Midge Abundance Research Articles

Midges as quantitative temperature indicator species: Lessons for palaeoecology

Calibration data sets give a unique opportunity to establish patterns of biological existence and their statistical associations with environmental variables. By use of calibration data sets, environmental variables can be inferred quantitatively. The resulting long time-series may assist in distinguishing natural environmental variability from human-induced variability, both in terms of climate change and biotic turnover. However, the validity of the palaeoenvironmental reconstructions depends on their accuracy, precision and sensibility. Before performing palaeoenvironmental inferences, key mechanisms controlling contemporary species’ distribution, abundances and dynamics should be identified and understood. An inference model is developed to produce reconstructions. A major challenge lies in validating and interpreting the reconstructions. Calibration data sets involving midges (Diptera: Chironomidae) suggest that climate has a broad-scale, regional control over midge existence and abundance, often over-riding the influence of local within-lake variables. In recent years, the use of midges as quantitative indicators of past temperatures has greatly expanded. As the number of reconstructions increase, especially in Fennoscandia and North America, it seems the among-site variability is so large that it is unlikely to be due only to local differences in climate. Hence, we question whether the long climate gradients in calibration data sets can accurately be used to calibrate local variables, when most local gradients in time and space are short. Ten Holocene chironomid-inferred temperature curves from Fennoscandia are compared. We illustrate some general principles in palaeoecology by identifying factors that may cause bias. Especially, we consider how calibration data sets simplify the complexity of the real world by maximizing single ecological gradients and by not taking into account co-varying variables. We give some recommendations and criteria that chironomid analysis should meet in order to improve the reliability of the temperature inferences. Finally, we discuss how the complex interactions between species and environment may have implications when we aim at predicting future biodiversity.

Hydrological change in lakes inferred from midge assemblages through use of an intralake calibration set

Midge (Insecta: Diptera: Nematocera) assemblages were examined in surface sediment samples from Lake Pieni‐Kauro and the Saavanjoki River, eastern Finland, using their sedimentary remains. The aim was first to identify the forcing factors behind midge distribution within an aquatic ecosystem and second to develop new midge‐based calibration models for the reconstruction of past environmental conditions, with a special focus on paleohydrology. The third objective was to apply the models to a midge stratigraphy. The effect of sampling‐point selection in paleolimnological studies and its possible influence on chironomid‐inferred temperature reconstructions was also assessed. The species assemblages in Lake Pieni‐Kauro showed high levels of heterogeneity within the surface sediment samples, signifying that the assemblages predominantly incorporate locally dwelling fauna, instead of integrating remains from a larger area. Stream flow and water depth were the most important factors explaining the midge distributions in the lake. In addition, sampling distance from littoral vegetation (DLV), proximity of wetland, distance from shore, and organic content of the sediment were significantly correlated statistically with the midge assemblages. In the lacustrine samples, absolute midge abundance and taxon richness were highest at intermediate water depths. Because hydrological variables were the most important factors controlling the species' distributions, paleohydrological calibration models for water depth and stream flow were developed. Additionally, a transfer function for the sampling DLV was developed that can be used to track changes in the past location of littoral vegetation stands, which is often closely related to hydrological factors. The models' test use on the subfossil midge assemblages of the previously available downcore sediment sequence showed coherent and expected results, compared with previous studies and the modern observed environmental conditions of the lake. Based on the results of this study, these models can provide reliable estimates of past hydrological variability that is closely related to climatic changes and thus may provide a valuable tool for environmental management and global change assessments. This study also indicates that care should be taken in choosing the sampling point in chironomid‐based calibration studies because the influence of depth may distort the temperature estimations.

Does weather affect biting fly abundance in avian nests?

Environmental factors may strongly affect avian‐biting fly interactions in different ways because insects are heterothermic organisms that depend greatly on environmental variables to activate their metabolism and behaviour. We studied the effects of weather on both blackfly (Simuliidae) and biting midgeCulicoides(Ceratopogonidae) abundance in nests of three passerine species: blue titsCyanistes caeruleus, great titsParus majorand pied flycatchersFicedula hypoleuca,breeding in the same area. We controlled for different host‐related factors (hatching date, brood size and host species). Blackfly abundance was negatively related to minimum temperature. In addition, blackfly and biting midge abundances were negatively affected by wind speed measured at 07.00 h, but blackfly abundance was positively associated to wind speed at 18.00 h. We found higher blackfly and biting midge abundances in nests with larger broods breeding later in the season, and significantly higher biting midge abundance in pied flycatcher nests as compared to tit nests. These results represent, to our knowledge, the first report of both environmental and host‐related effects on haematophagous fly abundance in the nests of wild hole‐nesting birds.

Seasonal and diel patterns of biting midges (Ceratopogonidae) and mosquitoes (Culicidae) on the Parris Island Marine Corps Recruit Depot

The Marine Corps Recruit Depot on Parris Island, SC, is surrounded by tidal salt marshes, which are breeding habitats for many pestiferous biting flies. Knowledge of biting fly behavior patterns is needed to develop effective pest management strategies in urban areas adjacent to salt marshes. We measured biting midge (Ceratopogonidae) and mosquito (Culicidae) seasonal abundance and diel activity patterns on Parris Island using CO(2)-baited suction traps from November 2001 - November 2004. Of the three biting midge species collected, Culicoides furens was most abundant (86.2% of total) and was present in high numbers from late March to November. Culicoides hollensis (12.0% of total) was present during spring and fall but absent in summer and winter; and Culicoides melleus (1.7% of total) was present in spring through fall but absent in winter. Abundance of C. furens had a positive linear correlation with air temperature and rainfall. There were nonlinear correlations between air temperature and C. hollensis and C. melleus numbers, which were most abundant at moderate temperatures. Of 18 mosquito species collected, the most abundant were Aedes taeniorhynchus (42.7% of total), Aedes sollicitans (26.3% of total), Culex salinarius (15.6% of total), Culex quinquefasciatus (7.3% of total), and Aedes vexans (5.7% of total); other species comprised <5% of collections. Aedes taeniorhynchus numbers were positively correlated with temperature and rainfall, and Cx. salinarius was correlated with soil moisture. Activity of most biting midges and mosquitoes were highest the first two hours following sunset. Species of biting flies were present in all months, suggesting that year-round control measures are necessary to reduce exposure to potential disease vectors and nuisance biting.

Benthic Invertebrates and Periphyton in the Elwha River Basin: Current Conditions and Predicted Response to Dam Removal

The impending removal of two dams on the Elwha River in Washington State offers a unique opportunity to study ecosystem restoration at a watershed scale. We examine how periphyton and benthic invertebrate assemblages vary across regulated and unregulated sections of the Elwha River and across different habitat types, and establish baseline data for tracking future changes following dam removal. We collected multiple years of data on physical habitat, water chemistry, periphyton, and benthic invertebrates from 52 sites on the Elwha River and a reference section on the Quinault River, a neighboring basin. We found that substrate in regulated river sections was coarser and less heterogeneous in size than in unregulated sections, and summer water temperature and specific conductivity higher. Periphyton biomass was also consistently higher in regulated than unregulated sections. Benthic invertebrate assemblage structure at sites above both dams was distinct from sites between and below the dams, due in large part to dominance of mayfly taxa compared to higher relative abundance of midges and non-insect taxa at downstream sites. Following dam removal, we anticipate that both periphyton and benthic invertebrate abundance and diversity will temporarily decrease between and below dams as a result of sediment released from behind the reservoirs. Over the long-term, increased floodplain heterogeneity and recolonization by anadromous fish will alter benthic invertebrate and periphyton assemblages via increases in niche diversity and inputs of marine-derived nutrients. The extended timeline predicted for Elwha River recovery and the complexities of forecasting ecological response highlights the need for more long-term assessments of dam removal and river restoration practices.

Development of a pheromone trap monitoring system for orange wheat blossom midge, Sitodiplosis mosellana, in the UK

Field-trapping experiments with synthetic 2,7-nonadiyl dibutyrate, the female-produced sex pheromone of the orange wheat blossom midge, Sitodiplosis mosellana (Géhin), demonstrated that pheromone traps were highly attractive to males and caught very few non-target organisms. Different formulations of pheromone were tested to identify the optimum release rate and dispenser type for use in pheromone traps in the UK. Key findings were that racemic pheromone was as effective as enantiomerically pure (2S,7R)-2,7-nonadiyl dibutyrate, that release rates higher than 0.5 microg day(-1) were not necessary and that the optimal formulation was a 1 mg pheromone loading in a rubber septum. Pheromone traps gave a reliable indication of peak midge emergence, onset of flight and abundance of midges throughout the season. A strong correlation between maximum trap catch and crop infestation levels was obtained.

Spatial and temporal distribution of bluetongue and its Culicoides vectors in Bulgaria

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midges was carried out between 2001 and 2003, at 119 sites within a 50 x 50-km grid distributed across Bulgaria, using light trap collections around the time of peak adult midge abundance. Sentinel and ad hoc serum surveillance of hosts susceptible to bluetongue infection was carried out at around 300 sites between 1999 and 2003. Following the initial incursion of bluetongue virus 9 (BTV-9) into Bourgas province in 1999, affecting 85 villages along the southern border, a further 76 villages were affected along the western border in 2001, with outbreaks extending as far north as 43.6 degrees N. The BTV-9 strain in circulation was found to have a low pathogenicity for Bulgarian sheep populations, with less than 2% of susceptible individuals becoming sick and seroconversions detected up to 30 km from recorded outbreaks in the south. The major Old World vector Culicoides imicola Kieffer was not detected among over 70,000 Culicoides identified in summer collections, suggesting that BTV-9 transmission in Bulgaria was primarily carried out by indigenous European vectors. The most likely candidates, the Palaearctic species complexes - the Culicoides obsoletus Meigen and C. pulicaris L. complexes - were widespread and abundant across the whole country. The C. obsoletus complex represented 75% of all individuals trapped in summer and occurred in high catch sizes (up to 15,000 individuals per night) but was not found across all outbreak sites, indicating that both Palearctic complexes probably played a role in transmission. Within the C. pulicaris complex, only C. pulicaris s.s., C. punctatus Meigen and C. newsteadi Austen were sufficiently abundant and prevalent to have been widely involved in transmission, whilst within the C. obsoletus complex most trapped males were C. obsoletus s.s. Adult vectors were found to be largely absent from sites in west Bulgaria for a period of at least 3 months over winter, which, taken along with the spatiotemporal pattern of outbreaks in the region between years, indicates the virus may be overwintering here by an alternative mechanism - either by covert persistence in the vertebrate host or possibly by persistence in larval stages of the vector.

Abundance of Gall Midges on Poulsenia armata (Moraceae): Importance of Host Plant Size and Light Environment in Tropical Rain Forests1

ABSTRACTWe studied the effects of contrasting light environments on the relationship between the host plant size of Poulsenia armata and the abundance of two gall midges in a tropical rain forest in Veracruz, Mexico. The number and density of two gall morphs (i.e., laminar and vein‐petiole galls) were positively correlated with plant size only in trees found in the forest but not in gaps. The availability of foliar area of P. armata trees was greater in forest gaps than in the forest. The foliar area was positively correlated with the abundance of laminar galls in trees in forest sites, but not with vein‐petiole galls. We concluded that the abundance of two morphs of gall midges on P. armata was associated with host plant size only in the forest trees. Larger plants had more galls than small plants, although this relationship was affected by local light environments.

THE EFFECTIVENESS OF THE MOSQUITO MAGNET®TRAP FOR REDUCING BITING MIDGE (DIPTERA: CERATOPOGONIDAE) POPULATIONS IN COASTAL RESIDENTIAL BACKYARDS

This study evaluated the effectiveness of single Mosquito Magnet' traps to consistently reduce biting midge populations in a coastal northwest Florida residential neighborhood. Midge abundance from 5 backyards, each with a Mosquito Magnet trap, was compared with 3 backyards without traps (controls). Midge populations were sampled once weekly for 24 h in each backyard by using a Centers for Disease Control (CDC) suction trap baited with carbon dioxide. In addition, midge accumulations from Mosquito Magnet traps were collected once a week at the time of CDC trap operation while biting midge populations were manually sampled from each backyard by using a "sand fly bat" (i.e., a wire-handle flyswatter fitted with a 10.5-cm2 plastic 14 X 14 mesh screen). Eighteen midge species were collected during the study but the majority (99.9%) collected from all backyards were (in descending order): Culicoides mississippiensis, C. furens, and C. melleus. Midge populations from CDC traps in yards with Mosquito Magnets were significantly lower on 2 of 45 wk (March 28 and April 3) when compared with control backyards. Weekly reduction attributed to Mosquito Magnets was not consistent and ranged from 4.2 to 85.3%. No significant difference was found in mean midge abundance on sand fly bats from yards with Mosquito Magnets compared with control yards. On the average, cooperators with Mosquito Magnet traps reported that their seasonal level of midge reduction (as related to a monthly ranked degree of annoyance) was variable and often not consistently below their threshold.

Spatial distribution of Culicoides species in Portugal in relation to the transmission of African horse sickness and bluetongue viruses.

Surveillance of Culicoides (Diptera: Ceratopogonidae) biting midge vectors was carried out at 87 sites within a 50 x 50 km grid distributed across Portugal, using light trap collections at the time of peak midge abundance. Culicoides imicola (Kieffer) made up 66% of the 55 937 Culicoides in these summer collections. It was highly abundant in the central eastern portion of Portugal, between 37 degrees 5' N and 41 degrees 5' N, and in a band across to the Lisbon peninsula (at around 38 degrees 5' N). Of all the complexes, its distribution was most consistent with that of previous outbreaks of Culicoides-borne disease, suggesting that it may remain the major vector in Portugal. Its distribution was also broadly consistent with that predicted by a recent climate-driven model validating the use of remote sensing datasets for modelling of Culicoides distribution. Adult C. imicola were found to have overwintered at 12 of 20 sites re-surveyed in winter but it did so in very low numbers. Culicoides obsoletus (Meigen) and Culicoides pulicaris (Linnaeus) complex midges were widespread despite their low summer abundance. The observed coincidence of high abundances of C. imicola and high abundances of C. pulicaris in summer lead us to suggest that C. imicola could bring African horse sickness virus or bluetongue virus into contact with C. pulicaris and the latter complex, together with C. obsoletus, could then transmit these viruses across much wider areas of Europe. The fact that adult C. pulicaris are present in high abundances in winter may provide a mechanism by which these viruses can overwinter in these areas.

MACROINVERTEBRATE COMMUNITY STRUCTURE AS A PREDICTOR OF WATER DURATION IN WISCONSIN WETLANDS1

ABSTRACT: Fifty‐four Wisconsin wetlands were surveyed in spring 1996 to determine relationships between macroinvertebrate community structure and a suite of 11 environmental attributes. Canonical correspondence analysis (CCA) showed that, after alkalinity, hydroperiod was the next most significant environmental factor influencing macroinvertebrate community structure within the wetlands sampled. CCA and direct gradient biplots were used to identify indicator taxa characteristic of the spring macroinvertebrate communities in persistent and ephemeral wetlands, and taxa characteristic of semi‐terrestrial habitats adjacent to wetlands. Two models were developed to permit the prediction of a wetland's hydroperiod class. One model assigns a range of probabilities that a wetland has a hydroperiod longer or shorter than eight months based on the occurrence or abundance of fairy shrimp, mayflies, scuds, mosquitoes, and phantom midges. A second model predicts that a wetland's hydroperiod is longer or shorter than five months based on the joint occurrences of seven persistent indicator taxa. Data used in both models were derived from a rapid bioassessment of three shoreline D‐frame net sweeps. The use of a coarse level taxonomic identification (primarily order and family) allows the approach to be performed in the field or laboratory. The macroinvertebrate models allow a manager to estimate a wetland's hydroperiod when long term water duration records do not exist. This ability is important to water resource managers because hydroperiod classification (i.e., water permanency) is one criterion used in differentiating wetlands from lakes in Wisconsin and because Wisconsin's legal system affords lakes substantially greater protection than wetlands.

Abundance and seasonal trend of dominant Chironomid midges in the middle reach of the Chikuma River(&lt;Feature II&gt;Ecological disturbance caused by floods in the Chikuma River)

Abundance and seasonal trend of dominant Chironomid midges in the middle reach of the Chikuma River(&lt;Feature II&gt;Ecological disturbance caused by floods in the Chikuma River)

Seasonal abundance and survivorship of Culicoides sonorensis (Diptera: Ceratopogonidae) at a southern California dairy, with reference to potential bluetongue virus transmission and persistence.

Seasonal abundance and survivorship of Culicoides sonorensis Wirth & Jones were examined at a dairy in southern California from January 1995 to December 1997. Insects were collected one to two times per week using five CDC-type suction traps (without light) baited with CO2 at a constant release rate of 1,000 ml/min. Female and male abundance was greatest during late summer and early fall and was directly correlated with mean monthly air temperature. Parity of females was lowest during late summer and early fall. The gonotrophic cycle was estimated to require 3-4 during hot summer months and up to 14 d during cool winter months. Estimated extrinsic incubation of bluetongue virus (BLU) was 9-10 d during August and September. The estimated daily survival ranged from < 60% in the summer to > 95% in the winter, resulting in an expectation of life of only 2-3 d in summer and > 10 d in winter. The probability of females surviving the extrinsic incubation period for BLU virus, and the expectation of infective life were both lowest during late summer and early fall. During 1997, midge abundance during late summer was not high enough to overcome very low survivorship, and the absolute number of females expected to survive the extrinsic incubation period was relatively low. However, in 1995 and 1996, very high midge abundance compensated for low survivorship during summer and the number of females expected to survive the extrinsic incubation period was relatively high. Although abundance was generally very low during the cool winter and spring, host-seeking females were captured throughout the year, and their winter survival was high. Overwintering of BLU virus by continued transmission of the virus by active midges appears possible.

Distribution and seasonal occurrence of Forcipomyia taiwana (Diptera: Ceratopogonidae) in the Nantou area in Taiwan.

We studied the distribution of Forcipomyia taiwana (Shiraki) in Taiwan, and found this species almost island-wide. Midge seasonality was studied for 4 yr at 3 sites in Nantou, central Taiwan, to identify the extent and causes of midge population outbreaks. The midge population in 1995 was significantly lower than in 3 other years because several typhoons inundated breeding sites. Maximum populations of F. taiwana occurred in June, July, and August. There was a highly significant correlation between the monthly abundance of F. taiwana and temperature and rainfall. A step-up multiple regression indicated that temperature was the most important factor leading to the outbreaks of F. taiwana. Temperature increases from 15 degrees C to near 30 degrees C will increase the midge abundance.

Distribution and abundance of Chironomidae (Diptera, Insecta) in an impacted watershed in South-east Brazil

Patterns of abundance and distribution of chironomid midges (Diptera, Chironomidae) in the middle Rio Doce basin were analysed. Human activities (mining, steel processing, and Eucalyptus spp. forestry) contribute to environmental degradation and low water quality in this watershed. Physical and chemical water traits (dissolved oxygen, pH, total alkalinity, electric conductivity, phosphorus and nitrogen concentrations) of 20 sampling points were used in a Principal Component Analysis (PCA) to establish the best and worst water quality. Sampling points recorded as the most polluted showed low genus richness of Chironomidae, less than five genera from the total 23, and dominance of the genus Chironomus, a bioindicator of environmental stress. Following Chironomus, the second most frequent and abundant genus was Cricotopus, whose distribution could not be related to pollution levels. The Tanypodinae sub-family showed certain sensitivity to low dissolved oxygen concentrations and high nutrients levels, and was not found at points of high pollution levels.

Spikelet Flowering Time: Cause of Sorghum Resistance to Sorghum Midge (Diptera: Cecidomyiidae)

Resistance of sorghum, Sorghum bicolor (L.) Moench, to sorghum midge, Stenodiplosis sorghicola (Coquillett), has not been well understood. In this study, possible causes of resistance were examined by comparing time of oviposition with times spikelets of resistant and susceptible sorghums flowered and thus were vulnerable to damage. Spikelets of resistant genotypes began flowering during the night, at 0100 hours (CDT), and most were closed and no longer vulnerable by the time sorghum midges began to oviposit in the field at 0800 hours. Peak flowering of resistant sorghums was between 0300 and 0700 hours. Most spikelets of susceptible sorghums, however, were flowering after daylight, at 0800 hours, when sorghum midge abundance began to increase. At 1000 hours, the time most sorghum midges (2.5 per panicle) were in the field, percentages of spikelets penetrable by a pin the diameter of a sorghum midge ovipositor were 32 and 62% for resistant and susceptible sorghums, respectively. Damage to panicles of resistant sorghums averaged 29.6%, whereas susceptible sorghums were more than twice as damaged (68.2%). Delaying for 5 h the daily flowering period of a resistant hybrid to coincide with time of peak sorghum midge abundance in the field resulted in 3.2 times as many sorghum midges emerging and 2.2 times as much damage as to panicles of the resistant hybrid that flowered at the normal time. Damage and numbers of sorghum midges emerging were not significantly different between normal and changed panicles of a susceptible hybrid. Most spikelets of resistant sorghums flowered and closed early and thus evaded damage before ovipositing sorghum midges were in the field. These results support the hypothesis that resistance is caused by asynchrony between time of sorghum spikelet flowering and presence of sorghum midge.

TROPHIC INTERACTIONS AMONG DETRITUS, BENTHIC MIDGES, AND PREDATORY FISH IN A FRESHWATER MARSH

I conducted field experiments in a western New York marsh to quantify concurrently the impacts of resource limitation and predation on benthic midge populations (Chironomus plumosus, Chironomus tentans, and Glyptotendipes barbipes). Biomass of cattail litter (Typha sp.), numbers of small insectivorous fish (primarily juvenile carp, Cyprinus carpio, and to a lesser extent juvenile brown bullhead, Ictalurus nebulosus), or numbers of large fish (primarily adult brown bullhead, which will consume both midges and small fish) were manipulated in mesh-walled mesocosms (1.5 × 1.5 × 1.2 m). Using core sampling, midge population responses to manipulations were monitored from early May through late August. Trophic responses of marsh midges to resources and predation changed temporally over the summer. In June, neither resource limitation nor predation by fish significantly influenced midge numbers. In July, after juvenile carp and brown bullhead first became abundant from the spawn, these small insectivorous fish significantly reduced midge larval densities. At that time, midge densities still did not respond to variable detritus supplies. By August, both predation by small fish and available supplies of cattail litter significantly affected midge numbers. Because midges did not respond to a nonnutritive mimic of cattail litter, it suggests that resource limitation of midge abundance was nutritionally based. Feeding by large adult bullhead had no apparent direct or indirect influence on midge densities in any month. Small fish largely disappeared from the study habitats by August, but populations of midge larvae did not rebound because they had stopped breeding for that year. This study supports emerging concepts on the integrated influences of top-down and bottom-up trophic interaction on food web function. Predation and resource limitation were simultaneously influencing midge abundance. Results also emphasize how life history phenologies of predators and prey can contribute to temporal variation in food web structure and function.

The community dynamics of epiphytic midge larvae across the pelagic–littoral interface: do animals respond to changes in the abiotic environment?

In some littoral systems, abiotic heterogeneity results from the edge of vegetation towards the shore as macrophytes gradually impede mixing between pelagic and littoral water. During the summer of 1994, we investigated whether such abiotic heterogeneity influenced epiphytic midge larvae (Diptera:Chironomidae) inhabiting a stand of Scirpus americanus in Saginaw Bay, Lake Huron. After macrophytes became well established, gradients in six parameters of water quality (turbidity, alkalinity, pH, dissolved oxygen, conductivity, and chloride) formed horizontally from the macrophyte edge towards the shore. In outer portions of the stand where physico-chemical properties were influenced by the influx of pelagic surface waves, chironomid abundance increased to 1076 larvae · stem-1. Diversity (H prime ) in these areas remained constant over the summer with grazing and filter-feeding taxa equally represented. Further into the macrophyte bed where water quality indicated highly reduced mixing, midge abundance never exceeded 27 individuals · stem-1 and larval biomass was reduced 2-4 fold. Loss of filter-feeding taxa resulted in a dramatic decline in diversity in these areas after formation of the abiotic gradients. This study suggests that pelagic-littoral water exchange may result in environmental heterogeneity that directly or indirectly influences epiphytic invertebrate community structure and function.

Evaluation of Insecticides for Suppression of Sorghum Midge on Sorghum,1996

Abstract Selected insecticides were evaluated for sorghum midge control at the Texas Agricultural Experiment Station Research Farm near College Station, TX. Seed of hybrid sorghum (AT X 399 x RT X 430) was planted 29 May on rows spaced 30 in. apart. Insecticide treatments were compared in plots, 6 rows X 40 ft long, arranged in a RCB design with 4 replications. Insecticides were applied to the middle 2 rows of plots. Insecticides were applied between 0800 and 0900 h CDT by using a hand-held backpack sprayer with TX-3 hollow cone nozzles at 35 psi, producing a finished spray volume of 4.9 gpa. Insecticides first were applied 23 Jul when 10-50% of the panicles were flowering; insecticides then were applied 26 Jul when 90-100% of the panicles were flowering. Adult sorghum midge abundance was assessed just prior to each application by counting the number of sorghum midges enclosed in clear plastic bags on 10 individual sorghum pan-icles. The panicles were cut from the plant and returned to the laboratory for examination and sorghum midge counts. Grain yield data were collected from the 2 middle rows per plot. Panicles were hand harvested from 2 selected 8.75-ft sections of row/plot and mechanically threshed. Data were statistically analyzed by using ANOVA and LSD.

春期, 河口湖周辺域に大量飛来する"不快昆虫"としてのユスリカ成虫に関する研究

The species composition and abundance of the chironomid midges were investigated by using a board trap during the period from March to May 1994 at three different stations along the shoreline in the eastern part of Lake Kawaguchi. A total of 38,498 adult midges were collected, the great majority (98.4%) of which were Biwatendipes tsukubaensis Sasa et Ueno. This was followed by Glyptotendipes tokunagai Sasa, (1.1%) and then a very low representation of Chironomus yoshimatsui Martin et Sublette and C. plumosus Linnaeus (0.5%). The dominant species of chironomids which emerged from the littoral region of the lake, however, changed with the month. First, massive emergence of B. tsukubaensis began from mid-March to late April, and then G. tokunagai from late March to early May. From mid-April, C. yoshimatsui emerged and was followed by C. plumosus. Thus, the period in which the four main chironomid species continuously emerged was from mid-March to early May. Therefore, throughout the spring season people living around the lake have the strong impression that the nuisance of chironomid midges has continuously increased and that these are attracted to the light of hotels, houses and some buildings during the breeding season.