Population growth and persistence when prey is diminishing in single-species and two-species systems of the predatory mites Euseius finlandicus, Typhlodromus pyri and Kampimodromus aberrans

Population growth and persistence of Euseius finlandicus (Oudemans), Typhlodromus pyri Scheuten and Kampimodromus aberrans (Oudemans) (Acari: Phytoseiidae) were studied in single-species and two-species systems on apple seedlings primarily infested by Panonychus ulmi Koch (Acari: Tetranychidae) in an environmentally controlled greenhouse. During the experiment, the seedlings developed natural infestations by Tetranychus urticae Koch (Acari: Tetranychidae), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), and powdery mildew. Several weeks after the start of the experiment a condition of diminishing prey availability was created by use of hexythiazox treatments. Without heterospecific competitors, T. pyri attained a higher population level than E. finlandicus or K. aberrans when similar amounts of food (spider mites) were available to each. Population growth of T. pyri was decisively favoured by the presence of T. urticae. In the single-species systems each predatory species persisted to the end of the experiment in spite of diminishing prey. In two-species systems with T. pyri/E. finlandicus and T. pyri/K. aberrans that were started with the same number of individuals of each species, only T. pyri was left at the end of the experiment. Typhlodromus pyri became more numerous than the other species when prey was abundant (which was in accordance with the results of the single-species groups) and finally displaced E. finlandicus and K. aberrans towards the end of the experiment. The following factors may have contributed to the dominance of T. pyri: (1) the ability of adult females to survive longer without food than those of E. finlandicus and K. aberrans, (2) the ability to complete juvenile development and to sustain reproduction with phytoseiid prey and (3) an advantage in foraging behaviour over K. aberrans and E. finlandicus at low spider mite levels. Euseius finlandicus predominated in the two-species system E. finlandicus/K. aberrans, but both species persisted to the end of the experiment.     

Juvenile Survival and Development in Euseius Finlandicus, Typhlodromus Pyri and Kampimodromus Aberrans (Acari: Phytoseiidae) Feeding on Con- and Heterospecific Immatures

Juvenile survival and development in Euseius finlandicus (Oudemans), Typhlodromus pyri Scheuten and Kampimodromus aberrans (Oudemans) feeding on con- and heterospecific phytoseiid immatures were investigated in the laboratory at 25 ± 1 °C and 65 ± 5% RH. More than 50% of T. pyri protonymphs preying on larvae of K. aberrans or E. finlandicus reached the adult stage. The mean developmental time of T. pyri from the protonymphal stage to adulthood was 6.3 days when feeding on K. aberrans and 7.5 days when feeding on E. finlandicus. The majority (approximately 90%) of K. aberrans protonymphs feeding on larvae of T. pyri or E. finlandicus died before reaching the deutonymphal stage; in both cases only one individual completed juvenile development. Euseius finlandicus larvae require food to reach the subsequent life stage, in contrast to larvae of T. pyri and K. aberrans, which usually do not feed at all: 10% of E. finlandicus immatures feeding on larvae of K. aberrans or T. pyri completed juvenile development (mean developmental time from larva to adult 7.0 and 6.7 days, respectively). Cannibalizing immatures of T. pyri and K. aberrans were able to reach adulthood, whereas those of E. finlandicus were not. Unfed immatures of T. pyri lived longer than the corresponding stages of E. finlandicus and K. aberrans. The present study indicates that phytoseiid immatures are suitable prey for developing stages of polyphagous phytoseiids. Since E. finlandicus, T. pyri and K. aberrans partly inhabit the same plant species, their immatures can be regarded as potential prey for competitive phytoseiids in times of food scarcity.     

Larval size relative to larval feeding, cannibalism of larvae, egg or adult female size and larval–adult setal patterns among 13 phytoseiid mite species

Phytoseiid mite larvae vary in size and feeding type. We compared larval size to feeding by larvae, cannibalism of larvae by adult females, egg and adult female size and the setae lengths of larvae and adults among 13 species. There was no relationship between size of larvae and either feeding by larvae or cannibalism of larvae by adult female mites. Correlations were highest between larval size as measured by idiosoma plus extended leg lengths and adult female size of idiosoma plus extended leg lengths (r²=0.746), while next highest was larval idiosoma length and adult female idiosoma length (r²=0.662) and then larval idiosoma length and egg length (r²=0.579). Based on idiosoma length, Phytoseiulus persimilis had the largest larvae (non-feeding) among species and Euseius finlandicus had the smallest larvae (obligatory feeding). However, based on idiosoma length plus extended leg length, obligatory feeding larvae (on pollen or mites) of E. finlandicus and Euseius hibisci were largest and facultative feeding larvae (on mites) of Neoseiulus californicus and obligatory feeding larvae (on mites) of Galendromus occidentalis were the smallest. Among species with non- or facultative feeding larvae, Amblyseius andersoni and Neoseiulus barkeri had larger larvae and Typhlodromus pyri and Neoseiulus fallacis had smaller larvae when leg lengths were included in larval size. Setae lengths of larvae versus adult females (after adjustment for body sizes) showed high correlation for j6 (r²=0.942) and s4 (r²=0.854), but low correlation for larval Z4 versus adult female Z4 (r²=0.084) or Z5 (r²=0.063). Overall, larval morphological traits were most closely correlated to traits of other life stages, although for setae there were some exceptions. Differences in the functions of setae j6, s4 and Z4 in the larva versus adult female are discussed.     

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.     

南非盲走螨实验种群的发育历期及生命表

在27℃条件下,以粗脚粉螨Acarus siro L.为饲料饲养观察南非盲走螨Typhlodromus(Anthoseius) transvaalensis(Nesbitt)的生长发育和繁殖情况,组建实验种群生命表。结果表明,南非盲走螨行孤雌生殖,卵、幼螨、前若螨、后若螨、成螨产卵前期各阶段发育历期分别为2.00,0.72,1.96,1.53,1.77d,完成1个世代发育需7.98d,雌成螨平均寿命14.82d、平均产卵量25.75粒,各种群生命参数分别为:净增殖率R0=25.01,世代平均周期T=13.71,内禀增长率rm=0.23,周限增长率λ=1.26,种群倍增所需日数t=2.95。采用小空间湿度控制法,测定不同湿度对南非盲走螨卵的孵化和成螨产卵的影响。结果表明,卵发育和孵化的最适湿度为75.0%~85.0%,96.0%的相对高湿度对成螨的产卵和存活均有不利影响。以橘全爪螨Panonychus citri McGregor不同螨态为猎物时,南非盲走螨对橘全爪螨幼螨的捕食量最大,日平均捕食量为5.40头,而对橘全爪螨雌成螨则几乎不取食。     

Euseiusfinlandicus (Acari: Phytoseiidae) as a potential biocontrol agent against Tetranychus urticae (Acari: Tetranychidae): life history and feeding habits on three different types of food

Life history and reproductive parameters of the generalist predatory mite Euseius (Amblyseius) finlandicus (Oudemans) were studied in the laboratory at 25 +/- 1 degrees C, with a 16L:8D photoperiod and 60 +/- 15% RH, to investigate its response to different food sources: an eriophyid mite Aceria sp., tulip pollen Tulipa gesnerana L., and two-spotted spider mite Tetranychus urticae Koch. Total developmental time of the immature stages was the shortest on eriophyid mites, followed by pollen, and then spider mites. Fecundity was highest on pollen (43.69 eggs; 1.63 eggs/female/day), then eriophyid mites (39.73 eggs; 1.37 eggs/female/day) and lowest on spider mites (18.16 eggs; 0.80 eggs/female/day). Intrinsic rate of increase (Rm), net reproductive rate (Ro) and finite rate of increase (lambda) followed the same pattern [pollen (0.168, 27.96 and 1.183, respectively), eriophyid mites (0.153, 20.81 and 1.167), spider mites (0.110, 9.44 and 1.119)]. Mean generation time (days) was the shortest on pollen (19.90), followed by eriophyid mites (20.02), and then spider mites (20.59). Average spider mite larvae consumed by E. finlandicus during immature stages were 9.18 for males and 11.85 for females. Adult E. finlandicus females consumed an average of 166.38 spider mite protonymphs during adult stage compared to an average of 66.55 by males. The number of prey protonymphs consumed per day by females was highest in the oviposition period, lower in the pre-oviposition period and the lowest in the post-oviposition period. The eriophyid mite as a prey recorded the shortest developmental time, while pollen as food recorded the highest oviposition rate in E. finlandicus. The potential of this predator as a biocontrol agent against T. urticae is discussed.     

Factors affecting the presence of Typhlodromusspp. (Acarina: Phytoseiidae) in the calyx cavities of apple fruits and implications for integrated pest management

Predatory mites of the family Phytoseiidae include several species of importance as biological control agents of phytophagous mites in various crops including apples. We report on the post-harvest presence of the motiles of two species, Typhlodromus occidentalis and Typhlodromus pyri, in the calyx cavities of apple fruits of three cultivars. The mean numbers of motiles per fruit were as high as 6.10. The phytoseiid densities were lowest in cv. Bonza and tended to be greater in samples taken in late autumn, particularly in cv. Red Delicious. No significant effect (p > 0.05) was observed for different insecticide treatments. Phytoseiids remained present within fruits of cv. Granny Smith left on the orchard floor in winter. Together with an observed reduction in the numbers of T. occidentalis in the early spring, this suggests that fruits constitute an overwintering refuge. The findings are discussed in relation to the implications for biological control, in particular the minimization of the removal of natural enemies from orchards. This revised version was published online in November 2006 with corrections to the Cover Date.     

Inter- and intraspecific predation on immatures by adult females in Euseius finlandicus, Typhlodromus pyri and Kampimo dromus aberrans (Acari: Phytoseiidae)

In a series of experiments, the interspecific predation and cannibalism on immatures by the adult females of Euseius finlandicus, Kampimodromus aberrans and Typhlodromus pyri were examined under laboratory conditions. The three species showed differing tendencies to prey on each other's motile immature stages. Euseius finlandicus females consumed more larvae and protonymphs than the females of T. pyri and K. aberrans. In cages without free water E. finlandicus ate a range of 6.51 larvae or 5.31 protonymphs of T. pyri and 5.27 larvae or 5.95 protonymphs of K. aberrans per female per day. Kampimodromus aberrans and T. pyri females exhibited a greater tendency to prey on heterospecifics than on conspecifics. When feeding on phytoseiid immatures and without free water, T. pyri females survived longer and laid more eggs than the females of E. finlandicus and K. aberrans. Adult females of E. finlandicus and T. pyri having free water and preying on heterospecific protonymphs were able to maintain egg laying during the whole experimental period of 12 days. The females of all three species had difficulties in piercing phytoseiid eggs, and the number of sucked eggs per female per day was low. Kampimodromus aberrans females ate 0.48 eggs of T. pyri daily, which was the highest recorded number. The great tendency to interspecific predation on motile immature phytoseiids by the females of E. finlandicus is discussed with regard to the dominance of this species on deciduous trees and bushes in Austria.     

Intra- and interspecific predation by adult female Metaseiulus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae) when provisioned with varying densities and ratios of Tetranychus urticae (Acari: Tetranychidae) and phytoseiid larvae

The phytoseiid mites Metaseiulus occidentalis (Nesbitt) and Typhlodromus pyri Schueten are used together and alone as biological control agents against tetranychid pest mites of apple. Their effectiveness as control agents may be impacted by intraguild predation. The effects of prey species and prey density on the rates of inter- and intraspecific predation and oviposition by these two predators were investigated through a series of experiments. Adult female predators were given prey as mixed populations of phytoseiid larvae and larvae of a more preferred species, the spider mite, Tetranychus urticae Koch, at different densities and ratios. Typhlodromus pyri, more of a generalist predator, showed higher rates of predation and cannibalism on phytoseiid immatures at most prey densities and ratios. Manly preference indices indicated that T. pyri switched to feed on phytoseiid larvae at higher prey levels and ratios of T. urticae than M. occidentalis. This greater ability to use phytoseiid larvae as prey may help stabilize T. pyri populations when more preferred prey is unavailable. This may, in part, explain the observed persistence of T. pyri populations when M. occidentalis populations were decreasing in orchard test plots.     

Effects of humidity on eggs and immatures of Neoseiulus fallacis,Amblysieus andersoni,Metaseiulus occidentalis and Typhlodromus pyri (Phytoseiidae): implications for biological control on apple,caneberry, strawberry and hop

The lethal humidity (LH₅₀) responses at 20°C of eggs of two strains of Neoseiulus fallacis (Garman) were 71.6 and 69.7%; of three strains of Amblyseius andersoni (Chant) were 62.9, 62.0 and 62.4% and of one strain each of Typhlodromus pyri Scheuten and Metaseiulus occidentalis Nesbitt were 55.0 and 28.4%, respectively. Eggs of three genetically distinct strains of A. andersoni from Oregon, the Netherlands and Italy did not respond differently from one another nor did eggs of freely hybridizing N. fallacis from Michigan and Oregon. Mortality of larvae through development to early protonymphs at 50% RH, 20°C. was 91.9, 82.3, 46.2 and 31.0% for fed mites and 98.1, 83.2, 67.0 and 89.7% for unfed mites of Oregon strains of N. fallacis, A. andersoni, T. pyri and M. occidentalis, repectively. Fed larvae-protonymphs of M. occidentalis and T. pyri were more tolerant of low humidity than fed larvae-protonymphs of N. fallacis and A. andersoni. Mortality was less for fed than unfed larvae-protonymphs of M. occidentalis and T. pyri, but there were no differences for A. andersoni and N. fallacis. Levels of feeding by predator larvae on T. urticae and cannibalism by phytoseiid protonymphs contributed to species differences. Responses to humidity are discussed in relation to geographic and host plant distributions and biological control by single or mixed species populations of phytoseiids.     

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.     

Predatory mites of the Phytoseiidae family in integrated and ecological pest management systems in orchards in Slovakia

During 2005–2007, 1,332 individuals of predatory mites were found in integrated and ecological orchards in Slovakia. Seven predatory mite species of the family Phytoseiidae, namely Phytoseius echinus, Phytoseiulus macropilis, Euseius finlandicus, Typhlodromus pyri, Paraseiulus triporus, Amblyseius andersoni and Neoseiulella tiliarum, were identified. Out of 1,332 individuals, 519 (39.0%) were found in the apple orchards and 813 (61.0%) in the pear orchards. Out of all predatory mite individuals, 460 (34.5%) were found in the integrated pest management system (IPM) and 872 (65.5%) in the ecological pest management system (EPM). In apple orchards, P. echinus was dominant and constituted 49.3% of the detected mites. In pear orchards, E. finlandicus was dominant and constituted 48.7% of the detected mites. Typhlodromus pyri was also abundant, especially in pear orchards. The other species were less abundant.     

Changes in intraspecific aggregation and the coexistence of predaceous apple mites

The leaves of an apple tree are a patchy environment for leaf-inhabiting predaceous and phytophagous mites, consisting of discrete patches of leaf resources connected by relatively inhospitable petioles and branches. We investigated four species of predaceous mites ( Amblyseius andersoni , Galendromus occidentalis , Typhlodromus pyri (Acari: Phytoseiidae), and Zetzellia mali (Acari: Stigmaeidae)) inhabiting 'Red Delicious' apple trees ( Malus pumila ). These mites experience intra-guild predation (IGP), and we hypothesized that the vulnerable species would show increased aggregation when they are in plots with other predators. We also hypothesized that the increase in aggregation will be proportional to the vulnerability of the predator to IGP. We measured intraspecific aggregation with a binomial model that measures P(I), the amount of space a species occupies at a given average density, and compares this statistic among species at a common average density: samples that exhibit lower values of P(I) at a particular average density are considered to be more aggregated. We measured P(I) for the predaceous mites over four years, combining counts of all life stages. Data were segregated into groups with plots containing each predator alone, and each predator together with combinations of other predators. G. occidentalis and Z. mali showed significant increases in aggregation when other predators were present, with G. occidentalis showing the greatest change. T. pyri showed significant change only in the presence of Z. mali . A. andersoni , the largest mite studied here, showed no change in aggregation in the presence of other predators. We discuss possible causes of these changes in intraspecific aggregation and how they may promote long-term coexistence of predaceous mites.     

Impact of relative humidity and water availability on the life history of the predatory mite Amblyseius swirskii

The predatory mite Amblyseius swirskii (Athias-Henriot) (Acari: Phytoseiidae) is currently used as an efficient biological control agent of thrips, whiteflies and spider mites, which are economically damaging pests of ornamental plants and vegetable crops grown in greenhouses and fields worldwide. Currently, the effects of relative humidity (RH) and water availability on the optimal growth of A. swirskii are unknown. Here, we test the combined effects of different levels of RH (33%, 53%, 73% and 92%) and water availability on the development and reproduction of male and female A. swirskii feeding on the dried fruit mite, Carpoglyphus lactis (Linnaeus). While eggs failed to hatch at 33% RH, the survival rates of the immature stages at?≥?53% RH increased solely in response to water availability and not due to changes in RH. Regarding growth and development, low RH extended the egg–adult duration and pre-oviposition period. We also found that the negative effects of low RH on fecundity were partially or completely eliminated when drinking water was available. For the life table parameters, the highest values of net reproductive rate (R₀) and intrinsic rate of natural increase (r) were achieved at the highest RH and when drinking water was available. Overall, water availability mitigated the negative effect of low RH on female reproduction, and female development was more sensitive to water availability than male development. Lastly, a comparison of similar research on A. swirskii suggested that water availability and RH are more influential on r than food source or temperature.

     

Phytoseiid mites in protected crops: the effect of humidity and food availability on egg hatch and adult life span of Iphiseius degenerans, Neoseiulus cucumeris, N. californicus and Phytoseiulus persimilis (Acari: Phytoseiidae)

The effect of relative humidity on egg hatch success for Iphiseius degenerans, Neoseiulus californicus and N. cucumeris was described by a binomial model with a parallel slope. The shape of the response differed for Phytoseiulus persimilis and a model with separate parameters gave a significantly better fit. Fitted response curves showed that I. degenerans, N. cucumeris, N. californicus and P. persimilis were ranked by decreasing tolerance to low humidity, with egg mortalities of < 0.5, 3, 12 and 16% respectively at 75-80% RH at 20 degrees C. Egg stage duration for I. degenerans and N. cucumeris was unaffected over the range 60-82% RH. For N. californicus and P. persimilis egg duration was significantly longer at 60 and 70% than for either 82 or 90% RH. No effect of relative humidity was found on the mean life span of adult females when food was available continuously to the mites. N. californicus lived significantly longer (58 days after the first egg was laid) than the other species. No significant difference was observed in mean life span between adult females of I. degenerans and N. cucumeris (25 and 28 days respectively). The mean life span of adult female P. persimilis (19 days) was significantly shorter than the other species. In the absence of both food and water, the survival of adult female mites was reduced to 2-4 days. Survival time was at least doubled when free water was available in the absence of food. Mean survival of adult female mites with water but without food was 10 days for N. cucumeris, 18 days for N. californicus, 6 days for P. persimilis and 4 days for I. degenerans. Survival of adult female N. cucumeris and N. californicus was increased significantly, to 20 and 22 days respectively, when fungal hyphae were present along with water but in the absence of other food.     

Phytoseiid Mites on Unsprayed Apple Trees in Oregon, and Other Western States (USA): Distributions, Life-Style Types and Relevance to Commercial Orchards

In unsprayed apple trees in eastern Oregon, Galendromus flumenis (Chant), Galendromus occidentalis (Nesbitt), Typhlodromus caudiglans Schuster and Metaseiulus citri (Garman and McGregor) were common phytoseiid mites; common plant-feeding mites were the eriophyid, Aculus schlechtendali Nalepa, the brown mite, Bryobia rubrioculus (Scheuten) and Eotetranychus spp.; apple rust mites seemed to be the primary prey for phytoseiids; the spider mites, Tetranychus urticae Koch and Panonychus ulmi (Koch) were scarce except for a few local outbreaks; the stigmaeid Zetzellia mali (Ewing) was at 10% of sites and its densities were inversely related to phytoseiid densities; phytoseiids were absent at some sites, particularly at high elevations where winters are severe. In seven Oregon ecoregions, G. flumenis was often at lower elevations in valleys with moderate winters; T. caudiglans was often at higher elevations; G. occidentalis was often at intermediate elevations, in young trees, and near where pesticides were used; it dominated in unsprayed trees only in almost treeless, sage-covered areas; M. citri was usually in older apple trees near agriculture. In mixed phytoseiid populations, M. citri, a generalist, and G. occidentalis, a specialist, occurred more often than expected; G. occidentalis was mostly found with T. caudiglans, a generalist; G. flumenis, a generalist, occurred less with others, possibly because it competes with both specialists and generalists. Analyses of species' distributions with multiple regression and genetic models gave explanatory r2s of 0.019-0.318. Of 29 variables, altitude of site, intensity of agricultural management, tree age, plant types, and Z. mali levels helped explain phytoseiid species presence. In the western USA, G. flumenis dominated in middle-southern latitudes; T. caudiglans dominated in the north near the Canadian border; G. occidentalis dominated in middle latitudes in parts of Washington, Idaho, Montana, and Wyoming; M. citri was at a few sites in these four states. Distributional and independent variable data were used to predict species presence at sites in Oregon with a 70% success rate. We discuss phytoseiid life-style types, community dynamics, presence in organic/conventional orchards, and trends as more selective IPM methods are used in apple orchards.     

Verified and potential pathogens of predatory mites (Acari: Phytoseiidae)

Several species of phytoseiid mites (Acari: Phytoseiidae), including species of the genera Amblyseius, Galendromus, Metaseiulus, Neoseiulus, Phytoseiulus and Typhlodromus, are currently reared for biological control of various crop pests and/or as model organisms for the study of predator-prey interactions. Pathogen-free phytoseiid mites are important to obtain high efficacy in biological pest control and to get reliable data in mite research, as pathogens may affect the performance of their host or alter their reproduction and behaviour. Potential and verified pathogens have been reported for phytoseiid mites during the past 25 years. The present review provides an overview, including potential pathogens with unknown host effects (17 reports), endosymbiotic Wolbachia (seven reports), other bacteria (including Cardinium and Spiroplasma) (four reports), cases of unidentified diseases (three reports) and cases of verified pathogens (six reports). From the latter group four reports refer to Microsporidia, one to a fungus and one to a bacterium. Only five entities have been studied in detail, including Wolbachia infecting seven predatory mite species, other endosymbiotic bacteria infecting Metaseiulus (Galendromus, Typhlodromus) occidentalis (Nesbitt), the bacterium Acaricomes phytoseiuli infecting Phytoseiulus persimilis Athias-Henriot, the microsporidium Microsporidium phytoseiuli infecting P. persimilis and the microsporidium Oligosproridium occidentalis infecting M. occidentalis. In four cases (Wolbachia, A. phytoseiuli, M. phytoseiuli and O. occidentalis) an infection may be connected with fitness costs of the host. Moreover, infection is not always readily visible as no obvious gross symptoms are present. Monitoring of these entities on a routine and continuous basis should therefore get more attention, especially in commercial mass-production. Special attention should be paid to field-collected mites before introduction into the laboratory or mass rearing, and to mites that are exchanged among rearing facilities. However, at present general pathogen monitoring is not yet practical as effects of many entities are unknown. More research effort is needed concerning verified and potential pathogens of commercially reared arthropods and those used as model organisms in research.     

Diapause induction and duration in the phytoseiid miteTyphlodromus pyri

A photoperiod of 8L/16D for two weeks was used to distinguish between diapausing and non-diapausingTyphlodromus pyri Scheuten. A diet ofPanonychus ulmi orTetranychus urticae, or pollen ofVicia faba did not influence preovipositional periods of diapausing mites. In mid-September, 88% ofT. pyri collected from an insectary were in diapause. The critical day-length appeared to be between 12.5 and 13.5 h. Diapause duration was greatest in mites collected in September–November, becoming progressively less in mites collected later in the winter. By mid-April, ca. 50% of mites collected from the orchard and insectary oviposited promptly when cultured in the laboratory.Typhlodromus pyri eggs and larvae were present on leaves in early May. At this time, only 4% ofP. ulmi winter eggs had hatched. Diapause terminated most quickly inT. pyri kept in an 18L/6D photoperiod, followed by 24L/0D and 0L/24D. Longest preoviposition periods were recorded for mites kept in 8L/16D photoperiods.     

Water uptake in the cat flea Ctenocephalides felis (Pulicidae: Siphonaptera)

To counteract water loss due to excretion, cuticular transpiration and respiration, various groups of arthropods have developed mechanisms for active uptake of water vapor from unsaturated air. In this study, active uptake capabilities and water loss rates were examined in the various developmental stages of the cat flea, Ctenocephalides felis. To determine critical equilibrium humidity, the lowest relative humidity at which active water uptake can occur, pre-desiccated immature and adult fleas were placed in a series of humidity regimes ranging from 44 to 93% RH. Active uptake occurred in larval stages at relative humidities above 53% and in pre-pupae at 75-93% RH. Pupae and adults did not demonstrate active uptake at any humidity. Optimal uptake for larvae occurred between 20 and 30 degrees C. When placed over Drierite (<10% RH), larval and adult stages demonstrated a higher rate of water loss than pre-pupal and pupal stages. Active water uptake is necessary to ensure proper development of the larvae of C. felis. Active uptake ceases after the larval-pupal ecdysis and it appears that adults have lost the ability to actively uptake water.     

Larval survival and feeding by immature Metaseiulus occidentalis,Neoseiulus fallacis,Amblyseius andersoni and Typhlodromus pyri on life stage groups of Tetranychus urticae Koch and phytoseiid larvae

When 20 newly hatched larvae either of Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Amblyseius andersoni Chant or Typhlodromus pyri Scheuten were held in arenas without food at 95% RH and 20°C, the percentages of mites surviving to protonymphs were 5.0, 81.3, 86.3, and 83.8%, respectively. Unfed M. occidentalis larvae starved within 2–3 days, while immatures of the other three species lived up to 12–14 days, with some becoming adults by cannibalizing and/or scavenging. Phytosciid larvae given eggs, larvae/protochrysalis/protonymphs (L/P), deutochrysalis/deutonymphs (D) or teleiochrysalis/female adult (T/A) of Tetranychus urticae Koch, fed at different incidences during 6 h tests. Larvae of T. pyri never fed, but almost all larvae of M. occidentalis fed on eggs and L/Ps and 60–70% of M. occidentalis larvae fed on Ds and T/As. N. fallacis and A. andersoni larvae fed at incidences from 20–75% depending on the stage of spider mite given. Larvae fed more commonly on eggs and L/Ps than Ds and T/As for M. occidentalis and N. fallacis but not A. andersoni. Protonymphs and deutonymphs of all four species, readily fed on T/As after 3 h of exposure, but incidences were higher for A. andersoni and T. pyri. Feeding on phytoseiid larvae by protonymphs and deutonymphs also was more common for A. andersoni and T. pyri. Except for M. occidentalis, deutonymphs fed more than protonymphs on phytoseiid larvae. Results are discussed in relation to individual species life histories and the value of these traits in predicting a species role in a biological control system.