Haskett, Michael J.

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83m. Stone FruitsBiologyCherry Ermine Moth, Prunus spp., and othersMichael J. HaskettWashington State Department of AgriculturePlant Services DivisionYakima, WashingtonAnother Exotic Ermine Moth, the Cherry Ermine Moth, Yponomeuta padeUus,Discovered in the Pacific NorthwestIn 1992 Forestry Canada Columbia reported that apple ermine moth, Yponomeutamalinellus (AEM) was found on a new host, hawthorn {Crataegus) in British Columbia.Hawthorn is not known to be a host of malinellus in its native range. AgricultureCanada investigated the situation and subsequently identified the specimens as cherryermine moth (Y. padellus), CEM. Hawthorn is a known host of CEM in Eurasia. In thespring of 1993 ermine moth larvae were found in B.C. on hawthorn (C. laevigata, and C.monogyna), cherry plum (Prunus cerasifer), mountain ash (Sorbus aucuparia and 5.sitchensis), and service berry (Amelanchier alnifolia). Associations with these host, whichare among those known for CEM in Eurasia, further confirmed the identification. Theinfested area includes part of Vancouver Island, and sites on the mainland within a fewmiles of the U.S. border near Blaine, Washington.Biology: In addition to the host listed above, plum (Prunus domestica), sweet cherry(Prunus avium), almond (Prunus communis), peach (Prunus persica), and blackthorn(Prunus spinosa) are the hosts of CEM in Eurasia. CEM behavior is similar to that ofAEM. Like AEM it overwinters as first instar larvae under hybernacula, emerging inthe spring to feed on foliage. Larvae form a communal web and periodically move as agroup to a new cluster of leaves. Observations in B. C. indicate that CEM larvaldevelopment may be earlier than AEM. Adult flight may begin and end earlier. WhileAEM has been trapped into September, suspected CEM catches in WSDA traps in 1993(see below) stopped in mid-August.Taxonomy: Separation of the ermine moth species is difficult, because there are noreliable distinguishing morphological features for larvae or adults. However, in Eurasiasignificant differences are reported in appearance of cocoons and webs surroundingclusters of pupae. The CEM cocoons and webs are described as loose, while cocoons ofAEM are opaque and cluster webs are dense. In British Columbia CEM pupae wereeasily visible within the cocoon, while AEM pupae are enclosed in a dense cocoon. InEurasia species can be separated by host association (Herrebout et al, 1976). Also, thespecies are considered to be reproductively isolated according to mating studiesconducted in Europe. In mating pheromone response studies CEM males did notrespond to AEM females. In hybridization studies by Hendrikse (1986) offspring ofCEM x AEM did not reach adulthood.84According to Hendrikse there is no evidence for hybridization under natural conditions.Potential Impact: In the literature from Eurasia CEM is described variously as an"economic," "major,"and "very harmful" pest One paper reported completedefoliation of cherry trees. There is no information in the literature that would excludeits potential range from wherever hosts are available in North America.As with AEM, there is a potential for economic impact on the fruit tree nurseryindustry. Washington nurseries export large volumes ofprunus. Quarantine restrictionssimilar to those for AEM could be enacted by other states or countries requiringregulatory treatments for prunus stock. Regulatory procedures would have to bedeveloped for this pest Since the hosts list including hawthorn and mountain ash, whichare popular ornamentals as well as fruit bearing prunus species, significant defoliation inresidential, and park trees could lead to increased pesticide use.1993 Survey: After learning in June of 1993 about the B.C. detections, WSDA fielded atrap survey in cooperation with USDA/APHIS in three northwestern Washingtoncounties closest to B. C. (San Juan, Skagit and Whatcom). In July and August wingtraps baited with CEM pheromone supplied by the USDA Otis Methods Developmentlab were distributed from Blaine south to Mt. Vernon, and on Orcas and San JuanIslands. Traps were placed in hosts trees of cherry ermine moth including native andornamental hawthorn, domestic and wild cherry, cherry plum, plum, mountain ash, andservice berry. Most traps were placed in hawthorns since they appear to be the mostfavored host in British Columbia. Trap placement started on July 7 with all traps up inSan Juan and Whatcom counties by July 28. Traps were inspected about every twoweeks. The survey was extended to Skagit County on August 11 after numerousdetections in Whatcom county.Results: Suspected cherry ermine moths were detected in numerous widely scatteredsites in San Juan and Whatcom counties (Table 1).Table 1. 1993 Cherry Ermine Moth Trap Distribution and ResultsCOUNTYSan JuanSkagitWhatcomNUMBER OFSITES11027106NUMBER OFPOSITIVE SITES90060NUMBER OFMOTHS4080167Percentage of positive sites was 81 and 57 in San Juan, and Whatcom countiesrespectively. None were detected in Skagit County. However, this could be a functionof a low level of trapping, and placement late (August 11) in the flight season.85The last moths were caught sometime in the July 29 to August 18 period in WhatcomCounty. Ermine moths were caught in all host species that were trapped.Identification/confirmation: These specimens have not been confirmed as anintroduction of cherry ermine moth byUSDA. USDA was supposed to provide theidentification support by developing the genetic methodology, but this plan lost out tohigher priorities. Also, no positive host association has been made in Washington.Since high populations ofAEM are common in the survey area, it was difficult to avoidplacing traps near apple trees infested with AEM. Although the literature says that thepheromones in the Yponomeuta group are species specific, there is an unknown potentialfor random catches of AEM in the CEM traps.

Another exotic ermine moth, the cherry ermine moth, Yponomeuta padeuus, discovered in the Pacific Northwest

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Another exotic ermine moth, the cherry ermine moth, Yponomeuta padeuus, discovered in the Pacific Northwest

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