Determining the optimal timing of foliar insecticide applications for control of soybean aphid (Hemiptera: Aphididae) on soybean

Field experiments were performed over 3 yr to examine the impact of insecticide application timing to control soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), populations and to prevent soybean yield losses. Experiments were conducted in early and late-planted soybean, Glycine max (L.) Merr. Insecticide applications were made based on soybean growth stages. In 2001, applications were made at V1, V3, R2, and R3 growth stages; in 2002 and 2003, applications were made at R2, R3, and R4 stages. Additional treatments consisted of an unsprayed control and a multiple spray treatment that received insecticide applications at 7-10-d intervals. Soybean aphid densities were recorded throughout the growing season, and yields were measured. Soybean aphid populations varied considerably across years and planting dates. In general, late-planted soybean exhibited higher aphid pressure than early planted soybean, and experiments in 2002 had lower aphid numbers than those in 2001 and 2003. The multiple spray treatment significantly increased yield over the control in four of the six experiments, the exceptions being 2002 late planted and 2003 early planted. This suggests that soybean aphid populations were not large enough to cause yield losses in these two experiments. The R3 spray treatment increased yield in three of the six experiments (2001 late planting, 2002 early planting, and 2003 late planting), the R2 spray treatment increased yield in two of six experiments (2001 and 2003 late plantings), and the V1 application increased yield over the control in the 2001 late-planted experiment. Results suggest that when aphid populations are high insecticide applications made at R2 and R3 plant stages are most effective in preventing yield loss.     

Efficacy assessment of Aphidius colemani (Hymenoptera: Braconidae) for suppression of Aphis gossypii (Homoptera: Aphididae) in greenhouse-grown chrysanthemum

To assess biological control as a management tool for the cotton aphid, Aphis gossypii Glover (Homoptera: Aphididae), the efficacy of Aphidius colemani Viereck (Hymenoptera: Braconidae) for suppression of A. gossypii in greenhouse-grown chrysanthemums, Dendranthema grandiflora (Tzvelev), was compared with a pesticide standard, imidacloprid (Marathon 1% G) and an untreated check. No significant differences were found between aphid populations in the two treatments. A. colemani and imidacloprid kept aphid numbers very low, with the correspondent aphid populations exhibiting very low intrinsic rates of increase (r(m) = -0.0369 and r(m) = 0.0151, respectively), in contrast to the exponential growth of aphid populations (r(m) = 0.1085) observed on the untreated plants. Parasitism levels in A. colemani plots ranged from 48.93 to 83.38%. Esthetic damage parameters, including exuviae, honeydew, and sooty mold on leaves, were significantly different between treatments and untreated control, and damage levels were minimal with the insecticide treatment and natural enemy releases. The cost of A. colemani releases was 4.7 times greater than the cost of the imidacloprid treatment.     

施钾与蚜害处理后马铃薯叶片中多酚氧化酶活性的变化

蚜虫危害是影响马铃薯Solanum tuberosum产量和品质的重要因素之一, 而多酚氧化酶（polyphenol oxidase, PPO）与植物的抗性密切相关。为了阐明施钾条件下马铃薯与桃蚜Myzus persicae的关系, 本实验通过比色法、 iTRAQ技术和蛋白免疫印迹法研究了对照（不施钾, 不接虫）、 接虫、 施钾以及施钾＋接虫4种处理后马铃薯叶片中多酚氧化酶活性的变化。结果表明： 施钾显著降低桃蚜种群数量。随着桃蚜发育期延长, 桃蚜的种群数量显著低于对照, 且6 g/株施钾量对桃蚜种群数量的抑制效果最强。以6 g/株作为施钾量, 对不同处理后马铃薯叶片中多酚氧化酶活性研究显示, 施钾、 接虫+施钾处理均使马铃薯叶片中PPO活性显著提高, 分别比对照增加了44%和67%。通过液相色谱 质谱/质谱联用仪（LC-MS/MS） 分析, 接虫、 施钾、 接虫+施钾处理均不同程度上调了PPO蛋白表达量。Western杂交结果显示： 施钾、 接虫+施钾处理显著增加了PPO的相对表达量, 且接虫+施钾处理使该相对表达量达到最高。结果说明, 施钾、 接虫+施钾处理通过诱导马铃薯叶片中的PPO活性, 从一个侧面提高了马铃薯抗蚜虫能力。     

Effects of two types of semiochemical on population development of the bird cherry oat aphid Rhopalosiphum padi in a barley crop

1 Field experiments were performed in barley using volatile semiochemicals affecting population density (density‐related substances – DRS) and spring migration (methyl salicylate) in bird cherry oat aphid Rhopalosiphum padi (L.). Natural infestations of aphids were used, and semiochemical dosages were chosen to be biologically relevant based on previous studies. A simple formulation method for active substances using wax pellets was developed. 2 The effect of treatments on aphid populations was analysed in terms of initial colonization of the crop, temporal dynamics of the population and maximum aphid incidence. 3 Treatments caused a significant delay in aphid establishment in the crop, and reduced the average infestation by 25–50% compared with the untreated control. At a moderate attack rate, the treatments with methyl salicylate and DRS gave a significant reduction in maximum aphid numbers. 4 The significant control effect of the treatment encourages further investigation both to increase understanding of the ecological role of the active substances, and to establish the limitations for their use in plant protection.     

Changes in herbivore control in arable fields by detrital subsidies depend on predator species and vary in space

Prey from the decomposer subsystem may help sustain predator populations in arable fields. Adding organic residues to agricultural systems may therefore enhance pest control. We investigated whether resource addition (maize mulch) strengthens aboveground trophic cascades in winter wheat fields. Evaluating the flux of the maize-borne carbon into the food web after 9 months via stable isotope analysis allowed differentiating between prey in predator diets originating from the above- and belowground subsystems. Furthermore, we recorded aphid populations in predator-reduced and control plots of no-mulch and mulch addition treatments. All analyzed soil dwelling species incorporated maize-borne carbon. In contrast, only 2 out of 13 aboveground predator species incorporated maize carbon, suggesting that these 2 predators forage on prey from the above- and belowground systems. Supporting this conclusion, densities of these two predator species were increased in the mulch addition fields. Nitrogen isotope signatures suggested that these generalist predators in part fed on Collembola thereby benefiting indirectly from detrital resources. Increased density of these two predator species was associated by increased aphid control but the identity of predators responsible for aphid control varied in space. One of the three wheat fields studied even lacked aphid control despite of mulch-mediated increased density of generalist predators. The results suggest that detrital subsidies quickly enter belowground food webs but only a few aboveground predator species include prey out of the decomposer system into their diet. Variation in the identity of predator species benefiting from detrital resources between sites suggest that, depending on locality, different predator species are subsidised by prey out of the decomposer system and that these predators contribute to aphid control. Therefore, by engineering the decomposer subsystem via detrital subsidies, biological control by generalist predators may be strengthened.     

Effect of fungicide application on activity of Neozygites fresenii (Entomophthorales: Neozygitacaea) and cotton aphid (Homoptera: Aphididae) suppression

The development of resistance in aphid populations highlights the importance of biological control as a pest management tactic. Four treatments were evaluated to determine the effects of pesticides on the population dynamics of Aphis gossypii Glover and Neozygites fresenii (Nowakowski) Batko: (1) weekly applications of the insecticide imidacloprid (Provado 1.6 F); (2) weekly applications of the fungicide chlorothalonil (Bravo 720); (3) applications of imidacloprid (Provado 1.6 F) when aphid densities exceeded 30 aphids per leaf, and (4) untreated control. Differences in aphid density among the four treatments were shown only to be significant during the 1997 growing season; however, aphid densities were greater in the chlorothalonil treatment than in the other treatments during each growing season. Percentage of N. fresenii-killed aphids was most often highest in the chlorothalonil treatment as well. The fungal epizootic caused by N. fresenii was delayed approximately 1 wk in the chlorothalonil treatment when compared with the other treatments. This delay allowed the aphids to temporarily escape suppression by the fungus and to continue to increase in density until the density-dependent effects of the epizootic overwhelmed the aphid population. N. fresenii also appeared to persist in the system when imidacloprid was in use and does appear responsible for initial aphid reductions. Treatment did not appear to have a large influence on yield outcome. Yield was variable from year to year and from location to location.     

Pre-flowering and post-flowering insecticide applications to control Aphis fabae on field beans: their biological and economic effectiveness

Most spring-sown field beans are treated with insecticides to control Aphis fabae, but there is usually a risk of toxicity to pollinating honeybees if insecticides are applied during flowering. An experiment was repeated at Rothamsted for 6 consecutive years, comparing treatments before and after flowering. It is concluded that (1) pre-flowering treatments (demeton-S-methyl spray at 0–25 kg a.i. ha^-1 or phorate granules at 1–12 kg a.i. ha^-1) were more effective and profitable than post-flowering treatments, (2) application of phorate granules before flowering gave the greatest economic return, and minimised the danger to foraging bees and (3) aphid populations varied considerably from year to year, as did the relationship between aphid infestation and yield, but our evidence supports the suggestion that insecticide spray treatments are profitable if 5% or more of the plant stems are infested at the end of primary aphid migration.     

The influence of nitrogen fertiliser on the population development of the cereal aphids Sitobion avenae (F.) and Metopolophium dirhodum (Wlk.) on field grown winter wheat

The effect of nitrogen fertiliser on populations of the cereal aphids Sitobion avenae and Metopolophium dirhodum on winter wheat was investigated in a three year field experiment. Naturally occurring aphid populations were monitored on three nitrogen treatments; none, nitrogen application using Canopy Management guidelines (130–210 kg ha^-1) and conventional practice (190 kg ha^-1). Inoculations of laboratory reared S. avenae were used to enhance field populations on half the plots. Natural populations of M. dirhodum remained below the current UK spray threshold level of two-thirds of shoots infested at the start of flowering, or five aphids per shoot in all years, whilst populations of S. avenae exceeded the threshold in all years. The response of the two species to nitrogen differed. Significantly higher populations of M. dirhodum were recorded in both treatments which received nitrogen in all years, whilst the response of S. avenae varied between years. In 1994 and 1995 when environmental conditions favoured aphid development, higher populations were recorded in the two treatments which received nitrogen. In 1993 when high rainfall created unfavourable conditions, higher populations were recorded in the plots receiving no nitrogen. Differences in peak density and cumulative aphid index of S. avenae resulted from differences in the rate of population increase between ear emergence and peak density on the different treatments. Populations prior to ear emergence were higher in the plots which received nitrogen but the differences were not statistically significant. There was no evidence of a difference in the timing of population decline in the different treatments. In 1993 higher levels of infection by entomopathogenic fungi were observed in all treatments. Significantly higher levels of infection were recorded in the treatments receiving nitrogen, which may have accounted for the lower S. avenae populations recorded. It is possible that the larger canopies recorded in these treatments produced conditions which favoured infection by fungi, thereby limiting aphid population growth. The results indicate that application of nitrogen increases natural populations of M. dirhodum, and under favourable conditions, populations of S. avenae. However, in suboptimal climatic conditions, the application of nitrogen fertiliser can lead to lower populations of 5. avenae. The data also suggest that there is no consistent difference between a conventional and Canopy Managed approach to nitrogen fertiliser use in terms of the risk of infestation by cereal aphids.     

Effect of soil potassium availability on soybean aphid (Hemiptera: Aphididae) population dynamics and soybean yield

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deficient foliage on life table parameters of soybean aphids, and field experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deficient and nondeficient soybean leaves. Soybean aphids in the K-deficient treatment exhibited significantly greater intrinsic rate of increase (r(m)), finite rate of increase (lambda), and net reproductive rate (Ro) relative to aphids feeding on nondeficient leaves. No significant difference was observed in mean generation time (T) between the two treatments. However, the field experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in significant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No significant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deficient plants, aphid abundance in the field may be dependent on additional factors, such as dispersal, that may affect final densities within plots.     

Vertical and Temporal Distribution of Aphis gossypii Glover and Coccinellid Populations on Different Chilli (Capsicum annuum) Varieties

The vertical and temporal distribution of an aphid, Aphis gossypii Glover, and the coccinellid populations on six chilli varieties were studied. The total number of apterous aphid per plant stratum was significantly different among plant strata of a particular variety (treatment) as well as among the treatments. Generally, the total number of aphids was significantly greater in the lower stratum than in the middle and upper strata. However, the varieties with erect and open plant architecture (Kulai and MC 11) had significantly less number of apterous aphids at all strata as compared to varieties with compact or prostrate plant architectures. There was a significant difference in the total number of coccinellids per plant strata among the treatments but not within a treatment. The distribution of apterous aphid populations varied significantly among sampling periods and treatments. The temporal distribution of coccinellids showed a similar trend as that of apterous aphids. The total number of alate aphids caught per week was significantly different among the sampling periods. However, its population was significantly greater during the early season and gradually declined as the season progressed except during June 18 to 24. The importance of recording the most observed coccinellids species, which limit the aphid populations at each particular plant stratum per variety, and the conditions that favor natural enemies are also discussed.     

Remotely sensing arthropod and nutrient stressed plants: a case study with nitrogen and cotton aphid (Hemiptera: Aphididae)

Remote sensing can be used in combination with ground sampling to detect aphid- (Aphis gossypii Glover) infested cotton (Gossypium hirsutum L.). Changes in wavelengths in the near-infrared (NIR) have proven useful for such detection, but these changes can be confused with other factors stressing plants, such as water deficiency and nutrient status. This study was designed to test the utility of this technology to distinguish between two factors stressing plants: nitrogen deficiency and aphids. Field plots were created by applying varying rates of nitrogen to cotton at different dates in the growing season in 2003 and 2004. Subplots were created by applying disruptive insecticides, which increased aphid populations in a portion of the subplots. Airplane and satellite remote sensing data in 2003 and 2004 were supplemented with ground sampling of aphid populations in both years. Insecticide application, nitrogen application rate and date influenced aphid abundance. Cotton with higher aphid populations could be distinguished from cotton with natural aphid infestations independent of plant nitrogen status using a NIR wavelength in 2003 and a proprietary 2004 index. Complex distinctions among varying nitrogen treatments and aphid abundance were not possible using this data. In the future, possible confounding factors should be investigated from the perspective of their change on crop physiology before remote sensing can be used in an integrated pest management (IPM) program.     

Aphid suppression by natural enemies in mulched cereals

Large populations of natural enemies are the basis for natural pest control. Effects of mulch on predator–prey interactions in arable fields are poorly known, despite its potential to enhance ground‐dwelling predators and thereby reduce pest infestations. We studied the densities of predators and parasitoids, and their impact on cereal aphids in the presence and absence of mulch. Released populations of the bird cherry aphid, Rhopalosiphum padi (L.) (Homoptera: Aphididae), and two naturally occurring aphid species, were monitored under experimentally reduced densities of: (i) ground‐dwelling predators, (ii) flying predators and parasitoids, and (iii) with straw mulch. The three treatments were applied in a 2 × 2 × 2 factorial design in a field of spring wheat (Triticum aestivum L.). The exclusion of ground‐dwelling predators increased aphid populations by 55% in June and 40% in July, respectively. Mulched plots had 25% lower aphid densities in June. This was presumably due to enhanced densities of spiders (Araneida) in mulched plots. The exclusion of flying predators and parasitoids led to 94% higher aphid populations in late July (109 vs. 56 individuals per 100 shoots), irrespective of mulch or ground predator manipulation. This was attributed to the larvae of gall midges Aphidoletes cf. aphidimyza (Rondani) (Diptera: Cecidomyiidae) and hoverflies (Diptera: Syrphidae). The results indicate that a scarcity of predators and a bare soil surface renders crops more susceptible to arthropod pests. Farming schemes should aim at enhancing both ground‐dwelling and flying predators for elevated levels of natural pest control.     

Effect of exposure to fluoride,nitrogen compounds and SO2 on the numbers of spruce shoot aphids on Norway spruce seedlings

Summary Development of spruce shoot aphid (Cinara pilicornis Hartig) populations was monitored in natural and artificial infestations of Norway spruce (Picea abies Karst.) seedlings, exposed to air pollutants in an experimental field. The pollutants, applied both singly and in mixtures, were gaseous sulphur dioxide, NaF (30 mg l^-1 F) and Ca(NO₃)₂ or (NH₄)₂SO₄ in aqueous solutions (200 mg l^-1 N). Aphid numbers on 10 seedlings in each treatment and two control plots were counted at 2-week intervals. At the beginning of the experiment aphid numbers did not differ between treatments. Aphid populations peaked in late June and early July. All the pollutants and their combinations significantly increased the numbers of aphids per seedling. Four apterous females were transferred to spruce seedlings which were growing in containers in the same plots. After 4–5 weeks aphid numbers were significantly higher in the fluoride treatment and in the combined treatment of fluoride, nitrogen and SO₂. The pollution treatments did not have a significant effect on shoot growth. Concentrations of F and S in needles were higher in treatments involving these pollutants. There were no significant differences in the concentrations of free amino acids in shoot stems between control and fluoride treatment. However, the relatively low concentration of arginine in the F treatment at the end of the growing season might indicate disturbances in the nitrogen metabolism of spruce seedlings.     

Effect of autumn and winter meteorological variables on spring aphid populations in the Po valley, Northern Italy

Prediction of aphid populations is crucial to the successful application of control strategies. In previous studies clear relationships between aphid catches and meteorological variables were highlighted. The primary objective of this study was to quantify the effects of autumn and winter meteorological variables on the aphid species populations the following spring. The data on all the species caught at two Italian sites (Ozzano Emilia and Budrio) up to 31 May from 1992 to 1999 were used for this study. Different models were found according to the aphid biological cycle (i.e. holocycle, anholocycle, holo-anholocycle). A fourth group of minor species, designated as 'others', was properly modelled as holo-anholocycle species. A satisfactory fit was observed when holocycle species were plotted against minimum temperature and precipitation in October, anholocycle species against minimum temperature and precipitation in December–January, holo-anholocycle species and 'others' against wind speed and number of frosty days in November, and minimum temperature and precipitation in December–January. Model response was more consistent at Budrio (open flat site) than at Ozzano Emilia (flat site delimited by a hill). A coherent pattern was found with an overall comparison of the estimates against observations. The possibility offered by these empirical models for forecasting spring aphid populations of all species at a given site is clearly of interest. This first study encouraged further investigation aimed at validating models before applying them in practice.     

Tripartite Interactions of Barley Yellow Dwarf Virus,Sitobion avenae and Wheat Varieties

The tripartite interactions in a pathosystem involving wheat (Triticum aestivum L.), the Barley yellow dwarf virus (BYDV), and the BYDV vector aphid Sitobion avenae were studied under field conditions to determine the impact of these interactions on aphid populations, virus pathology and grain yield. Wheat varietal resistance to BYDV and aphids varied among the three wheat varieties studied over two consecutive years. The results demonstrated that (1) aphid peak number (APN) in the aphid + BYDV (viruliferous aphid) treatment was greater and occurred earlier than that in the non-viruliferous aphid treatment. The APN and the area under the curve of population dynamics (AUC) on a S. avenae-resistant variety 98-10-30 was significantly lower than on two aphid-susceptible varieties Tam200(13)G and Xiaoyan6. (2) The production of alatae (PA) was greater on the variety 98-10-30 than on the other varieties, and PA was greater in the aphid + BYDV treatment on 98-10-30 than in the non-viruliferous aphid treatment, but this trend was reversed on Tam200(13)G and Xiaoyan6. (3) The BYDV disease incidence (DIC) on the variety 98-10-30 was greater than that on the other two varieties in 2012, and the disease index (DID) on Tam200(13)G was lower than on the other varieties in the aphid + BYDV and BYDV treatments in 2012, but not in 2011 when aphid vector numbers were generally lower. (4) Yield loss in the aphid + BYDV treatment tended to be greater than that in the aphid or BYDV alone treatments across varieties and years. We suggested that aphid population development and BYDV transmission tend to promote each other under field conditions. The aphids + BYDV treatment caused greater yield reductions than non-viruliferous aphids or virus treatment. Wheat varietal resistance in 98-10-30 affects the aphid dispersal, virus transmission and wheat yield loss though inhibits aphid populations from increasing.     

Identification of novel aphid-killing bacteria to protect plants

Aphids, including the peach-potato aphid, Myzus persicae, are major insect pests of agriculture and horticulture, and aphid control measures are limited. There is therefore an urgent need to develop alternative and more sustainable means of control. Recent studies have shown that environmental microbes have varying abilities to kill insects. We screened a range of environmental bacteria isolates for their abilities to kill target aphid species. Tests demonstrated the killing aptitude of these bacteria against six aphid genera (including Myzus persicae). No single bacterial strain was identified that was consistently toxic to insecticide-resistant aphid clones than susceptible clones, suggesting resistance to chemicals is not strongly correlated with bacterial challenge. Pseudomonas fluorescens PpR24 proved the most toxic to almost all aphid clones whilst exhibiting the ability to survive for over three weeks on three plant species at populations of 5–6 log CFU cm⁻² leaf. Application of PpR24 to plants immediately prior to introducing aphids onto the plants led to a 68%, 57% and 69% reduction in aphid populations, after 21 days, on Capsicum annuum, Arabidopsis thaliana and Beta vulgaris respectively. Together, these findings provide new insights into aphid susceptibility to bacterial infection with the aim of utilizing bacteria as effective biocontrol agents.     

Differential effects of weather and natural enemies on coexisting aphid populations

Study of mechanisms responsible for regulating populations of living organisms is essential for a better comprehension of the structure of biological communities and evolutionary forces in nature. Aphids (Hemiptera: Sternorrhyncha) comprise a large and economically important group of phytophagous insects distributed worldwide. Previous studies determined that density-dependent mechanisms play an important role in regulating their populations. However, only a few of those studies identified specific factors responsible for the observed regulation. Time series data used in this study originated from the untreated control plots that were a part of potato (Solanum tuberosum L.) insecticide trials in northern Maine from 1971 to 2004. The data set contained information on population densities of three potato-colonizing aphid species (buckthorn aphid, Aphis nasturtii; potato aphid, Macrosiphum euphorbiae; and green peach aphid, Myzus persicae) and their natural enemies. We used path analysis to explore effects of weather and natural enemies on the intrinsic growth rates of aphid populations. Weather factors considered in our analyses contributed to the regulation of aphid populations, either directly or through natural enemies. However, direct weather effects were in most cases detectable only at P ≤ 0.10. Potato aphids were negatively affected by both fungal disease and predators, although buckthorn aphids were negatively affected by predators only. Parasitoids did not have a noticeable effect on the growth of any of the three aphid species. Growth of green peach aphid populations was negatively influenced by interspecific interactions with the other two aphid species. Differential population regulation mechanisms detected in the current study might at least partially explain coexistence of three ecologically similar aphid species sharing the same host plant.     

Within-Plant Bottom-Up Effects Mediate Non-Consumptive Impacts of Top-Down Control of Soybean Aphids

There is increasing evidence that top-down controls have strong non-consumptive effects on herbivore populations. However, little is known about how these non-consumptive effects relate to bottom-up influences. Using a series of field trials, we tested how changes in top-down and bottom-up controls at the within-plant scale interact to increase herbivore suppression. In the first experiment, we manipulated access of natural populations of predators (primarily lady beetles) to controlled numbers of A. glycines on upper (i.e. vigorous-growing) versus lower (i.e. slow-growing) soybean nodes and under contrasting plant ages. In a second experiment, we measured aphid dispersion in response to predation. Bottom-up and top-down controls had additive effects on A. glycines population growth. Plant age and within-plant quality had significant bottom-up effects on aphid size and population growth. However, top-down control was the dominant force suppressing aphid population growth, and completely counteracted bottom-up effects at the plant and within-plant scales. The intensity of predation was higher on upper than lower soybean nodes, and resulted in a non-consumptive reduction in aphid population growth because most of the surviving aphids were located on lower plant nodes, where rates of increase were reduced. No effects of predation on aphid dispersal among plants were detected, suggesting an absence of predator avoidance behavior by A. glycines. Our results revealed significant non-consumptive predator impacts on aphids due to the asymmetric intensity of predation at the within-plant scale, suggesting that low numbers of predators are highly effective at suppressing aphid populations.     

Establishment, Spread and Initial Impact of Aphis chloris Koch (Hemiptera: Aphididae), Introduced into Australia for the Biological Control of St John's Wort

The aphid, Aphis chloris Koch, quickly established following field release at numerous sites throughout south-eastern Australia. Local populations built up to levels at which migratory alates were produced within the first season. Dispersal of these alates over large distances led to widespread colonization of St John's wort infested areas within 2-3 years. Detailed observations at the primary release site at Pierce's Creek, ACT, showed that aphid populations undergo a seasonal cycle of population growth throughout the summer, followed by a migratory phase with alate production and dispersal in autumn and a population decline over winter. This pattern was repeated at other release sites monitored over a 5-year period from 1987 to 1991 inclusive, without populations building up to damaging levels. Natural enemies, competition from existing biological control agents, climatic factors and emigration appear sufficient to limit such outbreaks. While caged plants did show a decline in vigour and seed production under heavy aphid attack, such damage was intermittent in open field situations. The present study suggests that, while A. chloris is now widespread, it will not make an important contribution to the overall control of St John's wort.     

Responses of summer cereal aphid populations to reduced rate aphicide applications in field plots of winter wheat

Abstract 1 Recommended and reduced rate applications of pirimicarb and alpha‐cypermethrin were applied to winter wheat crops to control summer infestations of grain aphid (Sitobion avenae) and rose‐grain aphid (Metopolophium dirhodum). 2 Aphid numbers were assessed weekly and the yield response to treatment application was compared with accumulated aphid days on the crop. 3 Responses to aphicide treatment varied between sites according to variations in the subsequent development of aphid populations under varying weather conditions and differential pressures from aphid natural enemies. 4 Alpha‐cypermethrin treatment reduced spider density at most sites, and also resulted in a resurgence of aphid populations at three sites.