Agricultural and Forest Entomology (2003) 5, 173–181 Influence of flowering cover crops on Anagrus parasitoids (Hymenoptera: Mymaridae) and Erythroneura leafhoppers (Homoptera: Cicadellidae) in New York vineyards Greg English-Loeb*, Marc Rhainds*†, Tim Martinson*‡ and Todd Ugine*§ *Department of Entomology, Cornell University, New York State Agricultural Experiment Station, Geneva, New York 14456, U.S.A., yGreenhouse and Processing Crops Research Centre, Harrow, Ontario, NOR 1G0, Canada, zCornell Cooperative Extension, Finger Lakes Grape Program, Cornell University, County Office Building, Penn Yan, NY 14427, U.S.A. and §Department of Entomology, Cornell University, Ithaca, NY 14853, U.S.A. Abstract 1 We tested the hypothesis that providing nectar-producing cover crops will enhance the biological control of grape leafhoppers (Erythroneura spp.) by Anagrus wasps in commercial vineyards in New York, U.S.A. 2 We established three cover crops between vine rows in a commercial vineyard: buckwheat (Fagopyrum esculentum (Moench)), clover (Trifolium repens L.) and mowed sod (Dactylis glomerata L.). 3 There was no effect of cover crop on adult Anagrus in 1996, whereas in 1997 adults were more abundant within edge vines with buckwheat compared to vines with clover or sod; adults were more abundant at the vineyard edge, especially early in the season. 4 Parasitism of ‘sentinel’ leafhopper eggs was higher on vines with buckwheat compared to parasitism on vines with clover or sod in 1996; a similar, non- significant trend, was observed in 1997. 5 Neither the abundance nor the distribution of leafhoppers was influenced by cover crops, although in 1997 there was a trend toward greater numbers of nymphs on edge vines with buckwheat. 6 In a cage experiment, parasitism by Anagrus of leafhopper eggs on grapes was greater when adults had access to flowering buckwheat rather than buckwheat without flowers. 7 In a laboratory study, longevity of female Anagrus was increased when pro- vided with honey or sugar water compared to water only or nothing. 8 Our results suggest that parasitism of grape leafhoppers by Anagrus may be enhanced by providing floral resources within vineyards in New York, although it is unclear whether this will produce meaningful reductions in pest abundance. Keywords Conservation biological control, cover crops, egg parasitoid, leaf- hoppers, Mymaridae, pro-ovigeny. Introduction Conservation of natural enemies in agricultural systems has pesticide use), (2) providing supplementary resources been recognized for many years as an important component (e.g. nectar or alternative hosts), and/or (3) providing shel- of biological control (Ehler, 1998). Natural enemies can be ter (e.g. shade or overwintering sites) (Pickett & Bugg, 1998; enhanced by: (1) reducing mortality factors (e.g. modifying Landis et al., 2000). The egg parasitoid/leafhopper system in vineyards in the western U.S.A. represents one of the better studied systems for conservation of a natural enemy (Anagrus Haliday spp.) (Hymenoptera: Mymaridae) Correspondence: G. English-Loeb. Fax: 315 787 2326; e-mail: for biological control of an important crop pest (grape [email protected] leafhopper Erythroneura elagantula Osborn) (Homoptera: # 2003 The Royal Entomological Society 174 Greg English-Loeb et al. Cicadellidae). In this system conservation efforts have Materials and methods concentrated on either: (1) increasing the supply of non-pest leafhopper eggs as necessary overwintering Field experiments evaluating the impact of ground hosts for wasps (Kido et al., 1984; Murphy et al., 1996, cover on incidence of Erythroneura leafhoppers and 1998) or (2) providing nectar to adult wasps by planting Anagrus parasitoids flowering cover crops in row middles (¼ ground between each row of vines) during the field season (Daane & Field experiments were carried out in a commercial vineyard in Costello, 1998; Nicholls et al., 2000). Augmenting over- the Finger Lakes region near Dresden, New York, in 1996 and wintering hosts by planting prune trees Prunus domestica L. 1997. The 1.4-ha experimental site consisted of sixty 80-m-long that support populations of the prune leafhopper rows spaced 3 m apart, with Vitis vinifera L. ‘Chardonnay’ vines Edwardsiana prunicola (Edwards) near vineyards increases planted 2 m apart in each row. Rows ran perpendicularly to a abundance of Anagrus in the vineyard and parasitism rates woodlot located on the south edge of the experimental site. of pest leafhoppers (Murphy et al., 1996, 1998). The use of Experimental units, consisting of five contiguous 80-m-long flowering cover crops in vineyards reduces leafhopper rows, were assigned to one of the following ground cover treat- populations, but whether this is due to enhanced biological ments: (1) sod (primarily orchardgrass, Dactylis glomerata L.), control or reduced vine vigour is under debate (Daane & already established in the experimental site, served as a control, Costello, 1998). and was mowed when it reached 0.5 m; (2) buckwheat Fago- Anagrus spp. are also important natural enemies of grape pyrum esculentum (Moench) was seeded between rows of vines leafhopper pests in vineyards in the eastern U.S.A. in late May of 1996 and 1997; and (3) ladino clover Trifolium (Williams & Martinson, 2000). Several species of Anagrus repens L. was planted between rows of vines in late May of parasitize several species of Eyrthroneura leafhoppers in 1996, and remained established through the 1997 season. New York vineyards (Martinson & Dennehy, 1995; Experiments were replicated four times, using a completely Triapitsyn, 1998). As is true for the western system, wasps randomized block design. In 1997, a prebloom application of overwinter in non-pest leafhopper eggs (several different carbaryl (Sevin1 50W at label rate) was inadvertently sprayed species using several different plant hosts) outside of the in two replicates, and data from these two replicates were vineyard and then migrate into the vineyard in the spring excluded from analyses. Experiments were terminated earlier and summer to attack pest leafhoppers (Corbett & Rosenheim, than anticipated in 1997 because the entire vineyard was treated 1996; Williams & Martinson, 2000). Although parasitism levels with carbaryl in early August to control potato leafhoppers in New York vineyards can reach high levels (> 90%), this Empoasca fabae Harris. tends not to occur until late in the season. Moreover, parasitism The following data were collected. (1) Density of adult levels early in the season typically are much greater at the edge leafhoppers and parasitoids was monitored with yellow of a vineyard compared to the interior, suggesting that Anagrus sticky traps suspended on the low canopy wire adjacent to first migrates to vineyard edges and then expands into the the fruit zone of vines, using 10 traps spaced 8 m apart in the vineyard interior over several generations utilizing pest centre row of each experimental unit. Traps were replaced leafhopper eggs (Williams & Martinson, 2000). every 4–7 days (28 May to 14 August 1996, 9 June to 21 July After emerging from grape leafhopper eggs in the labora- 1997), and the number of adults on each trap recorded. (2) tory/insectary, adult Anagrus will readily feed on honey Density of leafhopper nymphs was assessed by sampling before initiating search for hosts (G.E-L., unpublished five leaves of two shoots on vines spaced 8 m apart in the observations). Other Mymarids (Anaphes sp., Gonatocerus centre row of each experimental unit (four times between 1 sp.) have been observed visiting flowers, presumably to July and 13 August in 1996; twice on 7 and 17 July in 1997). obtain nectar (Jervis et al., 1993). Studies with egg parasit- (3) Parasitism by Anagrus females was assessed with ‘senti- oids have shown that availability of carbohydrates in the nel’ leafhopper eggs. Sentinel eggs were established by form of sugar, honey or honeydew will enhance adult wasp confining field-collected leafhoppers (E. bistrata McAtee survival and parasitism (Jervis et al., 1996; Baggen & Gurr, and E. vitifex Fitch complex, referred to as E. bistrata here- 1998). Hence, we hypothesized that providing nectar- after) into clip cages (4 cm in diameter) placed onto one leaf producing cover crops will enhance biological control of of a vine for 2 days (Williams & Martinson, 2000), thereby grape leafhoppers in New York vineyards. Specifically, we providing an even-aged cohort of susceptible hosts of tested the following hypotheses. (1) In comparison with row roughly the same density at all sample sites. One batch of middles planted with non-nectar producing grasses, the sentinel eggs was established every 8 m along the central presence of nectar-producing cover crops in row middles row of each experimental unit. After 3 weeks of field of a commercial vineyard will increase abundance of exposure, sentinel eggs were categorized as parasitized or Anagrus adults, encourage colonization of the vineyard non-parasitized (Wells et al., 1988; Williams & Martinson, interior, elevate parasitism rates of leafhopper eggs on 2000). Parasitism, using the sentinel egg method, was meas- vines and reduce leafhopper densities. (2) The presence of ured twice in 1996 (mid-June and mid-August) and once in nectar-producing flowers of the cover crop, not just the 1997 (early July). To assess the impact of spatial location on vegetative portion of the plant, promotes greater parasitism incidence of leafhoppers and parasitoids, sampling sites rates of leafhopper eggs. (3) Survival of adult Anagrus will along rows were classified as either near the edge or in the be enhanced when fed sugar water or honey mixed with interior of the vineyard (< 40 m or > 40 m from the first vine water relative to water alone or nothing. bordering the woodlot). # 2003 The Royal Entomological Society, Agricultural and Forest Entomology, 5, 173–181 Cover crop and parasitism of leafhopper eggs 175 Greenhouse experiment evaluating the impact of sealed using modelling clay. Liquid food was wicked from flowering plants on rate of parasitism by female a holding container into the tube where it flowed to the tip Anagrus by capillary action.