Low Insect Densities Research Articles

Pest survey card on Agrilus planipennis

This pest survey card was prepared in the context of the EFSA mandate on plant pest surveillance (M-2017–0137), at the request of the European Commission. Its purposeisto guide the Member States in preparing data and information forAgrilus planipennis surveys. These are required to design statistically sound and risk-based pest surveys, in line with current international standards.The buprestid beetle A. planipennis is a highly destructive Union quarantine and priority pest of ashtrees (Fraxinus spp.) native to Asia. The pest has ravaged ash resources in North America and is currently spreading in European Russia and eastern Ukraine.The introduction of plant material of host taxa into EU Member States from areas where the pest is present is regulated.All European Fraxinusspecies are suitable hosts. Larvae feed on the phloem of infested ash causing extensive dieback and tree death. The beetle requires one year to complete one generation,ortwo years in colder climates. Adults are found in spring and summer. Climatic conditions in the EU territories are suitable for the establishment of A.planipennis and host trees are widely available across the EU in forests,parks and cities.The pest spreads by active flight and human-assisted dispersalat an average rate of 1,500 m per year. Infested trees show distinctivesymptoms and signs, but due to their late appearance surveillance based on symptoms is not suited for detection at low insect densities. The use of traps baited with attractants targeting adult beetles is an effective method to detect the pest at early stages of the infestation and is the recommended approach for implementing surveillance within the EU. The updated pest survey card for Agrilus planipennis is published and available online in the EFSA Plant Pest Survey Cards Gallery at the following link:https://arcg.is/09S94u

Temporal changes in stored-product insect populations associated with boot, pit, and load-out areas of grain elevators and feed mills

Commercial grain elevator and feed mill facilities can quickly become infested with stored-product insect pests, compromising the protection of the stored raw and processed cereal products. Elevators and feed mills were sampled monthly for adult stored-product insects in grain residues from the boot-pit areas and in bulk load-out samples from 2009 to 2010. The grain samples collected from the boot, pit, and load-out areas consisted of corn, soybeans, or a mixture of the two grains. Low insect densities were found in the boot-pit area during the cool winter months. Insect numbers increased in the spring and peaked during the warm summer months, prior to declining in the fall following a pattern of higher insect densities during higher ambient temperatures. The rice weevil, Sitophilus oryzae (L.), was the most prevalent species collected in all of the sampled grain residues, representing 69.2 and 35.8% of total insects collected in feed mills and elevators, respectively, during 2009 and was also commonly collected in 2010. Other commonly collected insect species included, the red flour beetle, Tribolium castaneum (Herbst); rusty grain beetle, Cryptolestes ferrugineus (Stephens); and sawtoothed grain beetle, Oryzaephilus surinamensis (Linnaeus). Our results showed that failing to clean out boot residual grain and a lack of sanitation of the pit area resulted in high numbers of insects that were transferred through the elevator leg to other locations within a facility. We conclude that the lack of sanitation at elevator and feed mill facilities allowed high numbers of insects to develop.

A promising biological control agent for the invasive alien plant, Pereskia aculeata Miller (Cactaceae), in South Africa

Pereskia aculeata Miller (Cactaceae) is an invasive alien plant from Central and South America that has become a problematic environmental weed in South Africa. A potential biological control agent, the stem-wilter, Catorhintha schaffneri Brailovsky & Garcia (Coreidae), was collected in southern Brazil and imported into quarantine in South Africa. Field host range data suggested that C. schaffneri has a host range restricted to P. aculeata. No-choice nymph survival tests were then conducted on 27 test plant species in 9 families. Survival to the adult stage was only recorded on P. aculeata and the closely related Pereskia grandifolia Haw. (Cactaceae). Mortality was significantly higher on P. grandifolia with only 3% of the nymphs reaching the adult stage compared with 74% on P. aculeata indicating that P. aculeata is the primary host plant. P. grandifolia is native in South America and is of no agricultural importance in South Africa so any feeding on P. grandifolia in South Africa would have no negative environmental or economic consequences. In other tests, adult survival on P. aculeata [25.8 days (SE ± 3.74)] was significantly longer than on other test plant species [4.3 days (SE ± 0.36)] further confirming the host specificity of the species. Impact studies conducted in quarantine indicated that C. schaffneri is damaging to P. aculeata, significantly reducing the number of leaves and the shoot lengths of plants, even at relatively low insect densities. C. schaffneri is safe for release in South Africa and is likely to be a damaging and effective agent.

紫花苜蓿对牛角花齿蓟马为害的光合生理响应

PDF HTML阅读 XML下载 导出引用 引用提醒 紫花苜蓿对牛角花齿蓟马为害的光合生理响应 DOI: 10.5846/stxb201301250157 作者: 作者单位: 甘肃农业大学 草业学院,甘肃农业大学 草业学院,甘肃农业大学 草业学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家现代牧草产业技术体系建设专项（CARA-35）；教育部高校博士学科点基金项目（20106202110003）；国家自然科学基金项目（31260579） Photosynthetic physiological response of Medicago sativa to Odontothrips loti damage Author: Affiliation: College of Grassland Science, Gansu Agricultural University,College of Grassland Science, Gansu Agricultural University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为了探索紫花（Medicago sativa L.）苜蓿对优势种害虫——牛角花齿蓟马（Odontothrips loti Haliday）为害的光合生理响应机制，揭示苜蓿对牛角花齿蓟马为害的补偿机制，以抗蓟马苜蓿无性系R-1和感蓟马苜蓿无性系I-1为材料，测定不同虫口密度牛角花齿蓟马为害后R-1、I-1无性系气体交换参数、叶绿素荧光诱导动力学参数的变化。结果表明：随着牛角花齿蓟马虫口密度的增加，R-1无性系叶绿素含量先升高后降低，I-1无性系叶绿素含量降低，R-1、I-1无性系的净光合速率（Pn）和水分利用效率（WUE）降低，胞间CO2浓度（Ci）、气孔导度（Gs）和蒸腾速率（Tr）升高；在相同虫口密度下，R-1无性系的叶绿素含量、Pn、WUE均高于I-1无性系。随着虫口密度的增加，R-1、I-1无性系的初始荧光（F0）升高，PSⅡ实际光合效率（ФPSⅡ）、非光化学淬灭系数（NPQ）、光化学淬灭系数（qP）、PSⅡ潜在活性（Fv/F0）和PSⅡ原初光能转化效率（Fv/Fm）均降低；在相同虫口密度下，R-1无性系的F0低于I-1无性系，R-1无性系的ФPSⅡ、qP、Fv/F0和Fv/Fm均高于I-1无性系。从各个指标的变化幅度来看，随着虫口密度的增加，R-1无性系气体交换参数和绿素荧光动力学参数的增幅、降幅均小于I-1无性系。说明牛角花齿蓟马为害造成了紫花苜蓿PSⅡ反应中心受损，使得紫花苜蓿对光能的利用能力下降，光合效率降低。但在低虫口密度（1、3头/枝条）下，R-1无性系具有较高的光合效率，光合补偿效应显著大于I-1无性系，说明R-1无性系对牛角花齿蓟马为害具有较强的抗性。 Abstract:Plant photosynthetic capability usually changes after damage by a herbivorous pest. Photosynthetic compensation is the physiological response of the plant to pest damage with the level of compensation varying with the change in pest damage. This paper explores the photosynthetic response mechanism of alfalfa to the dominant insect-Odontothrips loti -and explains the compensatory mechanism of alfalfa to thrip damage. The thrip resistant clone, R-1 and susceptible clone, I-1 were used to investigate the gas exchange and chlorophyll fluorescence parameter changes under different insect densities (0, 1, 3, 5, and 7 per branch, respectively), Photosynthesis equipment, GFS-3000 (Walz,Germany) and modulated chlorophyll fluorometer imaging-PAM (Walz,Germany) were used. For the 7 per branch treatment, the results indicate that the chlorophyll content of R-1 initially increased and then decreased, while the chlorophyll content of I-1 decreased. For R-1, the chlorophyll content was 11.32% lower than CK (0 thrip per branch), and for the 3, 5, and 7 per branch treatments of I-1, the chlorophyll contents were 14.05%, 22.02% and 26.27% lower than CK, respectively. For both R-1 and I-1, the net photosynthetic rate (Pn) and water use efficiency (WUE) decreased, while the intracellular concentration of CO2 (Ci), stomatal conductance (Gs) and transpiration rate (Tr) increased. For R-1, the Pn of 3, 5, and 7 per branch treatments were 6.98%, 19.03% and 20.11% lower than CK, and the WUE of all the treatments were 16.32%, 23.95%, 37.12% and 45.89% lower than CK. For I-1 treatments, the Pn of all the treatments were 5.38%, 8.77%, 22.47% and 35.66% lower than CK, and the WUE were 25.23%, 31.05%, 45.78% and 61.81% lower than CK, respectively. The chlorophyll content, WUE and Pn of R-1 were all greater than I-1 under the same insect density. As insect density increased, the initial fluorescence (F0) increased, which for the R-1 clone resulted in F0 for 5 and 7 per branch treatments of 6.99% and 9.13% higher than CK, respectively. For the I-1 clone, all the treatments were 2.81%, 6.45%, 12.36% and 14.93% higher than CK, respectively. The actual photosynthetic efficiency (ФPSⅡ) of PSⅡ, non-photochemical quenching coefficient (NPQ), photochemical quenching coefficient (qP), potential activity (Fv/F0) of PSⅡ and original light transformation efficiency (ФPSⅡ) of PSⅡ decreased for both R-1 and I-1. Among which the Fv/F0 of 3, 5 and 7 per branch treatments for the R-1 clone were 5.07%, 16.74% and 21.19% lower than CK and the Fv/Fm of 5 and 7 per branch treatments were 3.50% and 4.63% lower than CK, respectively. For the I-1 clone, Fv/F0 of all the treatments were 8.24%, 13.68%, 22.88% and 28.04% lower than CK, and the Fv/Fm were 1.67%, 2.91%, 5.31% and 6.86% lower than CK, respectively. Under the same insect density, R-1 was found to have a lower F0 but higher ФPSⅡ, qP, Fv/F0 and Fv/Fm, when compared with I-1. As a rule, the gas exchange parameter and chlorophyll fluorescence kinetic parameter of R-1 fluctuated less than I-1, indicating that the thrip's rasping-sucking damage had injured the chloroplast tissue of alfalfa leaves, decreased the anabolism of chlorophyll, aggravated leaf transpiration, decreased WUE, and therefore affected alfalfa photosynthesis. The thylakoid membrane in the alfalfa leaves and PSⅡ reaction center were injured, which decreased the absorption of light energy, and impeded the photosynthetic electron transport, reducing its photosynthetic efficiency. While under lower insect densities (1 per branch, 3 per branch), the R-1 clone had a stronger capability to adjust for water loss and usage after being damaged by the thrip, demonstrating adaptability to the thrip's rasping-sucking damage through internal regulation, lowering PSⅡ damage, with higher absorption, transmission, use and conversion efficiency. Therefore the R-1 clone was found to have a stronger resistance to thrips when compared with the I-1 clone, as expressed by the higher photosynthetic efficiency and photosynthetic compensation effect. 参考文献 相似文献 引证文献

An Insect-Feeding Guild of Carnivorous Plants and Spiders: Does Optimal Foraging Lead to Competition or Facilitation?

Carnivorous plants and spiders, along with their prey, are main players in an insect-feeding guild found on acidic, poorly drained soils in disturbed habitat. Darwin's notion that these plants must actively attract the insects they capture raises the possibility that spiders could benefit from proximity to prey hotspots created by the plants. Alternatively, carnivorous plants and spiders may deplete prey locally or (through insect redistribution) more widely, reducing each other's gain rates from predation. Here, we formulate and analyze a model of this guild, parameterized for carnivorous sundews and lycosid spiders, under assumptions of random movement by insects and optimal foraging by predators. Optimal foraging here involves gain maximization via trap investment (optimal web sizes and sundew trichome densities) and an ideal free distribution of spiders between areas with and without sundews. We find no facilitation: spiders and sundews engage in intense exploitation competition. Insect attraction by plants modestly increases sundew gain rates but slightly decreases spider gain rates. In the absence of population size structure, optimal spider redistribution between areas with and without sundews yields web sizes that are identical for all spiders, regardless of proximity to sundews. Web-building spiders have higher gain rates than wandering spiders in this system at high insect densities, but wandering spiders have the advantage at low insect densities. Results are complex, indicating that predictions to be tested empirically must be based on careful quantitative assessment.

Natural occurrence of Zoophthora radicans (Entomophthorales: Entomophthoraceae) on Thaumastocoris peregrinus (Heteroptera: Thaumastocoridae), an invasive pest recently found in Brazil

Occurrence of Zoophthora radicans infecting nymphs and adults of Thaumastocoris peregrinusCarpintero and Dellape, 2006 is reported in Brazil. This is a new record of host for this fungal species and the first fungal pathogen associated with this pest worldwide. Infection of Z. radicans on T. peregrinus populations on commercial Eucalyptus plantation (Eucalyptus spp.) reached up to 100%, and low insect densities were associated with high levels of fungal infection in three out of seven plots. This pathogen seems to be virulent against T. peregrinus and may play an important role in population regulations of this invasive pest through naturally induced epizootics.

Evaluation of sampling units and sampling plans for adults of Cryptolestes ferrugineus (Coleoptea: Laemophloeidae) in stored wheat under different temperatures, moisture contents, and adult densities

Development and evaluation of optimum size and number of sample units is required for cost-effective management of stored grain beetles. In this study, we evaluated the sampling parameters and accuracy of insect density detection and estimation, developed the optimum size and number of sample units, and conducted a feasibility study of the insect detection and density estimation. The measured insect densities in 92% of random samples were less than the introduced insect densities and 67.4 ± 10.8% of random samples did not contain adults when the introduced insect density was 0.1 A/kg (adult/kg). If the random sampling technique was used and 15% of the stored wheat bulk was sampled, 72% of determined means of insect densities of the sampling sets were lower than the introduced insect densities. Increasing the size of sample units did not improve the accuracy of the estimation of insect densities; however, it did considerably increase the probability of insect detection when insect densities were lower than 1.0 A/kg. We recommend at least 7 kg per sample unit for insect detection (especially when insect densities < 0.1 A/kg) and the optimum number of sample units with 15 kg grain per unit should be >24 for a fixed precision of 0.35 when insect densities < 0.1 A/kg. This might be a challenge for grain storage practice. Therefore, using sampling technique to estimate insect densities and detect insects at low insect densities (<0.1 A/kg) might not be practicable.

Three-dimensional spatial distribution of adults of Cryptolestes ferrugineus (Coleoptera: Laemophloeidae) in stored wheat under different temperatures, moisture contents, and adult densities

Spatial and temporal distributions of adults of Cryptolestes ferrugineus in stored wheat were determined in a 1.5 t bin of wheat held at 20, 25 and 30 °C and 11%, 13% and 15% grain moisture contents (wet basis). The introduced insect densities were 0.1 (low), 1.0 (medium), and 10.0 (high) adults/kg wheat and the 1.5 t of wheat was sampled at 5 locations with 45 kg in a sample unit (referred to as primary unit, about 15% of the wheat was sampled). At each location, the 45 kg sample unit was separated into three 15 kg vertical layers (referred to as subunits). Geostatistical analysis showed that: 1) insect numbers at medium or high density and in the vertical direction were better correlated than that at low insect density and in the horizontal direction, respectively; 2) this correlation decreased with increasing grain temperatures; and 3) the temporal continuous property might not exist or there was a weak temporal continuity. Aggregation was the highest at the low insect density and then decreased with the increase of insect density due to a repelling effect amongst adults at high insect density. The normal distribution model was appropriate for the description of the count frequency in 32 out of 36 sampling sets (88.9%) when 15 kg subunit data were used. In addition, adults of C. ferrugineus had clumped distribution about 95% of the time and uniform dispersion about 5% of the time. This is the first research illustrating the spatial and temporal distributions of adult C. ferrugineus using large sample units and known insect densities.

Densovirus induces winged morphs in asexual clones of the rosy apple aphid, Dysaphis plantaginea

Winged morphs of aphids are essential for their dispersal and survival. We discovered that the production of the winged morph in asexual clones of the rosy apple aphid, Dysaphis plantaginea, is dependent on their infection with a DNA virus, Dysaphis plantaginea densovirus (DplDNV). Virus-free clones of the rosy apple aphid, or clones infected singly with an RNA virus, rosy apple aphid virus (RAAV), did not produce the winged morph in response to crowding and poor plant quality. DplDNV infection results in a significant reduction in aphid reproduction rate, but such aphids can produce the winged morph, even at low insect density, which can fly and colonize neighboring plants. Aphids infected with DplDNV produce a proportion of virus-free aphids, which enables production of virus-free clonal lines after colonization of a new plant. Our data suggest that a mutualistic relationship exists between the rosy apple aphid and its viruses. Despite the negative impact of DplDNV on rosy apple aphid reproduction, this virus contributes to their survival by inducing wing development and promoting dispersal.

Food limitation and insect outbreaks: complex dynamics in plant–herbivore models

1. The population dynamics of many herbivorous insects are characterized by rapid outbreaks, during which the insects severely defoliate their host plants. These outbreaks are separated by periods of low insect density and little defoliation. In many cases, the underlying cause of these outbreaks is unknown. 2. Mechanistic models are an important tool for understanding population outbreaks, but existing consumer-resource models predict that severe defoliation should happen much more often than is seen in nature. 3. We develop new models to describe the population dynamics of plants and insect herbivores. Our models show that outbreaking insects may be resource-limited without inflicting unrealistic levels of defoliation. 4. We tested our models against two different types of field data. The models successfully predict many major features of natural outbreaks. Our results demonstrate that insect outbreaks can be explained by a combination of food limitation in the herbivore and defoliation and intraspecific competition in the host plant.

Fieberiella florii (Homoptera: Auchenorrhyncha) as a Vector of "Candidatus Phytoplasma mali".

Laboratory trials were carried out to transmit "Candidatus Phytoplasma mali" to healthy apple seedlings with the leafhopper Fieberiella florii. Experiments on serial inoculation access period and molecular analyses performed on test plants and insects confirmed the ability of the leaf-hopper to carry and transmit the phytoplasma. Field surveys by means of yellow sticky traps were conducted in northwestern Italy to verify the abundance and the natural infectivity of F. florii in apple orchards and in wild vegetation in areas surrounding apple orchards. Despite the high percentages of infected specimens obtained in the apple orchards (5.7%) and in the wild vegetation areas (20.0%), the risk of apple tree infection by F. florii in nature is probably low because of the very low insect density recorded. In spite of the low number of specimens collected, the presence of the leafhopper in apple orchards in summer, when the main vector, the psyllid Cacopsylla melanoneura, feeds on alternative hosts, is meaningful. Moreover, the high degree of polyphagy of the leafhopper opens up new interesting prospects for the epidemiology of apple proliferation.

Movement and distribution of adult rusty grain beetle, Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), in stored wheat in response to different temperature gradients and insect densities.

The movement and distribution of adult Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae) in grain provide important information for detection of insect pests and for simulations of their distribution in grain bins. Adult movement and distribution were determined in 100 by 100 by 1000-mm wheat (14.5 +/- 0.2% moisture content) columns at four insect densities, three temperature gradients, and dynamic (changing) temperature conditions. Insect density was a minor factor influencing insect movement and distribution in grain columns with temperature gradients. Dispersal resulted in a uniform distribution at a higher insect density (higher than two adults per kilogram of wheat), and aggregation occurred at a low insect density. Adults wandered in the first 6 h after introduction, and there were fewer adults wandering in the vertical direction than in the horizontal direction. Adults moved faster in the vertical direction than in the horizontal direction, and the maximum speed of the movement was 6 m/d in the horizontal direction, and >10.8 m/d in the vertical direction through wheat. Adults could detect temperature gradients in <1 h and preferred warmer temperatures when they had a choice. Insect distribution in horizontal wheat columns at any temperature gradient was unstable for 24 h. Twenty-four hours after introduction, adults gradually overcame their positive geotactic behavior if the upper temperature was more biologically suitable or was not <27.5 degrees C. Adults responded faster to higher temperature gradients than to lower temperature gradients. There was a similar pattern of adult distribution in 144 h.

Interactions of colonisation density and leaf environments on survival of Trioza eugeniae nymphs

Summary1. Female eugenia psyllids Trioza eugeniae oviposit on the margins of expanding young Syzygium paniculatum leaves. The developing nymphs, feeding within pit‐shaped galls on the leaves, cause the leaves to become curled and deformed. The degree of leaf curling was correlated positively with densities of T. eugeniae nymphs.2. High relative humidity increased persistence of nymphs on leaves at low insect densities, but persistence did not differ between high or low relative humidity conditions when nymphal densities were high and leaves were greatly curled.3. Direct insolation increased nymphal mortality. Nymphs on the abaxial leaf surface in the direct sun had lower mortality than similarly exposed nymphs on the adaxial leaf surface.4. Field populations showed high preference for abaxial leaf surfaces and a stronger preference for shaded adaxial surfaces than for exposed adaxial surfaces.5. Adverse environmental conditions of direct insolation and low relative humidity may be mitigated by leaf curl associated with moderate populations, however competition at high nymphal density supersedes any potential benefit arising from leaf curling and has a negative effect on nymphal survival.

A Theoretical Assessment of the Effects of Vector-Virus Transmission Mechanism on Plant Virus Disease Epidemics

ABSTRACT A continuous-time and deterministic model was used to characterize plant virus disease epidemics in relation to virus transmission mechanism and population dynamics of the insect vectors. The model can be written as a set of linked differential equations for healthy (virus-free), latently infected, infectious, and removed (postinfectious) plant categories, and virus-free, latent, and infective insects, with parameters based on the transmission classes, vector population dynamics, immigration/emigration rates, and virus-plant interactions. The rate of change in diseased plants is a function of the density of infective insects, the number of plants visited per time, and the probability of transmitting the virus per plant visit. The rate of change in infective insects is a function of the density of infectious plants, the number of plants visited per time by an insect, and the probability of acquiring the virus per plant visit. Numerical solutions of the differential equations were used to determine transitional and steady-state levels of disease incidence (d*); d* was also determined directly from the model parameters. Clear differences were found in disease development among the four transmission classes: nonpersistently transmitted (stylet-borne [NP]); semipersistently transmitted (foregut-borne [SP]); circulative, persistently transmitted (CP); and propagative, persistently transmitted (PP), with the highest disease incidence (d) for the SP and CP classes relative to the others, especially at low insect density when there was no insect migration or when the vector status of emigrating insects was the same as that of immigrating ones. The PP and CP viruses were most affected by changes in vector longevity, rates of acquisition, and inoculation of the virus by vectors, whereas the PP viruses were least affected by changes in insect mobility. When vector migration was explicitly considered, results depended on the fraction of infective insects in the immigration pool and the fraction of dying and emigrating vectors replaced by immigrants. The PP and CP viruses were most sensitive to changes in these factors. Based on model parameters, the basic reproductive number (R(0))-number of new infected plants resulting, from an infected plant introduced into a susceptible plant population-was derived for some circumstances and used to determine the steady-state level of disease incidence and an approximate exponential rate of disease increase early in the epidemic. Results can be used to evaluate disease management strategies.

Tritrophic interactions: willows, herbivorous insects and insectivorous birds.

Insectivorous birds can increase plant growth by consuming herbivorous insects and reducing insect damage. However, plant traits such as the level of chemical defense may affect the quantity and quality of insects, and alter the foraging behavior of birds. Therefore, I predicted that plant traits can also modify the effect of birds on leaf damage and plant growth. This study compared the effect of insectivorous birds on the herbivory and growth of two chemically different willow species, weakly defended Salix phylicifolia and strongly defended S. myrsinifolia under two fertilization levels. Half of the willows were protected from birds using a translucent gill-net, which did not limit access by insects. The effect of birds on the densities of leaf-chewing insects and leaf damage was considerable on unfertilized S. phylicifolia but less obvious on fertilized ones. The effect of bird predation was negligible on S. myrsinifolia, which had very low insect densities in all treatments. Birds increased the growth of the experimental willows, but the effect was clear only in unfertilized S. phylicifolia. I suggest that birds avoided foraging on willows with low populations of insects and little visible damage. The study shows that bird predation can alter the patterns of insect densities we see on willows, emphasizing the importance of considering multitrophic effects when studying plant-insect interactions.

Diversity and abundance of insect herbivores foraging on seedlings in a rainforest in Guyana

Summary1. Free‐living insect herbivores foraging on 10 000 tagged seedlings representing five species of common rainforest trees were surveyed monthly for more than 1 year in an unlogged forest plot of 1 km2 in Guyana.2. Overall, 9056 insect specimens were collected. Most were sap‐sucking insects, which represented at least 244 species belonging to 25 families. Leaf‐chewing insects included at least 101 species belonging to 16 families. Herbivore densities were among the lowest densities reported in tropical rainforests to date: 2.4 individuals per square metre of foliage.3. Insect host specificity was assessed by calculating Lloyd’s index of patchiness from distributional records and considering feeding records in captivity and in situ. Generalists represented 84 and 78% of sap‐sucking species and individuals, and 75 and 42% of leaf‐chewing species and individuals. In particular, several species of polyphagous xylem‐feeding Cicadellinae were strikingly abundant on all hosts.4. The high incidence of generalist insects suggests that the Janzen–Connell model, explaining rates of attack on seedlings as a density‐dependent process resulting from contagion of specialist insects from parent trees, is unlikely to be valid in this study system.5. Given the rarity of flushing events for the seedlings during the study period, the low insect densities, and the high proportion of generalists, the data also suggest that seedlings may represent a poor resource for free‐living insect herbivores in rainforests.

Sex attractant dispensers for monitoring antler moth Cerapteryx graminis(L.) (Lep., Noctuidae): Effect of component ratio and dispenser type

Abstract: Male antler moths (Cerapteryx graminis) were attracted to traps baited with dispensers loaded with mixtures varying between 7.3 and 4.6 of Z11–16:Ald and Z11–16:Ac. The blends between 7–20% of Z11–16:Ac and 93–80% of Z11–16:Ald in its evaporated phase yielded the greatest catches in field trials. No variations in trap catches within these ratios were noticed. Additionally the emission rates of the attractive blend varying between 37 and 534 ng/h, trap catches decreased by 80% over the same period. The addition of Z11–16.OH had a strong inhibiting effect on the trap catches. Trap catches of different types of dispensers having evaporation area‐to‐volume between 1.2 mm−1 and 1.8 mm−1 were dependent on emission rates and ratios of Z11–16:Ald and Z11–16:Ac in evaporated phase. Minifer type dispensers with evaporation area‐to‐volume 1.5 mm−1 and higher evaporation rates are more economic and convenient to use. Attractant traps started to catch at earlier dates than light traps and were more attractive at lower insect densities.

Nonlinearity of a Generic Variance–Mean Equation for Stored-Grain Insect Sampling Data

Equations predicting the variance for a mean insect density have been widely used to calculate the precision of density estimates. Traditionally, the logarithm of the variance is regressed against the logarithm of the mean giving a linear equation. We fit a single nonlinear variance-mean regression equation to 4 stored-product insect sampling data sets. This generic nonlinear regression equation described the stored-product insect sampling data for 25 additional studies, 3 different sampling methods, and the 6 most commonly encountered species. The asymptotic slope of this generic nonlinear regression equation increased with insect density, and at mean densities of 0.01, 0.1, 1, 10, and 100 insects per sample unit was 1.06, 1.32, 1.64, 2.05, and 2.55, respectively. This density-dependent change in the asymptotic slope explains the differences among studies in the slopes of linear regression equations. We generated a similar regression equation by randomly assigning insects to sampling units to simulate random dispersal of insects in a grain mass. This suggests that the observed insect sampling distributions could be the result of random dispersal, and that the mechanism underlying the regression equation is fairly general. Compared with the predictions of the generic nonlinear regression equation, the linear regression equation overpredicted the 95% CL within the 0.3-3 insects per sample unit density range, and underpredicted them at higher or lower insect densities. This generic nonlinear regression equation can be used to calculate the precision of mean insect density estimates over a 0.025-100 insects per sample unit density range and thus reduce the cost of developing new sampling programs.

Efficiency of various insects in germplasm regeneration of carrot, onion and turnip rape accessions

AbstractSeed regeneration is one of the most important tasks in genebank work. To regenerate germplasm of allogamous, entomophilous plant species in isolation facilities, insects are often used as pollen vectors. The objective of this study was to determine the effect of pollinator species, pollinator densities, pollinator combinations, and flower preferences on the seed quantity and quality of Daucus carota, Allium cepa, and Brassica rapa. The isozyme phosphoglucoisomerase (PGI) served as genetic marker in determining outcrossing rates and pollen dispersal distances. Field plots and isolation cages without insects were used as controls. The pollinators studied consisted of the following insect species from German native fauna: red mason bees (Osmia rufa L.), hoverflies (Eristalis tenax L.), and blowflies (Calliphora sp. and Lucilia sp.). In D. carota and B. rapa, higher seed yields were achieved in isolation cages than in field plots, but in A. cepa lower seed yields were obtained in the isolation cages. Although O. rufa showed no liking for A. cepa, unintentional pollination was effected by this insect in isolation cages. Lower insect densities were necessary for O. rufa than for the various fly species.

Function of pipistrelle social calls: field data and a playback experiment

The study aimed to determine whether the so-called social calls that are produced by foraging bats of two phonic types ofPipistrellus pipistrellusserve a social function. First, the relationship between insect availability and the rate of production of social calls was measured at a foraging site of both phonic types. Second, playback experiments of social calls of the two phonic types were conducted in the field to determine the response of foraging bats to these calls, and to determine whether the calls are used in communication within or between phonic types. Two hypotheses are suggested for the function of social calls: that they may be used either to attract other bats to a food patch, or in agonistic interactions between bats in defence of a food patch. At relatively low insect densities, the rate of social call production of both phonic types increased significantly as insect density decreased. When social calls of each phonic type were broadcast, there was a significant reduction in bat activity of the same phonic type. In contrast, playbacks of social calls resulted in no change in activity of the other phonic type. The results supported the food patch defence hypothesis, that social calls are used to warn off other bats of the same phonic type when insects are scarce. The results also supported the hypothesis that the two phonic types are sibling species. Social calls were shown to serve a social function in intraspecific communication, but there was no communication between phonic types. 1997 The Association for the Study of Animal Behaviour