Richard J. Lobinske

Influence of temperature on developmental rate, wing length, and larval head capsule size of pestiferous midge Chironomus crassicaudatus (Diptera: Chironomidae).

Abstract Larvae of Chironomus crassicaudatus Malloch were reared individually at nine constant temperatures from 12.5 to 32.5°C (2.5°C increments) for 120 d. Duration of immature stages (egg, four instars, and pupa), head capsule width of fourth instars, and wing length were recorded. Some adults emerged at all temperatures, except at 12.5°C where individuals developed to fourth instars during the experiment. Sharpe and DeMichele’s four-parameter model with high-temperature inhibition described the temperature-dependent developmental rates. The slowest development was observed at 15°C, with developmental rate peaking between 25 and 27.5°C. Developmental rate increased rapidly with increasing temperature up to 20°C, slowed between 20 and 27.5°C, and decreased at temperatures >27.5°C. No developmental inhibition at high temperatures was observed in eggs. The most apparent high-temperature inhibition of development was recorded in fourth instars, which comprised the largest proportion of developmental time. Males developed faster than females, but females had wider larval head capsules and longer wings than males. Adult size was negatively related with temperature in both sexes, but this relationship was steeper in males than in females. Larval size peaked at 20°C, whereas the head capsule width was reduced at temperatures higher and lower than 20°C.

Spatio-temporal effects of selected physico-chemical variables of water, algae and sediment chemistry on the larval community of nuisance Chironomidae (Diptera) in a natural and a man-made lake in central Florida

Spatio-temporal distributions of Chironomus crassicaudatus, Chironomus decorus, Glyptotendipes paripes, Cryptochironomus fulvus and Tanypodinae midge larvae and selected associated environmental variables (physico-chemical variables of water, sediment chemistry and algal composition) were studied for one year in natural Lake Monroe and man-made Konomac Lake in central Florida. Ordination analysis (CCA with variation partitioning) showed that in each lake, sediment variables were the most important environmental variables. However, the most important proportion of species variability in pooled data from both lakes was explained by lake-specific combinations of water, sediment and algal variables. Chironomid larvae were ordinated with increasing depth as follows: G. paripes, C. fulvus, C. crassicaudatus, Tanypodinae, and C. decorus. This trend was similar for both lakes individually as well as for the pooled data. As water depth increased, organic matter content and associated metals concentrations in sediment increased. Glyptotendipes paripes displayed significant, negative correlation with water depth and sediment total carbon content, while C. decorus showed a significant positive correlation with these variables; C. crassicaudatus did not show any significant correlation with either of these variables. The algal composition in the pooled data from both lakes was another important factor affecting the larval distributions. The proportion of G. paripes and C. decorus larvae increased with filamentous algal density, and C. crassicaudatus larvae with increasing Cyanobacteria. Although both study lakes were very shallow, the effect of water depth (alone or shared with environmental variables) on chironomid larval community composition was substantially higher than the seasonality (sampling month) effect.

Horizontal and Vertical Distribution of Soil Macroarthropods Along a Spatio-Temporal Moisture Gradient in Subtropical Central Florida

Abstract Distributions of soil macroarthropods were studied monthly for 1 yr (February 2001 to January 2002) in three depth strata (0–8, 8–16, and 16–24 cm) at six sampling sites along a moisture gradient stretching from the shore of Lake Yale, central Florida, to an upland hammock. Annual mean density of total soil macroarthropods at these sites varied from 312 to 1,809 individuals/m2; highest density was recorded near the center of the gradient. The most abundant groups of soil arthropods were Isopoda, predominantly Armadillidium vulgare (Latreille), and Diptera larvae (mostly Limoniidae, Chironomidae and Bibionidae). Species of five genera of Chironomidae (Paraphaenocladius sp., Pseudosmittia sp., Metriocnemus sp., Bryophaenocladius sp., and Smittia sp.) were found. Total number of macroarthropod species at individual sites varied between 40 and 70. The majority (61–92%) of soil macroarthropods from all sites was recovered from the near-surface stratum. Proportion of soil macroarthropods found in the two deeper strata increased with distance from the shoreline, elevation above lake water level, soil carbon content, and acidity of soil. The two sites located near the shoreline were continually flooded from September to January after the lake water level increased by up to 30 cm. Two inland sites were periodically (June–September) flooded by rain water. Flooding at either site caused decreased density of soil macroarthropods, with the effect of lake flooding being more pronounced. Density of soil macroarthropods at flood-affected sites peaked during spring, whereas seasonal changes in density of these invertebrates at most upland sites were less pronounced and peaked in autumn. Results indicated that seasonal migration and recolonization by soil macroarthropods along the moisture gradient are important strategies to overcome flood-affected population losses.

Qualitative and Quantitative Studies on Chironomidae (Diptera) and Selected Physico-Chemical Parameters in Two Tributaries of the Wekiva River, Central Florida

Aquatic midge (Chironomidae: Diptera) larval densities, 24-h adult emergence, and larval and adult dry biomass were estimated monthly for two years in two tributaries of the Wekiva River, central Florida, along with selected physico-chemical water parameters. Twenty-four genera of midges were identified in Blackwater Creek and 26 in Rock Springs Run, with subfamily Chironominae dominating the midge fauna. Larval densities in the former stream ranged from 56 to 757 per m 2, with 24-h periods adult emergence ranging from 0 to 95 per m 2 . The latter stream supported 138 to 1277 larvae per m 2 with 0 to 68 emergent adults per m 2 taken during 24-h periods. Mean larval biomass in Rock Springs Run (42 mg per m 2 ) was significantly (P<0.05) higher than in Blackwater Creek (27 mg per m 2 ), while mean adult biomass in both habitats was essentially identical (1.1 mg per m 2 ). Annual midge productivity estimates (1.12 g dry wt per m 2 ) in each stream indicated that both were oligotrophic. Water volume was the overriding abiotic factor noted in both habitats, influencing many of the observed water parameters and altering the midge generic composition, especially in Blackwater Creek.

Laboratory Estimation of Degree-Day Developmental Requirements of Glyptotendipes paripes (Diptera: Chironomidae)

Abstract Eggs from field-collected Glyptotendipes paripes Edwards were hatched and the immature life stages individually reared under 11 constant temperatures between 10.0 and 35.0°C (2.5°C increments) in the laboratory. No egg hatch was observed at 10.0°C for up to 30 d. At 35.0°C, egg hatch was normal but the larvae did not survive to second instar. The developmental zero growth was estimated at 9.0°C. Degree-day requirement for G. paripes development from egg to adult was estimated at 717 DD above 9.0°C. No significant difference between development time of males and females was noted and the sex ratio was near 1:1.

Ecological Studies of Spatial and Temporal Distributions of Larval Chironomidae (Diptera) with Emphasis on Glyptotendipes paripes (Diptera: Chironomidae) in Three Central Florida Lakes

Abstract Larval population distributions of Chironomidae (Diptera), Glyptotendipes paripes Edwards in particular, were examined over a 2-yr period in two central Florida lakes (Dora and Yale), and for 1 yr in Lake Wauburg in relation to selected water and sediment physicochemical properties. The nutrient status of the study lakes varied from transitional mesotrophic/eutrophic to hypereutrophic. Glyptotendipes paripes larvae were the most common in Lake Wauburg, while Cladotanytarsus spp. were numerically the most abundant in Lakes Dora and Yale. Mean density of G. paripes in Lake Dora declined sharply during the study period to very low levels and remained low through the remainder of the investigation. Glyptotendipes paripes densities in Lake Wauburg remained high during the entire study period. Populations of G. paripes in Lake Yale generally peaked during summer and fall and decreased considerably during the winter. Estimated G. paripes annual productivity ranged widely from 0.2 g/m2 (Lake Dora) to 156.9 g/m2 (Lake Wauburg). Canonical correspondence analyses indicated that the primary influences on distributions of chironomid larvae in the study lakes were water depth, dry weight of sediment, and the presence of sand, muck or vegetation. Although G. paripes larval distributions tended to be associated with shallower, sandy substrates in Lakes Dora and Wauburg, these larvae were distributed over or in the muck bottom areas of Lake Yale.

Population Survey and Control of Chironomidae (diptera) in Wetlands in Northeast Florida, USA

Abstract A qualitative and quantitative population survey of immature and adult Chironomidae was conducted for 1 year in a country club wetlands in northeast Florida, USA. Glyptotendipes paripes and Goeldichironomus carus were the 2 predominant chironomid species in the wetlands. Adults of these 2 species emerged at nuisance levels from Apr through Jun, and in Aug and Sep. Polypedilum, Cryptochironomus, Tanytarsini, and Tanypodinae collected in low numbers during the survey were not identified to species. In laboratory bioassays, LC90 values of technical grade temephos against G. paripes and G. carus were 0.01 and 0.009 ppm, respectively. For s-methoprene the LC90 values were 0.082 and 0.055 ppm, and for Bacillus thuringiensis serovariety israelensis (Bti) 1.056 and 0.467 ppm, respectively. In experimental field plots in the wetlands, 5% AI Skeeter Abate® (temephos) pellets at 0.1 kg AI/ha reduced midge larvae by 52-86% and at 0.2 kg/ha by 74-92% during 4 weeks posttreatment. Sand formulated technical powder of Bti at 1,000,000 and 2,000,000 ITU (International Toxic Units) Bti/m2 reduced midge larvae by 47-52% and 82-88%, respectively, during 6 to 20 days posttreatment. STRIKE® pellets (4.25% AI s-methoprene) at 0.14 kg AI/ha suppressed a maximum of 80% total chironomid adult emergence at 7 days posttreatment; this IGR at 0.28 kg AI/ha reduced adult emergence up to 92% during 15 days posttreatment. Temephos and Bti were more cost-effective and provided midge control for relatively longer period than s-methoprene in the field evaluations.

Influence of Chironomidae (Diptera) faecal pellet accumulation on lake sediment quality and larval abundance of pestiferous midge Glyptotendipes paripes

Two opposite distribution patterns of larval Glyptotendipes paripes in relation to organic carbon content in sediments of central Florida lakes were discovered. In a majority of examined lakes, G. paripes larvae were most abundant in sand sediment and their density rapidly declined with increased carbon content (type 1 lakes); however, in some cases the opposite was true (type 2 lakes). To elucidate this anomaly, field-collected organic sediments from types 1 and 2 lakes and sand sediment were studied for G. paripes development in the laboratory. Type 1 organic sediment consisted predominantly of fine particles (<0.25 mm diameter) with low dissolved oxygen levels, whereas type 2 organic sediments consisted primarily of chironomid large faecal pellet aggregates (>0.25 mm diameter), with significantly higher levels of dissolved oxygen concentrations that were similar to sand sediment. Type 2 organic sediment and sand sediment were conducive to higher survival of G. paripes larvae than fine organic sediment. The larvae in type 2 organic sediment produced longer tubes than in other sediment types. This observation indicates that accumulation of chironomid faecal pellets in lake sediments may change physical properties, such as dissolved oxygen level and consequently alter conditions for survival of chironomid larvae and possibly other benthic fauna.

Life History and Productivity of Hexagenia limbata (Ephemeroptera: Ephemeridae) and Selected Physico-Chemical Parameters in Two Tributaries of the Wekiva River, Central Florida

Nymphal densities and size frequency distribution of Hexagenia limbata (Serville), a burrowing mayfly, were determined monthly for two years in two tributaries of the Wekiva River, central Florida, along with selected physico-chemical water parameters. Blackwater Creek supported a mean number of 112 (range 0-434) and Rock Springs Run 89 nymphs per m 2 (range 11-258). The mayfly species displayed a univoltine life history with adult emergence peaking in August. Productivity in Blackwater Creek was estimated at 4.688 g per m 2 and in Rock Springs Run at 3.123 g per m 2 . Productivity/biomass ratios were estimated at 4.09 and 4.59 in Blackwater Creek and Rock Springs Run, respectively. The nymphal densities in both streams were positively correlated with water pH and negatively correlated with water volume. Apparently, water volume was the overriding abiotic factor in both streams, influencing several measured water parameters and as well as nymphal populations during the study period.

PREDATION BY BLUEGILL (LEPOMIS MACROCHIRUS) ON LARVAL CHIRONOMIDAE (DIPTERA) IN RELATION TO MIDGE STANDING CROP IN TWO CENTRAL FLORIDA LAKES

Large swarms of non-biting midges (Diptera: Chironomidae) emanating from some central Florida lakes can cause severe nuisance and economic problems for businesses, residents, and visitors within the dispersal range of these insects (Ali 1995). Midges are also a cause of allergies to humans (Cranston 1995). Because of these problems, a systematic research program on the bionomics and management possibilities of midge populations in central Florida has continued for the past two decades (Ali 1996). As a part of this program, a preliminary investigation of fish predation on chironomid midge larvae for the biological control perspective of midges was conducted. Midge predatory fish (bluegill,Lepomis macrochirus) were collected from two lakes on four occasions to elucidate any relationships between consumption of midge larvae by these fish and the associated larval composition and distributions in the lakes. Information concerning fish predation on midge larvae, species or habitat specific, would be useful in devising new control strategies. Fish were collected (May 1999, July, September and December 2000) from Lakes Dora and Yale (Lake County, Florida) by electrofishing under permit from Florida Fish and Wildlife Conservation Commission. Collections were made between 0830 and 1200 h and up to twenty fish were collected from near-shore areas. Fish were identified and killed immediately, maintained on ice while transported to the laboratory, and stored at -10?C until examined. For examination, each fish was thawed and the foregut was dissected (Bowen 1996), and the contents transferred to 4-dram vials containing 70% ethanol. Gut contents were examined under variable magnification of a dissecting microscope and enumerated. Chironomidae head capsules and associated fragments were wet mounted on slides and examined at 400x magnification using a phase-contrast microscope and identified to lowest possible taxonomic level using the keys of Epler (1995). Only head capsules with sufficient morphological features remaining for identification were counted for gut content enumeration, other fragments were used to improve identification where possible. Five to 20 fish were successfully collected per sampling occasion (Table 1). Midge larvae of the tribe Tanytarsini (>90% Cladotanytarsus spp.) were most numerous in gut contents of fish from both lakes (Table 1), comprising 55.9-62.8% of total consumed midge larvae from Lake Dora and 4.8-48.1% from Lake Yale. Geoldichironomus spp. larvae were the next most common in the gut contents of fish from Lake Dora (0.0-27.5% of total larval chironomids). Other midge larvae consumed by fish from Lake Dora included Chironomus crassicaudatus, Glyptotend ipes paripes, Cryptochironomus spp., Pseudochironomus spp. and Tanypodinae. Seasonal mean number of total midge larvae in fish gut contents ranged from 4.7 to 44.0. Midge larvae were present in the gut contents of all fish from Lake Dora, except those collected in December 2000, when 40% of collected fish had empty guts. This was likely due to low water temperatures reducing feeding activity, as suggested for bluegill during winter months by Gilinsky (1984). Pseudochironomus spp. larvae were the second most prevalent midge larvae in the fish gut contents of Lake Yale, forming up to 46.2% of total midge larvae, followed by C. crassicaudatus (collected only during May 1999), G. paripes, Cryptochironomus spp., and Tanypodinae. Seasonal mean number of larvae per fish in Lake Yale ranged between 1.0 and 18.9. Bluegill feeding on midge larvae in Lake Yale was also reduced during December 2000, though only one fish had an empty gut. Other food items identified from fish in these two lakes included immature Insecta (Odonata, Ephemeroptera and Trichoptera), Crustacea (Decapoda, Amphipoda and Ostracoda), Nematoda, Oligochaeta, Gastropoda, and some unidentifiable material. These food items numerically were only a small part of total gut contents in most fish examined (data not shown). To estimate relative selective feeding by bluegill on examined chironomid larvae, percent composition of chironomid larvae in gut contents of collected fish was compared to overall percent composition of chironomid larvae in study lakes and percent composition of midge larvae in the nearshore areas with firm sediments representative of the areas from where the fish were caught, collected concurrently and reported by Lobinske (2001) (Fig. 1). In Lake Dora, Tanytarsini were most common, exhibiting similar percent compositions in fish gut contents in the entire lake as well as in nearshore areas. During July, Septem-