Life Table Construction under Different Temperatures and Insecticide Susceptibility Analysis of Uroleucon formosanum (Hemiptera: Aphididae).

Uroleucon formosanum is an important aphid pest of lettuce, but basic information on its biology is scarce. In this study, effects of three constant temperatures (17, 21, and 25 °C, simulating the mean temperature range in greenhouses) on the development and fecundity of U. formosanum were analyzed by constructing a life table. U. formosanum could develop and reproduce under all three temperatures, but the survival rate, development, and fecundity of U. formosanum were affected by temperature. The intrinsic rate of increase was lowest at 17 °C (0.17) and it was significantly less than at 21 °C (0.20) and 25 °C (0.23). Furthermore, U. formosanum had the lowest finite rate of increase (1.19) and the largest mean generation time (20.21) at 17 °C. These results mean that U. formosanum is less adapted to the lower temperatures (17 °C) among these three set temperatures. To screen insecticides for control, susceptibility of U. formosanum to six insecticides including chlorpyrifos, abamectin, beta-cypermethrin, imidacloprid, nitenpyram, and thiamethoxam was evaluated. U. formosanum was relatively sensitive to all six test insecticides. Chlorpyrifos had the highest toxicity to U. formosanum (LC50 = 3.08 mg/L). These data may help to develop integrated management strategies for better population control of U. formosanum.

The complete mitochondrial genome of Uroleucon erigeronense (Thomas, 1878) (Hemiptera: Aphididae).

We have sequenced mitochondrial genome of Uroleucon erigeronense (Thomas, 1878) isolated from Erigeron canadensis in Korea. The circular mitogenome of U. erigeronense is 15,691 bp long including 13 protein-coding genes, two ribosomal RNA genes, 22 transfer RNAs, and a single control region of 968 bp. AT ratio is 84.2%. Additional phylogenetic studies of aphid mitogenomes are required due to the inconsistency found in the three phylogenetic trees.

A further contribution to the knowledge of Uroleucon species (Hemiptera, Aphididae) living on Adesmia (Fabaceae) in southern South America, with description of a new species from Chile.

Uroleucon (Hemiptera, Aphididae, Macrosiphini) is a highly diverse and widely distributed genus. Most of its species are hosted by plants of the Asteraceae or Campanulaceae, but three species from the southern end of South America have specialized to live on plants of the genus Adesmia (Fabaceae). New morphological and chorological data are provided for U. adesmiae Mier Durante and Ortego and U. naheulhuapense Nieto Nafría von Dohlen, with a description of the alate viviparous female of the latter species. U. australe Nieto Nafría Mier Durante, sp. n. is described from apterous viviparous females, oviparous females and males from four localities in the Chilean regions of Aysén and Magallanes; it is very close to U. nahuelhuapense, both morphologically and genetically. Contrary to what is typical for aphids, the males of U. australe have a greater number of distinguishing characters than are found in viviparous females. A modification of the identification key to the apterous viviparous females of the known Uroleucon species in South America by Nieto Nafría et al. (2019) is presented.

The species of Uroleucon (Hemiptera: Aphididae) living on Adesmia (Fabaceae) in Argentina, with the description of a new species.

Uroleucon Mordvilko is the largest genus in the Macrosiphini (Hemiptera, Aphididae) and most of its species live on species of Asteraceae. Uroleucon nahuelhuapense Nieto Nafría von Dohlen sp. n. is described from apterous viviparous females collected on Adesmia boronioides (Fabaceae) in a locality of Neuquén province (Argentina). The morphological characters and the sequence of the tRNAleu-COII mitochondrial locus support the inclusion of the new species in the genus Uroleucon. Apterous viviparous females of Uroleucon adesmiae Mier Durante Ortego collected in two Argentinean localities have also been studied and ranges of several quantitative features have been modified. The identification key for the Uroleucon species known in South America by Nieto Nafría et al. (2007) has been modified to include the new species.

Specificity of plant-plant communication for Baccharis salicifolia sexes but not genotypes.

Plants are able to adjust their anti-herbivore defenses in response to the volatile organic compounds (VOCs) emitted by herbivore-damaged neighbors, and some of these changes increase resistance against subsequent herbivory. This phenomenon of plant-plant communication is thought to be widespread, but recent investigations have cautioned that it can be context dependent, including variation in the strength of communication based on the identity of plants and their associated herbivores. Here, we performed three greenhouse experiments using multiple male and female genotypes of the dioecious woody shrub Baccharis salicifolia and its specialist aphid Uroleucon macolai to test for specificity of plant-plant communication with respect to plant sex and genotype. Moreover, we evaluated plant sexual dimorphism and genotypic variation in VOC emissions (i.e., the "speaking" side of the interaction) and response of plants to VOC exposure (i.e., the "listening" side of the interaction) in order to identify the chemical mechanisms underlying such specificity. We did not find genotypic specificity of communication; emitter plants damaged by U. macolai significantly reduced subsequent U. macolai performance on receivers, but these effects were indistinguishable for communication within vs. among genotypes. In contrast, we found sex specificity of communication; male emitter plants reduced subsequent U. macolai performance on male and female receiver plants equally, while female emitter plants only did so for female receivers. We found sexual (but not genotypic) dimorphism in speaking but not listening; of the seven compounds induced by U. macolai feeding (speaking), pinocarvone was approximately fivefold greater in female than in male plants, while exposure of plants to pinocarvone emissions (listening) reduced U. macolai performance equally in both male and female plants. Together, our study demonstrates novel evidence for sexually dimorphic specificity of plant-plant communication and the chemical mechanism underlying this effect.

Predator-prey interactions in a ladybeetle-aphid system depend on spatial scale.

The outcome of species interactions may manifest differently at different spatial scales; therefore, our interpretation of observed interactions will depend on the scale at which observations are made. For example, in ladybeetle-aphid systems, the results from small-scale cage experiments usually cannot be extrapolated to landscape-scale field observations. To understand how ladybeetle-aphid interactions change across spatial scales, we evaluated predator-prey interactions in an experimental system. The experimental habitat consisted of 81 potted plants and was manipulated to facilitate analysis across four spatial scales. We also simulated a spatially explicit metacommunity model parallel to the experiment. In the experiment, we found that the negative effect of ladybeetles on aphids decreased with increasing spatial scales. This pattern can be explained by ladybeetles strongly suppressing aphids at small scales, but not colonizing distant patches fast enough to suppress aphids at larger scales. In the experiment, the positive effects of aphids on ladybeetles were strongest at three-plant scale. In a model scenario where predators did not have demographic dynamics, we found, consistent with the experiment, that both the effects of ladybeetles on aphids and the effects of aphids on ladybeetles decreased with increasing spatial scales. These patterns suggest that dispersal was the primary cause of ladybeetle population dynamics in our experiment: aphids increased ladybeetle numbers at smaller scales because ladybeetles stayed in a patch longer and performed area-restricted searches after encountering aphids; these behaviors did not affect ladybeetle numbers at larger spatial scales. The parallel experimental and model results illustrate how predator-prey interactions can change across spatial scales, suggesting that our interpretation of observed predator-prey dynamics would differ if observations were made at different scales. This study demonstrates how studying ecological interactions at a range of scales can help link the results of small-scale ecological experiments to landscape-scale ecological problems.

Herbivore specificity and the chemical basis of plant-plant communication in Baccharis salicifolia (Asteraceae).

It is well known that plant damage by leaf-chewing herbivores can induce resistance in neighbouring plants. It is unknown whether such communication occurs in response to sap-feeding herbivores, whether communication is specific to herbivore identity, and the chemical basis of communication, including specificity. We carried out glasshouse experiments using the California-native shrub Baccharis salicifolia and two ecologically distinct aphid species (one a dietary generalist and the other a specialist) to test for specificity of plant-plant communication and to document the underlying volatile organic compounds (VOCs). We show specificity of plant-plant communication to herbivore identity, as each aphid-damaged plant only induced resistance in neighbours against the same aphid species. The amount and composition of induced VOCs were markedly different between plants attacked by the two aphid species, providing a putative chemical mechanism for this specificity. Furthermore, a synthetic blend of the five major aphid-induced VOCs (ethanone, limonene, methyl salicylate, myrcene, ocimene) triggered resistance in receiving plants of comparable magnitude to aphid damage of neighbours, and the effects of the blend exceeded those of individual compounds. This study significantly advances our understanding of plant-plant communication by demonstrating the importance of sap-feeding herbivores and herbivore identity, as well as the chemical basis for such effects.

Ocorrência de afídeos em alface (Lactuca sativa L. ) em cultivo hidropônico / Occurrence of aphids on lettuce (Lactuca sativa L. ) under hydroponic cultivation

The occurrence of aphids was evaluated on lettuce hydroponically grown at the Escola Agrotécnica of the State University of São Paulo (UNESP) located in Jaboticabal County, State of São Paulo, Brazil, from January to December 1999. The total number of each species of aphids present in weekly samplings performed during the period was found to be correlated with the average temperature recorded within the respective sampling period. The occurrence of three species, Uroleucon ambrosie (Thomas), Myzus persicae (Sulzer) and Macrosiphum euphorbiae (Thomas) was recorded, with the highest population densities being coincident with mean temperatures below 21.5°C. The highest population densities of U. ambrosie occurred from May to June. In the second week of May and third week of November, two maximum population peaks were recorded for M. persicae. The species M. euphorbiae was predominant over the others and the highest populations of this species were observed from May to June and from late July to early September. A negative correlation was found between populations of aphids and temperature. This correlation, however, was statistically significant only for M. euphorbiae and U. ambrosiae.

A ocorrência de afideos foi avaliada em alface cultivada hidroponicamente na área de produção da Escola Agrotécnica da Universidade Estadual de São Paulo (UNESP), em Jaboticabal, São Paulo, de janeiro a dezembro de 1999. Foi constatado que o número total de cada espécie de afideo, presentes em amostragens conduzidas semanalmente durante o período, foi correlacionada com a média de temperaturas registradas dentro do período de amostragem. Foi registrada a ocorrência de três espécies de afideos, Uroleucon ambrosiae (Thomas), Myzus persicae (Sulzer) e Macrosiphum euphorbiae (Thomas), sendo as maiores densidades populacionais coincidentes com médias de temperaturas inferiores a 21,5°C. As maiores densidades populacionais de U. ambrosiae ocorreram de maio a junho. Na segunda semana de maio e na terceira semana de novembro foram registrados dois picos populacionais máximos de M. persicae. A espécie M. euphorbiae predominou sobre as demais e as maiores populações dessa espécie foram observadas nos períodos de maio a junho e final de julho a início se setembro. Foi constatada correlação negativa entre populações de afideos e temperatura. Esta correlação, entretanto, foi estatisticamente significativa somente para M. euphorbiae e U. ambrosiae.

Adaptive allocation of resources and life-history trade-offs in aphids relative to plant quality.

The need to allocate a limited amount of energy between different life-history traits is a fundamental assumption in life-history theory. However, it has often turned out to be extremely difficult to measure the competing processes that contribute to costs or benefits for individual organisms. The present investigation begins by analysing how an aphid clonal lineage adapts its reproductive investment to moderate changes in host plant quality (e.g. during the life cycle of its host). Using Centaurea jacea and Uroleucon jaceae as a model plantaphid system, I show that reproductive investment can be far more complex than indicated by dry or wet mass of the gonads alone. The number of embryos of a particular size class or developmental state present in the reproductive system of an aphid is highly flexible and is influenced by the quality of the host plant. Next, the effects of a particular reproductive investment on survival during periods of food deprivation are analysed for aphids originating from host-plants of different qualities. When food stress is severe the ability to rapidly resorb and reallocate resources committed to offspring is important for survival. However, this ability is limited. I argue that, in periods of food stress, young, unsclerotized embryos might serve as a kind of energy buffer similar to a fat body and are therefore not relevant to cost-benefit calculations. However, embryos that are beginning to sclerotize within the ovarioles are not available for resorption and resource reallocation. They compete for nutrients with their mother and contribute to costs. Therefore, it is suggested that the reproductive investment of an aphid should not be equated with reproductive costs in a general al way. The dynamics of adaptive resource allocation and resorption are a key feature of an aphid's life history, and the implications for life-history theory are discussed.

Physiological responses of Uroleucon jaceae (L.) to seasonal changes in the quality of its host plant Centaurea jacea L.: multilevel control of adaptations to the life cycle of the host.

Exploiters of short-lived plants have evolved strategies in response to physiological changes that occur during the development of their hosts. The ability to adapt to host quality changes is necessary particularly if the mobility of an animal is poor or risk-constrained. In the plant-aphid system Centaurea jaceae-Uroleucon jaceae, the responses of the aphid to the seasonal changes in its host plant grown in poor and good quality soil were investigated. Coarse- and fine-tuned physiological reactions were observed in discrete aphid generations which were reared on plants grown either in a growth chamber or in a greenhouse. The number of ovarioles and developmental time depended on extrinsic factors (length of photoperiod) not directly related to plant quality. The reproductive investment of the aphids was also independent of their total dry weight. However, within the gonadal system high correlations were found at the embryonic level (e.g. the number of sclerotized embryos or the length of the oldest embryos per ovariole were highly correlated with gonadal dry weight). Aphids which were living on the 4-leaf stage of high-quality host plants showed a significantly higher investment in their gonads than aphids feeding on senescenting hosts. Factor analysis corroborated that aphids reared on poor-quality hosts revealed no grouping of variables measured, whereas those which were reared on high-quality plants showed clustering in respect of somatic (tibia length, dry weight of soma) and gonadal (number of sclerotized and unsclerotized embryos, length of the oldest embryos, ovariole number, gonad dry weight) factors. Three different levels of adaptive response to plant quality are distinguished: individual response to host quality, maternal influences on offspring and response to changes not specific to habitat (photoperiod). These different levels of regulation are thought to enable the aphids to adapt to a host of a given nutritional quality and anticipate deteriorating habitat quality simultaneously. It is concluded that physiological constraints in aphids are only revealed when aphids are exposed to severe nutritional stress for several generations.

APHID DISTRIBUTION AND THE EVOLUTION OF GOLDENROD RESISTANCE.

Although there is considerable evidence indicating that herbivory is detrimental to plant fitness, some recent studies of the evolution of plant resistance have concluded that insects do not impose selection on their host plants. A previously untested assumption that underlies most studies of the evolution of plant resistance is that insect distribution patterns are controlled directly by the effects of plant genotype on insect preference and performance. The experiments described here explicitly tested this assumption using the specialist herbivore Uroleucon tissoti (Homoptera: Aphididae) and its host plant Solidago altissima (Asteraceae). Measures of aphid preference and performance were used to predict aphid distribution patterns, and then the predicted distribution patterns were compared with the natural distribution pattern. Although goldenrod genotype had a strong effect on aphid distribution, aphid distribution was not controlled directly by the effect of goldenrod genotype on aphid preference and performance. Instead, a second experiment demonstrated that aphid and spittlebug (Philaenus spumarius and Lepyronia quadrangularis Homoptera: Cercopidae) distribution is controlled largely by genetic variation for resistance to a suite of "branch-causing" herbivores. These herbivores induce branching and aphids and spittlebugs are more abundant on branched plants than unbranched plants. These results indicate that any natural selection imposed by aphids and spittlebugs on goldenrod will depend on the presence or absence of branch-causing herbivores. Thus, selection for plant resistance may depend as much on the assemblage of insect species present as on the identity of each individual species.