Original Release Site Research Articles

Parasitism of a successful weed biological control agent, Neogalerucella calmariensis

AbstractWe investigated parasitism of the purple loosestrife beetle, Neogalerucella calmariensis (L.) (Coleoptera: Chrysomelidae), an introduced weed biological control agent, at 13 sites in eastern Ontario and western Quebec, Canada. Beetles were parasitized by gregarine gut protozoans (Apicomplexa: Eugregarinida) and much less commonly by nematodes (Nematoda: probably Mermithidae) and ectoparasitic mites (Acari: Erythraeidae). Female beetles had more gregarines than did males and the gregarine load was marginally higher in individuals from the original release sites than in individuals from recently colonized sites. Despite its overall success as a biological control agent, N. calmariensis harbours a substantial parasite load.

Colonization and establishment of Peristenus relictus (Hymenoptera: Braconidae) for control of Lygus spp. (Hemiptera: Miridae) in strawberries on the California Central Coast

Two braconid parasitoids (Hymenoptera) of European origin, Peristenus relictus and Peristenus digoneutis, were released into non-crop vegetation at four locations in the Monterey Bay region of coastal Central California for their permanent establishment and control of Lygus spp. (Hemiptera: Miridae) infesting strawberries. At two sites, parasitoids were released into wild vegetation known to support Lygus spp. near conventionally-managed strawberry fields. Parasitoids were also released into Lygus spp. specific alfalfa, Medicago sativa, trap crops intercropped in two different organic strawberry fields. P. relictus has persisted for over 4 years since last released into the original release site of wild vegetation and for two years at the first organic strawberry release site. Populations of P. relictus were significantly correlated with Lygus spp. collected from alfalfa trap crops from 2005 to 2007 ( r 2 = 0.60; p < 0.005). At this organic strawberry farm, mean densities of Lygus spp. in strawberries have fallen significantly ( p < 0.05) from a pre-release seasonal high of 2.7 nymphs per 50 suctions (bug-vac machine) in 2003 to 0.8 nymphs in 2007. Bordering wild vegetation composed of winter/spring annuals at three different sites supported both native Lygus spp. and Closterotomus ( =Calocoris) norvegicus, an exotic mirid in California that is attacked by P. relictus in Europe. C. norvegicus dominated sampled vegetation in spring to early summer, when Lygus spp. were nearly absent, allowing for the persistence and early build-up of P. relictus at the edge of the strawberry agroecosystem, with no detectable damage to strawberries. An overwintering population of P. digoneutis has not been found in the four release sites.

Establishment of Peristenus digoneutis and P. relictus (Hymenoptera: Braconidae) in California for the control of Lygus spp. (Heteroptera: Miridae)

Lygus hesperus Knight is native to the western United States and is a perennial pest of numerous crops in California. It is responsible for triggering the early season application of insecticides on cotton, Gossypium hirsutum L., and strawberries, Fragaria L. Despite several surveys conducted in alfalfa (Medicago sativa L.) grown in central California, nymphal parasitoids associated with L. hesperus and L. elisus have not been found. Two exotic parasitoids were released into California beginning in 1998. Peristenus relictus (Ruhte), formerly P. stygicus Loan, and P. digoneutis Loan were collected from several locations in southern Europe and released at up to six locations over a 6-year period. At the original release site in Sacramento, a 0.25-ha plot of alfalfa, parasitism by P. digoneutis and P. relictus combined increased from zero to 90%, 3 years after the last releases were made. Parasitoids have been recovered from vacant fields of weedy annuals within 2 km of this site. Recoveries at more southerly release sites in central California have been poor.

CFRAMP's Large Pelagic Fish Tagging Program

CFRAMP's Large Pelagic Fish Tagging Program was established to examine the distribution and movement patterns of Thunnus atlanticus (blackfin tuna), Acanthocybium solandri (wahoo), Coryphaena hippurus (dolphinfish), and Scomberomorus cavalla (king mackerel), large pelagic fish species of commercial importance to several Caribbean countries. The Program explored several means to facilitate fish tag and release activities, involving collaborative partnerships with national fisheries administrations, the recreational fishing sector, and individual commercial fishers. A Iotal of 1,143 fish were tagged and released in the coastal waters of several islands within the Eastern Caribbean: 787 blackfin tuna, 250 wahoo, 89 dolphinfish, and 17 king mackerel. To date, only 13 recaptures have been reported. Eleven (11) blackfin tuna, released in the coastal waters of St Vincent and the Grenadines were recaptured near to, or at original release sites after times at liberty ranging from 5 d to 1,230 d. Similarly, 2 king mackerel, released off the west coast of Trinidad, were recaptured very near original release sites after 74 and 129 d at liberty.

Spatial and seasonal distribution patterns of juvenile and adult raggedtooth sharks (Carcharias taurus) tagged off the east coast of South Africa

Understanding the movement patterns of raggedtooth sharks (Carcharias taurus) is crucial in defining habitat use and evaluating the effects of exploitation and anthropogenic activities. Between 1984 and 2004, 1107 C. taurus juveniles (&lt;1.8-m TL) and 2369 C. taurus maturing subadults and adults (&gt;1.8-m TL) were tagged and released along the east coast of South Africa. In total, 125 C. taurus juveniles and 178 C. taurus maturing subadults and adults were recaptured, representing recapture rates of 11.2% and 7.5% respectively. The average distance travelled by juvenile sharks was 18.7 km (95% CI = 10.8–26.6 km). Juvenile sharks displayed site fidelity to summer nursery areas. The average distance travelled by maturing and adult sharks was 342 km (95% CI = 275–409 km). One female shark, however, was recaptured 1897 km from its original release site. The average rate at which pregnant sharks moved south from their gestation to pupping grounds was 2.6 km day–1 (95% CI = 2.04–3.16 km day–1). This study highlights the differences in movement patterns between C. taurus juveniles and adults and suggests philopatric behaviour in both life-history stages.

RANGE EXPANSION OF THE FIRE ANT DECAPITATING FLY, PSEUDACTEON TRICUSPIS, EIGHT TO NINE YEARS AFTER RELEASES IN NORTH FLORIDA

In the fall of 2005 and the spring of 2006, the fire ant decapitating fly Pseudacteon tricuspis (Diptera: Phoridae) was observed 145-275 km out from the original release sites in northern Florida, occupying an area of about 86,500 km2. Average expansion rates of 26-57 km/year were considerably faster than previous observations. Considering these rates and other releases, we estimate that almost all of the state of Florida will harbor resident populations of P. tricuspis in the next 3 to 5 years.

Infection of naïve, free-living brushtail possums ( Trichosurus vulpecula) with the nematode parasite Parastrongyloides trichosuri and its subsequent spread

Despite the importance of spatial processes in host–parasite interactions, parasite dispersal has been the subject of few experimental studies. Introduced marsupial common brushtail possums ( Trichosurus vulpecula) are a major environmental and agricultural pest in New Zealand. Parastrongyloides trichosuri, an intestinal rhabdiasoid nematode parasite specific to possums, is being evaluated as a self-disseminating delivery system for engineered fertility control vaccines. This study addressed whether an artificial infection could be established in a naïve, free-living possum population, by measuring the post-release dynamics of possum–parasite interactions at the release site, and by following the spread of the parasite into surrounding possum populations. Infection was established efficiently by applying infective larvae to the skin of possums on a single occasion. All experimentally infected possums recaptured 3 weeks after infection had parasite eggs in their faeces. Over the subsequent 2.5 years, infection spread steadily over an area of about 6000 ha. Infection persisted at the original release site for the 3.5 years of the study and at a nearby site infected by natural spread for more than 3 years. Seasonal changes in faecal egg counts were similar at the two sites. The rapid establishment of the parasite and its spread provide additional support for its ongoing development as a vaccine delivery system.

DISPERSAL OF THE FIRE ANT DECAPITATING FLY, PSEUDACTEON CURVATUS (DIPTERA: PHORIDAE) IN NORTHEAST MISSISSIPPI

Pseudacteon curvatus Borgmeier is one of three species of phorid decapitating flies currently approved for release in the U.S. for the suppression of the red, black, and hybrid imported fire ants, Solenopsis invicta Buren, S. richteri Forel, and S. invicta x richteri, respectively. Two biotypes of P curvatus are established in the U.S. The Las Flores, Argentina biotype prefers black and hybrid imported fire ants (Porter & Briano 2000) and is established at sites in Alabama, Mississippi, and Tennessee (Graham et al. 2003; Thead et al. 2003; Vogt & Streett 2003; Vail et al. 2004; Ward et al. 2004). The Formosa, Argentina biotype prefers red imported fire ants and is established at sites in Florida (R. J. Vasquez & S. D. Porter, pers. comm.). This study reports dispersal of flies of the Las Flores biotype, first released in spring, 2002 in a grazed pasture (Knox site) in Clay Co., MS (3.25 ha, 33040'05.87N, 88034'48.02W) (Fig. 1) (Vogt & Streett 2003). By Sept. 2002, flies had established on a mixture of black and hybrid imported fire ants and had spread up to 600 m from the original release site (Vogt & Streett 2003). Additional releases, with the same protocol, were made during spring 2002 and 2003 in a grazed pasture (Prima site) in Clay Co., MS, about 8.8 km and 149.70 SE of the Knox site (Fig. 1). Fly presence was confirmed at both sites during 2003 (J. T. V. & L. G. T., unpubl. data). Observations were made outside the release sites on 23 dates from May-Sept. 2004, between 09:25 and 15:45 hours at 134 active fire ant mounds. Sampling areas were randomly selected and located on roadsides that were bordered by forests with overhanging vegetation or by grazed pastures. The presence of P curvatus was determined by making a round depression (about 4-5 cm wide and 5-10 cm deep) in black and hybrid imported fire ant mounds. Hovering flies were counted within and around the depression. Ants were macerated and dropped into the depression to release semiochemicals that attract the flies (Porter et al. 2004). All sampled areas were georeferenced. Mounds were observed for up to 35 min. If flies were found in an area, we moved and sampled farther from the release sites. An area was re-sampled later unless flies were found farther from the release sites along a similar compass bearing. Average air temperature during sampling was 29.9 ? 2.6?C (?SD), with a mean relative humidity of 66.3 18.5%, and a mean wind speed of 1.2 ? 1.45 km/h.

FIELD RELEASES OF THE DECAPITATING FLY PSEUDACTEON CURVATUS (DIPTERA: PHORIDAE) FOR CONTROL OF IMPORTED FIRE ANTS (HYMENOPTERA: FORMICIDAE) IN ALABAMA, FLORIDA, AND TENNESSEE

The little decapitating fly, Pseudacteon curvatus Borgmeier, was released at 11 sites in Alabama, Florida, and Tennessee as a potential self-sustaining biocontrol agent of imported fire ants. We used a biotype from Buenos Aires Province, Argentina that parasitizes black fire ants (Solenopsis richteri Forel). Generally, several thousand flies were released as larvae in parasitized ant workers over a 1-2 week period. Pseudacteon curvatus flies were successfully established on hybrid fire ants (Solenopsis invicta x Solenopsis richteri) at a site near Talladega, Alabama where they have persisted more than two years and expanded out 5-20 km from the original release site. Flies failed to establish in Florida and Tennessee although a few 1st-generation field-reared flies were recovered at four sites in Florida. This fly is only the second parasitoid species to be successfully released against imported fire ants or any other pest ant species. Possible reasons for failures at the other sites include insufficient vegetation cover, competition with another Pseudacteon species in Florida, severe winter kill of ants at a site in Tennessee, and the possibility that the biotype of P. curvatus released was not a viable parasitoid of red imported fire ants.

Establishment and impact of Galerucella calmariensis L. (Coleoptera: Chrysomelidae) on Lythrum salicaria L. and associated plant communities in Michigan

Abstract Purple loosestrife, Lythrum salicaria L. (Lythraceae) is an invasive wetland perennial plant of Eurasian origin that is widely established in North America and is considered a threat to native wetland flora and fauna. Two European beetles, Galerucella calmariensis L. and Galerucella pusilla Duft. (Coleoptera: Chrysomelidae) have been introduced and widely distributed in North America for biological control of Lythrum salicaria . Experimental releases of Galerucella spp. beetles were made in three locations in Michigan in 1994. In 1997 we initiated a project to rear, redistribute, and evaluate the impacts of Galerucella calmariensis in 19 additional sites throughout Michigan. G. calmariensis became established at 100% of the 24 release locations monitored in these studies and have persisted for up to seven years while G. pusilla apparently failed to establish. Large populations of G. calmariensis developed from each of the 1994 releases and caused 100% defoliation of L. salicaria. From 1995 to 2000, L. salicaria stem height was reduced 73–85%, percent plant cover was reduced 61–95%, and richness of nontarget plant species increased significantly at four out of five sites. By 2001, L. salicaria stem height and percent cover were reduced 38–81% and 32–74%, respectively, and nontarget plant species richness increased significantly at all five sites in contrast to the situation in 1995. Beetles have spread 3–10 km from these original release sites. Of the 19 additional sites monitored for 3–5 years post-release, 50% (4/8) of the 1997 releases have developed into large G. calmariensis populations and produced severe damage to L. salicaria . Thirty-three percent (2/6) of the 1998 releases have generated moderate impacts while all 1999 releases (5/5) remain without clear impacts. The successful establishment, spread, and impacts of G. calmariensis indicate the critical need for additional research on its role in the restoration of desirable plant communities in areas formerly dominated by L. salicaria .

Population dynamics and dispersal of two exotic biological control agents of spotted knapweed, Urophora affinis and U. quadrifasciata (Diptera: Tephritidae), in southwestern Virginia from 1986 to 2000

Abstract A gall fly, Urophora affinis Frfld. (Diptera: Tephritidae), released at two sites in southwestern Virginia in 1986 for the biological control of spotted knapweed, Centaurea maculosa Lam., was monitored annually through 2000 to determine its population density and dispersal rate. Between 1986 and 1991, the mean number of U. affinis per knapweed capitulum increased 10-fold at these original release sites. By spring 2000, it was recovered at 44 of 55 sites sampled but its density at each original release site has not exceeded the 1991 level. Rate of spread averaged 1.3 km/year. A second species, Urophora quadrifasciata (Meigen) that was not released in Virginia, was first recovered in 1995 comprising 30% of the two Urophora species. From 1996 to 2000 it was recovered at all sites sampled. Its rapid increase made it the dominant species, comprising 87.5% of the two species within two years. Although U. quadrifasciata has spread more rapidly than U. affinis, the proportion of the two species has stabilized since 1998 with the population of U. quadrifasciata being three times that of U. affinis. Eighty-two percent of the capitula of spotted knapweed sampled were infested. Each infested capitulum contained 1–3 U. affinis or 1–6 U. quadrifasciata with 11.7% of the capitula being infested by both species. Sex ratio consistently showed a slightly higher number of males than females in both species. Comparison of both species present in 20 sites showed that despite a 9-year head start, U. affinis was the dominant species in only 2.6, 2.4, and 3.5% of the capitula in 1998, 1999, and 2000, respectively. The highest number of each species recorded per capitulum was a mean for all sampled sites of 1.68 U. quadrifasciata in 1997 and 0.4 U. affinis in 1991. Although U. quadrifasciata quickly became the dominant species in sites occupied by U. affinis, the latter has persisted, suggesting that the two species can coexist. Data derived from two sample sizes of 100 and 1000 capitula were not significantly different.

Establishment of Hylobius transversovittatus Goeze (Coleoptera: Curculionidae), a biological control agent of purple loosestrife, in Virginia

Abstract Hylobius transversovittatus Goeze (Coleoptera: Curculionidae), an exotic root feeding weevil, has been released in the USA and Canada for biological control of purple loosestrife Lythrum salicaria L. (Lythraceae), an aggressive emergent aquatic weed of Eurasian origin that has replaced native wetland vegetation. Questions have remained about the establishment and impact of this agent on purple loosestrife in North America. In this report, we present the first detailed account of the establishment and impact of H. transversovittatus in Coeburn and Goshen, Virginia. The weevil was imported from Germany. Adults of H. transversovittatus (n=53) and eggs (n=3935) were first released in Coeburn between 1992 and 1994. After the site was dredged in 1995, 512 eggs were placed in plants in 1995/96, followed by a release of 30 adults in 1999. In Goshen, 19 adults and 2800 eggs were released from 1994 to 1996. Adult weevils were placed on plants at the center of an infested field and eggs were placed in plants or in soil near roots. Establishment was based on digging whole plants and examining roots for larvae. In Coeburn, recovery of H. transversovittatus larvae ( X =0.33 larva per root) was first detected in 1994 at the original release site and larvae were found in roots 400 m downstream of the release point in 2000. Thirteen percent of the roots excavated (n=135) were infested with H. transversovittatus. In Goshen, H. transversovittatus larvae were first detected in 1997 with 2% of the roots infested ( X =0.02 larva per root, n=60). By 2000, the infestation rate increased to 28%. Dry weights of infested and noninfested roots at each site were not different. There was also no difference in mean dry root weight of purple loosestrife between the two sites. Excavation of roots to determine the presence and quantity of H. transversovittatus larvae is laborious but it is more accountable than searching for adults or eggs. H. transversovittatus is well established at both sites in Virginia.

Larra bicolor (Hymenoptera: Sphecidae: Larrinae) Collected in Pheromone- and Phenylacetaldehyde-Baited Traps

Several efforts have been made to import natural enemies of Scapteriscus mole crickets since their arrival in the southeastern USA about 1900. One of these natural enemies was the sphecid wasp Larra bicolor F. Populations of L. bicolor from Bolivia were released between October 1988 and June 1989, and became established in Alachua County, Florida (Frank et al. 1995). Since there is no demonstrated method to sample for L. bicolor, the nectar-bearing plant Spermacoce verticillata L. was established near several release sites so that wasp visits could be observed. Wasps were not observed until the fall of 1993, and wasps continued to be seen through September 1994. By 1995, it was concluded that L. bicolor had dispersed at least a distance of 4 km from release sites (Frank et al. 1995). Our note documents the collection of L. bicolor adults in agricultural fields in northwestern Alachua County that are at least 22 km from the original release sites. From 18 June to 10 October 1997, white plastic funnel traps (bucket or Universal Moth Traps, International Pheromone Systems, Wirral, Merseyside, England) were placed in an area planted to over 470 ha. of cotton, Gossypium hirsutum L., to attract beet armyworm, Spodoptera exigua (Hubner) and fall armyworm, S. frugiperda (J. E. Smith) (Lepidoptera: Noctuidae). Traps were baited with either commercially-produced sex pheromones, phenylacetaldehyde (C6H5CH2CHO, a floral attractant obtained from Aldrich Chemical Co., Milwaukee, WI) in plastic caps (20 mm diameter, 13 mm height; 0.2 or 0.5 ml phenylacetaldehyde per cap), or a combination of pheromone and phenylacetaldehyde. Pheromone lures were attached to the bottom of a cork that was placed in a hole in the canopy of the bucket trap. The phenylacetaldehyde cap was hot-gun glued (Arrow Fastener Co., Saddle Brook, NJ) to the bottom of the cork, which was placed in the trap canopy. The combination lure was composed of a cork with attached cap and the pheromone lure attached to the outside of the cork. Three tests were conducted in separate cotton fields. The first used Hercon? (Hercon Environmental Corp., Emigsville, PA) pheromone lures for S. exigua, the second used Scentry? (Ecogen, Inc., Langhorne, PA) lures for S. exigua, and the third used Tr6c6? (Trec6, Inc., Salinas, CA) lures for S. frugiperda. Four replications of the three treatments were placed within each field along pivot roads or along the field edges. Traps were observed three times weekly and pheromone and phenylacetaldehyde lures were replaced every two weeks. Larra bicolor was collected in 2 of the 3 fields over seven different dates. The first wasp was collected in the Hercon field 18 June, with subsequent collections in the Trece field 23 June (1 collected) and 11 July (2 collected). Higher numbers of wasps were collected in the fall, as 53 wasps were found in late September--early October. Peak capture was 29 September when 48 wasps were collected over a 5 day period in 6 separate traps. Of the total 57 L. bicolor collected, 32 were found in traps baited with the pheromone-phenylacetaldehyde combination, 23 were found in the phenylacetaldehyde-baited traps, and only 2 were found in the pheromone-baited traps.

Return Rates and Reproductive Output of Captive-Reared Female Mallards

From 1993 to 1995, we evaluated the se of captive-reared, released female mallards (Anas platyrhynchos) to increase local breeding populations. A total of 146 females in 1992, 480 in 1993, and 1,140 in 1994 was released onto pothole habitat. Return rates for females released in 1992 and resighted in 1993 were 18-24%. Return rates for females released later were much lower, ranging from 2 to 10%. Released females homed to an average of 1.17 km (SE = 0.28, n = 28) from their original release site. Released birds had low direct recover rates, which suggests poor prefledging or premigratory survival. Comparisons of reproductive output of released females to wild conspecifics were limited by low return rates. Attempting to increase local breeding populations of mallards with released birds is not a viable management technique.

ESTABLISHMENT, DISTRIBUTION, AND IMPACT IN SOUTHERN NEW ENGLAND OF LATHROLESTES NIGRICOLLIS (THOMPSON) (HYMENOPTERA: ICHNEUMONIDAE), AN INTRODUCED PARASITOID OF THE BIRCH LEAFMINER, FENUSA PUSILLA (LEPELETIER) (HYMENOPTERA: TENTHREDINIDAE)

AbstractLathrolestes nigricollis (Thompson) (Hymenoptera: Ichneumonidae) was released in New England against Fenusa pusilla (Lepeletier) in 1979–1980 and again in 1989–1990. By 1991, the parasitoid was widely established in southern New England. From 1979 to 1990 the commonness of leafminers at the original release site in the first generation declined from 50–54% of leaves mined to under 3%. Over 4 years at five sites, parasitism of larval birch leafminers increased between leafminer generations from 10.3% (G1) to 27.6% (G2) to 39.2% (G3). In Massachusetts, parasitism decreased (from 28 to 14%) with increasing distance from the original release site, while corresponding damage increased (from 6% of leaves mined to 33%). In areas local to the original release site (&lt;4 km) parasitism has reduced damage from birch leafminer to inconsequential levels. Some sites in other parts of southern New England, particularly roadside sites, still have high levels of mined leaves in spite of the parasitoid’s presence in the general area.

Effects of the Landscape on Shorebird Movements at Spring Migration Stopovers

We monitored the inter-wetland movements of 115 radio-tagged Pectoral Sand-pipers (Calidris melanotos) at three migration stopovers in the Great Plains of North America during April and May from 1992 to 1995. While resident at a stopover, individuals were very localized in their movements. Over 40% of the birds made no inter-wetland movements, and over 90% of individuals moved less than 10 km from their original release site. Characteristics of wetlands where birds were released did not affect bird movements. However, the structure of the surrounding landscape explained up to 46% of variation in individual bird movements. As the distance between wetlands decreased, and the proportion of the landscape composed of wetlands increased, individual birds moved between wetlands more frequently and moved longer distances from their release site. These movement patterns indicate that a more connected landscape allows shorebirds to exploit more feeding sites with reduced searching costs; a result consistent with foraging theory. We estimate a degree of landscape connectivity at which a wetland complex functions as a single large wetland as measured by sandpiper feeding patterns. Our data provide support for the idea that complexes of small, closely spaced wetlands can be important migration stopovers and may have significant conservation value.

The ectoparasites of brushtail possum Trichosurus vulpecula in New Zealand

The ectoparasites of the brushtail possum Trichosurus vulpecula were examined at 15 original release sites in New Zealand. Three species of fur mite—Atellana papilio Domrow, 1958, Petrogalochirus dycei (Domrow, 1960), and Murichirus anabiotus Domrow, 1992—were present in all population samples from the North, South, Stewart, and Kawau Islands. M. anabiotus was absent from the Chatham Islands. A. papilio was isolated from 82 (98%) of the 84 digested pelts, P. dycei from 78 (93%) of 84, and M. anabiotus was found in 67 (93%) of the 72 pelts digested from populations where the mites were present. The follicle mite Marsupiopus trichosuri Fain, 1968 was detected in two (7%) and one (3%) of pelts examined from Kawau Island and the Orongorongo Valley, respectively. Trichosurolaelaps crassipes Womersley, 1956 was present on 99% of possums and absent only from Kawau Island. Nymphs and larvae of the cattle tick Haemaphysalis longicornis were isolated from four (33%) of the 12 Northland pelts. The loss of ectoparasitic mites resulting from the transfer of possums from their native Australia to New Zealand has been minimal in mites with a direct life cycle. Acariasis of the rump and tail was attributed to M. trichosuri, and .A. papilio is implicated in fur breakage.

Distribution of leptospirosis in possums from New Zealand and its offshore islands

Abstract Extract As part of a larger project investigating methods of brushtail possum (Trichosurus vulpecula) biocontrol, possum sera were collected from 15 sites throughout New Zealand and its offshore islands. These sites were selected to cover the original release sites of possums in New Zealand.

Colonization and hyperparasitism ofCotesia rubecula (Hym.: Braconidae), a newly introduced parasite ofPieris rapae, in Virginia

A Yugoslavian strain ofCotesia rubecula (Marshall) (Hymenoptera: Braconidae) was released in spring broccoli for control of the imported cabbageworm,Pieris rapae (L.), in Montgomery Co., Virginia, in 1987.C. rubecula reproduced and parasitized imported cabbageworm larvae in fall broccoli in 1987. It was found in moderate numbers in the summer and fall crops in 1988, and by fall had dispersed 0.8 km from the original release site. However, noC. rubecula were detected in our broccoli plots in Montgomery Country in 1989 or 1990. The hymenopteran hyperparasitesIsdromas lycaenae (Walker)(Ichneumonidae), Spilochalcis torvina (Cresson) (Chalcididae), andTetrastichus galactopus (Ratzeburg) (Eulophidae) were found attackingC. rubecula. Hyperparasites emerged from 31.8% and 41.1% of theC. rubecula cocoons in 1987 and 1988, respectively.T. galactopus was the most numerous hyperparasite in 1987, butS. torvina was dominant in 1988. Hyperparasite activity was low during early spring, but increased in July in both years. By August 1988, only hyperparasites emerged from theC. rubecula cocoons collected in the field. In spite ofC. rubecula's success in overwintering, hyperparasites, especiallyS. torvina, may be a limiting factor in the establishment ofC. rubecula in southwestern Virginia.

Pest control by predators and parasites

The feasibility of controlling the two-spotted spider mite in apple orchards by inundative releases of the phytoseiid predatorPhytoseiulus persimilis, was studied in a field trial in northern Israel. Half a million predators released per acre, maintained high populations forca 2 months until the spider mite population dropped below the economic threshold.P. persimilis demonstrated a dispersal capacity of at least 90 m from its original release site. The ability of the predator to switch to alternative prey (the European red mite) and the economic feasibility of this non-chemical approach to spider mite control, are discussed.