The role of grasslands in the yearly life-cycle of Rhopalosiphum padi (Homoptera: Aphididae) in Sweden.

The population density of the bird cherry-oat aphid (Rhopalosiphum padi) was monitored in spring sown barley and in grasslands (leys and pastures) and a suction trap was used to monitor the flight periodicity of the aphids. Emigrants from the primary host (bird cherry) colonised both grass and cereals in spring and a migration from cereals to grasses took place in mid-summer. There was a negative correlation between the sizes of summer and autumn migration. There was a positive relationship between late summer growth in leys and the size of autumn migrations. It is concluded that the size of the autumn migration is mainly dependent on aphid population growth in grasslands during late summer and autumn.     

Spread of barley yellow dwarf virus and relative importance of local aphid vectors in central Washington

Data from bioassays of field collected aphids, barley indicator plants exposed to natural conditions, and various types of aphid traps were used to describe the spread of barley yellow dwarf virus (BYDV) in wheat and barley near Prosser, Washington. Bioassays were also used to assess the relative importance of local vector species. Of alate aphids collected from grain in the 1982 and 1983 fall migration seasons, 3.4–14–5% transmitted BYDV. Data from concurrent and post-migration assays of resident aphids (apterae and nymphs) reflected an increase in the proportion of infected plants in the field. Maximum increase in the percentage of viruliferous aphids occurred in late November and December of 1982 and November of 1983. The 1982 increase occurred after aphid flights had ceased for the year, suggesting active secondary spread. Collections in pitfall traps and infected trap plants from November to February confirmed aphid activity and virus spread. Rhopalosiphum padi was the most important vector in central Washington in 1982 and 1983 because of its abundance and relative BYDV transmission efficiency. Metopolophium dirhodum was more winter-hardy than R. padi and equal to R. padi in its efficiency as a vector; however, it was not as abundant as R. padi except during the mild winter of 1982–83, when it was a major contributor to secondary spread. Sitobion avenae may be important in years when it is abundant, but it was only a quarter as efficient as R. padi. Rhopalosiphum maidis was a much less efficient vector than R. padi and it only reached high populations in late autumn barley.     

Forecasting migration of cereal aphids (Hemiptera: Aphididae) in autumn and spring

The migration of cereal aphids and the time of their arrival on winter cereal crops in autumn and spring are of particular importance for plant disease (e.g. barley yellow dwarf virus infection) and related yield losses. In order to identify days with migration potentials in autumn and spring, suction trap data from 29 and 45 case studies (locations and years), respectively, were set‐off against meteorological parameters, focusing on the early immigration periods in autumn (22 September to 1 November) and spring (1 May to 9 June). The number of cereal aphids caught in a suction trap increased with increasing temperature, global radiation and duration of sunshine and decreased with increasing precipitation, relative humidity and wind speed. According to linear regression analyses, the temperature, global radiation and wind speed were most frequently and significantly associated with migration, suggesting that they have a major impact on flight activity. For subsequent model development, suction trap catches from different case studies were pooled and binarily classified as days with or without migration as defined by a certain number of migrating cereal aphids. Linear discriminant analyses of several predictor variables (assessed during light hours of a given day) were then performed based on the binary response variables. Three models were used to predict days with suction trap catches ≥1, ≥4 or ≥10 migrating cereal aphids in autumn. Due to the predominance of Rhopalosiphum padi individuals (99.3% of total cereal aphid catch), no distinction between species (R. padi and Sitobion avenae) was made in autumn. As the suction trap catches were lower and species dominance changed in spring, three further models were developed for analysis of all cereal aphid species, R. padi only, and Metopolophium dirhodum and S. avenae combined in spring. The empirical, cross‐classification and receiver operating characteristic analyses performed for model validation showed different levels of prediction accuracy. Additional datasets selected at random before model construction and parameterization showed that predictions by the six migration models were 33–81% correct. The models are useful for determining when to start field evaluations. Furthermore, they provide information on the size of the migrating aphid population and, thus, on the importance of immigration for early aphid population development in cereal crops in a given season.     

The role of refuge areas in the phenology of Rhopalosiphum padi in low rainfall cropping areas of South Australia

Extensive surveys of possible aphid habitats in South Australia indicated that irrigated perennial grass pastures in the Mount Lofty Ranges and Lower Murray Valley were summer refuges for Rhopalosiphum padi (L.) (Hemiptera: Aphididae). Large numbers of aphids build up in these pastures each year during autumn (April and May) with numbers peaking in May. The size of the May peak was related to the number of aphids surviving the summer. The proportions of alates were highest in May and August/September. Both peaks coincided with a photoperiod of between 11.2 and 11.5 h, and partial correlations suggested that aphid density, photoperiod and temperature were all significant determinants of alate production.     

Aphid and host‐plant genotype × genotype interactions under elevated CO2

1. Elevated CO₂ can alter plant physiology and morphology, and these changes are expected to impact diet quality for insect herbivores. While the plastic responses of insect herbivores have been well studied, less is known about the propensity of insects to adapt to such changes. Genetic variation in insect responses to elevated CO₂ and genetic interactions between insects and their host plants may exist and provide the necessary raw material for adaptation. 2. We used clonal lines of Rhopalosiphum padi (L.) aphids to examine genotype‐specific responses to elevated CO₂. We used the host plant Schedonorus arundinaceus (tall fescue; Schreb), which is capable of asexual reproduction, to investigate host plant genotype‐specific effects and possible host plant‐by‐insect genotype interactions. The abundance and density of three R. padi genotypes on three tall fescue genotypes under three concentrations of CO₂ (ambient, 700, and 1000 ppm) in a controlled greenhouse environment were examined. 3. Aphid abundance decreased in the 700 ppm CO₂ concentration, but increased in the 1000 ppm concentration relative to ambient. The effect of CO₂ on aphid density was dependent on host plant genotype; the density of aphids in high CO₂ decreased for two plant genotypes but was unchanged in one. No interaction between aphid genotype and elevated CO₂ was found, nor did we find significant genotype‐by‐genotype interactions. 4. This study suggests that the density of R. padi aphids feeding on tall fescue may decrease under elevated CO₂ for some plant genotypes. The likely impact of genotype‐specific responses on future changes in the genetic structure of plant and insect populations is discussed.     

The effect of landscape complexity and microclimate on the thermal tolerance of a pest insect

Landscape changes are known to exacerbate the impacts of climate change. As such, understanding the combined effect of climate and landscape on agroecosystems is vital if we are to maintain the function of agroecosystems. This study aimed to elucidate the effects of agricultural landscape complexity on the microclimate and thermal tolerance of an aphid pest to better understand how landscape and climate may interact to affect the thermal tolerance of pest species within the context of global climate change. Meteorological data were measured at the landscape level, and cereal aphids (Sitobion avenae, Metopolophium dirhodum and Rhopalosiphum padi) sampled, from contrasting landscapes (simple and complex) in winter 2013/2014 and spring 2014 in cereal fields of Brittany, France. Aphids were returned to the laboratory and the effect of landscape of origin on aphid cold tolerance (as determined by CT_min) was investigated. Results revealed that local landscape complexity significantly affected microclimate, with simple homogenous landscapes being on average warmer, but with greater temperature variation. Landscape complexity was shown to impact aphid cold tolerance, with aphids from complex landscapes being more cold tolerant than those from simple landscapes in both winter and spring, but with differences among species. This study highlights that future changes to land use could have implications for the thermal tolerance and adaptability of insects. Furthermore, not all insect species respond in a similar way to microhabitat and microclimate, which could disrupt important predator–prey relationships and the ecosystem service they provide.     

基于吸虫塔（Suction Trap）的蚜虫测报预警网络的构建

吸虫塔（suction trap）是用来监测麦类蚜虫和大豆蚜Aphis glycines迁飞种群动态的大型植保测报设备,在欧洲和北美洲已经呈网络安装分布,为蚜虫的预警和防控提供重要依据。作者借鉴欧美吸虫塔的工作原理和设计,设计并生产了符合我国地域特征的吸虫塔设备,在东北、华北、华中、华东、西北等地布点安装了21台,用于监控我国麦类蚜虫和大豆蚜的迁飞动态,初步形成覆盖我国小麦主产区和大豆主产区的吸虫塔网络系统。此吸虫塔总高8.8m,由底部轴流风机运转产生的负压在塔顶部形成吸力,将迁飞经附近的小型昆虫吸入塔管,最后落入下部的样品收集瓶中,以此获得其迁飞的动态数据。吸虫塔网络的构建和完善,不仅为麦类蚜虫和大豆蚜的监控提供支撑,同时也为其它小型迁飞性昆虫监测、种群动态、生物多样性、生物信息学等研究提供数据。     

Models for spring migration of two aphid species Sitobion avenae (F.) and Rhopalosiphum padi (L.) infesting cereals in areas where they are entirely holocyclic

1 Cereals can be attacked severely by the grain aphid, Sitobion avenae (F.), and the bird cherry‐oat aphid, Rhopalosiphum padi (L.). The time of migration from winter hosts in spring is important regarding input to decision support systems concerning insecticide treatment of aphids. 2 The present study aimed to construct two separate migration models, which could be used immediately for advisors and farmers but also be part of a decision support system for the chemical control of aphids in winter wheat and spring barley. 3 Winter wheat (Triticum sativum Lam.) and spring barley (Hordeum vulgare L.) fields were monitored from 1991–2005 for the occurrence of grain aphids and bird cherry‐oat aphids, and the data were used to construct migration models. 4 The models were constructed based on all 9 years data and subsequently validated by using all 9 years data, excluding 1 year at a time. 5 The migration model for the grain aphid producing the best forecast was obtained with migration date M (number of days from 1 June), degree‐days (DD) of April (T_a) and DD of May (T_m), with the model being M= 265.0 ? 10.2 log_e(T_a) ? 35.1 log_e(T_m). 6 The migration model for the bird cherry‐oat aphid producing the best forecast was obtained with migration date M (number of days from 15 May), DD of April (T_a) and DD from 1–15 May (T_m1), with the model being M= 294.4 ? 34.7 log_e(T_a) ? 22.5 log_e(T_m1). 7 The models only worked well in areas where the grain aphid and the bird cherry‐oat aphid are entirely holocyclic.     

The price of protection:a defensive endosymbiont impairs nymph growth in the bird cherry-oat aphid,Rhopalosiphum padi

Bacterial endosymbionts have enabled aphids to adapt to a range of stressors,but their effects in many aphid species remain to be established.The bird cherry-oat aphid,Rhopalosiphum padi(Linnaeus),is an important pest of cereals worldwide and has been reported to form symbiotic associations with Serratia symbiotica and Sitobion miscanthi L-type symbiont endobacteria,although the resulting aphid phenotype has not been described.This study presents the first report of R.padi infection with the facultative bacterial endosymbiont Hamiltonella defensa.Individuals of R.padi were sampled from populations in Eastern Scotland,UK,and shown to represent seven R.padi genotypes based on the size of polymorphic microsatellite markers;two of these genotypes harbored H.defensa.In parasitism assays,survival of H.defensa-infected nymphs following attack by the parasitoid wasp Aphidius colemani(Viereck)was 5 fold higher than for uninfected nymphs.Aphid genotype was a major determinant of aphid performance on two Hordeum species,a modern cultivar of barley H.vulgare and a wild relative H.spontaneum,although aphids infected with H.defensa showed 16%lower nymph mass gain on the partially resistant wild relative compared with uninfected individuals.These findings suggest that deploying resistance traits in barley will favor the fittest R.padi genotypes,but symbiontinfected individuals will be favored when parasitoids are abundant,although these aphids will not achieve optimal performance on a poor quality host plant.     

Comparison of α- and β-mannosidase activity in the three cereal pests,Haplothrips tritici Kurdjumov (Thysanoptera: Phlaeothripidae), Rhopalosiphum padi L. (Homoptera: Aphididae) and Eurygaster integriceps Puton (Hemiptera: Scutelleridae)

The Sunn pest, Eurygaster integriceps, the bird cherry-oat aphid, Rhopalosiphum padi, and wheat thrips, Haplothrips tritici are the major pests of wheat and other cereals in a wide area of the world. All these three insect species could produce damage to the wheat to some extent. Therefore, the purpose of the present study was to determine α- and β-mannosidase of the three mentioned insect pests. These insects were collected from the wheat farm and their guts (the Sunn pest and the aphid) and salivary glands of Sunn pest were removed. However, regarding tiny body of thrips, the whole body used in order to extract the enzymes. The enzymes, including α- and β-mannosidase activity, were measured by the hydrolysis of p-nitrophenyl-α-d-mannopyranoside (pNPαGal) and p-nitrophenyl-β-d-mannopyranoside (pNPβGal), respectively, using phosphate citrate buffer (pH 5.0). Mannosidases were not active in all three tested insect species, and also there were significant differences in activities of the two enzymes in three species. The greatest activity of α-mannosidases was observed in the Sunn pest salivary glands, E. integriceps, and the least activity was found in Sunn pest midgut with no activity. However, the activity of β-mannosidase was established in Sunn pest midgut, but there was no activity in the aphid midgut, R. padi. Activities of these two enzymes were modest in the thrips, H. tritici. The greatest amount of β-mannosidases in the Sunn pest midgut makes sense, since the Sunn pest is the main pest in the wheat farm that can feed on wheat grains. In the wheat grains, the highest amount of glycoproteins and glycolipids are present. Thus, it has been known that these enzymes (α- and β-mannosidases) are active on digestion of carbohydrates.     

Density and distribution of soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae) in response to UV radiation

Increasing ultraviolet radiation (UV) has led to greater interest in its current and potential effects on organisms, including herbivorous insects. Here we report the short-term effects of UV on soybean aphids (Aphis glycines Matsumura), a common phytophagous pest of soybeans. We used two complementary approaches to examine how modifying UV radiation affects this phloem-feeding herbivore via changes to soybean aphid densities and their within plant distribution. We found that artificially adding UV in a lab setting decreased soybean aphid population size compared to a low UV control; however, blocking UV radiation in the field had minimal effects on aphid density. Further observations suggest that soybean aphid location could mediate UV effects; feeding on the underside of leaves may shield aphids from some harmful effects of UV. Our results demonstrate the potential importance of UV to insect herbivores and how behavior may influence such effects.     

Searching for wheat resistance to aphids and wheat bulb fly in the historical Watkins and Gediflux wheat collections

Insect pests can reduce wheat yield by direct feeding and transmission of plant viruses. Here we report results from laboratory and field phenotyping studies on a wide range of wheat, including landraces from the Watkins collection deriving from before the green revolution, more modern cultivars from the Gediflux collection (north‐western Europe) and modern UK Elite varieties, for resistance to the bird cherry‐oat aphid, Rhopalosiphum padi (Homoptera: Aphididae) and the English grain aphid, Sitobion avenae (Homoptera: Aphididae). A total of 338 lines were screened for R. padi and 340 lines for S. avenae. Field trials were also conducted on 122 Watkins lines to identify wheat bulb fly, Delia coarctata, preference on these landraces. Considerable variation was shown in insect performance among and within different wheat collections, with reduced susceptibility in a number of varieties, but phenotyping did not identify strong resistance to aphids or wheat bulb fly. Field trials showed within collection differences in aphid performance, with fewer aphids populating lines from the Watkins collection. This differs from development data in laboratory bioassays and suggests that there is a pre‐alighting cue deterring aphid settlement and demonstrates differences in aphid preference and performance on older plants in the field compared with seedlings in the laboratory, highlighting the need for phenotyping for aphid resistance at different plant growth stages. No association was identified between performance of the different insect species on individual varieties, potentially suggesting different nutritional requirements or resistance mechanisms.     

Characterisation of bird cherry-oat aphid (Rhopalosiphum padi L.) behaviour and aphid host preference in relation to partially resistant and susceptible wheat landraces

The bird cherry-oat aphid (Rhopalosiphum padi L.) is a major pest of wheat (Triticum aestivum L.) and can cause up to 30% yield losses. Heritable plant resistance to aphids is both an economically and ecologically sound method for managing aphids. Here we report how the behaviour and performance of R. padi differs on two resistant, one susceptible wheat landrace and a susceptible elite wheat variety. Feeding behaviour differed among the genotypes, with aphids on resistant lines spending longer in the pathway phase and less time phloem feeding. These behaviours suggest that both inter- and intracellular factors encountered during pathway and phloem feeding phases could be linked to the observed aphid resistance. Locomotion and antennal positioning choice tests also revealed a clear preference for susceptible lines. Although feeding studies revealed differences in the first probe indicating that the resistance factors might also be located in the peripheral layers of the plant tissue, scanning electron microscopy revealed no difference in trichrome length and density on the surface of leaves. Aphids are phloem feeders and limiting the nutrient uptake by the aphids may negatively affect their growth and development as shown here in lower weight and survival of nymphs on resistant genotypes and decreased reproductive potential, with lowest mean numbers of nymphs produced by aphids on W064 (54.8) compared to Solstice (71.9). The results indicate that resistant lines markedly alter the behaviour, reproduction and development potential of R. padi and possess both antixenosis and antibiosis type of resistance.     

Influence of drought on interactions between Rhopalosiphum padi and ground dwelling predators – A mesocosm study

Climate change will lead to extreme droughts, but it is difficult to predict how this will affect crop pests. In particular, it is unclear how interactions between natural enemies and pests will be influenced. In the field, bird cherry-oat aphids (Rhopalosiphum padi (L.)) have been observed to reside close to, or below the ground surface during dry conditions. We hypothesized that this will increase the niche overlap between R. padi and ground-dwelling predators such as carabid beetles and wolf spiders and that aphid numbers will therefore decline during dry conditions. A fully factorial mesocosm experiment was conducted testing the combined effects of drought and predator presence on aphid position and abundance on barley (Hordeum vulgare) plants. In support of our hypothesis, we found that (a) aphids moved below ground during dry conditions, (b) predators reduced aphid numbers, but only during dry conditions, and (c) predators reduced the proportion of aphids below ground in dry conditions. This increased predation effect during dry conditions was, however, compensated for by a corresponding increase in aphid performance on the plants and so the net effect of drought on aphid numbers ended up being neutral. Thus, pests can be affected by drought in complex ways via a combination top-down and bottom-up mechanisms. Predicting how pest populations will be affected by droughts in the future is thus a formidable research challenge.     

The potential of hydroxamic acids in tetraploid and hexaploid wheat varieties as resistance factors against the bird‐cherry oat aphid,Rhopalosiphum padi

The potential for exploiting natural wheat resistance to control the cereal aphid Rhopalosiphum padi, the most important aphid pest of small grain cereals in the UK, was investigated as an alternative approach to the use of insecticides. The investigation focussed on a group of secondary metabolites, the hydroxamic acids or benzoxazinones, present naturally as glucosides, but which hydrolyse on tissue damage to give biologically active aglycones, e.g. 2,4‐dihydroxy‐7‐methoxy‐1,4‐benzoxazin‐3‐one (DIMBOA) which are associated with natural plant defence. These can be important for resistance against insects, fungi, bacteria and nematodes for a range of cultivated monocotyledonous plants and could ultimately be combined with other defence mechanisms to provide a general approach to cereal aphid control. Levels of hydroxamic acids, particularly DIMBOA‐glucoside, were determined in hexaploid (Triticum aestivum) and tetraploid (Triticum durum) wheat varieties and differences were found between species and varieties. The effect of feeding by R. padi on the level of hydroxamic acids in the leaf tissue was also investigated. Thus, after 24 h of aphid feeding, as an apparently localised hydrolytic defence reaction in the leaf, levels of DIMBOA‐glucoside decreased noticeably. When aphids were fed on sucrose solution containing low doses of DIMBOA there was a significant mortality compared to the sucrose control. However, the levels of and variation in hydroxamic acids in the wheat varieties investigated were insufficient for significant differences in aphid behaviour and development.     

The use of egg counts and suction trap samples to forecast the infestation of spring-sown field beans, Vicia faba, by the black bean aphid, Aphis fabae

Daily suction trap samples at a height of 12·2 m collected throughout the year, winter egg and ‘spring’ population counts on the spindle tree, Euonymus europaeus, and initial infestations of the black bean aphid, Aphis fabae, on field bean, Vicia faba, crops are available from Southern England since 1970. In different areas, estimates of the sizes of the autumn migrations, the over-wintering egg populations, the spring fundatrigeniae and the spring migrations, have been used to forecast field bean crop infestation levels which, in turn, project subsequent trap catches of alatae. The forecasts of crop infestation become progressively more accurate from the autumn migration to the following spring migration, accounting for 28%, 54%, 54% and 64% of the variance respectively. In areas where traps are sited, the spring migration trap samples give the most accurate estimate of the size and timing of crop infestation. Autumn trap catches are particularly useful as very early forecasts of likely very large or very small populations on field beans about 8 months later, but otherwise they lack precision. Egg sampling in winter provides a considerably more accurate forecast approximately 5 months before crop infestations. In spring (May), fundatrigeniae sampled on spindle are most useful for predicting time of migration, and provide approximately 2 weeks' warning for insecticide application, if needed. Finally, trap sampling of the spring migration provides the latest estimate of both the sizes of crop infestations and the timing of insecticide treatment. The E. europaeus and aerial sampling systems are complementary, the traps providing systematic, continuous information and the E. europaeus samples greater detail. Combined, they can provide excellent long-term fore-warning of the need for chemical control and short-term warning of control timing. Forecasts have been 90% correct in eight years out of nine. The error in the ninth year may be due to immigration from the European mainland.     

Behavioural response of winged aphids to visual contrasts in the field

To test the behavioural response of winged aphid spring migrants to visual contrasts, we conducted a field trial in which water traps (painted in seven different shades of green and yellow) were set up on uncovered soil and on coloured boards (also painted in seven different colours including black, brown and various shades of green). In total, 56 trap–background combinations were tested. Out of the 4904 aphid individuals caught, 64.5% belonged to Aphis ssp. Using spectral measurements of both traps and backgrounds, as well as information on insect spectral sensitivity, an empirical colour choice model was built based on photoreceptor adaptation to the background, and colour opponency of the green and blue photoreceptor. Specifically, the visual input variable C* represents the difference between green–blue colour opponency values of the trap and the background. When C* > 0, the number of aphids linearly increased with C*. The model explained 64% of the behavioural response of the aphids. Applied to intercropping scenarios of sugar beet, the behavioural model showed a higher visual attractivity of a monocrop sugar beet than intercropped sugar beet. Implications for the use of mulches and for increasing plant diversity in cropping systems are discussed.     

Seasonal Phenology and Species Composition of the Aphid Fauna in a Northern Crop Production Area

Background

The species diversity of aphids and seasonal timing of their flight activity can have significant impacts on crop production, as aphid species differ in their ability to transmit plant viruses and flight timing affects virus epidemiology. The aim of the study was to characterise the species composition and phenology of aphid fauna in Finland in one of the northernmost intensive crop production areas of the world (latitude 64°).

Methodology/Principal Findings

Flight activity was monitored in four growing seasons (2007–010) using yellow pan traps (YPTs) placed in 4–8 seed potato fields and a Rothamsted suction trap. A total of 58,528 winged aphids were obtained, identified to 83 taxa based on morphology, and 34 species were additionally characterised by DNA barcoding. Seasonal flight activity patterns analysed based on YPT catch fell into three main phenology clusters. Monoecious taxa showed early or middle-season flight activity and belonged to species living on shrubs/trees or herbaceous plants, respectively. Heteroecious taxa occurred over the entire potato growing season (ca. 90 days). Abundance of aphids followed a clear 3-year cycle based on suction trap data covering a decade. Rhopalosiphum padi occurring at the end of the potato growing season was the most abundant species. The flight activity of Aphis fabae, the main vector of Potato virus Y in the region, and Aphis gossypii peaked in the beginning of potato growing season.

Conclusions/Significance

Detailed information was obtained on phenology of a large number aphid species, of which many are agriculturally important pests acting as vectors of plant viruses. Aphis gossypii is known as a pest in greenhouses, but our study shows that it occurs also in the field, even far in the north. The novel information on aphid phenology and ecology has wide implications for prospective pest management, particularly in light of climate change.     

Assessing the risk of primary infection of cereals by barley yellow dwarf virus in autumn in the Rennes basin of France

In the Rennes basin, Rhopalosiphum padi is anholocyclic and represents more than 90% of suction trap catches of potential vectors of barley yellow dwarf virus (BYDV) during autumn. From 1983 to 1987 the possibility of predicting the risk of BYDV infection of batches of barley test seedlings (sampling units) exposed each week from September to December near a 12.2 m high suction trap was investigated. Three kinds of variables were checked as possible predictors: weekly mean or maximum temperatures; weekly catches of R. padi (including or excluding males); and percentage of sampling units infested by aphids. Three contrasting examples were observed: during the first three years (1983–1985), infection was high and its change with time followed temperature, aphid catches and plant infestation changes; in 1986, high numbers of aphids caught and a high proportion of plants infested resulted in only low infection and in 1987, both infestation and infection were very low. Simple linear regression analysis showed that the more reliable predictors of infection were the proportion of infested plants and to a lesser extent the numbers of trapped aphids. Multiple linear regressions including either of the three groups of ‘predicting’ variables did not result in any improvement in the prediction. At a practical level, the use of counts of aphid catches would seem a better compromise between accuracy and consistency of prediction and ease of gathering data than that of plant infestation but any significant improvement of the prediction should be sought in an early estimate of the amount of virus available to aphids before they colonise the plants.     

南京地区棉蚜的飞行活动节律及其飞行能力

昆虫的飞行活动规律及飞行能力是研究其能否迁飞的基础。通过采用春季到秋季20 m高空黄盆诱蚜、高空所诱蚜和春季木槿树上有翅蚜的卵巢解剖,以及春夏秋三季田间有翅蚜的吊飞试验等方法,研究了南京地区棉蚜Aphis gossypii的飞行活动节律和飞行能力。结果表明,有翅棉蚜的日羽化高峰出现在19:00～20:00。2001年南京地区棉蚜的春、秋两季迁飞高峰分别在5月8日和10月25日。5月份高空诱集的棉蚜中,95.7%个体的卵巢小管数在7条以下,而木槿上羽化后1天的有翅蚜中有35.2%个体的卵巢小管数在7条以上;高空诱蚜和木槿上蚜的平均卵巢小管数存在极显著差异,分别为3.94±1.65和5.88±1.92。8月中下旬棉田棉蚜存在低空飞行行为,并且出现飞行高峰时有翅蚜的卵巢小管数平均在6条以下,超过6条则停止飞行。羽化后1～2天有翅棉蚜吊飞个体的飞行比率和平均飞行距离表现为春、秋季显著大于夏季,三季的最长飞行距离分别为3.89 km、6.15 km和1.44 km。