Final report for ONE21-382
Project Information
The American grape berry moth (GBM), Paralobesia viteana (Lepidoptera: Tortricidae) is an economically important pest of grapes. The larvae of this insect burrow inside the fruit upon hatching to consume and contaminate several grapes within the same cluster. Current GBM management relies on extensive pesticide applications that do not always provide effective control due to asynchrony in GBM egg-laying. This study explores the potential of harnessing natural enemies, specifically larval parasitoids, to establish a sustainable alternative to traditional pesticide-based GBM management. To do this, we 1) identified larval parasitoids naturally present in vineyards, 2) quantified their parasitism rates in the field, and 3) developed a rearing methodology for one of the parasitoid species. Parasitoid samplings were conducted biweekly in six commercial Concord vineyards in Erie County, Pennsylvania, during the 2023 and 2024 growing seasons. GBM-infested samples were monitored daily to track the emergence of both parasitoids and GBM, enabling the calculation of parasitism rates. We identified six parasitoid species: Enytus obliteratus, Campoplex tortricidae, Scambus sp, Glypta sp (Hymenoptera: Ichneumonidae); Bracon variabilis (Hymenoptera: Braconidae), and Goniozus fratellus (Hymenoptera: Bethylidae) praying on GBM larvae. From these B. variabilis, E. obliteratus, and G. fratellus were the most abundant. The parasitism rates of these species varied over the growing seasons and reached maximums of 64.8%, 18.6%, and 13.8%, respectively. Additionally, we developed a protocol for rearing E. obliteratus in laboratory conditions. Our results demonstrate that GBM has several natural enemies that help control populations in the field. Although more research is needed to incorporate natural enemies in GBM management programs, we are encouraging growers to be more mindful of their spraying practices to protect these beneficial species. The results of this study have been disseminated to grape growers and the scientific community.
This project aimed to 1) Identify larval parasitoids of grape berry moth in Northwestern Pennsylvania, 2) quantify their parasitism rates in the field, and 3) create a rearing protocol for at least one of the parasitic species identified. This project is the baseline for future experiments of grape berry moth control using larval parasitoids. Our long-term goal is to either rear and release parasitic wasps or modify the vineyard landscape to promote higher parasitoid populations as part of an integrated pest management program to control grape berry moths in commercial vineyards. In the long term, this project is likely to reduce production costs and increase farmers' income by decreasing GBM infestations and reducing the use of toxic insecticides.
Grape is the highest-value fruit crop in the U.S., assessed at over $6.5 billion. This crop is economically important for the Northeastern states that dedicate nearly 52,000 acres to grape production (United States Department of Agriculture, 2018). However, the environmental conditions of the Northeast make grape production challenging as various diseases and insect pests constantly threaten grapevines. Among these, the grape berry moth (GBM), Paralobesia viteana (Lepidoptera: Tortricidae), is one of the most destructive pests in grapevines (Isaacs et al., 2012). The larvae of this insect damage grape clusters by direct feeding and by increasing susceptibility to fungal pathogens (e.g. Botrytis bunch rot) (Fermaud and Le Menn 1992). Management of GBM currently relies on applications of insecticides timed using a degree-day model (Tobin et al., 2003; Saunders et al., 2013). Grape growers spend thousands of dollars on pesticide sprays every year, risking human and environmental health. Consequently, there is a need to implement new sustainable practices that reduce the use of toxic pesticides. Biological control is one of the most effective ways to control insect pests, and GBM has a number of natural enemies that could be exploited for this purpose.
Biological control of insect pests using natural enemies is a sustainable and effective pest management strategy. GBM is native to eastern North America and has coevolved with numerous natural enemies in its original habitat. GBM populations develop in wild grapes early in the season and then move to cultivated grapes, where they cause significant losses by feeding inside the berries (Nagarkatti et al., 2002). Studies in the finger lakes (NY) and the Lake Erie Region (NY and PA) have identified several egg and larval parasitoids of GBM, but the effectiveness of larval parasitoids for controlling this insect has not been tested. Larval parasitoids hold great potential for controlling GBM because their development is in perfect synchrony with their host. Additionally, parasitoids should be able to control GBM in both wild and cultivated grapes. Augmentative releases of larval parasitoids timed with GMB development have great potential to reduce populations below economic injury levels. Furthermore, parasitoids could offer long-lasting pest control if they are able to establish successfully in field conditions, but research is needed to determine the feasibility of this strategy.
Growers are highly interested in effective, affordable, and long-lasting pest control strategies to implement in their vineyards. Our approach for controlling GBM with natural enemies could benefit more than 2,000 family farms of various sizes located in the Northeast region. Farmers are constantly looking for effective ways to control GBM at a reasonable cost, making this “new” approach feasible to be adopted by farmers. The use of biological control agents within an integrated pest management strategy is expected to reduce production costs, increase farmers’ income, and reduce human and environmental health risks by decreasing the use of toxic insecticides.
In this study, we surveyed GBM larval parasitoids in six vineyards in Erie County (Pennsylvania) and assessed their parasitism rates throughout the 2023 and 2024 growing seasons. We also developed a rearing methodology for one of these parasitoid species. Our results provide knowledge of the current diversity of GBM larval parasitoids in commercial vineyards of northwest Pennsylvania and provide the foundation for future studies to test the effectiveness of the identified species on GBM control in field conditions.
Citation List
Fermaud, M., and Le Menn, R. (1992) Transmission of Botrytis cinerea to grapes by grape berry moth larvae. The American Phytopathological Society Vol 82. No. 12, 1393-1398
Isaacs, R., Teixeira, L., Jenkins, P., Botero, N., Loeb, G., and Saunders, M. (2012) Biology and management of grape berry moth in north American vineyard ecosystems 361-381. In: Bostanian N., Vincent C., and Isaacs R. Arthropod management in vineyards: pest approaches and future directions. Springer Dordrecht Heidelberg New York London.
Nagarkatti, S., Muza, A. J., Saunders, M.C., and Tobin, P.C. (2002) Role of the egg parasitoid Trichogramma minutum in biological control of the grape berry moth, Endopiza viteana. BioControl 47: 373-385.
Saunders, M., Isaacs R., and Loeb G. (2013). Focus on females provides new insights for grape berry moth management. Cornell University.
Tobin, P.C., Nagarkatti, S., and Saunders, M.C. (2003) Phenology of grape berry moth (Lepidoptera: Tortricidae) in cultivated grape at selected geographic locations. Environmental Entomology 32 (2): 340-346.
United States Department of Agriculture. 2018. USDA/NASS QuickStats Ad-Hoc Query Tool. https://quickstats.nass.usda.gov/results/74D22A96-6C00-3E67-BE02-02077A38EA4B.
Cooperators
- - Producer
Research
Parasitoid sampling. Our samplings took place from June to September (2023 and 2024) in six vineyards planted with Concord grapes; these vineyards were selected for having historically high GBM infestations. Four of the six sampling sites are located in North East, PA (east of Erie City), whereas the remaining two sites are located west of Erie City (the location of each site is illustrated in Figure 1.). In each sampling site, we collected 100-150 grapes with signs of GBM infestation every two weeks. These samples were taken to the laboratory at the Penn State Erie campus, placed in plastic containers with a fine screen mesh, and incubated at 25C with a photoperiod of 15 h day and 9 h dark. The samples were inspected daily for the emergence of larval parasitoids. Additionally, GBM pupae were thoroughly inspected for parasitoids that didn’t emerge until the GBM larvae transitioned to the pupal stage. The percent of parasitism was calculated as the number of parasitoids that emerged divided by the sum of parasitoids and moths emerged. The resulting number was multiplied by 100. Some of the emerged parasitoid adults were preserved in ethanol for further taxonomic identification, and the rest were used to start colonies in the lab.
Parasitoid identification. Adult parasitoids were stored in plastic tubes with 70% ethanol and identified to the genus or to the species level using taxonomic keys for the different insect families. The identification of each species was confirmed by comparison with properly curated specimens from the Frost Entomological Museum at Penn State University, the Cornell University Insect Collection, and the USDA Systematic Entomology Laboratory of the Smithsonian Institution in Washington D.C. We took images from each parasitoid specimen for publication.
Rearing protocol of Enytus obliteratus. Upon adult emergence, male and female parasitoids were transferred to plastic cages containing diluted honey and water in cotton balls as a food source. We provided GBM-infested grapes containing first instar larvae for parasitoid oviposition. To determine parasitism rates and adult longevity, we individualized 30 parasitoid couples, provided GBM larvae daily, and retrieved them 24 h later during the lifetime of the adult parasitoids. We kept record of the number of GBM and parasitoids that emerged. The parasitoids were kept in a growth chamber at 25 ± 1 °C, 75% humidity, and a photoperiod of 16:8 h [L:D].
Parasitoid identification.
In 2023, we collected GBM-infested samples from June 15- Sep. 4. The first sampling was conducted in wild grapes located at the edges of the vineyards, whereas the subsequent samplings were done in commercial Concord vineyards. We collected a total of 113 parasitoids belonging to six different species within three Hymenoptera families. The identified species were Enytus obliteratus, Campoplex tortricidae, Scambus sp, Glypta sp (Hymenoptera: Ichneumonidae); Bracon variabilis (Hymenoptera: Braconidae), and Goniozus fratellus (Hymenoptera: Bethylidae). From these, B. variabilis and G. fratellus are ectoparasitoids and the others are endoparasitoids. The most abundant parasitoid species were B. variabilis and E. obliteratus, comprising 56.6 % and 18.6 % of all parasitoids found, respectively.
In 2024, we conducted samplings from June 24 to Sep. 2 only in commercial vineyards. We attempted to collect samples from wild grapes in early and mid-June but collected very few and couldn’t obtain samples from all sites. We collected a total of 159 parasitoids belonging to the same species found in 2023. From these, B. variabilis was the most abundant, representing 64.8 % followed by G. fratellus and E. obliteratus comprising 13.8% and 10.69%, respectively of all parasitoids found.
The abundance of these parasitoids in the field varied throughout the growing season; B. variabilis was found from late July to September, whereas E. obliteratus was only present from June to mid-August. Notably, G. fratellus was only found late in the season (from late July to September, Figure 2.). This is helpful because it could avoid interspecific competition of parasitoids for the same prey.
Parasitism rates in the field.
In 2023, the highest parasitism rate was observed in the first sampling of the season in wild grapes (30.95% on average). However, the sample size was very small. The second highest parasitism rate was found in the sampling of Aug 7, with an average of 16.4% across sites, while the lowest was the sampling of July 11, with 2.7%. Site 1 had the highest parasitism across sampling dates with an average of 21.7% followed by site 6 with 13.6% and site 2 with 12%. Site 3 had the lowest parasitism rates, with an average of 3.4% (Table 1.). In 2024, the average highest parasitism rate across sites was 16.4% in the sampling conducted on Aug 5th, followed by the sampling conducted on July 23 (15.27%). The lowest parasitism rates were found on Jun 24, with 1.6%. Site 1 had the highest parasitism across sampling dates, with an average of 19.3% followed by site 4, with 9%. Site five had the lowest parasitism rate with 3% (Table 2). Furthermore, B. variabilis reached parasitism rates of 37.2% and 51% in early August 2023 and 2024, respectively. The highest parasitism rates of E. obliteratus were 7% and 16,3% in early July 2023 and 2024, respectively.
E. obliteratus rearing.
This parasitoid species took on average 22 days (n = 35) to develop from egg to adult. As adults, females and males lived on average 16.6 and 16.4 (n = 30) days, respectively. On average, the parasitism rate of this species was 30% in laboratory conditions, and females lay eggs from the second day of mating until death. This is a very active parasitoid of first and second-instar larvae that is easy to rear in laboratory conditions. One of the challenges that we had rearing this insect was that we couldn’t keep the colony during winter because the GBM colony declined during this time. GBM grew very well in Concord grapes until September, but when we changed the food for table grapes purchased at the store, the colony declined. To fix this, we decided to grow GBM in an artificial diet during winter, but the colony still declined in March of the following year. Improving the GBM diet or growing the parasitoid in another host that is much easier to rear will help keep the colony of this parasitoid during winter and will allow field releases early in the growing season.
The GBM, P. viteana has an abundant number of larval parasitoids that naturally control their populations in field conditions in northwest Pennsylvania. This project represented a first step toward our understanding of the native natural enemies present in the area and their use in pest management programs. We successfully identified six Hymenoptera parasitoids from our samplings in six commercial Concord vineyards over two consecutive years (2023 and 2024). These vineyards were conventionally sprayed following the current management recommendations, indicating that natural control still occurs despite pesticide use. The most abundant parasitoid species were the ectoparasitoid, B. variabilis, and the endoparasitoid E. obliteratus, from which we recorded natural parasitism rates as high as 51% and 37%, respectively. Subsequently, we aimed to rear both species in laboratory conditions to study their life cycle and parasitism potential. Despite being successful at rearing both species, we found E. obliteratus to be a more amenable species to work with. As originally planned, we identified larval parasitoids of GBM naturally preying on this insect in northwest Pennsylvania and have developed a rearing procedure for one of these species. Additionally, we were able to determine their natural parasitism rates in field conditions and the time of the year at which these parasitoids are more abundant; we also learned some aspects of their ecology and life cycle. Our initial proposal also included the rearing and release of one parasitoid species in field conditions. We were able to rear and release B. variabilis and E. obliteratus in 2023, but we did that late in the growing season and, therefore, were unable to determine their success in reducing GBM in the field. Ideally, these parasitoids should be released early in the growing season for them to have a marked effect in lowering GBM populations. We found out that more work on rearing their GBM host is needed to enable parasitoid rearing over the winter. Despite this, our project was very successful and generated reliable data that will be included in two scientific publications and one extension article (currently under preparation). Although more research is needed to improve parasitoid rearing, we are encouraging growers to be more mindful of their spraying practices to protect the beneficial species; these practices include spraying vineyard borders only when reaching economic thresholds, not emptying their tanks in vineyard borders, and promoting the establishment of flowering plants in vineyard perimeters as a food source for beneficial fauna.
Education & Outreach Activities and Participation Summary
Participation Summary:
The results of this study have been disseminated to grape growers and the scientific community. The project PI delivered the preliminary results obtained in 2023 in three grower meetings held in the summer of 2024, reaching ~60 growers and 4 extension educators. Each year, Penn State University partners with Cornell University to hold biweekly coffee pot meetings at various locations within the Lake Erie Region (in NY and PA). These meetings are held in grower’s farms and offer the opportunity to openly communicate with growers, provide project updates, and address any concerns they may have. Additionally, Miss Neetu Khanal, the graduate student who conducted the parasitoid field samplings, has delivered preliminary information from this project in two events: a graduate student exhibition held at Penn State University in March 2024 and at the annual meeting of the Entomological Society of America that took place in Nov. 2024. Neetu is also preparing an extension article to share the results with grape growers, while the project PI is preparing two scientific publications to be submitted to peer-reviewed journals. The project PI will continue sharing results from this project with grape growers, extension educators, industry representatives, scientists, and the general community in outreach events in the upcoming years.
Learning Outcomes
About 60 grape growers so far have gained knowledge and awareness of GBM natural enemies and practices for their conservation. We will continue our educational efforts in subsequent years.
Growers have reported gaining knowledge of GBM natural enemies; they get excited when seeing specimens preserved in ethanol and pictures. They say they have never seen them in the field because they are so small. Also, many growers were not aware of how they could change farmer practices to enhance the preservation of natural enemies.
Project Outcomes
The cooperating farmer is very excited about the project. This is a person who cares about the environment and is open to new practices that enhance farm sustainability. This person is eager to follow the recommendations given to enhance the population of natural enemies. He was so surprised to see natural parasitism rates of up to 50%! However, this project did not focus on measuring farm practice changes and therefore we don't have data to report on this aspect.
The project was a great success, and the methods were appropriate for accomplishing our objectives. Proof of this is the manuscripts that we are currently preparing for publication and will be added as products once they are accepted. We obtained more data than initially anticipated and have applied for more funding to continue this research. Finding those many parasitoid species was phenomenal. We were very surprised by the high parasitism rates in mid-season despite the regular insecticide use in the sampled vineyards. We were so fascinated by the biology and ecology of the different parasitoid species, which made working on this project an enjoyable and rewarding experience. Although we did accomplish the main project objectives, there is more research needed to include them in pest management strategies. For instance, we need to improve parasitoid rearing in laboratory conditions; we can do this by improving the rearing methodology of their GBM host or by finding another insect host that is easier to rear. E. obliteratus has been reported as a parasitoid of the oriental fruit moth larvae, Grapholita molesta, an important pest of stone fruits (peaches and apples, cherries, etc), and it is very easy to rear. Future research should explore the use of G. molesta for E. obliteratus rearing. We also need to understand the life cycles and parasitism potential of more GBM parasitoid species, as of now, we only have that information for E. obliteratus. Being able to rear some of these parasitoids in laboratory conditions and keep the colonies over the winter will allow us to test their potential to control GBM population in the field. At the vineyard landscape level, it would be helpful to test different floral resources that provide food for adult parasitoids and help maintain their populations in the field. The results from these studies will greatly benefit grape farmers in Eastern America where GBM is endemic and causes significant crop damage.