Effects of agroforestry on phytoseiid mite communities (Acari: Phytoseiidae) in vineyards in the South of France

The abundance and diversity of phytoseiid mites were surveyed from April to September 2003 to 2005 in vineyards (Grenache and Syrah cultivars) co-planted with rows of Sorbus domestica or Pinus pinea and in monoculture plots of grapes in the South of France. Densities of phytoseiid mites were different on the two tree species, with P. pinea a more suitable host than S. domestica. Typhlodromus (Typhlodromus) exhilaratus was the dominant species occurring on grapes and on co-planted rows of S. domestica and P. pinea, whereas T. (T.) phialatus was the most abundant species in monoculture plots of both S. domestica and P. pinea. Factors determining the dominance of T. (T.) phialatus over T. (T.) exhilaratus in monoculture trees are discussed. In this study, agroforestry management did not affect phytoseiid diversity in vineyards, but did affect phytoseiid density, especially in 2005. The results obtained in 2003 and 2004 are not easy to discuss in this regard because of the low densities of mites observed during these 2 years (very dry climatic conditions and pesticide applications).     

A Genetic Analysis of Mancozeb Resistance in Typhlodromus Pyri (Acari: Phytoseiidae)

A field population of Typhlodromus pyri (Acari: Phytoseiidae) tolerant to mancozeb was selected in the laboratory. After 10 mancozeb selections the LC₅₀ value for mancozeb was 73 times higher in the selected-10 strain compared to the standard susceptible strain. A genetic analysis using reciprocal crosses and backcrosses of female F₁ progeny found no maternal effect. Resistance in the selected-10 strain was codominant in expression, dominance value was about −0.1. Backcrosses between F₁ females and the susceptible strain indicate that the resistance to mancozeb could be principally conferred by a predominant gene, but additional factors would also be involved.     

Toxicity of a number of pesticides to strains ofTyphlodromus pyri andAmblyseius andersoni (Acari: Phytoseiidae)

Side effects of ten pesticides used in orchards and vineyards were tested with a laboratory method on several Dutch and Italian strains of the predatory mitesTyphlodromus pyri Scheuten andAmblyseius andersoni (Chant). Resistant and susceptible strains of both species were studied. Results showed that a test which evaluates mortality of various developmental stages and fecundity of adult females is better than one that measures only survival of adult females. A definite resistance to certain pesticides was found in ItalianT. pyri andA. andersoni. The level of resistance to parathion, azinphos-methyl and carbaryl was particularly high in some strains ofA. andersoni. The high level of resistance to certain pesticides was often associated with a marked reduction in fecundity.      

Comparative life-history traits of three phytoseiid mites associated with Tetranychus urticae (Acari: Tetranychidae) colonies in clementine orchards in eastern Spain: implications for biological control

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25°C, 80 ± 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (r _m) was significantly higher for P. persimilis (0.344 day⁻¹) than for N. californicus (0.244 day⁻¹) and both were higher than the r _m value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.     

Predatory behaviors of Neoseiulus californicus and Galendromus helveolus (Acari: Phytoseiidae) attacking Oligonychus perseae (Acari: Tetranychidae)

Predatory behaviors of Neoseiulus californicus (McGregor) and Galendromus helveolus (Chant) attacking Oligonychus perseae Tuttle, Baker and Abbatiello on avocado leaves were videotaped and analyzed. Behaviors were recorded for “fresh” predators that were used ≤ 48 hr post receipt from a commercial insectary and “cold stored” predators that were maintained at 12°C for ≈ 14 days. Fresh and cold stored G. helveolus were observed to attack O. perseae only after invading webbed nests. Conversely, fresh and cold stored N. californicus employed three different modes of predatory attack: (1) intercepting and attacking migrant O. perseae outside of web nests; (2) attacking prey through nest webbing; or (3) invading and attacking O. perseae inside nests. Predatory efficacy of both N. californicus and G. helveolus was reduced following cold storage, as both species engaged in certain predatory behaviors less frequently in comparison to predators that were not stored at low temperatures. Our observed results for N. californicus and G. helveolus attacking O. perseae are interpreted in relation to the chaetotaxy hypothesis, which proposes that phytoseiid invasion efficiency and propensity of webbed nests is facilitated by dorsal setal lengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

有益真绥螨与巴氏新小绥螨的集团内捕食和同类相残作用

【目的】有益真绥螨Euseius utilis是北方地区广泛分布的一种多食性植绥螨,而巴氏新小绥螨Neoseiulus barkeri目前在我国广泛应用于农业害虫的生物防治中。本研究旨在对巴氏新小绥螨在本地的应用进行风险评估及为与有益真绥螨的联合释放提供依据。【方法】本研究在室内通过一系列实验,比较了实验室饲养的巴氏新小绥螨和采自内蒙古农业大学校园的有益真绥螨的雌成螨对同种或异种未成熟螨的捕食量、存活时间及产卵量的差异,检测了有益真绥螨与巴氏新小绥螨两种植绥螨相互之间的攻击强度以及种内和种间的相互作用。【结果】两种植绥螨都难以刺吸同种或异种植绥螨的卵,而对同种或异种植绥螨幼螨的捕食量最大,其次是对若螨。在无共同食物的情况下,有益真绥螨雌成螨对同种植绥螨幼螨的攻击性比对异种植绥螨幼螨的攻击性强(BreslowDay检验:χ~2=13.84,df=1,P0.001),且有益真绥螨对同种植绥螨幼螨的捕食量(9.10±1.65头)高于对异种植绥螨幼螨的捕食量(5.31±1.43头)(T检验:t=5.487,P0.001),巴氏新小绥螨对异种植绥螨幼螨的捕食量(7.48±0.75头)高于对同种植绥螨幼螨的捕食量(4.75±0.58头)(T检验:t=9.110,P0.05)。【结论】有益真绥螨更倾向于捕食同种幼螨而发生同类相残;巴氏新小绥螨更倾向于捕食异种幼螨而发生集团内捕食。     

Location,reproduction and movement of Neoseiulus californicus (Acari: Phytoseiidae) during the autumn,winter and spring in orchards in the south of France

Field samples and experiments conducted in apple orchards in the south of France showed that Neoseiulus californicus (McGregor) searched for prey on the trees and in the ground cover as late as mid-November 1993, and at least as early in the spring as the end of February 1994. Overwintering females fed, expanded and produced viable eggs within 7.9±0.3 (SE) days given the natural light regime, adequate food and temperatures of 17.0±20.6°C. The first generation of N. californicus developed in the field during March and April 1994. N. californicus nymphs, females and males readily moved over bare ground and through a grass ground cover to trap plants located on stakes 1 m above the ground. In the laboratory, the rate of movement of adult females on 0.5 mm copper wire was a linear function of temperature above a threshold of 11.9±0.9°C. At 25°C they travelled 10 m per h. The migration rate of N. californicus to trap plants on stakes placed in an orchard 13 Apr. increased in 2 weeks from 0.07 to 0.57 predators/trap plant/degree-day, while the migration rate to plants placed directly in the ground cover was 1.45 predators/trap plant/degree-day. The largest population of N. californicus in April occurred on Barley, Hordeum murinum L. This plant produces pollen in April and May, and may be useful in biocontrol programs.     

Life-history of predatory mites Neoseiulus californicus and Phytoseiulus persimilis (Acari: Phytoseiidae) on four spider mite species as prey, with special reference to Tetranychus evansi (Acari: Tetranychidae)

The commercially available strains of Phytoseiulus persimilis Athias-Henriot, the biological control agent of Tetranychus urticae Koch, perform poorly in the Western Mediterranean, probably because they are not well adapted to local climatic conditions. For that reason, efforts are being focused on the development of a biological control programme using native phytoseiid mites. Four species of red spider mites can be found in vegetable crops in eastern Spain: T. urticae, Tetranychus turkestani Ugarov and Nikolski, Tetranychus ludeni Zacher and the recently introduced Tetranychus evansi Baker and Pritchard. To evaluate their potential role as biological control agents, the present study evaluates the life-history of local populations of Neoseiulus californicus (McGregor) and P. persimilis when fed on T. urticae, T. turkestani, T. evansi, and T. ludeni in the laboratory. Results indicate that N. californicus and P. persimilis are able to feed and complete their development on the four tested red spider mite species. The predators may exhibit a particularly high capacity for population increase when fed on T. urticae, T. turkestani, and T. ludeni, thus may be able to provide effective control of these species in the field. When fed T. evansi, however, predator performance was poor; significant increase in development and preoviposition times, and a reduction in oviposition period and fecundity were recorded. The resultant low capacity for population growth suggests poor ability of the two tested predators to suppress T. evansi populations on commercial crops. It is unlikely therefore that P. persimilis and N. californicus, now being widely used to control T. urticae in greenhouse crops in Central Europe, will be able to halt any spread of T. evansi to greenhouse crops in temperate areas.     

Side effects of mancozeb on Typhlodromus pyri (Acari: Phytoseiidae) in vineyards: results of multi-year field trials and a laboratory study

The side effects of mancozeb on the predatory mite Typhlodromus pyri were studied in 4-year field trials on grapevine and in the laboratory. In the field, the effect of mancozeb varied according to previous mancozeb use. In vineyards where mancozeb had commonly been used over years, this fungicide is generally slightly toxic, in some cases moderately toxic and rarely toxic. In plots were mancozeb has never been used, its effect on T. pyri was more pronounced and varied from moderately toxic to toxic. Despite the toxicity of mancozeb, T. pyri populations have never been eradicated. Laboratory results obtained with the French CEB guideline no. 167 confirmed those of the 4-year field study: mancozeb was significantly more toxic to T. pyri populations collected in plots where it had rarely been used before the field experiment. In plots where mancozeb had been used for a long time, the susceptibility of T. pyri populations to this fungicide was reduced and female survival, fecundity but also viability of female progeny were less affected by mancozeb. Even though toxicity of mancozeb increased in controlled conditions, a significant correlation was established between field and laboratory results.     

Detecting variability and selecting for pesticide resistance in two species of phytoseiid mites

Methods used for evaluating the effects of pesticides and selecting for pesticide resistance in phytoseiid mites are reviewed from recent literature. In particular slide dip, leaf dip, and leaf disc spray methods are compared. The selection of predatory mites (Typhlodromus pyri Scheuten andPhytoseiulus persimilis Athias-Henriot) for resistance to 3 synthetic pyrethroids (SP-cypermethrin, deltamethrin, and fenvalerate) is described. Tolerance of field populations to all 3 SP was low inP. persimilis but moderate inT. pyri. Field samples of both mite species on leaf discs were sprayed and the survivors were reared in laboratory and/or glasshouse cultures. These cultures were sprayed with repeated doses of SP; initiallyT. pyri was selected with cypermethrin andP. persimilis with fenvalerate. The survival rate ofT. pyri increased at each selection. After 6 selections the survival rate of the laboratory culture was 10 times that of the original field samples. Tests indicated crossresistance inT. pyri to fenvalerate and deltamethrin. Selection with cypermethrin is continuing. In the first 12 months repeated selections ofP. persimilis with fenvalerate gave no significant change in survival rate.

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Résumé Les méthodes utilisées pour évaluer les effets des pesticides et pour sélectionner la résistance à ces mêmes produits, des acariens phytoseiides sont analysées d'après la littérature récente. La sélection des acariens prédateurs (Typhlodromus pyri S{upcheuten} etPhytoseiulus persimilis A{upthias}-H{upenriot}) pour leur résistance aux 3 pyréthrinoides de synthèse (cyperméthrine, deltaméthrine et fenvalerate) est décrite. La tolérance des populations naturelles aux 3 pyréthrinoides de synthèse était basse pourP. persimilis, mais modérée pourT. pyri. Les échantillons des 2 espèces d'acariens prélevés à l'extérieur furent traitès sur des disques de feuilles et les survivants furent élevés au laboratoire et/ou dans des cultures en serre. Ces élevages furent traités avec des doses répétées d'un pyréthrinoide, cyperméthrine initialement pourT. pyri et fenvalerate pourP. persimilis. Le taux de survie deT. pyri augmentait à chaque sélection. Après 6 sélections, le taux de survie de l'élevage de laboratoire était 10 fois celui des échantillons d'origine. Les essais révélaient une résistance croisée deT. pyri à la fenvalerate et à la deltaméthrine. La sélection avec la cyperméthrine se poursuit. Au cours des 12 premiers mois, les sélections répétées deP. persimilis avec la fenvalerate ne donnait pas de changement significatif dans le taux de survie.

     

Neoseiulus Californicus (Acari: Phytoseiidae) as a Potential Control Agent of Tetranychus Urticae (Acari: Tetranychidae): Effect of Pest/Predator Ratio on Pest Abundance on Strawberry

Neoseiulus californicus (McGregor) is a promising agent for successful Tetranychus urticae Koch control through conservation techniques, in strawberry crops in La Plata (Buenos Aires, Argentina). In prey–predator interaction, initial relative densities have an important effect on system dynamics. The economic threshold level (ETL) used for this pest in the present study was 50 active mites per leaflet. In our laboratory experiments, initial T. urticae to N. californicus ratio had a significant effect on the population abundance of T. urticae at a 7-day period. When pest/predator ratio was 5/1 (at initial pest densities from 5 to 15 females/leaflet) the final number of active T. urticae/leaflet was significantly lower than the ETL, while at 20 females/leaflet this number did not differ from the ETL. At 7.5/1 ratio, the final number of active T. urticae/leaflet, at initial pest densities from 5 to 15 females/leaflet, reached the ETL without surpassing it. At 10/1 and 15/1 ratios, pest densities exceeded the ETL only at 15 initial T. urticae/leaflet. Most greenhouse and field observations were consistent with the predictions of a graphical model based on experimental results. This predator was very effective in limiting pest densities at a 7-day period and within the range of pest–predator ratios and absolute densities used in this study. Conservation of N. californicus promoting favorable pest/predator ratios may result in early control of T. urticae.     

Biological control of strawberry tarsonemid mite Phytonemus pallidus and two-spotted spider mite Tetranychus urticae on strawberry in the UK using species of Neoseiulus (Amblyseius) (Acari: Phytoseiidae)

Two species of Neoseiulus, N. californicus and N. cucumeris, showed potential for biocontrol of phytophagous mites on strawberry. N. californicus controlled Tetranychus urticae on potted strawberry plants in a gauze-sided glasshouse at temperatures comparableto early summer in the UK (8–20°C). Both species of phytoseiid reducednumbers of the tarsonemid Phytonemus pallidus on potted strawberry plants under glasshouse conditions (15–23°C). In several experiments reductions in the range of 71–81% in numbers of tarsonemid active stages and eggs, compared to non-release plants, were obtained. The importance of establishing a suitable predator: prey ratio at an earlystage was demonstrated in an experiment where an initial ratio of 1 N. cucumeris: 10 P. pallidus gave a greater degree of controlthan 1:20 or 1:40.     

Effects of starvation on reproduction of the predacious mite <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> (Acari: Phytoseiidae)

Effects of starvation on gravid females of Neoseiulus californicus were investigated at 20°C and 85% RH. When females that had been reared with abundant prey were swapped, just after laying their first egg, to conditions without any prey and water, they laid 1.8 eggs and survived for 4.3 days. In the body of well-fed females, an egg with eggshell and/or two oocytes were observed in the ventral and dorsal regions, respectively. The larger oocyte had two roundish nuclei and abundant yolk granules, and was enveloped with a vitelline membrane. These two nuclei were not fused but were just close to each other. The smaller oocyte had a nucleus, but had not yet formed yolk granules and vitelline membrane. Females after 12 h starvation had an egg in the ventral region and an oocyte in the dorsal region of the body. After more than 24 h starvation females maintained an oocyte in the dorsal region of the body, but had no egg in the ventral region. The oocyte was filled with abundant yolk granules and contained two irregular nuclei when females were starved for 24 h, but when starved for more than 36 h it contained one irregular nucleus. These findings suggest that (1) gravid females maintained an oocyte in the dorsal region after laying two eggs during starvation, (2) the oocyte was not absorbed during starvation, (3) the oocyte advanced vitellogenesis and the fusion of two nuclei, and (4) the vitellogenic oocyte was not enveloped with an eggshell and had not started embryogenesis.     

Prey-food types of Neoseiulus fallacis (Acari:Phytoseiidae) and literature versus experimentally derived prey-food estimates for five phytoseiid species

The ability of Neoseiulus fallacis (Garman) to survive, reproduce and develop on a range of prey-food types was studied by holding adult females with each of 27 different prey-foods for 7 days. Survival and activity of adult females, eggs produced per female per day and quantity of immatures produced per female per day were estimated. Survival, reproduction and development were the highest and activity the lowest when held with Tetranychus species. Reproduction, survival and development were lower on non-tetranychid food although examples from nearly all prey-food types provided higher measured values than when without food. Proportional reproduction of N. fallacis on Tetranychus spider mites, other spider mites, eriophyid mites, other mites, insects and pollen was calculated. Proportions then were compared to values derived from a prey-food model based on the frequency of literature citations. The overall fit between data sets was good for the specialist type II species N. fallacis. Reproductive proportions for experimentally derived and literature-based data were estimated for four other phytoseiids that represent the specialist and generalist life style types I–IV: Phytoseiulus persimilis A. H., Typhlodromus pyri Scheuten, Euseius finlandicus (Oudemans) and Euseius hibisci (Chant). The literature model, based on records of feeding tests, did well in predicting feeding preference based on ovipositional rates for the specialist type I, P. persimilis, but was less accurate for the generalist type III, T. pyri and the generalists type IV, E. finlandicus and E. hibisci. Means to improve prey-food preference estimates for all life style types of phytoseiid species are discussed.     

Food scarcity reduces female longevity of <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> (Acari: Phytoseiidae)

A commercial strain of Neoseiulus californicus (Spical^®) has a conspicuously long postoviposition period in comparison with other strains of N. californicus or other phytoseiid mites. In many insects and mites, life span is shorter for multiple-mated females than for single-mated females, and is shorter under poor prey conditions than under ample prey conditions. We previously showed that the postoviposition period of multiple-mated females was 40% shorter than that of single-mated females, but that it was never shorter than 30 days. Here we focused on the effect of prey abundance on the postoviposition period. We examined three groups of multiple-mated females: mites that were fed ample prey (group I), mites that were subjected to repeated cycles of 2 days of fasting followed by 2 days of ample prey (group II), and mites that were subjected to repeated cycles of 4 days of fasting followed by 2 days of ample prey (group III). The postoviposition periods of groups II and III were 90% shorter than that of group I. Also the total adult longevity was significantly shorter in groups II and III than in group I. Total egg production in group III was about half that in groups I and II, although the oviposition periods in groups II and III were significantly longer than that in group I. These results suggest that the prolonged postoviposition period in single-mated females of the Spical strain may only appear under laboratory conditions, without multiple mating or starvation.     

Sublethal effects of esfenvalerate residues on pyrethroid resistant Typhlodromus pyri (Acari: Phytoseiidae) and its prey Panonychus ulmi and Tetranychus urticae (Acari: Tetranychidae)

The effect of residues of esfenvalerate on oviposition of the resistant strain of the predatory mite Typhlodromus pyri and its main prey, European red mite Panonychus ulmi and two-spotted spider mite Tetranychus urticae, were investigated. T. pyri showed a significant linear reduction in oviposition after 24h in the presence of increasing levels of esfenvalerate residue applied at the field rate. Furthermore, when given a choice, T. pyri preferred to lay eggs on residue-free surfaces. Of the two prey species, only P. ulmi showed significant avoidance of increasing levels of residues of the field rate concentration of esfenvalerate, as measured by runoff mortality, however both P. ulmi and T. urticae, when given a choice, showed a preference for esfenvalerate-free surfaces. As with the predatory mite T. pyri, both prey species showed a significant linear reduction of oviposition with increasing esfenvalerate residues and a preference to lay eggs on esfenvalerate-free surfaces. Esfenvalerate residues as high as 15X field rate were not repellent to pyrethroid-resistant T. pyri. The possible effects of these sublethal effects on predator-prey dynamics and implications for integrated mite control programmes in apple orchards are discussed.     

Colonization of Languedoc vineyards by phytoseiid mites (Acari: Phytoseiidae): influence of wind and crop environment

A natural increase of phytoseiid mite populations (Kampimodromus aberrans, Typhlodromus pyri and Phytoseius plumifer) was observed in vineyards in Languedoc, Burgundy and Corsica under integrated pest management strategies. The aim of the present study was to characterize the mechanisms of this colonization in space and time in Languedoc. The abundance of phytoseiid mites in the vegetation close to three grape fields was determined twice a year (May and July). Aerial (funnels with water) and soil (felt strip) traps were placed in and around grape fields, in order to assess the colonization potential provided by aerial dispersal and ambulatory locomotion. The populations of phytoseiid mites in the crops were studied twice a month in order to gain information on the make up of the dispersal populations. The species K. aberrans was found in largest quantities in the traps, in the natural vegetation and in the crops. Predatory mite dispersal occurred essentially by aerial dispersal and was dependent on the wind intensity and wind direction. Identical sex ratios were observed in migrant populations and in populations present in the grape fields, woody areas and hedges. A large proportion of immatures was found to move by aerial dispersal. The colonization potential (rapidity, intensity and regularity) was directly associated with the abundance of the phytoseiids and the proximity of natural vegetation. A deep, dense and tall woody area containing suitable host plants for predatory mites constituted the most stable source of phytoseiid mites. Natural colonization of vineyards provides considerable phytoseiid mite potential that could be managed in an agricultural landscape.     

Interactions among phytophagous mites, and introduced and naturally occurring predatory mites, on strawberry in the UK

In choice test experiments on strawberry leaf disc arenas the phytoseiid mites Neoseiulus californicus and N. cucumeris were more effective than Typhlodromus pyri as predators of the phytophagous mites Tetranychus urticae and Phytonemus pallidus. There were no preferences shown for either prey by any of these predators. In multiple predator leaf disc experiments both Phytoseiulus persimilis and N. cucumeris significantly reduced numbers of T. urticae eggs and active stages; this effect was seen when the two species were present alone or in combination with other predator species. Neoseiulus californicus was less effective at reducing T. urticae numbers, and T. pyri was not effective; no interaction between predator species was detected in these experiments. When T. urticae alone was present as prey on potted plants, P. persimilis and N. californicus were the only phytoseiids to significantly reduce T. urticae numbers. These two predator species provided effective control of T. urticae when P. pallidus was also present; however, none of the predators reduced numbers of P. pallidus. There were no significant negative interactions when different species of predators were present together on these potted plants. In field experiments, releases of both P. persimilis and N. cucumeris significantly reduced T. urticae numbers. However, there was a significant interaction between these predator species, leading to poorer control of T. urticae when both species were released together. These results show the importance of conducting predator/prey feeding tests at different spatial scales.     

Influence of prey on developmental performance, reproduction and prey consumption of Neoseiulus californicus (Acari: Phytoseiidae)

The Spical strain of the predatory mite Neoseiulus californicus (McGregor) is used as a biological control agent, but little is known about its preferred prey and host plants in Japan. Here we studied the development, reproduction and prey consumption of the Spical strain when fed on eggs of five different spider mite species deposited on both their laboratory-rearing plant and cherry, on which all five spider mite species developed well. The developmental periods of immature N. californicus females and males were significantly affected by the prey species they fed on, but not by the plants. No difference was found between males and females. The developmental period was shorter on eggs of two Tetranychus species than on eggs of Panonychus ulmi. Immature females had a higher predation rate than immature males. Preoviposition period, oviposition period and the number of eggs laid per female were not significantly affected by either the plants or the type of prey eggs. The postoviposition period and total adult longevity were shorter on eggs of P. ulmi than of the other four prey species, but there was no effect of plant substrate. The postoviposition period of the Spical strain was much longer than that of other N. californicus strains or other predatory mite species: the postoviposition period of the Spical strain was more than three times longer than the oviposition period, accounting for more than 75% of the total adult longevity. This suggests that the females need multiple mating to reach full egg load, but this remains to be tested. Total consumption by N. californicus adults was lower for eggs of P. ulmi than for eggs of the other four species, apparently because of the shorter postoviposition period when fed on eggs of P. ulmi. The intrinsic rates of natural increase (r _m) on the rearing plant did not differ among prey species, whereas those on cherry were significantly different: the value was higher on Tetranychus urticae eggs than on eggs of other species. Only when N. californicus fed on T. urticae eggs, the r _m-values were significantly different between the rearing plant and cherry (higher on cherry). Thus, the Spical strain of N. californicus could feed on eggs of all five spider mite species, deposited on a variety of plants with similar r _m-values, suggesting that it could be successfully used to control spider mites in orchards and various crop fields of Japan.     

Short-term changes in consumption and oviposition rates of Neoseiulus californicus strains (Acari: Phytoseiidae) after a diet shift

Short-term effects on consumption and oviposition rates of four strainsof Neoseiulus californicus (McGregor) after a diet shiftwere evaluated. The new feeding conditions experienced by the predators weresixfixed densities of eggs or protonymphs of Tetranychusurticae Koch placed on excised strawberry leaflet discs andmaintained under laboratory conditions (25±1°C,75–85% RH, 16L: 8D). The observations were made on the first and thefifthday of the experiment. The phytoseiids came from three long-term mass-rearedstrains fed on T. urticae, Dermatophagoides farinaeHughes,or Quercus spp. pollen, respectively. The fourth strainwascollected directly in a strawberry field. Time since diet transfer can be addedto the factors (i.e. feeding history and prey density) already known to affectthe functional and numerical responses of N. californicus,both when it feeds on prey eggs and protonymphs. If consumption rates wereaveraged over all strains and densities, 9.04 and 11.41 eggs, and 6.97 and 6.48protonymphs were consumed on the first and the fifth day, respectively. If thesame was done for oviposition rates, predators feeding on eggs produced 1.46and2.36 eggs/female/day, whereas predators feeding on protonymphs produced 1.35and2.29 eggs/female/day. Time had the greatest impact on the functional responseofthe strain that had previously fed on tetranychids, while an effect of time onthe numerical response was detectable in all strains.