Seasonal dispersal of pests: one surge or two?

Many agricultural pest species occur in seasonal metapopulations with a period of asexual reproduction. We use evolutionary theory to predict timing of dispersal for such species, and identify four sequential phases: no dispersal, dispersal from initially occupied patches, dispersal from later colonized patches, and no dispersal. The third type of phase occurs only when reproductive rates are relatively high; we speculate that this could explain why among aphids there can be either one or two waves of dispersal during a season, depending on the species. Our model also explains other features of aphid biology, including a summer crash in colony size, and a decline in the number of colonies towards the end of each reproductive season. The presence of an additional surge of dispersal becomes more likely as season length increases, and does not require further evolution. This could have profound implications for pest management during future climatic warming.     

Proteins Identified from Saliva and Salivary Glands of the Chinese Gall Aphid Schlechtendalia chinensis

Aphid saliva plays an essential role in the interaction between aphids and their host plants. Several aphid salivary proteins have been identified but none from galling aphids. Here the salivary proteins from the Chinese gall aphid are analyzed, Schlechtendalia chinensis, via an LC‐MS/MS analysis. A total of 31 proteins are identified directly from saliva collected via an artificial diet, and 141 proteins are identified from extracts derived from dissected salivary glands. Among these identified proteins, 17 are found in both collected saliva and dissected salivary glands. In comparison with salivary proteins from ten other free‐living Hemipterans, the most striking feature of the salivary protein from S. chinensis is the existence of high proportion of proteins with binding activity, including DNA‐, protein‐, ATP‐, and iron‐binding proteins. These proteins maybe involved in gall formation. These results provide a framework for future research to elucidate the molecular basis for gall induction by galling aphids.     

Wind‐modulated landscape effects on colonization of Brussels sprouts by insect pests and their syrphid antagonists

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Shifting daylength regimes associated with range shifts alter aphid‐parasitoid community dynamics

With climate change leading to poleward range expansion of species, populations are exposed to new daylength regimes along latitudinal gradients. Daylength is a major factor affecting insect life cycles and activity patterns, so a range shift leading to new daylength regimes is likely to affect population dynamics and species interactions; however, the impact of daylength in isolation on ecological communities has not been studied so far. Here, we tested for the direct and indirect effects of two different daylengths on the dynamics of experimental multitrophic insect communities. We compared the community dynamics under “southern” summer conditions of 14.5‐hr daylight to “northern” summer conditions of 22‐hr daylight. We show that food web dynamics indeed respond to daylength with one aphid species (Acyrthosiphon pisum) reaching much lower population sizes at the northern daylength regime compared to under southern conditions. In contrast, in the same communities, another aphid species (Megoura viciae) reached higher population densities under northern conditions. This effect at the aphid level was driven by an indirect effect of daylength causing a change in competitive interaction strengths, with the different aphid species being more competitive at different daylength regimes. Additionally, increasing daylength also increased growth rates in M. viciae making it more competitive under summer long days. As such, the shift in daylength affected aphid population sizes by both direct and indirect effects, propagating through species interactions. However, contrary to expectations, parasitoids were not affected by daylength. Our results demonstrate that range expansion of whole communities due to climate change can indeed change interaction strengths between species within ecological communities with consequences for community dynamics. This study provides the first evidence of daylength affecting community dynamics, which could not be predicted from studying single species separately.     

小麦禾谷缢管蚜峰期蚜量发生程度的影响因素分析

16年观测资料表明,影响禾谷缢管蚜峰期蚜量发生程度的因素有：冬前蚜量基数,年前11月份平均相对湿度,蚜峰期前一个月月平均温度、月总日照时数和月温湿系数。运用模糊综合评判法检验其发生程度,历史符合率达93.8％。1996年试报正确。     

Vectoring ability of aphid clones of Rhopalosiphum padi (L.) and Sitobion avenae (Fabr.) and their capacity to retain barley yellow dwarf virus

Vectoring ability of four aphid clones, Rp-M and Rp-R26 of Rhopalosiphum padi and Sa-R1 and Sa-V of Sitobion avenae, to transmit barley yellow dwarf (PAV, MAV and RPV) luteoviruses (BYDV) was compared in controlled conditions. Significant differences between highly efficient vectors (HEV), Rp-M and Sa-Rl, and poorly efficient vectors (PEV), Rp-R26 and Sa-V, were found in transmission of their specific viruses with acquisition and inoculation access periods (AAP, IAP) of 5 days. BYD-RPV was occasionally transmitted by both clones of S. avenae. None of 150 tested apterous adults of the Rp-R26 transmitted BYD-MAV, while 10% of transmission was observed from those of the Rp-M in a parallel test. An improved ELISA and immuno-PCR were adapted to test for viruses in aphids. The results obtained by the improved ELISA indicated there was a good correlation between virus detection in single aphids of HEV clones after a 5 day AAP and virus transmission by them. In contrast, the percentages of virus-carrying aphids of PEV clones were generally higher than those of their transmission rates. BYD-MAV and BYD-RPV were also detected by the improved ELISA in single aphids of their PEV clones, with the exception of BYD-RPV in those of Sa-V. However, after a 2-day IAP, the improved ELISA in most cases failed to detect these viruses in single aphids of PEV clones. Detection by immuno-PCR demonstrated that all three viruses could be acquired and retained by the aphids of both HEV and PEV clones. But, as visualised from electrophoretic bands, after the 2-day IAP the amplified products from aphid extracts of PEV clones were reduced. The detection in a batch of nine aphids by the improved ELISA revealed that virus content in PEV clones decreased more rapidly than that in HEV clones during transmission. Thus, the difference in transmission efficiency of the aphid clones within species was not caused by an inability to acquire virus, but was determined by variation in vectoring ability between them. This was due to differences in ability to prevent the passage of virions from haemocoel to salivary duct and/or different capacities for the retention of BYDV.     

Neem seed oil inhibits aphid transmission of potato virus Y to pepper*

Transmission of potato vims Y to sweet pepper by the green peach aphid, Myzus persicae (Sulzer), was inhibited by foliar applications of 1.0% or 2.0% neem seed oil to infected source plants or to uninfected recipient plants. Neem seed oil interfered with virus acquisition and inoculation in a manner comparable to that of a commercial horticultural oil, while an oil-free neem seed extract did not reduce rates of transmission compared with controls. The finding that neem seed oil inhibits virus transmission, while oil-free neem seed extract does not, suggests that the presence of the oil rather than biologically active limonoids such as azadirachtin interfere with virus transmission. None of the treatments affected rates of infection when potato virus Y was transmitted mechanically, or the resulting virus titre and symptom expression. In addition to direct control of insect pests, formulated neem oils may help reduce or delay the spread of non-persistent plant viruses.     

EVOLUTION OF AN APHID-PARASITOID INTERACTION: VARIATION IN RESISTANCE TO PARASITISM AMONG APHID POPULATIONS SPECIALIZED ON DIFFERENT PLANTS

The evolution of associations between herbivorous insects and their parasitoids is likely to be influenced by the relationship between the herbivore and its host plants. If populations of specialized herbivorous insects are structured by their host plants such that populations on different hosts are genetically differentiated, then the traits affecting insect-parasitoid interactions may exhibit an associated structure. The pea aphid (Acyrthosiphon pisum) is a herbivorous insect species comprised of genetically distinct groups that are specialized on different host plants (Via 1991a, 1994). Here, we examine how the genetic differentiation of pea aphid populations on different host plants affects their interaction with a parasitoid wasp, Aphidius ervi. We performed four experiments. (1) By exposing pea aphids from both alfalfa and clover to parasitoids from both crops, we demonstrate that pea aphid populations that are specialized on alfalfa are successfully parasitized less often than are populations specialized on clover. This difference in parasitism rate does not depend upon whether the wasps were collected from alfalfa or clover fields. (2) When we controlled for potential differences in aphid and parasitoid behavior between the two host plants and ensured that aphids were attacked, we found that pea aphids from alfalfa were still parasitized less often than pea aphids from clover. Thus, the difference in parasitism rates is not due to behavior of either aphids or wasps, but appears to be a physiologically based difference in resistance to parasitism. (3) Replicates of pea aphid clones reared on their own host plant and on a common host plant, fava bean, exhibited the same pattern of resistance as above. Thus, there do not appear to be nutritional or secondary chemical effects on the level of physiological resistance in the aphids due to feeding on clover or alfalfa, and therefore the difference in resistance on the two crops appears to be genetically based. (4) We assayed for genetic variation in resistance among individual pea aphid clones collected from clover fields and found no detectable genetic variation for resistance to parasitism within two populations sampled from clover. This is in contrast to Henter and Via's (1995) report of abundant genetic variation in resistance to this parasitoid within a pea aphid population on alfalfa. Low levels of genetic variation may be one factor that constrains the evolution of resistance to parasitism in the populations of pea aphids from clover, leading them to remain more susceptible than populations of the same species from alfalfa.     

DIFFERENCE IN PROBING BEHAVIOUR OF TEA APHID ON VEGETATIVE PARTS OF TEA PLANT AND NON‐HOST PLANTS*

Abstract Electrical penetration graph (EPG) investigation showed that the secreting (El) and sucking (E2) times of tea aphid stylet in tea phloem were much longer than that on non‐host plants such as soybean and wheat. However, non‐feeding wave (np) was shorter than that on soybean and wheat. Duration of both El and E2 of stylet in tea phloem of 1st leaf, bud, 4th leaf and tender stem occupied 30.2%, 22.3%, 9.2% and 8.2% of the total experimental time, respectively. E2 wave was accompanied by honeydew secretion, with a time lag. Tea aphid preferred the tender parts, in which amino acids and other nutritional components were very rich. While the stylet of hungry tea aphid was forced to pierce phlom of non‐host plant (soybean or wheat), El and E2 waves were also produced, but the action of stylet could be disrupted by tea shoot volatile (10–6 V/V linalool, etc.) emitted near to the antennae. It was considered that before and under probing tea aphid made use of olfactory clues.