Erythroneura Elegantula Research Articles

Survey of Vineyard Insects and Plants to Identify Potential Insect Vectors and Noncrop Reservoirs of Grapevine Red Blotch Virus

Grapevine red blotch virus (GRBV) is a DNA virus in the family Geminiviridae. This pathogen is the causal agent of grapevine red blotch disease, which affects cultivated grapevines and leads to negative effects on crop quality and yield. GRBV is present in commercial vineyards across North America, indicating that spread might have been largely human mediated. That said, recent surveys have demonstrated that there appears to be secondary transmission, most likely by an insect vector. In this study, vineyard insects and plants were surveyed to identify potential candidate vectors and noncrop plants that could act as reservoirs for this pathogen. Results reconfirm that GRBV is limited to Vitis spp., including both cultivated and wild grapevines. Eleven insect genera or species, field collected in vineyards, tested positive for GRBV using quantitative polymerase chain reaction. These insect taxa include unknown Aphididae, the cicadellids Aceratagallia spp., Acinopterus angulatus, Caladonus coquilleti, Colladonus montanus reductus, Colladonus sp., Empoasca spp., Erythroneura elegantula, and Scaphytopius graneticus, along with the membracid Spissistilus festinus and an unknown delphacid. Of these organisms, S. festinus is already known to be capable of transmitting GRBV, and Scaphytopius graneticus may merit closer evaluation as a candidate vector. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Use of Ground Covers to Control Three-Cornered Alfalfa Hopper, Spissistilus festinus (Hemiptera: Membracidae), and Other Suspected Vectors of Grapevine Red Blotch Virus

Grapevine red blotch virus (GRBV) is the causal agent of grapevine red blotch disease, which affects wine grapes and leads to reduced crop yield and quality. The pathogen-plant-vector relationship of GRBV is not well understood; however, some possible vectors have been identified: Caladonus coquilletti (Van Duzee; Hemiptera: Cicadellidae), Colladonus reductus (Van Duzee; Hemiptera: Cicadellidae), Erythroneura spp., Melanoliarus sp. (Hemiptera: Cixiidae), Osbornellus borealis DeLong. & Mohr (Hemiptera: Cicadellidae), Scaphytopius granticus (Ball; Hemiptera: Cicadellidae), Spissistilus festinus (Say). Of these species, S. festinus has been shown to transmit the virus to uninfected grapevines, making it of particular interest. Since the pathogen-plant-vector relationship of GRBV is not yet completely understood, pesticide use is not necessarily the best way to manage these possible vectors. Here we test if ground cover removal, by discing in spring, could reduce the activity of potential GRBV vectors. We show that S. festinus presence in the canopy was reduced in disc rows compared to just mowing the ground vegetation, whereas there were no differences in presence in the canopy between disc and mow rows of the other possible insect vectors. Erythroneura elegantula (Osborn; Hemiptera: Cicadellidae), a common pest of grapevines but not a candidate GRBV vector, was found to have higher densities in the canopy in disc rows compared to mow rows, an effect possibly mediated by changes in vine vigor associated with ground covers. We conclude that if S. festinus is a primary vector of GRBV, discing ground covers in early spring may be a viable way to reduce their presence in the vine canopy.

Influence of Vineyard Vegetational Borders on Western Grape Leafhopper (Erythroneura elegantula Osborn), its Egg Parasitoids (Anagrus spp.) and Generalist Insect Predators

Studies have shown that vegetational diversity in or around cropping systems can enhance naturalenemy abundance, although the impact on herbivores is less certain. We studied the influence of vineyardvegetational borders on density of the western grape leafhopper, Erythroneura elegantula, its majorparasitoids, Anagrus spp., and two generalist predators, Orius spp. and Leptothrips mali. Two studyvineyards had planted, perennial flowering hedgerows, one bordered a natural riparian zone, and onehad a sparse border of native trees. From April to September 2007, we counted leafhopper nymphs andadults of Anagrus spp., Orius spp. and L. mali within 10 m of the border, and at additional 20 m intervalsup to 90 m. At two sites with a diverse border, leafhopper density was stable nearest the border; at otherdistances leafhopper density decreased between the first and second generations. This effect was notseen at the sparse border site. Anagrus spp. density was enhanced at one site with a diverse border, butonly late season. There was no border effect on the generalist insect predators, by site or early vs. lateseason. Regression analysis showed a positive relationship between leafhopper and Anagrus spp. density,suggesting that the parasitoids were responding to higher leafhopper density. We conclude that, dependingon the nature of the border vegetation, there can be an effect on leafhopper nymphal density, but in thisstudy there is no evidence that it was due to natural enemies.

Landscape diversity and crop vigor outweigh influence of local diversification on biological control of a vineyard pest

AbstractThe influence of local and landscape habitat diversification on biological control of the Western grape leafhopper (Erythroneura elegantula Osborn) by its key parasitoids Anagrus erythroneurae S. Trjapitzin & Chiappini and Anagrus daanei Triapitsyn was studied in wine grape vineyards. At the landscape scale, Anagrus rely on alternative host species in non‐crop habitats outside of the vineyard to successfully overwinter, while at the local scale vineyard diversification can provide resources, such as shelter and floral nectar, which improve parasitoid performance. In a two‐year experiment, plots with and without flowering cover crops were compared in vineyards representing a gradient of landscape diversity. While the cover crops did attract natural enemies, their populations were unchanged in the crop canopy and there was no difference in parasitism rate, leafhopper density, crop quality, or yield. Vineyards in diverse landscapes had higher early‐season abundance of Anagrus spp., which was linked to increased parasitism and decreased late‐season populations of E. elegantula. Leafhopper densities were also positively associated with crop vigor, regardless of landscape or cover crops. Flowering cover crops did increase abundance of some natural enemy species as well as parasitism rate in vineyard landscapes with intermediate levels of diversity, indicating a local × landscape interaction, although this did not lead to reductions in E. elegantula densities. These findings indicate that, in this agroecosystem, landscape diversity mediates and in many ways outweighs the influence of local diversification and that E. elegantula densities were regulated by a combination of biological control and crop vigor.

Evaluating the Toxicity of Candidate Organic and Conventional Insecticides on Western Grape Leafhopper and Virginia Creeper Leafhopper (Hemiptera: Cicadellidae) under Vineyard and Laboratory Conditions

Abstract The western grape leafhopper (Erythroneura elegantula Osborn) and the Virginia creeper leafhopper (Erythroneura ziczac Walsh) are the two leafhopper pests frequently observed in Washington State vineyards. Organic viticulturists have difficulties controlling these leafhopper pests, and outbreaks can result in economic loss. We vineyard-tested the efficacy of several candidate bioinsecticides and conventional insecticides against the western grape leafhopper and the Virginia creeper leafhopper. This study included the initial testing of several alternative candidate insecticides for leafhopper control. Controlled laboratory bioassays also were completed, and the 50% and 90% lethal concentrations were calculated for the nonsystemic insecticides tested. Of the bioinsecticides tested, pyrethrum (PyganicTM, Valent Bioscience Corporation, Libertyville, IL) was the only product that provided effective control of leafhoppers in both the vineyard and laboratory components of this study. In vineyard effic...

Host Plant Associations of Anagrus spp. (Hymenoptera: Mymaridae) and Erythroneura elegantula (Hemiptera: Cicadellidae) in Northern California.

Anagrus erythroneurae S. Trjapitzin & Chiappini and Anagrus daanei Triapitsyn are the key parasitoids of the western grape leafhopper (Erythroneura elegantula Osborn) in northern California vineyards. Erythroneura elegantula overwinters as an adult in reproductive diapause. To successfully overwinter, Anagrus spp. must locate an alternate leafhopper host that overwinters in an egg stage that they can parasitize. These alternate leafhopper hosts are thought to be primarily located in the natural habitats surrounding vineyards. This study identifies the noncrop host plants utilized by Anagrus spp. not only during the overwintering period but throughout the entire year, as well as the leafhopper species associated with these host plants. Over a 2-yr period, Anagrus spp. and leafhoppers were sampled from numerous plants in natural and cultivated habitats surrounding vineyards. Results from this study confirm previously known Anagrus spp. host plants, but also identify new host plant species. Some of the host plants harbored Anagrus spp. year-round while others were utilized only during certain periods of the year. Leafhoppers associated with Anagrus spp. host plants may potentially serve as the alternate host utilized by Anagrus spp. on these plants, but this was not confirmed in the current study. Records of E. elegantula demonstrate their cyclical movement between the vineyard floor (winter), temporary noncrop hosts (spring/fall), and the grape vine canopy (summer).

Landscape Diversity and Crop Vigor Influence Biological Control of the Western Grape Leafhopper (E. elegantula Osborn) in Vineyards.

This study evaluated how the proportional area of natural habitat surrounding a vineyard (i.e. landscape diversity) worked in conjunction with crop vigor, cultivar and rootstock selection to influence biological control of the western grape leafhopper (Erythroneura elegantula Osborn). The key natural enemies of E. elegantula are Anagrus erythroneurae S. Trjapitzin & Chiappini and A. daanei Triapitsyn, both of which are likely impacted by changes in landscape diversity due to their reliance on non-crop habitat to successfully overwinter. Additionally, E. elegantula is sensitive to changes in host plant quality which may influence densities on specific cultivars, rootstocks and/or vines with increased vigor. From 2010–2013, data were collected on natural enemy and leafhopper densities, pest parasitism rates and vine vigor from multiple vineyards that represented a continuum of landscape diversity. Early in the season, vineyards in more diverse landscapes had higher Anagrus spp. densities and lower E. elegantula densities, which led to increased parasitism of E. elegantula. Although late season densities of E. elegantula tended to be lower in vineyards with higher early season parasitism rates and lower total petiole nitrogen content, they were also affected by rootstock and cultivar. While diverse landscapes can support higher natural enemy populations, which can lead to increased biological control, leafhopper densities also appear to be mediated by cultivar, rootstock and vine vigor.

Characterization of the feeding behavior of three Erythroneura species on grapevine by histological and DC‐electrical penetration graph techniques

AbstractFeeding behavior of three leafhopper species – Erythroneura vitis (Harris), Erythroneura ziczac (Walsh), and Erythroneura elegantula (Say) (Hemiptera: Cicadellidae) – reared on grapevine, Vitis vinifera L. cv. ‘Seyval blanc’ (Vitaceae), was investigated using histological techniques and DC‐electrical penetration graphs (DC‐EPG). Histological studies revealed that the Erythroneura species induced white stipples on the leaves and that these leafhoppers produced thin salivary sheaths in grapevine leaf tissues. The DC‐EPG system allowed the characterization of five waveforms associated with stylet penetration and feeding in leaf tissues. These waveforms were characteristic of feeding phases corresponding to epidermis penetration pathway, salivation, and ingestion. We calculated 28 parameters (e.g., number of probes, duration of phases, and time spent in the various tissues) to describe and compare the feeding behavior of the Erythroneura species. We conclude that the three Erythroneura species are mainly mesophyll feeders but may probably also feed in other tissues such as xylem.

Vineyard proximity to riparian habitat influences Western grape leafhopper (Erythroneura elegantula Osborn) populations

The purpose of this study was to evaluate the impact of vineyard proximity to riparian habitat on the biological control and population densities of the Western grape leafhopper, Erythroneura elegantula Osborn (Hemiptera: Cicadellidae). Natural enemy and pest populations were monitored over a two-year period at multiple vineyard sites adjacent to riparian habitat in northern California. At each site, natural enemy and pest population data were collected along a transect that extended from the riparian habitat into the vineyard. Additionally, a subset of the original research sites were further evaluated for crop vigor, pest density and parasitism rates between the vineyard edge and interior. Results from this study indicate that lower E. elegantula egg deposition and nymph abundance at the vineyard edge were primarily due to reduced crop vigor at the sampled sites and that the most likely cause for these changes were differences in microclimate and soil fertility that were found to be associated with proximity to the riparian habitat.

Influence of Intensity and Duration of Regulated Deficit Irrigation on <I>Erythroneura elegantula</I> (Hemiptera: Cicadellidae) on Grape

We conducted studies in a Paso Robles, CA, grape (Vitis vinifera L.) vineyard in 2002 and 2003 to estimate the impact of regulated deficit irrigation (RDI) intensity and duration on western grape leafhopper, Erythroneura elegantula Osborn. Treatments were based on deficit intensity, 50 and 25% of standard irrigation (moderate and severe deficits, respectively), and deficit duration, 3 or 6 wk time, initiated at the grape phenological stage of berry set. The standard irrigation served as the control, and was intended to be as close to 100% of evapotranspiration (1.0 ETc) for grape in this area. Each week we took counts ofleafhopper nymphs and estimated stomatal conductance, and at the end of each leafhopper generation we counted live, hatched and parasitized leafhopper eggs. Second generation leafhopper nymphal density was lowered by about 38 and 70% in 2002 and 2003, respectively, but in 2003 only the severe deficit had a negative effect on the third generation. This same pattern was seen in oviposition: second generation egg density was reduced by about 44% in the deficit treatments, but in the third generation only the severe deficit was lower than the control. There was little difference between the 3 vs. 6 wk duration in nymphal or egg density. The differences among treatments in second generation peak nymphal density were greater than the differences in second generation hatched eggs, suggesting that in addition to egg mortality, the deficits also affected nymphal mortality. Management strategies for maintaining leafhopper density low in the second generation and third generations include maintaining a sub-1.0 ETc irrigation strategy after the main RDI period, or reinstating the RDI to correspond to the third generation.

Biology and host specificity of Gonatocerus deleoni (Hymenoptera: Mymaridae), a potential biocontrol agent of Homalodisca vitripennis (Hemiptera: Cicadellidae) in California, USA

The host-specificity and biological traits of Gonatocerus deleoni Triapitsyn, Logarzo & Virla (Hymenoptera: Mymaridae), a potential candidate for biological control of the glassy-winged sharpshooter (GWSS), Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae), were determined under laboratory conditions. G. deleoni is a solitary egg parasitoid native to Argentina, originally reared from sentinel eggs of Tapajosa rubromarginata (Signoret) (Cicadellidae). With GWSS as a fictitious host, G. deleoni’s average development time from oviposition to adult emergence was 18.8 ± 1.4 days, with males developing faster than females (18.0 ± 1.3 days, males; 19.0 ± 1.3 days, females). The average parasitism rate on 1–8-day-old eggs was 45.7% but this was significantly affected by the age of the egg, ranging from 1.4% to 69.9% (egg ages 8 and 3, respectively). The average sex ratio was 0.34 (percent males) and sex ratio was not significantly affected by egg age. G. deleoni was able to develop in eggs of GWSS and Homalodisca liturata Ball (both in the tribe Proconiini), but was unable to develop on eggs of Graphocephala atropunctata (Signoret) (different tribe, same subfamily) or Erythroneura elegantula Osborn (different subfamily).

Diversity and invasion within a predator community: impacts on herbivore suppression

Summary 1. Management strategies to enhance ecosystem services in agroecosystems often seek to increase predator biodiversity. Invaders commonly dominate predator communities in agricultural landscapes, however, and the impacts of exotic predators on native predators and ecosystem services are largely unknown. Exotic predators may complement native predator diversity and enhance herbivore suppression, or they may disrupt herbivore suppression through predator interference. 2. We examined the impacts of a dominant exotic predator within the diverse predator community of a California vineyard. Interactions between the exotic wandering spider Cheiracanthium mildei, its closest native ecological homologue (the wandering spider Anyphaena pacifica) and a native spider displaying a different hunting mode (the cobweb‐weaving spider Theridion melanurum) were tested in a manipulative field experiment, with the grape leafhopper Erythroneura elegantula acting as a shared herbivore prey source. 3. We found that the exotic wandering spider suppressed both grape leafhoppers and other unmanipulated leafhopper species that were present in cages. Native spiders had little or no impacts on leafhopper suppression. Thus, C. mildei appears to drive predatory impacts in this system, although evidence also indicated that it is limited by intraspecific interactions. The superior predatory ability displayed by this spider may be shared by other invasive predators that dominate agroecosystems. 4. Despite its effects on leafhoppers, C. mildei negatively impacted a range of spider species, including A. pacifica, T. melanurum, and other unmanipulated native spiders. These impacts are likely to have been mediated through intraguild predation. The wandering hunting mode of C. mildei may have facilitated its role as an intraguild predator. 5. Synthesis and applications. Our results highlight the sometimes conflicting aims of biological control and conservation. Here, a dominant invasive predator increased ecosystem services but also caused declines in numbers of native predators. As disturbed conditions in agroecosystems are likely to put invasive predators at an adaptive advantage, efforts to conserve biodiversity in agricultural landscapes should focus on shifting the outcomes of species interactions to favour native species.

Regulated Deficit Irrigation and Density of <I>Erythroneura</I> spp. (Hemiptera: Cicadellidae) on Grape

This study looked at regulated deficit irrigation (RDI) on leafhoppers in the genus Erythroneura (Erythroneura elegantula Osborn, or western grape leafhopper, and Erythroneura variabilis Beamer) (Hemiptera: Cicadellidae), which are serious pests of cultivated grape (Vitis vinifera L.) in California. RDI is an irrigation strategy that reduces irrigation during a critical point in the phenology of a cultivated perennial crop, to improve vegetative balance and crop quality. Erythroneura spp. are known to respond negatively to vine water stress, and the second generation ofleafhoppers begins during a potential RDI initiation period, between berry set and veraison (beginning of fruit maturation). In experiments at commercial wine grape vineyards, I imposed deficits of between 25 and 50% of crop full evapotranspiration (ET(c)) between berry set and veraison, with control treatments based on the growers' standard irrigations (typically between 0.8 and 1.0 ET(c)), and then we counted leafhopper nymphs weekly, and leafhopper eggs after the second generation. Results show a consistent reduction of second generation nymphal density with this type of RDI, with average density approximately 50% lower under deficit treatments in all three studies. Deficit irrigation reduced second generation egg density by 54% at one site and by 29.9% at another. These results confirm previous studies regarding the sensitivity of Erythroneura spp. to grapevine water stress, and, in addition, they show that a season-wide irrigation deficit is not necessary for reduction in leafhopper density. Results suggest that lower oviposition at least partly explains the lower nymphal density in the deficit treatments.

The impact of sulfur on the reproductive success of Anagrus spp. parasitoids in the field

Pesticides targeted at pest species have often been demonstrated to have strong adverse effects on the survival of biological control agents in short-term laboratory bioassays; however, studies examining the influence of pesticides on the actual reproductive success of biological control agents in the field are rare. Because natural enemy reproduction is often directly tied to biological control success, effects of pesticides on reproduction are of central importance. Here we use a new technique to examine the influence of sulfur, a fungicide widely used in grape production, on the reproductive success of Anagrus erythroneurae (Hymenoptera: Mymaridae) and Anagrus daanei (Hymenoptera: Mymaridae), egg parasitoids of the grape leafhopper, Erythroneura elegantula (Homoptera: Cicadellidae). Sulfur has previously been shown to be highly toxic to Anagrus spp. in short-term laboratory and field bioassays, creating the expectation that sulfur should also reduce Anagrus reproductive success in the field. Surprisingly, in two studies, the first comparing the oviposition success of Anagrus collected live in paired sulfur-treated versus untreated vineyards and the second comparing the lifetime reproductive success of Anagrus collected at the end of their lives in unpaired sulfur-treated versus untreated vineyards, we found no effect of sulfur on parasitoid reproductive success. In this system, traditional short-term assays of laboratory toxicity do not appear to predict effects on parasitoid reproductive success, suggesting that demographic approaches to assessing the disruptive effects of pesticides may have an important role in designing IPM programs.

The effect of sulfur on biological control of the grape leafhopper, Erythroneura elegantula, by the egg parasitoid Anagrus erythroneurae

We examined the toxicity of a fungicide, sulfur, to the egg parasitoid Anagrus erythroneurae (Hymenoptera: Mymaridae) Trjapitsyn and Chiapini and the vineyard leafhopper pest Erythroneura elegantula Osborn (Homoptera: Cicadellidae) and tested whether or not the use of sulfur in the field affects biological control of E. elegantula. Using field cage bioassays, we demonstrated that sulfur is toxic to adult A. erythroneurae parasitoids, but not toxic to adult E. elegantula leafhoppers. We nonetheless found in a field experiment that sulfur produced no changes in rates of parasitism or E. elegantula egg density, and generated only a very small increase in the density of E. elegantula nymphs. These results suggest that sulfur, although toxic to A. erythroneurae, is not highly disruptive of E. elegantula biological control in vineyards. Our results suggest that simple bioassays of acute toxicity may not accurately predict the impact of agricultural chemicals on biological control.

Identity, Abundance, and Phenology of <I>Anagrus</I> spp. (Hymenoptera: Mymaridae) and Leafhoppers (Homoptera: Cicadellidae) Associated with Grape, Blackberry, and Wild Rose in Washington State

Abstract In 2001 and 2002, we monitored densities of western grape leafhopper, Erythroneura elegantula Osborn, and Virginia creeper leafhopper, Erythroneura ziczac Walsh (Homoptera: Cicadellidae), eggs from June through September in managed and nonmanaged vineyards in Washington state. Anagrus parasitoids (Hymenoptera: Mymaridae) were reared from sampled parasitized leafhopper eggs. Densities of nonparasitized and parasitized E. elegantula eggs, and nonparasitized E. ziczac eggs, were significantly higher in nonmanaged grapevines, although this pattern was not consistent for the latter two groups. Densities of parasitized E. ziczac eggs were consistently low across management regimes. Anagrus erythroneurae S. Trjapitzin & Chiappini, Anagrus daanei S. Triapitsyn, and Anagrus tretiakovae S. Triapitsyn emerged from parasitized E. elegantula eggs, whereas latter two mymarid species also parasitized E. ziczac eggs. Of these species, A. tretiakovae was the most common parasitoid of Erythroneura leafhopper eggs ...

Water use of mature Thompson Seedless grapevines in California

Water use of Thompson Seedless grapevines was measured with a large weighing lysimeter from 4 to 7 years after planting (1990–1993). Above-ground drip-irrigation was used to water the vines. Vines growing within the lysimeter were pruned to four and six fruiting canes for the 1990 and 1991 growing seasons, respectively, and eight fruiting canes in the last 2 years. Maximum leaf area per vine at mid-season ranged from 23 to 27 m2 across all years. Reference crop evapotranspiration (ETo) averaged 1,173 mm between budbreak and the end of October each year, with a maximum daily amount of approximately 7 mm each year. Maximum daily vine water use (ETc) was 6.1, 6.4, 6.0, and 6.7 mm (based upon a land area per vine of 7.55 m2) for 1990, 1991, 1992, and 1993, respectively. Seasonal ETc was 718 mm in 1990 and ranged from 811 to 865 mm for the remaining 3 years of the study. The differences in water use among years were probably due to the development of the vine's canopy (leaf area), since they were pruned to differing numbers of fruiting canes. These differences were more pronounced early in the season. Soil water content (SWC) within the lysimeter decreased early in the growing season, prior to the initiation of the first irrigation. Once irrigations commenced, SWC increased and then leveled off for the remainder of the season. The maximum crop coefficient (K c) calculated during the first year (1990) was 0.87. The maximum K c in 1991, 1992, and 1993 was 1.08, 0.98, and1.08, respectively. The maximum K c in 1991 and 1993 occurred during the month of September, while that in 1992 was recorded during the month of July. The seasonal K c followed a pattern similar to that of grapevine leaf area development each year. The K c was also a linear function of leaf area per vine using data from all four growing seasons. The decrease in K c late in the 1991, 1992, and 1993 growing seasons, generally starting in September, varied considerably among the years. This may have been associated with the fact that leafhoppers (Erythroneura elegantula Osborn and E. variabilis Beamer) were not chemically controlled in the vineyard beginning in 1991.

Habitat diversification tactic for improving biological control: parasitism of the western grape leafhopper

AbstractIn a previous study we demonstrated greater abundance of the parasitoid Anagrus epos (Girault) in grape vineyards located downwind of prune trees that function as overwintering habitats. This study examines whether these higher A. epos numbers translated into higher egg parasitism rates of the grape leafhopper, Erythroneura elegantula (Osborn). Paired commercial wine‐grape vineyard plots, one with and one without adjacent prune trees, were studied within a complete block design in northern and central California. A. epos was the key mortality factor affecting E. elegantula eggs. Point estimates of A. epos parasitism rates were significantly greater in vineyards associated with prune trees during the first E. elegantula generation in both 1991 and 1992. No consistent differences in parasitism rates were observed during the second or third generations. The results indicated that prune trees enhance early season parasitism rates. Cumulative estimates of egg parasitism across E. elegantula generations demonstrated that enhanced early‐season parasitism resulted in a net season‐long increase in the degree of mortality imposed by A. epos on E. elegantula eggs. Two factors were found to influence parasitism rates: the abundance of early‐season A. epos adults moving into vineyards and the density of E. elegantula eggs in vineyards. Our results indicate that diversification of vineyards using prune trees supports overwintering populations of a specialist parasitoid and thereby alters host‐parasitoid interactions to favor enhanced parasitism in vineyards.

Influence of Temperature on Grape Leafhoppers in Southcentral Washington

The 2 most important leafhopper pests of grapes in Washington are the Western grape leafhopper, Erythroneura elegantula Osborn, and Erythroneura ziczac Walsh. The influence of different constant temperatures on the egg and nymphal stages of E. ziczac and on the nymphal stage of E. elegantula was examined. Development times of E. ziczac eggs ranged from 33.1 d at 15°C to 8.6 d at 32.5°C. E. ziczac nymphal development ranged from 40.2 d at 16°C to 11.1 d at 29.5°C. The average number of degree-days required for development from oviposition to imaginal molt was 435.4. This was slightly higher than the previously published value of 390.5 DD for field reared E. ziczac . E. elegantula nymphal development ranged from 38.0 d at 16.0°C to 11.8 d at 32.5°C. The average number of degree-days required for E. elegantula development from eclosion to imaginal molt was 246.3. Constant temperature data for the egg and nymphal stages of E. ziczac and for the nymphal stage of E. elegantula was fitted to a developmental model based on enzyme reaction kinetics. The egg and nymphal stages of E. ziczac fitted the model with r 2 values of 0.9992 and 0.9990, respectively. The E. elegantula nymphal stage fitted the model with an r 2 value of 0.9996. Lethal freezing temperatures for E. ziczac adults collected on 28 January, 4 February, and 14 November, 1994 were −27.1, −26.3, and −27.2°C, respectively. Freezing temperatures for E. elegantula on the same dates were −24.6, −24.1, and −25.3°C, respectively.

Release Strategies Affect Survival and Distribution of Green Lacewings (Neuroptera: Chrysopidae) in Augmentation Programs

We evaluated 3 aspects of release strategies used to augment green lacewings ( Chrysoperla spp.): the delivery system, the release rate and timing, and the lacewing developmental stage released. Tests were conducted in vineyards with either the common green lacewing, Chrysoperla carnea (Stephens); the Comanche lacewing, Chrysoperla comanche Banks; or Chrysoperla rufilabris (Burmeister). Lacewings were released to suppress 2 leafhopper pests, Erythroneura variabilis Beamer and the western grape leafhopper, Erythroneura elegantula Osborn. Two commercial delivery systems were compared. In the 1st delivery system, a mixture of lacewing eggs and com grit was placed in paper cups, which were distributed to every 5th vine in every other row. This delivery system resulted in poor egg hatch and larval dispersal. Egg hatch was low (≈60%) in the paper cups, compared with egg hatch when lacewings were reared in individual cells (≈91%). The poor egg hatch is attributed primarily to cannibalism. Larval dispersal from paper cups with com grit was 25% lower than that from cups without com grit, resulting in incomplete distribution of lacewings throughout the vineyard. In a 2nd delivery system, lacewing eggs, combined with com grit, were dropped onto the vines from a moving flatbed trailer. Egg hatch was ≈62%. Eggs were delivered to each vine and vine row, although delivery of eggs was uneven. More eggs were dropped at the beginning (≈11 eggs per vine) of each release batch than at the end (≈5 eggs per vine). Using a noncommercial delivery system, release rates between 6,175 and 1,235,000 eggs or larvae per hectare were tested. No correlation between release rate and prey density was found. Releases timed to ≈50–70% leafhopper egg hatch had a greater effect on leafhopper densities than releases timed to peak leafhopper nymph densities. In the 3rd experiment, we tested the effectiveness of egg versus larval releases. In egg release plots, there was ≈70% egg mortality and leafhopper densities were not significantly different from no-release plots. In larval release plots, ≈50% of the larvae survived until the 3rd instar and there was a significant reduction in leafhopper densities.