Effects of augmentative releases of the coccinellid, Adalia bipunctata, and of insecticide treatments in autumn on the spring population of aphids of the genus Dysaphis in apple orchards

The impact of augmentative releases of indigenous predators and insecticide applications to control the autumn aphid forms of the genus Dysaphis (Homoptera: Aphididae), major pest insects on apple trees, was assessed in one-year field experiments in Switzerland. Eggs and larvae of the two-spot ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) were released on 4-year old apple trees in various numbers at five different dates in autumn 1998 when sexuales of the aphids were present. Additionally, Pyrethrum HP was sprayed at the same five dates to compare the effectiveness of these augmentative releases to a commonly applied insecticide. Augmentative releases of larvae before mid-October significantly prevented the deposition of overwintering eggs by aphids of the genus Dysaphis and consequently reduced the number of hatched fundatrices in spring, 1999. There was a significant negative functional response among the number of released coccinellid larvae in autumn 1998 and the number of observed fundatrices on apple trees in spring 1999. Applications of Pyrethrum HP before mid-October were more effective than augmentative releases of larvae of A. bipunctata. The release of coccinellid eggs had no impact on the number of fundatrices of the genus Dysaphis in the next spring because they did not hatch due to bad weather conditions. The weather conditions in autumn seemed to have an impact on the autumn migration of the winged aphids back to their primary host. The prevention of egg deposition of aphids in autumn is a promising control strategy and deserves further exploration for practical use.     

Effects of autumn kaolin treatments on the rosy apple aphid, Dysaphis plantaginea (Pass.) and possible modes of action

Abstract:  Autumn applications of the repellent processed-kaolin particle film (Surround® WP) might be an alternative to the insecticides commonly used in spring to control the rosy apple aphid, Dysaphis plantaginea (Pass.) (Hom., Aphididae). To assess the mode of action and the impact of kaolin on autumn forms of D. plantaginea , trials were conducted in field cages and in open-fields in autumn 2003. Choice and no-choice experiments in field cages showed that winged aphids landed in significantly lower numbers and gave birth to significantly fewer females on kaolin-treated branches compared with the untreated control. In a first open-field trial, single applications at 10 different dates and with two different concentrations of kaolin were conducted after harvest to assess the influence of the kaolin concentration on the autumn forms of D. plantaginea . No differences were found between the different concentrations and spraying dates. In a second open-field trial, single and multiple applications of kaolin were tested at different dates after harvest. Repeated applications of kaolin significantly reduced females in autumn and fundatrices in spring, whereas single kaolin treatments had no significant effect on D. plantaginea . None of the kaolin treatments reduced aphids below the economic threshold. In conclusion, kaolin showed promising results to control autumn forms of D. plantaginea. However, with a more detailed forecasting model for the autumnal flight of this aphid, treatments could be conducted more precisely and more effectively, especially in years with exceptional climatic conditions, such as in 2003.     

Seasonal coincidence between rosy apple aphid fundatrices and their parasitoids: implications for an early biological control of Dysaphis plantaginea

The potential contribution of the aphid parasitoid Ephedrus persicae Froggatt (Hymenoptera: Braconidae, Aphidiinae) in regulating stem mothers of the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) was investigated in culture conditions using both species' phenological emergence data in spring and host stage suitability trials. In 2003, emergence of E. persicae started on April 1st, i.e., 108.2 degree-days (base: 4.5 degrees C; start date: January 1st) later than its host on March 10th. When less than 3% of parasitoids had emerged on April 12th, more than 97% of D. plantaginea stem mothers had moulted beyond their 1st instar. The latest parasitoids left their diapause mummies in late April as the majority of fundatrices had reached the adult stage. Parasitisation trials demonstrated the suitability for E. persicae of all developmental stages of rosy apple aphid fundatrices, including mature individuals. No offspring were deposited by fundatrices parasitised as Ist-instar nymphs but later instars did produce a progeny whose size was substantially reduced compared with unparasitised individuals, and scaled against their age at the time of parasitisation. Although the temperature accumulation required for emergence in spring is reached later for E. persicae than for its host aphids, thus allowing part of the stem mother population to temporarily escape parasitisation and reach maturity, the marked reduction in fecundity of individuals parasitised even as late-instar nymphs does confer to E. persicae a non-negligible role in potentially regulating D. plantaginea.     

Kaolin particle films suppress many apple pests, disrupt natural enemies and promote woolly apple aphid

Multiple applications of hydrophobic kaolin particle film in apple orchards suppressed numbers of blossom weevil (Anthonomus pomorum), brown leaf weevil (Phyllobius oblongus), attelabid weevil (Caenorhinus pauxillus), leafhoppers (Empoasca vitis and Zygina flammigera) and green apple aphid (Aphis pomi) colonies. The kaolin treatments reduced the apple sawfly (Hoplocampa testudinea) fruit infestation on cultivar J. Grieve, and the fruit damage caused by oyster scale (Quadraspidiotus ostreaeformis), mussel scale (Lepidosaphes ulmi), early caterpillars, leaf rolling moths (Tortricidae), fruitlet‐mining tortrix moth (Pammene rhediella) and codling moth (Cydia pomonella). There was no effect on the number of colonies of rosy leaf curling aphid (Dysaphis devecta), nor on the fruit damage caused by common earwig (Forficula auricularia) and apple sawfly on cv. G. Delicious. The level of infestation of rosy apple aphid (Dysaphis plantaginea), leaf miner moths (Phyllonorycter blancardella, Lyonetia clerkella), and agromyzid flies (Phytomyza heringiana) increased in the kaolin‐treated plots. Kaolin treatments promoted woolly apple aphid (Eriosoma lanigerum) infestation, which became severe, while it reduced the abundance of polyphagous predators like F. auricularia, predaceous Heteroptera and Coleoptera, the red velvet mite (Allothrombium fuliginosum), spiders (Araneae) and the abundance of common black ant (Lasius niger). The treatments also reduced parasitism of the apple sawfly by the ichneumonid Lathrolestes ensator. Many weeks after ending the kaolin treatments, the number of predaceous Coleoptera and especially the number of spiders remained low in the kaolin‐treated plots.     

Weak spatial and temporal population genetic structure in the rosy apple aphid, Dysaphis plantaginea, in French apple orchards

We used eight microsatellite loci and a set of 20 aphid samples to investigate the spatial and temporal genetic structure of rosy apple aphid populations from 13 apple orchards situated in four different regions in France. Genetic variability was very similar between orchard populations and between winged populations collected before sexual reproduction in the fall and populations collected from colonies in the spring. A very small proportion of individuals (～2%) had identical multilocus genotypes. Genetic differentiation between orchards was low (F(ST)<0.026), with significant differentiation observed only between orchards from different regions, but no isolation by distance was detected. These results are consistent with high levels of genetic mixing in holocyclic Dysaphis plantaginae populations (host alternation through migration and sexual reproduction). These findings concerning the adaptation of the rosy apple aphid have potential consequences for pest management.     

Conservation biological control of rosy apple aphid, Dysaphis plantaginea (Passerini), in eastern North America

Because of the potentially serious damage rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), can cause to apple fruit and branch development, prophylactic insecticides are often used for control. If biological control could be relied on, the amount of pesticide applied in orchards could be reduced. This study examined biological control of rosy apple aphid in eastern West Virginia and the potential for enhancement through conservation biological control, in particular, the effect of interplanting extrafloral nectar-bearing peach trees. By 20 d after first bloom, only 2% of fundatrices initially present survived to form colonies based on regression of data from 687 colonies. Exclusion studies showed that many of the early colonies were probably destroyed by predation; the major predator responsible seemed to be adult Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). Mortality before apple bloom was most important in controlling rosy apple aphid population growth but by itself is not sufficiently reliable to prevent economic injury. Interplanting of extrafloral nectar-bearing trees did not increase biological control, and interplanting with 50% trees with extrafloral nectar glands reduced biological control. The number of leaf curl colonies in the 50% interplanted orchards was lower than in monoculture orchards, suggesting a preference of alate oviparae for more diverse habitats, supporting the resource concentration hypothesis but not at a level sufficient to prevent injury. Predation and parasitism after the formation of leaf curl colonies was not adequate to control rosy apple aphid populations.     

Temporal and spatial variability of rosy apple aphid Dysaphis plantaginea populations: is there a role of the alternate host plant Plantago major?

• 1 The rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae) is a pest of economic importance to the apple industry worldwide, particularly in organic apple orchards where no acceptable controls are available. In the Similkameen Valley of British Columbia, Canada, the rosy apple aphid population size varies widely between orchards and between years. To explain this variation, potential environmental correlates of aphid density were evaluated. The architecture of the alternate host was also evaluated for its effect on rosy apple aphid summer survival and reproduction.
• 2 The percentage of trees infested by rosy apple aphids among orchards was in the range 8–94% for trees having at least one cluster with more than ten aphids in 2007 and in the range 0–39% in 2008.
• 3 A general linear model correlating aphid densities to the environmental variables of abundance of the alternate host (plantain Plantago spp.), foliar nitrogen, tree age and planting density, and reduced by stepwise regression, indicated that foliar nitrogen and tree age explained 33% of the variation. Abundance of the summer, alternate food plant, plantain, was not related to later aphid densities on apple trees.
• 4 Plantain architecture, however, influenced aphid numbers and 25‐fold more aphids were found on low‐lying plantain leaves than on more upright leaves. Experimental manipulation of leaf angle and leaf size showed that significantly more aphids occurred on low angle, large leaves. Finally, mowing that encouraged low lying plants prior to spring aphid migration was associated with a four‐fold greater number of both winged and wingless aphids on the plantain.

     

Aphids at crossroads: when branch architecture alters aphid infestation patterns in the apple tree

Plant architecture highly constrains pest infestation but is rarely considered in studies on plant–insect interactions. We analysed the relationships between apple tree architectural traits manipulated by tree training and within-branch development of Dysaphis plantaginea (rosy apple aphid, RAA), a major apple pest, during its multiplication wingless phase in spring. We hypothesised that the degree of branching had an effect on RAA within-branch infestation. In an experimental apple orchard, the infestation by aphid wingless forms was surveyed in two consecutive spring seasons within branches manipulated to design contrasted architectures differing in shoot numbers, shoot density and branching orders. Whatever the branch management system, aphid infestation was higher on long versus short, fruiting versus vegetative, and growing versus non-growing shoots. Either less infested shoots or less severe infestation were observed in the most branched system. A pattern of within-branch short-distance infestation was confirmed. Moreover, the number of branching points between two shoots exerted a high constraint on this infestation pattern. Beside possible trophic effects due to plant growth patterns already documented in the literature, a high degree of branching is likely to be a key-architectural trait to constrain within-branch aphid infestation. This opens new perspectives on the manipulation of branch architecture as a mean giving partial control of pests towards sustainable fruit production.     

The potential of three native insect predators to control the rosy apple aphid, Dysaphis plantaginea

The potential of three aphidophagous predators, Adalia bipunctata, Aphidoletes aphidimyza, and Episyrphus balteatus to control the rosy apple aphid, Dysaphis plantaginea Pass., a major pest on apple in Europe, was assessed by means of laboratory and field cage experiments in Northern Switzerland. Under laboratory conditions, all three predators efficiently preyed upon D. plantaginea on apple seedlings. The searching success of larvae of A. bipunctata for individual aphids was not dependent on the size of branches of apple trees varying in leaf surface area from 150 cm² to 960 cm². Fifty and 70% of individual aphids were found and killed 6 hours and 48 hours, respectively, after release of single second instar larva of A. bipunctata. In a first field cage experiment in 1996, A. bipunctata, and to a lesser extent E. balteatus, proved to be effective and consistent predators of D. plantaginea during spring conditions, being little affected by cool temperatures and wet weather. In a subsequent field cage experiment in 1997, larvae of A. bipunctata and E. balteatus were released singly and in combination on aphid infested apple seedlings to study interactions between these two promising control agents. Both species had a significant negative effect on aphid population increase. The two species did not significantly interact and thus, their joint effect is best explained by an additive model. Combined releases of the two predator species reduced aphid densities to 5% of the control. This indicates the potential for augmentative releases of these native aphid predators to control D. plantaginea.     

Feeding and egg distribution studies of Heringia calcarata (Diptera: Syrphidae), a specialized predator of woolly apple aphid (Homoptera: Eriosomatidae) in Virginia apple orchards

Predation by the aphidophagous syrphid fly Heringia calcarata (Loew) on woolly apple aphid, Eriosoma lanigerum (Hausmann), was studied in the laboratory and in Virginia apple orchards. Feeding studies compared the prey suitability of three temporally sympatric aphid pests of apple: spirea aphid, Aphis spiraecola Patch; rosy apple aphid, Dysaphis plantaginea (Passerini); and woolly apple aphid. Significantly more H. calcarata larvae survived and completed development on a pure diet of woolly apple aphid than on rosy apple aphid, and none survived on spirea aphid. Final larval weights were significantly greater, and the larval developmental period was significantly shorter on woolly apple aphid than on rosy apple aphid, but neither the duration of pupal development nor adult weight differed between diets. H. calcarata larvae consumed an average of 105 woolly apple aphids during their development. Na?ve, neonate larvae given access to all possible pair combinations of woolly apple aphid, rosy apple aphid, and spirea aphid consumed significantly more woolly apple aphids in all pairings that included woolly apple aphid. When given a choice of rosy apple aphid and spirea aphid, significantly more rosy apple aphids were consumed. Weekly counts of syrphid eggs found in woolly apple aphid, rosy apple aphid, and spirea aphid colonies collected from apple trees showed that two generalist hover fly predators, Eupeodes americanus (Wiedemann) and Syrphus rectus Osten Sacken, were present in colonies of all three aphid species and that E. americanus was the most abundant syrphid predator in A. spiraecola and D. plantaginea colonies. H. calcarata eggs were found only in woolly apple aphid colonies and were more abundant there than E. americanus and S. rectus. These data suggest that H. calcarata is a specialized predator of woolly apple aphid in the apple ecosystem in Virginia.     

Climate-ameliorating measures influence photosynthetic gas exchange of apple leaves

Sunburn has become one of the major threats to apple fruit production in South Africa and other countries with Mediterranean climate. Some climate‐ameliorating measures have been developed to control sunburn in apples. Effects of the climate‐ameliorating measures, viz. evaporative cooling, Surround^® WP and shade net, on leaf gas exchange of a 5‐year‐old orchard of ‘Cripps’ Pink’ apple were investigated during hot summer days in Stellenbosch, South Africa. Evaporative cooling increased net photosynthetic rate (A) and stomatal conductance (g_s) because of its lowering of leaf temperature and leaf‐to‐air vapour pressure difference (VPD). Shade net also reduced leaf temperature because of reduction in photosynthetic photon flux density (PPFD). Quantum efficiency of photosynthesis was increased under shade net to compensate for reduced PPFD. Shade net also reduced transpiration rate more than A, resulting in increased midday water‐use efficiency. The diurnal trends of A and g_s in the Surround WP and control treatments were similar, indicating limited ameliorative impact of Surround WP. Furthermore, Surround WP typically reduced maximum rate of carboxylation and the light‐saturated rate of electron transport. In all treatments, A decreased by 70% when leaf temperature increased from 35°C to 40°C. In conclusion, all treatments affected leaf photosynthetic gas exchange. Evaporative cooling enhanced leaf A and g_s because of distinct ameliorative effects on leaf temperature and VPD. Shade net reduced leaf temperature with no consistent effects on leaf gas exchange attributes. Surround WP had limited or no impact on leaf temperature and negatively affected leaf gas exchange attributes.     

Molecular interactions between rosy apple aphids, Dysaphis plantaginea, and resistant and susceptible cultivars of its primary host Malus domestica

The use of crop varieties resistant or tolerant to insect pests or other stress factors is one approach in non‐chemical crop‐protection. Knowledge of the biochemical and molecular background of insect–plant interactions is a prerequisite for optimizing breeding for resistance. However, the resistance genes involved in plant–aphid interactions have so far only been identified and characterized in very few plant species. Our work aims to elucidate the molecular and biochemical mechanisms involved in resistance of apple trees, Malus domestica L. (Rosaceae), against its primary aphid pest, the rosy apple aphid, Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), which is considered a serious economic pest of apple. Gene expression in both resistant and susceptible apple cultivars after infestation with rosy apple aphids was investigated by employing the cDNA‐AFLP method (cDNA–Amplified Fragment Length Polymorphism). From approximately 12 500 cDNA fragments detected on polyacrylamide gels, 21 bands were apparently up‐ or down‐regulated only in the resistant cultivar ‘Florina’ after aphid infestation compared to the susceptible cultivar ‘Topaz’ and/or mechanically wounded or non‐infested leaves. These fragments were cloned, sequenced, and the pattern of gene expression for six fragments was subsequently verified by virtual Northern blots. Sequence comparisons of these fragments to GenBank accessions revealed homologies to already known genes, most of them isolated from Arabidopsis thaliana L. Among them, a putative RNase‐L‐inhibitor‐like protein, a pectinacetylesterase, an inositol‐phosphatase‐like protein, a precursor of the large chain of the ribulose‐1,5‐biphosphate‐carboxylase, and defence‐related genes such as a vacuolar H(+)‐ATPase subunit‐like protein and an ADP‐ribosylating enzyme were identified. The results are discussed in relation to a putative role of these genes in conferring aphid resistance in apple trees.     

苹果绵蚜种群的空间分布型及其应用——Ⅰ.秋季种群

生物种群的空间分布是一种高度特化的生物学特性,是长期适应自然环境的结果。在理论上,研究种群的空间分布有助于理解种群的生态学特性以及种群与所处环境的相互关系;在实践中,种群的空间分布是确定生物统计分析的资料代换方法和制定抽样技术方案的依据。 苹果绵蚜Eriosoma lanigerum(Hausm.)是苹果树的毁灭性害虫。50年代云南仅昆明地区有苹果绵蚜的分布,现在苹果绵蚜已侵入到云南许多苹果产区。1978年苹果绵蚜侵入到丽江县,其危害相当严重。过去的工作主要集中在生物学和防治方面,空间分     

DL‐β‐Aminobutyric acid application negatively affects reproduction and larval development of the rosy apple aphid,Dysaphis plantaginea,on apple

The rosy apple aphid, Dysaphis plantaginea (Passerini) (Hemiptera: Aphididae), is one of the major pests of European apple orchards, commonly controlled by the use of synthetic insecticides. In the present work, the non‐protein amino acid DL‐β‐aminobutyric acid (BABA), known to induce plant resistance against a wide range of abiotic and biotic stresses, has been tested for its protective effect against this pest on apple. We first verified the lack of any contact effect of BABA on the insect itself. Next we applied BABA as a soil drench to apple and monitored its effect on the population development of aphids after artificial infestation. We demonstrated that BABA strongly reduced the population growth and that this compound severely affected various life‐history characteristics of the aphid such as female longevity and fecundity, nymph mortality, and larval development.     

Efficacy of Three Strategies Based on Insecticide,Oil and Elicitor Treatments in Controlling Aphid Populations and Potato virus Y Epidemics in Potato Fields

Potato virus Y (PVY), the potato virus with the highest economic impact in Europe, is transmitted by aphids in a non‐persistent manner. A two‐year field experiment was conducted in Switzerland to evaluate the efficacy of three strategies for controlling aphid populations and the spread of PVY, consisting of treatment with one insecticide (Karate Zeon^®), one elicitor (Bion^®) and one oil (Telmion^®), respectively. The elicitor strategy proved to be ineffective for controlling aphid populations and inadequate for controlling PVY spread. The insecticide strategy gave incomplete protection from aphid infestations, owing to the selection of aphid‐resistant clones. The insecticide gave too little protection against PVY spread for it to be considered a suitable candidate for the purpose. The oil strategy had no effect on aphid populations, but was the best option to reduce PVY spread.     

In-field production of parasitoids of Dysaphis plantaginea by using the rowan aphid Dysaphis sorbi as substitute host

A system was developed to provide the parasitic wasp Ephedrus persicae Froggatt (Hymenoptera: Braconidae: Aphidiinae), which attacks the rosy apple aphid Dysaphis plantaginea (Passerini) (Homoptera: Aphididae), with the alternative host Dysaphis sorbi Kaltenbach (Homoptera: Aphididae) in apple orchards. Rowan trees (Sorbus aucuparia L.) arranged along the side of an unsprayed orchard were artificially infested in late February 2002 with eggs of D. sorbi. Colonies of D. sorbi successfully developed from the introduced eggs and persisted on several trees until the end of June. The only primary parasitoid species emerging from a sample of mummified aphids collected in spring from the infested rowan trees was the braconid wasp species E. persicae. In a host-switching experiment, nymphs of D. plantaginea proved suitable for female parasitoids originating from mummified D. sorbi. A series of mummies collected from the rowan trees in early summer contained diapausing parasitoids and hyperparasitoids that only hatched in April of the following spring. These observations suggest the possibility of establishing a local population of E. persicae in apple orchards, so that D. plantaginea can be readily attacked by diapause-emerging parasitoids in early spring.     

Hypersensitivity in apple to feeding by Dysaphis plantaginea: effects on aphid biology

Effects on rosy apple aphid (Dysaphis plantaginea) of hypersensitivity to aphid feeding in apple were assessed in a series of insectary experiments in 1980–82. Hypersensitive plants rapidly produced tissue necroses at aphid feeding sites. Inoculation with apterae demonstrated that, in comparison with aphids on susceptible plants, aphids on hypersensitive plants showed symptoms characteristic of host antibiosis, including increased mortality, failure to reproduce and slower development. Embryo number indicated that fecundity of surviving adults was lower on hypersensitive plants and mean relative growth rate of aphids was reduced. Hypersensitivity did not prevent colonisation by gynoparae returning from the summer host, nor subsequent egg-laying. It conferred, however, a strong resistance against colonisation after egg-hatch the following spring. The potential of hypersensitivity as a field-resistance is discussed.     

Decline of soybean aphid (Homoptera: Aphididae) egg populations from autumn to spring on the primary host, Rhamnus cathartica

Soybean aphid, Aphis glycines Matsumura (Homoptera: Aphididae), is a severe pest of soybeans in North America. Soybean aphid populations cycle between a secondary summer host, where populations reproduce parthenogenetically and a primary host, where populations overwinter as eggs. In North America, the secondary host is soybean, and the primary hosts are Rhamnus cathartica L. (Rhamnaceae) and R. alnifolia L'Her. A location with abundant populations of soybean aphid on R. cathartica was identified near Guelph, Ontario, Canada, in October 2004, and eggs on trees were counted at multiple sites within that location each autumn and spring over the next 2 yr. Dynamics of naturally occurring soybean aphid populations on the primary host were assessed with respect to (1) decline of overwintering eggs from autumn to spring, (2) development of spring populations on R. cathartica, and (3) development of soybean aphid populations on soybean immediately adjacent to overwintering sites. Counts of aphid eggs declined by approximately 70% between autumn and spring sampling periods in 2004-2005. Significant differences in counts of aphid eggs relative to sampling height were observed in the canopy of R. cathartica. No edge effects were observed in the development of soybean aphid populations in soybeans adjacent to overwintering sites in this study. Very few eggs were collected at the same study location in the autumn of 2005, and no aphid eggs were collected from samples taken in the spring of 2006. Egg counts taken in the autumn of 2006 were intermediate in number relative to counts taken in the autumn of 2004 and 2005.     

Erratum

Abstract: Fertilization levels for ornamental crops may influence pest population dynamics, crop quality, and pest management strategy. We examined the effect of fertilization on population growth and within‐plant distribution of melon or cotton aphid, Aphis gossypii Glover, on potted chrysanthemum, Dendranthema grandiflora (Tzvelev). In terms of pest management implications, we also investigated the effect of fertilization on the number of insecticide applications needed to control A. gossypii on potted chrysanthemum. Population growth rate of A. gossypii increased with fertilization levels from 0 to 38 ppm N and reached a plateau from 38 to 488 ppm N. Increased fertilization beyond 38 ppm N, 10% of the commercial standard, did not result in higher aphid number. Aphids responded to nutrient availability of plants by distributing themselves in areas with higher level of nitrogen. More aphids were found in the apical and middle strata of the plants than the basal stratum, which had the lowest nitrogen content. Leaf nitrogen content increased with increased fertilization level and was consistently higher in the apical and middle strata than the basal stratum. Increased fertilization from 0 to 375 ppm N did not result in higher number of insecticide applications. All three insecticides (bifenthrin, kinoprene or pymetrozine) were effective in keeping the aphid infestation below a pre‐determined level, five aphids per plant, but pymetrozine required the least number of applications. For chrysanthemum, a fast‐growing crop and heavy utilizer of nitrogen, increased fertilization shortened the time to flowering, which would allow growers to harvest their crop sooner and reduce the time for aphid population growth. Reduction in time to harvest could result in significant reduction of insecticide usage by reducing the time for aphid population growth. As a result, high fertilization together with minimal runoff may be a useful tactic to an integrated pest management (IPM) programme for managing A. gossypii on potted chrysanthemums.     

Effects of augmentative releases of eggs and larvae of the ladybird beetle, Adalia bipunctata, on the abundance of the rosy apple aphid, Dysaphis plantaginea, in organic apple orchards

The impact of augmentative releases of larvae and eggs of the indigenous ladybird beetle Adalia bipunctata (L.) (Coleoptera: Coccinellidae) against the rosy apple aphid Dysaphis plantaginea Pass. (Homoptera: Aphididae), a major pest insect on apple trees, was assessed in field experiments in Switzerland, during 1997. In a first experiment, eggs and larvae were released on 3-year old apple trees infested with five aphids at four different predator-prey ratios (0:5, 1:5, 1:1, 5:1). In a second experiment, eggs and larvae were released at a predator-prey ratio of 5:1 on branches of apple trees naturally infested with aphids. In both experiments, the interaction with ants was taken into account and the releases were done at two different times in spring. The results showed that an augmentative release of larvae significantly prevented the build-up of colonies of D. plantaginea. Significant reductions in aphid numbers were recorded at the two highest predator-prey ratios, 1:1 and 5:1. Larvae were efficient just before flowering of apple trees at a time when growers normally have to spray their trees. On trees where ants were present the larvae of A. bipunctata were significantly less efficient. Effects of eggs of A. bipunctata, however, were less reliable. At the first date of release (5 April), they did not hatch, probably as a consequence of bad weather conditions.