The lack of effect of low temperature and high turbidity on operational Bacillus thuringiensis subsp. israelensis activity against larval black flies (Diptera: Simuliidae).

Black fly suppression programs are conducted across a wide range of environmental conditions, targeting a variety of pest species with diverse life histories. Operational applications of Vectobac 12AS (Bacillus thuringiensis subsp. israelensis) were conducted during times characterized by water temperature and turbidity extremes. Applications were conducted in the Yellow River in central Wisconsin targeting Simulium annulus and S. johannseni when water temperatures were 1-2 degrees C. Applications were conducted in the Green River in western North Carolina targeting the S. jenningsi group after a rain event, when portions of the treatment zone experienced turbidities of 276 nephelometric turbidity units. Excellent larvicidal activity was observed in both programs, with 97% mortality or greater being observed at distances over 5 km downstream of a treatment site. Mortality data for larval black flies in 2 operational suppression programs conducted in 2011 demonstrated a negligible effect of near-freezing water temperatures and exceptionally high turbidity on Bti activity.

Chironomus calligraphus (Diptera: Chironomidae), a new pest species in Georgia.

Chironomid midges are ubiquitous and ecologically important aquatic insects. However, some species can become pests when they occur in extremely high numbers, particularly those that colonize man-made habitats. Chironomus calligraphus is a Neotropical, pan-American species that has recently been found in the Nearctic region. This paper represents the 1st reported occurrence of C. calligraphus in Georgia. Extensive larval populations were found in the leaf sheaths and root masses of cattails and in the firm sandy substrates of a wastewater lake at an industrial site in coastal Georgia. Chironomus calligraphus was causing a significant economic impact at this site.

Comparison of morning and evening larvicide applications on black fly (Diptera: Simuliidae) mortality.

The downstream movement, or drift, of larval black flies as well as many other aquatic insects has been well documented. This phenomenon has most often been associated with the dusk-to-overnight time frame. Operationally, larvicide applications targeting black flies are typically initiated early in the day and can extend until near sunset. To determine if larvicide applications conducted late in the day would be affected by the drift behavior of larval black flies, 6 larvicide applications were conducted. Three applications were conducted at midmorning and 3 during the evening. Larvicidal applications of Bacillus thuringiensis subsp. israelensis insecticidal proteins targeting Simulium appalachiense demonstrated no difference in larval mortality between morning and evening applications. These findings indicate that the larvae responded in a similar manner to the larvicide during the late morning to early afternoon and evening to night. The drift behavior of larval black flies does not appear to be an impediment to black fly suppression activities.

Field evaluation of bactimos pt against chironomid midge (Diptera: Chironomidae) larvae in residential ponds.

We evaluated Bactimos PT (Bacillus thuringiensis subsp. israelensis [Bti]) against larval populations of Glyptotendipes paripes at 30 kg/ha in man-made lakes on Hilton Head Island, SC. Three treatments were "whole-pond" treatments, while the 4th consisted of treating a "band" along the edge of a pond where significant larval populations had been observed. Larval populations were reduced by an average of 95% at day 7, 70% at day 14, and 50% at day 21 posttreatment in the whole-pond treatments. Initial larval suppression with the band treatment was similar to the whole-pond treatments, indicating that suppression activities can be targeted to specific areas of a larval habitat.

Mitigating the effects of the green alga Scenedesmus quadricauda on the efficacy of Bacillus thuringiensis var. israelensis against larval black flies.

The green alga Scenedesmus quadricauda has been shown to decrease the efficacy of Bacillus thuringiensis var. israelensis (Bti) to black fly larvae in laboratory experiments. In this study, 2 approaches to mitigating the effects of S. quadricauda were tested, increasing the dose of Bti exposed to the larval black flies and increasing the length of the exposure period. Results showed that increasing the dose as well as increasing the exposure time were effective methods for mitigating the effects of S. quadricauda on Bti efficacy. Assessment of larval mortality at different exposure periods to Bti indicate that the manifestation of toxicity or acquisition of toxic doses of the Bti formulation takes place approximately 2-3 times slower when S. quadricauda is present. These results provide information that might be useful in developing a plan of action to combat this complex situation in field operations.

Ochlerotatus japonicus japonicus (Theobald) in Georgia and North Carolina.

Although the 1st published record of Ochlerotatus japonicus japonicus in Georgia (Rabun County) occurred in 2004, we report here a 2002 collection and identification in Fulton County, Georgia (metro Atlanta). The finding of Oc. j. japonicus in Fulton County represents the most southern record of this species in the United States to date. Also, subsequent collections in North Carolina and 4 additional counties in northeast Georgia are reported.

Effects of algae on the efficacy of Bacillus thuringiensis var. israelensis against larval black flies.

Personnel from several black fly control programs have reported that the efficacy of Bacillus thuringiensis var. israelesis (Bti) is reduced during periods when algal concentrations are high in the waterways. Although the reduction in Bti-induced mortality in black fly larvae is presumed to be related to the presence of algae, no scientific data support this theory. In this study, 4 genera of algae (Microcytis, Scenedesmus, Dictrosphaerium, and Chlorella) commonly detected in Pennsylvania rivers where Bti-induced mortality in black fly larvae has been reduced were assessed to determine their respective effects on Bti-induced mortality by using an orbital shaker bioassay with laboratory-reared black fly larvae (Simulium vittatum cytospecies IS-7). A significant reduction in Bti-induced mortality was observed when Scenedesmus was present in the flasks at concentrations > or = 16,000 cells/ml. The Bti-induced mortality of larvae was not significantly reduced when Chlorella, Dictyosphaerium, or Microcytis was present in the flasks, even at concentrations > or = 250,000 cells/ml. These results indicate that the presence of certain types of algae can reduce the mortality of black flies exposed to Bti. Although not clearly defined, the mechanisms involved may be related to algal morphology due to overall size and structures associated with certain types of algae, and possible interference with feeding.

Influence of developmental stage on susceptibilities and sensitivities of Simulium vittatum IS-7 and Simulium vittatum IIIL-1 (Diptera: Simuliidae) to chlorpyrifos.

Determination of the most sensitive and susceptible organismal life stage is important for use of the organism in toxicity assessments of environmental pollutants. In the present study, the sensitivities and susceptibilities of larval developmental stages of two black fly sibling species, Simulium vittatum Zetterstedt cytospecies IS-7 and S. vittatum Zetterstedt cytospecies IIIL-1, were determined using the organophosphate-insecticide chlorpyrifos. Differences in sensitivity and susceptibility were determined through analysis of slopes and median lethal concentration values produced from 24-h orbital shaker toxicity tests, respectively. The results showed no difference in sensitivity or susceptibility between sibling species. However, early instar (second and third) as well as mid-instar (fourth and fifth) groupings of S. vittatum IS-7 were significantly more susceptible than late-instar (sixth and seventh) larval groupings. Likewise, mid-instar groupings of S. vittatum IIIL-1 were more susceptible than late-instar larval groupings. However, neither species showed significant differences in sensitivity among instar groupings. The results of the present study indicate that the mid-instar groupings of black fly larvae are the best choice for use in toxicity tests, both because of their increased susceptibility compared to late-instar groupings and because of their ease in handling and manipulating in the laboratory compared to early instar groupings.

Susceptibility of black fly larvae (Diptera: Simuliidae) to lawn-care insecticides individually and as mixtures.

Urban and suburban watersheds have the potential to be highly impacted by chemicals, especially insecticides to control insect pests on lawns, ornamental plants, and home gardens. Three of the most common lawn-care insecticides detected in urban watersheds, carbaryl, chlorpyrifos, and malathion, have been evaluated using an acute orbital shaker toxicity test to determine their respective concentrations that produce 50% mortality (LC50) in Simulium vittatum Zetterstedt cytospecies IS-7 larvae. Results of the 48-h LC50 tests show chlorpyrifos to be the most toxic to black fly larvae (LC50 = 0.28 microg/L) followed by carbaryl (LC50 = 23.72 microg/L) and malathion (LC50 = 54.20 microg/L). These insecticides were also tested as binary and ternary mixtures using the toxic unit (TU) approach. Toxicity was shown to be greater than additive for the ternary mixture of chlorpyrifos-carbaryl-malathion (LC50 = 0.56 TU) and the binary mixtures of chlorpyrifos-malathion (LC50 = 0.72 TU) and carbaryl-malathion (LC50 = 0.78 TU). The binary combination of chlorpyrifos and carbaryl was shown to be additive (LC50 = 0.98 TU). These results indicate that aquatic invertebrate populations in urban and suburban streams may experience a higher-than-expected increase in toxicity-related effects when all three chemicals are present in the waterway.