Progress report for OS22-153
Project Information
Sugarcane borer management in sugarcane and rice in the EAA relies on biological control provided by parasitic wasps released during biological control programs in the 1930s, 1950s, and 1990s (Roldán et al. 2020b). Ants, including the red imported fire ant, are also thought to participate in sugarcane borer control in sugarcane. Currently, the sugarcane borer does not need to be managed with insecticides in either sugarcane or rice. Encouraged by the success of sugarcane borer management in the EAA, the proposed project aims to improve rice stink bug management by initiating the development of a rice stink bug biological control program in Florida.
Parasitoids using O. pugnax eggs as hosts have been observed in the United States (Bhavanam et al. 2021). These parasitoids include Telenomus podisi (Hymenoptera: Scelionidae), which parasitizes O. pugnax in Arkansas and Georgia, with parasitism levels as high as 90% (Sudarsono et al. 1992, Tillman 2010). In Central America, T. podisi parasitizes O. insularis in rice and weedy habitats (Zachrisson and Polanco 2017). Telenomus podisi occurs in Florida (Buschman and Whitcomb 1980). Thus, we hypothesize that T. podisi parasitizes rice stink bugs in Florida and might be used in a biological control program for conventional and organic rice. The commercial use of augmentative releases of T. podisi produced by Koppert Biological Systems (www.koppert.com.br/podisibug/) for stink bug management in soybean in Brazil supports our approach for the development and evaluation of a biological control strategy in Florida rice.
The proposed project will first identify parasitoids attacking O. pugnax and O. insularis, which are the two main rice stink bug species in Florida rice. Parasitism rate will be quantified in rice fields and adjacent habitats on conventional and organic farms. Subsequently, T. podisi, which is expected to be the most abundant parasitoid of Oebalus spp., will be reared and released in field cages on commercial farms to determine whether parasitoids can effectively suppress rice stink bug populations under Florida conditions. The solution resulting from the proposed project will be a foundation for an augmentative biological control strategy in Florida rice.
The proposed project will represent a first step towards biological control in rice in the EAA, which is a region dominated by sugarcane production. Although biological control of the sugarcane borer in sugarcane in the EAA has been the focus of studies since the 1930s, biological control of rice stink bugs has never been studied. Thus, results of the proposed project are unlikely to provide a short-term solution to the rice stink bug issue. However, the two years of on-farm research will provide critical results for future, more comprehensive studies. In addition, early involvement of growers will generate interest in and support for biological control as a way to achieve greater sustainability.
The ultimate goal of the proposed project is to protect conventional and organic rice yields in Florida while decreasing reliance on pyrethroid applications, which are potentially contributing to the development of pesticide resistance, the disruption of sugarcane borer biological control, environmental contamination, and the public's perception that modern agriculture is addicted to pesticides.
Objectives
The proposed on-farm research project will have two objectives:
- Identify rice stink bug parasitoids and quantify parasitism rates in Florida
- Determine whether parasitoid releases in field cages can control rice stink bugs under Florida conditions
Objective 1. Identify rice stink bug parasitoids and quantify parasitism rates in Florida
Surveys will be conducted during the two years of the proposed project to determine rice stink bug egg parasitism and predation rates, and to identify parasitoids emerging from stink bug eggs and adults. These surveys will represent the first research step towards understanding the role of natural enemies and how they can be manipulated for rice stink bug management. Each year, four surveys will be conducted between June and September (i.e., 1 survey/month). For each survey, four conventional and four organic fields between the flowering and hard dough stages will be sampled. Fields will be >1 mile apart and the same field might be sampled more than once if crop phenology allows or if a ratoon crop is produced.
For each field, sampling for rice stink bug adults and egg masses will be conducted. For adults, four 25-sweep samples will be collected using a 15-inch sweep net. Adults will be placed in a popup screen cage (12”*12”*12”), inspected for tachinid parasitoid eggs, and maintained in a climate-controlled room at 25°C, 40-60% RH, 12:12 (L:D) until parasitoid emergence. For eggs, all rice plants within ten 1-square meter quadrats randomly selected along a zigzag pattern will be inspected. Egg masses will be individually placed in glass scintillation vials capped with a cotton ball and maintained in a climate-controlled room until parasitoid or stink bug nymph emergence.
Sentinel egg masses will be produced in the laboratory. In short, field-collected O. pugnax and O. insularis adults will be maintained in popup screen cages in a climate-controlled room, fed with rice panicles, and allowed to lay eggs on paper towels. Within 24 hours of oviposition, egg masses will be frozen at -18°C. For each field of each survey, five egg masses for each O. pugnax and O. insularis will be placed in the rice field and in an adjacent weedy border. Sentinel egg masses will be collected into glass scintillation vials capped with a cotton ball 48 to 72 hours after deployment in the field. Egg masses will be observed for signs of predation and will be maintained in a climate-controlled room until parasitoids or stink bug nymphs emerge. Rice stink bug parasitoids will be counted and identified to species with the assistance of taxonomists at the Florida Department of Agriculture and Consumer Services – Division of Plant Industry (FDACS-DPI) in Gainesville, FL.
Parasitism rate of adults, parasitism rate of sentinel eggs, and predation rate of sentinel eggs for each survey will be compared for each stink bug species among production systems (conventional vs. organic) and habitats (field vs. border) using generalized linear mixed models with a binomial distribution (PROC GLIMMIX, SAS Institute 2016). Parasitism of natural eggs might also be compared if the sample size is appropriate.
Objective 2. Determine whether parasitoid releases in field cages can control rice stink bugs under Florida conditions
Field experiments will be conducted during late summer 2023 to determine whether parasitoids released in field cages have the potential to control rice stink bugs under Florida conditions. These experiments will be preliminary, representing a proof of concept demonstrating that parasitoid releases might be used for rice stink bug management in Florida.
Telenomus podisi is expected to be the most abundant parasitoid species attacking O. pugnax and O. insularis in Florida rice fields and adjacent habitats. Thus, T. podisi collected using sentinel eggs (objective 1) will be reared in the laboratory using a method comparable to that of Braz et al. (2021). In short, O. pugnax and O. insularis eggs produced in a climate-controlled room (objective 1) will be collected and frozen within 48 hours of oviposition. Previously frozen eggs will be placed in 60-ml glass culture tubes with eggs parasitized 12-14 days earlier. Honey droplets will be used as a food source for adult parasitoids. Upon adult parasitoid emergence, oviposition into previously frozen eggs will be allowed for 24-48 hours to maintain the laboratory population or to provide adults aged 24-36 hours for releases in field cages.
Two field cages will be deployed simultaneously in each of two organic rice fields. In each field, the two field cages will be placed 10 ft apart on rice at the heading stage. Each cage will be infested with 20 O. pugnax and 20 O. insularis adults (1:1 sex ratio), which will be allowed to lay eggs for 2 days. Subsequently, 10 T. podisi adults will be released in one cage, the other cage serving as a control without parasitoids. This number of parasitoids is five times greater than the release rate used in studies conducted in Brazil for Euschistus heros management in soybeans (de Freitas Bueno et al. 2020). Two days after T. podisi release, stink bug eggs will be collected in each cage and maintained in a climate-controlled room until parasitoid or stink bug nymph emergence.
Parasitism rates between cages with and without parasitoids will be compared using generalized linear mixed models with a binomial distribution (PROC GLIMMIX, SAS Institute 2016). Parasitism rates between 25% and 75% will be considered encouraging results strongly supporting additional laboratory and on-farm research. In case of parasitism rates <5%, releases will be repeated using greater parasitoid release rates.
The technician partially supported by the proposed project will work with a graduate student who has experience in rearing and handling egg parasitoids such as Trichogramma spp., Telenomus remus, and T. podisi at the Insect Biology Laboratory, University of São Paulo/Luiz de Queiroz College of Agriculture, in Brazil. Thus, the personnel involved in this proposed on-farm project are qualified.
Cooperators
- (Educator)
Research
Year 1
Six conventional and three organic rice fields were selected in early July, August, and September 2022 for collection of rice stink bug parasitoids. In each of the 27 fields, adults were collected using a 15-inch sweep net in a 100-sweep (organic fields) or 200-sweep (conventional fields) sample. Adults were separated by species and kept in screen cages in the laboratory for parasitoid emergence. In addition, eggs naturally deposited in rice fields were collected by inspecting all plants in ten 1-m2 quadrat samples selected throughout each field. Collected egg masses were observed for signs of prior parasitoid emergence, and egg masses with viable eggs were placed individually in glass vials kept in the laboratory for parasitoid emergence.
Sentinel eggs of O. insularis and O. pugnax produced in the laboratory were also deployed in rice fields and field margins to complement observations of naturally deposited eggs. In each field and margin, sentinel eggs were placed at five locations approximately 50 m apart. At each location, two sentinel egg masses (O. insularis only, or O. insularis and O. pugnax ) placed 1 m apart were clipped on rice plants or weeds. These sentinel egg masses were collected after 72 h and kept in glass vials in the laboratory for parasitoid emergence.
Year 1
We collected 2,996 rice stink bug adults. Differences in adult abundance and parasitism rate were not detected between conventional and organic fields (P > 0.05). However, there was a trend for less O. insularis adults in conventional fields than organic in fields, and the parasitism rate was 1.1 and 0.6%, respectively. For O. pugnax adults, parasitism rate was 1.7 and 6.9% in conventional fields and organic fields, respectively. Thirty-seven adult parasitoids were observed. The tachinid fly Beskia aelops was the only species collected.
We collected 1,414 eggs that had been naturally deposited in rice fields. For these eggs, differences in egg abundance, parasitism rate, and parasitoid emergence were not detected between conventional and organic fields (P > 0.05). Egg parasitism rate was 60.9 and 70.1% in conventional fields and organic fields, respectively. Successful parasitism, determined as the percentage of parasitized eggs with parasitoid emergence holes, was as high as 90.0%. Three hundred ninety-eight parasitoid wasps were observed. Most of these scelionid wasps were Telenomus sp.
For sentinel eggs, approximately 500 eggs were deployed in each field. However, nearly half of these eggs were lost, with more eggs lost in conventional fields than in organic fields (P < 0.05). For the recovered eggs, as many as 9.4% were parasitized, and parasitoids emerged from as many as 15.2% of these eggs. Fifty-two parasitoid wasps were observed. They were all scelionid wasps (Telenomus sp).
Educational & Outreach Activities
Participation Summary:
Year 1
One meeting was conducted in May 2022 at initiation of this project with the Director of Rice and Organic Farming and a Crop Protection Specialist for Florida Crystals Corporation, which grows >80% of the rice produced in Florida. This meeting, which also involved Extension Agent Matthew VanWeelden and Graduate Student Carolina Tieppo Camarozano, assisted in developing a specific plan for on-farm sampling during summer 2022. Aspects of biological control for conventional and organic farming were also discussed.
Educational events held in Belle Glade, FL included the 5th Florida Rice Field Day (August 16, 2022 - 62 participants) and two meetings of Florida Rice Growers Inc. (December 12, 2022 and March 1, 2023 - 20 participants per meeting). Results of on-farm sampling were discussed, and the value of a potential rice stink bug biological control program was promoted.
Learning Outcomes
Biological control of insect pests
Project Outcomes
Parasitism of rice stink bug eggs by scelionid wasps (almost exclusively Telenomus sp.) was relatively high. Telenomus wasps have been commercially reared and used in biological control programs in other crop systems in other countries. Thus, a biological control program relying on the release of Telenomus wasps to increase stink bug egg parasitism and decrease rice stink bug populations might represent a viable areawide management strategy.