Alberto Pozzebon

Grape downy mildew spread and mite seasonal abundance in vineyards: evidence for the predatory mites Amblyseius andersoni and Typhlodromus pyri

Abstract Mite populations, in particular those belonging to the Phytoseiidae family were monitored in a commercial vineyard comprising two varieties (Prosecco and Pinot gris). On Prosecco, densities of Amblyseius andersoni , and to a lesser extent of Typhlodromus pyri increased when downy mildew symptoms occurred on a high number of leaves. On Pinot, A. andersoni was the dominant species and its densities markedly increased when downy mildew spread. A. andersoni populations were significantly larger on leaves with downy mildew symptoms than on leaves without symptoms and their densities were positively correlated to the extent of leaf surface showing symptoms. The effect of downy mildew on T. pyri populations was less marked. There were no relationships between downy mildew spread and spider mite abundance ( Panonychus ulmi ). Untreated plots or plots treated with folpet to control downy mildew were monitored in an experimental vineyard colonized by A. andersoni . A. andersoni populations increased when downy mildew symptoms spread and their densities were significantly higher in the control than on folpet plots. In another experimental vineyard, T. pyri densities were significantly higher in the control (severely infected by downy mildew) than on copper hydroxide plots. Isoelectric focusing electrophoresis (IEF) was employed to detect downy mildew in mites and glucose phosphate isomerase (GPI) was selected from among different enzymes. A stain corresponding to downy mildew in addition to the phytoseiid intrinsic stains was detected in a high proportion of A. andersoni and T. pyri collected from infected leaves. Downy mildew stains were not detected in P. ulmi females collected from infected leaves. Most A. andersoni and T. pyri females confined on symptomatic leaves became positive to IEF a few hours later.

Toxicity of thiamethoxam to Tetranychus urticae Koch and Phytoseiulus persimilis Athias-Henriot (Acari Tetranychidae, Phytoseiidae) through different routes of exposure.

BACKGROUND Knowledge of the impact of insecticides on Tetranychus urticae Koch and its predator Phytoseiulus persimilis Athias-Henriot is crucial for IPM. This study evaluates the effect of thiamethoxam on T. urticae and its predator by considering different routes of exposure (topical, residual and contaminated food exposures) and their combinations. RESULTS Thiamethoxam effects on T. urticae were higher when residual and contaminated food exposures were considered. The total effect was higher than 90% where contaminated food exposure was involved. On P. persimilis, the total effect was higher in residual and contaminated prey exposures compared with topical exposure, and all combinations of routes of exposure attained a total effect higher than 90%. CONCLUSION Thiamethoxam was found to be toxic to T. urticae and P. persimilis; however, the impact of the insecticide depended on the routes of exposure and their combinations. Lethal and sublethal effects occurred in residual and contaminated food exposures, while only sublethal effects occurred in topical exposure of predators and prey. The toxicity of thiamethoxam on prey and predator increased with the number of exposure routes involved. By limiting exposure to thiamethoxam to ingestion of contaminated food only, the impact of the pesticide was more favourable to P. persimilis than to its prey.

Effects of potential food sources on biological and demographic parameters of the predatory mites Kampimodromus aberrans, Typhlodromus pyri and Amblyseius andersoni.

Kampimodromus aberrans, Typhlodromus pyri and Amblyseius andersoni are generalist predatory mites important in controlling tetranychid and eriophyoid mites in European vineyards. They can persist by exploiting various non-prey foods when their main prey is absent or scarce. A comparative analysis of the effects of various prey and non-prey foods on the life history of these predators is lacking. In the laboratory, predatory mites were reared on herbivorous mites (Panonychus ulmi, Eotetranychus carpini and Colomerus vitis), a potential alternative prey (Tydeus caudatus) and two non-prey foods, i.e. the pollen of Typha latifolia and the mycelium of Grape downy mildew (GDM) Plasmopara viticola. Developmental times, survival, sex ratio and fecundity as well as life table parameters were estimated. Kampimodromus aberrans developed faster on E. carpini, C. vitis or pollen than on P. ulmi and laid more eggs on pollen than on prey. Low numbers of this predator developed on GDM infected leaves. Tydeus caudatus was not suitable as prey for any of the three predatory mites. Kampimodromus aberrans showed the highest intrinsic rate of population increase when fed on pollen. Developmental times of T. pyri on prey or pollen were similar but fecundity was higher on pollen than on P. ulmi. Typhlodromus pyri had higher intrinsic rates of population increase on C. vitis and pollen than on P. ulmi; E. carpini showed intermediate values whereas GDM resulted in the lowest rm values. Development of A. andersoni females was faster on pollen and C. vitis than on P. ulmi and GDM. Fecundity was higher on pollen and mites compared to GDM. Life table parameters of A. andersoni did not differ when predators were fed with prey or pollen while GDM led to a lower rm value. On a specific diet A. andersoni exhibited faster development and higher fecundity than T. pyri and K. aberrans. These findings improve knowledge on factors affecting the potential of predatory mites in controlling phytophagous mites in European vineyards.

Does pollen availability mitigate the impact of pesticides on generalist predatory mites

The effect of the provision of pollen on the impact of pesticides on the predatory mite Kampimodromus aberrans was assessed at individual and population levels. In the laboratory we evaluated the influence of pollen amount and pollen application frequency on lethal and sub-lethal effects of chlorpyrifos and spinosad. In a potted plant experiment, the effects of pesticides and pollen were assessed on predatory mite population abundance. In the laboratory, survival and fecundity of predatory mites were reduced by insecticides, and spinosad was more toxic than chlorpyrifos. In the same experiment, high pollen application frequency alleviated the sub-lethal effect induced by chlorpyrifos. On potted plants, pollen applications reduced the impact of chlorpyrifos on K. aberrans, whereas without pollen applications the impact of spinosad and chlorpyrifos on the predatory mite population was similar. Results obtained here highlight that the provision of fresh pollen is of particular importance for predatory mites when pesticides are applied.

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.

Management of Phytophagous Mites in European Vineyards

The first infestations of spider mites in European vineyards were detected in the second half of the nineteenth century after the invasion of powdery mildew, downy mildew and phylloxera from North America. Serious problems associated with Tetranychus urticae Koch were detected in Italy and Austria and local outbreaks of Panonychus ulmi (Koch) were recorded. At that time the eriophyid Colomerus vitis (Pagenstecher) was known but not considered important, probably because sulfur was largely used to control grape diseases. Two additional species were described at the beginning of the twentieth century: the spider mite Eotetranychus carpini (Oudemans) and the eriophyid Calepitrimerus vitis (Nalepa). At that time, problems with mites injurious to grapes were negligible but the situation suddenly changed after World War II. Most of these problems were immediately associated with the extensive use of chlorinated hydrocarbon insecticides and later, by ethylene-bis-dithiocarbamate fungicides (EBDC). Three spider mite species were involved in the outbreaks: E. carpini, P. ulmi and T. urticae (Rambier 1958; Rota 1962; Zangheri and Masutti 1962). Most researchers of the time thought that mite outbreaks were due to the detrimental effects of pesticides on natural enemies of spider mites. However, there was little evidence to support this fact. Meanwhile, according to Chaboussou (1965) infestations were caused by changes in plant physiology induced by organic pesticides, favorable to mite demographic parameters (‘trophobiosis’). Chaboussou (1965) and others also tried to classify the most common pesticides according to their effect on spider mites. However, contradictory results were reported and no scientific proof could be obtained, and trophobiosis remained a matter of great debate among entomologists.

Pesticide side-effects on predatory mites: the role of trophic interactions

The control of spider mites in protected crops is often critical due to the development of mite resistance to acaricides. Studies of the side-effects of pesticides on beneficial mites are required in order to improve integrated spider mite management. Pesticide side-effects on predatory mites of the family Phytoseiidae can be studied at the field or laboratory level. In the field, phytoseiid abundance can be related to the presence of prey and/or alternative foods, which can affect the response of predatory mites to pesticides. We investigated whether pesticide side-effects on phytoseiids may be mediated by trophic interactions. In the laboratory we evaluated the effects of two insecticides (derived from pyrethrins and Beauveria bassiana) on the predatory mite Phytoseiulus persimilis by testing the same under various exposure conditions (leaf residues, treated prey, topical application). The effects of these insecticides on P. persimilis were higher when the predators were fed with treated prey. Furthermore, we investigated the effects of pyrethrins on the predatory mite Amblyseius andersoni on vines with low or high incidence of the plant pathogenic fungus Plasmopara viticola (grape downy mildew, GDM). GDM mediated interactions between pyrethrins and A. andersoni since it is alternative food for this predatory mite. The implications of these studies for the development of toxicological methods and integrated pest management are discussed.

Role of supplemental foods and habitat structural complexity in persistence and coexistence of generalist predatory mites

Plant traits can influence the interactions between herbivore arthropods and their natural enemies. In these interactions generalist predators are often present, preying on herbivores and also on other arthropods in the same trophic guild. Variation in the strength of intraguild predation (IGP) may be related to habitat structural complexity and to additional resources outside the narrow predator-prey relationship. In this paper we study the food web interactions on grape, which involves two generalist predatory mites. We evaluated the effects of grape powdery mildew (GPM) as supplemental food, and habitat structural complexity provided by domatia. The inoculation of GPM resulted in higher predatory mite densities and reduced the negative impact of unfavorable leaf structure for one species. Access to domatia was the main factor in promoting population abundance and persistence of predatory mites. Access to domatia and GPM availability favored the coexistence of predatory mites at a low density of the intraguild prey. Our findings suggest that structural and nutritional diversity/complexity promote predatory mite abundance and can help to maintain the beneficial mites - plants association. The effect of these factors on coexistence between predators is influenced by the supplemental food quality and relative differences in body size of interacting species.

A Fundamental Step in IPM on Grapevine: Evaluating the Side Effects of Pesticides on Predatory Mites.

Knowledge on side effects of pesticides on non-target beneficial arthropods is a key point in Integrated Pest Management (IPM). Here we present the results of four experiments conducted in vineyards where the effects of chlorpyrifos, thiamethoxam, indoxacarb, flufenoxuron, and tebufenozide were evaluated on the generalist predatory mites Typhlodromus pyri Scheuten and Amblyseius andersoni (Chant), key biocontrol agents of herbivorous mites on grapevines. Results show that indoxacarb and tebufenozide had a low impact on the predatory mites considered here, while a significant impact was observed for chlorpyrifos, flufenoxuron, and thiamethoxam. The information obtained here should be considered in the design of IPM strategies on grapevine.

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.