The sequence diversity in the mitochondrial cytochrome-c oxidase I (COI) gene was evaluated as a tool for resolving differences among species of European adelgids collected from several localities across the Czech Republic. Members of 7 genera and 16 species were examined, and as outgroups, two species of Phylloxeridae were used. Sequence divergences within species were on average less than 0.15%, whereas divergences between species ranged from 0.0 to 4.12% for congeneric and to 13.24% for intergeneric comparisons. It is concluded that DNA barcoding of Adelgidae is a powerful tool for identifying genera, but at the species level it works only in those cases where there are no species complexes. Nevertheless, it can be used as a complement to traditional, morphological taxonomy.
The impact of transgenic Bt-maize, expressing the Cry1Ab protein, on aphids, leafhoppers, cutworms and wireworms was evaluated at the farm scale by comparing their abundance on Bt-plots and those sown with the isogenic variety over three consecutive growing seasons. The impact of Bt-maize was different on each of the three-herbivore groups. There were significantly more aphids on the Bt-maize but in terms of aphid species, the difference was only statistically significant for Sitobion avenae and not for the other three most abundant species (Metopolophium dirhodum, Rhopalosiphum padi and Macrosiphum euphorbiae). The analysis of aphid age structure showed consistently more individuals on Bt-plots; differences were significant for alates, apterous adults and young nymphs of R. padi, apterous adults and apterous fourth instar nymphs of S. avenae, alates, apterous adults and apterous fourth instar nymphs of M. dirhodum. Leafhoppers (Zyginidia scutellaris), particularly mature nymphs, were also more abundant on the Bt-maize. In spite of this there was no difference in leafhopper damage to Bt and non Bt-maize. The reasons for this are unclear but may be due to changes in Bt-maize that favoured aphids and leafhoppers. Differences in aphid and leafhopper densities were not high enough to affect yield. However, they may have affected the availability of prey for polyphagous predators such as Orius sp. The Bt-maize did not affect the incidence of cutworms (Agrotis segetum) or wireworms (Agriotes lineatus). These results indicate that Bt-maize does not have a negative impact on the non-target maize biocenosis at the farm scale.
A two-year field experiment was conducted to determine whether a conservation biological control strategy could be applied to enhance the biological control of green apple aphids, Aphis spp., in a high-density and scab-resistant apple orchard at the non-bearing stage. The natural occurrence of aphid predators and their impact on aphid populations were evaluated in 2005. The impact of predation on aphid densities was evaluated by comparing a predator exclusion treatment with a control. In 2006, the possibility to enhance predator abundance/performance and aphid biological control with a flowering ground cover was tested: trees were grown either with a flowering ground cover of phacelia, Phacelia tanacetifolia Bentham, and buckwheat, Fagopyrum esculentum Moench, or with a conventional ground cover of mixed Poaceae species. In 2006, it was also determined whether aphid densities differ between Liberty and Topaz, 2 scab-resistant cultivars. Results indicate that the predatory arthropod community was dominated by Coccinellidae, Cecidomyiidae, and various spider species. The ladybird community was dominated by the exotic species Harmonia axyridis Pallas, and the abundance of this species was correlated with aphid density. Naturally occurring predators had little impact on aphid abundance, although the proportion of trees with aphid colonies was greater in the predator exclusion treatment on two consecutive dates in 2005. Ground cover types had no impact on aphid densities. The oviposition response of Cecidomyiidae to aphid density was greater in Liberty trees with flowering ground cover than with the conventional ground cover. Conversely, the response of ladybird adults to aphid density was more important in Topaz trees with the conventional ground cover than with the flowering ground cover. Finally, no difference occurred in aphid abundance between Liberty and Topaz trees. Those results are discussed from a biological control and ecological point of view.
The abundance and distribution of coccinellids in non-crop habitats was studied using removal sampling and visual observation. Coccinellids were most frequently found on grassland habitats. Coccinellid abundance appeared to be most strongly correlated with the percentage ground cover of thistle, grasses and nettles. The most commonly collected coccinellids were Coccinella septempunctata and Adalia bipunctata comprising 60% and 35% of the catches respectively. Most coccinellids were found on Rubus spp. with nettles (Urtica dioica) and grasses being the next most favoured plant species. Adalia bipunctata was the most commonly found coccinellid species on nettles and birch (Betula spp.) whereas C. septempunctata was the most commonly found species on grasses, Rubus spp. and oak (Quercus spp.). These results are discussed in light of current thinking on the importance of "island" habitats as pali of an integrated pest management programme.
An experiment was conducted to compare the predation efficiency of the coccinellids Harmonia axyridis and Coleomegilla maculata on potato plants, Solanum tuberosum, and on a wild aphid-resistant species, Solanum tarijense. Harmonia axyridis females reduced aphid populations more than C. maculata females. Aphid predation by the predators was reduced on S. tarijense compared to S. tuberosum. Coleomegilla maculata spent less time on S. tarijense than on S. tuberosum. Harmonia axyridis spent the same amount of time on both plant species. The plant species did not affect IGP between larvae. Compared to S. tuberosum, the resistant plant offers M. persicae an enemy-free space against both coccinellid predators., Bruno Fréchette ... [et al.]., and Obsahuje seznam literatury
The aphid parasitoid Aphidius ervi was collected and subsequently reared on Sitobion avenae on wheat or Acyrthosiphon pisum on alfalfa. Parasitoids from both origins were exposed in an olfactometer to alfalfa or wheat volatiles after plant experience (wheat or alfalfa) or after oviposition experience (S. avenae on wheat or A. pisum on alfalfa). The results showed the importance of adult experience, conditioning and innate preferences on the responses of A. ervi toward volatiles and provided a mechanistic explanation to the high prevalence of A. ervi on aphids on cereals and legumes in central Chile.
This paper examines some biological aspects and the predatory capacity of Chrysoperla externa fed nymphs of Sipha flava and reared at different temperatures. Recently hatched larvae were placed individually in Petri dishes, fed ad libitum with S. flava and reared at either 12, 16, 20, 24, 28 or 32 ± 1°C, a RH of 70 ± 10% and a 12-h photophase. The experiment was fully randomized with 30 replicates of each treatment. The duration and survival in each instar, and larval and pupal stages (pre-pupa + pupa) were analyzed. To determine the predatory capacity of larvae they were each provided daily with three-day-old nymphs of the aphid, in a number greater than they could consume. Ninety C. externa larvae were kept individually in Petri dishes at 24 ± 1°C, and their daily consumption recorded during development. Temperature influenced the rate of larval and pupal development. There was a decrease in the duration of development with increase in temperature. Regression analyses, based on quadratic equations, were used to describe the effect of temperature on the duration of development in the different instars of C. externa. This revealed that the base temperature increased as the larvae developed towards the adult phase. The survival of larvae in the first and second instars was similar at 12, 16, 20, 24, 28 and 32°C but none of the third instar larvae completed their development at 12°C and 32°C. The average daily and total consumption of aphids by third instar larvae was about 48 times greater than that of first instar larvae. The larvae ate an average of 10, 37 and 479 aphids in the first, second and third instars, respectively.
In agro-ecosystems, habitat loss and fragmentation may alter the assemblage of aphidophagous insects, such as foliar-foraging (coccinellids) and ground-foraging predators (carabids), potentially affecting intraguild interactions. We evaluated how habitat loss (0, 55 and 84%), fragmentation (1, 4 and 16 fragments) and their combination affected the abundance and species richness of coccinellids and carabids, and aphid abundance, both in the short-term (summer: December to February) and over a longer time span (autumn: March to May), when different demographic mechanisms may participate. We created four types of 30 × 30 m patches (landscapes) in which alfalfa was grown: Control (1F - 0%, 30 × 30 m patch of alfalfa with no fragmentation or habitat loss), 4F - 55% (4 alfalfa fragments, with 55% total habitat loss), 4F - 84% (4 alfalfa fragments, with 84% total habitat loss), and 16F - 84% (16 alfalfa fragments, with 84% total habitat loss). Each landscape type was replicated five times. Insects were sampled by sweep-netting and pitfall traps, from December (summer) to May (autumn). Total abundance and species richness of carabids, in the short-term, was highest in the 16F - 84% landscapes. Total abundance of adult coccinellids was similar among landscapes, but at the species level Hyperaspis sphaeridioides, in the short-term, and Adalia bipunctata, in the long-term, had their highest densities in fragments within landscapes with high habitat loss (84%), independently of habitat fragmentation. Species richness in the long-term was higher in the landscapes with 84% habitat loss. Among aphids, in the long term Aphis craccivora was less abundant in landscapes with high habitat loss and fragmentation (16-84%), while Therioaphis trifolii showed the opposite trend. These results suggest that habitat loss and fragmentation may increase the density and diversity of aphidophagous insects, while their effects on aphids are more variable.
Determination of embryonic stages is an important prerequisite for the long-term cryopreservation of eggs and embryos of the predatory gall midge Aphidoletes aphidimyza. This paper describes the embryonic development of this insect based on light microscopy. Gall midge embryogenesis lasts, on average, 102 h at 17°C and 144 h at 15°C. Living embryos can be quickly separated into ten stages that are clearly defined by specific morphological markers. The necessity for selecting definite embryonic stages for cryobiological storage is discussed.
Interactions between syrphid predators and their prey are poorly known. The adaptations of syrphids to aphid defences and the consequences for the evolution of life history traits in these predators especially are mostly unstudied. This is the first of two papers investigating the evolution of prey specialization in aphidophagous hoverflies. The study focuses on two questions: (1) Are differences in the body size of syrphid predators reflected in differences in the size of their prey? (2) Are differences in body size, body mass and development time of the syrphid predators correlated with the defence strategies of their aphid prey (e.g. mobility, toxicity)? Platycheirus clypeatus (Meigen, 1822), Platycheirus fulviventris (Macquart, 1829), Melanostoma mellinum (Linnaeus, 1758), and Melanostoma scalare (Fabricius, 1794), which differ considerably in their prey specialization, but are closely related, were chosen as model species. Life history data for these syrphids came from a laboratory study, and that for the aphids from a literature survey. These syrphid species can be arranged on a gradient of increasing prey specialization, from 32 prey species for the generalist M. mellinum and only 3 for the specialist P. fulviventris. Differences in prey specialization were even more evident when the defence ability of the various species of aphid prey was considered. For instance, the specialization on ant-attended aphids in M. scalare. Larvae exhibited a one or two weeks diapause which made the determination of developmental time imprecise. Body size of the predators was not reflected in that of their aphid prey. The postulated relationship between body size of the predator and the defence strategies of their prey was not supported by our data. A comparison of a wider range of syrphid species from different taxonomic groupings together with a phylogenetic correction procedure might reveal clearer trends. The second part of this paper (Dziock, in prep.) will investigate the correlation between prey specialization and reproductive strategies (i.e. clutch size, egg size and number) and will put the results into a broader framework.