Leaf pubescence mediates the abundance of non-prey food and the density of the predatory mite Typhlodromus pyri

Plants with leaves having numerous trichomes or domatia frequently harbor greater numbers of phytoseiid mites than do plant with leaves that lack these structures. We tested the hypothesis that this pattern occurs, in part, with Typhlodromus pyri because trichomes increase the capture of pollen or fungal spores that serve as alternative food. Using a common garden orchard, we found that apple varieties with trichome-rich leaves had 2–3 times more pollen and fungal spores compared to varieties with trichome-sparse leaves. We also studied the effects of leaf trichome density and pollen augmentation on T. pyri abundance to test the hypothesis that leaf trichomes mediate pollen and fungal spore capture and retention and thereby influence phytoseiid numbers. Cattail pollen (Typha sp.) was applied weekly to mature ‘McIntosh’ and ‘Red Delicious’ trees grown in an orchard and, in a separate experiment, to potted trees of the same varieties. ‘McIntosh’ trees have leaves with many trichomes whereas leaves on the ‘Red Delicious’ trees have roughly half as many trichomes. With both field-grown and potted trees, adding cattail pollen to ‘Red Delicious’ trees increased T. pyri numbers compared to ‘Red Delicious’ trees without pollen augmentation. In contrast, cattail pollen augmentation had no effect on T. pyri populations on ‘McIntosh’ trees. Augmentation with cattail pollen most likely supplemented a lower supply of naturally available alternative food on ‘Red Delicous’ leaves and thereby enhanced predator abundance. These studies indicate that larger populations of T. pyri on pubescent plants are due, in part, to the increased capture and retention of pollen and fungal spores that serve as alternative foods. This revised version was published online in July 2006 with corrections to the Cover Date.     

The predatory mite Typhlodromus pyri (Acari: Phytoseiidae) causes feeding scars on leaves and fruits of apple

Typhlodromus pyri Scheuten (Acari: Phytoseiidae) is the most important predator of Panonychus ulmi (Koch) (Acari: Tetranychidae) in orchards and vineyards. It was recently found that adult T. pyri females cause microscopic scars on apple leaves. The present laboratory experiments were carried out to confirm the production of scars on apple leaves and to assess if females cause scars on fruits as well. Scar production on apple leaves and/or fruits was investigated under various nutritional conditions: no food, pollen of Scots pine (Pinus sylvsestris L.) only, nymphs of P. ulmi only, and pollen + prey. Both on leaves and fruits, either offered alone or in combination, feeding scars were produced under all nutritional conditions, but mostly in the 'no food' treatment. The predators consumed significantly more P. ulmi nymphs when offered alone than when offered in combination with pollen. T. pyri laid eggs under all nutritional conditions, but mostly in the 'pollen + prey' treatment and least when no food was offered. T. pyri females caused scars on both leaves and fruits when offered simultaneously, but more on leaves than on fruits. The scars were also bigger on leaves than on fruits in all experiments. T. pyri survived and reproduced on plant material in the absence of other food sources. Whether the scars produced on leaves and fruits harm the quality of fruits or the yield of apple cannot be concluded from the present experiments.     

Biological control of the two-spotted spider mite Tetranychus urticae on strawberries by the predatory phytoseiid mite Typhlodromus pyri (Acari, Tetranychidae, Phytoseiidae)

The ‘Mikulov’ strain of the predatory mite Typhlodromus pyri Scheuten from south Moravian vineyards was released on cultivated strawberries infested with the two-spotted spider mite, Tetranychus urticae Koch. The strawberries were grown in field plantations and under glass. Typhlodromus pyri on vine shoots were successfully introduced into the field strawberry plantation but they produced no demonstrable control of the spider mites and they eventually declined in density with their prey. In contrast, T. pyri gave good control of spider mites in the glasshouse despite the occurrence of low humidity and water stress of the plants.     

Powdery mildew (Ascomycotina: Erysiphales) — an alternative food for the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae)

The ability of Typhlodromus pyri Scheuten to feed on powdery mildew was investigated. Adult females of T. pyri which had previously been fed on the pollen of Pinus sylvestris L. were offered three powdery mildew species and their feeding behaviour was observed. The females fed readily on the conidia of Erysiphe orontii Cast. from tobacco and Oidium fragariae Harz. from strawberry while no feeding was observed on Erysiphe polygoni DC. from red clover, even after the mites were starved for 2 days. Erysiphe orontii was tested for its effect on the survival, oviposition and development of T. pyri. The results showed that the conidia of E. orontii can supply mites with the water and nutrients necessary for their normal development. Mature females successfully mated and reproduced, although their oviposition rate was low. This revised version was published online in November 2006 with corrections to the Cover Date.     

The 'island method'– a new laboratory test method to determine side-effects of plant protection products on the predatory mite Typhlodromus pyri Scheuten (Acari, Phytoseiidae)

Abstract: The model introduced here is an open test which produces experimental results of the same quality as a former test model and at the same time achieves considerable savings in both time and materials. The characteristic feature of the present method is that the mites are kept on a treated glass surface floating on water. The water forms a natural barrier ensuring that the mites cannot escape from the treated area.     

Biparental inheritance of RAPD markers in males of the pseudo-arrhenotokous mite Typhlodromus pyri.

In pseudo-arrhenotokous mites, haploid males develop from fertilized eggs that undergo paternal genome loss (PGL) during early embryogenesis. We present evidence that some of the paternal genome may be retained in males of the predatory mite Typhlodromus pyri Scheuten (Acari: Phytoseiidae). Two reproductively compatible populations were differentiated by two random amplified polymorphic DNA markers and the inheritance pattern in the offspring was analysed. Maternal transmission rates are variable and independent of the sex of the offspring and of the marker. These data suggest a nuclear origin and independent segregation of the markers. One marker (330 base pairs (bp)) was paternally transmitted to male as well as female offspring, the other (990 bp) was paternally transmitted to all females and some of the male offspring. We propose that the paternal set of inactivated chromosomes may be partially retained in some tissues of the haploid males or, alternatively, that a B chromosome does not follow the process of PGL in male embryos, thereby segregating with the maternal set. The possible mechanisms controlling the condensation and the segregation of the chromosome(s) retained are discussed on the basis of current hypotheses on chromosome inactivation in insects.     

Effect of seven different pollens on bio-ecological parameters of the predatory mite Typhlodromus foenilis (Acari: Phytoseiidae)

Development, immature survival, reproduction, and life table parameters of the predatory mite Typhlodromus foenilis Oudemans were evaluated on seven different plant pollens (almond, apple, pear, cherry, apricot, plum, and walnut). Experiments were conducted in environmental chambers at 20 +/- 1 degrees C with 65 +/- 5% RH and a photoperiod of 16:8 (L:D). T. foenilis successfully completed its development on all pollen diets. Female mean developmental time from egg to adult emergence ranged from 11.3 +/- 0.12 to 14.28 +/- 0.23 d, whereas that of males was from 10.81 +/- 0.17 to 14.17 +/- 0.17 d. The average life span of adult females varied from 41.0 +/- 1.46 to 65.45 +/- 3.89 d, and total fecundity ranged from 11.78 +/- 0.65 to 39.09 +/- 2.38 eggs/female. The intrinsic rate of increase of T. foenilis was highest on almond pollen (r(m) = 0.104/d) and was the shortest on walnut pollen (r(m) = 0.055/d). The results show that this predatory mite develops well on all pollens, with almond and apricot pollens being of high nutritional value. This study provides further information for mass rearing of T. foenilis, and these findings are discussed in relevance with the establishment of this species in the field.     

Performance of a pyrethroid-resistant strain of the predator mite Typhlodromus pyri (Acari: Phytoseiidae) under different insecticide regimes

An organophosphate pyrethroid-resistant strain of Typhlodromus pyri Scheuten imported from New Zealand was reared on potted apple trees in an outdoor insectary. From 1988 to 1995, the population was selected one to three times per year with a dilute solution (1.7 ppm) of the pyrethroid cypermethrin. Petri dish bioassays with cypermethrin in 1995 indicated that the insectary-reared T. pyri had an LC50 of 81 ppm versus 0.006 ppm for native T. pyri taken from a research orchard. The bioassays suggested that recommended orchard rates of cypermethrin would cause heavy mortality in native populations of T. pyri but only moderate losses in the imported New Zealand strain. Bioassays in 1996 with the organophosphate insecticide dimethoate indicated both New Zealand and native T. pyri were susceptible and that recommended orchard rates of dimethoate likely would cause high mortality of T. pyri in apple orchards. These findings from bioassays were supported by data from orchard trials. In June and July 1993, insectary-reared New Zealand T. pyri were placed on five apple trees in each of eight 38-tree plots in the research orchard. In late August 1994, New Zealand T. pyri from orchard trees that had been sprayed twice by airblast sprayer with the full recommended rate of 50 g (AI)/ha (83 ppm) cypermethrin were placed on the other 33 trees in each of six plots. In the summers of 1994-1996, plots were treated with one of the following insecticide regimes: (1) conventional integrated pest management (IPM) (registered neurotoxic insecticides considered harmless or slightly toxic to T. pyri); (2) advanced IPM (use of newer, more selective insecticides); (3) pyrethroid (at least one full-rate application of cypermethrin); (4) dimethoate; and (5) dimethoate plus pyrethroid. Densities of European red mite, Panonychus ulmi (Koch), were highest in all plots treated with dimethoate and in pyrethroid plots not yet inoculated with New Zealand T. pyri. Densities of apple rust mite, Aculus schlechtendali (Nalepa), and of the stigmaeid predator Zetzellia mali (Ewing) were highest in plots treated with dimethoate and were nearly absent in the IPM plots. Densities of T. pyri were high enough for effective biocontrol in the IPM plots and in the pyrethroid plots 1-2 yr after release of the New Zealand strain, provided pyrethroid was applied just before the resistant strain was released in the orchard. A recurring theme of this study was the generally negative association between densities of phytophagous mites and those of T. pyri, suggesting the ability of this predator to suppress their prey. In contrast, the positive association between phytophagous mites and Z. mali suggests the inability of this predator to regulate their prey at least under the conditions of this study.     

Temperature and diet effects on immature development of predatory mite Typhlodromus athenas Swirski and Ragusa (Acari: Phyotseiidae)

Temperature and food quality both can influence growth rates and developmental time of herbivorous insects and mites. Typhlodromus athenas Swirski and Ragusa is an indigenous mite in the Mediterranean region and data on its temperature dependent development are lacking. In the current study, temperature-dependent development and survival of T. athenas immature stages were evaluated on eggs and all stages of Tetranychus urticae Koch, as well as on almond (Prunus amygdalis Batsch) pollen, under seven constant temperatures ranging from 15 to 35°C, 65% RH, and a photoperiod of 16:8 (L:D) h. On both diets survival was considerably high at all temperatures. The longest developmental period of immature stages was recorded at 15°C, whereas the shortest was at 30°C. Female immatures on almond pollen had shorter developmental time compared to that on twospotted spider mites. Food had a significant effect on female total developmental time at temperatures lower than 25°C. The lower developmental thresholds, estimated by a linear model, for egg-to-adult of females and males fed on pollen were 8.60 and 8.77°C, respectively, whereas on T. urticae they were 10.15 and 10.62°C, respectively. Higher values of tmin for total development were estimated by a nonlinear model (Lactin-2), and ranged from 10.21°C for both females and males on almond, to 11.07 for females and 10.78°C for males on prey. Moreover, this model estimated optimal and lethal temperatures accurately. The results of this study indicate that T. athenas appears better adapted to higher temperatures that occur in the Mediterranean region and may be a useful biological control agent.     

A laboratory study on the predatory mite,Typhlodromus pyri (Acarina: Phytoseiidae). II The effect of temperature and prey consumption on the numerical reponse of adult females

The numerical response of adult female T. pyri feeding on different levels of ERM larvae, and at a range of temperatures was examined. The duration of the pre-oviposition period decreased as larval consumption increased, and the rate of oviposition was linearly related to the rate of consumption of larvae. Mathematical models were used to describe these relationships in terms of temperature and consumption of ERM larvae. The results were discussed in relation to the nature of the T. pyri/ERM interaction in New Zealand apple orchards.     

Intraspecific competition in immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

Intraspecific competition in immature Amblyseius fallacis, Amblyseius andersoni, Typhlodromus occidentalis and Typhlodromus pyri was examined in the laboratory using small cages at five different predator densities (two, four, eight, 16 and 32) in the absence and presence of prey 100 eggs of two-spotted spider mite, Tetranychus urticae (Koch), at 25 ± 1°C, 80% RH and 16L:8D photoperiod. In the absence of spider mite prey, some individuals of immature phytoseiids showed increased development and surival with increasing predator densities up to certain limits, but none survived to the adult stage, except for a single male each of A. andersoni and A. fallacis who completed development by cannibalizing on conspecifics at a density of 32 predators per cage. In the absence of spider mite prey, the mean immature survival time was independent of the initial predator density, but the variance of survival time increased with predator density. In the presence of prey, the proportion of immatures surviving to adulthood generally decreased with initial predator density and dropped sharply to almost none at the predator density of 32 for A. fallacis, eight for A. andersoni, 16 for T. occidentalis and four for T. pyri. The number of prey consumed per predator during the first day generally decreased with predator density in all four species, as prey available per predator decreased and the competition for food increased with predator density. Our data indicate that scramble competition is operating in these four species. Although cannibalism was occasionally observed, especially after the exhaustion of prey and in the generalist predators such as A. andersoni, the immatures of these phytoseiids were less influenced by the interference of conspecifics than by the increasing difficulty of finding food at high predator densities. The implications of this study for understanding phytoseiid population dynamics and their use in biological control are discussed.     

Distribution of the Predatory Mite Typhlodromus pyri (Acari: Phytoseiidae) on Different Apple Cultivars

The effect of apple cultivar on the distribution of the predatory mite Typhlodromus pyri was studied in an experimental orchard where spider mites occurred at negligible densities. Seven apple scab-resistant cultivars, showing some differences in their leaf morphology, were considered. In particular, their leaf blade was classified according to four levels of pubescence. The distribution of T. pyri along the shoots was also studied. In the first experimental year the colonization of different cultivars by T. pyri showed definite patterns, sometimes influenced by the occurrence of eriophyids. One year later, T. pyri abundance again showed some differences among cultivars in conditions of prey scarcity. In both years large phytoseiid populations were recorded on the cultivar N.Y. 18491, despite the low eriophyid occurrence, probably because of its highly pubescent leaf undersurfaces. In contrast, Prima and TSR 29T219, characterized by slightly pubescent leaf undersurfaces, supported low phytoseiid densities independently of prey availability.     

An integrative morphological and molecular diagnostics for Typhlodromus pyri (Acari: Phytoseiidae)

Tixier, M‐S., Okassa, M. & Kreiter, S. (2011). An integrative morphological and molecular diagnostics for Typhlodromus pyri (Acari: Phytoseiidae). —Zoologica Scripta, 41, 68–78. Phytoseiidae species are predators used in biological control programmes to limit mite pests out‐breaks in the world. Specific diagnostic is thus very important to ensure the success of pest management. This study aims to determine the species status of populations within the main species in vineyards and orchards: Typhlodromus (Typhlodromus) pyri, considering four molecular markers (COI, Cytb mtDNAs, 12SrRNA, ITSS) and 34 morphometrical characters. With the three mitochondrial DNA fragments considered, unexpected high genetic distances were observed between two groups, whereas both nuclear DNA and morphological analyses did not show such distinction. Furthermore, the GYMC and the 4 × rule tests emphasised the existence of a single species. Similarly, cross‐breeding experiments between specimens of the two groups showed no reproductive incompatibility. Therefore, despite the great intraspecific variation emphasised by the three mtDNA markers, we conclude that all the specimens considered belong to the same species. The present study clearly underlines the difficulty to conclude on species status using only mt markers and genetic distances, and stresses the necessity to apply multiple approaches for species definition. It also shows the confidence of the morphology for delineating this species.     

Effect of several different pollens on the bio-ecological parameters of the predatory mite Typhlodromus athenas Swirski and Ragusa (Acari: Phytoseiidae)

The development, survivorship, and reproduction of the predacious mite Typhlodromus athenas Swirski and Ragusa were studied in the laboratory by rearing the predator on nine different plant pollens [almond(Prunus amygdalis Batsch), apple (Malus domestica Borkh.), apricot (Prunus armeniaca L.), cherry (Prunus avium L.), pear (Pyrus communis L.), plum (Prunus domestica L.), walnut (Juglans regia L.), olive (Olea europaea L.), Typha sp.], and pollen collected from bee hives. All experiments were conducted in environmental chambers at 20 ± 1°C, 65% RH, and a photoperiod of 16:8 (L:D) h. Survival during immature development ranged from 81.1 to 96.0%. The shortest mean developmental time from egg to adult with respect to the range of pollen species was recorded for females and males fed on almond pollen (10.76 ± 0.18 and 10.45 ± 0.21 d, respectively), while the longest was on beehive pollen (26.97 ± 0.23 and 24.00 ± 0.25 d for females and males, respectively). Female longevity varied from 51.63 ± 5.52 d (olive pollen) to 102.81 ± 6.60 d (pear pollen), while fecundity ranged from 5.33 ± 2.35 eggs per female (beehive pollen) to 26.43 ± 1.73 eggs per female (almond pollen). The diet consisting of almond pollen resulted in the highest intrinsic rate of natural increase (r(m)) (1.00 d(-1)) and pollen collected from bee hives resulted in the lowest (0.013 d(-1)). These results showed that various pollen could favor the development of T. athenas, and also support the view that alternative food resources may play an important role in the field for sustaining and increasing the predator's population.     

Interspecific competition and predation between immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

Interspecific competition and predation in immature Amblyseius fallacis (Garman), Amblyseius andersoni Chant, Typhlodromus occidentalis (Nesbitt) and Typhlodromus pyri Scheuten were examined in small cages at three egg densities (0, 20 and 80) of two-spotted spider mite, Tetranychus urticae Koch, in the laboratory at 25±1°C,80% RH and 16L: 8D photoperiod. For the six possible between-species comparisons, the large polyphagous A. andersoni always outcompeted the other three predator species, which were either smaller and/or less polyphagous; the small oligophagous T. occidentalis was always eliminated by the other three predator species, which were either larger and/or more polyphagous. The small and polyphagous T. pyri tied with the large and oligophagous A. fallacis. The outcome of the interaction was generally similar at the three prey densities except in (1) the A. fallacis-A. andersoni system where the advantage of A. andersoni over A. fallacis was reduced when 20 or 80 eggs per cage were present at the start of the interaction and (2) the A. fallacis-T. occidentalis system where the advantage of A. fallacis over T. occidentalis increased with prey density. This study indicates that predator size, predator degree of polyphagy and prey density can affect the competitiveness of immature phytoseiids.     

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 r ( m ) 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 r ( m ) 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.     

Hedges as potential sources ofTyphlodromus pyri,the most important predatory mite in vineyards of Northern Switzerland

This paper presents the results of an acarological survey started in 1984 in hedges bordering vineyards in Northern Switzerland where natural populations of the economically important predatory miteTyphlodromus pyri occur. The objective of these investigations was to identify those plant species in the hedges and forest margins adjacent to vineyards that carry high populations of this important predator, and to evaluate the potential role of hedges as ecological refuges and sources ofT. pyri. We found high and consistent densities ofT. pyri onRubus fruticosus, and less regularly onCornus sanguinea, Corylus avellana andLonicara xylosteum. We conclude that hedges can provide ecological refuges and sources of this economically important predatory mite where earlier applications of inappropriate pesticides have eliminated these important antagonists. However, the inoculative release ofT. pyri along with the increase of the internal ecological diversity of the vineyard achieved by proper management of the green over plants (“weed”) will have a strong influence on predator densities within the vineyards.      

Olfactory response of Typhlodromus pyri (Acari: Phytoseiidae) to synthetic methyl salicylate in laboratory bioassays

The herbivore‐induced plant volatile (HIPV) methyl salicylate (MeSA) is widely present in the chemical profile of several plant species and is known to attract natural enemies, including predatory mites. In this study, the response of Typhlodromus pyri, a key predator of pest mites in west coast vineyards, to synthetically produced MeSA was tested using a Y‐tube olfactometer in laboratory bioassays. Six doses ranging from 0.002 to 200 μg of MeSA diluted in 0.1 ml hexane were tested. Significantly higher proportions of T. pyri preferred MeSA at doses 0.02, 0.2 and 20 μg. No differences in response to MeSA were detected at the highest (200 μg), intermediate (2 μg) and lowest (0.002 μg) doses. Mite response to MeSA was a function of dose when fitting polynomial and logistic regression models using dose and square of the log dose prediction factors. Results indicate that synthetic MeSA may be applied to attract predatory arthropod populations in vineyards to enhance biological control of pest mites.     

Temperature-related development and population parameters for Typhlodromus pyri (Acari: Phytoseiidae) found in Oregon vineyards

The beneficial mite Typhlodromus pyri is a key predator of grapevine rust mite Calepitrimerus vitis in Pacific coastal vineyards. Rust mite feeding has been associated with damage such as stunted, deformed shoot growth and reductions in fruit yield. The life history traits of T. pyri were assessed at seven constant temperatures (12.5, 15, 17.5, 20, 25, 30 and 35 °C) to determine population parameters providing data to better predict biological control of C. vitis populations by T. pyri in vineyards. Successful development from the egg to adult stage was observed at temperatures ranging from 15 to 30 °C. Constant exposure to 12.5 and 35 °C resulted in 100 % mortality in immature T. pyri. Developmental times, fecundity and longevity were highest at 25 °C. The estimated minimum and maximum developmental thresholds were 7.24 and 42.56 °C, respectively. Intrinsic rate of increase (r ( m )) was positive from 15 to 30 °C indicating population growth within this range of temperatures. Net reproductive rate and intrinsic rate of increase were greatest at 25 °C. These developmental parameters can be used to estimate population growth, determine seasonal phenology and aid in conservation management of T. pyri. Results presented in this study will aid in evaluating the effectiveness of T. pyri as a key biological control agent of C. vitis during different periods of the growing season in Pacific Northwest vineyards.     

The effect of powdery mildew on the number of prey consumed by Typhlodromus pyri (Acari: Phytoseiidae)

Abstract:  Prey consumption by Typhlodromus pyri Scheuten was studied in the presence and absence of apple powdery mildew, Podosphaera leucotricha (Ell. and Everh.) under constant laboratory conditions. Eggs of Tetranychus urticae Koch were offered to predatory mites as a prey. Seven densities ranging from five to 100 T. urticae eggs per arena were used. Mildew conidia (approximately 0.5 mg) were added to half of the arenas by brushing them from infected apple leaves. A single adult female of T. pyri was introduced onto each arena and number of prey eggs consumed was counted 12 h later when the predator was offered new T. urticae eggs again and the procedure was repeated once. Data showed that predators consumed in both experimental periods nearly all prey in experiments with densities up to 40 eggs per arena and no mildew. However, the number of eggs consumed decreased more than twofold when mildew conidia were supplied, even at high prey densities. Differences in predation rate between treatments with and without mildew were highly significant. The results thus indicate that availability of mildew as an alternative food can reduce prey suppression by T. pyri . Possible implications of these findings in biological control of spider mites by generalist predatory mites are discussed.