Lewis mite, Eotetranychus lewisi (Photo courtesy: Daniel Gilrein, Cornell University)

Lewis spider mite or Lewis mite, Eotetranychus lewisi (McGregor) (Phylum Arachnida, sub-class Acarina, family Tetranychidae) is a pest of many host plants.  In the US, it has been reported on citrus and greenhouse poinsettias.  Lewis mites have been seen on strawberries and raspberries in the Ventura area for some time, but growers appear to be noticing increased infestations in the recent years.  Some growers have also seen them in Santa Maria in the recent years, but they have so far not been reported from the Watsonville area.  Considering the recent trend, growers might keep them in mind while scouting for pests.  Environment, natural enemies, cropping patterns, pesticide usage and other agronomic practices are among the factors that influence the status of pests.  It is not yet clear why infestations are increasing, but here is some information on Lewis mite.

Host range and distribution: According to an earlier report (Bolland et al, 1998), Lewis mite is distributed mostly in the western hemisphere and some parts of Africa infesting 65 species of plants including food and multipurpose plants like Erythrinia edulis, Citrus spp., Prunus sp., papaya, fig, ornamentals like Cleome sp., Bauhinia spp., Rosa sp., Euphorbia spp. (poinsettia, snow-on-the-mountain, fire-on-the-mountain), weeds like silverleaf nightshade, and various other hosts.  It has later spread to parts of Europe and East Asia.  Lewis mite infestation on strawberries was reported from Philippines nearly a decade ago (Raros, 2001).

Biology: Males are about 0.25 mm and females are about 0.36 mm long.  Species identification is tricky and requires both sexes to be examined microscopically.  They can be confused with twospotted spider mite (TSSM), Tetranychus urticae in their general appearance.  But, comparing adult females, Lewis mites are smaller than TSSM and have several small spots on their body while TSSM have a single dark spot on either side of the body.  Lewis mite has five life stages – egg, larva, protonymph, deutonymph and adult.  Eggs are round, whitish to light orange.  Females lay 60-90 eggs over a period of about a month.  It takes about 12-14 days from egg to adult stage at 21^oC (70^oF).

Twospotted spider mite (right, UC IPM)

Damage: Symptoms of damage vary according to the host plant.  On poinsettia, Lewis mite feeds on the underside of the leaves and causes very fine stippling or flecking on foliage, which can be initially mistaken for nutrient deficiency.  Infestations can build to high levels in poinsettia before mites and their webbing are noticed.  Since their infestation in strawberries currently coincides with TSSM infestations, exclusive Lewis mite damage symptoms in strawberries are yet to be determined.  In some hosts like papaya, damage resembles symptoms of viral infection and may cause distortion and yellowing of young leaves.  According to Daniel Gilrein, an extension entomologist from Cornell University, fine flecking from Lewis mite feeding almost resembles nitrogen deficiency and can delay detection until populations build up.  Leaves turn brown and webbing can be seen as the damage advances.

Management: In research on greenhouse poinsettias (D. Gilrein, pers. comm.), abamectin (Avid for ornamentals, Agri-Mek and generics for food crops), acequinocyl (Kanemite and Shuttle-O), bifenazate (Acramite and Floramite), fenpyroximate (Akari and Fujimite), spiromesifen (Judo and Oberon) were found effective in controlling Lewis mite.  These are also among the miticides recommended by UC IPM for spider mites on strawberries.   However, there have been some suspected resistance issues in some populations of Lewis mite in strawberry growing areas of California, but some of these materials act primarily as contact miticides and issues of coverage cannot be ruled out in all cases.

What to do: Look for Lewis mites while scouting for TSSM especially in fields close to infested ornamentals.  Keep in mind that there could be resistance or efficacy problems with some miticides in certain areas with TSSM or Lewis mites.  It is always a good practice to rotate miticides with different modes of action for better management and reducing the risk of resistance development.   The mode of action is indicated on most lables (e.g. Agri-Mek is a Group 6 Insecticide) If you suspect resistance in TSSM or Lewispopulations in your area, perform a simple test to evaluate the effectiveness of the intended miticides.  Dip several mite-infested leaves in a cup of miticide solution (concentration similar to the field application rate), let them dry and then cover (to keep foliage from drying out completely) and place in a cool area away from direct sun.  Check to see if any mites have survived 24 and 48 hours after dipping.  The effectiveness of the miticide will be indicated by the number of mites alive or dead.  For comparison, dip several similar mite-infested leaves in normal water and treat similarly, observing the survival of mites on those leaves as well.  This can be a useful comparison for new, untested miticides as well as for older products where miticide resistance is suspected.

UC researchers are working on this issue and will have some more information in the near future.  If you suspect or find Lewis mites in your fields, please contact me at skdara@ucdavis.edu or 805-788-2321.

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References

Bolland H. R., J. Gutierrez and C.H.W. Fletchtmann.  1998.  World Catalogue of the Spider Mite Family (Acari: Tetranychidae.) Brill, Leiden (NL).

European and Mediterranean Plant Protection Organization.  2006.  Eotetranychus lewisi.  OEPP/EPPO Bulletin 36: 161-163.

Gilrein, D.  2011.  Cornell Cooperative Extension of Suffolk County, LIHREC, Riverhead, NY.

Raros, L.A.C.  2001.  New mite pests and new host records of phytophagous mites (Acari) from the Philippines.  Philippine Agricultural Scientist 84: 341-351.

Basil plants that originated from a central coast nursery were recently found infected with downy mildew pathogen, Peronospora belbahri in a home and garden store in California.  This is a new pathogen that can cause serious damage to culinary and ornamental basil plants.

Symptoms include yellowing of the area between the veins on the upper leaf surface and growth of fungal mycelia and purplish grey spores on the lower surface.  Yellowing on the upper leaf surface can be confused with nutritional deficiency, so careful examination of the lower side is important.

Fungal spores on the lowerside of the basil leaf (Photo by: Heather Scheck, Santa Barbara County Ag Commissioner Pathologist)

Basil downy mildew was first reported in the United States in 2007 in Florida and in several eastern states by 2008.  It was also found in California by 2009.  Infected seeds and plants are main sources of infection.  Growers should try to obtain clean seeds.  Spores can be dispersed by wind and close spacing and overhead irrigation can also aid in the dispersal of the inoculum.

Regular monitoring of the fields for early detection of the infection and timely application of the fungicides is important for managing this disease.  Proper ventilation and temperature control in the greenhouses is also critical as prolonged leaf wetness, high humidity, and cool weather promote the disease development.

Additional information about the disease and management
guidelines can be found at: http://vegetablemdonline.ppath.cornell.edu/NewsArticles/BasilDowny.html

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Life stages of the European pepper moth, Duponchelia fovealis.  Eggs (top left, photo credit: Lance Osborne, University of Florida), larva (top middle, photo credit: Bryan Vander Mey, UCCE), pupa in an opened cocoon (top right, photo credit: James Hayden, Florida Department of Agriculture and Consumer Services, Division of Plant Industry) and adult male (left) and female (right) moths (bottom, photo credit: James Hayden)

European pepper moth (EPM), Duponchelia fovealis Zeller is an invasive pest in the US.  It was first discovered in San Diego County in 2004 and again in July, 2010.  EPM has a CDFA pest rating of C, which means it is currently widespread in California.  APHIS, National Plant Board, and industry stakeholders have established an EPM task force to address the pest issue.  I have been invited to be a part of the Technical Working Group along with my UCCE colleagues, James Bethke and Steve Tjosvold to work on research and outreach related to this pest.  Information on the economic impact of this pest in California or in the US is unknown, but here is some general information about this pest.

EPM belongs to the family Crambidae.  Crambids are known as grass moths or close-wing moths.  Older literature classifies this pest under the family Pyralidae.  Some sources also refer to EPM as southern European marshland pyralid.  Peppered moth, Biston betularia (Common name: measuringworms, Family: Geometridae, Order: Lepidoptera) from Europe is not related to this species.  It can be confusing when the name European peppered moth also appears in some sources, but verifying the scientific name helps confirm the identity.

Origin and Distribution: EPM is a pest native to the Mediterranean region and the Canary Islands.  It is also reported to be an important greenhouse pest in the Netherlands for the past two decades.  It is an established pest in many European countries, the Middle East and Africa.  EPM is now reported to be present in several central and southern California counties and in Arizona, Colorado, Oklahoma, Texas, Georgia and Florida.  EPM was also reported in a southern Ontario, Canada greenhouse in 2005.

Host range: EPM is a polyphagous pest and has a very wide host range that includes several crop plants like corn, peppers, tomatoes, squash, and strawberries and ornamental plants like azalea, begonia, geranium, and poinsettia.   Due to its feeding behavior and preference to infest foliage and plant parts near or below the soil line, crops that have such plant structure may be more vulnerable to this pest.

Biology: Eggs are oval, 0.5-0.7 mm long, whitish-green initially and turn bright red as they mature.  Females can lay up to 200 eggs either individually or in batches of 3-10 in a roof-tile pattern.  Larvae are creamy white to brown with dark spots on their body and have a dark head capsule.  They measure up to 20-30 mm when they are fully developed.  Pupa is 9-12 mm long, yellowish to light brown initially and turn dark with maturity.  A cocoon is spun around the pupa with silk, frass, and soil particles under the foliage, below the soil line or attached to the pots.  Adults have brown to grey wings with a wing span of about 20 mm.  Adults are good fliers.  Males have a long, slender abdomen that is turned upwards.  Length of the life cycle depends on temperature, but varies from 6-8 weeks.  Egg stage lasts for 4-9 days, larval stage for 3-4 weeks, pupal stage for 1-2 weeks, and adult stage for 1-2 weeks.  They produce multiple generations especially in greenhouses (up to 8 to 9) or in warm areas such as California and southeastern US.  They can be limited to greenhouses in cooler regions or during cooler seasons of the year and seen in the fields under ideal conditions.

Mature European pepper moth larva in the potting soil below the surface 
(Photo credit: Lyle Buss, University of Florida)

Damage: EPM larvae feed on roots, stems, foliage, inflorescences and fruits.  They can also feed on the organic matter in the soil. Although they have a preference for feeding at the plant base, damage can be inflicted higher in the plant.  Sometimes, larvae emerging from the eggs laid on the top of the foliage can burrow their way down through the stem.  Damage ranges from holes in the foliage, wilting, defoliation, girdling of the stem to stem collapse.  Damaged areas are also exposed to fungal diseases like Botrytis.  Larvae prefer moist conditions and hide under the foliage that is in contact with soil, just below the soil line or in the tunnels formed by spinning the leaves together.  In potted plants where the foliage is not in contact with the soil, larvae can be found in webbing near the edges of the pots.

Stem girdling of peppers by larval feeding of the European pepper moth.  Photo credit: Bryan Vander Mey, UCCE.

Management: Sanitation to remove debris and infestation sites like lower leaves in contact with the soil and use of drier potting medium appear to help reduce the infestation.  Biological control with Bacillus thuringiensis, predatory mites (Stratiolaelaps miles, Hypoaspis miles and H. aculeifer), predatory beetle (Dalotia coriaria), parasitoid wasps (Trichogramma evanescens and T. cacoeciae), and entomopathogenic nematodes (Heterorhabditis bacteriophora and Steinernema sp.) are reported to be effective.  Chemical control can be difficult with contact insecticides as the larvae hide in protected areas.  However, control with acephate, azadirachtin, chlorpyrifos, emamectin, imidacloprid, pyrethrins, and spinosad was found to be effective in areas where they are registered to be used.

What to do: If you notice EPM damage on your crop, please contact me at skdara@ucdavis.edu or 805-781-5940.

Additional details about EPM and more photos can be found at the below sources.

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References:

Bethke,  J. and B. Vander Mey.  2010. Duponchelia fovealis. Pest Alert, University of California Cooperative Extension, San Diego.

Brambila, J. and I. Stocks.  2010.  The European pepper moth, Duponchelia fovealis Zeller (Lepidoptera: Crambidae), a Mediterranean pest moth discovered in central Florida.  Pest Alert, Florida Department of Agriculture and Consumer Services, Division of Plant Industry.

Messelink, G. and W. Van Wensveen.  2003.  Biocontrol of Duponchelia fovealis (Lepidoptera: Pyralidae) with soil-dwelling predators in potted plants.  Comm. Appl. Biol. Sci., Ghent University 68: 159-165.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1000&context=systentomologyusda

http://entnemdept.ufl.edu/creatures/veg/leps/european_pepper_moth.htm

http://mrec.ifas.ufl.edu/lso/dupon/dupon.html

http://nationalplantboard.org/docs/spro/spro_duponchelia_2011_08_05.pdf

http://www.freshfromflorida.com/pi/pest_alerts/pdf/duponchelia_fovealis.pdf