Are naringenin and quercetin useful chemicals in pest-management strategies?

The effects of two polyphenolic flavonoids (flavanone naringenin and flavonol quercetin) on development, fecundity, and mortality of the pea aphid, Acyrthosiphon pisum Harris (Hemiptera: Aphididae), were determined in vitro, on an artificial diets. Also determined in vitro (DC EPG method), on sucrose–agarose gels, were the effects of flavonoids on the probing and feeding behavior of adult apterae. When added to a liquid diet, higher concentrations of studied flavonoids increased the developmental time, the pre-reproductive period, and mortality and decreased fecundity and the intrinsic rate of natural increase of A. pisum. In most events associated with stylet activity (as indicated by EPG waveform g-C), differences in probing behavior did not statistically differ between the control gel and those with flavonoids; quercetin at 10, 100, and 1,000 µg cm^?3 prolonged the number of gel penetrations; and quercetin only at 10,000 μg cm^?3 prolonged the time the first g-C waveform was observed. Addition of flavonoids to the gels generally reduced passive ingestion from fluids of the gels (EPG waveform g-E2). At higher concentrations (>1,000 µg cm^?3) the flavonoids completely stopped salivation (EPG waveform g-E1) and passive ingestion from fluids of the gels (EPG waveform g-E2). In events associated with active ingestion (EPG waveform g-G), however, differences in feeding behavior did not statistically differ between the control gel and those with flavonoids. The present findings demonstrate detrimental effects of the flavanone naringenin and flavonol on the behavior of the pea aphid. This can be employed in a biotechnological projects for plant breeding resistant to herbivores, including aphids.     

Effect of the lectin PHA on the feeding behavior of the grain aphid

The electrical penetration graph (EPG) method was used to quantify the effect of the lectin PHA (phytohemagglutinin) on the feeding behavior of the grain aphid Sitobion avenae F (Hemiptera: Aphididae). Addition of PHA to an artificial diet affected aphid probing behavior. In general, increasing concentrations of PHA in sucrose-agarose gels significantly reduced the number of aphid probes and extended their duration. Aphids feeding on the gels with lectin (without concentration 50 μg · cm⁻³) had a prolonged activity (EPG pattern C) that was corresponded to prolonged penetration of the epidermis and mesophyll for aphids feeding on plants. Such insects also showed a significant reduction in salivation and passive ingestion from gels and a reduction in the total number of gel penetrations. At concentrations ≤250 μg · cm⁻³, PHA reduced feeding behavior on gels, and the EPG data were interpreted to correspond with reduced salivation into phloem sieve elements (EPG pattern E1) and reduced ingestion of phloem sap (EPG pattern E2). PHA also delayed the onset of the first E1 and E2 patterns. At higher concentrations (≥500 μg · cm⁻³), PHA completely stopped salivation and passive ingestion from gels. Similarly, higher concentration of PHA strongly reduced activity on gels that corresponded to activity in xylem (EPG pattern G); high PHA delayed the onset of the first G pattern and reduced total time of pattern G activity.     

Assessment of the biological control capability of <Emphasis Type="Italic">Hippodamia variegata</Emphasis> (Col.: Coccinellidae) using functional response experiments

Lady beetles are among the most successful predators of aphids in different environments. The functional responses of different life stages of Hippodamia variegata (Goeze) towards cotton aphids were examined in two different set-ups, a two-dimensional Petri dish set-up with detached leaves and a three-dimensional set-up with whole plants. In addition, the functional responses in two-dimensional set-ups towards cotton aphids and the pea aphids were compared. H. variegata exhibited a functional type II response to both cotton aphids and pea aphids irrespective of life stage and spatial scale of the set-up. Females and fourth instars generally had higher search rates than third instars whereas handling times were consistently lower for the fourth instar stage compared with the preceding juvenile stage and with females. The spatial dimensions did not have any significant influence on the functional responses towards cotton aphids, except for third instars which in the three-dimensional set-up reduced their search rate and increased their handling time. Fourth instars reacted in the same way to both Aphis gossypii and Acyrthosiphon pisum whereas the functional response parameters for third instars and females were significantly different on the two prey species. Our study, a part of this first-step evaluation of H. variegata as a biocontrol agent against A. gossypii and A. pisum under field condition, suggest that the voracity of all tested stages of H. variegata towards both aphid species hold good promises for a use of especially fourth instars and females in inundative biocontrol.     

The influence of the aphid-specific pathogen Conidiobolus obscurus (Entomophthoromycota: Entomophthorales) on the mortality and fecundity of bamboo aphids

Bioassays and scanning electron microscopy of Conidiobolus obscurus for bamboo aphids as well as its effects on the fecundity of bamboo aphids were carried out to estimate bamboo aphid biocontrol potential. Multi-concentration bioassay and fecundity assessment were performed on aphid species of Takecallis taiwanus, Takecallis arundinariae, Melanaphis bambusae, and Metamacropodaphis bambusisucta. C. obscurus can effectively infect four species of bamboo aphids, and most cadavers appeared in the first 2 days after inoculation. The final mortalities reached 74–91 % at high concentrations of conidia among the tested species. Based on the fitted time–concentration–mortality models, the estimates of the median lethal concentration (LC₅₀) of the fungal conidia differed significantly among different aphid species and decreased with observation days. The lowest LC₅₀ was estimated to be 57 conidia mm^?2 for T. taiwanus on day 5 after conidial shower. Moreover, the C. obscurus-infected aphids only produced 3.9–18.2 % progeny of the corresponding healthy aphids, which strongly presented fungal influence on host fecundity. In conclusion, C. obscurus has the ability of restraining the development of bamboo aphid populations, which is suitable for further application in aphid biocontrol in bamboo forests.     

Bioinsecticidal effect of the flavonoids pinocembrin and quercetin against <Emphasis Type="Italic">Spodoptera frugiperda</Emphasis>

Flavonoids function in many aspects of plant–insect interactions, but the responses of insects to these compounds vary greatly. In this study, we determined the effects of two widely distributed flavonoids, pinocembrin and quercetin, on the feeding behavior, survival, and development of the fall armyworm Spodoptera frugiperda J.E. (Smith) (Lepidoptera: Noctuidae). In a choice test, S. frugiperda larvae strongly rejected leaves treated with pinocembrin at concentrations of 10, 50, or 100 μg/cm². Larvae fed normally on leaves treated with quercetin at 10 and 50 μg/cm², but showed 57 % deterrence when fed on leaves treated with 100 μg/cm² quercetin. At concentrations of 0.01–1 µg/cm², pinocembrin and quercetin functioned as phagostimulants for S. frugiperda. In a multiple-choice experiment, S. frugiperda larvae preferred to consume untreated leaves or those treated with 0.1 µg/cm² pinocembrin, but rejected leaves treated with 5–50 µg/cm² pinocembrin. In a no-choice feeding experiment, larvae fed on leaves treated with 5 and 50 μg/cm² pinocembrin consumed less than those fed on leaves treated with 0.1 and 1 μg/cm² pinocembrin or untreated leaves. Pinocembrin at 1–50 μg/cm² negatively affected larval weight and survival, thus showing a toxic effect. In contrast, leaf consumption and larval weight were not significantly affected by quercetin at 0.1, 1, 5, and 50 μg/cm², and mortality rates only slightly increased. Because of its dual activity, pinocembrin could be used for insect control in a stimulo-deterrent diversionary strategy: the same compound could promote both stimulate (low doses) and deter insect activity (high doses).     

Influence of nonhost plant diversity and natural enemies on the potato leafhopper, Empoasca fabae, and pea aphid, Acyrthosiphon pisum, in alfalfa

We examined the effects of nonhost plant diversity and predators on the potato leafhopper, Empoasca fabae (Harris), the pea aphid, Acyrthosiphon pisum (Harris), and their primary host plant, alfalfa, Medicago sativa L. Potato leafhopper intensity (i.e., leafhoppers/alfalfa stem density) and plant damage (i.e., hopperburn) were significantly greater in alfalfa mono- than in polycultures of alfalfa mixed with nonhost plant species. There was no significant effect of nonhost plant diversity on pea aphid intensity or on predator abundance. Predator:prey ratios were higher in poly- than in monoculture. One predator, Nabis sp., was selected for further study. A microcosm experiment indicated that Nabis is an effective predator of both herbivores, and suggested that nonhost plant diversity may enhance the predation of leafhoppers by Nabis. These results suggest that nonhost plant diversity and Nabis limit leafhopper populations and protect alfalfa from herbivory. The potential for nonhost plants to increase herbivore movement and vulnerability to predation is discussed.     

Effect of plant secondary metabolites on legume pod borer, Helicoverpa armigera

The effect of various flavonoids, lectins and phenyl β-d-glucoside on larval survival, weights and the activities of digestive (total serine protease and trypsin) and detoxifying [esterase and glutathione-S-transferase] enzymes of Helicoverpa armigera larvae at 5 and 10 days after treatment (DAT) was studied through diet incorporation assay. Flavonoids (quercetin, cinnamic acid, caffeic acid, chlorogenic acid, catechin, trihydroxyflavone, gentisic acid, ferulic acid, protocatechuic acid and umbelliferone) were incorporated in artificial diet at 100, 500 and 1000 ppm, lectins: groundnut leaf lectin (GLL), concavalin (ConA) and phenyl β-d-glucoside at 2.5 and 5 μg mL^?1. Flavonoids such as chlorogenic acid, caffeic acid and protocatechuic acid at 1,000 ppm were more toxic to H. armigera larvae at 10 DAT than quercetin, catechin, cinnamic acid, trihydroxyflavone, gentisic acid, ferulic acid and umbelliferone. Larval growth and development were significantly reduced in H. armigera larvae fed on a diet with GLL and ConA at 5 μg mL^?1 compared to the larvae fed at 2.5 and 1.25 μg mL^?1 concentrations. The enzyme activities of the larvae were significantly reduced in flavonoid-treated diets. The flavonoids such as chlorogenic acid, caffeic acid, gentisic acid, trihydroxyflavone, catechin and protocatechuic acid, and lectins, GLL and ConA can be utilized in insect control programs.     

Untersuchungen zur Verteilung und Wirksamkeit eines durch die Wurzel aufgenommenen Insektizids mit Hilfe von Blattläusen (Homoptera: Aphididae)

A thiophosphoric acid ester is administered to the roots ofVicia faba L. and its distribution is tested in different concentrations. By the aid of radioactivity the systemic character of the used insecticide Triazophos is demonstrated. The translocated quantity of the insecticide is tested in its effects by aphids. The tests are performed onAulacorthum circumflexum (Buckt.). The uptake of Triazophos per aphid ranges from 0.88·10^?3 μg to 1.1·10^?3 μg. This quantity isn't sufficient enough to obtain letal effects. The phytotoxic effect of the insecticide doesn't allow to administer higher concentrations.     

Entwicklung, Fraßleistung und Beutepräferenz vonHippodamia convergens Guer.-Men. (Col., Coccinellidae) mitThrips tabaci Lind. (Thys., Thripidae) sowie zwei Aphidenarten als Beute

Thrips tabaci Lind. is very difficult to control and thus one of the most important pests of leek in Europe. As an alternative to insecticides biological control may be carried out by making use of beneficial insects, the Coccinellidae being one of the most important predatory families. In the present study laboratory trials were carried out withHippodamia convergens Guer.-Men., one of the polyphagous representatives of the lady birds, to figure out the feeding activity, development and prey preference ofH. convergens against the onion thrips in comparison with two aphid species. H. convergens developed fully when fed exclusivelyT. tabaci larvae, although mortality was considerably higher and development took much longer. When fed thrips the complete development lasted 29,8 days on an average, the mortality reaching 88%. When offeredAcyrthosiphon pisum (Harris)H. convergens took only 24 days for development with a mortality of only 16%. Above all, the fourth larval instar and the pupa suffered from a very high mortality, reaching 45 and 50% respectively. WithA. pisum as a prey mortality decreased to only 6%. The duration of the pupal development was not affected by the prey species. The feeding activity ofH. convergens increased significantly during the development. The larvae of the second and fourth instar predated 28 and 170 thrips larvae respectively per day as a maximum. The adults achieved the highest feeding activity, predating more than 300 thrips larvae in 24 hours. When adding up the number of prey individuals per day for each developmental instar, the L₂ larvae predated more than 90 and the L₄ larvae more than 1000 thrips larvae. When offered thrips larvae andMyzus persicae (Sulz.) simultaneously, there was an increasing prey preference during the development ofH. convergens from first larval instar to adult. As to the last instars there was 20–25% less predation of thrips larvae compared to the aphids during 24 hours.     

Greenhouse trials for the control of aphids on cut-roses with the chalcidAphelinus abdominalis Dalm. (Aphelinidae,Hymen.)

For the control of the aphid speciesMacrosiphum euphorbiae, an important aphid species on greenhouse cut roses in Austria, with the parasitoidAphelinus abdominalis, trials were carried out in the rose varieties Frisco, Kardinal and Vivaldi at a commercial producer on a greenhouse area of 630 to 700m². Both the inundative release of 9,6A. abdominalis/m² in total and the release of 2,2A. abdominalis/m² in total, within an open rearing system were investigated and the percentage of infested rose shoots in combination with the degree of infestation were evaluated. The results showed that an effective reduction of present or newly developing aphid populations was possible for several weeks under the conditions of a commercial greenhouse production. The amount of insecticides used against aphids decreased by up to 75% in comparison to greenhouses were only chemical pest control was carried out. The suitability of the different introduction methods ofA. abdominalis for the control of aphids on greenhouse cut roses is discussed.     

Populations of aphids, whiteflies and associated predators and parasites on different vegetables cultivated in plastic greenhouses

During 1996 and 1997, populations of aphids and whiteflies and their parasites were studied in plastic greenhouses under a chemical control program and in those free of pesticides. In the greenhouses free of pesticides, the parasite A. colemani destroyed 14.7?% of the aphids. B. tabaci had no effect on the cucumbers during the spring cultivation. However, it attacked the autumn cultivation. The parasite E. mundus killed 30?% of these nymphs. The parasite A. colemani parasitized up to 10?% of aphids on tomato plants in greenhouses free of chemical pesticides. The parasite E. mundus killed 15.7?% of whitefly nymphs. In greenhouses under a chemical pesticides program, aphids and whiteflies were found on the plants at the end of the plantation season, after the pesticide spraying had stopped. Although the pest population was low, the parasite A. colemani parasitized 8?% of the aphid population. Whiteflies were not found on tomato plants in greenhouses under extensive pesticides use.     

Beobachtungen zur Entwicklung der Frühjahrspopulationen vonMetopolophium dirhodum (Wlk.) auf dem Winterwirt

The rose-grain aphid,Metopolophium dirhodum (Wlk.), is a species living onRosa spp. as winter hosts and Gramineae as summer hosts. Thus, the planting of roses along roadsides and highways may be of importance in connection with the migration of the aphids to cereals. In March 1982 the nymphs hatched from eggs, which were laid in autumn on long shoots. One or two days after hatching they fed on buds in batches up to 15 individuals. Somewhat later they dispersed on the hostplants. The nymphal mortality of the first generation was high, namely about 79%. For further population development the number of fundatrices was less important due to their high reproduction capacity. Nymphs and adults of the first generation often changed their feeding site on the shoots. The specimens of the 2nd and 3rd generation were more stationary and formed dense colonies. The population density drastically increased during the 3rd generation. The development of the aphid populations on the primary host took place during 2–3 generations and lasted until the beginning of June, when the winged forms left the hosplant. In the second generation, i. e. at the beginning of May, the first emigrantes appeared and the size of the aphid colonies increased up to 115 individuals. Most colonies consisted of less than 11 aphids namely 30.9%. Natural enemies were present in large numbers during the end of May when the populations of aphids decreased due to emigration. They did not influence the density of aphid colonies, except the predacious larvae of hover-flies. Trophobiosis between ants and rose-grain aphids was not observed on the primary hostplant.     

Loss of host fidelity in highly inbred populations of the parasitoid wasp <Emphasis Type="Italic">Aphidius ervi</Emphasis> (Hymenoptera: Braconidae)

Inbreeding frequently reduces the fitness of organisms, but little is known about how this phenomenon can affect the biological control. Host fidelity provides an adaptive advantage to aphid parasitoids, allowing females to find their aphid host more quickly in heterogeneous environments. This trait is mediated by the learning of signals, mainly chemical cues emitted from the host in which parasitoids developed (natal). This article is aimed at studying whether host fidelity can be altered after many generations of inbreeding reproduction in caged laboratory populations, for which host preference and fitness parameters were measured in the parasitoid wasp Aphidius ervi. Also, the effect of the natal/non-natal hosts was studied, using parasitoids originated from the pea aphid (Acyrthosiphon pisum) and the grain aphid (Sitobion avenae). We observed a loss of host fidelity in the studied A. ervi populations, irrespective of their natal aphid host, which contrasts with previous reports showing preference for natal hosts in outbred laboratory populations. The loss of host fidelity is discussed in terms of the origin of populations; the sex ratio was strongly biased toward males and long-time maintenance under laboratory conditions. Our results highlight the need for controlling the genetic diversity of caged parasitoids before they are released into fields, as a long period of inbreeding could negatively affect the biological control.     

白蜡虫肠道微生物分析及立克次氏体分子检测

肠道微生物对于昆虫的生长和发育起着重要作用,不仅参与维生素合成、脂肪和碳水化合物的吸收与利用、孤雌生殖、信息素的合成,同时在抵御外来菌的侵入与定植以及在加强免疫系统的功能中也起着重要作用[1-2]。对于刺吸式昆虫来说,由于植物枝干韧皮部汁液营养组成不均衡,碳水化合物含量丰富而必需氨基酸组分欠缺或含量较低[3],这些昆虫体内的共生细菌能提供寄主昆虫所缺乏的必需氨     

A push–pull strategy to control aphids combines intercropping with semiochemical releases

Even if insect pest populations can be reduced by increasing plant diversity through intercropping, natural enemies are not always favored in such systems. Alternatively, semiochemical substances have been tested to enhance biological control, with inconsistent results. Combining both strategies can be an interesting way to maximize pest control. In this work, a 2-year setup involving wheat–pea strip intercropping combined with the release of E-β-farnesene (EBF) or methyl salicylate (MeSA) was tested as a push–pull strategy to simultaneously repel aphids and attract beneficials. Two types of slow-release formulation (i.e., oil and alginate beads) containing EBF or MeSA were deployed with the intercropping. The abundance of aphids was significantly decreased, while hoverfly larvae and mummified aphids increased on both pea plants and wheat tillers by the release of oil-formulated EBF and MeSA. The proportion parasitism of the aphid-parasitism rate [mummies/(aphids + mummies)] was also increased by treating both crops in both years. Releasing EBF through oil rather than alginate beads proved significantly better for attracting natural enemies and reducing aphids. Aphids were negatively correlated with the density of hoverflies (both adults and larvae) and numbers of mummies. All these results showed that combining intercropping with the release of EBF or MeSA formulated in oil can significantly reduce aphid density and attract their natural enemies. Therefore, the combination of both strategies could help farmers reduce the use of insecticides.     

角倍蚜干母发生期和数量变化及秋迁蚜生殖能力

对角倍蚜干母的发生期、数量变化、趋光行为及秋迁蚜生殖能力进行了研究,结果表明:保存于峨眉、昆明实验室和地下室的虫袋,干母发生期分别为4月19-22日、3月31日至4月4日和4月7-10日,与原产地峨眉相比较,保存于昆明实验室和地下室的虫袋,干母发生期分别提前了19、12 d,但发生节律没有明显差异;干母发生期持续4 5 d,发生期中间的1 2 d发生量占总量的70%以上;干母发生时间集中在10:00-16:00,发生量占日发生总量的80%以上;干母对直射自然光或灯光有明显趋性。秋迁蚜密度、单头产若蚜量和怀卵量随着倍子体积的增加而增加,平均体积为(28.2±0.8)cm3的中倍子的秋迁蚜密度、单头产若蚜量和怀卵量分别为(387.7±52.3)头·cm-3、(26.4±3.8)头、(27.6±4.2)头,与体积为(5.4±0.3)cm3的小倍子相比分别增加了46.7%、24.5%和23.8%(p0.05)。在冬寄主藓类存在的条件下,秋迁蚜产若蚜的时间更为集中,持续时间缩短。14:00和18:00迁飞的秋迁蚜,迁飞后即开始产若蚜,并在4 h达到高峰,持续时间分别为30、28 h,而8:00迁飞的秋迁蚜,迁飞2 h后开始产若蚜,16 h后才达到高峰,持续时间为36 h。     

角倍蚜干母分批上树对虫瘿数量和分布的影响

对角倍蚜分批上树及接种方法对虫瘿数量和分布的影响进行了研究,结果表明:(1)迁飞接种(同批上树)时,单株虫瘿数为15.65个,而迁飞加挂袋(分批上树-A)及挂袋2次(分批上树-B)时,单株虫瘿数分别为48.39个和161.84个,增加了2.09倍和9.34倍;同时单叶虫瘿数也从1.69个增加到2.77个和3.42个;单株有虫瘿复叶数从8.70片增加到17.87片和46.00片;有虫瘿枝条率从21.65%增加到59.74%和91.58%。(2)迁飞接种时,虫瘿分布于当年生枝条第1~7片复叶,其中1~5片复叶为虫瘿主要分布叶片;迁飞加挂袋及挂袋2次时,虫瘿分布于当年生枝条的第1~8片及第1~11片复叶,其中第3~6片复叶为虫瘿主要分布叶片。(3)无论是干母同批上树还是分批上树,单叶虫瘿数均以1~3个为主,虽然分批上树时单叶平均虫瘿数从1.23个增加到1.47个和2.53个,但仍然低于单叶最适虫瘿数5~6个,对虫瘿的大小和生长没有不良影响。综上所述,干母分批上树可以显著增加角倍蚜虫瘿数量,提高虫瘿的分散度,充分发挥盐肤木形成虫瘿的潜力。     

Bioactivities of caffeic acid methyl ester (methyl-(E)-3-(3,4-dihydroxyphenyl)prop-2-enoate): a hydroxycinnamic acid derivative from Solanum melongena L. fruits

Feeding deterrent and growth inhibitory effects of caffeic acid methyl ester (CME) isolated from the fruit extract of eggplant, Solanum melongena L. along with two known phenolic acids, caffeic acid (CA) and chlorogenic acid (CG) and azadirachtin (taken as active control), were evaluated against Spodoptera litura Fab. and Achaea janata L. (Lep., Noctuidae). The structure of CME was determined on the basis of extensive spectroscopic (UV, FTIR, ¹H, and ¹³C NMR) data analysis. CME has exhibited strong feeding deterrent activity against S. litura and A. janata larvae with ED₅₀ values of 52.02 and 41.02 μg/cm² leaf area, respectively. CA and CG were relatively less effective compounds when compared with CME. The results also revealed that the isolated compound CME caused marked larval growth inhibition in S. litura and A. janata larvae after 7 days of feeding on a treated diet. The effect on growth of larvae was concomitant with the reduced feeding and digestibility of ingested food. So the activities of digestive proteases within the midgut of larvae were examined using specific substrates to understand the digestive physiology in the larval guts. The bulk of the activity was associated with serine proteases comprising trypsin-, chymotrypsin-, and elastase-like enzymes, which decreased in diets containing CME, whereas, interestingly increased with CG. From the results, we conclude that CME isolated from S. melongena fruit extract shows feeding deterrent and larval development inhibitory activities that may prove useful in the management of S. litura and A. janata larvae.     

Entomophthoralean fungi associated with the common nettle aphid (<Emphasis Type="Italic">Microlophium carnosum</Emphasis> Buckton) and the potential role of nettle patches as reservoirs for the pathogens in landscape

Populations of the common nettle aphid, Microlophium carnosum Buckton, inhabiting nettle patches in an agricultural landscape were surveyed for entomophthoralean infection during 1998, 1999 and 2001. Five pathogenic species were identified from the aphid in the course of the survey. Erynia neoaphidis Remaudière & Hennebert, Neozygites fresenii (Nowakowski) Remaudière & Keller, and Neozygites microlophii Keller affected aphid colonies every year. Two minor pathogens, Entomophthora planchoniana Cornu and Conidiobolus obscurus (Hall & Dunn) Remaudière & Keller, were observed only in 2001.An artificial transmission of the three main fungi was carried out to prove horizontal transmission of infection between the common nettle aphid and different aphid species co-occurring in landscape. N. microlophii, probably monophagous pathogen, did not infect any of the six recipient aphid species in the experiment. Transmissions of E. neoaphidis and N. fresenii conidia were successful with five and four aphid species, respectively. The average mortality of tested aphids after transmission ranged from 0 to 33.33?% for E.?neoaphidis and from 0 to 15?% for N. fresenii.The potential of nettle patches as natural reservoirs for pathogens in the agroecosystem is discussed.     

Defoliation and growth relationships for mid-rotation Sitka spruce attacked by the green spruce aphid, Elatobium abietinum (Walker) (Homoptera: Aphididae)

Green spruce aphid (Elatobium abietinum) feeds primarily on the 1-year-old and older needle leaves of spruce (Picea spp.) and is a major defoliator of commercial Sitka spruce plantations in the UK and other maritime regions of north-west Europe. The impact of E. abietinum on mid-rotation (23-28-year-old) Sitka spruce in Radnor Forest, in mid-Wales, was determined by comparing aphid population densities, defoliation and growth between plots of trees that were either treated with insecticide or were left untreated. The experimental treatments were maintained for 5 years and over this period (2002-2006) peak E. abietinum densities in the untreated plots varied from 5 to 36 aphids per 100 needles. These densities, which were representative of low to moderate rates of infestation, were associated with low rates of defoliation (0-8%), but they had a significant (P ? 0.01) impact on mean radial increment (RI) and mean volume increment (VI). In 2005, the year with the highest aphid populations, peak densities in the untreated plots averaged 14 aphids per 100 needles and this rate of infestation reduced RI by 17%, VI by 10% and the dry weight of current-year needles by 10%. On average, across all years, infestation by E. abietinum reduced mean annual VI by 6%. Comparisons with previous studies on the impact of the aphid on 4-year-old, 7-year-old and 9-year-old Sitka spruce (Straw et al., 2005) indicate that defoliation by E. abietinum, on a per capita basis, decreases as trees grow older, but that the impact on VI increases. The different growth response of young and mid-rotation Sitka spruce to infestation is related to differences in canopy structure, particularly in the ratio of current-year needles to older needles, and the greater demands on photosynthetic production in older trees that arise from the need to support an increasing quantity of non-photosynthetic structural tissues in branches, stem and roots.