Monarch butterfly oviposition on swallow-worts (Vincetoxicum spp.)

As black swallow-wort, Vincetoxicum nigrum L. Moench, and pale swallow-wort, V. rossicum (Kleopow) Barbar., spread throughout the northeastern United States and southern Canada, there is concern about the impact of these invasive plants on populations of the native North American monarch butterfly Danaus plexippus L. Recent laboratory studies in New York and Ontario, Canada, have found little or no oviposition by monarch butterflies on the two Vincetoxicum species. In Rhode Island, we found 10.5-21.7% oviposition on Vincetoxicum species relative to common milkweed Asclepias syriaca L. in choice tests and 11.9-20.3% in no-choice tests in 2 yr of laboratory testing. These results were supported by field cage trials where monarchs given a choice between V. nigrum and A. syriaca laid 24.5% of their eggs on V. nigrum. In surveys of three pasture fields in Rhode Island where relative coverage of A. syriaca exceeded that of V. nigrum by a 0.77:0.23 ratio, 15.4% of monarch eggs were found on V. nigrum plants. In V. nigrum stands with very little A. syriaca (6.25 stems/ha), monarch egg density on V. nigrum was found to be over five times greater than in the three mixed pasture fields. In none of our laboratory or field evaluations was there any survival of monarch larvae on Vincetoxicum species. It seems that in Rhode Island, Vincetoxicum species serve as an oviposition sink for monarch butterflies. These findings suggest that East Coast butterflies may differ in host selection from those in central New York and southern Ontario, Canada.     

Effect of an alternate weed host, hairy nightshade, Solanum sarrachoides, on the biology of the two most important potato leafroll virus (Luteoviridae: Polerovirus) vectors, Myzus persicae and Macrosiphum euphorbiae (Aphididae: Homoptera)

Hairy nightshade, Solanum sarrachoides (Sendtner), is a ubiquitous weed in potato agro-ecosystems and nonagricultural lands of southeastern Idaho and the Pacific Northwest. This weed increases the complexity of the Potato leafroll virus (PLRV) (Luteoviridae: Polervirus)-potato pathosystem by serving as aphid and virus reservoir. Previous field studies showed higher densities of green peach aphid, Myzus persicae (Sulzer), and potato aphid, Macrosiphum euphorbiae (Thomas), the two most important vectors of PLRV, on S. sarrachoides compared with potato plants in the same fields. Some of the S. sarrachoides plants sampled in these surveys tested positive for PLRV. Viral infections can alter the physiology of plant hosts and aphid performance on such plants. To understand better the potential effects of S. sarrachoides on the PLRV-potato-aphid pathosystem, the life histories of M. persicae and M. euphorbiae were compared on virus-free and PLRV-infected S. sarrachoides and potato. Individual nymphs of each aphid species were held in clip cages on plants from each treatment to monitor their development, survival, and reproductive output. Nymphal survival for both aphids across plant species was higher on S. sarrachoides than on potato, and, within plant species, it was higher on PLRV-infected plants than on noninfected plants. With a few exceptions, similar patterns occurred for fecundity, reproductive periods, adult longevity, and intrinsic rate of increase. The enhanced performance of aphids on S. sarrachoides and on PLRV-infected plants could alter the vector population dynamics and thus the PLRV-disease epidemiology in fields infested with this weed.     

Food web structure of aphids and their parasitoids in Belgian fruit agroecosystems

Community structures of aphids and their parasitoids were studied in fruit crop habitats of eastern Belgium in 2014 and 2015. Quantitative food webs of these insects were constructed separately for each year, and divided into subwebs on three host‐plant categories, fruit crop plants, non‐crop woody and shrub plants and non‐crop herbaceous plants. The webs were analyzed using the standard food web statistics designed for binary data. During the whole study period, 78 plant species were recorded as host plants of 71 aphid species, from which 48 parasitoid species emerged. The community structure, aphid / parasitoid species‐richness ratio and trophic link number varied between the two years, whereas the realized connectance between parasitoids and aphids was relatively constant. A new plant–aphid–parasitoid association for Europe was recorded. Dominant parasitoid species in the study sites were Ephedrus persicae, Binodoxys angelicae and Praon volucre: the first species was frequently observed on non‐crop trees and shrubs, but the other two on non‐crop herbaceous plants. The potential influence, through indirect interactions, of parasitoids on aphid communities was assessed with quantitative parasitoid‐overlap diagrams. Symmetrical links were uncommon, and abundant aphid species seemed to have large indirect effects on less abundant species. These results show that trophic indirect interactions through parasitoids may govern aphid populations in fruit crop habitats with various non‐crop plants, implying the importance for landscape management and biological control of aphid pests in fruit agroecosystems.     

Vector activity of three aphid species (Hemiptera: Aphididae) modulated by host plant selection behaviour on potato (Solanales: Solanaceae)

Viral diseases non-persistently transmitted by aphids are of great economic importance in several annual crops. Transmission efficiency of these non-persistent phytoviruses is dependant on vector efficiency (i.e. vector intrinsic ability to transmit the virus) but also on the vector activity that implies the early steps of aphid host plant selection process (i.e. brief intracellular stylet punctures after landing) and to their interplant movement ability. In Europe, Macrosiphum euphorbiae (Thomas 1878) is considered as one of the most serious virus vectors on potato (Solanum tuberosum L. 1753). Nevertheless, several alate aphid species that do not colonise potato plants are trapped in potato crops. Therefore, we investigated, through laboratory experiments, vector activity of one potato colonising aphid, M. euphorbiae, and two non-colonising potato aphids, the bird cherry-oat aphid Rhopalosiphum padi (L. 1758) and the pea aphid Acyrthosiphon pisum (Harris 1776). A settling experiment was used to evaluate dispersal activity, and the electrical penetration graph (EPG) technique was used to investigate probing activity on potato plants. Results showed that M. euphorbiae exhibited a better vector activity than other two aphid species in terms of landing and probing. By contrast, interplant movements were only recorded on non-colonising aphids, suggesting a better vector activity than M. euphorbiae in terms of locomotive behaviour. These data confirm the involvement of A. pisum and R. padi in the spread of non-persistent viruses.     

Effects of honeydew sugar composition on the longevity of Aphidius ervi

Feeding on sugar‐rich foods such as nectar and honeydew is important for survival of many adult parasitoids. Especially in agricultural systems, honeydew is often the most prevalent carbohydrate source. However, relative to plant nectar, honeydew may be relatively unsuitable, as a result of an unfavourable sugar composition or the presence of secondary plant compounds. We studied survival of the aphid parasitoid Aphidius ervi Haliday (Hymenoptera: Braconidae) on honeydew collected from various aphid species feeding on potato (Solanum tuberosum L., cv. Desiree) (Solanaceae), wheat (Triticum aestivum L., cv. Bobwhite) (Poaceae), or artificial diet, as well as the sugar composition of the different honeydews. Honeydews from the tested aphid species on potato, wheat, or artificial diet were found to be relatively suitable food sources for adult A. ervi, although not always as suitable as a 2 M sucrose solution. There were differences in honeydew sugar composition among the different aphid species on the various host plants. Multivariate statistics showed that the factor ‘aphid species’ had a significant influence on the sugar composition of the honeydew, explaining 27% of the variation in the potato system and 89% in the wheat system. When exploring the relationship between carbohydrate composition of the honeydews from aphids on potato and wheat plants, and their nutritional value for A. ervi, data revealed that differences in parasitoid longevity can to some extent be explained by carbohydrate composition. Furthermore, our results confirm that sucrose and its hexose components glucose and fructose are very suitable carbohydrate sources for hymenopteran parasitoids and show that parasitoid survival on an equimolar solution of the two monosaccharides glucose and fructose does not exceed performance on the disaccharide sucrose.     

Plant response to touch affects the behaviour of aphids and ladybirds

Touching between leaves of the same plant and/or by neighbouring plants is one of the most common mechanical stimuli to which an individual plant has to respond on a daily basis. The possible ecological implications of a plant’s response to touch on plant–insect interactions have not been explicitly investigated. We examined whether plant response to 1 min daily touching over a period of 6 days affects host plant acceptance by the bird cherry-oat aphid Rhopalosiphum padi L. on maize and by the black bean aphid Aphis fabae Scop. on bean, as well as olfactory preference of an aphid predator, seven-spotted ladybird Coccinella septempunctata L. Maize plants responded to touch with significant reduction in plant height, total plant biomass, leaf weight, leaf surface, shoot/root ratio and specific leaf area (SLA), while bean plants responded with reduced stem height and reduced SLA. Both aphid species showed significantly reduced acceptance of touched plants compared with untouched plants. The two aphid species and male and female ladybirds preferred volatiles from untouched plants over those from touched plants. Volatiles in the headspace of touched and untouched plants were collected and identified. Stepwise discriminant analyses identified (E)-nerolidol and (E)-β-caryophyllene in maize and 6-methyl-5-hepten-2-one and an unidentified sesquiterpene in bean as the best discriminating compounds in the volatile profiles of touched plants. Our study suggests that touch-induced changes in plants can potentially affect host plant selection by aphids and habitat searching by ladybirds. Thus, touch-induced changes in plants may have significant effects at higher trophic levels.     

Reproduction and feeding behavior of Myzus persicae on four cereals

Green peach aphid, Myzus persicae (Sulzer), does not overwinter outdoors in Minnesota; it arrives each spring on low-level jet streams from the south. After arrival, anholocylic reproduction occurs on numerous herbaceous species, including many common weeds, before movement to potato, Solanum tuberosum L. In investigating aphid feeding behavior on barrier crops, we observed winter wheat, Triticum aestivum L., colonized by green peach aphid. The Northern Great Plains grows 94,000 ha of potatoes and 20.5 million ha of small grain cereals each year, the latter potentially providing an early emerging and widely distributed green peach aphid host to influence early season potato colonization. Life tables statistics indicated green peach aphid had its highest reproductive potential among cereals on winter wheat, with rye (Secale cereale L.) > barley (Hordeum vulgare L.) > oats (Avena sativa L.). Green peach aphid was found to colonize barley, rye, and winter wheat, but not oats. Mean generation time, net reproductive rate, doubling time, and finite rate of increase were significantly different between host plants. Electrical penetration graph technique indicated mean nonpenetration duration by green peach aphid was significantly different among plant species, and significantly longer on winter wheat than on the other cereals. Mean xylem phase duration was not significantly different among plant species but sieve element salivation was of longest duration on potato. Phloem sap ingestion (E2) was also significantly different among plant species with longest E2 duration on winter wheat. This study demonstrates that this aphid can effectively use key cereals at the vegetative stage.     

Immediate alteration of Macrosiphum euphorbiae host plant-selection behaviour after biotic and abiotic damage inflicted to potato plants

The effects of potato [Solanum tuberosum L. (Solanaceae)] plant damage on the host plant-selection behaviour of the potato aphid, Macrosiphum euphorbiae Thomas (Homoptera: Aphididae), were studied. The damage inflicted to the plant was only of short duration and observations on aphid behaviour were made immediately following plant damage. The underlying questions of the study were to know how much time it takes for plant defence mechanisms to be activated and if this activation had noticeable repercussions on aphid behaviour. We considered stresses of various natures: biotic (pre-infestation by conspecifics or by Colorado potato beetles) and abiotic (scissor cuts). Aphid responses to host plant semiochemicals were investigated using a darkened arena bioassay and the probing behaviour was assessed using the electrical penetration graph technique. Aphids were attracted to their host plant (undamaged or damaged). In a preference test (undamaged plant vs. damaged plant), plants previously infested by conspecifics were preferred to undamaged plants, but this preference was not observed for heterospecific and abiotic damage. However, aphid probing behaviour was not modified on plants previously infested by conspecifics, whereas some changes were observed subsequently to heterospecific and abiotic damages. Our data present evidence that plants can respond to biotic and abiotic stresses soon after the damage is inflicted and when the damage is of short duration. The diverse consequences of these various local plant responses on M. euphorbiae behaviour are discussed in the context of plant defence strategies against aphid colonization.     

Relative suitability of crested wheatgrass and other perennial grass hosts for the Russian wheat aphid (Homoptera: Aphididae)

The Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae), reproduces parthenogenetically in North America and must survive year-round on host plants, including in late summer when small grains are not in cultivation. During this time, cool-season perennial wheatgrasses (Poaceae: Triticeae) contribute substantially to aphid survival, crested wheatgrass (Agropyron spp.) particularly. In greenhouse studies, the number of aphids per plant was measured after four infestation periods on unvernalized and vernalized wheatgrasses. Before placement on these test plant species, aphids were reared either on winter wheat or on the grass host species on which aphid progeny were counted. On vernalized plants, aphids reared on wheat resulted in more aphids per test plant than when the aphids were reared on wheatgrasses, but on unvernalized plants the number of aphids per test plant did not differ significantly regardless of rearing host. Aphids on crested wheatgrass were similar in number to the other grasses when plants were unvernalized. However, when plants were vernalized, crested wheatgrass supported significantly more aphids than some of the other hosts. Aphid numbers increased on all test species as infestation period lengthened, and plant growth was largely unaffected by aphid feeding. These results suggest if sufficient moisture is available during summer when small grains are not in cultivation, all host species observed are capable of sustaining aphids. Crested wheatgrass is an abundant and important host of the Russian wheat aphid in its northern range of the western United States, but other less prevalent wheatgrasses also may contribute to aphid survival during late summer when small grains are not in cultivation.     

The effect of host plants on genotype variability in fitness and honeydew composition of Aphis fabae

Aphid species can be polyphagous, feeding on multiple host plants across genera. As host plant species can have large variation in their phloem composition, this can affect aphid fitness and honeydew composition. Previous research showed significant intraspecific genotype variation in the composition of the honeydew carbohydrates of the black bean aphid Aphis fabae, with the ant attractant trisaccharide melezitose showing especially large variation across different genotypes. In this study, we test if variation in melezitose and carbohydrate composition of aphid honeydew could be linked to the adaptation of specific aphid genotypes to particular host plants. To this end, 4 high and 5 low melezitose secreting genotypes of the black bean aphid Aphis fabae were reared on 4 common host plants: broad bean, goosefoot, beet, and poppy. The carbohydrate composition, and in particular melezitose secretion, showed important aphid genotype and host plant interactions, with some genotypes being high melezitose secreting on 1 host plant but not on another. However, the interaction effects were not paralleled in the fitness measurements, even though there were significant differences in the average fitness across the different host plants. On the whole, this study demonstrates that aphid honeydew composition is influenced by complex herbivore–plant interactions. We discuss the relevance of these findings in the context of ant–aphid mutualisms and adaptive specialization in aphids.     

The effect of banker plant species on the fitness of Aphidius colemani Viereck and its aphid host (Rhopalosiphum padi L.)

Banker plants, a type of open-rearing unit, are increasingly used in greenhouse crops to sustain natural enemy populations at times of low pest abundance. The most common banker plant system is a non-crop, cereal plant which supports Rhopalosiphum padi L. as an alternative host for Aphidius colemani Viereck. Although bottom-up effects of plants are known to affect natural enemies, this aspect has generally been ignored in previous investigations of banker plant efficacy. Here, we tested four cereal plant species with three varieties each to investigate host plant effects on R. padi and A. colemani. Though limited differences were observed in laboratory experiments spanning one aphid or parasitoid generation, longer greenhouse experiments spanning several generations revealed significant plant effects on both insects. R. padi performed poorly on oats (Avena sativa L.), resulting in wasps with the longest female development time, lowest emergence rates, and the lowest number of wasps produced per unit. Rye (Secale cereal L.) – intermediate in terms of aphid performance – produced a significantly male-biased wasp population with the smallest males. Conversely, R. padi placed onto either wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) performed consistently well in terms of aphid and parasitoid fitness and abundance, though neither species was obviously superior over the other. Overall, cultivars within each plant species did not significantly affect outcomes. As each plant species tested had different positive effects on aphid and parasitoid phenotypes, the potential benefits of mixing of cereal species is an area for future investigation.     

Local and systemic responses induced by aphids in Solanum tuberosum plants

The aphids Macrosiphum euphorbiae (Thomas) and Myzus persicae (Sulzer) (Homoptera: Aphididae) are serious pests of potato (Solanum tuberosum L.) (Solanaceae), notably in transmitting several plant viruses. Heterospecific interactions may occur between these two species as they are often seen at the same time on the same potato plant in the field. As aphid infestation is known to induce both local and systemic changes, we conducted experiments to determine the effect of previous infestation on probing behaviour and feeding‐related parameters. We used the DC electrical penetration graph technique to characterize the influence of previous infestation by conspecific M. persicae or by heterospecific Ma. euphorbiae on M. persicae feeding behaviour at both local and systemic levels, i.e., on previously infested leaves and on non‐previously infested leaves of infested plants, respectively. Conspecific and heterospecific infestation led to similar modification of M. persicae feeding activities. However, the effects of previous infestation occurring at the local level were opposite to those observed at the systemic level. Myzus persicae food acceptance was slightly enhanced on previously infested leaves, whereas it was inhibited on non‐infested leaves of infested plants, which indicated an induced resistance mechanism. Our results advance the understanding of the mechanisms involved in aphid–host plant acceptance and colonization processes on potato plants in conspecific and heterospecific situations.     

Role of larval host plant experience and solanaceous plant volatile emissions in Tuta absoluta (Lepidoptera: Gelechiidae) host finding behavior

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), is considered to be a major pest that damages tomato (Solanum lycopersicum L; Solanaceae) crops in South American, European, and Mediterranean countries. This insect species is polyphagous (i.e., feeds on many types of food); hence, it could also develop on other cultivated host plants, principally solanaceous plants, such as potato (S. tuberosum L.; Solanaceae) and eggplant (S. melongena L.; Solanaceae). Therefore, we tested the hypothesis that host plant choice by adult T. absoluta is influenced by plant volatile organic compounds and larval host plant experience. One tomato cultivar (cv.) ‘Moneymaker’ and three potato cv. ‘Charlotte’ ‘Bintje,’ and ‘Nicola’ were tested. Using a flying tunnel, we observed that females reared on tomato preferred flying toward tomato and, to a lesser extent, potato cv. ‘Charlotte.’ These preferences might be explained by the high release of terpenes by these two plants. When conducting oviposition choice assays, we found no preference between tomato and potato in the number of eggs laid by females that had been previously reared on either host plant. This study indicates that the host finding behavior of T. absoluta is mediated by solanaceous volatiles, while oviposition behavior appears to depend on additional stimuli. These results provide baseline information for use in the development of new control strategies against T. absoluta using semiochemicals and plant breeding.     

我国新发现一种外来蚜虫——刺槐附毛斑蚜Appendiseta robiniae

记述了采自北京刺槐上的1种中国的记录外来蚜虫——刺槐附毛斑蚜,它原产于北美,寄主为刺槐,在当地一些地区较为常见,并已扩散到欧洲等地。描述了有翅孤雌蚜、无翅雌性蚜和有翅雄性蚜的鉴别特征,并提供了生态图片。最后讨论了它的潜在危害性及蚜虫寄主植物、蚜群生活状及生态照片在蚜虫识别上的重要性。     

Tomato-aphid-hoverfly: a tritrophic interaction incompatible for pest management

Trichome-based tomato resistance offers the potential to reduce pesticide use, but its compatibility with biological control remains poorly understood. We evaluated Episyrphus balteatus De Geer (Diptera, Syrphidae), an efficient aphidophagous predator, as a potential biological control agent of Myzus persicae Sulzer (Hemiptera, Aphididae) on trichome-bearing tomato cultivars. Episyrphus balteatus’ foraging and oviposition behavior, as well as larval mobility and aphid accessibility, were compared between two tomato cultivars (Lycopersicon esculentum Mill. ‘Moneymaker’ and ‘Roma’) and two other crop plants; broad bean (Vicia faba L.) and potato (Solanum tuberosum L.). Hoverfly adults landed and laid more eggs on broad beans than on three species of Solanaceae. Hoverfly larval movement was drastically reduced on tomato, and a high proportion of hoverfly larvae fell from the plant before reaching aphid prey. After quantifying trichome abundance on each of these four plants, we suggest that proprieties of the plant surface, specifically trichomes, are a key factor contributing to reduced efficacy of E. balteatus as a biological agent for aphid control on tomatoes. Handling editor: Stanislaw Gorb     

Host plant choice experiments of Colorado potato beetle (Coleoptera: Chrysomelidae) in Virginia

Field and laboratory-choice experiments were conducted to understand aspects of host plant orientation by the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in Virginia. In laboratory bioassays, L. decemlineata oriented to volatiles emitted by potato, Solanum tuberosum L., foliage over both tomato, Lycopersicon esculentum L., and eggplant, Solanum melongena L., foliage, and eggplant over tomato foliage, all of which had been mechanically damaged. Field choice tests revealed more L. decemlineata adults, larvae, and egg masses on eggplant than on tomato. In other experiments, counts of live L. decemlineata on untreated paired plants and counts of dead beetles on imidacloprid-treated plants did not differ between potato and eggplant. L. decemlineata was significantly attracted to eggplant over both tomato and pepper. To determine whether feeding adults affected orientation to host plants, an imidacloprid-treated eggplant or potato plant was paired with an untreated eggplant or potato plant covered in a mesh bag containing two adult male beetles. Significantly more adults were attracted to eggplant with feeding male beetles paired with another eggplant than any other treatment combination. These results indicate that the presence of male L. decemlineata on plants affects host plant orientation and suggests that the male-produced aggregation pheromone may be involved.     

Olfactory responses of Rhopalosiphum padi to three maize,potato, and wheat cultivars and the selection of prospective crop border plants

Understanding host plant volatile – aphid interactions can facilitate the selection of crop border plants as a strategy to reduce plant virus incidence in crops. Crop border plant species with attractive odours could be used to attract aphids into the border crop and away from the main crop. As different cultivars of the same crop can vary in their olfactory attractiveness to aphids, selecting an attractive cultivar as a border crop is important to increase aphid landing rates. This study evaluated olfactory responses of the bird cherry‐oat aphid, Rhopalosiphum padi (L.) (Hemiptera: Aphididae), to three cultivars each of maize [Zea mays L. (Poaceae)], potato [Solanum tuberosum L. (Solanaceae)], and wheat [Triticum aestivum L. (Poaceae)] with the aim of selecting an attractive crop border plant to reduce the incidence of the non‐persistent Potato virus Y [PVY (Potyviridae)] in seed potatoes. Volatiles emitted by the crop cultivars were collected and identified using coupled gas chromatography/mass spectrometry. Quantitative and qualitative differences were found among cultivars. Behavioural responses of alate R. padi to odours of the cultivars and synthetic compounds identified from the plants were determined with a four‐arm olfactometer. Rhopalosiphum padi was attracted to odours emitted from maize cultivar 6Q‐121, but did not respond to odours from the remaining eight crop cultivars. Volatile compounds from maize and wheat cultivars that elicited a behavioural response from R. padi and contributed to differences in plant volatile profiles included (Z)‐3‐hexenyl acetate (attractant) and α‐farnesene, (E)‐2‐hexenal, indole, and (3E,7E)‐4,8,12‐trimethyltrideca‐1,3,7,11‐tetraene (TMTT) (repellents). We conclude that maize cv. 6Q‐121 is potentially suitable as a crop border plant based on the behavioural response of R. padi to the olfactory cues emitted by this cultivar. The findings provide insight into selecting crop cultivars capable of attracting R. padi to crop border plants.     

Sources of variation in the interaction between three cereal aphids (Hemiptera: Aphididae) and wheat (Poaceae)

The relative contributions of host plant, herbivore species and clone to variation in the interaction between cereal aphids and wheat were investigated using five clones each of three species, Rhopalosiphum padi (Linnaeus), Sitobion avenae (Fabricius) and Schizaphis graminum (Rondani), on seedlings of two cultivars of Triticum aestivum L. and one cultivar of Triticum durum Desf. More individuals and biomass of R. padi than of the other two species were produced on seedlings. The three wheat cultivars lost similar amounts of biomass as a result of infestation by aphids, with the amount lost depending on aphid species: S. avenae caused the lowest loss in biomass. Variation in aphid biomass production was due mostly to differences among aphid species (70%), less to the interaction between wheat type and aphid species (7%), and least to aphid clone (1%). The specific impact of the aphids on the plants ranged from 1.7 to 3.7 mg of plant biomass lost per mg of aphid biomass gained, being lowest for R. padi and highest for S. graminum. Variation in plant biomass lost to herbivory was due mostly to unknown sources of error (95%), probably phenotypic differences among individual seedlings, with 3% due to aphid species and none attributable to aphid clone. For these aphid-plant interactions, differences among aphid clones within species contributed little to variation in aphid and plant productivity; therefore, a small sample of clones was adequate for quantifying the interactions. Furthermore, one clone of each species maintained in the laboratory for about 200 parthenogenetic generations was indistinguishable from clones collected recently from the field.     

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.     

Behavior of bird cherry-oat aphid and green peach aphid in relation to potato virus Y transmission

Potato virus Y is transmitted to potato in a nonpersistent manner by many aphid species, some of which do not colonize this crop. The behavior of bird cherry-oat aphid, Rhopalosiphum padi (L.) on potato, Solanum tuberosum L., a plant species that is not colonized by this aphid, was described and compared with that of the potato-colonizing green peach aphid, Myzuspersicae (Sulzer). A higher proportion of winged morph of R. padi than M. persicae left the plant, but aphids that stayed in contact with the plant took the same mean time to initiate the first probe and it lasted the same mean time compared with M. persicae. Electronic penetration graph technique was used to study the probing behavior of the aphids during Potato virus Y (family Potyviridae, genus Potyvirus, PVY) transmission tests. Transmission rate decreased from 29 to 8% when the acquisition time increased from 5 min of continuous probing to 1 h with M. persicae, but it remained low (2 and 1%) with R. padi. Most of the difference in transmission rate between acquisition time with M. persicae and between aphid species was related to the change in the time and behavior taking place between the last cell puncture of the acquisition phase to the first cell puncture of the inoculation phase. Results presented here clearly demonstrated the importance of host plant selection and probing behavior in the transmission of nonpersistent plant viruses. They also stress the need to consider the behavior of the aphid in the design of laboratory tests of virus vector efficacy.