Survey and Rearing of Grape Berry Moth Larval Parasitoids in Northwest Pennsylvania

Progress report for ONE21-382

Project Type: Partnership
Funds awarded in 2021: $29,998.00
Projected End Date: 04/30/2024
Grant Recipient: Penn State University
Region: Northeast
State: Pennsylvania
Project Leader:
Dr. Flor Acevedo
Penn State University
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Project Information

Project Objectives:

This project seeks to 1) Identify larval parasitoids of grape berry moth in Northwestern Pennsylvania, 2) create a rearing protocol for at least one of the parasitic species identified, and 3) test the efficacy of at least one parasitic species in reducing grape berry moth infestations in a commercial vineyard plot. This project will be the baseline for future experiments of grape berry moth control using larval parasitoids. Our long-term goal is to include the release of parasitic wasps as part of an integrated pest management program to control grape berry moth in commercial vineyards. If successful, this project is likely to reduce production costs and increase farmers income by decreasing GBM infestations and by reducing the use of toxic insecticides.   

Introduction:

Grape is the highest value fruit crop in the US, 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 in 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 (Table 1), 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. If proven feasible, this “new” approach is likely 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.     

Cooperators

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  • Mark Terrell - Producer

Research

Materials and methods:

In this study, we will Identify larval parasitoids of GBM from samples collected in wild and cultivated grapevines in Northwestern PA. These parasitoids will be reared in laboratory conditions to determine their predatory capacity, the target GBM life stage they prey on, and their life cycle. Afterwards, we will choose at least one parasitoid species for mass rearing and release back into the field. Below are the procedures for each proposed objective.

Methods for objective 1.  “To identify larval parasitoids of grape berry moth in Northwestern Pennsylvania.” During the first year of the project (growing season of 2022), we will sample GBM larvae in six sites with historically high GBM infestations. These vineyards are located in the Erie county of Northwest PA and have been monitored for several years by our extension specialist Andrew Muza. Four of the six sampling sites are located in North East, PA (east to Erie city), whereas the remaining two sites are located west of Erie city; the location of each site is illustrated in Figure 2. Samples will be collected every two weeks from commercial vineyards and wild grapes growing adjacent to cultivated plots. The samplings will start one week after the wild grapes bloom (~ first week of June) and continue throughout the growing season. We will make an effort to sample at least 100 GBM-infested grapes per sampling site. These samples will be taken to the laboratory at the Penn State Lake Erie Regional Grape Research and Extension Center (LERGREC) located in North East, PA (662 N. Cemetery Rd, North East, PA16428); the samples will be placed in plastic containers with a fine screen mesh and will be incubated at 25C with a photoperiod of 15 h day and 9 h dark. The samples will be inspected daily for the emergence of larval parasitoids. Additionally, GBM pupa will be thoroughly inspected for parasitoids that may not emerge until the GBM larvae transitions to the pupal stage. We will keep record of the number of parasitoids recovered per number of GBM-infested grapes to calculate the percentage of parasitism per species. We will also keep record of the time at which the parasitoids emerge and the GBM-developmental stage. Some of the emerged parasitoid adults will be preserved in ethanol for further taxonomic identification, and the rest will be used to start colonies in the lab.

Methods for objective 2. “To create a rearing protocol for at least one of the parasitic species identified.” Emerged adult parasitoids will be transferred to pop-up cages containing diluted honey and water in cotton balls as a food source; the cage will also contain living GBM stages for oviposition. GBM larvae will be provided daily and retrieved 24 h later during the lifetime of the adult parasitoids. We will keep record of the number of parasitoids reared and their developmental time. Parasitoids will be reared in incubators at LERGREC at 25C with 15 h day/ 9 h dark photoperiod. GBM colonies for parasitoid rearing will be maintained using table grapes purchased at grocery stores for food and oviposition; the insects will be kept in plastic containers with a fine breathing mesh at 25C with 15 h day/ 9 h dark photoperiod.

Methods for objective 3. “To test the efficacy of at least one parasitic species in reducing grape berry moth infestations in a commercial vineyard plot.” During the second year of the project (growing season of 2023), we will release at least one of the laboratory-reared parasitoid species at the wood edges of a commercial vineyard plot with historically high GBM infestation. We expect to do at least one parasitoid release early in the growing season (June). The parasitoid release needs to be synchronized with the presence of susceptible GBM stages in the field. For instance, if the parasitoids oviposit on recently hatched GBM larvae, we need to make sure they are released shortly after GBM oviposition. To find the appropriate time for parasitoid release, we will use the GBM degree-day model to predict the developmental stage of this insect in the field (Tobin et al., 2003). Additionally, we will randomly sample GBM-infested grapes and dissect them in the lab to confirm the occurrence of the appropriate GBM life stage before parasitoid release. In the subsequent weeks, we will do periodic evaluations (every two weeks) of GBM infestation by visual inspection of at least 50 randomly selected grape clusters within the first five rows of the vineyard edges.

Because natural GBM parasitism does occur in the field, we will also measure GBM infestations from a “control” vineyard plot with historically high insect pressure in which parasitoids will not be released. Both vineyard plots will be free of insecticide applications during the time of the experiment.

Differences in the percentage of parasitism will be calculated between control vineyard plots and those with parasitoids released using a Chi-squared test at a significant level of alpha = 0.05.  

Expected accomplishments by the end of the project. By the end of this project, we expect to have a list of GBM larval parasitoid species recovered from the field, a rearing protocol for at least one of the parasitoid species, and at least one field trial of the efficacy of one parasitic species in reducing grape berry moth infestations in a commercial vineyard plot. However, testing the efficacy of parasitoids in field conditions will depend on our ability to rear a large number of the given species in laboratory conditions. In case this cannot be accomplished, the project will still provide relevant information to the composition of natural enemies of GBM in northwestern PA that could potentially be used in sustainable pest management strategies.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

The results of this study will be disseminated to growers and industry partners through local and regional extension meetings held in person and virtually. For example, the Penn state grape and enology team hosts periodic webinars that address key topics in viticulture and enology. Attendance to these webinars varies from 45-150 people from different states in the Northeast of the US. Penn State University also partners with Cornell University to hold weekly coffee pot meetings with grape growers from NY and PA during each year’s growing season as part of a regional agreement. Additionally, results will be shared through scientific and extension publications that will be available online. All the project PIs have extension appointments, which facilitate the dissemination of the results to grape growers.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.