SEASONAL TRAPPING

In 2019 and 2020, pheromone-baited traps were used to capture H. halys in the canopy of sassafras trees located in woodlands adjacent to row crops at the Prattville Agricultural Research Unit in Prattville, Alabama, USA (32.4286°N, 86.4458°E) and in woodlands next to a pecan orchard at the USDA, ARS Fruit & Tree Nut Research Lab in Byron, Georgia, USA (32.3910°N, 83.4321°E). We note that the sassafras trees in this study were mature trees that flowered and produced fruit. A stink bug trap consisted of an insect-collecting device made from a 2.8 L clear plastic PET® jar (United States Plastic Corp., Lima, Ohio, USA) with a screw-cap lid (10.2 mm in diam) seated atop a 1.22 m tall yellow pyramid trap base (Cottrell et al. 2000). Each trap was baited with a commercial set of 2 aggregation lures: H. halys male aggregation pheromone (PHER) and the synergist (MDT) (Trécé BMSB DUAL lure; Trécé Pherocon, Adair, Oklahoma, USA). To eliminate the likelihood of stink bug escape, an insecticide kill strip (10% λ-cyhalothrin and 13% piperonyl butoxide) (Saber extra insecticide ear tags, Sagebrush Tags, De Smet, South Dakota, USA) was placed inside the insect-collection device of each trap (Cottrell 2001). Lures in traps were replaced bi-weekly, but kill strips were not replaced during a season. Once per wk, H. halys captured in traps were placed in zip top bags (US Plastics Corporation, Lima, Ohio, USA) and stored at the USDA Southeast Watershed Unit in Tifton, Georgia, USA, for identification, which was based on Rice et al. (2014) and his experience rearing a colony of this species. At the Prattville site, traps in 3 trees were sampled each wk from 24 Apr through 10 Oct in 2019, and traps in 2 trees were sampled from 10 Apr through 1 Oct in 2020. At the Byron site, 1 tree was sampled each wk from 24 Jun 2019 through 4 Nov 2020. A single trap was deployed in the canopy of each tree sampled. Observations on H. halys presence and feeding of H. halys on sassafras trees were noted when trap samples were collected. Seasonal means for the number of adult stink bugs per trap were calculated (PROC MEANS; SAS 2012). For the sassafras tree at the Byron site, trap capture was averaged by mo because data was collected over 18 mo.

SENTINEL EGG MASSES

Egg masses came from a H. halys colony reared in cages (27.9 cm long × 26.7 cm wide × 20.3 cm tall) on whole bean pods, apple slices, and raw peanuts at the USDA, ARS Southeast Watershed Unit in Tifton, Georgia, USA. Knit cloth (97% cotton, 3% spandex) (Jo-Ann Stores, LLC, Hudson, Ohio, USA) was used as a substrate for oviposition. Three cone-shaped knit cloths (12.7 cm²) were placed on the bottom of an ovipositional cage. A portion of the cloth with an egg mass was cut from the cloth. Any damaged eggs were gently removed from an egg mass when eggs were counted. Refrigerated egg masses (≤ 12 h old when placed in a refrigerator with a temperature range of 2.8 to 3.3 °C for 24 h) were used. Unlike frozen egg masses, refrigerated eggs retain typical shape and color when deployed in the field. Refrigerated eggs do not hatch, therefore eliminating the possibility of first instars feeding on parasitized eggs. At the Prattville site, paperclips were used to suspend the sentinel egg masses on stems of sassafras trees in a patch within the woodlands. In 2019, fifteen to 25 egg masses were deployed on 7 May, 11 Jun, 11 Jul, and 7 Aug. In 2020, 6 egg masses were deployed on 11 Jul, and 10 to 15 egg masses were deployed on 13 Aug, 21 Aug, and 2 Sep. The number of egg masses deployed on a particular date depended on the number of egg masses produced by the colony. Egg masses were retrieved after 72 h, and any predators present on the eggs at that time were noted. If a parasitoid female was detected on an egg mass during removal from sassafras, the female was collected and brought into the laboratory for identification.

Sentinel eggs masses retrieved from the field were held in an environmental chamber (25 ± 2.0 °C; 50 ± 10% RH; 12:12 h (L:D) photoperiod) until parasitoid emergence. Afterwards, each individual egg in an egg mass was dissected to check for dead immature parasitoids. At the same time, predation was assessed, and damage was divided into the 4 categories detected: (1) complete chewing; (2) stylet sucking; (3) punctured sucking; and (4) egg removal. Determination of parasitoid immature stages was based on descriptions of Tr. basalis immatures in Volkoff & Colazza (1992) and on descriptions of Tr. basalis and An. reduvii every 24 h from oviposition in H. halys eggs to pupation (PGT, unpublished data). Trissolcus species adults were identified using the Talamas et al. (2015b) key. Anastatus species adults were identified using the Burks (1967) key. Voucher specimens of parasitoids are deposited in the Florida State Collection of Arthropods, Gainesville, Florida, USA.

SEASONAL TRAPPING

The mean total number of H. halys captured in traps varied across the season and by yr and site. At the Prattville site, only adults were captured in tree traps in sassafras early season; 3 wk before mid-May in 2019 and 5 wk before mid-May in 2020 (Fig. 1A). Second instars were detected first in traps on 16 May 2019 and 15 May 2020. At the Byron site, low numbers of H. halys adults were detected in traps during early spring of 2020, but numbers of adults began to increase in traps by mid-May, and second instars were captured in traps on 6 May 2020 (Fig. 1B). Altogether, these data suggest that H. halys females entered sassafras trees and then began ovipositing on their leaves around late Apr to early May. Then, third, fourth, and fifth instars were captured in traps from late-May through early to mid-Sep at each site each yr, and subsequently new adults were captured in traps over time, a strong indication that H. halys nymphs developed into adults on sassafras. Each of the developmental stages of H. halys collected in traps were observed to feed on either leaves, stems, or fruit of sassafras when trap samples were collected. Later in the season as sassafras began to senesce, mainly only adults were captured in traps. In Prattville, the peak number of late season H. halys adults was 393 on 26 Sep 2019 and 229 on 25 Sep 2020 (Fig. 1A). In Byron, the peak number of late season H. halys adults was 61 and 22 on 15 Sep 2019 and 16 Sep 2020, respectively (Fig. 1B). Many of these late season H. halys were red in color and presumably was the fall overwintering population of this stink bug species at these sites. Thus, at each site for both yr of the study, H. halys adults entered sassafras early in the season and nymphs developed to adults on this host plant throughout the summer with adults peaking in Sep. Most adults were present in overwintering sites by mid-Nov at the Byron site. We conclude that 1 expanded generation develops in sassafras over the season.

SENTINEL EGG MASSES

Trissolcus euschisti (67.7%) and A. reduvii (18.3%) were the primary parasitoid species that emerged from H. halys sentinel egg masses. Telenomus podisi (5.3%), Ooencyrtus sp. (4.0%), Tr. basalis (2.4%), and Tr. brochymenae (2.3%) also emerged from these egg masses. Females of each of these parasitoid species were observed ovipositing in H. halys sentinel eggs in sassafras based on identification of females on field egg masses in which adult parasitoids of the same species emerged. In 2019, parasitism per egg mass ranged from 0.2 to 14.3% (Table 1). In 2020, parasitism tended to be higher than in 2019, ranging from 32.3 to 39.2%.

Stylet sucking by Pentatomidae (62.3%) and chewing by Gryllidae and Tettigoniidae (32.0%) were the primary types of predation detected for H. halys sentinel egg masses in sassafras. Egg removal by Formicidae (5.2%) and punctured sucking feeding damage by Salticidae (0.5) also were detected on H. halys sentinel egg masses. During removal of H. halys sentinel egg masses from sassafras, mostly H. halys, including second through fifth instars and adults, were observed feeding on the egg masses. Occasionally, a grasshopper was observed chewing on an egg mass. In 2019, predation per egg mass ranged from 18.8 to 69.4% (Table 1). In 2020, predation per egg mass ranged from 3.3 to 41.0%. In both yr of the study, total percent mortality tended to increase over time resulting in relatively high mortality in Aug.