Side-effects of three pesticides on the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae)

Side-effects of three commonly used pesticides in Iran were evaluated on an introduced strain of the predatory mite. Phytoseiulus persimilis Athias-Henriot, reared for about 10 years without exposure to any pesticides. Application of pesticides was carried out either to detached bean leaves using a Potter tower at 1 mg wet deposit per cm2 or by a hand sprayer on bean plants until run off. According to an EPPO decision making scheme, pirimiphos-methyl was found to be harmful (E=90.8%) and heptenophos harmless (E=-3.7%) to the predatory mite in the residual initial toxicity tests. For determination of the hazard class of malathion a field test was found to be necessary (E=59.8%). Categories of 1, 2, 3 were determined for heptenophos, malathion and primiphos-methyl, respectively, using IOBC classification. Despite being harmful, it is possible to use pirimiphos-methyl 10 days before release of P. persimilis. Investigation of the contribution of both lethal and sub-lethal effects to total impact indicated the dominance of lethality in the case of pirimiphos-methyl, while malathion acted by both mechanisms. Heptenophos did not have negative effects on fecundity of P. persimilis but rather caused a higher rate of fecundity in comparison with the control. The mortality found in the heptenophos test was not significantly different from the control.     

Comparison of thermal activity thresholds of the spider mite predators Phytoseiulus macropilis and Phytoseiulus persimilis (Acari: Phytoseiidae)

The lower and upper thermal activity thresholds of the predatory mite Phytoseiulus macropilis Banks (Acari: Phytoseiidae) were compared with those of its prey Tetranychus urticae Koch (Acari: Tetranychidae) and one of the alternative commercially available control agents for T. urticae, Phytoseiulus persimilis Athias-Henriot. Adult female P. macropilis retained ambulatory function (CT_min) and movement of appendages (chill coma) at significantly lower temperatures (8.2 and 0.4 °C, respectively) than that of P. persimilis (11.1 and 3.3 °C) and T. urticae (10.6 and 10.3 °C). As the temperature was raised, P. macropilis ceased walking (CT_max) and entered heat coma (42.7 and 43.6 °C), beyond the upper locomotory limits of P. persimilis (40.0 and 41.1 °C), but before T. urticae (47.3 and 48.7 °C). Walking speeds were investigated and P. persimilis was found to have significantly faster ambulation than P. macropilis and T. urticae across a range of temperatures. The lower thermal activity threshold data indicate that P. macropilis will make an effective biological control agent in temperate climates.     

Plant architecture and prey distribution influence foraging behavior of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

The arrangement, number, and size of plant parts may influence predator foraging behavior, either directly, by altering the rate or pattern of predator movement, or, indirectly, by affecting the distribution and abundance of prey. We report on the effects of both plant architecture and prey distribution on foraging by the predatory mite, Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae), on cucumber (Cucumis sativus L.). Plants differed in leaf number (2- or 6-leafed), and there were associated differences in leaf size, plant height, and relative proportions of plant parts; but all had the same total surface area. The prey, the twospotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), were distributed either on the basal leaf or on all leaves. The effect of plant architecture on predator foraging behavior varied depending on prey distribution. The dimensions of individual plant parts affected time allocated to moving and feeding, but they did not appear to influence the frequency with which predators moved among different plant parts. Overall, P. persimilis moved less, and fed upon prey longer, on 6-leafed plants with prey on all leaves than on plants representing other treatment combinations. Our findings suggest that both plant architecture and pattern of prey distribution should be considered, along with other factors such as herbivore-induced plant volatiles, in augmentative biological control programs.     

Disease prevalence and transmission of Microsporidium phytoseiuli infecting the predatory mite, Phytoseiulus persimilis (Acari: Phytoseiidae)

Isolated colonies of the predatory mite, Phytoseiulus persimilis, were used to gain information regarding prevalence and transmission of Microsporidium phytoseiuli. Two colonies of P. persimilis were reared on spider mite (Tetranychus urticae)-infested bean plants in isolated cages. Disease prevalence of predators from Colony 1 remained relatively low (between 0 and 15%) over 57 weeks of observation whereas disease prevalence of predators from Colony 2 increased over 3 months (from 12 to 100%). Disease prevalence among predators from Colony 1 had increased to 100% 2 months after weekly sampling had ceased for this colony and periodic sampling confirmed that disease prevalence among individuals of both colonies remained at 100%. Microsporidian spores were not detected in randomly chosen samples of T. urticae prey mites that were removed and examined biweekly during this period. Although numerous microsporidian spores were observed in smear preparations of fecal pellets examined by light microscopy, spores were not observed on leaf surfaces or predator feces when examined by SEM. The latter appeared as intact aggregates composed of numerous dumbbell-shaped crystals and it is unlikely that spores are liberated from intact fecal pellets onto leaf surfaces. Vertical transmission of M. phytoseiuli was 100%; horizontal transmission was low (14.3%) and occurred only when immature P. persimilis were permitted to develop in contact with infected immature and adult predators. The mean number of eggs produced per mated pair was highest when uninfected females were mated with uninfected males (63.2 eggs per mated pair). Although mean egg production decreased when one or both parents were infected, not all differences were significant. Male predatory mites did not contribute to infection of their progeny. Results suggest that routine examination of P. persimilis for microsporidian spores is essential for the management of M. phytoseiuli within P. persimilis colonies. Low disease prevalence and lack of obvious disease signs or symptoms, as in the case of M. phytoseiuli, increase the probability that these pathogens will escape notice unless individuals are routinely examined for pathogens.     

Leaf hairs influence searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis (Acari: Phytoseiidae)

The effect of leaf hairs on searching efficiency of adult female Phytoseiulus persimilis was investigated. For this purpose we used the ornamental crop Gerbera jamesonii and determined the predator's searching efficiency on three cultivars that differ largely in the density of leaf hairs on the undersurface of the leaves. Walking speed of the mites was highest on the cultivar with the lowest leaf hair density. Walking activity, defined as the percentage of time spent walking, was not dependent on leaf hair density of the cultivars. At both prey densities tested, time until first predation increased with leaf hair density. The predation rate of adult female P. persimilis is affected by trichome density, particularly when prey density is low. At prey densities of 1.3 and 2.5 Tetranychus urticae eggs cm–2, predation rate was inversely related to leaf hair density. At a prey density of 8.0 eggs cm–2 no significant effect of leaf hair density on predation rate was found. These negative effects on searching efficiency and predation success at low prey density of P. persimilis suggest that biological control of T. urticae on gerbera may be hampered by leaf hairs. © Rapid Science Ltd. 1998     

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

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

A novel disease affecting the predatory mite Phytoseiulus persimilis (Acari, Phytoseiidae): evidence for the involvement of bacteria

Adult female Phytoseiulus persimilis Athias-Henriot (Acari, Phytoseiidae) of a laboratory population show drastic changes in foraging behavior, anatomy and life history compared to typical laboratory populations. We demonstrated earlier that the set of characteristic symptoms, called non-responding (NR) syndrome, is transmitted horizontally between and among predator generations via feces and debris deposited by symptomatic females. Here, we prove that bacteria present in feces and debris deposited by symptomatic females are involved in the induction of the NR-syndrome. The potential of predator products to induce the NR-syndrome was assayed by keeping healthy adult female predators during a period of 3 days on prey-infested bean leaves, which had previously been sprayed with an aqueous suspension of feces and debris. The NR-syndrome was clearly induced in those predators that had been exposed to a suspension collected from symptomatic females (incubation time 4-6 days, 93% shrunken females), whereas predators exposed to a suspension collected from non-symptomatic females did not show the NR-syndrome. Moreover, predators from the first group transmitted infectious products themselves already 5 days after the initial exposure, whereas this was not the case for the second predator group. The bioassay used in the present study is important for laboratories and companies as it can be applied for testing the presence of the novel disease in populations of P. persimilis. To investigate the involvement of bacteria in syndrome induction we (1) eliminated bacteria from a feces-and-debris suspension of symptomatic females by passing the suspension through a bacterial microfilter and (2) added the antibiotic tetracycline to a suspension of feces and debris from symptomatic females. A suspension of feces and debris collected from symptomatic females did not induce the NR-symptom after bacteria had been eliminated, whereas an untreated portion of the same suspension did so. Moreover, the NR-syndrome was induced in predators exposed to an aqueous suspension of the residues that had not passed the bacterial filter. A suspension of feces and debris collected from symptomatic females, to which the antibiotic tetracycline had been added, did not induce the NR-syndrome whereas the same suspension did induce all symptoms when no tetracycline was added. These findings prove that bacteria are involved in the induction of the NR-syndrome. The results are discussed in the context of mite pathology and biological control.     

The effect of temperature on the functional response of Phytoseiulus persimilis (Acari: Phytoseiidae)

Environmental variables, such as temperature, are important in determining the efficiency of biological control in ornamental crops. This paper examines the effect of temperature on the functional response of adult female Phytoseiulus persimilis to eggs of the spider mite, Tetranychus urticae. The functional response was determined using a new functional response assay technique with plant stems as an arena, rather than leaf discs. The use of plant stems allows the influence that plant structure has on predation to be incorporated into the assay. Control assays were also used (without predators) to estimate natural losses of prey. The data were analysed using a binomial model, with the use of Abbot's formula to correct for the losses in the controls. A combined equation to describe the effect of temperature and prey density on the predation rate of Phytoseiulus persimilis was derived. The results showed that more prey are eaten as the temperature increases from 15 degrees C to 25 degrees C, but the number of prey eaten then declines at 30 degrees C, although not to the levels seen at 20 degrees C. The implication of these results for biological control in ornamental crops, where the temperature can often exceed 30 degrees C, is discussed.     

联苯肼酯对智利小植绥螨的安全性及二者对二斑叶螨的联合控制作用

【目的】评价联苯肼酯对智利小植绥螨Phytoseiulus persimilis的安全性,以及该药剂与捕食性天敌智利小植绥螨联合使用的效果。【方法】采用室内生物测定与田间试验的方法测定了联苯肼酯对智利小植绥螨成螨和若螨致死率与繁殖能力的影响,以及二者联合使用对茄子上二斑叶螨的控制效果。【结果】结果表明143 mg/L联苯肼酯对智利小植绥螨成螨和若螨的存活和生殖能力均无显著影响,处理后96 h对若螨的最高致死率为2.30%,成螨为2.04%;处理组8 d的平均产卵量为15.08粒/雌,与对照平均产卵量15.45粒/雌无显著差异;处理组所产卵的平均孵化率为98.63%,与对照组平均孵化率98.13%无显著差异;联苯肼酯悬浮剂在143 mg/L浓度下对二斑叶螨的控制效果表现为速效性高于单独使用智利小植绥螨,但持效性低于智利小植绥螨,防效在第22天时开始下降。二者联合使用表现出较好的速效性与持效性,处理后第2天防效达97.35%,第18天时达100%。【结论】联苯肼酯对智利小植绥螨具有极高的安全性,该药剂与智利小植绥螨联合使用对二斑叶螨具有良好的控制效果。     

Toxicity of plant essential oils to Tetranychus urticae (Acari: Tetranychidae) and Phytoseiulus persimilis (Acari: Phytoseiidae)

Fifty-three plant essential oils were tested for their toxicity against eggs and adults of Tetranychus urticae Koch as well as adults of Phytoseiulus persimilis Athias-Henriot, by using a filter paper diffusion bioassay without allowing direct contact. Responses varied according to oil type and dose, and mite species. In a plastic container (4.5 by 9.5 cm) bioassay at 14 x 10(-3) microl/ml air, caraway seed, citronella java, lemon eucalyptus, pennyroyal, and peppermint oils gave > 90% mortality against adult T. urticae, whereas 82 and 81% mortality was observed with sage and spearmint oils, respectively. With the exception of sage oil, the other six essential oils were highly effective against T. urticae eggs at 9.3 x 10(-3) microl/ml air. Against adult P. persimilis, these six test oils caused > 90% mortality at 7.1 x 10(-3) microl/ml air. Particularly peppermint oil at 4.7 x 10(-3) microl/ml air was highly toxic. In an acrylic cage (30 by 30 by 40 cm ) test, lemon eucalyptus, pennyroyal, peppermint, and spearmint oils were highly effective against adult T. urticae at 1.4 x 10(-3) microl/ml air. These results indicate that the mode of delivery of these essential oils was largely a result of action in the vapor phase via the respiratory system. The essential oils described herein merit further study as potential fumigants for T. urticae control.     

Plant species modifies the functional response of Phytoseiulus persimilis (Acari: Phytoseiidae) to Tetranychus urticae (Acari: Tetranychidae): implications for biological control

The functional response of the predatory mite Phytoseiulus persimilis Athias-Henriot to eggs of its prey, the spider mite Tetranychus urticae Koch was examined on three plant species. Experiments were done to determine whether differences in the functional response on the three plant species were due to the morphological features of the crop directly on the predator or through an effect of the plant species on the prey. The results show that crop morphology is the only factor influencing the predatory ability of P. persimilis on the three plant species. Fewer eggs were eaten on Ceanothus thyrsiflorus var. 'Autumnal Blue', the plant species with hairy leaves, and greater numbers of prey consumed on Choisya ternata, a species with smooth leaves. However, similarly few eggs were eaten on the smooth, but waxy leaved Euonymus japonicus as on Ceanothus thyrsiflorus, demonstrating that morphological characters of leaves other than the possession of hairs and trichomes may affect the rates of predation. The implications of these results for the tritrophic interactions between plant, predator and prey, and the development of suitable biological control strategies are discussed.     

Olfactory response of Phytoseiulus persimilis (Acari: Phytoseiidae) to untreated and Beauveria bassiana-treated Tetranychus urticae (Acari: Tetranychidae)

Determination of attraction and avoidance behavior of predators is important in concomitant use of multiple natural enemies to control a pest. The olfactory response of the predatory mite Phytoseiulus persimilis was studied to odors related to Tetranychus urticae adults infected by Beauveria bassiana DEBI008 in 0, 24, 48 and 72 h intervals, both in absence and in presence of plants. In plant-present experiments, P. persimilis attraction was neither towards adults of T. urticae infected by 0.02 % Tween 80 (as control), nor to the ones infected by B. bassiana for 0 or 24 h, whereas significant attraction towards the control was observed when tested against T. urticae infected by B. bassiana for 48 or 72 h. In absence of plants, P. persimilis displayed significant avoidance of T. urticae infected by B. bassiana for 48 or 72 h, when their alternative option was 0.02 % Tween 80-infected T. urticae adults. These results indicate that P. persimilis can recognize the presence of B. bassiana and that the predator avoids the fungus. This suggests that the two natural enemy species can be used together in biological control programmes.     

Rainforest habitat resistance to the migration of Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) in south-eastern Queensland

Abstract  This paper tests the hypothesis that habitat differences affect the migratory ability of the Chilean predatory mite, Phytoseiulus persimilis , an introduced biological control agent of the spider mite, Tetranychus urticae . It is suggested that habitat resistance accounts for the species' inability to invade rainforests in south-eastern Queensland, Australia. Like its prey, P. persimilis migrates to distant plants on air currents. To test our hypothesis, populations of the Chilean predatory mite were established on potted bean plants in both remnant rainforest and adjacent open fields, and their migration monitored using sticky traps. Overall it was found that prey populations on leaves were similar in both habitats, but those of predators were about 20% lower in rainforest. However, the numbers of both predators and prey caught on sticky traps in rainforest were about 6% and 25%, respectively, of those caught in open fields, indicating a strongly reduced rate of aerial migration in the forest. The number of P. persimilis caught on the sticky traps increased with increasing populations of predators on foliage. Thus, dense vegetation inhibits the movement of air currents and inhibits colonisation by both predators and, to a lesser extent, spider mites. These results suggest that the inhibition of aerial migration is one reason for lower numbers of P. persimilis in forest habitats, both because its own vagility is restricted, and because its prey is less able to disperse.     

Attraction of Phytoseiulus persimilis (Acari: Phytoseiidae) towards volatiles from various Tetranychus urticae-infested plant species

Plants infested with the spider mite Tetranychus urticae Koch, may indirectly defend themselves by releasing volatiles that attract the predatory mite Phytoseiulus persimilis Athias-Henriot. Several plants from different plant families that varied in the level of spider mite acceptance were tested in an olfactometer. The predatory mites were significantly attracted to the spider mite-infested leaves of all test plant species. No differences in attractiveness of the infested plant leaves were found for predatory mites reared on spider mites on the different test plants or on lima bean. Thus, experience with the spider mite-induced plant volatiles did not affect the predatory mites. Jasmonic acid was applied to ginkgo leaves to induce a mimic of a spider mite-induced volatile blend, because the spider mites did not survive when incubated on ginkgo. The volatile blend induced in ginkgo by jasmonic acid was slightly attractive to predatory mites. Plants with a high degree of direct defence were thought to invest less in indirect defence than plants with a low degree of direct defence. However, plants that had a strong direct defence such as ginkgo and sweet pepper, did emit induced volatiles that attracted the predatory mite. This indicates that a combination of direct and indirect defence is to some extent compatible in plant species.     

Copulation, egg production and sex-ratio in Phytoseiulus persimilis and Amblyseius bibens (Acari: Phytoseiidae)

In Phytoseiulus persimilis Athias-Henriot and Amblyseius bibens Blommers a relation was found between the duration of copulation and the resultant egg production. After 15 min of copulation no eggs were produced but after respectively 30, 60 and 90 min an increasing number of eggs were deposited. In P. persimilis the total number of eggs can be produced after one copulation of long duration but in A. bibens several copulations are necessary for total egg production. Evidence was found that egg deposition depends on the quantity of sperm transferred during insemination. Relatively more males developed from eggs deposited during the first day of egg deposition but males are produced throughout the whole egg-laying period. Females of P. persimilis remain fertile throughout their life until they have deposited their total possible number of eggs. Three to 4 egg-laying periods could be induced by copulations of 30 min duration. At each period relatively more males developed from eggs laid during the first days. Males of P. persimilis were found to be very fertile. The results obtained are discussed in relation to the reproductive strategy of both species.

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Zusammenfassung Bei Phytoseiulus persimilis Athias-Henriot und Amblyseius bibens Blommers wurde ein Zusammenhang gefunden zwischen Kopulationsdauer und der resultierenden Eiproduktion. Nach 15 Minuten Kopulation wurden keine Eier produziert; nach 30, 60 und 90 Minute Kopulation hingegen wurde eine steigende Zahl Eier abgelegt. Bei P. persimilis kann die totale Eizahl nach einer einzigen Kopulation von langer Dauer produziert werden, während bei A. bibens mehrere Kopulationen notwendig sind. Es wurden Anhaltspunkte gefunden, dass die Eizahl von der während der Besamung übertragenen Spermienmenge abhängt. Aus während der ersten Tage der Eiproduktion abgelegten Eiern entwickelten sich relativ mehr Männchen, doch wurden Männchen während der ganzen Eiablageperiode produziert. Weibchen von P. persimilis bleiben während ihres ganzen Lebens, bis sie alle Eier abgelegt haben, fertil. Drei bis vier Eiablageperioden konnten durch Kopulationen von 30 Minuten Dauer induziert werden. Bei jeder Periode entwickelten sich aus den in den ersten Tagen abgelegten Eiern relativ mehr Männchen. Männchen von P. persimilis erwiesen sich als sehr fertil. Die Resultate werden im Zusammenhang mit der Vermehrungsstrategie beider Arten diskutiert.

     

Impact of nC24 agricultural mineral oil deposits on the searching efficiency and predation rate of the predatory mite Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae)

Walking activity, walking straightness, walking speed and searching efficiency of the predatory mite Phytoseiulus persimilis Athias-Henriot were measured on French bean leaf discs that were sprayed with either distilled water, or one of 0.25%, 0.50% and 1.00% w/w aqueous emulsions of an n C24 agricultural mineral oil (AMO). There was no significant difference in percentage of time that mites spent walking in the control (water-sprayed) conditions and in any of the oil treatments. Walking paths were significantly straighter in the oil treatments than in the control, but differences among the oil treatments did not differ significantly. Walking speeds in the oil treatments were significantly slower than in the control and decreased with increasing oil concentration. Deposits of oil at all concentrations significantly suppressed searching efficiency in comparison with control, and searching efficiency in the 1.00% oil treatment was significantly lower than in the 0.25% oil treatment. First predation of P. persimilis on AMO-contaminated eggs of two-spotted mite ( Tetranychus urticae Koch) on unsprayed leaf discs was significantly delayed in all oil treatments in comparison with the control. However there was no significant effect on the overall predation rate. In the tests of P. persimilis predation on AMO-contaminated T. urticae eggs on sprayed leaf discs, the number of first predation occurrences in the first hour was significantly lower in 0.50% and 1.00% oil treatments than in the control. Overall predation rates were significantly reduced by oil but they did not differ significantly among the oil treatments.     

Functional Response of Phytoseiulus persimilis (Acari: Phytoseiidae) on Untreated and Beauveria bassiana - Treated Adults of Tetranychus urticae (Acari: Tetranychidae)

The functional response of the predatory mite, Phytoseiulus persimilis Athias- Henriot was examined on either non-inoculated or inoculated adults of the spider mite, Tetranychus urticae Koch by Beauveria bassiana DEBI008 with four time intervals; 0, 24, 48 and 72-h treatments, at 25?±?1?°C, 60–70?% RH and a photoperiod of 16:8?h (L: D). Results indicated that functional responses of P. persimilis on both untreated and B. bassiana treated adults of T. urticae are type II. Data analysis showed that handling time of predator was increased on treated T. urticae with the increase of the time after spray in comparison with that of untreated adults of T. urticae (3.5143, 3.8152, 4.0735, 7.6829 and 11.7789?h.), respectively. Differences among treatments for handling time were significant. Attack rates were close to each others and there was no significant difference in attack rates of different time interval treatments. With the increase of the time after spray adults of the spider mite, T. urticae by B. bassiana caused intensive increasing in handling time of P. persimilis and accordingly it caused intensive decreasing in feeding rate of predator.     

Alternating temperatures affect life table parameters of Phytoseiulus persimilis, Neoseiulus californicus (Acari: Phytoseiidae) and their prey Tetranychus urticae (Acari: Tetranychidae)

Increasing energy costs force glasshouse growers to switch to energy saving strategies. In the temperature integration approach, considerable daily temperature variations are allowed, which not only have an important influence on plant growth but also on the development rate of arthropods in the crop. Therefore, we examined the influence of two constant temperature regimes (15 °C/15 °C and 20 °C/20 °C) and one alternating temperature regime (20 °C/5 °C, with an average of 15 °C) on life table parameters of Phytoseiulus persimilis and Neoseiulus californicus and their target pest, the two-spotted spider mite Tetranychus urticae at a 16:8 (L:D) h photoperiod and 65 ± 5 % RH. For females of both predatory mites the alternating temperature regime resulted in a 25–30 % shorter developmental time as compared to the corresponding mean constant temperature regime of 15 °C/15 °C. The immature development of female spider mites was prolonged for 7 days at 15 °C/15 °C as compared to 20 °C/5 °C. With a daytime temperature of 20 °C, no differences in lifetime fecundity were observed between a nighttime temperature of 20 and 5 °C for P. persimilis and T. urticae. The two latter species did show a higher lifetime fecundity at 20 °C/5 °C than at 15 °C/15 °C, and their daily fecundity at the alternating regime was about 30 % higher than at the corresponding mean constant temperature. P. persimilis and T. urticae showed no differences in sex ratio between the three temperature regimes, whereas the proportion of N. californicus females at 15 °C/15 °C (54.2 %) was significantly lower than that at 20 °C/5 °C (69.4 %) and 20 °C/20 °C (67.2 %). Intrinsic rates of increase were higher at the alternating temperature than at the corresponding mean constant temperature for both pest and predators. Our results indicate that thermal responses of the studied phytoseiid predators to alternating temperature regimes used in energy saving strategies in glasshouse crops may have consequences for their efficacy in biological control programs.