A new species of the aphid genus Uroleucon Mordvilko, 1914 (Hemiptera: Sternorrhyncha: Aphididae) on Launaea acanthodes from Iran.

A new aphid species, Uroleucon (Lambersius) loxdalei sp. nov. (Hemiptera: Aphididae: Aphidinae: Macrosiphini) living on Launaea acanthodes (Asteraceae) and collected from the highlands in the Kerman province of Iran, is described and illustrated. The new species is morphologically most similar to U. (Lambersius) bielawskii (Szelegiewicz). This holocyclic aphid is monoecious, and not attended by ants. Biometric data are given and the key to the aphids associated with Launaea species is provided.

A new species of Metopolophium Mordvilko, 1914 (Hemiptera: Aphididae: Aphidinae) on Rosa beggeriana from Iran.

A new species of the genus Metopolophium Mordvilko, 1914 (Hemiptera: Aphididae: Aphidinae: Macrosiphini) is described and illustrated. Apterous and alate viviparous females, oviparous females, and apterous males of Metopolophium rogeri sp. nov. on Rosa beggeriana (Rosaceae) are collected from Kerman Province, Iran. The new species is morphologically most similar to M. alpinum Hille Ris Lambers, 1966, but is characterized by the low ratio of processus terminalis to basal segment of antennal segment VI, high ratio of siphunculus to cauda length and the presence of many more accessory setae on the ultimate rostral segment. This holocyclic aphid is monoecious and not attended by ants. The biometric data are given, and the key to the aphids associated with Rosa species in Blackman and Eastop (2021) is modified to accommodate the new species.

Previous herbivory modulates aphid population growth and plant defense responses in a non-model plant, Carthamus tinctorius (Asteraceae).

Plants have a variety of defense mechanisms that are often induced following attacks by herbivores; this benefits those plants by decreasing performance or preference of herbivores that attack the plants later. We investigated the effects of previous exposure of plants to the safflower aphid, Uroleucon carthami, cotton bollworm, Helicoverpa armigera, and mechanical wounding on subsequent safflower aphid infestations using commercial safflower (Carthamus tinctorius) cultivars and wild safflower species (C. oxyacantha). The experiments were conducted in a greenhouse with two treatments: previously induced plants via direct herbivory or mechanical wounding, and control plants that had never experienced herbivory. To test the performance of safflower aphid on different plant treatments, five unwinged aphids were placed on each plant and allowed to reproduce for 14 days. Finally, the total numbers of aphids on each plant were counted and the percentage of produced winged individuals was calculated. The number of aphids on plants that were previously infested or injured was significantly lower than in control plants. Percentage of winged aphids was significantly higher on induced plants, which is an indicator for unsuitable conditions. Also, significant increase in total phenolic content and hydrogen peroxide was observed in induced plants, showing that the levels of these compounds were either treatment, cultivar and/or genotype × treatment dependent, highlighting the specificity of these interactions. Overall, among the safflower cultivars the lowest number of aphids and the highest percentage of winged aphid individuals were observed on Mahali-Isfahan cultivar and wild safflower, showing that this cultivar is more sensitive to herbivory and/or responds to it more than other cultivars. These findings could contribute to a better utilization of induced defense in the integrated pest management of safflower fields.

Aphid alarm pheromone alters larval behaviour of the predatory gall midge, Aphidoletes aphidimyza and decreases intraguild predation by anthocorid bug, Orius laevigatus.

Intraguild predation is the killing and consuming of a heterospecific competitor that uses similar resources as the prey, and also benefit from preying on each other. We investigated the foraging behaviour of the gallmidge, Aphidoletes aphidimyza, a predator of aphids used for biological control that is also the intraguild prey for most other aphid natural enemies. We focus on how aphid alarm pheromone can alter the behaviour of the gallmidge, and predation by the anthocorid bug Orius laevigatus (O. laevigatus). We hypothesised that gallmidges would respond to the presence of (E)-ß-farnesene (EBF) by leaving the host plant. Since feeding by Aphidoletes gallmidge larvae does not induce EBF emission by aphids, this emission indicates the presence of an intraguild predator. We found that gallmidge larvae reduced their foraging activities and left the plant earlier when exposed to EBF, particularly when aphids were also present. Contrastingly, gallmidge females did not change the time visiting plants when exposed to EBF, but lay more eggs on plants that had a higher aphid density. Lastly, EBF reduced the number of attacks of the intraguild predator, O. laevigatus, on gallmidge larvae, potentially because more gallmidges stopped aphid feeding and moved off the plant at which point O. laevigatus predated on aphids. Our work highlights the importance of understanding how intraguild predation can influence the behaviour of potential biological control agents and the impact on pest control services when other natural enemies are also present.

Coexistence through mutualist-dependent reversal of competitive hierarchies.

Mechanisms that allow for the coexistence of two competing species that share a trophic level can be broadly divided into those that prevent competitive exclusion of one species within a local area, and those that allow for coexistence only at a regional level. While the presence of aphid-tending ants can change the distribution of aphids among host plants, the role of mutualistic ants has not been fully explored to understand coexistence of multiple aphid species in a community. The tansy plant (Tanacetum vulgare) hosts three common and specialized aphid species, with only one being tended by ants. Often, these aphids species will not coexist on the same plant but will coexist across multiple plant hosts in a field. In this study, we aim to understand how interactions with mutualistic ants and predators affect the coexistence of multiple species of aphid herbivores on tansy. We show that the presence of ants drives community assembly at the level of individual plant, that is, the local community, by favoring one ant-tended species, Metopeurum fuscoviride, while preying on the untended Macrosiphoniella tanacetaria and, to a lesser extent, Uroleucon tanaceti. Competitive hierarchies without ants were very different from those with ants. At the regional level, multiple tansy plants provide a habitat across which all aphid species can coexist at the larger spatial scale, while being competitively excluded at the local scale. In this case, ant mutualist-dependent reversal of the competitive hierarchy can drive community dynamics in a plant-aphid system.

Secondary bacterial symbiont community in aphids responds to plant diversity.

Biodiversity is important for ecosystem functioning and biotic interactions. In experimental grasslands, increasing plant species richness is known to increase the diversity of associated herbivores and their predators. If these interactions can also involve endosymbionts that reside within a plant or animal host is currently unknown. In plant-feeding aphids, secondary bacterial symbionts can have strong fitness effects on the host, e.g. resistance to natural enemies or fungal pathogens. We examined the secondary symbiont community in three species of aphid, each feeding on a unique host plant across experimental plots that varied in plant species richness. Aphids were collected in May and June, and the symbiont community identified using species-specific PCR assays. Aphis fabae aphids were found to host six different symbiont species with individual aphids co-hosting up to four symbionts. Uroleucon jaceae and Macrosiphum rosae hosted two and three symbiont species, respectively. We found that, at the aphid population level, increasing plant species richness increased the diversity of the aphid symbiont community, whereas at the individual aphid level, the opposite was found. These effects are potentially driven by varying selective pressures across different plant communities of varying diversities, mediated by defensive protection responses and a changing cost-benefit trade-off to the aphid for hosting multiple secondary symbionts. Our work extends documented effects of plant diversity beyond visible biotic interactions to changes in endosymbiont communities, with potentially far-reaching consequences to related ecosystem processes.

Intraspecific differences in plant chemotype determine the structure of arthropod food webs.

It is becoming increasingly appreciated that the structure and functioning of ecological food webs are controlled by the nature and level of plant chemicals. It is hypothesized that intraspecific variation in plant chemical resistance, in which individuals of a host-plant population exhibit genetic differences in their chemical contents (called 'plant chemotypes'), may be an important determinant of variation in food web structure and functioning. We evaluated this hypothesis using field assessments and plant chemical assays in the tansy plant Tanacetum vulgare L. (Asteraceae). We examined food webs in which chemotypes of tansy plants are the resource for two specialized aphids, their predators and mutualistic ants. The density of the ant-tended aphid Metopeurum fuscoviride was significantly higher on particular chemotypes (borneol) than others. Clear chemotype preferences between predators were also detected. Aphid specialist seven-spotted ladybird beetles (Coccinella septempunctata) were more often found on camphor plants, while significantly higher numbers of the polyphagous nursery web spider (Pisaura mirabilis) were observed on borneol plants. The analysis of plant chemotype effects on the arthropod community clearly demonstrates a range of possible outcomes between plant-aphid-predator networks. The findings help to offer a deeper insight into how one important factor--plant chemical content--influences which species coexist within a food web on a particular host plant and the nature of their trophic linkages.

Complex effects of fertilization on plant and herbivore performance in the presence of a plant competitor and activated carbon.

Plant-herbivore interactions are influenced by host plant quality which in turn is affected by plant growth conditions. Competition is the major biotic and nutrient availability a major abiotic component of a plant's growth environment. Yet, surprisingly few studies have investigated impacts of competition and nutrient availability on herbivore performance and reciprocal herbivore effects on plants. We studied growth of the specialist aphid, Macrosiphoniella tanacetaria, and its host plant tansy, Tanacetum vulgare, under experimental addition of inorganic and organic fertilizer crossed with competition by goldenrod, Solidago canadensis. Because of evidence that competition by goldenrod is mediated by allelopathic compounds, we also added a treatment with activated carbon. Results showed that fertilization increased, and competition with goldenrod decreased, plant biomass, but this was likely mediated by resource competition. There was no evidence from the activated carbon treatment that allelopathy played a role which instead had a fertilizing effect. Aphid performance increased with higher plant biomass and depended on plant growth conditions, with fertilization and AC increasing, and plant competition decreasing aphid numbers. Feedbacks of aphids on plant performance interacted with plant growth conditions in complex ways depending on the relative magnitude of the effects on plant biomass and aphid numbers. In the basic fertilization treatment, tansy plants profited from increased nutrient availability by accumulating more biomass than they lost due to an increased number of aphids under fertilization. When adding additional fertilizer, aphid numbers increased so high that tansy plants suffered and showed reduced biomass compared with controls without aphids. Thus, the ecological cost of an infestation with aphids depends on the balance of effects of growth conditions on plant and herbivore performance. These results emphasize the importance to investigate both perspectives in plant herbivore interactions and characterize the effects of growth conditions on plant and herbivore performance and their respective feedbacks.

Multiple cues for winged morph production in an aphid metacommunity.

Environmental factors can lead individuals down different developmental pathways giving rise to distinct phenotypes (phenotypic plasticity). The production of winged or unwinged morphs in aphids is an example of two alternative developmental pathways. Dispersal is paramount in aphids that often have a metapopulation structure, where local subpopulations frequently go extinct, such as the specialized aphids on tansy (Tanacetum vulgare). We conducted various experiments to further understand the cues involved in the production of winged dispersal morphs by the two dominant species of the tansy aphid metacommunity, Metopeurum fuscoviride and Macrosiphoniella tanacetaria. We found that the ant-tended M. fuscoviride produced winged individuals predominantly at the beginning of the season while the untended M. tanacetaria produced winged individuals throughout the season. Winged mothers of both species produced winged offspring, although in both species winged offspring were mainly produced by unwinged females. Crowding and the presence of predators, effects already known to influence wing production in other aphid species, increased the percentage of winged offspring in M. tanacetaria, but not in M. fuscoviride. We find there are also other factors (i.e. temporal effects) inducing the production of winged offspring for natural aphid populations. Our results show that the responses of each aphid species are due to multiple wing induction cues.