Midge Density Research Articles

Macroinvertebrates of a California seasonal wetland and responses to experimental habitat manipulation

Responses of macroinvertebrate populations to temporal change and to management of plant cover and water depth were examined in 12 experimental ponds designed to mimic seasonally flooded (early autumn to early spring) wetlands in Suisun Marsh, California. Ponds were flooded in September 1988. Initially, rat-tailed maggots (Eristalis tenax), brine fly larvae (Ephydra millbrae), and mosquito larvae (Culex tarsalis) were numerically dominant components of the fauna in the ponds, but these populations did not persist beyond December. Water boatmen (Trichocorixa verticalis), midge larvae (Cricotopus sylvestris andChironomus stigmaterus), and hydrophilid beetle larvae (Berosus ingeminatus) were numerically dominant components of the fauna in both autumn and winter, but water boatmen and midge densities declined by March. Amphipods (Eogammarus confervicolus) and three-spined stickleback (Gasterosteus aculeatus) were introduced during initial floodings in September, and they subsequently increased to become numerically dominant components of the pond fauna by February and March 1989. Higher numbers of adult water boatmen and hydrophilid beetles colonized habitats that had 50% of the plant cover removed by mowing than habitats that had not been mowed (100% plant cover). Since mowing also reduced numbers of mosquito larvae, this approach may benefit waterfowl management and reduce public health concerns.

Shifts in the Effects of Tuft-weaving Midges on Filamentous Algae

-During summer low-flow periods massive growths of filamentous green algae (dominated by Cladophora glomerata) in the Eel River of Northern California become infested with chironomid larvae that weave the algae into retreats, or Field experiments suggest that these midges (primarily Pseudochironomus richardsoni) have negative early effects, and positive later effects on the biomass of algae they inhabit. During initial colonization and tuft construction by midges, weight loss of Cladophora and associated epiphytes in stream enclosures increased with increasing midge densities. In an in situ incubation experiment, chlorophyll a content and final damp weight of Cladophora and epiphytes were higher with old, feces-filled tufts, or with nitrate fertilizer, and were lower in controls or with new midge tufts. These results suggest that tuft-weaving midges have complex effects on algae they inhabit that change with the ontogeny of midges and the age of the retreats they construct.

Grain Sorghum Resistance to Midge by Yield Loss vs. Visual Scores

Biology of the sorghum midge, Contarinia sorghicolà (Coquillett), necessitates testing of sorghum, Sorghum bicolor (L.) Moench, cultivars in field plots in multiple locations and/or years to identify resistant genotypes. Using converted exotic sorghum cultivars, this study was conducted to compare visual damage scores across locations and years vs. indirect resistance measurements (percentage yield loss and number of midge per panicle) in a single location and year with two planting dates. Visual damage ratings were made at physiological maturity on the percentage of blasted kernels per panicle in replicated, randomized‐complete‐block field experiments at three locations in 1983 through 1985. In 1985, indirect measurements and visual damage ratings were made at one location. A significant positive relationship was found between visual midge damage rating and percentage yield loss (r = 0.347), and between visual midge damage rating and midge number (r = 0.220). Percentage yield loss did not increase the reliability of identification of resistant cultivars. Cultivars identified with resistance by both methods were IS8232C, IS8237C, IS8112C, IS2740C, IS3390C, IS7132C, IS2685C, IS957C, IS7193C, IS2144C, and IS12572C. The correlation between percentage yield loss and midge number (r = 0.090) was nonsignificant. Both methods depend on high midge density to differentiate resistant and susceptible genotypes. When midge were not abundant good differentiation was not obtained. Indirect resistance measurements were more time consuming than a single visual rating at maturity, and when multiple years or locations were required, the visual damage rating was a more effective method of germplasm evaluation.

EVALUATION OF SURVEY METHODS FOR ESTIMATING SORGHUM MIDGE (DIPTERA: CECIDOMYIIDAE) DENSITIES IN GRAIN SORGHUM

Six methods for sampling field populations of ovipositing sorghum midge, Contarinia sorghicola, in grain sorghum panicles were compared to an absolute sampling method. The methods evaluated were the visual, tap, remove, shake, beat-bucket, and grab. Population estimates obtained by visual examination were similar to absolute estimates when population density was low but significantly differed at mean midge densities above 9.2/panicle. The remaining sampling method density estimates were significantly less than the absolute method estimates. The visual examination method was relatively time efficient taking ca. one minute per panicle to complete. The effect of panicle compactness (open, medium, and compact) on the precision of the visual examination was investigated. Accuracy of the visual examination method significantly decreased as panicle compactness increased. This may be a result of either obstructed vision or increased density of midges with compactness or a combination of both.

Suppression of Sorghum Midge, 1988

Abstract Two organophosphate and 2 pyrethroid insecticides were evaluated for sorghum midge control at the Texas Agricultural Experiment Station Research Farm near College Station. Grain sorghum was planted 5 May on rows spaced 40 inches apart. Sixteen rows of mixed hybrid sorghum of varying maturity ranges were planted 2 wk before adjacent to the test plots to increase sorghum midge abundance within the test plots during the flowering period. Treatments were compared in 8-row by 75-ft-long plots arranged in a randomized complete block design with 4 replicates. Applications were made with a self-propelled, high-clearance sprayer to all rows using TX-6 hollow-cone nozzles at 40 psi with a spray volume of 8 gal/acre. Insecticide applications were begun when 20-25% of the panicles were flowering. Treatments were applied 2, 6, and 10 Jul. Because of a rainfall that occurred 10 Jul during the spray operations the last application of Dyfonate was made 11 Jul. Karate plots received only 2 applications, on 2 and 6 Jul. Rainfall of 0.90, 0.45, and 1.33 inches occurred 4, 10, and 12 Jul, respectively, and may have influenced the outcome of the study. Data on ovipositing adult midge density, kernel damage, and grain yield were collected from the middle 6 rows of each plot. Adult sorghum midge abundance was determined just prior to each application and consisted of enclosing 10 individual sorghum panicles/plot with clear plastic bags. Panicles were subseqeuntly excised and returned to the laboratory for examination and counting of adult midges. Visual estimates of the percentage of midge damage were made by 4 independent observers on 8 Aug, with each observer estimating the percentage damage to 5 panicles/plot. Panicles were hand-harvested from 2 randomly selected 13-ft sections of row/plot and mechanically threshed.

Insecticides for Suppression of Sorghum Midge on Dryland Grain Sorghum, 1987

Abstract Grain sorghum (1.8 acres) was planted 19 May on rows spaced 40 inches apart. Twelve rows of mixed-hybrid sorghums of varying maturity ranges were planted prior to and adjacent to the test plot to increase abundance of sorghum midge during anthesis of sorghum panicles in the test plots. Five insecticide treatments and an untreated check were compared in a randomized block design with 4 replications. Experimental plots were 8 rows wide and 80 ft long. Applications were made to the middle 6 rows with a high-clearance self-propelled sprayer. Insecticide applications began when 30-40% of the panicles were flowering and when average adult midge density was 0.7 midges/panicle. Treatments were applied 24 and 30 Jul and 4 Aug. Adult midge density was determined 1 day prior to application of insecticide treatments. Sampling consisted of securing and collecting individual sorghum panicles in plastic bags. Samples were examined in the laboratory and midges were counted. Prior to the first insecticide application, midge density was determined from sampling 25 randomly selected panicles/replication. On the 2 subsequent sampling days, 5 panicles were sampled from each treatment plot. Visual estimates of the percentage of midge-damaged spikelets were made by 4 independent observers, with each observer rating 10 randomly selected panicles/plot. Panicles were hand harvested from 2, 2-m sections of treated row/plot. The harvested sorghum panicles were threshed, and the grain was weighed. Data were analyzed by conventional analysis of variance and multiple comparison procedures.

Survey of 13 Polk County, Florida Lakes for Mosquito (Diptera: Culicidae) and Midge (Diptera: Chironomidae) Production

A survey was conducted at 30 sites in 13 lakes in Polk County, Florida to: (1) determine the extent of mosquito and midge production in the lake sites, (2) define more precisely some of the environmental factors that influence mosquito and midge densities, and (3) determine if the physical appearance of a site would enable accurate estimates of the mosquito and midge production potential. Although the emphasis of this survey was on Coquillettidia perturbans (Walker), data were collected on the mosquitoes Anopheles, Culex, Mansonia, and Uranotaenia and the chironomid midge Glyptotendipes paripes Edwards. Results of previous studies in marshes indicate that higher numbers of Coquillettidia larvae are found in sites with (1) dense stands of emergent vegetation, (2) substrates characterized by a thick layer of detritus, (3) water depths less than 1 m, and (4) dense stands of shoreline vegetation. Production in sites with these characteristics was found to be greater than previously realized. Estimates of Coquillettidia production made at the beginning of the study were found to be correct in 20 of the 30 instances. Production potentials that were over- or under-estimated were due primarily to changes in trap locations (due to fluctuating water levels) in which dramatic changes in habitat conditions occurred. It appears that, with only cursory observation, an accurate estimate of a site's potential for mosquito and midge production can be made.

Chemical Control of Sorghum Midge on Grain Sorghum, 1986

Abstract 2.2 acres of grain sorghum were planted 15 May on rows spaced 40 inches apart. Twelve rows of mixed hybrid sorghums of varying maturity ranges were planted prior and adjacent to the test plot site to increase midge populations. Nine insecticide treatments and an untreated check were compared in a randomized block design with 4 replications. Experimental plots were 8 rows wide and 45 ft long, but only the middle 4 rows were sprayed. Applications were made with a high-clearance, self-propelled sprayer using TX-3 hollow cone nozzles and calibrated to deliver 5.9 GPA at 42 psi and 3 mph. Insecticide applications began when 30-40% of the panicles were flowering and when average adult midge density was 2.5 midges/panicle. Treatments were applied 11, 15 and 19 Jul. The first application was made under slightly adverse wind conditions (10-15 mph gusts). Adult midge density was determined 1 day prior to application of insecticide treatments. Sampling consisted of securing and collecting individual sorghum panicles in plastic bags. Samples were examined in the laboratory and midges were counted. Prior to the first insecticide application, midge density was determined from sampling 25 randomly selected panicles per replication. On the 2 subsequent sampling days, 5 panicles were sampled from each treatment plot. Visual estimates of percent midge damaged spikelets were made by 6 independent observers, with each observer rating 10 randomly selected panicles/plot. Panicles were hand harvested from one 20-ft section of treated row per plot. The harvested sorghum panicles were threshed and the grain was weighed. Data were analyzed by conventional analysis of variance and multiple comparison procedures.

Sorghum Midge (Diptera: Cecidomyiidae) Management with Resistant Sorghum and Insecticide

Field evaluations were conducted in 1982 and 1984 to compare the efficacy of diazinon for control of sorghum midge, Contarinia Sorghicola (Coquillett), infesting resistant and susceptible sorghum hybrids. In 1982, diazinon application resulted in significantly higher yields of the resistant hybrid than the susceptible hybrid when the same treatments were made and midge density was high (ca. 50 per panicle). Highest yields of the resistant hybrid occurred when plants were treated five times at 3-day intervals, but greatest economic returns were obtained when plants were treated three times at 5-day intervals. Even when untreated, the resistant hybrid produced higher net returns than the susceptible hybrid following any of the diazinon treatments. Although percent yield improvement of treated sorghum was higher for the susceptible hybrid than the resistant, the susceptible hybrid yielded only as much as the untreated resistant hybrid, and only ca. 50% as much as the treated resistant hybrid. When midge densities were low, but above the economic injury level, yields of the resistent hybrid were about equal whether treated or untreated with insecticide. The susceptible hybrid yielded 50% as much as the untreated resistant hybrid and 25–50% less when both hybrids were treated the same. When variable diazinon applications were based on percent panicle flower, and when midge density was high, the resistant hybrid responded more efficiently to the diazinon treatments in terms of yield and net value compared with the susceptible hybrid.

Adult Sorghum Midge (Diptera: Cecidomyiidae) Nonpreference for a Resistant Hybrid Sorghum

Adult density and oviposition of sorghum midge, Contarinia sorghieola (Coquillett), on a resistant and susceptible sorghum, Sorghum bicolor (L.) Moench hybrid, were assessed under field conditions at College Station, Tex., during 1983 and 1984. Approximately 33% more female midges visited flowering panicles of a susceptible hybrid than those of a resistant hybrid. Moreover, ca. 25% more female midges were collected on flowering panicles of either hybrid that had not previously been infested with midges compared with panicles that had already been exposed to midges. Number of eggs laid in spikelets by 20 caged females per panicle, or by naturally occurring females in the field, was from 4- to 5-fold greater for midges infesting a susceptible than a resistant hybrid. Differences in number of eggs and egg-infested spikelets of the two hybrids were consistent in a free-choice or no-choice situation. These results indicated that nonpreference for oviposition was much more important than nonpreference for adult visitation as a component of nonpreference resistance of the agronomically improved sorghum hybrid AT×2755 × T×2767.

Chemical Control of Sorghum Midge On Sorghum, 1985

Abstract Sorghum was planted 6 May on rows spaced 40 inches apart. A mixture of sorghum hybrids with different maturity ranges was used to increase and maintain midge density. Twelve rows of the mixed hybrids were planted on 2 Apr; 4 rows on each side of the experimental plot area and 4 rows through the middle of the test area. Plots were arranged in a randomized complete block design and treatments replicated 4 times. Treatment plots were 10 rows wide and 80 ft long with a 4-ft alley between blocks. Plots were bordered in front and back by a 40-ft untreated buffer area. The inner 6 rows of each plot were treated with a high-clearance self-propelled sprayer calibrated to deliver 4 gal of solution per acre through two TX-3 hollow cone nozzles per row at 42 psi and 4 mph Applications were begun on 4 Jul when approximately 20% of the panicles were flowering. Three applications of each insecticide were made at 5 day intervals. The sorghum received 0.1 inch of rain immediately following the first application. Counts of adult midge density levels were made the day before each treatment. Adult midge density was determined by securing a plastic bag around individual panicles, clipping the panicles, and examining them in the laboratory for midges. Midge density prior to treatment was based on midge numbers on 25 panicles per replication. Midge density for the remaining 2 applications was based on adults per 5 panicles per plot.

Effects of Resistant Sorghum Hybrids on Sorghum Midge (Diptera: Cecidomyiidae) Biology

Fewer ovipositing female sorghum midges, Contarinia sorghicola (Coquillett), were found on flowering panicles of two resistant grain sorghum hybrids, ATx2755 x RTx2767 and ATx2761 x RTx2767, than on susceptible hybrids, ATx2752 x RTx430 and ATx3042 x RTx2737, on a few occasions during the 1981 growing season. However, these differences in adult abundance occurred erratically and did not follow any apparant pattern. It was doubtful that the resistance of these hybrids could be attributed to an effect on the number of ovipositing midges. Determination of the number of progeny produced per female that oviposited in panicle spikelets of susceptible and resistant hybrids was complicated by competition between midges at high population densities. An interference index was used to compensate for this competition. Midges infesting resistant hybrids produced 50 to 60% fewer progeny per female than midges infesting susceptible hybrids, regardless of midge density. This percentage of reduction became ineffectual in preventing economic damage to resistant hybrids as midge densities reached high levels. There was a slight, but nonsignificant, increase in the developmental time of midges infesting resistant sorghum hybrids. These results suggest that the effects of midge resistant sorghums would be cumulative in reducing midge density through time.

Seasonal responses of lentic midge assemblages to environmental gradients

We examined biotic and abiotic factors associated with density and diversity of larval midges (Diptera: Chironomidae) in the littoral zone of Par Pond, an 1100 ha cooling reservoir located near Aiken, South Carolina, USA. A total of 144 core samples were removed from 12 areas during each of 3 sample periods. Principal component analysis. Mantel analysis, and various univariate statistical tests were used to detect seasonal differences in (1) associations among areas and genera of Chironomidae, and (2) responses of midges to a multi‐faceted environmental gradient. Water temperature, which in this case was a function of both season and thermal effluents, was the factor most strongly associated with relative changes in density and diversity within the chironomid assemblages. Plant biomass and/or plant diversity were significant factors correlated with midge density and diversity. Both particle size and organic content of the substratum, which varied little across stations, were relatively unimportant factors. Despite the presence of a multifaceted environmental gradient, the composition and relationships within the midge assemblages were remarkably similar across areas although total abundance and diversity varied.On the basis of their similarity in structure and function, we classify the midge assemblages within the reservoir as members of the same community. However, in response to dissimilar or unequal selective forces (principally the area‐specific effects of thermal effluents), these assemblages appear to behave environmentally as multiple units rather than as a single component of the benthic community in Par Pond.

Factors Affecting Chironomid Larval Abundances in Three Vertical Aquatic Weed Habitats

Multivariate analyses are used to separate chironomid larval habitats, describe relationships between midge larval populations, and evaluate influences of biotic and abiotic variables on abundances in a lake system. Insect predators of 5 types of chironomid larvae had only a minor to moderate influence on midge densities in all habitats examined. Availability of aquatic weed did not have a major influence on abundance of larval midges. Water quality had greater influence in midwater and bottom habitats than in the surface.

Chironomid Larval Density at Various Depths in a Southern California Water-Percolation Reservoir 1

In a southern California reservoir, benthic larval density of chironomid midges was assessed 10 times between Aug. 1974 and July 1975, at >1 m, 3–4 m, and 6–8 m water depths. Larvae belonging to 9 midge genera were taken. Tanytarsus spp., Chironomus spp., and Procladius spp. were predominant, forming more than 85% of the total chironomid larvae recovered on any sampling occasion from the entire basin. The monthly qualitative composition of midge fauna differed slightly between the 3 depth levels, but the quantitative composition changed markedly from one level to the next. Midge density was consistently higher in the >1 m deep areas than in the 3–4 m and the 6–8 m deep levels. Tanytarsus spp. were predominant at the >1 m depths. Chironomus spp. and Procladius spp. were more prevalent in the other 2 deeper regions.

Removal of Substrate for the Control of Chironomid Midges in Concrete-lined Flood Control Channels 1

The effectiveness of mechanical removal of substrates for the control of benthic chironomid midge populations in a concrete-lined flood control channel system (draining domestic and industrial waste water and storm water) was studied. Substrates from a 0.80 km long section of one of the channels were mechanically removed. Fine sand and detritus were the 2 predominant types of substrates in the area cleared. Preand post-removal benthic samples were taken at 3 sites in the area cleared of substrates. One site, serving as check, was located upstream in the uncleared area. Midge larvae and pupae belonging to 5 genera were taken. In pre-removal samples taken from the area cleared of substrates, larvae of Cricotopus spp. and Dicrotendipes sp. predominated and formed 89.1% of the total midge fauna. Pupae constituted 10.1% of the total immature midges. The average midge density in the area cleared of substrates was 1303/0.09 m2 prior to the removal of substrates. Samples collected 3 days after removal showed a reduction of 87.0% in the total midge fauna. Satisfactory midge control lasted for 2 weeks. Benthic midge populations recovered completely after 4 weeks.

The spatial Distribution of Culicoides impunctatus Goet. under woodland and moorland Conditions and its Flight Range through Woodland

Weekly observations on two populations of Culicoides impunctatus Goet. were made in 1948 at Bannachra and Wester Bannachra, near Loch Lomond, throughout the whole of the C. impunctatus season by means of “ sticky ” traps. Each site had an area of 5 acres of which half was composed of woodland and half of moorland. Twenty-two catching stations, each consisting of three traps placed 2 ft., 6 ft., and 10 ft. above the ground were erected on each site, equal numbers being placed in the woodland and moorland. There were therefore 132 traps to be changed weekly and a total of 67,033 Culicoides were trapped of which 65,576 (97·9 per cent.) were C. impunctatus. In 1949 observations were repeated only in Bannachra woodland.The results have been analysed in the light of two alternatives (1) that C. impunctatus is a single biological entity and (2) that C. impunctatus is composed of two biological races.When the seasonal effect was eliminated the stations showed very real differences between their weekly catches. Some stations recorded a large catch every week whilst others always recorded low catches. The total seasonal catch at each station was plotted on plans of the two sites and it then became apparent that there were two centres of high C. impunctatus density at Bannachra, one in the woodland and the other on the moorland, whilst at Wester Bannachra there were two foci in the woodland and a very diffuse zone of high midge density on the moorland. It has been shown that the centre of high midge density in Bannachra woodland was associated with a concentrated breeding place which supplied all the adults for the woodland (2½ acres) and moreover this centre remained unaltered in 1949. The importance of these observations on the control of C. impunctatus is discussed.After the breeding place in Bannachra woods was discovered it became clear that the majority of adult C. impunctatus moved in an eastward direction from the breeding place and very few went westwards. This was attributed to the influence of the prevailing SW. wind. Knowing the centre of breeding in Bannachra woods it was possible to calculate the regression of the midge density on the distance from the breeding site. It was found that there was a linear relationship between the logarithm of the catch and the distance from the breeding site. A useful statistic is the reciprocal of the regression which may be designated as the density coefficient. It is the distance at which the density has decreased to l/10th of its initial value. The density coefficients for male and female C. impunctatus are 62·5 yards and 64·9 yards respectively. An attempt has been made to separate the effects of “ dilution ” and “ mortality ” on the density of C. impunctatus.The mortality of male and female C. impunctatus is shown to be normally distributed with respect to the logarithm of the distance flown. These distributions are male l·867±0·197 (=73·6 yds. ; 46·8–115·9 yds.) and female 1 ·885±0·197 (=76·7 yds. ; 48·8–120·8 yds.).From the density/distance formula the average distances flown by male and female C. impunctatus have been calculated. They are 79·0 yards (males) and 81·4 yards (females).The analysis of the vertical distribution of C, impunctatus revealed that each station had its own definite pattern. The stations sited amidst the birch saplings showed very real differences between themselves which were not related to the ground flora. It is suggested that these are related to the height of the leaf canopy. Evidence was also produced which pointed to the fact that in the oak wood where the base of the leaf canopy was about 20 ft. from the ground, C. impunctatus had a self-imposed “ ceiling ” of little more than 10 ft.The ground flora was found to have an appreciable effect upon the vertical distribution of C. impunctatus on the moorland. Thus where the ground flora provided only very shallow shelter, i.e., about 6 ins. in depth, equal numbers of adults were captured at each height, but when the stations were sited amongst Juncus sp. or in small sheltered clearings in the herb layer then more adults were caught on the 2-ft. trap. However, the shelter provided by bracken Pteridium aquilinum appeared to be less attractive and there were fewer adults caught on the 2-ft. traps at stations sited in dense bracken than at other moorland stations.In the woodland the females were slightly more abundant on the 2-ft. trap and the males more numerous on the 10-ft. trap but the differences in distribution, although significant, were small. On the moorland the males were more abundant at 2 ft. and the females at 6 ft.Although the general pattern was very similar there were highly significant differences between the horizontal and vertical distributions of the two races of C. impunctatus.