Valeria Malagnini

Pollen availability and abundance of predatory phytoseiid mites on natural and secondary hedgerows

Mites occurring on a number ofnatural and secondary (i.e., planted) hedgerowslocated in north-eastern Italy were monitoredwith particular attention being paid tophytoseiids (Acari: Phytoseiidae). Pollendiversity and abundance were analysed tohighlight potential relationships betweenpollen availability and phytoseiids. Secondaryhedgerows were structured in modules containinga single species (field maple, hornbeam,dogwood, hazel, and elderberry) andmodules containing a mixture of theabove-mentioned species. These hedgerows werelocated in an experimental farm where they werecontiguous to a vineyard. Natural hedgerowswere located in the same area. The pollen ofPoaceae was the most important component ofnon-arboreal pollen (NAP), and that ofelderberry of arboreal pollen (AP). Pollendiversity was higher on natural than onsecondary hedgerows. Generally, pollendensities reached relatively high levels fromlate April to late June and decreased insummer. Pollen was more abundant on naturalthan on secondary hedgerows and phytoseiidabundance showed a similar trend. On elderberryand hornbeam in natural hedgerows a potentialrelationship between pollen availability andthe abundance of phytoseiids, in particular ofEuseius finlandicus (Oudemans) was found.Experimental pollen applications increased thefecundity and the abundance of this species.

Transmission of grapevine Pinot gris virus by Colomerus vitis (Acari: Eriophyidae) to grapevine

Grapevine Pinot gris virus (GPGV) is a new virus reported in Europe and several other grape-growing countries. In an attempt to identify a vector for GPGV, samples of the eriophyid mite Colomerus vitis collected from buds and erinea in GPGV-infected vines were analysed by RT-PCR, using specific primers. Molecular analysis revealed the presence of GPGV in C. vitis. Transmission trials were conducted using C. vitis collected from GPGV-infected vines. Mites were able to transmit GPGV to healthy grapevines, suggesting that C. vitis is a potential vector of this virus.

A method to assess the effects of pesticides on the predatory mite Phytoseiulus persimilis (Acari Phytoseiidae) in the laboratory

Abstract Phytoseiulus persimilis Athias-Henriot (Acari Phytoseiidae) is a major predator of Tetranychus urticae (Acari Tetranychidae). The performance of P. persimilis in controlling T. urticae may be altered by pesticides used to manage other pests. Therefore, knowledge of the side-effects of pesticides is essential for IPM. A number of laboratory methods were suggested to evaluate pesticide side-effects on predatory mites. Most methods assess residual effects only, and a number of them are characterised by high predator escape rates from experimental units. A method aimed at evaluating the topical and residual effects of pesticides on P. persimilis is herein described. Mites were treated by microimmersion and then reared in holding cells, on bean leaves previously dipped in a pesticide solution. Three insecticides (pyrethrins, spinosad and thiamethoxam), an insecticide-acaricide (abamectin), and two fungicides (azoxystrobin and tolylfluanide) were evaluated. The strain of P. persimilis used for evaluation was collected from unsprayed vegetable plants. All the pesticides affected the survival and fecundity of P. persimilis. Pesticides did not affect the egg-hatching of P. persimilis females exposed to pesticides. Pyrethrins and abamectin proved to be more toxic than other pesticides, and thiamethoxam was more toxic than spinosad, azoxystrobin and tolylfluanide. The escape rate from experimental units was lower than 5% in all trials. Additional experiments were performed on P. persimilis eggs by dipping leaves with eggs in the pesticide solution. None of the pesticides affected egg survival. Semi-field trials conducted on potted bean plants obtained results similar to those reported in laboratory trials.

Biological control of mites in European vineyards and the impact of natural vegetation

In vineyards, generalist phytoseiids are important in keeping phytophagous mites at economically acceptable levels. Among these predators, Typhlodromus pyri and Kampimodromus aberrans have proven to be most effective, because they increase in numbers in response to mite pests and alternative prey/food, they persist under conditions of prey scarcity, and they can tolerate several fungicides and insecticides. Natural colonization of commercial vineyards by phytoseiids may take several years. Therefore, strains showing field resistance to certain insecticides (e.g., organophosphates) and fungicides (e.g., mancozeb) are of practical interest. Here we report results obtained with releasing T. pyri and K. aberrans strains with different pesticide histories, with emphasis on factors affecting their persistence, i.e., alternative food availability (pollen or downy mildew), leaf morphology, and selective pesticides. Natural vegetation surrounding vineyards may impact the densities of phytoseiids in neighbouring crops. For example, phytoseiid densities on plants surrounding vineyards under IPM in Southern France (Languedoc-Roussillon) were correlated with leaf structures, and K. aberrans density appeared positively affected by high trichome densities and presence of domatia. Also pollen density was significantly correlated with trichome density and domatia (hair tufts). Predatory mites disperse mainly by air currents and hence their dispersion depends on wind intensity and direction. Crop colonization potential (speed, intensity, uniformity) was directly associated with phytoseiid densities and the proximity of natural vegetation. A deep, dense, and tall woody area with suitable host plants constitutes the stablest source of phytoseiids. Natural colonization of vineyards by phytoseiid mites has great potential and it may well be promoted by careful management.

Ecological and Genetic Differences between Cacopsylla melanoneura (Hemiptera, Psyllidae) Populations Reveal Species Host Plant Preference

The psyllid Cacopsylla melanoneura is considered one of the vectors of ‘Candidatus Phytoplasma mali’, the causal agent of apple proliferation disease. In Northern Italy, overwintered C. melanoneura adults reach apple and hawthorn around the end of January. Nymph development takes place between March and the end of April. The new generation adults migrate onto conifers around mid-June and come back to the host plant species after overwintering. In this study we investigated behavioural differences, genetic differentiation and gene flow between samples of C. melanoneura collected from the two different host plants. Further analyses were performed on some samples collected from conifers. To assess the ecological differences, host-switching experiments were conducted on C. melanoneura samples collected from apple and hawthorn. Furthermore, the genetic structure of the samples was studied by genotyping microsatellite markers. The examined C. melanoneura samples performed better on their native host plant species. This was verified in terms of oviposition and development of the offspring. Data resulting from microsatellite analysis indicated a low, but statistically significant difference between collected-from-apple and hawthorn samples. In conclusion, both ecological and genetic results indicate a differentiation between C. melanoneura samples associated with the two host plants.

Phytoseiid mites — pollen relationships: observations in a vineyard and the surrounding vegetation

The present work is part of a long-term research project devoted to studying the influence of natural vegetation on phytoseiid colonization in vineyards. Observations were carried out in an experimental site including a vineyard and a contiguous hedgerow made up of Acer campestre, Sambucus nigra, Cornus sanguinea, Carpinus betulus and Corylus avellana and structured in pure or mixed modules. The aims of this study were: to evaluate pollen diversity and abundance on the foliage of grapevines and of plants included in the hedgerow, by using acetolysis; to study mite colonization in the vineyard and on different plant species with special emphasis on phytoseiid-pollen relationships.

Differences between sympatric populations of Eotetranychus carpini collected from Vitis vinifera and Carpinus betulus: insights from host-switch experiments and molecular data

Eotetranychus carpini (Oudemans) is an important pest of grapevine (Vitis vinifera L.) in southern Europe. This mite is also found on a number of different plants, including Carpinus betulus L., which commonly occurs in stands and hedgerows bordering vineyards, where it may serve as a potential mite reservoir. The economic importance of this pest has motivated a number of studies aimed at investigating whether the mites found on V. vinifera and C. betulus are conspecific. The results obtained to date have been inconclusive. In this study, we used biological and molecular approaches to investigate this issue. First, we conducted host-switch experiments to test the ability of E. carpini to develop on an alternative host plant, using mite populations originally collected on either C. betulus or V. vinifera plants from the same area. Second, we investigated DNA-based differentiation using nucleotide sequences of the ITS1-5.8S-ITS2 region of the ribosomal DNA of individual E. carpini from the populations examined in our host-plant experiments. We also analyzed sequences of individuals collected in other regions (Italy and Slovenia) to estimate species variation. The results from our host-switch experiments suggest the differentiation of mites collected on the two hosts. Mites collected from C. betulus did not survive and reproduce on V. vinifera and vice versa. Our molecular work revealed significant genetic differentiation between the mites collected from the two hosts, but no evidence of genetic variation among specimens collected from the same host species. Our results indicate the existence of host races of E. carpini.