Pest Insects and Natural Enemies in Transitional Organic Cotton in Georgia

This research was conducted in experimental plots in Georgia from 2004 through 2006 and assessed the prospects for transitioning to a totally organic management system for cotton. The seasonal abundance of insect pests and their natural enemies over the 3-yr transitional period are reported herein. The heliothines, Heliothis virescens (F.) and Helicoverpa zea (Boddie), and stink bugs, mainly Nezara viridula (L.), Euschistus servus (Say), and Euschistus quadrator (Rolston), were the 2 groups of insect pests found on cotton. Heliothine larvae were observed each year of the study but, in general, infestations of heliothines were higher in 2004 than in the other 2 yrs. Stink bugs were observed in relatively high numbers, and the percent of cotton bolls damaged by these pests was high only during year 2 of the study. Over the 3-yr period, the red imported fire ant, Solenopsis invicta Buren, various spiders, including Oxyopes scalaris Hentz and Peucetia viridans (Hentz), the big-eyed bug, Geocoris punctipes (Say), and the pirate bug, Orius insidiosus (Say), were the most abundant predators of the heliothines and stink bugs. The endoparasitoid Toxoneuron nigriceps Viereck and an ascovirus also contributed to larval mortality of H. virescens. The endoparasitoid Trichopoda pennipes (F.) parasitized adults of N. viridula.

Populations of Stink Bugs (Heteroptera: Pentatomidae) and their Natural Enemies in Peanuts

The objective of this on-farm study was to determine if peanuts harbor populations of stink bugs (Heteroptera: Pentatomidae) and their natural enemies in Georgia. Eight species of phytophagous stink bugs were found in peanuts over the 5-yr study. The predominant stink bug species were Nezara viridula (L.), Euschistus servus (Say), Euschistus quadrator (Rolston), and Oebalus pugnax pugnax (F.). The remaining 4 species, Acrosternum hilare (Say), Euschistus tristigmus (Say), Euschistus ictericus (L.), and Thyanta custator accerra McAtee, were found in relatively low numbers. All developmental stages of N. viridula, E. servus, E. quadrator, A. hilare, and O. p. pugnax were collected at various times in the study indicating that these 5 species of stink bugs were developing on this crop. Seasonal abundance of N. viridula and E. servus nymphs and adults provided further support that these 2 species of stink bugs developed on peanuts. At least 1 generation of N. viridula and E. servus occurred in peanuts each year, and generally some of the adults that developed on peanuts oviposited on peanuts producing another generation of nymphs in this crop. Because only adults of T. c. accerra, E. tristigmus, and E. ictericus were found in peanuts, these 3 stink bug species probably were not developing on this crop. Adult stink bugs were parasitized by the tachinid parasitoids Trichopoda pennipes (F.) and Cylindromyia spp. Stink bug eggs were parasitized by the scelionids, Trissolcus basalis (Wollaston), Trissolcus thyantae Ashmead, Trissolcus brochymenae (Ashmead), Telenomus podisi Ashmead, and Gryon obesum Masner, and an unknown encyrtid species. Geocoris punctipes (Say), Geocoris uliginosus (Say), Orius insidiosus (Say), Podisus maculiventris (Say), and Oxyopes salticus Hentz preyed on stink bugs in peanuts. Peanuts harbor populations of stink bugs and their natural enemies, and thus the role peanuts play in landscape ecology of stink bugs needs to be ascertained to better understand how to manage stink bug populations in landscapes in which peanuts are associated with other crops.

Mortality of the Corn Earworm (Lepidoptera: Noctuidae) on Sorghum Panicles in Georgia

The mortality of the corn earworm, Helicoverpa zea (Boddie), on sorghum panicles in Georgia was determined in a 2-yr study. Percent total real mortality (rx) of H. zea exceeded 99% for each year and planting date. Percent total real mortality was highest for eggs followed by 1st instars. Parasitization and predation were the primary mortality factors for eggs on sorghum panicles. Larval mortality was due in part to predation, parasitization, and infection by pathogens. Trichogramma pretiosum Riley was the only egg parasitoid observed on sorghum panicles. Orius insidiosus (Say) was the predominant predator of H. zea. Other predators observed feeding on H. zea included the big-eyed bug, Geocoris punctipes (Say), the spined soldier bug, Podisus maculiventris (Say), green lynx spiders, Peucetia viridans (Hentz), and lady beetles (mainly Hippodamia convergens Guérin-Méneville). A variety of parasitoids attacked larvae on sorghum. The braconid Cotesia marginiventris (Cresson) parasitized small to medium-sized larvae. The tachinids Eucelatoria rubentis Coquillett and Archytas marmoratus (Townsend) parasitized large larvae. Two pathogens, HzNPV, a naturally-occurring nuclear polyhedrosis virus of H. zea, and the fungus, Entomophthora aulicae (Reichardt) G. Winter, caused mortality of larvae. In conclusion, biological control by natural enemies of H. zea on sorghum panicles resulted in significant mortality for this pest.

Survival of Geocoris punctipes Say (Hemiptera: Lygaeidae) Following Exposure to Selected Reduced-Risk Insecticides

Survival of Geocoris punctipes Say adults following exposure to azadirachtin, spinosad, thiamethoxam, diazinon, and imidacloprid was assessed in laboratory assays and greenhouse tests. In the laboratory assays, adults were continuously exposed for 48 h to filter papers treated with the individual insecticides. Survival was greatest following exposure to the untreated control (100 ± 0.0%), azadirachtin (95.0 ± 2.2%), and imidacloprid (81.7 ± 7.9%). Mean (± SEM) survival following exposure to spinosad (55.0 ± 11.2%) and thiamethoxam (46.6 ± 3.3%) was significantly lower, whereas diazinon killed all adults within 12 h of exposure. In the greenhouse tests, adults were continuously exposed to bush beans, Phaseolus vulgaris L., foliage treated with the individual insecticides. Mean (± SEM) survival following 144 h of continuous exposure to treated foliage was 97.5 ± 2.5% for the untreated control, 92.5 ± 5.3% for azadirachtin, 92.5 ± 3.7% for diazinon, 72.5 ± 8.4% for imidacloprid, 70.0 ± 8.4% for spinosad, and 57.5 ± 8.8% for thiamethoxam. Statistically significant differences were observed with thiamethoxam versus diazinon, azadirachtin and the control. The results for the filter paper assay and the greenhouse tests are encouraging in terms of potential natural enemy conservation in IPM programs employing these insecticides.