Entomology

Collection, Release and Establishment of Peristenus digoneutis, a European Bug Parasitoid, on the California Central Coast

Principle Investigators Dr. Kim A. Hoelmer Research Entomologist, USDA ARS, Beneficial Introduction Research Unit and Acting Director, ARS Overseas Biological Control Laboratories 501 S. Chapel St. Newark, DE 19713 (302) 731-7330 ext. 242 [email protected]

Co-Investigators Dr. Carol Shennan, Professor Department of Environmental Studies University of California Santa Cruz, CA 95064

Dr. Charles H. Pickett Senior Environmental Scientist California Department Food & Agriculture Sacramento, CA

Summary Western tarnished plant bugs (lygus bugs, Lygus hesperus) are a key pest of strawberries on the California central coast. Two European lygus bug natural enemies, the parasitic wasps Peristenus relictus and Peristenus digoneutis, were previously released in Santa Cruz and Monterey Counties as part of an earlier California Strawberry Commission-funded project to reduce lygus bug populations. One of these wasps, P. relictus, has since become established in California and has contributed to lygus bug reductions in strawberries. The second, P. digoneutis, did not become established; this was likely attributable to a poor climatic match between where it was collected and released. This project aims to improve lygus bug control through the collection, release and establishment of a new P. digoneutis population collected in the region of Brittany, France, which was identified by climate matching as the area in the wasps’ native range with a climate that best-matches the strawberry-growing regions of coastal central California.

93 2013 - 2014 RESEARCH PROJECTS Based on this wasp’s performance in Europe and the northeastern United States where it has already established, we anticipate that its establishment will benefit California strawberry growers by further diminishing lygus bug populations. Initial surveys began in late 2012 in Brittany to locate sites for collection of P. digoneutis, and collections were made during 2013 and 2014 for shipment to the U.S. for mass rearing and field release in California.The first releases were made in fall 2013. Surveys are being conducted in California to monitor for establishment, and additional releases will be made in 2014.

Introduction In North America tarnished plant bugs (mirid plant bugs of the genus Lygus) are serious pests of many crop cultures (seed alfalfa, oil seeds, cotton, vegetables, soybeans, tree and soft fruits). Lygus bugs are a key pest of strawberries on the California central coast (UC IPM 2014). A European natural enemy of lygus bugs, the parasitoid wasp Peristenus digoneutis, was released by USDA researchers several decades ago and became established in the northeastern US states (Day 1996), and has been expanding into the north central states and northwards into Canada (Day et al., 2000, 2008; Tilmon and Hoffman, 2003).

Because lygus bugs lack an effective native North American nymphal parasitoid that can reduce its numbers in California strawberries, efforts have been made to identify and release European lygus bug parasitoids to reduce lygus populations. As part of a California Strawberry Commission-funded project, two European parasitoids, P. relictus and P. digoneutis, were released in Santa Cruz and Monterey counties from 2002 to 2006 (Pickett et al., 2007, 2009).

Peristenus relictus has since established in central and northern California and has contributed to significant lygus bug reductions in strawberries. It has dispersed into surrounding regions and can be expected to gradually decrease lygus bug populations along the central coast (Pickett et al., 2013). Peristenus digoneutis was also released on the central coast, but did not become established. We believe the population of P. digoneutis that was released was probably not climatically well-matched to Monterey Bay strawberry growing regions and thus failed to establish. Because P. relictus does not typically maintain lygus bug populations below economic thresholds we anticipate that by releasing a population of P. digoneutis on the central coast with greater climatic compatibility, the biological control of lygus will be improved.

Additional parasitism by P. digoneutis should add to, rather than replace, the existing biological control provided by P. relictus. In Europe P. digoneutis tends to dominate in cooler regions, with P. relictus dominating in warmer areas. Peristenus digoneutis should also attack lygus in the spring when P. relictus is less active. Increasing parasitism in the spring would be especially beneficial for second-year strawberries, which often face nymphal lygus populations very early in their second growing season.

Thus, the goal of this project is to establish a population of P. digoneutis that is well-suited to the climate of strawberry- growing regions of coastal central California.

Materials and Methods Using CLIMEX software (Sutherst et al., 2004), French Brittany was determined to be the closest climate match for the Monterey Bay region within the known geographic range of P. digoneutis in Europe. Explorations and collections were therefore conducted in 2012, 2013 and 2014 in the French Brittany region (Figure 1) in the general vicinity of Matignon (department/county of Côtes d’Armor) (Figure 2) by Mr. Dominique Coutinot (senior support scientist and quarantine officer, USDA ARS European Biological Control Laboratory in Montpellier, France) with the support and cooperation of Mr. Xavier Langlet (Regional Authority for Food, Agriculture, and Forestry, Bretagne).

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Figure 1. France with the region of French Brittany (Bretagne) indicated by the ellipse

Figure 2. French Brittany showing the Matignon area of explorations indicated by shaded ellipse

In 2012, initial surveys were conducted to locate alfalfa fields that would be suitable for mass collections of lygus bugs and other mirids for this project. Prior to 2012, the last explorations for lygus parasitoids in this region had been made in the 1980’s for release into the northeastern U.S. (unpublished USDA ARS records). Over the past several decades the nature of agricultural production in Brittany (and throughout northern Europe) has changed considerably, and agricultural land is now used mainly for growing wheat, barley, corn, and rapeseed (canola). It has become quite rare to find a plot of alfalfa. The only host plants found during the 2012 surveys were some fields of that were grown for breeding goats and occasional volunteer patches of alfalfa within grassy areas.

95 2013 - 2014 RESEARCH PROJECTS During repeat visits to the area during the spring and summer of 2013, European tarnished plant bug nymphs (Lygus rugulipennis) were collected by sweep-netting in alfalfa (Medicago sativa) in the area of Henanbihen (Figure 3). Nymphs were placed in containers with fresh green beans as food and the collections were returned to EBCL and held in the laboratory until parasitoid larvae emerged from parasitized lygus nymphs and spun cocoons for pupation. The cocoons of P. digoneutis were placed in dishes with moistened vermiculite and shipped to the USDA ARS Beneficial Introduction Research Unit (BIIR) in Newark, DE via airfreight (SDV LI Montpellier, France) under a current APHIS foreign importation permit.

Figure 3. Collection site in Henanbihen, France (photo: D. Coutinot)

After arrival at the ARS BIIR laboratory, the material was held in the quarantine facility for emergence of adult parasitoids from the cocoons. Emerged adults were screened for hyperparasitoids and were identified to species. The live, emerged P. digoneutis were sent to Mr. Thomas Dorsey (Director, Philip Alampi Beneficial Insect Laboratory - New Jersey Department of Agriculture, Division of Plant Industry, Bureau of Biological Pest Control), for mass rearing at the Alampi Laboratory in Trenton, NJ. A colony of lygus bugs maintained on the Cohen artificial diet provided the nymphs for parasitism by female P. digoneutis. The parasitized nymphs were maintained at the Alampi lamp until emergence of F1 generation adult wasps, which were then shipped to California for field release by UC Santa Cruz research associate Diego Nieto and colleagues in alfalfa trap crops adjacent to strawberry fields in Prunedale, CA.

In July 2014, surveys and field collections were again made in the same area of Matignon. Lygus rugulipennis and L. maritimus nymphs were collected from lambs quarters ( album) and chamomile (Matricaria species). All cocoons formed are scheduled to be shipped to the U.S. in early August 2014. Additional explorations, collections and exports are planned for September 2014 to increase the gene pool and strengthen the mass-rearing colony in New Jersey. The Alampi lab is scheduled to ship adult P. digoneutis from the Brittany colony to California for field release during the summer and fall of 2014.

Shipments of 200 P. digoneutis adults were sent by Thomas Dorsey from the Philip Alampi Laboratory on October 17 and October 24, 2013. These parasitoids were received and released in two strips of alfalfa at an organic strawberry ranch in Prunedale, CA (Figures 4 and 5). These alfalfa rows were continuously maintained (e.g., weeded, fertilized and irrigated), to facilitate colonization resulting from 2013 releases and to encourage high host densities in preparation for releases in 2014. Temperature readings were recorded from a data logger to determine climate compatibility between the release site and P. digoneutis (Table 2). Strips of alfalfa were selected at two additional ranches for 2014 releases in Aromas, CA and Salinas, CA

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Table 1. Collections of P. digoneutis shipped to the U.S., 2013-2014

Mirids per 100 Parasitism Date Locality Latitude & Host mirid Host plant sweeps (cocoons Longitude formed) July 2013 La Vallée, 48°32’48 N L rugulipennis, alfalfa 44 5.93% Henanbihen 02°21’58 W L. maritimus July 2013 La Vallée 48°32’48 N C. norvegicus alfalfa 62 31.06% 02°21’58 W Sept. 2013 Le Colombier 48°29’02 N L. rugulipennis, alfalfa 128 2.98% 02°29’27 W L. maritimus July 2014 La Poterie 48°29’04 N L. rugulipennis, C. album, 30 0.96% 02°26’01 W L. maritimus Matricaria sp.

Figure 4. P. digoneutis in release containers (photo: D Nieto)

Figure 5. Release site in California (photo: D Nieto)

97 2013 - 2014 RESEARCH PROJECTS Table 2. Temperature readings taken by a data logger in 2013-2014 at the P. digoneutis release site in

Prunedale, CA.

Minimum Maximum Mean

October 2.1 34.3 17.9 November -0.8 26.9 10.8 December -7.2 26.3 8.1 January -2.4 28.6 10.3 February -0.6 23.4 11.1 March 2.5 26.7 12.6 April 3.9 31.8 12.8

Results and Discussion In May and June of 2014, approximately two dozen Closterotomus norvegicus nymphs were collected from mustard, radish and yarrow at the Prunedale release site. Collected nymphs were reared to allow adult parasitoids to emerge and be identified (i.e., P. relictus versus P. digoneutis). In July, parasitism data were collected at the Prunedale release site using three different techniques: first, hand-held vacuums were used to collect adult parasitoids. Thirty-two such 50-suction samples have been collected and analyzed. Second, approximately 185 Lygus spp. nymphs have been collected and reared. Thus far, several P. relictus adults have been collected using these methods, but P. digoneutis adults have yet to be recovered. Finally, 25 Peristenus spp. larvae, which were collected from dissected nymphs, will be shipped and identified to species via polymerase chain reaction (PCR) by Dr. Martin Erlandson at the Insect Pathology Laboratory, Agriculture and Agri-Food Canada.

Beginning in the first week of August 2014, releases of additional P. digoneutis adults will be made in Prunedale, Salinas and Aromas. Monthly collections at each of these three sites will continue through October, including the collection of adult parasitoids and the rearing of nymphs. An additional 75 Peristenus spp. larvae will also be analyzed via PCR.

Monitoring for establishment will continue throughout the project. If establishment occurs as anticipated, the buildup of the population, with attendant impact on lygus populations, is likely to take time and may not be immediately evident.

Selected References

• Day WH. 1996. An evaluation of biological control of the tarnished plant bug, Lygus lineolaris, in alfalfa by the introduced parasitoid Peristenus digoneutis (Braconidae). Envir. Entomol. 25: 512-518.

• Day WH, Tilmon KJ, Romig RF, Eaton AT and KD Murray. 2000. Recent range expansions of Peristenus digoneutis (Hymenoptera: Braconidae), a parasite of the tarnished plant bug (: ), and high temperatures limiting its geographic distribution in North America. Journal of the New York Entomological Society 108: 326-331.

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• Day WH, Romig RF, Faubert HH and KM Tatman. 2008. The continuing dispersion of Peristenus digonuetis Loan (Hymenoptera: Braconidae), an introduced parasite of the tarnished plant bug Lygus lineolaris (Palisot) (Hemiptera: Miridae) in Northeastern U.S.A. and Southeastern Canada. Entomological News. 119: 77-80.

• Pickett CH, Rodriguez R, Brown J, Coutinot D, Hoelmer KA, Kuhlmann U, Goulet H, Schwartz MD and PD Goodell. 2007. Establishment of Peristenus digoneutis and P. relictus (Hymenoptera: Braconidae) in California for the control of Lygus spp. (Heteroptera: Miridae). Biocontrol Science and Technology 17, 261–272.

• Pickett CH, Swezey SL, Nieto DJ, Bryer JA, Erlandson M, Goulet H and MD Schwartz. 2009. Colonization and establishment of Peristenus relictus (Hymenoptera: Braconidae) for control of Lygus spp. (Hemiptera: Miridae) in strawberries on the California Central Coast. Biological Control. 49: 27-37.

• Pickett CH, Nieto DJ, Bryer JA, Swezey SL, Stadtherr M, Wisheropp D, Erlandson M, and Pitcairn M. 2013. Post- release dispersal of the introduced lygus bug parasitoid Peristenus relictus in California. Biocontrol Science and Technology, 23: 861-871.

• Sutherst RW, Maywald GF, Bottomley W and A Bourne. 2004. The Match Climates indices. In: CLIMEX, version 2. Dymex Simulator Application 2.01.025, CD-ROM and User guide. CSIRO & Hearne Scientific Software, Melbourne, Australia.

• Tilmon KJ and MP Hoffmann. 2003. Biological control of Lygus lineolaris by Peristenus spp. in strawberry. Biological Control. 26: 287-292.

• UC IPM Online. 2014. University of California Pest Management Guidelines for Strawberry: Lygus Bug. Revision July 2014. http://www.ipm.ucdavis.edu/PMG/r734300111.html Accessed 23 Oct. 2014.

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