Thrips Densities Research Articles

Impact of Early-Season Thrips Management on Reducing the Risks of Spotted Wilt Virus and Suppressing Aphid Populations in Flue-Cured Tobacco

The influence of tray drench (TD) treatments, with and without foliar applications of the plant activator acibenzolar-S-methyl (Actigard), was examined in replicated field plots in 2000–2002. TD treatments of Actigard, imidacloprid (Admire), and these two products combined had little effect on seasonal mean thrips populations; however, thrips densities were lower in the Admire-treated plots at 4 and 5 wk after transplanting. Actigard and Admire TD treatments significantly reduced the seasonal incidence of tomato spotted wilt virus (TSWV) symptomatic plants in 2 yr in the study. The combination of both products was better in reducing TSWV than Actigard alone. Three early-season foliar sprays of Actigard had no effect on thrips population densities, but they did reduce TSWV incidence. The tobacco thrips, Frankliniella fusca (Hinds), comprised 92–95% of the thrips complex each year. Other thrips collected on tobacco foliage at very low densities included Haplothrips spp., Chirothrips spp., Limothrips cerealium (Haliday), other Frankliniella spp. and other unidentified species. Using nonstructural TSWV protein enzyme-linked immunosorbent assay, 1.5–2.3% of the F. fusca tested positive for nonstructural TSWV protein. Cured yields were higher in the TD treatments and the Actigard foliar treatments in the years with high TSWV in the untreated plots. The TD treatments and foliar Actigard had little impact on plant height or grade index; however, TD treatments with Admire had low tobacco aphid, Myzus nicotianae Blackman, populations through 10 wk after transplanting. The early-season Actigard and Admire treatment options are management decisions that can effectively reduce the risks of TSWV incidence in flue-cured tobacco.

Impact of Early-Season Thrips Management on Reducing the Risks of Spotted Wilt Virus and Suppressing Aphid Populations in Flue-Cured Tobacco

The influence of tray drench (TD) treatments, with and without foliar applications of the plant activator acibenzolar-S-methyl (Actigard), was examined in replicated field plots in 2000--2002. TD treatments of Actigard, imidacloprid (Admire), and these two products combined had little effect on seasonal mean thrips populations; however, thrips densities were lower in the Admire-treated plots at 4 and 5 wk after transplanting. Actigard and Admire TD treatments significantly reduced the seasonal incidence of tomato spotted wilt virus (TSWV) symptomatic plants in 2 yr in the study. The combination of both products was better in reducing TSWV than Actigard alone. Three early-season foliar sprays of Actigard had no effect on thrips population densities, but they did reduce TSWV incidence. The tobacco thrips, Frankliniella fusca (Hinds), comprised 92-95% of the thrips complex each year. Other thrips collected on tobacco foliage at very low densities included Haplothrips spp., Chirothrips spp., Limothrips cerealium (Haliday), other Frankliniella spp. and other unidentified species. Using nonstructural TSWV protein enzyme-linked immunosorbent assay, 1.5-2.3% of the F. fusca tested positive for nonstructural TSWV protein. Cured yields were higher in the TD treatments and the Actigard foliar treatments in the years with high TSWV in the untreated plots. The TD treatments and foliar Actigard had little impact on plant height or grade index; however, TD treatments with Admire had low tobacco aphid, Myzus nicotianae Blackman, populations through 10 wk after transplanting. The early-season Actigard and Admire treatment options are management decisions that can effectively reduce the risks of TSWV incidence in flue-cured tobacco.

Density, dispersal, and feeding impact of western flower thrips (Thysanoptera: Thripidae) on flowering chrysanthemum at different spatial scales

Abstract. 1. This study evaluated the effect of dispersal on the density and feeding impact of a phytophagous insect in relation to the spatial distribution of its host plants.2. The interaction between density, dispersal, and feeding impact of western flower thrips on flowering chrysanthemum was quantified at three spatial scales, with infested and uninfested plants either isolated in 0.25 m2 individual cages, or enclosed together in 2.25 m2 communal cages or 75 m2 greenhouses.3. In individual cages, the rate of dispersal from chrysanthemum plants to blue sticky traps increased with the density of thrips for females but not males. Uninfested plants consistently had fewer thrips when they were individually caged rather than enclosed with plants infested with adults, indicating that dispersal mediates inter‐plant distribution of thrips.4. The feeding impact of thrips on inflorescences was evaluated using the absorbance of ethanol extracts at wavelengths characteristic of yellow carotenoid pigments associated with chrysanthemum inflorescences (415, 445, and 472 nm). Increasing absorbance of extracts with increasing density of thrips per inflorescence suggests that feeding by thrips results in ruptured cells leaching carotenoid pigments.5. In communal cages, the distribution of thrips was uniform for infested and uninfested plants, whereas the density and feeding impact of thrips in greenhouses were higher for infested than uninfested plants. These results suggest that short‐range dispersal by adults homogenises the density and feeding impact of thrips among host plants only on a small spatial scale.

イチゴにおけるミカンキイロアザミウマＦｒａｎｋｌｉｎｉｅｌｌａ ｏｃｃｉｄｅｎｔａｌｉｓ（Ｐｅｒｇａｎｄｅ）の被害解析

Low, medium and high densities of the western flower thrips, Frankliniella occidentalis (Pergande), were established in three rooms of a greenhouse to analyze the effect of thrips densities on fruit damage to strawberry plants. Thrips densities were monitored weekly by counting the total number of thrips on flowers, immature fruit and mature fruit, and using blue sticky traps. Fruit damage index was calculated with 4 damage categories for mature fruits. On flowers and fruits (immature and mature), the dominant stages of thrips were adult females and larvae, respectively. Multiple regression analysis of the damage index for larvae, adult females and males on mature and immature fruits 1 week and 2 weeks before harvest showed that fruit damage to mature fruit was significant for larvae on mature fruits (R2=0.775). Damage index (y) transformed to a logistic transformation also showed a significance in terms of percentage (x) of flowers infected with adults (y=0.00958x−0.847, R2=0.627); the control threshold was 21.6% for a damage index of 5. For estimation at this threshold, the sample size was 59.4 flowers.

Factors affecting the occurrence of western flower thrips, Flankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) in persimmon orchards

Wakayama Prefecture is one of the main production areas of persimmon in Japan. However, western flower thrips, Flankliniella occidentalis (Pergande) has been causing serious damage to persimmon fruit, especially variety Tonewase, when the fruit color turned yellow in early September since 1997. F. occidentalis overwintered on the perennial weed such as chickweed, Stellaria neglecta, and had two peaks of population density on undergrowth of persimmon orchards: one in June when perennial weeds were growing and the other in July-August when summer weeds were growing. Thus F. occidentalis maintained its population through various undergrowth. Since the weeding time was different between persimmon and mandarin orange orchards, the adult F. occidentalis dispersed from an orchard where they existed at a higher density to the adjacent orchards. Therefore, the population density of F. occidentalis was higher in a persimmon-mandarin orange cultivation area than in a persimmon mono-cultivation area. The thrips density on undergrowth of foxtail ears, Setalia viridis, was higher in the persimmon orchard than in the grassland nearby. This is provably because pesticides applied to persimmon trees suppressed the occurrence of natural enemies such as the minute bug, Orius sauteri, on weeds by drafting, causing a resurgence of F. occidentalis in persimmon orchards.

Biological Control of Thrips palmi (Thysanoptera: Thripidae) with Orius strigicollis (Hemiptera: Anthocoridae) on Cucumber in Plastic Houses in the Southern Region of Korea

Field evaluations were conducted to determine the efficacy of Orius strigicollis for biological control of Thrips palmi with different initial density in plastic houses. O. strigicollis released three times after 0, 5, 30, 100 thrips were inoculated per 30 cucumber plants. Three hundred and sixty predators were released in each plot. After inoculation of 5 T. palmi per 30 plants in each plot in plastic houses, T. palmi population increased rapidly with 16.3 individuals per plant in the fourth week, and O. strigicollis could not suppress T. palmi population because O. strigicollis population did not build up quickly. In the plot of 30 thrips inoculation, the density of O. strigicollis increased to 2.1 individuals per plant in the third week and 9.8 individuals per plant in the sixth week. The density of T. palmi increased to 33.8 individuals per plant in the sixth week. In the 100 thrips inoculation plot, the density of O. strigicollis increased to 9 individuals per plant in sixth week, which was similar to that in the 30 thrips inoculation plot. But the density of T. palmi increased rapidly from 2.9 to 384.7 individuals per plant in the sixth week. So, control of T. palmi by O. strigicollis did not appear. In autumn culture, in the 5 thrips inoculation plot, the density of O. strigicollis was so low that it could not suppress thrips density. In the 100 thrips inoculation plot, the density of T. palmi was so high that O. strigicollis could not suppress T. palmi density. In the 30 thrips inoculation plot, the density of O. strigicollis was 4.8 individuals per plant in the sixth week and the thrips population was suppressed. But O. strigicollis could not suppress the thrips population after sixth week because of low temperature and short photoperiod. These results indicate that control of T. palmi using O. strigicollis may be possible on cucumber in the spring culture.

Predation byOrius insidiosus(Heteroptera: Anthocoridae) on Life Stages and Species ofFrankliniellaFlower Thrips (Thysanoptera: Thripidae) in Pepper Flowers

Abstract We compared predation of Orius insidiosus (Say) on adult and second instars of Frankliniella occidentalis (Pergande) and on adults of F. occidentalis and F. tritici (Fitch) in arenas with pepper flowers. Also, we compared the dispersal of these thrips in the presence and absence of the predator. For each experiment, two densities of thrips (10 and 20 total thrips) and two time exposures (10 and 34 h) were tested. Second instars were more likely to move from the flower where they were released than were F. occidentalis adults. F. tritici dispersed more than F. occidentalis. The presence of the predator enhanced movement by thrips from flowers in which they were released. Despite differences in prey movement, O. insidiosus successfully preyed on all types of prey that were offered. However, O. insidiosus appeared to deal differently with each type of prey. Predation of both larvae and adults was most likely to occur inside flowers. In trials with adults and second instars of F. occidentalis, larvae...

Efficacy of entomopathogenic nematodes against western flower thrips Frankliniella occidentalis at different pupation depths

Abstract To study the effects of the pupation depth of western flower thrips (WFT), Frankliniella occidentalis (Pergande), on the efficacy of entomopathogenic nematodes (EPN), Heterorhabditis indica strain LN2 and Steinernema bicornutum were applied at dose rates of 100 and 400 infective juveniles (IJ) cm–2to WFT that had pupated at different depths. Additionally, the effects of EPN concentrations and thrips densities were tested on the pupation depth of WFT. A higher concentration of H. indica was required when the thrips pupated deeper. Yet applications of S. bicornutum even at a high concentration resulted in a significantly lower WFT mortality at greater rather than at shallower depths. Generally, WFT control levels of 5-57% were obtained depending on depth of pupation, EPN species, and concentrations. The results clearly indicate that WFT at high EPN concentrations seem to remain at a certain soil depth in order to avoid EPN attraction by moving around. Without or at low EPN concentrations, up to 80% of WFT pupated at the deepest depth of 3-5 cm. However, at higher thrips densities and EPN concentrations, 45-48% of WFT pupated in the medium depth of 1-3 cm. Thus, depth of pupation is an important factor in WFT control using EPN.

The efficiency of several sampling methods for Frankliniella occidentalis (Thysan., Thripidae) in strawberry flowers

Abstract:Methods for sampling western flower thrips Frankliniella occidentalis (Pergande) (Thysan., Thripidae) in strawberry flowers were evaluated in three commercial plots by monitoring the population densities of adult and immature thrips throughout the growing season. Three types of flowers were sampled: open, senescent and petal fall, and three procedures were compared: a visual examination of flowers, a turpentine‐funnel method and a shake method. Open flowers showed higher population densities of adults, whereas senescent or petal fall flowers had a higher number of eggs and more damage symptoms. Seasonal changes in population density were similar for the three sampling procedures, although the turpentine method recovered more insects, especially larvae, than the other two methods. The turpentine procedure was the most efficient as it extracted almost 100% of adults and, in plots with no chemical sprays, nearly 100% of second instars and 50% of first instars. Regular control of thrips with pesticides reduced the percentage of larvae recovered with this procedure. The visual method spotted 80% of adults and 33% of larvae. The shake method extracted nearly 80% of adults but only 18% of larvae. The visual method is recommended for routine field samplings, especially for sampling adults and in plots regularly sprayed with pesticides, as it constitutes a cost‐effective method when time and efficiency are considered.

Dispersal of Adult Western Flower Thrips (Thysanoptera: Thripidae) on Chrysanthemum Plants: Impact of Feeding-Induced Senescence of Inflorescences

The current study investigated the interaction among density, feeding impact, and dispersal of western flower thrips, Frankliniella occidentalis (Pergande), on potted flowering chrysanthemum plants. In cage experiments using chrysanthemum plants infested with either 0, 400, 800, or 1,200 thrips, the proportion of senescent inflorescences increased with time and with the number of thrips released on chrysanthemum plants. Positive correlations between the proportion of senescent inflorescences and the density of thrips per inflorescence for different time periods indicate that the feeding activity of thrips causes a premature senescence of inflorescences. On plants infested with 0 or 400 thrips, population density slightly increased for 10–14 d and then leveled off; on plants infested with 800 or 1,200 thrips, in contrast, population density remained high for 7–10 d and then steadily declined to very low levels. A high proportion of senescent inflorescences was positively correlated with the proportion of females that dispersed on blue sticky cards for different time periods, whereas the rate of dispersal by males was not consistently impacted by the quality of inflorescences. Releasing adult thrips marked with fluorescent powder in greenhouses indicated that the quality of inflorescences meditates the dispersal behavior of adult thrips up to a distance of 4 m: females are more likely to disperse from senescent than healthy inflorescences and preferentially colonize healthy inflorescences over senescent inflorescences. The dispersal behavior of adult thrips has important implications in terms of sex-specific optimal reproductive strategies, sampling procedures, and population dynamics.

Evaluation of Amblyseius cucumeris (Acari: Phytoseiidae) and Orius insidiosus (Hemiptera: Anthocoridae) for control of Frankliniella occidentalis (Thysanoptera: Thripidae) on greenhouse tomatoes

Abstract The effectiveness of inundative releases of the predatory mite Amblyseius cucumeris (Oudemans) and the predatory anthocorid Orius insidiosus (Say) for control of Frankliniella occidentalis (Pergande) on greenhouse tomatoes was evaluated in terms of the population dynamics of F. occidentalis and its associated biological control agents, and by the levels of fruit damage under greenhouse conditions over the course of two trials. Inundative introductions of A. cucumeris at the rate of one sachet (1000 predatory mites per sachet) per plant were made curatively at 4-week intervals at the mean initial thrips densities (±SE) of 120.8 ± 24.2 thrips per plant. Five weeks after the first introduction, thrips populations in the A. cucumeris release greenhouse were significantly reduced to low levels in both trials in comparison to the control greenhouse where no predators were released. As a result, the percentages of the damaged fruit in the A. cucumeris release greenhouse were controlled at acceptable levels (essentially

Determination of damage-yield loss relationships and economic injury levels of flower thrips on cowpea in eastern Uganda

Studies were carried out in eastern Uganda to assess the effect of legume flower thrips ( Megalurothrips sjostedti) injury on cowpea grain yields and to establish economic injury levels (EILs) and action thresholds for thrips on cowpea. The studies relied on various insecticide spray regimes to obtain different thrips densities per experimental unit and use of exclusion cages in the field to confine defined numbers of thrips populations. A significant negative relationship ( y=−0.011 x+1.77; r=0.87; P=0.003) was observed in the field studies between thrips densities and cowpea grain yields. The EIL was established at seven thrips per inflorescence. The study also revealed that three well timed (i.e., applied after bud initiation to minimize flower bud abortion) insecticide sprays are effective in the control of thrips. The three sprays are regarded effective in that thrips densities were kept below the established thresholds. More than three sprays also reduced thrips populations to less than seven per inflorescence but these were not economical.

A field trial of the entomogenous fungus Metarhizium anisopliae for control of onion thrips, Thrips tabaci

In Kenya, Thrips tabaci Lind., is an important constraint to onion production. The current strategy to use synthetic pesticides is inadequate and unsustainable. An isolate of Metarhizium anisopliae (Metsch.) Sorok. with high pathogenicity to legume thrips, Megalurothrips sjostedti, and western flower thrips, Frankliniella occidentalis, was tested in field trials as a potential alternative for control of onion thrips. Weekly and bi-weekly applications of the fungus M. anisopliae and bi-weekly spray of the chemical insecticide dimethoate (Rogor ® 50) were compared for 3 seasons. M. anisopliae was applied at the rate of 1×10 11 conidia ha −1 and dimethoate was applied at the recommended rate of 17.5 g a.i. ha −1. In all the trials, thrips density and damage were significantly lower in the fungal and chemical insecticide treatments compared with the untreated control. Onion bulb yield did not differ significantly among the treatments during the first season trial. However, in the second season trial, dimethoate-treated plots provided the greatest bulb yield (17 metric tons ha −1) and in the third season trial, M. anisopliae applied weekly recorded the highest yield (24 metric tons ha −1). With the exception of spiders, densities of nontarget organisms were higher in plots treated with M. anisopliae than in dimethoate-treated plots. The results indicate the potential of using M. anisopliae for the control of T. tabaci while protecting biodiversity in the onion agroecosystem.

The economic impact of Scirtothrips perseae Nakahara (Thysanoptera: Thripidae) on California avocado production

In 1996, Scirtothrips perseae Nakahara (Thysanoptera: Thripidae) invaded California avocado orchards and moved pest management practices that relied almost exclusively on biological control to strategies dependent on insecticides to maintain thrips densities below economically damaging levels. By 1998, average losses due to thrips feeding damage in untreated infested groves reduced industry revenues by 12%. Producer costs increased by about 4.5% when S. perseae populations required management. In the short run (i.e., the time period during which the industry adapts to managing a new pest), producers cannot fully adapt to increases in production costs and the annual cost of S. perseae to producers with a thrips infestation is estimated to be $8.65 million (US). In the long run (i.e., the time period after which the industry has fully adapted to the effects of a new pest), producers are able to fully reallocate resources to their most efficient use and the annual cost of S. perseae is calculated to be $5.22 million (US) per year. For the entire USA avocado industry, the annual short-run loss attributable to S. perseae in California is calculated to be $8.51 million (US) and $4.45 million (US) in the long run.

Effect of woodlots on thrips density in leek fields: a landscape analysis

The effect of woodlots, natural areas and agricultural land in the landscape on a generalist herbivore insect species in cropland was investigated. The abundance of onion thrips ( Thrips tabaci) was compared in leek ( Allium porrum) fields in 43 agricultural landscape plots of different sizes in The Netherlands. The total area of woodlots, other natural and agricultural areas within a radius of 1000 and 5000 m around each field was measured using a geographic information system (GIS) framework, LGN3 plus. Numbers of onion thrips were significantly lower in leek fields in agricultural landscapes with a larger total area of woodlots. The results suggest that woodlots decrease density of onion thrips and their symptoms in leek fields. Possible mechanisms are discussed.

Seasonal abundance of the western flower thripsFrankliniella occidentalis in the arava valley of Israel

Flowers of 22 plant species grown in the Arava region of Israel were sampled at periodic intervals to study the seasonal abundance ofFrankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Samples were collected from the most common cut-flower and vegetable plant species in this area during 1997 and from pepper in 1996–1998. Western flower thrips (WFT) was detected on 19 of the plant species surveyed, and it reproduced on numerous plant species. WFT counts peaked in late February–April and in October–December. The peak density of WFT during March in our survey corresponded to the peak flowering of cut-flower plants (during spring) and sweet pepper (during autumn). Thrips population was less abundant during autumn than in spring and was very low during summer. The possible reasons for fluctuations in thrips densities are abiotic factors (temperature and relative humidity), and availability of flowering plants. The high temperature (>40°C) and low humidity (∼20%) in summer caused a drastic reduction in WFT populations, although some flowering plant species were available in this season. WFT population remained low until October, when adults appeared in large numbers on flowering pepper. We assume that the thrips had survived the hottest months by aestivation and migrated to the plants when air temperature decreased. In most samples from the cut-flower fields, 84.8% were adult WFT; only during the period from the end of January to March, did the proportion of immature stages in the thrips population increase to 31.6%. Females always outnumbered males (71% females). In pepper fields during the first cropping month the thrips population included 96% adults; from November onwards, the proportions of adults and immatures were almost equal; and females outnumbered males. Organic pepper fields were not infested with thrips because of the presence of the predatory bugOrius albidipennis (Fieber).

Avocado thrips: New challenge for growers

Avocado thrips arrived in California in 1996. Since then, we have made substantial progress in our understanding of this pest. We now know the area of origin of the avocado thrips and have compiled an inventory of other potential pest thrips species on avocados in Mexico and Central America. Trials have helped us to identify several selective insecticides for use in treating avocado thrips in orchards. We have also determined the relationship between thrips densities on leaves and fruit scarring, and are studying cultural and biological control practices for use in an evolving integrated pest management (IPM) program.

Prey preference and reproductive success of the generalist predatorOrius laevigatus

In theory, selection favours predators that select prey in order to maximise reproductive success. We studied the association between preference and performance of the generalist predatorOrius laevigatuswith respect to two prey species: spider mites (Tetranychus urticae) and western flower thrips (Frankliniella occidentalis). Under ample prey supply, the predators had higher maximum reproductive success (measured as intrinsic population growth rater) on thrips than on spider mites; hence thrips represent a higher prey quality to the bugs. This was at odds with the observed preference of the predatory bug for plants (patches) with high densities of spider mites to plants with moderate densities of thrips in release‐recapture experiments. Thus, prey quality does not suffice to explain the preference of predators for plants with prey. The quality of a patch as an oviposition site (i.e. the number of eggs produced on a patch per bug per day) also did not match preference patterns. Hence, patch preference was not correlated to prey quality or oviposition rate on prey patches. However, patch productivity, i.e. the total number of offspring surviving until adulthood that can be produced by one female on a patch, was correlated with preference. This was further tested by offering the predators a choice between plants with high densities of spider mites and plants with high densities of thrips in an independent set of release‐recapture experiments. These two types of prey patches were found equivalent in terms of patch productivity. Indeed, the predators showed no preference for either of the two types of patches, which is in agreement with our predictions. This suggests that the predatory bugs select patches based on patch productivity rather than on prey quality or oviposition rate on a patch.

Occurence of thrips on Niagara table grape and its control with the insecticides thiacloprid and methiocarb associated with Metarhizium anisopliae

Thrips are reported as important pests on table grapes in United States and several countries of Europe. Damage caused by thrips, particulary Frankliniella occidentalis, was observed on niagara table grape crop in Limeira-SP, Brazil. During the blooming period, high thrips densities were observed feeding on pollen and small berries. The symptoms left were more visible after the development of the berries and were characterized by dark scars and suberized surface on berries, sometimes causing the berry to crack, and the seed to prolapse. The effect of insecticides thiacloprid or methiocarb, associated or not with the entomopathogenic fungus Metarhizium anisopliae were evaluated during the blooming period. For evaluation of thrips damage on fruits, the treatments were applied three additional times, 7, 14 and 21 days after the first application. The treatments were: a) M. anisopliae (strain 1037) 1x10(7) conidia/mL; b) thiacloprid 20mL/100L; c-d) methiocarb 100 and 150mL/100L; e) methiocarb 100mL/100L + M. anisopliae 1x10(7) conidia/mL. Only methiocarb, associated or not with the fungus, was effective in reducing thrips infestation, and no phytotoxic damage was observed. The efficiency of methiocarb 150mL/100L and the insecticide associated with the fungus for the control of the thrips population was 84.2 and 95.5%, respectively. In both cases, there was a reduction of approximately 70% in the number of berries with scars symptoms. For control of thrips on table grapes, chemical insecticides associated or not with M. anisopliae should be applied during the blooming period of the crop.

A field experiment on the effectiveness of spiders and carabid beetles as biocontrol agents in soybean

Abstract1 Spiders and carabid beetles are abundant generalist predators that prey upon insect pests of soybean. A field experiment was conducted to determine the impact of spiders and carabids on soybean yield. Prior to planting, three 7 × 7 m plots were fenced in order to reduce spider and carabid immigration. Carabids that emerged within the plots were not removed, but spiders that ballooned into these predator‐reduction plots or that entered by climbing the fence were removed by pitfall trapping and searching the vegetation. Three unmanipulated, unfenced plots served as the control treatment.2 Densities of spiders on soybean vegetation, and activity‐densities of spiders and carabids determined by pitfall trapping, were c. 75% lower in the spider‐carabid reduction treatment than in control plots. Despite clear differences between treatments in numbers and activity of these major generalist predators, the weight of soybeans harvested did not differ between control and spider‐carabid reduction plots.3 Paralleling the absence of an effect of predator reduction on soybean yield was the absence of any significant difference between treatments in densities of whiteflies (Aleyrodidae), leafhoppers (Cicadellidae), thrips (Thysanoptera), Lepidoptera larvae and herbivorous Coleoptera.4 Our experiment provides no evidence that spiders and carabid beetles at ambient densities affect soybean yield. Low populations of pest species or low predation pressure on soybean pests by spiders and carabids at the ambient densities of this experiment could be responsible for this result.