Open field trials of food-grade gum in California and Oregon as a behavioral control for Drosophila suzukii Matsumura (Diptera: Drosophilidae).

The invasion of Drosophila suzukii, spotted-wing drosophila, across Europe and the US has led to economic losses for berry and cherry growers, and increased insecticide applications to protect fruit from damage. Commercial production relies heavily on unsustainable use of conventional toxic insecticides. Non-toxic insecticide strategies are necessary to alleviate the disadvantages and non-target impacts of toxic conventional insecticides and improve Integrated Pest Management (IPM). A novel food-grade gum deployed on dispenser pads (GUM dispensers) was evaluated to mitigate D. suzukii crop damage in five commercial crops and nine locations. Trials were conducted at a rate of 124 dispensers per hectare in cherry, wine grape, blueberry, raspberry, and blackberry in California and Oregon, USA during 2019 and 2020. The majority of trials with the food-grade gum resulted in a reduction of D. suzukii egg laying in susceptible fruit. In some cases, such damage was reduced by up to 78%. Overall, results from our meta-analysis showed highly significant differences between GUM treatments and the untreated control. Modeling simulations suggest a synergistic reduction of D. suzukii damage when used in combination with Spinosad (Entrust SC) insecticide. These data illustrate commercial value of this tool as a sustainable alternative to manage D. suzukii populations within a systems approach.

Evaluating invasion risk and population dynamics of the brown marmorated stink bug across the contiguous United States.

BACKGROUND: Invasive species threaten the productivity and stability of natural and managed ecosystems. Predicting the spread of invaders, which can aid in early mitigation efforts, is a major challenge, especially in the face of climate change. While ecological niche models are effective tools to assess habitat suitability for invaders, such models have rarely been created for invasive pest species with rapidly expanding ranges. Here, we leveraged a national monitoring effort from 543 sites over 3 years to assess factors mediating the occurrence and abundance of brown marmorated stink bug (BMSB, Halyomorpha halys), an invasive insect pest that has readily established throughout much of the United States. RESULTS: We used maximum entropy models to estimate the suitable habitat of BMSB under several climate scenarios, and generalized boosted models to assess environmental factors that regulated BMSB abundance. Our models captured BMSB distribution and abundance with high accuracy, and predicted a 70% increase in suitable habitat under future climate scenarios. However, environmental factors that mediated the geographical distribution of BMSB were different from those driving abundance. While BMSB occurrence was most affected by winter precipitation and proximity to populated areas, BMSB abundance was influenced most strongly by evapotranspiration and solar photoperiod. CONCLUSION: Our results suggest that linking models of establishment (occurrence) and population dynamics (abundance) offers a more effective way to forecast the spread and impact of BMSB and other invasive species than simply occurrence-based models, allowing for targeted mitigation efforts. Implications of distribution shifts under climate change are discussed. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Characterization of Field-Derived Drosophila suzukii (Diptera: Drosophilidae) Resistance to Pyrethroids in California Berry Production.

The spotted-wing drosophila, Drosophila suzukii (Matsumura), is a global economic pest of berry crops and stone fruit. Since management of this pest primarily relies on calendar insecticide applications, and field-derived resistance to spinosad has already been documented in California caneberry production, there is significant concern for development of resistance to other insecticides. In this study, susceptibility of D. suzukii populations collected from caneberry and strawberry fields to two pyrethroids, zeta-cypermethrin, and bifenthrin, was assessed in 2019 and 2020. Resistance to both pyrethroids were observed in flies from all sampling sites. For flies collected from caneberries in 2019, the LC50 values ranged from 4.5 to 5.2 mg liter-1 with RR50s ranging from 7.5- to 8.7-fold. Our 2020 assays showed that susceptibility of flies to the discriminating dose of zeta-cypermethrin decreased significantly as the season progressed. For flies collected from strawberries in 2020, the LC50s ranged from 19.0 to 36.1 mg liter-1 and from 30.3 to 90.7 mg liter-1 for zeta-cypermethrin and bifenthrin, respectively. The RR50 values varied from 19.0- to 36.1-fold for zeta-cypermethrin and from 15.9- to 47.7-fold for bifenthrin. This study is the first report of field-derived pyrethroid resistance in D. suzukii from two major California berry production areas. Adoption of informed insecticide resistance management practices would be essential to prolong the efficacy of products available to control D. suzukii. Future molecular work is needed to unravel the underlying genetic mechanisms conferring the observed pyrethroid resistance and to develop robust diagnostics that can inform integrated pest management of this pest.

Development and validation of a larval bioassay and selection protocol for insecticide resistance in Drosophila suzukii.

The rapid invasion of Drosophila suzukii (Matsumura) throughout Europe and the Americas has led to an increased reliance on calendar-based broad-spectrum insecticide programs among berry and cherry growers. Relatively few active ingredients (AIs) are currently available for effective D. suzukii management, and studies from multiple growing regions indicate that susceptibility to at least some of these materials is declining. Greater effort is needed to understand the status of susceptibility across field populations and the potential for increased resistance to develop, as well as the possible fitness costs incurred by resistant individuals. However, current bioassay protocols used for resistance monitoring and selection studies (i.e. resistance risk assessments) are labor-intensive and costly, making large-scale studies difficult to conduct. Here, we first present a novel bioassay protocol using larvae that requires little effort or cost to implement beyond what is needed for basic D. suzukii laboratory colony maintenance. We then perform dose-response bioassays using this protocol to identify larval lethal concentrations for three commonly used insecticides (malathion, spinosad and zeta-cypermethrin) in a susceptible population. Finally, resistance risk assessments were conducted using a population of D. suzukii from commercial caneberry fields near Watsonville, CA. We find that five generations of larval selection with a discriminating dose is sufficient to significantly increase both larval (malathion and spinosad) and adult (spinosad) resistance to the target AIs. This approach provides a simple, cost-effective tool for assaying susceptibility of D. suzukii populations to insecticides and for selecting resistant insect lines for resistance management research.

Monitoring of Spotted-Wing Drosophila (Diptera: Drosophilidae) Resistance Status Using a RAPID Method for Assessing Insecticide Sensitivity Across the United States.

Drosophila suzukii (Matsumura) has spread rapidly, challenging berry and cherry crop production due to its ability to lay eggs into ripening fruit. To prevent infestation by this pest, insecticides are applied during fruit ripening and harvest. We field-tested the Rapid Assessment Protocol for IDentification of resistance in D. suzukii (RAPID) on seventy-eight populations collected across eight U.S. states in 2017 and 2018. Exposure to LC50 rates of malathion, methomyl, spinetoram, spinosad, and zeta-cypermethrin led to average female fly mortality of 25.0% in 2017, and after adjusting concentrations the average was 39.9% in 2018. Using LC99 × 2 discriminating concentrations in 2017 and LC90 × 8 rates in 2018, average female mortalities were 93.3% and 98.5%, respectively, indicating high overall susceptibility. However, using these high concentrations we found 32.0% of assays with survival of some female flies in 2017 and 27.8% in 2018. The adjustment in discriminating dose from 2017 to 2018 also reduced the proportion of assays with <90% survival from 17.6 to 2.9%. Populations with low mortality when exposed to spinosad were identified using this assay, triggering more detailed follow-up bioassays that identified resistant populations collected in California coastal region berry crops. Widespread evaluations of this method and subsequent validation in California, Michigan, and Georgia in 2019-2021 show that it provides a quick and low-cost method to identify populations of D. suzukii that warrant more detailed testing. Our results also provide evidence that important insecticide classes remain effective in most U.S. regions of fruit production.

Spatio-temporal Variation of Spinosad Susceptibility in Drosophila suzukii (Diptera: Drosophilidae), a Three-year Study in California's Monterey Bay Region.

Spinosyn insecticides are widely used in conventional berry production, and spinosad is regarded as the most effective insecticide for managing Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), spotted-wing drosophila, in organic berry crops. Following the 2017 identification of spinosad resistance in caneberry fields in the Watsonville area, Santa Cruz Co., California, we conducted a study to examine the seasonal and annual susceptibility of D. suzukii over a three-year period. Adult flies were collected from two conventional and two organic caneberry fields in the Monterey Bay region, California, at 'early', 'middle', and 'late' time points during the 2018-2020 growing seasons, and their susceptibility to spinosad was assessed. Results demonstrated that spinosad susceptibility in the D. suzukii field populations generally decreased during the fruit production season (from June through November), and over consecutive seasons. LC50 values of adults from the conventional sites were determined to be as high as 228.7 mg l-1 in 2018, 665.6 mg l-1 in 2019, and 2700.8 mg l-1 in 2020. For the organically managed fields, LC50s of adults were as great as 300.0 mg l-1 in 2018, 1291.5 mg l-1 in 2019, and 2547.1 mg l-1 in 2020. Resistance ratios based on the LC50 values were as high as 10.7-, 13.2-, and 16.9-fold in 2018, 2019, and 2020, respectively. These results should serve as a caution for growers in other production areas, facilitate informed choice of insecticides used in D. suzukii management, and emphasize the need to develop effective insecticide resistance management strategies for this insect.

Population genomics of Drosophila suzukii reveal longitudinal population structure and signals of migrations in and out of the continental United States.

Drosophila suzukii, or spotted-wing drosophila, is now an established pest in many parts of the world, causing significant damage to numerous fruit crop industries. Native to East Asia, D. suzukii infestations started in the United States a decade ago, occupying a wide range of climates. To better understand invasion ecology of this pest, knowledge of past migration events, population structure, and genetic diversity is needed. In this study, we sequenced whole genomes of 237 individual flies collected across the continental United States, as well as several sites in Europe, Brazil, and Asia, to identify and analyze hundreds of thousands of genetic markers. We observed strong population structure between Western and Eastern US populations, but no evidence of any population structure between different latitudes within the continental United States, suggesting that there are no broad-scale adaptations occurring in response to differences in winter climates. We detect admixture from Hawaii to the Western United States and from the Eastern United States to Europe, in agreement with previously identified introduction routes inferred from microsatellite analysis. We also detect potential signals of admixture from the Western United States back to Asia, which could have important implications for shipping and quarantine policies for exported agriculture. We anticipate this large genomic dataset will spur future research into the genomic adaptations underlying D. suzukii pest activity and development of novel control methods for this agricultural pest.

Drosophila suzukii (Diptera: Drosophilidae): A Decade of Research Towards a Sustainable Integrated Pest Management Program.

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) also known as spotted-wing drosophila (SWD), is a pest native to Southeast Asia. In the last few decades, the pest has expanded its range to affect all major European and American fruit production regions. SWD is a highly adaptive insect that is able to disperse, survive, and flourish under a range of environmental conditions. Infestation by SWD generates both direct and indirect economic impacts through yield losses, shorter shelf life of infested fruit, and increased production costs. Fresh markets, frozen berries, and fruit export programs have been impacted by the pest due to zero tolerance for fruit infestation. As SWD control programs rely heavily on insecticides, exceedance of maximum residue levels (MRLs) has also resulted in crop rejections. The economic impact of SWD has been particularly severe for organic operations, mainly due to the limited availability of effective insecticides. Integrated pest management (IPM) of SWD could significantly reduce chemical inputs but would require substantial changes to horticultural management practices. This review evaluates the most promising methods studied as part of an IPM strategy against SWD across the world. For each of the considered techniques, the effectiveness, impact, sustainability, and stage of development are discussed.

Temperature and Humidity Interact to Influence Brown Marmorated Stink Bug (Hemiptera: Pentatomidae), Survival.

High-temperature events can influence insect population dynamics and could be especially important for predicting the potential spread and establishment of invasive insects. The interaction between temperature and environmental humidity on insect populations is not well understood but can be a key factor that determines habitat range and population size. The brown marmorated stink bug, Halyomorpha halys (Stål), is an invasive agricultural pest in the United States and Europe, which causes serious economic damage to a wide range of crops. This insect's range continues to expand. It has recently invaded the Central Valley of California, which has a hotter and drier climate compared with the Eastern United States where this insect is established. We investigated how high-temperature events and relative humidity would impact the survival and reproduction of H. halys. Using incubators and humidity chambers, we evaluated the impact of humidity and short-term (2 d) high-temperature exposure on the survival and development of H. halys eggs, nymphs, and adults. We found that high temperatures significantly reduced H. halys survival. The impact of humidity on H. halys survival was dependent on temperature and life stage. Low humidity decreased first-instar survival but not third- to fourth-instar survival. High humidity increased first instar survival but decreased third- to fourth-instar survival. Humidity did not influence adult or egg survival. We also found that high temperatures decreased H. halys reproduction. Our findings have important implications for understanding the invasive ecology of H. halys and may be used to improve models predicting H. halys range expansion.

Transcriptome Analysis of Pyrethroid-Resistant Chrysodeixis includens (Lepidoptera: Noctuidae) Reveals Overexpression of Metabolic Detoxification Genes.

Chrysodeixis includens (Walker, [1858]) is one of the most important defoliator of soybean in Brazil because of its extensive geographical distribution and high tolerance to insecticides compared with other species of caterpillars. Because of this, we conducted bioassays to evaluate the efficacy of pyrethroid λ-cyhalothrin on a C. includens resistant strain (MS) and a susceptible (LAB) laboratory strain. High throughput RNA sequencing (RNA-seq) of larval head and body tissues were performed to identify potential molecular mechanisms underlying pyrethroid resistance. Insecticide bioassays showed that MS larvae exhibit 28.9-fold resistance to pyrethroid λ-cyhalothrin relative to LAB larvae. RNA-seq identified evidence of metabolic resistance in the head and body tissues: 15 cytochrome P450 transcripts of Cyp6, Cyp9, Cyp4, Cyp304, Cyp307, Cyp337, Cyp321 families, 7 glutathione-S-transferase (Gst) genes, 7 α-esterase genes from intracellular and secreted catalytic classes, and 8 UDP-glucuronosyltransferase (Ugt) were overexpressed in MS as compared with LAB larvae. We also identified overexpression of GPCR genes (CiGPCR64-like and CiGPCRMth2) in the head tissue. To validate RNA-seq results, we performed RT-qPCR to assay selected metabolic genes and confirmed their expression profiles. Specifically, CiCYP9a101v1, CiCYP6ae149, CiCYP6ae106v2, CiGSTe13, CiCOE47, and CiUGT33F21 exhibited significant overexpression in resistant MS larvae. In summary, our findings detailed potential mechanisms of metabolic detoxification underlying pyrethroid resistance in C. includens.

Timing the Implementation of Cultural Practices for Spissistilus festinus (Hemiptera: Membracidae) in California Vineyards Using a Stage-Structured Degree-Day Model.

The three-cornered alfalfa hopper, Spissistilus festinus (Say), was shown to transmit Grapevine red blotch virus (GRBV), the causative agent for Grapevine red blotch disease, in a greenhouse study on grapes. GRBV is a major concern of wine grape growers due to its economic impact on wine quality. Plants in the family Fabaceae are preferred hosts of S. festinus and are commonly planted as cover crops or present in a vineyard's native vegetation. In late winter, during grapevine dormancy, S. festinus migrate into vineyards to feed and reproduce on these cover crop and weed hosts. Tilling vineyard floor vegetation provides growers an opportunity to disrupt the life cycle of early instars that are relatively immobile, reducing the S. festinus first-generation population. Nymphal presence is difficult to detect. First through third instars were not detected in sweep net samples in a 2-yr weekly sampling study, whereas fourth and fifth instars were first found on the same sample date as emerging adults. A degree-day model was developed and successfully predicted when early S. festinus instars are present in the vineyard to aid in exploiting the time period when S. festinus is most susceptible to cultural control measures.

Olive Fruit Fly, Bactrocera oleae (Diptera: Tephritidae), Attraction to Volatile Compounds Produced by Host and Insect-Associated Yeast Strains.

The olive fruit fly, Bactrocera oleae (Rossi), is one of the most damaging insect pests of olives worldwide, requiring the use of insecticides for fruit protection in many orchards. Olive fruit flies are attracted to volatile composunds, including a female-produced pheromone, and host-plant and bacterial volatiles. Preliminary laboratory bioassays were conducted for olive fruit fly attraction to over 130 yeast strains from among 400 that were isolated from B. oleae adults and larvae or other insects, infested olives, and potential feeding sites. Kuraishia capsulata, Scheffersomyces ergatensis, Peterozyma xylosa, Wickerhamomyces subpelliculosus, and Lachancea thermotolerans appeared to attract B. oleae as well or better than did torula yeast pellets (Cyberlindnera jadinii; syn. Candida utilis). Volatile compounds emitted by these yeast strains were chemically identified, and included isobutanol, isoamyl alcohol, 2-phenethyl alcohol, isobutyl acetate, and 2-phenethyl acetate. The behavioral response of B. oleae adults to these volatile compounds at three concentrations was tested in a laboratory Y-tube olfactometer. The same volatile compounds were also tested in the field. Isoamyl alcohol was more attractive than the other compounds tested in both laboratory and field bioassays. Isobutanol was not attractive to B. oleae in either laboratory bioassay or field bioassay. Identifying yeast volatiles attractive to the olive fruit fly may lead to development of a more effective lure for detection, monitoring, and possibly control of B. oleae.

Tuta absoluta (Lepidoptera: Gelechiidae) Success on Common Solanaceous Species from California Tomato Production Areas.

Tuta absoluta (Meyrick) is a devastating pest of tomato that has invaded many regions of the world. To date, it has not been detected in North America, but the pest reached Costa Rica in 2014 and seriously threatens the southern, southwestern, and western United States including California. Although the primary host of T. absoluta is tomato, several other species of Solanaceae may serve as alternative hosts. In our study, we aimed to assess the potential risk that other solanaceous crops and wild species that are often present in and around California tomato fields could serve as hosts. To accomplish this, we conducted greenhouse and laboratory studies to determine whether two common cultivars of fresh market tomato, two common cultivars of tomatillo, and the wild plants, Solanum nigrum L., Solanum sarrachoides (Sendtner), and Datura stramonium L., are suitable hosts for reproduction and development of the pest. According to our results, D. stramonium and tomatillo were unable to sustain T. absoluta larval development in either greenhouse studies or laboratory studies, and therefore, they are not likely to contribute to T. absoluta establishment during an invasion. On the contrary, the two other solanaceous weeds, S. nigrum and S. sarrachoides, share a similar potential as tomato to be reproductive and developmental hosts of T. absoluta, and might play an important role in the establishment of the pest in California.

Spatial Associations of Vines Infected With Grapevine Red Blotch Virus in Oregon Vineyards.

Spread and in-field spatial patterns of vines infected with grapevine red blotch virus (GRBV) were documented in Oregon vineyards using field sampling, molecular diagnostics, and spatial analysis. Grapevine petiole tissue collected from 2013 to 2016 was tested using quantitative polymerase chain reaction for GRBV. At Jacksonville in southern Oregon, 3.1% of vines were infected with GRBV in 2014, and GRBV incidence reached 58.5% of study vines by 2016. GRBV-infected plants and GRBV-uninfected plants were spatially aggregated at this site in 2015, and infected plants were spatially associated between years 2015 and 2016. In a southern Oregon vineyard near Talent, 10.4% of vines were infected with GRBV in 2014, and infection increased annually to 21.5% in 2016. At Talent, distribution of the infected vines was spatially associated across all years. GRBV infection was highest at Yamhill, in the Willamette Valley, where 31.7% of the tested vines had GRBV infection in 2014. By 2016, 59.2% of the vines tested positive for GRBV. Areas of aggregation increased and were spatially associated across all years. From 2013 to 2015, GRBV was not detected at Milton-Freewater in eastern Oregon. Spatial patterns of GRBV infection support evidence of spread by a mobile insect vector. GRBV is a significant threat to Oregon wine grape production because of its drastic year-over-year spread in affected vineyards.

Attraction of the Green Lacewing Chrysoperla comanche (Neuroptera: Chrysopidae) to Yeast.

Many adult Chrysoperla comanche (Stephens) green lacewings were caught in traps baited with live yeast cultures during tests designed to catch olive fruit flies. All 13 yeast species tested were more attractive than the industry-standard dried torula yeast (Cyberlindnera jadinii; syn. Candida utilis). Live C. jadinii culture attracted significantly more lacewings than the inactive dried-pellet form of the same yeast species, demonstrating that volatiles from live yeast cultures attract adults of this lacewing. Odor profiles for two of the highly active yeasts tested herein (Lachancea thermotolerans and Solicoccozyma terrea) were similar to that for Metschnikowia pulcherrima, a yeast species isolated earlier from the gut diverticulum of Chrysoperla rufilabris. A new Metschnikowia species (M. chrysoperlae), along with two new Candida spp. that were recently realigned to one of the Metschnikowia clades (M. picachoensis and M. pimensis), were also identified from the diverticulum of C. comanche. Thus, one clade of Metschnikowia yeasts that commonly occur in floral nectar appears to exhibit mutualistic symbioses with Chrysoperla green lacewings. Both male and female C. comanche adults were attracted in the present study, and we speculate that males have exploited this symbiosis by offering Metschnikowia-laden regurgitant, including attractive volatiles, to females ('mating trophallaxis') as a nuptial gift.

Seasonal Dynamics of Spissistilus festinus (Hemiptera: Membracidae) in a Californian Vineyard.

The three-cornered alfalfa hopper, Spissistilus festinus (Say) was shown to transmit Grapevine red blotch virus (GRBV) in a greenhouse study. GRBV is the causal agent of Grapevine Red Blotch Disease, which reduces the quality of wine produced from infected grapes. Due to the general lack of prior concern regarding S. festinus on grapevines, the biology of this species in vineyards has been largely unknown. A 2-yr study with weekly sampling was conducted in a Californian vineyard to increase the knowledge of S. festinus seasonal dynamics and distribution. The overwintering S. festinus adults were first captured in the vineyard before bud break. Detection of late-instar S. festinus nymphs, the first in-field adult generation, and grape anthesis occurred concurrently in 2016 and 2017. Two in-field S. festinus generations were documented by peaks in sweep net sampling of vineyard groundcover in 2016, whereas only one generation was observed in 2017. There appears to be an inverse relationship between the number of S. festinus adults sampled on ground cover and the number of girdles in the grapevine canopy. Spissistilus festinus exhibited an aggregated distribution in the vineyard and a significant edge effect. Results from this study will contribute to the development of sampling and management guidelines and determine timing of control measures to reduce populations of S. festinus within vineyards to minimize the virus spread.

Identification and risk assessment of spinosad resistance in a California population of Drosophila suzukii.

BACKGROUND: The bioinsecticide spinosad is among the most widely used insecticides for managing spotted-wing drosophila, Drosophila suzukii (Matsumura), and is critical for preventing fruit infestation in organic berry production. Recent reports, however, have raised concerns that the efficacy of this material is declining in fields near Watsonville, CA, a major hub of commercial berry production in the USA and the first location where D. suzukii was reported in North America. RESULTS: In this study, we performed dose-response analyses on D. suzukii from commercial raspberry plantings near Watsonville as well as a second untreated site in California using a widely implemented bioassay protocol. We found that Watsonville flies exhibited spinosad LC50 values 4.3-7.7 times higher than those from the untreated location and 11.6-22.4 times higher than previously reported susceptible baselines. Additionally, tolerance to spinosad continued to increase after additional selection for five generations, though this result was only statistically significant after prolonged exposure to residues. CONCLUSIONS: These findings confirm that spinosad resistance is emerging in the Watsonville area and document the first known occurrence in the USA, presenting an urgent need for the development of alternative management strategies to control this pest. Additional work is needed to resolve the underlying molecular mechanism(s) that confers spinosad resistance in D. suzukii and assess the potential for this trait to spread into new populations. © 2018 Society of Chemical Industry.

Predicting Larval Stage Distribution of Lobesia botrana (Lepidoptera: Tortricidae) at Three Constant Temperatures.

European grapevine moth, Lobesia botrana (Denis and Schiffermüller), is an invasive pest species subject to regulatory control under the International Plant Protection Convention. An extensive infestation of this insect detected in California vineyards in October 2009 resulted in the initiation of postharvest research intended to ensure continuing trade of California table grapes by preventing the unintentional introduction of L. botrana to uninfested export destinations. Having the ability to accurately predict and confirm the particular stadia of larval development of insects obscured from direct observations, such as those being mass-reared in diet for use in phytosanitary control experiments, is necessary to be able to ensure that the most tolerant life stage is accurately targeted. Lobesia botrana were reared from egg to eclosion at three different temperatures: 16, 20, and 24°C (60% RH; 16:8 [L:D] h). Daily samples (≥15) were taken of larvae and pupae to determine the chronological distribution of life stages until daily samples comprised 100% pupae, after which only adults were counted. Head capsule measurements of all sampled larvae were taken (n = 2,820) and analyzed using nonlinear least squares (NLLS) fitting to Gaussian curves to describe stadia-specific head capsule demarcations and the probability of misclassifying instars due to overlapping life stage distributions.

Vitis vinifera (Vitales: Vitaceae) as a Reproductive Host of Spissistilus festinus (Hemiptera: Membracidae).

Feeding by the three-cornered alfalfa hopper, Spissistilus festinus (Say) (Hemiptera: Membracidae) results in girdling of grapevine petioles and shoots. Its significance as an economic pest of grape has increased since it was shown to transmit Grapevine red blotch virus (GRBV) in a greenhouse study. However, the status of grapevines as a reproductive host for S. festinus remained undetermined. Adult S. festinus were caged onto three regions of the grapevines: apical shoot, green shoot, and dormant cane. Their ability to reproduce was determined by weekly destructive sampling for 7 wk. Successful oviposition and nymphal emergence were observed on apical and green shoots, but not on dormant canes. However, insect development beyond the second nymphal instar did not occur. Knowledge of S. festinus reproduction on grapevines will be an important consideration in designing management guidelines to minimize the spread of GRBV in vineyards.