Emergence Trap Research Articles

Adaptations of an Emergence Trap for Use in Tropical Streams

AbstractAn emergence trap based on the MPI Schlitz model was designed for use in the tropics and it was tested over one year in Palawan, the Philippines. Instructions for construction and use are given here. Only commonly available materials were used, except for the collection assembly made of UV‐light permeable acrylic glass. Heavy and bulky assemblies were avoided to enable easy transportation in the field. A special modification allows a fast and easy replacement of the screen when damaged by flooding, as is often required when traps are used downstream of headwaters. This type of trap also allows sampling of a wide littoral strip. Problems concerning the use of emergence traps in the humid tropics are discussed based on experience at different longitudinal stream sections in Palawan. The results presented here suggest that this trap should be used especially for qualitative or semi‐quantitative approaches. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Composition and Longitudinal Patterns of Aquatic Insect Emergence in Small Rivers of Palawan Island, the Philippines

AbstractThis study presents the first emergence trap samples from streams in the Philippines and Greater Sunda. Aquatic insect emergence from two small rivers and longitudinal patterns including estuaries are compared. A decline of total emergence towards estuaries was observed, affecting all major orders. Diptera, namely Chironomidae, dominated all sites. High abundances in Ceratopogonidae, Odonata, and Coleoptera were found, compared to other emergence studies from tropical and temperate latitudes. Ephemeroptera displayed a highly variable contribution to the emergence from Palawan as well as in other comparative studies either supported by the appropriate conditions for certain functional groups or limited by environmental variables such as pH. Trichoptera are likely to tolerate a wider range of environmental conditions and they are consequently able to fill further niches where Ephemeroptera are under‐represented. Except for scarce abundances of Plecoptera observed in this and other studies from the tropics, no substantial differences in emergence composition at order level existed between temperate and tropical rivers, however, with a remarkable local variation. Components of riparian and non‐aquatic insects and non‐emergent fauna contributing to the collections are discussed based on trap features. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The impact of soil cultivation on arthropod (Coleoptera and Araneae) emergence on arable land

Summary Controversy exists over the impact of soil cultivation on soil macro-arthropods. Inappropriate sampling methodologies and experimental design have been partly responsible for the contradictory findings. In this study emergence trapping was utilized during 1998 from plots ploughed in winter, spring or left undisturbed in fields of wheat stubble or undersown grass leys. In 1999, emergence from winter-ploughed or undisturbed plots in fields of wheat stubble or undersown grass leys was compared, with and without frost protection. The catch was dominated by adult and larval Coleoptera, of which 68 and 77% were Carabidae in 1998 and 1999 respectively. In 1998 the period of peak emergence of Carabidae, Curculionidae and total Coleoptera were earlier from unploughed compared to ploughed treatments. None of the treatments influenced the time of arthropod emergence in 1999. In 1998 only Curculionidae were affected by ploughing, with more being captured from the winter-ploughed plots. In 1999 the emergence of six carabid species was lower from the ploughed plots, whereas Notiophilus biguttatus (Coleoptera: Carabidae) favoured the ploughed plots. Total Carabidae, other coleopteran adults and larvae and aranean groups were also lower in the ploughed plots. The provision of frost protection had no impact, but temperatures throughout the winter were relatively mild.

A quantitative field comparison of emergence traps with open and covered bottoms in a stream : general and Trichoptera

Two greenhouses were operated as emergence traps in a stream in southwestern Lower Austria from 1984 to 1989 at a distance of 28 m from each other. The stream bed under the traps was covered by a metal sheet alternately for one year, thus preventing emergence under the trap with covered bottom so that insects caught in this trap must have come from outside. The results have shown that insects from outside constitute a high but un quantifiable proportion of the total catch. In many instances there were more insects in the trap with a covered stream bed than in the open one. Therefore the emergence trap method is not adequate for quantitative surface-related studies, including secondary production.

HYDROLOGIC INFLUENCES ON INSECT EMERGENCE PRODUCTION FROM CENTRAL PLATTE RIVER WETLANDS

The physical template of freshwater ecosystems has a pervasive influence on biological communities and processes. To examine the influence of hydrology on wetland insect communities, we quantified insect emergence from five riparian sloughs in the central Platte River valley. Annual hydroperiods of the wetlands ranged from 94 to 365 d/yr, and frequency and magnitude of drying events were inversely proportional to hydroperiod length. Three emergence traps were placed in each wetland from April through November 1997. Most insects collected in traps were identified to genus, and individual dry mass (DM) also was determined. Abundance of emerging insects (24 124 individuals/m2) and emergence production (5.1 g DM·m−2·yr−1) were highest from the site with an intermediate hydroperiod of 296 d. Sites with longer and shorter hydroperiods had lower emergence abundance and production. Emergence production from the perennial site, which contained fish year-round, was only 0.26 g DM·m−2·yr−1. Diptera generally dominated emergence trap catches. Chironomidae, Culicidae, and Ceratopogonidae were among the dominant contributors to abundance, whereas Sciomyzidae and Muscidae were important contributors to biomass at most sites. Quadratic equations best described relationships between taxa richness and annual hydroperiod (r2 = 0.78, P < 0.05) or number of drying events/yr (r2 = 0.81, P < 0.05), reflecting a peak in richness at intermediate levels of both. These relationships followed predictions of the intermediate disturbance hypothesis, but specific mechanisms underlying patterns were difficult to discern. Like emergence production, taxa richness was also highest at intermediate hydroperiods. Hence, insect diversity (measured as richness) and emergence production were positively correlated (r2 = 0.85, P < 0.05). Results indicate that the hydrology of central Platte River wetlands exerts a strong influence on insect species richness and emergence production, and that intermittent sites harbor the highest insect diversity and produce more emergent insect biomass. However, trends in seasonal emergence patterns and taxonomic shifts across the hydrologic gradient in this study suggest that a landscape containing a mosaic of hydrologically distinct wetlands will maximize aquatic insect diversity and productivity at larger spatial and temporal scales.

Hydrologic Influences on Insect Emergence Production from Central Platte River Wetlands

The physical template of freshwater ecosystems has a pervasive influence on biological communities and processes. To examine the influence of hydrology on wetland insect communities, we quantified insect emergence from five riparian sloughs in the central Platte River valley. Annual hydroperiods of the wetlands ranged from 94 to 365 d/yr, and frequency and magnitude of drying events were inversely proportional to hydroperiod length. Three emergence traps were placed in each wetland from April through November 1997. Most insects collected in traps were identified to genus, and individual dry mass (DM) also was determined. Abundance of emerging insects (24 124 individuals/m2) and emergence production (5.1 g DM·m−2·yr−1) were highest from the site with an intermediate hydroperiod of 296 d. Sites with longer and shorter hydroperiods had lower emergence abundance and production. Emergence production from the perennial site, which contained fish year-round, was only 0.26 g DM·m−2·yr−1. Diptera generally dominated emergence trap catches. Chironomidae, Culicidae, and Ceratopogonidae were among the dominant contributors to abundance, whereas Sciomyzidae and Muscidae were important contributors to biomass at most sites. Quadratic equations best described relationships between taxa richness and annual hydroperiod (r2 = 0.78, P < 0.05) or number of drying events/yr (r2 = 0.81, P < 0.05), reflecting a peak in richness at intermediate levels of both. These relationships followed predictions of the intermediate disturbance hypothesis, but specific mechanisms underlying patterns were difficult to discern. Like emergence production, taxa richness was also highest at intermediate hydroperiods. Hence, insect diversity (measured as richness) and emergence production were positively correlated (r2 = 0.85, P < 0.05). Results indicate that the hydrology of central Platte River wetlands exerts a strong influence on insect species richness and emergence production, and that intermittent sites harbor the highest insect diversity and produce more emergent insect biomass. However, trends in seasonal emergence patterns and taxonomic shifts across the hydrologic gradient in this study suggest that a landscape containing a mosaic of hydrologically distinct wetlands will maximize aquatic insect diversity and productivity at larger spatial and temporal scales.

Emergence trap developed to capture adult large pine weevil Hylobius abietis (Coleoptera: Curculionidae) and its parasite Bracon hylobii (Hymenoptera: Braconidae).

A novel type of emergence trap capable of capturing and separating 'live' insect catches is described. The trap was shown to be 96% efficient at capturing newly emergent adult Hylobius abietis Linnaeus on bare ground and at least 82% efficient over stumps on a weedy Sitka spruce clearfell. The trap was more than 80% efficient at capturing Bracon hylobii Ratzeburg, the most commonly found parasite of H. abietis. It was also shown to be effective at capturing adult H. abietis of unknown age (98%), indicating that it could also be used to trap out H. abietis from known areas to estimate on-site overwintering densities. Fifty-four percent of newly emergent weevils were captured within 12 h of release on bare mineral soils. Forty-two percent of unknown age weevils and 52% of parasites were captured within 1 h of their release within the trap. The rapid rates of capture mean that when traps are checked frequently they can be used to reflect accurately temporal patterns of emergence. Its potential for use in control programmes and ecological studies is discussed.

A soil emergence trap for collections of phlebotomine sand flies.

The identification of breeding sites of sand flies is of great epidemiological interest. A soil emergence trap for investigating potential sand fly breeding sites is described. The trap was tested in two rural areas in the Mogi Guaçu River Valley where the American cutaneous leishmaniasis is an endemic disease. Seventy-three sand fly individuals of three species, Lutzomyia intermedia s. l., L. whitmani and L. pessoai, were collected on the forest floor and peridomicile.

Emergence of Periodical Cicadas (Magicicada cassini) From a Kansas Riparian Forest: Densities, Biomass and Nitrogen Flux

The 1998 emergence of 17-y periodical cicadas (Magicicada cassini) on Konza Prairie Research Natural Area (KPRNA), Kansas, was quantified using emergence trap transects and counts of emergence holes. Emergence density, biomass (emergence production) and associated nitrogen flux were estimated for the entire 100 ha gallery forest of Kings Creek, the major drainage network on KPRNA. Emergence commenced on 22 May 1998 and lasted for 24 d, with 87% of the individuals emerging within the first 9 d. Males dominated early during the emergence, and the sex ratio for the entire population was estimated at 54:46 male:female. Average emergence abundance and biomass estimated from trap transects located in low areas where cicadas were most abundant were 152/m2 and 34.9 g ash-free dry mass (AFDM)/m2, respectively. Based on emergence hole counts, average density and biomass for the 59 ha of gallery forest where cicadas emerged were 27.2 individuals/m2 and 6.3 g AFDM/m2, and emergence hole densities >100/m2 were evident in low areas of the drainage. Emergence density generally decreased with increasing elevation in the catchment. Belowground to aboveground N flux associated with M. cassini emergence in high density areas was ∼3 g N/m2, and the average for the entire emergence area was 0.63 g N/m2. The total number of individuals that emerged from the Kings Creek riparian forest was estimated at 19.6 million, which represents 4.6 metric tons AFDM and ∼0.5 metric tons N. This linear, fragmented, gallery forest of the Flint Hills supports a high density of M. cassini, and an emergence event constitutes a significant belowground to aboveground flux of energy and nutrients. Thus, the periodical cicada may be an exception to the notion that insects generally do not represent important resource pools at the ecosystem level.

Emergence trapping of mosquitoes (Diptera: Culicidae) in brackish forest habitats in Maroochy Shire, south-east Queensland, Australia, and a management option for Verrallina funerea (Theobald) and Aedes procax (Skuse)

This study details the use of emergence traps with sticky adhesive to capture adult mosquitoes emerging from brackish water pools located in almost impenetrable swamp oak and tea-tree forests in Maroochy Shire, south-eastern Queensland. Twenty emergence traps were set weekly for 12 weeks between March and June 1998, during which time a total of 825 adult mosquitoes were collected. Aedes procax (Skuse) (55%) was the most abundant species, followed by Verrallina funerea (Theobald) (16%) and Culex halifaxii Theobald (9%). Emergence of Ve. funerea was greatest after tidal inundation of pools with brackish water, whereas Ae. procax emerged in greatest numbers following heavy rainfall. As there are significant areas of swamp oak and tea-tree forest in Maroochy Shire and an increasing pressure for urbanisation in adjacent areas, the aerial application of persistent S-methoprene formulations is considered the most appropriate option for control.

Feeding ecology and emergence production of annual cicadas (Homoptera: Cicadidae) in tallgrass prairie.

The emergence phenology and feeding ecology of annual cicadas in tallgrass prairie are poorly documented. However, these large insects are abundant, and their annual emergence represents a potentially important flux of energy and nutrients from belowground to aboveground. We conducted a study at Konza Prairie Research Natural Area in eastern Kansas to characterize and quantify cicada emergence and associated energy and nutrient fluxes. We established emergence trap transects in three habitat types (upland prairie, lowland prairie, and riparian forest), and collected cicadas every 3 days from May to September. A subset of trapped cicadas was used for species- and sex-specific mass, nutrient, and stable isotope analyses. Five species were trapped during the study, of which three were dominant. Cicadetta calliope and Tibicen aurifera exhibited significantly higher emergence production in upland prairie than in lowland prairie, and were not captured in forested sites at all. T. dorsata emerged from all three habitat types, and though not significant, showed a trend of greater abundance in lowland grasslands. Two less abundant species, T. pruinosa and T. lyricen, emerged exclusively from forested habitats. Nitrogen fluxes associated with total cicada emergence were estimated to be ∼4 kg N ha-1 year-1 in both grassland habitats, and 1.01 kg N ha-1 year-1 in forested sites. Results of stable isotope analyses showed clear patterns of resource partitioning among dominant cicada species emerging from grassland sites. T. aurifera and C. calliope had δ13C and δ15N signatures indicative of feeding on shallowly rooted C4 plants such as the warm-season grasses dominant in tallgrass prairie ecosystems, whereas T. dorsata signatures suggested preferential feeding on more deeply rooted C3 plants.

The effects of drought upon epigeal Collembola from arable soils

Summary1 Springtails (Hexapoda, Collembola) are usually associated with moist microhabitats. However, some species show adaptations to ecosystems subjected to periodic desiccation. This study examined the effects of short‐term drought conditions upon epigeal Collembola collected from arable fields.2 An emergence trap was used in the laboratory to investigate collembolan activity, particularly the emergence of newly hatched juveniles from soils subjected to a simulated drought and to varied levels of simulated rainfall.3 Addition of water to soils subjected to a 4‐month simulated drought resulted in synchronized emergence of juveniles of Sminthurinus elegans, Sminthurus viridis and Bourletiella hortensis. As anhydrobiotic nymphs were not found in the soil, these juveniles are likely to have recently hatched from eggs in the soil.4 The same species were shown to emerge when desiccated soil samples were treated with simulated heavy rainfall. No emergence occurred in soils which received no water, whilst only a few juveniles were present under a regime of the lowest monthly rainfall recorded for the area in the spring.5 This study provides the first evidence that in northern European arable systems some epigeal Collembola can survive considerable periods of drought as eggs, emergence of which is triggered by rainfall. These findings have implications for the effects of predicted climatic changes upon collembolan populations, the recovery of collembolan communities following pesticide applications in agroecosystems, and also provide a plausible mechanism for dispersal of Collembola as wind‐blown eggs.

Emergence pattern of diptera in various sections of a northern German lowland stream

At four typical sections of the stream Kossau Diptera were caught by emergence traps. Two of the sections can be regarded as to a great degree undisturbed due to their morphology and vegetation at the banks. Two sections have undergone various anthropogenic changes. Representatives of the families Chironomidae, Ceratopogonidae, Psychodidae, Limoniidae, Ptychopteridae, Dixidae, Culicidae, Simuliidae, and Empididae were collected. Altogether, 106 species were identified. The majority of species belong to the family Chironomidae (74), followed by the Ceratopogonidae (8), Psychodidae, and Empididae (7 each). The numbers of species collected at each stream section ranged from 56 to 69. At the undisturbed and shaded sections 69 and 66 species were found, at the meadow sections 56 and 68 species. Hence, a general connection between the loss of a state close to the natural environment and the number of species can not be stated. A total of 29,349 Diptera emerged. The highest number of individuals was found at a stream section covered with aquatic macrophytes (16,797 ind.), the lowest at a forest section without macrophytes (2,554 ind.). The Chironomidae make up for more than 82% of all Diptera. The Simuliidae rank second accounting for 3 to 17%, followed by the Ceratopogonidae. Like the Ceratopogonidae, all other families comprise less than 1% of the individuals collected. Only a few species demonstrated a distinct preference for the two forest sections of the stream, whereas about 50% of the species occurred in at least three of the four sections. Regarding the species represented by more than two individuals per emergence trap, it became apparent that the correspondence between the forst and the meadow sections is rather small. A comparison of the emergence of individual families revealed that many species found in the Kossau also occur in another lowland stream, similar to the Kossau concerning width, current velocity, and water level. Furthermore, the ecological demands of several species turned out to be not as high as they were considered to be, mainly referring to the temperature: Species proven in the Kossau and in other summer-warm streams may no longer be regarded as ‘cold-stenothermic’.

Sediment Deposition within Fry Emergence Traps: A Confounding Factor in Estimating Survival to Emergence

We provide evidence that the effects of sediment infiltration and deposition within fry emergence traps can lead to a potential negative bias when estimating survival to emergence (STE) of salmonid fry. Fry emergence traps were placed over 12 redds of brown trout Salmo trutta located in sections of three streams in the upper Clark Fork River system in Montana. The redds were capped in March 1989 and monitored through June 1989. During this period, sediment deposition became noticeable inside 8 of the 12 traps. During the final removal of the traps, substrate core samples were collected from a location inside and outside of each emergence trap. Substrate size gradation analysis indicated that concentrations of fine sediments (≤0.84 mm in diameter) were significantly higher in samples collected inside the traps than outside. These results suggested that the local sediment transport capacity was reduced within the emergence traps, resulting in increased deposition of fines. An understanding of the hydrology, ambient sediment concentrations, and sediment transport capabilities of river systems is important when considering the use of fry emergence traps. Without consideration for this potential confounding factor, STE estimates that involve the use of fry emergence traps may underestimate actual STE values.

Seedcorn Maggot Control, 1997

Abstract Seed treatments and planting-time insecticides were tested in a loam soil near Ames, IA. The experimental design was a RCB with 4 replications. Treatments were applied to 20-ft-length rows with 30-inch row spacing. To attract ovipositing flies, a meat-and-bone meal bait was applied to shallow furrows, hand-made with hoes. A 20-ft section of 1 1/2-inch angle iron was filled with meat-and-bone meal and then leveled, leaving a small amount of bait (ca. 1/3 oz per row-ft) evenly distributed in the bottom of the angle iron. The angle iron was positioned directly above the open seed furrow and inverted. Bait was placed in furrows 24 Apr. Corn seeds were hand planted (8-inch seed spacing) directly into the bait on 29 Apr. Granular insecticide treatments were applied with modified Noble metering units mounted on a small-plot bicycle applicator. Regent 4 SC liquid insecticide was applied directly into the open seed furrow with a small-plot bicycle applicator. A microtube delivered a steady stream of dilution at 1 gpa using 24 psi. Seeds were covered with soil and the soil firmed by hand. On 31 May, stand counts were taken from 12 ft 7 inches of row and the seeds/seedlings from two 1-m sections of row were inspected for seedcorn maggot feeding and rated on the following 1-4 damage scale: 1 = seed/seedling undamaged, 2 = seed/seedling damaged, but plant established; 3 = seed/seedling damaged, plant showing some signs of stress; 4 = seed/seedling damaged, no plant or questionable establishment. On 2 Jun, 1 adult emergence trap was placed over each row that had received a granular insecticide treatment. Seed-treatment rows were excluded from the adult emergence analysis. The galvanized steel trap, a rectangular bottomless box, had the following dimensions: length 1.0 m, width 0.2 m, and height 0.1 m. Fastened to the top of each trap were two 0.25-liter mason jars with Tack Trap® applied to the inside bottom. On 12 Jun, the number of seedcorn maggot adults were counted in the collection jars.

The effect of vegetation patterns on oviposition habitat preference: A driving mechanism in terrestrial chironomid (Diptera: Chironomidae) succession?

AbstractRelationships between changes of two species of terrestrial chironomids (Smittia cf. aterrima and Bryophaenocladius cf. virgo) and changes of vegetation cover during succession were studied with respect to plant — chironomid interaction in particular stages of chironomid life cycle. Several vegetation types forming vegetation mosaics in suburban fallow were distinguished according to their spatial architecture (height; density etc.). Abundance of chironomid larvae in particular type of vegetation and an area covered by these vegetation types were studied for three years. During one year the effect of vegetation types on density of aerial drift, oviposition habitat preference and adult emergence was studied in detail. Aerial drift was studied using pan traps, oviposition using soil sampling and adult emergence using emergence trap. Main results were similar for both species. Chironomid larvae were abundant in soil in initial years of succession. They were concentrated in patches with open and low height vegetation. Later their abundance decreased corresponding to a reduction of open and low vegetation areas. Greater density of aerial drift and oviposition preference was observed in areas of open and low vegetation. The success of larval development agreed with oviposition preference for winter larval generation only. The less preferred habitats seemed to be more suitable for summer generation. The results indicated that successional changes of terrestrial chironomids can be explained by the effect of vegetation cover on oviposition habitat preference.

Seedcorn Maggot Control, 1996

Abstract Seed treatments and planting-time insecticides were tested in a loam soil near Ames, IA. The experimental design was a RCB with four replications. Treatments were applied to 20-ft length rows with 30-inch row spacing. To attract ovipositing flies, a meat-and-bone meal bait was applied to shallow, hand-made furrows. A twenty-foot section of 1 1/2 inch angle iron was filled with meat-and-bone meal and then leveled, leaving a small amount of bait (ca. 1/3 oz per row-ft) evenly distributed in the bottom of the angle iron. The angle iron was positioned directly above the open seed furrow and inverted. Bait was placed in furrows 24 Apr. Strong winds blew most of the bait from the furrows on 26 May. Furrows were rebaited on 1 May. Corn seeds were hand planted (8-inch seed spacing) directly into the bait on 5 May. Granular insecticide treatments were applied with modified Noble metering units mounted on a small-plot bicycle applicator. Regent 80WG liquid insecticide was applied directly into the open seed furrow with a small-plot bicycle applicator. A #15 disk orifice placed in-line delivered a steady stream of dilution at 1-0 gpa using 16 psi. Seeds were covered with soil and the soil firmed by hand. On 29 May, stand counts were taken from 14 ft 7 inches of row and the seeds/seedlings from two 1-m sections of row were inspected for seedcorn maggot feeding and rated on the following 1-4 damage scale: 1-seed/seedling undamaged; 2-seed/seedling damaged, but plant established; 3-seed/seedling damaged, plant showing some signs of stress; 4-seed/seedling damaged, no plant or questionable establishment. On 3 Jun, 1 adult emergence trap was placed over each row that had received a granular insecticide treatment. Seed-treatment rows were excluded from the adult emergence analysis. The galvanized steel trap, a rectangular bottomless box, had the following dimensions: length 1.0 m, width 0.2 m, and height 0.1 m. Fastened to the top of each trap were two 0.25-liter Mason jars with Tack Trap® applied to the inside bottom. On 14 Jun, the number of seed-corn maggot adults were counted in the collections jars.

THE EFFECT OF TILLAGE REGIME ON EMERGENCE OF ROOT MAGGOTS (DELIA SPP.) (DIPTERA: ANTHOMYIIDAE) FROM CANOLA

AbstractThe effect of four tillage regimes on the emergence of root maggots (Delia spp.) (Diptera: Anthomyiidae) was determined on experimental plots seeded the previous year to either Brassica rupa L. or Brassica napus L. The tillage regimes evaluated comprised no tillage, tillage in the spring only, tillage in the fall only, and tillage in both the fall and the spring. Emergence trap collections of Delia radicum (L.) and Delia floralis (Fallén) were made from the experimental plots from early May to mid-July of 1991 and 1992. In both years, emergence from untilled plots significantly exceeded that from plots subjected to any other tillage treatment. Tillage resulted in a decrease in emergence of 55–64% for D. radicum, and reduction of 53–72% for D. floralis. For D. floralis, greatest reductions in emergence following a tillage treatment occurred in plots tilled only in the fall or in plots tilled in both the fall and the spring; however for D. radicum, tillage in the fall, the spring, and in both the fall and the spring reduced emergence to approximately the same extent. Results of our study indicated that canola growers in regions of high population densities of root maggot should cultivate infested fields, preferably in fall, to reduce the emergence success of Delia spp.

Emergence Trap Studies on Biting Midges (Diptera: Ceratopogonidae) in Terrestrial Habitats in Southern Lower Saxony (Germany)

Emergence Trap Studies on Biting Midges (Diptera: Ceratopogonidae) in Terrestrial Habitats in Southern Lower Saxony (Germany)

Emergence of Pear Thrips (Thysanoptera: Thripidae) and its Relation to Foliar Damage

Adult emergence of pear thrips, Taeniothrips inconsequens (Uzel), from soil in forests predominating in sugar maple, Acer saccharum Marshall, was monitored, using 7.6- cm-diameter traps, at sites in north central, northeastern, central and southwestern Vermont from 1989 to 1991. The onset of emergence ranged from 2 April to 15 May, but generally occurred in mid-April in all regions. We measured the number of thrips in soil in September and how many emerged in the spring, and monitored the timing and rate of emergence to determine if damage could be predicted from these factors. Thrips density in the soil was not consistently correlated with damage, making it an unreliable predictive measure. A correlation between thrips damage and the timing or duration of emergence was also not detected. The number of thrips per emergence trap was positively correlated with damage in all study years, and from this correlation the predicted number of thrips per trap for moderate damage to occur was 18 in 1989, 13 in 1990 and 8 in 1991. Annual fluctuations in the threshold number of thrips required for damage could limit the use of thrips emergence data for predictive purposes.