Morphological and ecological traits promoting aphid colonization of the Hawaiian Islands

Species introductions into novel habitats, especially island ecosystems, can have devastating effects on ecosystem function and stability. Though none are native, at least 96 aphid species can now be found on one or more of the Hawaiian Islands. As aphids cause direct feeding damage and transmit plant viruses, it is important to identify the traits that have enabled these particular species to successfully colonize the archipelago. To address this question, nine morphological and ecological traits that may contribute to successful colonization were assessed for aphids present in Hawaii. As a comparative null model, we assessed the same traits for heterospecific congeners which are not present in the archipelago, but are present elsewhere in the world. Here we report that traits with higher frequencies among colonizing aphid species are: small apterae size, broad host range, anholocycly (i.e., permanent parthenogenesis), and presence in continental USA. Small aphids arriving from the mainland US and capable of feeding on numerous plant species may be intercepted less often by plant protection agents. It is also likely that asexually reproducing species are well suited to the Hawaiian subtropical climate, thereby eliminating the need for sexual phases and egg-laying for overwintering. By understanding the traits that enable aphids to successfully colonize remote islands, it is our hope that plant protection efforts may be enhanced, thereby reducing damage to native ecosystems.     

A negative effect of a pathogen on its vector? A plant pathogen increases the vulnerability of its vector to attack by natural enemies

Plant pathogens that are dependent on arthropod vectors for transmission from host to host may enhance their own success by promoting vector survival and/or performance. The effect of pathogens on vectors may be direct or indirect, with indirect effects mediated by increases in host quality or reductions in the vulnerability of vectors to natural enemies. We investigated whether the bird cherry-oat aphid Rhopalosiphum padi, a vector of cereal yellow dwarf virus (CYDV) in wheat, experiences a reduction in rates of attack by the parasitoid wasp Aphidius colemani when actively harboring the plant pathogen. We manipulated the vector status of aphids (virus carrying or virus free) and evaluated the impact on the rate of attack by wasps. We found that vector status did not influence the survival or fecundity of aphids in the absence of parasitoids. However, virus-carrying aphids experienced higher rates of parasitism and greater overall population suppression by parasitoid wasps than virus-free aphids. Moreover, virus-carrying aphids were accepted as hosts by wasps more often than virus-free aphids, with a greater number of wasps stinging virus-carrying aphids following assessment by antennal palpations than virus-free aphids. Therefore, counter to the prevailing idea that persistent vector-borne pathogens enhance the performance of their vectors, we found that infectious aphids actively carrying a plant pathogen experience greater vulnerability to natural enemies. Our results suggest that parasitoids may contribute to the successful biological control of CYDV by disproportionately impacting virus-carrying vectors, and thus reducing the proportion of vectors in the population that are infectious.     

Complex interactions between a plant pathogen and insect parasitoid via the shared vector-host: consequences for host plant infection

Plant viruses modify the development of their aphid vectors by inducing physiological changes in the shared host plant. The performance of hymenopterous parasitoids exploiting these aphids can also be modified by the presence of the plant pathogen. We used laboratory and glasshouse microcosms containing beans (Vicia faba) as the host plant to examine the interactions between a plant virus (pea enation mosaic virus; PEMV) and a hymenopterous parasitoid (Aphidius ervi) that share the aphid vector/host Acyrthosiphon pisum. Neither PEMV-infection of V. faba, nor the carriage of PEMV virions by A. pisum, affected the growth or morphology of the aphid, or the oviposition behaviour and development of A. ervi. The presence of developing Aphidius ervi larvae within Acyrthosiphon pisum did not affect the ability of the aphids to transmit PEMV. However, by reducing their longevity, parasitism ultimately decreased the time viruliferous aphids were able to inoculate plants. In terms of virus dispersal, parasitized aphids exhibited more movement around experimental arenas than unparasitized controls, causing a slight increase in the proportion of beans infected with PEMV. Exposure to adult Aphidius ervi caused Acyrthosiphon pisum to rapidly drop off bean plants and disperse to new hosts, resulting in considerably higher plant infection rates (70%) than that seen in control arenas (25%). The results of this investigation demonstrate that when parasitoids are added to a plant-pathogen-vector system, benefits to the host plant due to reduced herbivore infestation must be balanced against the consequences of parasitoid-induced aphid dispersal and a subsequent increase in the level of plant infection.     

The role of visual and olfactory plant cues in aphid behaviour and the development of non-persistent virus management strategies

Non-persistent viruses are transmitted by aphids in short feeding probes during the initial stages of aphid host plant selection behaviour. To control the transmission of these viruses, farmers rely on pesticides and cultural control practices, with varying success rates. As a result, there is a need for novel management practices that are more robust and specific to reducing aphid landing rates in crops. Aphid–plant–virus interactions involve a number of behaviours and processes to ensure survival of the insect vector and virus. So far, virus management tactics focused on reducing immigrating aphids in crops have emphasized the manipulation of visual rather than olfactory stimuli. An improved understanding of the synergistic or additive effects in which aphids use visual and olfactory stimuli to locate host plants could be used to improve on current non-persistent virus management tactics and develop novel strategies. The aim of this review is to evaluate current understanding of aphid vector behaviour and the ways that these behaviours have been exploited to develop management strategies, and to identify areas of research needed to further improve virus management.     

The influence of size and duration of aphid infestation on host plant quality, and its effect on sugar beet yellowing virus epidemiology

This paper studies the influence of previous infestation on the host quality of sugar beet (Beta vulgaris L.) for aphids and the influence of previous infestation on sugar beet yellowing virus epidemiology. Sugar beet previously infested with Myzus persicae (Sulzer) or Aphis fabae Scopoli (Homoptera: Aphididae) had an improved host quality for subsequently infesting aphids of the same species. There was a significant negative relationship between the number of M. persicae infesting a plant and the proportion of those that died with a dark deposit in their stomachs, and a significant positive relationship between the number that settled on a plant and the number that infested it previously. Nymphs feeding on previously infested plants grew more rapidly than those on control plants. The beneficial effect of previous infestation persisted for at least 2 weeks and prolongation of the infestation beyond 2 weeks was of no further benefit to the aphids. Field grown sugar beet, previously colonised by M. persicae, was more susceptible to natural infestation by M. persicae up to 5 days after exposure. Previously infested plants were also more susceptible to infection with beet mild yellowing virus (BMYV) but not beet yellows virus (BYV), suggesting that the aphids on the previously infested sugar beet settled more readily and were more inclined to feed (and thus transmit BMYV) than aphids on the previously uninfested plants. The consequences for the control of sugar beet yellowing virus vectors are discussed.     

Virus Resistance in Cereals: Sources of Resistance, Genetics and Breeding

In cereals, soil-borne viruses transmitted by the plasmodiophorid Polymyxa graminis (e.g., Barley mild mosaic virus , Barley yellow mosaic virus or Soil-borne cereal mosaic virus ), have increased in importance due to the increase of the acreage infested and because yield losses cannot be prevented by chemical measures. Due to global warming, it is also expected that insect transmitted viruses vectored by aphids (e.g., Barley yellow dwarf virus , Cereal yellow dwarf virus ), leafhoppers ( Wheat dwarf virus ) or mites (e.g., Wheat streak mosaic virus ), will become much more important even in cooler regions. The environmentally most sound and also most cost effective approach to prevent high yield losses caused by these viruses is breeding for resistance. Therefore, in contrast to other reviews on cereal viruses, this study briefly reviews present knowledge on cereal-infecting viruses and emphasizes especially the sources of resistance or tolerance to these viruses and their use in molecular breeding schemes.     

Cucurbit aphid‐borne yellows virus (CABYV) modifies the alighting,settling and probing behaviour of its vector Aphis gossypii favouring its own spread

Plant pathogens are able to influence the behaviour and fitness of their vectors in such a way that changes in plant–pathogen–vector interactions can affect their transmission. Such influence can be direct or indirect, depending on whether it is mediated by the presence of the pathogen in the vector's body or by host changes as a consequence of pathogen infection. We report the effect that the persistently aphid‐transmitted Cucurbit aphid‐borne yellows virus (CABYV, Polerovirus) can induce on the alighting, settling and probing behaviour activities of its vector, the cotton aphid Aphis gossypii. Only minor direct changes on aphid feeding behaviour were observed when viruliferous aphids fed on non‐infected plants. However, the feeding behaviour of non‐viruliferous aphids was very different on CABYV‐infected than on non‐infected plants. Non‐viruliferous aphids spent longer time feeding from the phloem in CABYV‐infected plants compared to non‐infected plants, suggesting that CABYV indirectly manipulates aphid feeding behaviour through its shared host plant in order to favour viral acquisition. Viruliferous aphids showed a clear preference for non‐infected over CABYV‐infected plants at short and long time, while such behaviour was not observed for non‐viruliferous aphids. Overall, our results indicate that CABYV induces changes in its host plant that modifies aphid feeding behaviour in a way that virus acquisition from infected plants is enhanced. Once the aphids become viruliferous they prefer to settle on healthy plants, leading to optimise the transmission and spread of this phloem‐limited virus.     

小麦蚜虫田间调查及监测技术

小麦蚜虫是世界范围内小麦生产中一类重要害虫。针对麦蚜世代历期短、繁殖力强,具有趋光、趋化及迁飞等生物学及行为习性;在田间多呈聚集分布,且麦蚜易受寄主植物抗性、天敌、气象因素及农田生态条件等生物与非生物因素影响等发生为害特点,本文阐述了我国小麦蚜虫田间调查、监测技术及防治策略,以期为我国小麦蚜虫综合防控提供基础科学支撑。     

STUDIES IN RUBUS VIRUS DISEASES

Raspberry leaf mottle virus is acquired by Amphorophora rubi in feeding periods of 1/2-2 hr. Longer feeding periods cause no significant fluctuations in infectivity. During continuous feeding on healthy plants, infectivity declines rapidly after 2 hr., but persists for at least 5 hr. if aphids are transferred frequently to fresh healthy plants. The estimated probability of infection by single aphids is 1 in 20. Rarely more than 50% of test plants, Rubus occidentalis , seedlings became infected, and this is thought to be due mainly to variation in plant susceptibility. Young leaves of infected Norfolk Giant are, however, better sources of virus than older leaves.     

Invasive aphids attack native Hawaiian plants

Invasive species have had devastating impacts on the fauna and flora of the Hawaiian Islands. While the negative effects of some invasive species are obvious, other species are less visible, though no less important. Aphids (Homoptera: Aphididae) are not native to Hawai’i but have thoroughly invaded the Island chain, largely as a result of anthropogenic influences. As aphids cause both direct plant feeding damage and transmit numerous pathogenic viruses, it is important to document aphid distributions and ranges throughout the archipelago. On the basis of an extensive survey of aphid diversity on the five largest Hawaiian Islands (Hawai’i, Kaua’i, O’ahu, Maui, and Moloka’i), we provide the first evidence that invasive aphids feed not just on agricultural crops, but also on native Hawaiian plants. To date, aphids have been observed feeding and reproducing on 64 native Hawaiian plants (16 indigenous species and 48 endemic species) in 32 families. As the majority of these plants are endangered, invasive aphids may have profound impacts on the island flora. To help protect unique island ecosystems, we propose that border vigilance be enhanced to prevent the incursion of new aphids, and that biological control efforts be renewed to mitigate the impact of existing species.     

Damage to sagebrush attracts predators but this does not reduce herbivory

Emissions of volatiles increase following herbivory from many plant species and volatiles may serve multiple functions. Herbivore‐induced volatiles attract predators and parasitoids of herbivores and are often assumed to benefit plants by facilitating top‐down control of herbivores; this benefit of induced emissions has been tested only a few times. Volatile compounds released by experimentally clipped sagebrush shoots have been shown to reduce levels of chewing damage experienced by other shoots on the same plant and on neighboring sagebrush plants. In this study, I asked whether experimental clipping attracted predators of herbivorous insects to sagebrush shoots. I also evaluated aphid populations and chewing damage on clipped and unclipped shoots and whether predators were likely to have caused differences in aphids and chewing damage. Shoots that had been clipped recruited more generalist predators, particularly coccinellids and Geocoris spp. in visual surveys conducted during two seasons. Clipping also caused increased numbers of parasitized aphids in one season. Ants were common tending aphids but were not significantly affected by clipping. Despite the increase in generalist predators, clipped plants were more likely to support populations of aphids that increased during both seasons compared to aphids on unclipped control plants. Clipped shoots suffered less damage by chewing herbivores in the 1‐year in which this was measured. Chewing damage was not correlated with numbers of predators. These results suggest that predators and parasitoids were attracted to experimentally clipped sagebrush plants but that these predators were not effective at reducing net damage to the plant. This conclusion is not surprising as much of the herbivory is inflicted by grasshoppers and deer, herbivores that are not vulnerable to the predators attracted to sagebrush volatiles. More generally, it should not be assumed that predators that are attracted by herbivore‐induced volatiles necessarily benefit the plant without testing this hypothesis under field conditions.     

Discovery and Targeted LC-MS/MS of Purified Polerovirus Reveals Differences in the Virus-Host Interactome Associated with Altered Aphid Transmission

Circulative transmission of viruses in the Luteoviridae, such as cereal yellow dwarf virus (CYDV), requires a series of precisely orchestrated interactions between virus, plant, and aphid proteins. Natural selection has favored these viruses to be retained in the phloem to facilitate acquisition and transmission by aphids. We show that treatment of infected oat tissue homogenate with sodium sulfite reduces transmission of the purified virus by aphids. Transmission electron microscopy data indicated no gross change in virion morphology due to treatments. However, treated virions were not acquired by aphids through the hindgut epithelial cells and were not transmitted when injected directly into the hemocoel. Analysis of virus preparations using nanoflow liquid chromatography coupled to tandem mass spectrometry revealed a number of host plant proteins co-purifying with viruses, some of which were lost following sodium sulfite treatment. Using targeted mass spectrometry, we show data suggesting that several of the virus-associated host plant proteins accumulated to higher levels in aphids that were fed on CYDV-infected plants compared to healthy plants. We propose two hypotheses to explain these observations, and these are not mutually exclusive: (a) that sodium sulfite treatment disrupts critical virion-host protein interactions required for aphid transmission, or (b) that host infection with CYDV modulates phloem protein expression in a way that is favorable for virus uptake by aphids. Importantly, the genes coding for the plant proteins associated with virus may be examined as targets in breeding cereal crops for new modes of virus resistance that disrupt phloem-virus or aphid-virus interactions.     

种植茼蒿对蚕豆苜蓿蚜的田间控制作用

[目的] 探讨不同生育期和不同种植方式的茼蒿对蚕豆蚜虫的诱集作用,为利用茼蒿控制蚕豆蚜虫提供理论依据。[方法] 在蚕豆田四周种植不同生育期（幼苗期、现蕾期、开花期）和不同行数（1行、2行）的茼蒿,观察不同处理的蚕豆田有蚜株率和蚜害等级,各处理设在互不干扰的小区内进行。[结果] 蚕豆四周种植不同生育期茼蒿后,蚕豆上有蚜株率和蚜害等级比例存在显著差异,且与茼蒿的生育期有明显的相关性,各处理有蚜株率从低到高分别为茼蒿开花期（28.33%） < 现蕾期（41.67%） < 幼苗期（55.00%）,并均显著低于对照（63.33%）;种植不同生育期茼蒿后,各处理蚕豆蚜害等级也不同,5级蚜害在种植开花期茼蒿处理后仅为5.00%,现蕾期为23.33%,幼苗期为33.33%,对照蚕豆上蚜害最高,达40.00%。分别种植1行（33.33%）和2行（23.33%）茼蒿后,最高有蚜株率均显著低于对照（66.67%）,低蚜害等级比例明显增高,高蚜害比例明显下降,且种植2行的效果更佳。[结论] 开花期的茼蒿对蚕豆蚜虫诱集作用最强,种植2行开花期茼蒿可以有效降低蚕豆蚜虫为害。在蚕豆生产上,种植茼蒿可以作为蚕豆蚜虫生态防控的重要手段之一。     

Insect infestations, incidence of viral plant diseases, and yield of winter wheat in relation to planting date in the northern Great Plains

Planting date effects on arthropod infestation and viral plant disease are undocumented for winter wheat, Triticum aestivum L., in South Dakota and the northern Great Plains. Winter wheat was planted over three dates (early, middle, and late; generally from late August to late September) to determine the effect on abundance of insect pests, incidence of plant damage, incidence of viral plant disease, and grain yield. The study was conducted simultaneously at two sites in South Dakota over three consecutive cropping seasons for a total of six site yr. Cereal aphids (Homoptera: Aphididae) were abundant in three site yr. Rhopalosiphum padi (L.), bird cherry-oat aphid, was the most abundant cereal aphid at the Brookings site, whereas Schizaphis graminum (Rondani), greenbug, predominated at Highmore. Aphid-days were greater in early versus late plantings. Aphid abundance in middle plantings depended on aphid species and site, but it usually did not differ from that in early plantings. Incidence of Barley yellow dwarf virus (family Luteoviridae, genus Luteovirus, BYDV) declined with later planting and was correlated with autumnal abundance of cereal aphids. Incidence of BYDV ranged from 24 to 81% among 1999 plantings and was < 8% in other years. Damage to seedling wheat by chewing insects varied for two site-years, with greater incidence in early and middle plantings. Wheat streak mosaic virus, spring infestations of cereal aphids, wheat stem maggot, and grasshoppers were insignificant. Yield at Brookings was negatively correlated with BYDV incidence but not cereal aphid abundance, whereas yield at Highmore was negatively correlated with aphid abundance but not BYDV incidence. Planting on 20 September or later reduced damage from chewing insects and reduced cereal aphid infestations and resulting BYDV incidence.     

Can plants use an entomopathogenic virus as a defense against herbivores?

It is by now well established that plants use various strategies to defend themselves against herbivores. Besides conventional weapons such as spines and stinging hairs and sophisticated chemical defenses, plants can also involve the enemies of the herbivores in their defense. It has been suggested that plants could even use entomopathogens as part of their defense strategies. In this paper, we show that Brassica oleraceae plants that are attacked by Myzus persicae aphids infected with an entomopathogenic parvovirus (M. persicae densovirus) transport the virus through the phloem locally and systematically. Moreover, healthy aphids that fed on the same leaf, but separated from infected aphids were infected via the plant. Hence, this is proof of the principle that plants can be vectors of an insect virus and can possibly use this virus as a defense against herbivores.     

Infection with an insect virus affects olfactory behaviour and interactions with host plant and natural enemies in an aphid

Aphid ecology and population dynamics are affected by a series of factors including behavioural responses to ecologically relevant chemical cues, capacity for population growth, and interactions with host plants and natural enemies. Using the aphid Rhopalosiphum padi (L.) (Homoptera: Aphididae), we showed that these factors were affected by infection with Rhopalosiphum padi virus (RhPV). Uninfected aphids were attracted to odour of uninfected aphids on the host plant, an aggregation mechanism. However, infected aphids were not attracted, and neither infected nor uninfected aphids were attracted to infected aphids on the plant. Infected aphids did not respond to methyl salicylate, a cue denoting host suitability. Infected aphids were more behaviourally sensitive to aphid alarm pheromone, and left the host plant more readily in response to it. RhPV reduced the lifespan and population growth rate of the aphid. The predacious ladybird, Coccinella septempunctata (L.) (Coleoptera: Coccinellidae), consumed more infected aphids than uninfected aphids in a 24‐h period, and the aphid parasitoid Aphidius ervi Haliday (Hymenoptera: Aphidiidae) attacked more infected than uninfected aphids. However, the proportion of mummies formed was lower with infected aphids. The results represent further evidence that associated organisms can affect the behaviour and ecology of their aphid hosts.     

Plant-aphid interactions: molecular and ecological perspectives

Many aphids are major agricultural pests because of their unparalleled reproductive capacity and their ability to manipulate host plant physiology. Aphid population growth and its impact on plant fitness are strongly influenced by interactions with other organisms, including plant pathogens, endophytes, aphid endosymbionts, predators, parasitoids, ants, and other herbivores. Numerous molecular and genomic resources have recently been developed to identify sources of aphid resistance in plants, as well as potentially novel targets for control in aphids. Moreover, the same model systems that are used to explore direct molecular interactions between plants and aphids can be utilized to study the ecological context in which they occur.     

寄主植物-蚜虫-天敌三重营养关系的化学生态学研究进展

综述了寄主植物－蚜虫－天敌三重营养关系的化学生态学研究,重点阐述了3个研究热点：①植物挥发性物质在蚜虫及其天敌选择寄主行为过程中的作用;②蚜虫信息素和蜜露对蚜虫天敌寄主选择行为的影响;③植物挥发性物质对蚜虫信息系作用的影响。对寄主植物－蚜虫－天敌三重营养关系的全面了解,将为蚜虫的综合治疗提供新思维。     

植物挥发性物质在蚜虫寄主定位中的作用

本文综述了植物挥发性物质的化学性质、研究方法及其在蚜虫寄主定位中的作用