Aphid Host Plant Research Articles

Changes in Aphid Host Plant Diet Influence the Small-RNA Expression Profiles of Its Obligate Nutritional Symbiont, Buchnera.

Plants are a difficult food resource to use, and herbivorous insects have evolved a variety of mechanisms that allow them to fully exploit this poor nutritional resource. One such mechanism is the maintenance of bacterial symbionts that aid in host plant feeding and development. The majority of these intracellular symbionts have highly eroded genomes that lack many key regulatory genes; consequently, it is unclear if these symbionts can respond to changes in the insect's diet to facilitate host plant use. There is emerging evidence that symbionts with highly eroded genomes express small RNAs (sRNAs), some of which potentially regulate gene expression. In this study, we sought to determine if the reduced genome of the nutritional symbiont (Buchnera) in the pea aphid responds to changes in the aphid's host plant diet. Using transcriptome sequencing (RNA-seq), Buchnera sRNA expression profiles were characterized within two Buchnera life stages when pea aphids fed on either alfalfa or fava bean. Overall, this study demonstrates that Buchnera sRNA expression changes not only with life stage but also with changes in aphid host plant diet. Of the 321 sRNAs characterized in this study, 47% were previously identified and 22% showed evidence of conservation in two or more Buchnera taxa. Functionally, 13 differentially expressed sRNAs were predicted to target genes related to pathways involved in essential amino acid biosynthesis. Overall, results from this study reveal that host plant diet influences the expression of conserved and lineage-specific sRNAs in Buchnera and that these sRNAs display distinct host plant-specific expression profiles among biological replicates.IMPORTANCE In general, the genomes of intracellular bacterial symbionts are reduced compared to those of free-living relatives and lack many key regulatory genes. Many of these reduced genomes belong to obligate mutualists of insects that feed on a diet that is deficient in essential nutrients, such as essential amino acids. It is unclear if these symbionts respond with their host to changes in insect diet, because of their reduced regulatory capacity. Emerging evidence suggests that these symbionts express small RNAs (sRNAs) that regulate gene expression at the posttranscriptional level. Therefore, in this study, we sought to determine if the reduced genome of the nutritional symbiont Buchnera in the pea aphid responds to changes in the aphid's host plant diet. This study demonstrates for the first time that Buchnera sRNAs, some conserved in two or more Buchnera lineages, are differentially expressed when aphids feed on different plant species and potentially target genes within essential amino acid biosynthesis pathways.

Türkiye'nin Doğu Karadeniz Bölgelesi'nden tespit edilen afit-konak bitki ilişkileri

Aphid-host plant relationship has fascinated scientist for a long time as they had some tight interactions. There is considerable amount of mountainous land area in Far Eastern Black Sea Region of Turkey which is almost 27% and about 165 aphid species have been determined. There has been no study conducted either to detect aphid fauna of region or aphid-host plant interaction up to last decades. Compared with determined aphid species diversity with floristic richness of region and each province, number of the aphid species recorded does not reflect real aphid composition of study area. According to proposed model related with aphid-host plant diversity around the world, both heavy rainfall and mix of higher vegetation biodiversity especially underbrush plant richness might explain unexpected lower aphid species diversity compared with higher plant diversity. Recent studies carried out clearly indicated that aphid-host plant relations should be studied in detail as these relations are become much more dynamic as a result of recent climatic changes.

Quality of aphid honeydew for a parasitoid varies as a function of both aphid species and host plant

Honeydew i.e., the sugar-rich excretion of phloem-sap feeders, is the most available sugar source in agroecosystems which enables parasitoids to increase their fitness. For the parasitoids of honeydew-producing insects, honeydew is associated with host presence, suggesting that parasitoids can find carbohydrate sources and hosts at the same place. Hence, these parasitoids may have evolved to efficiently use the honeydew produced by their main hosts as a carbohydrate source. In this context, we assessed the relationship between the adult fitness (in terms of longevity and fecundity) of the aphid parasitoid Aphelinus abdominalis (which prefer attack aphid species belonging to the Macrosiphini tribe), fed on honeydew produced by 19 different plant-aphid combinations, and parasitoid preference (i.e., the choice of female to oviposit) and ability to produce offspring in these combinations. Honeydew quality was modulated by both the plant and aphid host species. The honeydew produced by eight aphid species (e.g., Macrosiphum euphorbiae and Aphis craccivora) resulted in high parasitoid longevity (same longevity as the honey-fed positive control) and an increase in egg load between 24 and 48 h, compared to the negative control (fed only water). In contrast, nine aphid species (e.g., Brevicoryne brassicae and Aphis nerii) excreted low-quality honeydew that did not increase parasitoid longevity or egg load (similar to the negative control water-fed parasitoids). There was no relationship between A. abdominalis adult fitness when fed various honeydews and its preference as well as its ability to produce offspring in the hosts producing these honeydews. Several hypotheses that may explain this lack of relationship are discussed.

Untargeted Metabolomics Approach Reveals Differences in Host Plant Chemistry Before and After Infestation With Different Pea Aphid Host Races.

The pea aphid (Acyrthosiphon pisum), a phloem-sucking insect, has undergone a rapid radiation together with the domestication and anthropogenic range expansion of several of its legume host plants. This insect species is a complex of at least 15 genetically different host races that can all develop on the universal host plant Vicia faba. However, each host race is specialized on a particular plant species, such as Medicago sativa, Trifolium pratense, or Pisum sativum, which makes it an attractive model insect to study ecological speciation. Previous work revealed that pea aphid host plants produce a specific phytohormone profile depending on the host plant – host race combination. Native aphid races induce lower defense hormone levels in their host plant than non-native pea aphid races. Whether these changes in hormone levels also lead to changes in other metabolites is still unknown. We used a mass spectrometry-based untargeted metabolomic approach to identify plant chemical compounds that vary among different host plant-host race combinations and might therefore, be involved in pea aphid host race specialization. We found significant differences among the metabolic fingerprints of the four legume species studied prior to aphid infestation, which correlated with aphid performance. After infestation, the metabolic profiles of M. sativa and T. pratense plants infested with their respective native aphid host race were consistently different from profiles after infestation with non-native host races and from uninfested control plants. The metabolic profiles of P. sativum plants infested with their native aphid host race were also different from plants infested with non-native host races, but not different from uninfested control plants. The compounds responsible for these differences were putatively identified as flavonoids, saponins, non-proteinogenic amino acids and peptides among others. As members of these compound classes are known for their activity against insects and aphids in particular, they may be responsible for the differential performance of host races on native vs. non-native host plants. We conclude that the untargeted metabolomic approach is suitable to identify candidate compounds involved in the specificity of pea aphid – host plant interactions.

Behavioral and Ovipositional Response of Diaeretiella rapae (Hymenoptera: Braconidae) to Rhopalosiphum padi and Brevicoryne brassicae in Winter Wheat and Winter Canola.

Winter canola Brassica napus L. (Brassicales: Brassicaceae) was introduced to U.S. Southern Great Plains (Kansas, Oklahoma, Texas) growers to manage some difficult-to-control grassy weeds in winter wheat Triticum aestivum L. (Poales: Poaceae). Two braconid parasitoids, Diaeretiella rapae (M'Intosh) and Lysiphlebus testaceipes (Cresson) (Hymenoptera: Braconidae) are active in this cropping landscape. Both wasps move between crops but D. rapae has a limited ability to develop in the main wheat aphid hosts, so L. testaceipes could influence D. rapae's ability to maintain itself when canola is absent in the landscape. We compared behavioral responses of naturally emerged D. rapae and wasps that were excised before emergence to odor volatiles of host plant, aphid host and aphid-infested plants using two plant/aphid combinations (wheat/Rhopalosiphum padi (L.) and canola/Brevocoryne brassicae L. (Hemiptera: Aphididae). We also compared parasitism rates of D. rapae that were naturally emerged and excised from R. padi or B. brassicae on subsequent parasitism rates of R. padi or B. brassicae hosts. Naturally emerged wasps responded more strongly to host plant and host plant + aphid odors compared to excised wasps regardless of the host origin. Neither wasp group responded to odors from aphids alone. Both wasp groups were most attracted to odors from aphid-infested host plants, regardless of the combination. D. rapae parasitism rates on canola-reared aphids were higher than on wheat-reared aphids. D. rapae parasitism rates were lower when switched from its original host to the alternate host. Results suggest that D. rapae faces challenges to maintain significant populations in the wheat/canola landscape of the Southern Great Plains, especially in years when canola is not locally present.

Report on winter crop plant-aphid- aphidophagous Chrysopidae (Neuroptera: Insecta) association from Murshidabad district, West Bengal, India

The enhancement of natural predators through habitat manipulation and increasing vegetational diversity can improve herbivore control. Aphids drew attention as they are serious phytosaccivorous pests and a threat against crop plants. Members of Family Chrysopidae (Neuroptera: Insecta) are proven biological control agents against aphids. Natural predators can bring down pesticide use against pest in a proper IPM (Integrated Pest Management) strategy. For this, identification of the existing pest, their natural predators and the pest host plant are necessary. This study deals with the field survey for aphids, aphid host plant and Chrysopidae species associated with aphids. This investigation may provide some essential basic information of occurrence aphids, their crop plant association and aphidophagous Chrysopidae. This may help to formulate an integrated pest management (IPM) strategy against aphid pest of crop plants in near future.

Low Levels of Artificial Light at Night Strengthen Top-Down Control in Insect Food Web

Artificial light has transformed the nighttime environment of large areas of the earth, with 88% of Europe and almost 50% of the United States experiencing light-polluted night skies [1]. The consequences for ecosystems range from exposure to high light intensities in the vicinity of direct light sources to the very widespread but lower lighting levels further away [2]. While it is known that species exhibit a range of physiological and behavioral responses to artificial nighttime lighting [e.g., 3-5], there is a need to gain a mechanistic understanding of whole ecological community impacts [6, 7], especially to different light intensities. Using a mesocosm field experiment with insect communities, we determined the impact of intensities of artificial light ranging from 0.1 to 100 lux on different trophic levels and interactions between species. Strikingly, we found the strongest impact at low levels of artificial lighting (0.1 to 5 lux), which led to a 1.8 times overall reduction in aphid densities. Mechanistically, artificial light at night increased the efficiency of parasitoid wasps in attacking aphids, with twice the parasitism rate under low light levels compared to unlit controls. However, at higher light levels, parasitoid wasps spent longer away from the aphid host plants, diminishing this increased efficiency. Therefore, aphids reached higher densities under increased light intensity as compared to low levels of lighting, where they were limited by higher parasitoid efficiency. Our study highlights the importance of different intensities of artificial light in driving the strength of species interactions and ecosystem functions.

Effect of Temperature and Aphid-Host Plant Variety on Performance and Thermal Requirments of Coccinella undecimpunctata L. and Cheilomenes propinqua isis (mulsant)

In this study, the single and common effects of temperature (20, 25 and 30 ± 1˚C) and eggplant varieties (Classic, 0111, and Anan) on the developmental performance and heat requirements of Coccinella undecimpunctata L. and Cheilomenes propinqua isis (Mulsant) were examined. The predators were fed upon Aphis gossypii Glover that reared on the three eggplant Solanum melongena (L.) varieties. The two-way ANOVA showed that there was significant effects of temperature and host plant varieties on the total developmental times of both predators. However, the interaction between temperature and host plant variety interaction had only significant effect on the total developmental times of C. undecimpunctata. The results also revealed that the developmental times (DT) of both predators were decreased with increasing the temperature, whereas the developmental rates increased. Based on lower developmental threshold (T0) values, the more tolerant stage for coldness was the pupal stage of both C. undecimpunctata and C. propinqua isis on the three eggplant varieties. On the contrary, the more sensitive stage for low temperature degrees differed for both species: the eggs stage for C. undecimpunctata and the larval stage for C. propinqua isis. The minimum (T0) values for the entire development of both predators were recorded on Classic variety. The heat units (degree-days, DD’s) estimated for each stage showed that aphids produced on Classic variety lowered the amount of heat required by both predator species to complete their development. Further, the larval stage of both predatory species required more heat units to develop at each aphid-host plant variety combination than other stages. These results suggest that eggplant var. Classic has to be considered, in mass rearing programs, to produce a high nutritional prey for both predator species. This might maximize the population of these predators. As well, 30 °C would multiply the population of both predators under the same rearing conditions, and thus has to be generalized.

Companion Plants for Aphid Pest Management.

A potential strategy for controlling pests is through the use of “companion plants” within a crop system. This strategy has been used in several trials to fight against a major crop insect pest: the aphid. We reviewed the literature to highlight the major mechanisms by which a companion plant may act. Trials carried out under laboratory or field conditions revealed that companion plants operate through several mechanisms. A companion plant may be associated with a target crop for various reasons. Firstly, it can attract aphids and draw them away from their host plants. Secondly, it can alter the recognition of the host plant. This effect is mostly attributed to companion plant volatiles since they disturb the aphid host plant location, and additionally they may react chemically and physiologically with the host plant, making it an unsuitable host for aphids. Thirdly, it can attract natural enemies by providing shelter and food resources. In this review, the feasibility of using companion plants is discussed. We conclude that many factors need to be taken into account for a successful companion plant strategy. For the best long-term results, companion plant strategies have to be combined with other alternative approaches against aphids.

Harnessing the aphid life cycle to reduce insecticide reliance in apple and peach orchards. A review

Apple and peach orchards are chemical-intensive systems, and aphids are one of their major pests. Aphids alter fruiting and shoot development, and they can spread viruses. Decades of insecticide use have developed aphid resistance, which calls on research to provide alternatives to chemicals for pest management. Here, we review the literature to identify, for each stage of the aphid life cycle, existing alternatives based on either top-down (i.e. aphid predation or parasitism) or bottom up (i.e. increase of host plant resistance) processes. Firstly, it was found that most studies focus on top-down processes, namely on conservation biological control aiming to preserve existing populations of natural enemies: predators, parasitoids and nematodes. This is achieved by (i) providing shelters (i.e. planting hedges, weed or flower strips) or alternative preys in periods of aphid scarcity or (ii) choosing chemicals with the lowest disruptive effects. Those methods prove more efficient when used early in the season, i.e. before the exponential increase of aphid populations. Fostering the complex of natural enemies is also preferable than just supporting one single enemy. Secondly, other techniques, like (i) releasing biological control agents (entomopathogenic fungi, nematodes) or (ii) using pheromone lures to prevent autumnal sexual reproduction, are currently adapted for their use in orchard conditions. Thirdly, bottom-up regulation has to be devised as a long-term strategy, which could start by choosing a cultivar enabling genetic avoidance or developing genetic resistance. Then, aphid development can be reduced by the control of shoot growth or nitrogen accumulation in response to pruning or moderate water and nutrient inputs. At last, autumnal return of aphids could be disrupted by techniques such as kaolin applications that impair aphid host plant location. It is concluded that these alternative methods have to be adapted to local conditions and combined in long-term strategies in order to decrease the infestation risks throughout the orchard lifespan.

Expression differences in Aphidius ervi (Hymenoptera: Braconidae) females reared on different aphid host species.

The molecular mechanisms that allow generalist parasitoids to exploit many, often very distinct hosts are practically unknown. The wasp Aphidius ervi, a generalist koinobiont parasitoid of aphids, was introduced from Europe into Chile in the late 1970s to control agriculturally important aphid species. A recent study showed significant differences in host preference and host acceptance (infectivity) depending on the host A. ervi were reared on. In contrast, no genetic differentiation between A. ervi populations parasitizing different aphid species and aphids of the same species reared on different host plants was found in Chile. Additionally, the same study did not find any fitness effects in A. ervi if offspring were reared on a different host as their mothers. Here, we determined the effect of aphid host species (Sitobion avenae versus Acyrthosiphon pisum reared on two different host plants alfalfa and pea) on the transcriptome of adult A. ervi females. We found a large number of differentially expressed genes (between host species: head: 2,765; body: 1,216; within the same aphid host species reared on different host plants: alfalfa versus pea: head 593; body 222). As expected, the transcriptomes from parasitoids reared on the same host species (pea aphid) but originating from different host plants (pea versus alfalfa) were more similar to each other than the transcriptomes of parasitoids reared on a different aphid host and host plant (head: 648 and 1,524 transcripts; body: 566 and 428 transcripts). We found several differentially expressed odorant binding proteins and olfactory receptor proteins in particular, when we compared parasitoids from different host species. Additionally, we found differentially expressed genes involved in neuronal growth and development as well as signaling pathways. These results point towards a significant rewiring of the transcriptome of A. ervi depending on aphid-plant complex where parasitoids develop, even if different biotypes of a certain aphid host species (A. pisum) are reared on the same host plant. This difference seems to persist even after the different wasp populations were reared on the same aphid host in the laboratory for more than 50 generations. This indicates that either the imprinting process is very persistent or there is enough genetic/allelic variation between A. ervi populations. The role of distinct molecular mechanisms is discussed in terms of the formation of host fidelity.

Host plant and competitor identity matter in genotype × genotype × environment interactions between vetch and pea aphids

1. Selection does not only operate in a genotype (G) × environment (E) context, but can also be modulated by the activities of organisms interacting with their environment (G × G × E). 2. The influences of aphid clonal identity and host plant (Vicia faba) intraspecific genetic variation on the performance of five genotypes of pea aphid (Acyrthosiphon pisum) were investigated – with and without interaction with a competing heterospecific clone of vetch aphid (Megoura viciae) – across three cultivars of V. faba. 3. Pea aphid performance in the presence of a competing vetch aphid clone (G × G × E) compared with the absence of competition (G × E) revealed strong context-dependent, genotype-specific shifts in performance, influenced by plant cultivar, competitor presence and their interaction. 4. The performance of vetch aphid in competition with each pea aphid clone was also compared. Here, competitor's genotype and abundance underlay a remarkably varied response by vetch aphid across interactions. 5. The study shows that aphid genotypes exhibit a varying degree of risk spreading, contingent on competitor identity and the patterns of aggregation across three plant cultivars. Owing to feedback loops between species activities and selective forces acting on them, our findings suggest that there are context-dependent responses by competitors that are shaped via the interplay of the co-occurring species and their biotic environment. 6. This work highlights the complexity of species interactions and the importance of investigating reciprocity between competition and intraspecific genetic variation. A better understanding of the eco-evolutionary interactions between phloem-feeding insects and their host plants can potentially be used to enhance crop protection and pest control.

Innovative Approach for the Use of Huwa-San TR50 in Controlling Cotton Aphids (Aphis gossypii Glover)

Chemical control remains the main method of controlling the cotton aphid (Aphis gossypii Glover). Millions of dollars have been lost due to plant damage which resulted in reduced quality and yield of cotton. Nevertheless, A. gossypii can rapidly develop resistance to different groups of insecticides such as organophosphates, carbamates and pyrethroids. The potential of Huwa-San TR50 in controlling A. gossypii is yet to be tested. Huwa-San TR50 is a formula of hydrogen peroxide which has been stabilized by the addition of a small quantity of silver and has extensively used as a disinfectant. In this study, it was found to be very potent in killing A. gossypii and produced 93.5, 96.5, 97 and 95.5% mortality at 1000, 2000, 3000 and 4000 ppm, respectively, after 48 h of exposure. Furthermore, there was no significant difference between four Huwa-San TR50 concentrations after 48 h of exposure, on the mortality of A. gossypii. Huwa-San TR50 of up to 4000 ppm had no observable effects on the mortality and behavior of adult honeybee workers (Apis mellifera lamarckii) as compared with the control. Also, Huwa-San TR50 concentration of up to 3000 ppm had no observable effect on seven-spot ladybird beetles (Coccinella septempunctata) whereas a concentration of 4000 ppm produced 100% mortality after 24 h of exposure. Huwa-San TR50 concentrations of up to 2000 ppm failed to produce any symptoms on cucumber leaves. The differential effects of Huwa-San TR50 on aphids and beneficial insects, suggest the need for further investigation to understand the effects of Huwa-San TR50 on other host plants of aphids and aphid species.

Effect of ant attendance on aphid population growth and above ground biomass of the aphid's host plant

Ant-aphid mutualism is considered to be a beneficial association for the individuals concerned. The population and fitness of aphids affected by ant attendance and the outcome of this relationship affects the host plant of the aphid. The main hypothesis of the current study is that ant tending decreases aphid developmental time and/or increases reproduction per capita, which seriously reduces host plant fitness. The effect of attendance by the ant Tapinoma erraticum (Latreille, 1798) (Hymenoptera: Formicidae) on population growth and duration of different developmental stages of Aphis gossypii Glover (Hemiptera: Aphididae) were determined along with the consequences for the fitness of the host plant of the aphid, Vicia faba L., in greenhouse conditions. The initial aphid density was manipulated in order to study aphid performance due to density-dependent changes in ant attendance. The population growth rate of ant attended aphids was more than that of unattended aphids. However, the ratio of 1st-2nd nymphs to adults in aphid populations attended by ants was lower. The yields of bean plants on which the aphids were attended by ants were significantly greater than those of unattended plants. This study indicates that ants not only increase aphid fitness in terms of their population growth rate, but also benefit the host plant.

Symbiont Diversity of Aphis (Toxoptera) citricidus (Hemiptera: Aphididae) as Influenced by Host Plants.

Aphids are well known for their association with endosymbiont bacteria. Almost all aphids harbor Buchnera aphidicola as an obligate symbiont and several other bacteria as facultative symbionts. Associations of facultative symbionts and aphids are quite variable in terms of diversity and prevalence across aphid species. Facultative symbionts can have a major impact on aphid bioecological traits. A number of factors shape the outcome of the facultative symbiont-aphid association, including aphid clone, bacterial genotype, geography, and host plant association. The effects of host plant on aphid-facultative symbiont associations are the least understood. We performed deep sequencing of the bacterial community associated with field populations of the oligophagous aphid Aphis (Toxoptera) citricidus collected from different host plants. We demonstrate that (i) A. citricidus has low symbiont diversity, (ii) symbiont diversity is affected by host plant, and (iii) host plants affect the relative abundance of the obligate symbiont Buchnera and an unknown genus of Enterobacteriaceae.

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.

Herbivore Diet Breadth and Host Plant Defense Mediate the Tri-Trophic Effects of Plant Toxins on Multiple Coccinellid Predators.

Host plant defenses are known to cascade up food chains to influence herbivores and their natural enemies, but how herbivore and predator traits and identity mediate such tri-trophic dynamics is largely unknown. We assessed the influence of plant defense on aphid and coccinellid performance in laboratory trials with low- vs. high-glucosinolate varieties of Brassica napus, a dietary specialist (Brevicoryne brassicae) and generalist (Myzus persicae) aphid, and five species of aphidophagous coccinellids. The performance of the specialist and generalist aphids was similar and unaffected by variation in plant defense. Aphid glucosinolate concentration and resistance to predators differed by aphid species and host plant defense, and these effects acted independently. With respect to aphid species, the dietary generalist aphid (vs. specialist) had 14% lower glucosinolate concentration and coccinellid predators ate three-fold more aphids. With respect to host plant variety, the high-glucosinolate plants (vs. low) increased aphid glucosinolate concentration by 21%, but had relatively weak effects on predation by coccinellids and these effects varied among coccinellid species. In turn, coccinellid performance was influenced by the interactive effects of plant defense and aphid species, as the cascading, indirect effect of plant defense was greater when feeding upon the specialist than generalist aphid. When feeding upon specialist aphids, low- (vs. high-) glucosinolate plants increased coccinellid mass gain by 78% and accelerated development by 14%. In contrast, when feeding upon generalist aphids, low- (vs. high-) glucosinolate plants increased coccinellid mass gain by only 11% and had no detectable effect on development time. These interactive effects of plant defense and aphid diet breadth on predator performance also varied among coccinellid species; the indirect negative effects of plant defenses on predator performance was consistent among the five predators when transmitted via the dietary specialist aphid, but these effects varied substantially among predators—in both the magnitude and direction—when transmitted via the dietary generalist aphid. Accordingly, the cascading effect of plant defense on predators was stronger in magnitude and more consistent among predator taxa when transmitted by the specialist than generalist herbivore. Overall, these findings support a central role of herbivore diet breadth in mediating both the strength and contingency of tri-trophic interactions.

Aphids (Hemiptera: Aphididae) of different plant communities in an urban environment

AbstractA study was carried out in different type of habitats in an urban ecosystem of Bydgoszcz. The aim of the study was to determine aphid species spectrum and to compare dominance and species richness of the two aphid communities connected with the two different plant community structures in an urban ecosystem. There were two types of habitats: so-called southern slope, it was a part of the city on the hill, and so-called downtown – middle-northern part of the city. The differences were evaluated taking into consideration plant community structures. Observations of the occurrence of aphids were conducted every seven-ten days by monitoring of aphid host plants from the beginning of the appearance of aphids, that is from the end of April to the beginning of August, when aphids disappear. Aphids were counted in three replications: on the same host plant species, each time on different plant individuals bearing aphids in a given habitat. Based on the collected material, 32 aphid species were found on 31 plant species on southern slope areas, and 24 species of aphids on 23 plant species in downtown environments. In both years of the study of aphid species feeding on plants,

A review on the complexity of insect-plant interactions under varying levels of resources and host resistance: the case of Myzus persicae-Prunus persica

Introduction. Insect-plant interactions are affected directly or indirectly by stress factors. The effect of environmental resource availability on insect-plant interactions is here reviewed. Subsequently, the analysis focuses on aphid-host plant interactions, particularly in the system composed by the green peach aphid Myzus persicae and its primary host plant Prunus persica. Literature. Plant defenses arise in two ways: resistance and tolerance, both are affected by abiotic factors. The information gathered from studies (n = 29) on plant-aphid interactions addressing the reduction in water availability on plant resistance, showed that in 41,4% of the studies, drought stress elicits lower resistance, while 34.5%, 20.1% and 3.4%, showed higher, no change and conditional effects on plant resistance, respectively. Conclusions. Water stress elicits mixed effects on plant resistance to aphids. However, the literature review also suggests that cultural practices play a role in the fate of the peach-aphid interactions, whereas the development of predictive models aimed to assist crop-pest management systems still requires more basic information. Aphid responses to plant defenses under stressed conditions are still largely unexplored.

The delay in arrival of the parasitoid Diaeretiella rapae influences the efficiency of cabbage aphid biological control

The efficiency of the biological control strategies based on parasitoids, either as a release or a conservative measure, depends on the timely arrival or release of the parasitoids after colonization of the field by the pest. In this study, the effects of the delay between the cabbage aphid Brevicoryne brassicae (Hemiptera: Aphididae) infestation and the release of its parasitoid Diaeretiella rapae (Hymenoptera: Braconidae) and of the number of parasitoid releases on aphid population dynamics and host plant growth were investigated. When the parasitoids were released at the start of the infestation, 89.6 % of the aphids were parasitized one month later, and the damage to cabbage was low. The identical number of parasitoids released two weeks after the start of the infestation partially controlled the aphid population, but the growth of the cabbage was altered. The earliest introduction of the parasitoid to the crop led to an efficient host regulation, and the release in three times rather than in one time did not improve the control efficiency at this release delay. The implications for biological control strategies that use parasitoids of aphids are discussed.