Sampling methods, dispersion patterns, and fixed precision sequential sampling plans for western flower thrips (Thysanoptera: Thripidae) and cotton fleahoppers (Hemiptera: Miridae) in cotton

A 2-yr field study was conducted to examine the effectiveness of two sampling methods (visual and plant washing techniques) for western flower thrips, Frankliniella occidentalis (Pergande), and five sampling methods (visual, beat bucket, drop cloth, sweep net, and vacuum) for cotton fleahopper, Pseudatomoscelis seriatus (Reuter), in Texas cotton, Gossypium hirsutum (L.), and to develop sequential sampling plans for each pest. The plant washing technique gave similar results to the visual method in detecting adult thrips, but the washing technique detected significantly higher number of thrips larvae compared with the visual sampling. Visual sampling detected the highest number of fleahoppers followed by beat bucket, drop cloth, vacuum, and sweep net sampling, with no significant difference in catch efficiency between vacuum and sweep net methods. However, based on fixed precision cost reliability, the sweep net sampling was the most cost-effective method followed by vacuum, beat bucket, drop cloth, and visual sampling. Taylor's Power Law analysis revealed that the field dispersion patterns of both thrips and fleahoppers were aggregated throughout the crop growing season. For thrips management decision based on visual sampling (0.25 precision), 15 plants were estimated to be the minimum sample size when the estimated population density was one thrips per plant, whereas the minimum sample size was nine plants when thrips density approached 10 thrips per plant. The minimum visual sample size for cotton fleahoppers was 16 plants when the density was one fleahopper per plant, but the sample size decreased rapidly with an increase in fleahopper density, requiring only four plants to be sampled when the density was 10 fleahoppers per plant. Sequential sampling plans were developed and validated with independent data for both thrips and cotton fleahoppers.     

Sampling strategies for square and boll-feeding plant bugs (Hemiptera: Miridae) occurring on cotton

Sampling methods for square and boll-feeding plant bugs (Hemiptera: Miridae) occurring on cotton, Gossypium hirsutum L., were compared with the intent to assess if one approach was viable for two species occurring from early-season squaring to late bloom in 25 fields located along the coastal cotton growing region of south Texas. Cotton fleaphopper, Pseudatomoscelis seriatus (Reuter), damages squares early-season and dominated collections using five sampling methods (approximately 99% of insects collected). A major species composition shift occurred beginning at peak bloom in coastal fields, when verde plant bug, Creontiades signatus Distant, represented 55-65% of collections. Significantly more cotton fleahoppers were captured by experienced samplers with the beat bucket and sweep net than with the other methods (30-100% more). There were more than twice as many verde plant bugs captured by experienced and inexperienced samplers with the beat bucket and sweep net than captured with the KISS and visual methods. Using a beat bucket or sweep net reduced sampling time compared with the visual method for the experienced samplers. For both species, comparing regressions of beat bucket-based counts to counts from the traditional visual method across nine cultivar and water regime combinations resulted in only one combination differing from the rest, suggesting broad applicability and ability to translate established visual-based economic thresholds to beat bucket-based thresholds. In a first look at sample size considerations, 40 plants (four 10-plant samples) per field site was no more variable than variation associated with larger sample sizes. Overall, the beat bucket is much more effective in sampling for cotton fleahopper and verde plant bug than the traditional visual method, it is more suited to cotton fleahopper sampling early-season when plants are small, it transitions well to sample for verde plant bug during bloom, and it performs well under a variety of soil moisture conditions and cultivar selections.     

Determination of Oebalus pugnax (Hemiptera: Pentatomidae) spatial pattern in rice and development of visual sampling methods and population sampling plans

Commercial rice, Oryza sativa L., fields in southeastern Texas were sampled during 2003 and 2004, and visual samples were compared with sweep net samples. Fields were sampled at different stages of panicle development, times of day, and by different operators. Significant differences were found between perimeter and within field sweep net samples, indicating that samples taken 9 m from the field margin overestimate within field Oebalus pugnax (F.) (Hemiptera: Pentatomidae) populations. Time of day did not significantly affect the number of O. pugnax caught with the sweep net; however, there was a trend to capture more insects during morning than afternoon. For all sampling methods evaluated during this study, O. pugnax was found to have an aggregated spatial pattern at most densities. When comparing sweep net with visual sampling methods, one sweep of the "long stick" and two sweeps of the "sweep stick" correlated well with the sweep net (r2 = 0.639 and r2 = 0.815, respectively). This relationship was not affected by time of day of sampling, stage of panicle development, type of planting or operator. Relative cost-reliability, which incorporates probability of adoption, indicates the visual methods are more cost-reliable than the sweep net for sampling O.     

Effect of the red imported fire ant on cotton aphid population density and predation of bollworm and beet armyworm eggs

The effects of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), on cotton aphid, Aphis gossypii Glover, populations and its predation of bollworm, Helicoverpa zea (Boddie), and beet armyworm, Spodoptera exigua (Hübner), (both Lepidoptera: Noctuidae) eggs were evaluated in cotton under field conditions during 2001 and 2002 in central and northern Texas. In central Texas, cotton aphid populations were approximately 5.5 times greater and predation of sentinel bollworm eggs 2 times greater in the presence of S. invicta versus in its absence, although aphid populations did not reach economic levels. Most predation of beet armyworm egg masses, measured via direct nocturnal observations, was due to S. invicta (68%) and cotton fleahopper, Pseudatomoscelis seriatus (Reuter) (21%), where S. invicta was present, and by the mite Abrolophus sp. (52%), spiders (13%), and minute pirate bug (Orius sp.) (13%) where S. invicta was absent. Predation of sentinel bollworm eggs and beet armyworm egg masses was approximately 1.5 and 4.1 times greater, respectively, in the presence of S. invicta versus in their absence. In the presence of S. invicta, the relative frequencies of minute pirate bug and cotton fleahopper were higher, and of S. invicta and native ants lower in beat bucket samples compared with their relative frequencies in nocturnal observations of predation upon beet armyworm egg masses. In the absence of S. invicta seven of eight predators sampled were similarly represented in beat bucket samples and nocturnal observations of beet armyworm egg mass predation, whereas minute pirate bug occurred at a higher frequency in beat bucket samples relative to nocturnal observations. These observations suggested that the relative frequencies of minute pirate bug, cotton fleahopper, S. invicta and native ants in beat bucket samples do not closely reflect the frequency with which these predators prey on noctuid eggs. Overall, the results of this study show that although S. invicta may promote aphid populations early in the growing season, it is an important predator of bollworm and beet armyworm eggs later in the season.     

Comparison of sampling methods for determining relative densities of Homalodisca vitripennis (Hemiptera: Cicadellidae) on citrus

Four sampling methods that included A-Vac, D-Vac, pole-bucket, and beat-net devices were evaluated for estimating relative densities of glassy-winged sharpshooter, Homalodisca vitri-pennis (Germar) (Hemiptera: Cicadellidae) nymphs and adults on citrus (Citrus spp.) trees. All four methods produced similar temporal and spatial distribution profiles, although significant differences in quantities of H. vitripennis adults and nymphs caught by each device were observed. The four sampling methods also showed a consistent male bias in adult populations across a range of densities, suggesting that previously reported male-biased sex ratios in H. vitripennis adult populations are real and not a product of sampling bias. A strong relationship (R2 = 0.95) between the monitoring methods we evaluated and yellow sticky trap catches of female H. vitripennis adults suggest that yellow sticky trap catches may provide a good relative index of infestation levels in citrus trees. Based on quantitative analyses examining precision and cost, the pole bucket was the most efficient method for sampling nymphs, and it was as efficient as the beat-net method for sampling adults and both stages combined. In addition to these analyses, consideration of other sampling characteristics such as added flexibility in sampling and higher sensitivity in detecting infestations within individual trees helped to fortify the conclusion that the pole bucket was the best overall sampling method of those tested.     

How to catch foliage-dwelling spiders (Araneae) in maize fields and their margins: a comparison of two sampling methods

The foliage‐dwelling spider fauna was collected in maize fields and on stinging nettles in adjacent margins in Bavaria, South Germany. Two different sampling methods were evaluated: drop cloth sampling and suction sampling. The overall catch was dominated by juvenile spiders, web‐building spiders, and spiders of the families Theridiidae, Linyphiidae, Tetragnathidae and Araneidae (in decreasing order). Field margins harboured more species than maize fields, whereas the total spider abundance was higher in the maize crop. Web‐building spiders such as Theridiidae and Linyphiidae were prominent in maize by individual numbers. Suction sampling with a small suction device proved to be a more efficient and consistent sampling method for foliage‐dwelling spiders than drop cloth sampling. Density and species richness of foliage‐dwelling spiders in maize was shown to be fairly high, implying that spiders of higher strata may play a more important role in biological control than suspected up to now.     

Role of aphid predator guild in controlling spirea aphid populations on apple in West Virginia,USA

Spirea aphid populations and their predators were studied on apple to identify predators of importance in controlling aphid populations. Methods included random and non-random sampling from apple orchards in West Virginia, USA, sentinel aphid colonies, laboratory feeding studies, and predator exclusion studies. Aphidoletes aphidimyza (Diptera: Cecidomyiidae), chrysopids (Neuroptera: Chrysopidae), Harmonia axyridis (Coleoptera: Coccinellidae), and Orius insidiosus (Hemiptera: Anthocoridae) were the most abundant predators associated with spirea aphid colonies on apple. Parasitoids were all but absent in the study. Abundance of all predators was density dependent with greater responses to aphid populations at the orchard scale than to tree or individual colony scales. A. aphidimyza, O. insidiosus, chrysopids, and syrphids (Diptera) had the greatest degree of density dependence on aphid populations, and spiders showed inverse density dependence. Exclusion of predators with both cages and insecticides produced significantly higher aphid populations. Because of high abundance, good synchrony with aphid populations, and high impact per individual, H. axyridis adults were the most important spirea aphid predator on apple.     

Temporal variation in arthropod sampling effectiveness: the case for using the beat sheet method in cotton

Predatory insects and spiders are key elements of integrated pest management (IPM) programmes in agricultural crops such as cotton. Management decisions in IPM programmes should to be based on a reliable and efficient method for counting both predators and pests. Knowledge of the temporal constraints that influence sampling is required because arthropod abundance estimates are likely to vary over a growing season and within a day. Few studies have adequately quantified this effect using the beat sheet, a potentially important sampling method. We compared the commonly used methods of suction and visual sampling to the beat sheet, with reference to an absolute cage clamp method for determining the abundance of various arthropod taxa over 5 weeks. There were significantly more entomophagous arthropods recorded using the beat sheet and cage clamp methods than by using suction or visual sampling, and these differences were more pronounced as the plants grew. In a second trial, relative estimates of entomophagous and phytophagous arthropod abundance were made using beat sheet samples collected over a day. Beat sheet estimates of the abundance of only eight of the 43 taxa examined were found to vary significantly over a day. Beat sheet sampling is recommended in further studies of arthropod abundance in cotton, but researchers and pest management advisors should bear in mind the time of season and time of day effects.     

Utilization of early soybeans for food and reproduction by the tarnished plant bug (Hemiptera: Miridae) in the delta of Mississippi

Commercially produced maturity group (MG) IV soybeans, Glycine max L., were sampled during bloom for tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), during May and June 1999 (3 fields) and 2001 (18 fields). The adults and nymphs were found primarily in single population peaks in both years, indicating a single new generation was produced during each year. The peak mean numbers of nymphs were 0.61 and 0.84 per drop cloth sample in 1999 and 2001, respectively. Adults peaked at 3.96 (1999) and 3.76 (2001) per sweep net sample (25 sweeps). Tests using laboratory-reared and field-collected tarnished plant bugs resulted in very poor survival of nymphs on 16 different soybean varieties (MG III, one; IV, four; V, nine; VI, two). A large cage (0.06 ha) field test found that the number of nymphs produced on eight soybean varieties after mated adults were released into the cages was lower than could be expected on a suitable host. These results indicated that soybean was a marginal host for tarnished plant bugs. However, the numbers of adults and nymphs found in the commercially produced fields sampled in the study may have been high enough to cause feeding damage to the flowering soybeans. The nature of the damage and its possible economic importance were not determined. Reproduction of tarnished plant bugs in the commercially produced early soybean fields showed that the early soybeans provided tarnished plant bugs with a very abundant host at a time when only wild hosts were previously available.     

Predatory arthropod community composition in apple orchards: Orchard management,landscape structure and sampling method

Studies on predatory arthropods in agricultural areas seldom include Diptera other than hoverflies, partly because common sampling methods are less effective for capturing species that easily fly off when disturbed. To study the effect from this bias when describing the predator community, we compared traditional beat sampling of branches and suction sampling for describing the community of predatory arthropods in Swedish apple orchards, both organic orchards and orchards using integrated pest management (IPM). Our results indicate that the proportion of both predatory dipterans and parasitic hymenopterans increase dramatically when using suction sampling (Diptera: 32% vs. 20%, Hymenoptera: 25% vs. 7%). In fact, predatory dipterans were the most abundant predatory group when using suction sampling, in contrast to beat sampling where spiders were the most abundant group. One group of predatory flies that was particularly rich in both species and individuals in the surveyed apple orchards was dance flies in the family Hybotidae. Even though the bias of sampling method was evident, it was encouraging that the method choice did not affect the conclusions concerning management on predatory arthropod communities. With both methods, dipteran and coleopteran predators were more abundant in organic apple orchards whereas opilionids were more abundant in orchards managed according to IPM. The inclusion of landscape variables further indicated effects of landscape diversity and of deciduous forest cover, but the response varied in sign between predatory groups. Whereas both Coleoptera and Heteroptera were more abundant in orchards surrounded by more complex landscapes (high landscape diversity and/or high deciduous forest cover), spiders, opilionids and dipterans were rather less abundant in these orchards. To conclude, our study points to the potential importance of predatory dipterans in apple orchards, and we highly recommend future studies of arthropod predators in apple and other crops to actively include predatory Diptera.     

Toxicity of pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say) (Hemiptera: Anthocoridae)

The objective of this study was to evaluate the toxicity of some pesticides used in chrysanthemum crops to eggs and nymphs of Orius insidiosus (Say). The bioassays were carried out at 25 +/- 2 degrees C, 70 +/- 10% RH and 12h photophase. For the tests with eggs, stems of Bidens pilosa L. previously exposed to predator oviposition were dipped for five seconds in aqueous dilution of the pesticides, using 40 eggs per treatment. The pesticides were applied on nymphs using a Potter's tower. Forty first-instar and twenty second-instar nymphs of O. insidiosus were used per treatment in the tests with nymphs. The adults from eggs and nymphs treated were grouped in couples to study the pesticides effects on its reproductive parameters. None tested pesticide affected the viability of treated eggs. Azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine were harmless to first- and second-instar nymphs of O. insidiosus, whereas abamectin, acephate and chlorfenapyr were shown to be harmful to nymphs of both first and second instars. The pre-oviposition period, the daily number of eggs, number of eggs in ten days, and egg viability were not affected by azoxystrobin, benomyl, imibenconazole, iprodione, metalaxyl + mancozeb and triforine. These pesticides, for showing low toxicity to the predator, can be recommended in disease management programs for chrysanthemum crops, in association with O. insidiosus.     

Impact of predation on establishment of the soybean aphid, <Emphasis Type="Italic">Aphis glycines</Emphasis> in soybean, <Emphasis Type="Italic">Glycine max</Emphasis>

The soybean aphid, Aphis glycines Matsumura is a new invasive pest of soybean in North America. We studied the ability of the existing predator community in soybean to reduce A. glycines establishment in field studies using either predator exclusion, open, or leaky cages that allowed aphid emigration but limited predation. Cages were infested with uniform initial densities of A. glycines adults and subsequent populations of aphids and predators were monitored over 24 h. The most abundant predators in these trials included the carabid beetles Elaphropus anceps (Le Conte), Clavina impressefrons Le Conte, Bembidion quadrimaculatum Say and spiders (Salticidae and Lycosidae). Foliar predators were less abundant and included; Harmonia axyridis Pallas, Coccinella septempunctata (L.), and Orius insidious (Say). Over the 2-year study, we found statistically significant predation on adult A. glycines in one out of six trials at 15 h and two out of six trials at 24 h. There was never significant evidence for predation of nymphs in any trial, however overall survival (adults + nymphs) was significantly reduced in one out of six trials at 15 h and three out of six trials at 24 h. Based on these results we suggest that generalist predators can be a significant but variable factor influencing the establishment of A. glycines populations in soybean. The impact of existing predator communities should be further investigated as a means of managing A.␣glycines populations in North American soybean production systems.     

Voracity and prey preference of insidious flower bug (hemiptera: anthocoridae) for immature stages of soybean aphid (hemiptera: aphididae) and soybean thrips (thysanoptera: thripidae)

The generalist predator, Orius insidiosus (Say), is an important natural enemy of the soybean aphid, Aphis glycines Matsumura. Soybean thrips, Neohydatothrips variabilis (Beach), serve as an important prey resource for O. insidiosus in soybeans, sustaining the predator's population before the arrival of the soybean aphid. Although generalist predators can forage on a broad range of prey, they may show distinct preferences for particular prey, attacking prey at levels disproportionate to their relative numbers. To assess the preference of O. insidiosus for soybean aphid and soybean thrips, attack rates of nymphal and adult O. insidiosus were measured in the laboratory. For both adults and nymphs, the number of prey attacked increased as more prey were provided. For nymphs, the total number of prey attacked increased as the predator matured. In general, the number of prey attacked by adult predators was relatively constant as the predator aged. Both O. insidiosus nymphs and adults displayed a preference for soybean thrips, by disproportionately attacking soybean thrips over soybean aphid regardless of the relative densities of the two prey. We discuss implications of this preference on O. insidiosus life history characteristics and the potential impact on O. insidiosus-prey dynamics in the field.     

D-vac sampling for predatory arthropods in winter wheat

We evaluated the D-vac suction machine for sampling predatory arthropods in Oklahoma winter wheat fields. The efficiency of D-vac sampling was low for adult Coccinellidae and Carabidae. Sampling efficiency was greater for coccinellid larvae. Sampling efficiency was high for adult and immature Nabidae and Chrysopidae, for Araneae, and for adult Staphylinidae. For most predators, there were significant correlations between the number of individuals in D-vac samples and the number of individuals per m² in the field. The highest correlation was 0.82 for adult Staphylinidae. Correlations for most predators were <0.60. Significant partial correlations between D-vac sample estimates and ancillary abiotic and biotic variables occurred for most predators, indicating that D-vac sampling efficiency was affected environmental variables. Multiple regression models were constructed to relate population estimates from D-vac sampling to absolute density by adjusting estimates for influential abiotic and biotic environmental variables. Significant regression models were not achieved for adult Coccinellidae or adult Carabidae, and the coefficient of determination was low (0.18) for the model for adult Nabidae. Higher values of R² were achieved for larval Coccinellidae, Chrysopidae adults and larvae, Nabidae nymphs, Araneae, and adult Staphylinidae. Among abiotic variables, air temperature and wind velocity most frequently entered into step-wise regression models. Among biotic variables, wheat plant growth stage and wheat tiller density frequently entered into models.     

Survey of predators and sampling method comparison in sweet corn

Natural predation is an important component of integrated pest management that is often overlooked because it is difficult to quantify and perceived to be unreliable. To begin incorporating natural predation into sweet corn, Zea mays L., pest management, a predator survey was conducted and then three sampling methods were compared for their ability to accurately monitor the most abundant predators. A predator survey on sweet corn foliage in New York between 1999 and 2001 identified 13 species. Orius insidiosus (Say), Coleomegilla maculata (De Geer), and Harmonia axyridis (Pallas) were the most numerous predators in all years. To determine the best method for sampling adult and immature stages of these predators, comparisons were made among nondestructive field counts, destructive counts, and yellow sticky cards. Field counts were correlated with destructive counts for all populations, but field counts of small insects were biased. Sticky cards underrepresented immature populations. Yellow sticky cards were more attractive to C. maculata adults than H. axyridis adults, especially before pollen shed, making coccinellid population estimates based on sticky cards unreliable. Field counts were the most precise method for monitoring adult and immature stages of the three major predators. Future research on predicting predation of pests in sweet corn should be based on field counts of predators because these counts are accurate, have no associated supply costs, and can be made quickly.     

Analysis of the spatio-temporal distribution of Eurygaster integriceps (Hemiptera: Scutelleridae) by using spatial analysis by distance indices and geostatistics

Eurygaster integriceps Puton (Hemiptera: Scutelleridae) is the most serious insect pest of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in Iran. In this study, spatio-temporal distribution of this pest was determined in wheat by using spatial analysis by distance indices (SADIE) and geostatistics. Global positioning and geographic information systems were used for spatial sampling and mapping the distribution of this insect. The study was conducted for three growing seasons in Gharamalek, an agricultural region to the west of Tabriz, Iran. Weekly sampling began when E. integriceps adults migrated to wheat fields from overwintering sites and ended when the new generation adults appeared at the end of season. The adults were sampled using 1- by 1-m quadrat and distance-walk methods. A sweep net was used for sampling the nymphs, and five 180° sweeps were considered as the sampling unit. The results of spatial analyses by using geostatistics and SADIE indicated that E. integriceps adults were clumped after migration to fields and had significant spatial dependency. The second- and third-instar nymphs showed aggregated spatial structure in the middle of growing season. At the end of the season, population distribution changed toward random or regular patterns; and fourth and fifth instars had weaker spatial structure compared with younger nymphs. In Iran, management measures for E. integriceps in wheat fields are mainly applied against overwintering adults, as well as second and third instars. Because of the aggregated distribution of these life stages, site-specific spraying of chemicals is feasible in managing E. integriceps.     

Toxicity of diflubenzuron, pyriproxyfen, imidacloprid and diafenthiuron to the predatory bugOrius laevigatus (Het.: Anthocoridae)

The susceptibility of the predatory bugOrius laevigatus (Fieber) to the insect growth regulators diflubenzuron, pyriproxyfen, the nitroguanidine insecticide imidacloprid and the thiourea compound diafenthiuron was investigated in the laboratory. Fifth-instar nymphs were exposed to formulated materials of each compound and adults were exposed to formulated materials of diafenthiuron and imidacloprid. In each case, exposure via ingestion and residual contact was tested. Pyriproxyfen was harmless toO. laevigatus nymphs by both ways of exposure. The respective LC₅₀-values of diflubenzuron via ingestion and residual contact were 229.9 and 391.1 mg a.i./l. Diafenthiuron did not cause significant mortality to fifth-instar nymphs and adults via ingestion but was toxic by residual contact with LC₅₀-values of 329.4 mg a.i./l and 125.9 mg a.i./l for nymphs and adults respectively. Imidacloprid proved to be the most toxic compound with LC₅₀-values of 1.1 and 0.04 mg a.i./l for nymphs and 2.1 and 0.3 mg a.i./l for adults, via ingestion and residual contact, respectively. The results suggest that use of pyriproxyfen in an integrated pest management programme will not cause any problems but that imidacloprid, and to a lesser extent, also diflubenzuron and diafenthiuron could be harmful to the predator.     

Among-sampler variation in sweep net samples of adult Lygus hesperus (Hemiptera: Miridae) in cotton

The sweep net is a standard sampling method for adults of the western tarnished plant bug, Lygus hesperus Knight (Hemiptera: Miridae), in cotton (Gossypium spp.). However, factors that influence the relationship between true population levels and population estimates obtained using the sweep net are poorly documented. Improved understanding of these factors is needed for the development and application of refined treatment thresholds. Recent reports of significant among-sampler differences in sweep net-based population estimates of the adult tarnished plant bug, Lygus lineolaris (Palisot de Beauvois), seem to preclude meaningful comparisons of population estimates collected by different samplers. We used a mark-release-recapture method and the standard sweep net to evaluate among-sampler differences in population estimates of L. hesperus adults. Adult lygus, marked with fingernail polish to facilitate identification and prevent flight, were released into 10-m sample rows on the evening before 10-sweep samples were collected the following morning. The experimental design was a randomized complete block with three replications of three treatments (sampler). Separate experiments were conducted in two plantings each of Pima (Gossypium barbadense L.) and Acala (Gossypium hirsutum L.) cotton. Collections of marked bugs from each study were evaluated for effects of sampler, sample date, and their interaction. Although differences in lygus collections were observed among sample dates in some tests, no differences were detected in the population estimates by different samplers. These results demonstrate that the sweep net technique can be sufficiently standardized to allow direct comparison of population estimates obtained by different samplers.     

微小花蝽对温室白粉虱的捕食作用

研究微小花蝽Orius minutus(L.)对温室白粉虱Trialeurodes vaporariorum(Westwood)的捕食作用。结果表明,微小花蝽成虫对温室白粉虱各虫态的功能反应呈HollingⅡ型。微小花蝽成虫对温室白粉虱卵、1龄和2龄混合若虫及其3龄若虫的理论最大捕食量分别为123,74和52头/d。微小花蝽成虫对温室白粉虱卵的捕食效应随捕食者个体间干扰作用的增加而下降,符合Hassel-Varley方程,捕食作用率(E)随着微小花蝽数(P)增加而呈幂指数下降,模拟模型E=0.1021P-0.3189,干扰系数为0.3189。在15～40℃的温度范围内,随着温度的升高微小花蝽成虫对温室白粉虱卵的寻找效率提高,最高达1.1990,处置时间缩短,最低达到0.0035d。     

南方小花蝽对不同猎物捕食作用及利用效率

室内用棉蚜,花蓟马及棉花花粉饲养南方小花蝽,通过对南方小花蝽捕食两种猎物及取食棉花花粉后的体重的增长以及同时段内对棉蚜,花蓟马及棉花花粉减少的量的测定,得到南方小花蝽取食不同食物后的生长速率及其对食物的利用效率,同时还研究了南方小花蝽成虫和若虫对混合猎物（棉蚜,棉铃虫卵,红铃虫卵）中各猎物的捕食作用及其在多猎物（红铃虫卵,棉叶螨成螨,花蓟马若虫）不同密度水平下的捕食效应。结果表明,棉蚜与花蓟马可以较好地满足南方小花蝽正常生长发育所需的营养,南方小花蝽对两种猎物的利用效率显著高于棉花花粉,在混合猎物中南方小花蝽成虫和若虫均嗜食棉蚜,其次为红铃虫卵和棉铃虫卵;对于同一种猎物,南方小花蝽成虫和若虫在高密度下的日平均捕食量均显著高于低猎物密度下的日平均捕食量,而对于同一密度的不同猎物,南方小花蝽在低猎物密度时对供试的3种猎物无明显的选择性,在中,高密度时对供试的3种猎物则表现出明显的嗜食性差异。其嗜好程度依次为红铃虫卵,花蓟马若虫,棉叶螨成螨,通过研究有助于更好地了解与掌握南方小花蝽对不同食物的需求及其在田间的食物转换规律,从而更好地进行南方小花蝽的室内人工大量饲养,使南方小花蝽更好地成为棉田害虫种群综合治理中的重要组成部分并发挥其应有的作用。