Abundance, Activity, Diversity, and Species Interactions of Ground-Dwelling Ants (Hymenoptera: Formicidae) in Open Versus Canopied Habitats in Central Georgia (USA)

The red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), and ground-dwelling ant species native to Georgia were observed and studied in tree-canopied and open uncanopied habitats in two state parks in central Georgia. Population density, native species diversity, and interactions of native species with each other and with the invasive S. invicta were determined and compared in the two habitats. Sampling methods included pitfall traps, baits, collection of leaf litter, and visual searches. In comparison to the open uncanopied habitats, red imported fire ant population density was lower in tree-canopied habitats, and native ant species diversity was greater in the canopied habitats. We also observed native species competing with red imported fire ants more intensely in canopied than in open habitats primarily by foraging activity and by predation of S. invicta reproductives. Our results suggest that native ant species can suppress S. invicta population numbers and density and that competition by native ant species should be considered in approaches of managing red imported fire ant.

Impact of Genetic Background in Fitness Cost Studies: An Example from Glyphosate-Resistant Palmer Amaranth

Since its discovery in 2005, glyphosate-resistant Palmer amaranth has become a major problem for many farmers in the southern United States. One mechanism of resistance found in a Georgia population of glyphosate-resistant Palmer amaranth is amplification of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene throughout the genome, with some resistant plants containing and expressing more than 100EPSPSgenes. Such high numbers ofEPSPSgenes and protein production could result in a fitness cost to resistant plants due to (1) metabolic cost of overproduction of this enzyme and (2) disruption of other genes after insertion of theEPSPSgene. A greenhouse experiment was set up to investigate differences in growth and reproduction between glyphosate-susceptible and -resistant Palmer amaranth plants. Measurements included growth rate, plant height/volume ratio, final biomass, photosynthetic rate, inflorescence length, pollen viability, and seed set. This study found no significant fitness costs for plants with the resistance trait. This study also provided a clear example of how controlling for genetic background is important in fitness cost studies and how potentially misleading results can be obtained if only a few fitness traits are measured. These results indicate that glyphosate-resistant Palmer amaranth plants with highEPSPSgene copy numbers are likely to persist in field populations, even in the absence of glyphosate, potentially leading to long-term loss of glyphosate as a control option for Palmer amaranth.

Notodiscus (Charopidae) on South Georgia: some implications of shell size, shell shape, and site isolation in a singular sub-Antarctic land snail

Multivariate analysis shows that shells of Notodiscus sp. (Charopidae: Pulmonata) reported from South Georgia are smaller and proportionately taller than, but otherwise similar to, populations of Notodiscus hookeri (Reeve) from Iles Crozet and Iles Kerguelen. The origin of this solitary, and spatially limited, South Georgia population is enigmatic. It is confined to a remarkably small coastal lowland site which was glaciated at Last Glacial Maximum, precluding a Tertiary relict origin, and on the leeward north-east coast, ruling out post-glacial ocean rafting. The site is close to the King Edward Point settlement, yet the absence of any logistics connections with the Iles Crozet or Iles Kerguelen mitigates against anthropogenic introduction. The close proximity of the population to nests of blue-eyed shag (Phalacrocorax atriceps), Dominican gull (Larus dominicanus) and light-mantled sooty albatross (Phoebetria palpebrata) could imply the snail was originally introduced to South Georgia via these ocean transiting seabirds.

Recruitment of mackerel icefish (Champsocephalus gunnari) at South Georgia indicated by predator diets and its relationship with sea surface temperature

The South Georgia population of mackerel icefish (Champsocephalus gunnari) is exploited by both a fishery and predators, including gentoo penguins (Pygoscelis papua). Because considerable uncertainty surrounds recent estimates of stock size, there is a need to consider novel approaches that may give insight into the population dynamics of this species. We derive two indices of recruitment based on the occurrence of mackerel icefish in gentoo penguin diets, one of which is scaled by a survey estimate of the density of Antarctic krill (Euphausia superba), an alternative prey species for gentoo penguins. The closure of the fishery for much of the 1990s allowed the relationship between environmental conditions and recruitment to be studied without the confounding effects of fishing mortality. The recruitment indices were positively correlated with sea surface temperature with a lag time equal to the age of the fish. These results suggest strong links between mesoscale environmental processes and the smaller scale interaction between gentoo penguins and their mackerel icefish prey.

Biotype Composition of Hessian fly (Diptera: Cecidomiidae) Populations from Arkansas, Georgia, Illinois, North Carolina and Virginia

Fourteen populations of Hessian fly, Mayetiola destructor (Say), from Arkansas, Georgia, Illinois, North Carolina, and Virginia were evaluated for biotype composition, and two Arkansas populations were tested for response to Hessian fly resistance genes or gene combinations H3, H5, H6, H7H8, and H9 to H19 in wheat. The biotype composition of Hessian fly populations was estimated by confining individual gravid females on the four wheat differential cultivars ‘Monon’ (H3), ‘Magnum’ (H5), ‘Caldwell’ (H6), and ‘Seneca’ (H7H8). The response of Arkansas fly populations to resistance genes was evaluated in replicated tests with wheat germplasm lines or cultivars homozygous for these genes. Hessian fly populations from Arkansas were predominately biotype L, with low levels of biotypes F, G, J, M, and O, depending upon population. Biotype L was predominant in the Illinois, North Carolina, and Virginia populations, although biotype D was present in populations from extreme southwestern Illinois and Virginia and North Carolina. Biotypes G, J, L, M, and O were identified from the west-central Georgia population collected at Griffin, while only biotypes M and O were identified from the southwestern Georgia population, collected at Plains. All fly populations were virulent to resistance genes H3, H5, and H6, while the southwestern Georgia population was avirulent to H7H8. Plants with single resistance genes H9 to H19 varied significantly (P ≤ 0.05) in their resistance to the two Arkansas populations. Plants with single resistance genes H9, H10, H13, H14, and H16 to H19 conditioned resistance (88 to 100%) to both populations, while plants with single genes Hll, H12, or H15 were susceptible to one or both populations. Wheat germplasm lines developed in the Purdue/USDA program that carry single gene resistances H9, H13, H14, and H16 to H19 should provide useful sources of resistance for developing improved wheat cultivars adapted to the mid-south and southeastern United States.