recently published in BMC Genomics.
Funding for the study and an ongoing genome-sequencing project was provided USDA's-Agricultural Research Service and the USDA National Institute of Food and Agriculture.
This article is from Florida Grower News
- Author: Neil O'Connell
Brevipalpus mite species belong to a larger group or family of mites the Tenuipalpidae, referred to as flat mites. The genus Brevipalpus is considered the most important one in the family. The mites are small ranging in size from 200-400 micrometers in length, flattened and frequently red in color. They have been under increasing investigation because of their potential as plant pests and their involvement with vectoring plant viruses. The three most important species are B.californicus(Banks), B.obovatus(Donnadieu), and B.phoenicis(Geijskes). All three species occur on citrus as well as many other host plants in the same areas worldwide. A fourth species B.lewisi (McGregor) is found in more arid climates. B.phoenicis is a pest of citrus, coffee, tea and passionfruit and numerous ornamental plants. B.californicus is a pest on orchids. B.lewisi is a pest on citrus, grapes, pistachio, walnuts and pomegranate. It has never been assessed as a possible vector of citrus leprosis or other related viruses.
Typically, Brevipalpus mite development consists of a larval, protonymph, deutonymph and adult stage. The rate of development is strongly influenced by temperature, relative humidity and host plant. In developmental studies at eighty degrees Fahrenheit (F), development of B.obovatus was completed in 13 days with adult females living 40 days and depositing 50 eggs per female. In comparison, development of B.lewisi at 90 degrees and 35% relative humidity was completed in 17 days. Egg laying varied from six eggs per female per day at 90 degrees to 18 eggs per day at 80 degrees. Eggs were deposited in cracks or crevices on fruit surfaces.
Tenuipalpid mites inject toxic saliva into fruit, leaf, stem and bud tissues of citrus and other host plants. B.lewisi causes a russeting and cracking of the rind on pomegranate fruit, with damage first observed near the stem end. B.californicus feeding has been associated with severe stunting of citrus seedlings in Texas and corky swollen buds in Texas, Florida and Venezuela, a condition referred to as Brevipalpus gall. B.phoenicis has been associated with a fungal pathogen, Elsinoe fawcetti resulting in defoliation and death of citrus seedlings. Feeding damage by Brevipalpus mites on citrus in Texas is most prevalent on inside fruit in the lower tree canopy. Fruit lesions first appear as very slight yellowish circular areas in depressions on the fruit surfaces. These lesions gradually develop a central brown necrotic area and gradually become darker and corky in texture. The extent of this damage varies depending upon mite infestations and can cover half of the fruit surface. On some orange selections in Texas, lesions resulting from mite feeding have been referred to as leprosis-like spotting or nail-head rust, appearing as brownish blemishes on fruit particularly on the stylar end and on fruit in the inner canopy. Brevipalpus mites prefer damaged areas on citrus fruit or where depressions occur on the fruit surface; the mites tend to aggregate in these areas and lay their eggs. Brevipalpus lewisi and B.californicus feed primarily on citrus fruit. In Califonia, feeding injury by B.lewisi on citrus fruit results in scab-like isolated depressions. B.lewisi feeding in California pistachios results in dark, irregular and roughened scab-like blotches. In one observation in 2002 near Bakersfield, B.lewisi was readily found on the fruit in the outer canopy of Valencia trees with temperatures of 95-100 F and low relative humidity.
The most significant threat created by the three Brevipalpus mite species, B.californicus, B.obovatus, and B.phoenicis, is their involvement in vectoring a group of plant viruses. They have been identified from citrus in Brazil, Costa Rica, Honduras, South Africa, Florida and Texas B.phoenicis is recognized as the vector of citrus leprosis in Brazil, coffee ringspot virus, passionfruit green spot and various viruses of ornamental plants. In Argentina and Venezuela citrus leprosis was reportedly vectored by B.obovatus. B.californicus was the reported vector of leprosis in Florida.
Confusion has existed for decades concerning the differences between feeding injuries caused by Brevipalpus mites and leprosis virus infection on citrus. [The only accurate method for determination of infection by citrus leprosis virus is using transmission electron microscopy] [no longer true….there is a molecular method now available to identify presence of leprosis virus] to verify presence of virus particles or viral inclusion bodies. The abililty to correctly identify and separate Brevipalpus mite feeding injuries, citrus leprosis virus infections, and unrelated but similar maladies on citrus are essential for citrus producers, shippers and regulatory personnel involved in international movement of fruits and plants.
*Brevipalpus californicus, B.obovatus, B.phoenicis, and B.lewisi(Acari:Tenuipalpidae): a review of their biology, feeding injury and economic importance. Carl C. Childers, J. Victor French and Jose Carlos V. Rodrigues.