Spatial Distribution of Megacopta cribraria (Hemiptera: Plataspidae) Adults, Eggs and Parasitism by Paratelenomus saccharalis (Hymenoptera: Platygastridae) in Soybean

Direct and Indirect Competitive Interactions between Ooencyrtus nezarae and Paratelenomus saccharalis Parasitizing Megacopta cribraria Egg Patches

The present study investigated egg parasitoid interspecific interactions between a generalist, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and a specialist, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) in a laboratory setting using kudzu bug (Megacopta cribraria Fabricius, (Hemiptera: Plataspidae)) eggs as their shared host. Three experiments were conducted to evaluate the emergence of wasps from parasitized hosts after the simultaneous and sequential release of wasps, monitor aggressive behavior of P. saccharalis, and quantify intraguild predation of O. nezarae larvae on heterospecific P. saccharalis larvae. Results showed that total host egg parasitism was higher when both wasps were released simultaneously than if wasps were released sequentially. Ooencyrtus nezarae produced more total offspring than P. saccharalis in all sequential/simultaneous treatments but produced male offspring in most cases. In the aggressive behavioral experiment, specialist, P. saccharalis used head butting to fight O. nezarae, but no other aggressions were observed. In an experiment examining intraguild predation, O. nezarae was able to develop in host eggs parasitized by P. saccharalis four days earlier, acting as a superior larval competitor. These findings shed light on the potential interspecific interactions between O. nezarae and P. saccharalis, which may determine their relative abundance and influence their compatibility in kudzu bug biological control programs.

Kudzu Bug (Megacopta cribraria) and Associated Egg Parasitoids Emergence Rates in Alabama are Predicted by Weather Indices

The kudzu bug, Megacopta cribraria (Fabricius) (Hemiptera: Plataspidae), is a major economic pest of soybean in the southeastern United States. With climate warming, this pest is expected to move northward and cause additional crop damage. Parasitoid biocontrol is a potential method of integrated pest management for kudzu bug. Two species of egg parasitoid wasps have been observed emerging from kudzu bug egg masses in the southeastern United States: Paratelenomus saccharalis (Dodd) (Hymenoptera: Platygastridae) and Ooencyrtus nezarae (Ishii) (Hymenoptera: Encyrtidae). This paper used egg mass emergence data collected between 2018 and 2020 in Alabama soybean fields and compared the data to weather indices. Indices included the number of days with minimum temperatures below zero, accumulated rainfall (mm m-2), as well as species specific metrics of accumulated growing degree days, accumulated daily minimum temperature (°C), and accumulated daily maximum temperature (°C). Emergence of the generalist parasitoid, O. nezarae, was highly correlated with kudzu bug nymph abundance, accumulated degree day, accumulated daily temperatures, and precipitation. Ooencyrtus nezarae emergence was predicted in a stepwise regression equation by aggregated degree day and date of collection, which indicates that seasonality may be a predictor of its presence. In contrast, collections of the specialist parasitoid, P. saccharalis, were near-zero throughout the collection period, suggesting that this species may no longer be a usable biocontrol agent in the southeastern United States as a result of external limiting factors.

Use of Pyriproxyfen to Induce Oogenesis in Diapausing Megacopta cribraria (Heteroptera: Plataspidae), and Evaluation of Pyriproxyfen-Induced Eggs for Rearing the Parasitoid Paratelenomus saccharalis (Hymenoptera: Scelionidae)

Simple Summary

Rearing of many hymenopteran egg parasitoids requires a reliable supply of host eggs. The parasitoid Paratelenomus saccharalis can be reared on eggs produced from field collected kudzu bug, Megacopta cribraria, however field-collected hosts obtained during reproductive diapause do not readily produce eggs and must be reared under a long day-length photoperiod to terminate diapause. In this study we found that an exogenous application of pyriproxyfen was able to terminate diapause, leading to a significant increase in egg production. The eggs produced by pyriproxyfen-treated M. cribraria were accepted by the egg parasitoid Paratelenomus saccharalis, however parasitoid emergence was reduced when compared to eggs from untreated hosts. When the effects of pyriproxyfen treatment on egg production and parasitoid emergence were evaluated together, the net increase in parasitoid yield due to pyriproxyfen treatment was approximately 87%. This method has the potential to increase parasitoid yield and reduce production costs in egg parasitoid rearing programs.

Abstract

The mass rearing of hymenopteran egg parasitoids requires an abundant supply of host eggs. The onset of reproductive diapause and subsequent decline in egg production poses a challenge for parasitoid rearing when using host colonies augmented by field-collected insects. We investigated the application of pyriproxyfen, a juvenile hormone analog, to induce oviposition in diapausing adult kudzu bugs, Megacopta cribraria (Fabricius) (Heteroptera: Plataspidae), and the use of eggs produced by pyriproxyfen-treated kudzu bugs to rear the egg parasitoid, Paratelenomus saccharalis (Dodd) (Hymenoptera: Scelionidae). The effects of pyriproxyfen and photoperiod treatments on host mortality, egg production, and rates of parasitoid eclosion from the eggs were used to calculate the parasitoid yield for the different treatment regimes. A combination of pyriproxyfen and a long-day photoperiod increased the parasitoid yield by 87% compared to acetone and a long-day photoperiod. The general applicability of JH-analog mediated egg production for parasitoid rearing is discussed.

Spatial Distribution of Hunting Billbugs (Coleoptera: Curculionidae) in Sod Farms

The hunting billbug, Sphenophorus venatus vestitus Chittenden (Coleoptera: Curculionidae), is an important turfgrass pest, especially in sod farms. S. venatus vestitus larvae feed on the stems and roots of turfgrass. Damaged turfgrass is loosely held together and poses a challenge for machine harvesting. Additionally, the normal growth of turfgrass is affected, especially after winter dormancy. Because S. venatus vestitus larvae are hidden inside the stems or under the soil, larval management is challenging. To improve sampling and management, the spatial distribution patterns of S. venatus vestitus larvae and adults were assessed at four sod farm sites with a history of S. venatus vestitus infestation in central Georgia (USA). The larvae were sampled by soil cores using a hole cutter, whereas adults were collected using pitfall traps for 7 d. The spatial distributions of larvae and adults was analyzed using SADIE and variograms. The SADIE and variogram analyses revealed a significant aggregation pattern for adults, whereas aggregated distributions were detected for larvae with variogram analyses. The average ranges of spatial dependence for larval and adult samples were 3.9 m and 5.4 m, respectively. Interpolated distribution maps were created to visually depict S. venatus vestitus infestation hotspots within the sod farms.

Water Loss and Desiccation Tolerance of the Two Yearly Generations of Adult and Nymphal Kudzu Bugs, Megacopta cribraria (Hemiptera: Plataspidae)

Water loss rate, percentage total body water content (%TBW), cuticular permeability (CP), and desiccation tolerance were investigated in adult and immature stages of the invasive kudzu bug, Megacopta cribraria (Fab.) (Hemiptera: Plataspidae), a serious soybean pest and an urban nuisance. Adults and all five nymphal instars were weighed prior to and 2, 4, 6, 8, 10, and 24 h after desiccated at 30 ± 1°C and 0-2% RH. Both % initial mass and %TBW loss increased linearly with time of desiccation. Rates of loss ranged from approximately 1-7%/h. Mortality occurred at 10 h after desiccation. Desiccation tolerance (%TBW lost at death) ranged between 25.6% for first-generation adult females and 75% for first-generation fifth-instar nymphs. First-generation first-instar nymphs had significantly greater %TBW (88.9%) than the other generations and instars, whereas second-generation fifth instars had the lowest %TBW (62.4%). The CP value of first-generation adult females (12.3 ± 1.6 µg cm-1 h-1 mmHg-1) was the greatest across generations. First-generation first instars had the greatest mass loss (111.11 mg/g) among all instars and generations, whereas overwintered second-generation adult females had the lowest mass loss (18.39) across generations. This study demonstrated that desiccation stress differentially affected the survival of adult and nymphal kudzu bugs and may imply that environmental stress can affect the relative abundance of this species in the fields and around homes.