European Pepper Moth: A New Invasive Moth Threatens California Agriculture

by James A. Bethke and Bryan Vander Mey

California growers should be on the lookout for a new exotic pest, the European pepper moth (EPM). Many people won’t think much of this insect because it’s just another moth, but if ignored, it could become a serious pest on certain ornamental and agricultural crops. It has been a consistent pest of greenhouse crops in Europe, but has not been as destructive in field-grown crops.

EPM, Duponchelia fovealis Zeller (Lepidoptera: Pyralidae), originates in the Mediterranean area and the Canary Islands, and also has been known to occur in Africa and Asia Minor where it is a significant pest of agricultural crops including peppers, squash, tomatoes and corn. The Animal Plant Health Inspection Service (APHIS) of the USDA originally considered this moth an actionable pest because initially it was not known to occur in the United States and because it is a serious agricultural pest.

The moth was first identified in California in 2005 and was originally assigned an “A” rating, which meant that when found, there would have to be action taken to eliminate the risk of spreading the insect. Since 2010, the insect has been found widespread in San Diego County and has been detected elsewhere in the state, as well as numerous other states, so a move to reduce the severity of the rating is in progress. Regardless of the rating, concern from ornamental and vegetable plant producers is leading to the formation of a USDA APHIS Technical Working Group to study ways of reducing the impact that this pest may have on U.S. agriculture.

The caterpillars are difficult to detect because they typically feed at soil level around the crown of the plant and sometimes burrow into stems. Proliferation of the population can occur without notice. You should be aware of the potential this pest has to do serious crop damage and watch for it.

One of our biggest worries during the last poinsettia season was that poinsettias are on the host list. Unfortunately, we have observed larvae girdling poinsettia and causing significant damage on some growers’ crops. That means that everyone growing poinsettias this coming season should be looking for this moth and should consider initiating a preventative program or there may be unintended consequences.

We will do our best herein to educate you about this insect so that when you see it you will not be surprised and hopefully will have some management solutions. We are studying the life history and control for this pest and plan to have more results relatively soon.

Invasion History

EPM was first detected in this country in 2005 as live larvae in a shipment of begonias from San Diego County. It was thought to be eradicated, but a detection in Canada in April of 2010 was traced back to ornamental plant production in San Diego County. Following action by regulators and treatment applications by the grower and on the surrounding landscape by a commercial applicator, further surveys of the property could not detect any more moths or larvae. Unfortunately, a second detection occurred in July 2010, and a trace-back led to the same area of San Diego County but to a different grower. This detection triggered an extensive trace forward survey to determine the extent of the invasion in California and other states. During the months of September and October 2010, APHIS and state departments of Agriculture confirmed the presence of Duponchelia fovealis in portions of 13 additional states including Alabama, Arizona, Colorado, Florida, Georgia, Mississippi, New York, North Carolina, Oklahoma, Oregon, South Carolina, Texas and Washington. Survey data to date confirmed the presence of EPM in 16 counties in California.

The detection in July 2010 in San Diego County was very extensive at one production facility and caused the County Agriculture Commissioner’s office to put a hold on all plants throughout the facility. At a great cost to the company, it took approximately two weeks of intensive treatment applications and the destruction of mature plants in order to release portions of the crops for sale and distribution. Younger plants were treated preventatively. In all likelihood, growers of EPM host plants here in the county will have to monitor for the time being and treat preventatively to remain moth-free (see host plants below).

Life History

There is little scientific literature from which to develop a life history. Much of what is known is anecdotal observations from lepidopterists and official records from invaded countries in Europe.

Development from egg to adult is as long as 47 days at 68ºF, but will be much shorter in our warmer climates and especially in greenhouses. The adult (fig. 1A)  life span is from 1 to 2 weeks, and a female can lay up to 200 eggs, singly or in small batches. Eggs are small (0.5 x 0.7 millimeters), whitish to green in color and darken to a reddish color as they age (fig. 1B).  The adult forewings are gray to brown with distinctive markings and a wingspan of 0.75 to 0.83 inches (19 to 21 millimeters). The lowest lines on the outer wing have a tooth-like notch facing backward. Males have a longer, more slender abdomen than females. Larvae are creamy white to brown with a dark head capsule (fig. 1C) and lines of distinct dark spots along the abdomen. Larvae mature in about 4 weeks.

Fig. 1. European pepper moth (EPM) adult male (A), eggs (B), larva (C) and pupa (D).
Photos by J.A. Bethke and B. Vander Mey.

Mature larvae pupate inside a cocoon composed of webbing and soil particles (fig. 1D). The cocoon is usually attached to the undersides of leaves or the edge of the pot, and larvae take about 1 to 2 weeks to hatch. The number of generations per year is variable but is certain to be multiple generations in Southern California, where multiple year-round generations in greenhouse production is likely. We have started a colony in our greenhouse and have found the generations to be synchronous at this point, which may be an advantage for the timing of applications.

Damage

EPM causes severe damage to main stems, lower leaves and tissues that are adjacent to the potting soil. The larvae tend to create webbed tunnels and protective coverings, and often feed below the soil line in soft plant media. Girdling damage can be seen on poinsettia (fig. 2A), begonia (fig. 2B), kalanchoe (fig. 2C) and pepper (fig. 2D).

Fig. 2. Girdling damage by European pepper moth (EPM) larvae on poinsettia (A), begonia (B), kalanchoe (C) and pepper (D).
Photos by J.A. Bethke and B. Vander Mey.

Host Plants

The host list is comprised of plants in about 38 plant families and include field-grown vegetables and ornamentals, greenhouse-grown ornamentals and herbs, and tree and vine hosts. A summary of ornamental host plants from the literature include alternanthera, daisy (Bellis spp.), cineraria, gerbera, impatiens, begonia, elderberry, goosefoot, kalanchoe, azalea, croton, poinsettia, geranium (Pelargonium spp.), lisianthus, lilyturf, cuphia, coleus, mint, mallow (Malva spp.), calathea, oxalis, loosestrife, limonium, cyclamen, portulaca, ranunculus, rose, bouvardia, heuchera, waterhyssop (Bacopa spp.), pepper (Capsicum spp.) and elm. Summaries of agricultural plants that are attacked include celery, peppers, cucumbers, tomatoes, maize, pomegranate and certain herbs. In San Diego County, confirmed host plants include begonia, echeveria, gerbera and several varieties of kalanchoe and poinsettia. I anticipate that the EPM host list will grow.

Control

Control measures for adults include conventional registered pesticides applied where the adult will come into contact with them. In addition, aerosols or fogs applied in protected culture just before adults begin to fly at night will be effective. In general, the adults are relatively easy to kill.

In contrast, the larvae are very difficult to contact with pesticides, and stomach poisons do not always reach the feeding site. Therefore, some of the more effective compounds against this pest will not be as effective as one would expect. A preventative treatment of Bt or spinosad on smaller plants and cuttings will kill early instar larvae as they hatch and begin to feed, but the pesticide has to be applied at the feeding site. Pyrethroids are also a good choice for larval control, but may need to be synergized. An additional aid to effective treatment applications would be to trim off the leaves that lie on the soil surface: there will be less shelter for larvae and better pesticide coverage.

When larvae are more mature they are much more difficult to control because of the protection offered by webbing as described above. Therefore, knowing when a new generation begins will be an important factor in control. In addition, we observed larvae taking refuge deeper in the soil alongside the main stem. Preventative treatments of granular insecticides may protect plants from this type of infestation, but for best control, persistent applications of effective products using a heavy application or large droplet size and a directed spray may be necessary.

Monitoring

Monitoring techniques with documented efficacy include the use of a pheromone in Delta traps, funnel traps and water traps. Pheromone lures for EPM are available from Koppert, Biobest and Syngenta. We have observed large numbers of EPM caught in water traps in Southern California (a good description of the water trapping techniques used in the Netherlands can be downloaded using this url: http://documents.plant.wur.nl/wurglas/C_bestwatertrap.pdf). In addition, it appears that the EPM is attracted to the light brown apple moth pheromone lures as well.

Control Trials

We conducted two greenhouse trials on infested potted plants from cooperating growers.

The first trial was on a group of greenhouse-grown kalanchoe plants (Kalanchoe spp.). The plants were mature and flowering, and the vast majority of the plants contained larvae or evidence of an infestation. They were potted in Latvian peat in 4-inch pots. We treated the plants with several insecticides that we thought might help in an eradication effort (see Table 1) at the highest recommended rates on the label. The majority of the larvae were in late stages, and we observed that about 2% of the plants contained pupae. Very few plants contained more than one larva. The larvae were exceptionally well protected under leaves, in webbing and between leaf and soil surfaces. Therefore, pesticide contact with larvae was difficult. Foliar applications were made using a backpack sprayer and a large droplet size, and we made an effort to get the soil surface and main stem wet with the treatment application.

We assessed the presence of active larvae per plant at 24 and 72 hours after application. We selected 60 plants as a pre-treatment count and a different set of 60 plants for each of the two post-treatment assessments. The percent reduction in the number of larvae per treatment was determined (Table 1). Bifenthrin, acephate, and bifenthrin+acephate tank mix caused a 50 to 75% reduction in the mean number of live larvae per treatment.

Table 1. Efficacy of selected insecticides applied to European pepper moth-infested kalanchoe in 4-inch pots. Sixty new pots were selected for each assessment, and the percentage of pots with live infestations of caterpillars was recorded.

Percent reductions are the percent of change from the pretreatment count. Larger numbers are better.
Negative numbers indicate an increase in the number of plants infested from the pre-treatment count.
Products and rates tested are for experimental purposes only and may not be registered for use.
It is your responsibility to make sure you are using registered products and rates for control purposes.

The second trial was conducted on heavily infested potted verbena in an outdoor nursery environment. The caterpillars were not evident at first, but when the pots were turned over, we detected numerous larvae infesting the roots that protruded from the drainage holes in the bottom of the containers. We wanted to make sure the pesticide would contact the pest, so we tried two methods of application with selected pesticides (Table 2): some applications were made using a backpack sprayer, and some plants were drenched from above. Both methods are difficult and costly, but when faced with the Nursery Clean Stock Program and potential shut down, any control method may be of benefit.

Mortality was observed for three days after treatment applications. Acephate performed well as both a spray and a drench against this pest. Other products did not cause significant mortality compared to the control under the conditions of this trial.

Table 2. Efficacy of selected pesticides against European pepper moth (EPM) on potted verbena. Spray applications were made by turning the pots on their sides and applying the pesticides to the caterpillar on the roots and bottoms of the pots. Drench applications were made using label instructions for application to a 6-inch pot. Numbers are the average number of live larvae per pot. Means followed by different letters are significantly different, LSD (p=0.05).

Conclusion

EPM is a new pest of potentially great significance in California and elsewhere. It has proven to be a significant pest in Europe, especially in greenhouse ornamental and vegetable production. It will benefit you to be aware of the biology and control of this pest, and it will certainly pay to be on the lookout for it. Acephate was an effective treatment for controlling larvae in two preliminary trials. Currently, we are conducting both lab and greenhouse trials using selected pesticides on early instar larvae from colonies that we have initiated. Stay tuned for these results.

James Bethke is Farm Advisor for Nurseries and Floriculture and Bryan Vander Mey is Staff Research Associate, UC Cooperative Extension, San Diego County.