Southern green stink bug egg parasitoid (Trissolcus basalis)

Trissolcus basalis 
(Hymenoptera: Platygastridae)

Trissolcus basalis is a parasitoid of the Southern green stink bug, Nezara viridula, in addition to other parasitoid wasps such as Telenomus podisi, Ooencyrtus johnsoni, O. californicus, Trissolcus brochymenae and T. urichi (Moreira and Becker, 1986; Correa-Ferreira and Moscardi, 1995). T. basalis was released as a part of a classical biological control program for the United States, New Zealand, and Australia from 1949-1987. Strains of T. basalis were collected for this project from regions of Italy, Spain, and France. The southern green stink bug has been widely investigated and classified by Todd (1989), where it was referred to as one of the most important pentatomid insect pests in the world due to its highly polyphagous feeding behavior on many important food and fiber crops. Conversely, adults of the southern green stink bug parasitoid, T. basalis, have small, black bodies with yellowish-brown legs and clubbed antennae. Females are approximately 2 mm in length with downward elbowed antennae and a flattened abdomen. Adults live 23 days on average and at temperatures averaging 22°C. T. basalis adults can be distinguished from other nearctic Trissolcus species by the presence of coriaceous microsculpture on the mesoscutellum, pustulate setal bases, shallowly impressed episternal foveae on the mesopleuron, and an incomplete netrion sulcus (Buffington et al. 2015). 

T. basalis most likely occurs in all crops attacked by the southern green stink bug including cotton, grains, soybeans and other legumes, tomatoes and other solanaceous crops, sweet corn, sunflower, cole crops, cucurbits, fruit and nut crops. The southern green stink bug is also a serious pest of macadamia nuts (Macadamia integrifolia) and constrains nut production in regions like Hawaii (Wright et al. 2011). The primary reproductive hosts of southern green stink bugs are soybean (Glycine max), wild radish (Raphanus raphanistrum), thistles (family: Asteraceae), and rice (Oryza sativa). The southern green stink bug deposits eggs in tightly packed rows of ~60 eggs (Van den Berg et al., 1995). Each egg is glued against other eggs and to the plant tissue, with no gaps. Eggs are circular and yellowish in color. As they develop they become deep yellow, then pinkish, and finally bright orange. Nymphs emerge red in color and about 1 mm in length before they molt into a more distinct black color. Southern green stink bug nymphs undergo five nymphal stages in which their color changes progressively in successive instars before they reach adulthood (Kobayashi, 1959). Adult southern green stink bugs are about 15 x 8 mm in size with an obvious shield shape, bright green to reddish brown in color, and marked by three white dots on the scutellum, where it joins the prothorax. Adult southern green stink bugs emerge in the early spring to begin feeding nocturnally (Shearer and Jones, 1996), and soon after begin to mate and oviposit their eggs. Eggs are deposited in the upper canopy of the host plants, under fruit, leaves, or other protective structures. Eggs may take between 5 days and 3 weeks to hatch depending on the time of season. Female T. basalis parasitize the eggs of southern green stink bugs by ovipositing their own eggs directly into the stink bug eggs. The average number of eggs produced per female was 230-300 in one laboratory study. Adults emerge from the host eggs in 9 to 12 days with an average life-cycle of 23 days at 22°C. T. basalis parasitoid wasps are referred to as the primary parasitoid of southern green stink bugs, because they have been found to be the most frequent and consistent parasitoids of southern green stink bugs, in addition to other parasitoid hosts. In 1987, strains of T. basalis from Italy, Spain, and France were introduced in California where field results showed that 87% of the eggs per mass and 80% of all southern green stink bug egg masses examined by researchers were parasitized by T. basalis. Since then, T. basalis has been considered to be effective at controlling southern green stink bugs in these regions. However, recent studies indicate that control by T. basalis may not be as successful as previously thought. Further support of populations of T. basalis, as well as other parasitoid wasps can be achieved through the reduction of broad-spectrum insecticides in desired locations, as well as the support or maintenance of floral and nectar sources in desired habitats. Maintaining a ready supply of moisture is imperative by placing a shallow pool or small pans of water around desired locations. In addition to broad-spectrum insecticides, the use of herbicides should also be considered when supporting populations of natural enemies, as herbicides can reduce floral and nectar availability that is key to the survival of many parasitoid wasps.