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.     

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.     

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.     

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.     

The effect of chrysanthemum leaf trichome density and prey spatial distribution on predation of Tetranychus urticae (Acari: Tetranychidae) by Phytoseiulus persimilis (Acari: Phytoseiidae)

The effect of plant architecture, in terms of leaf hairiness, and prey spatial arrangement, on predation rate of eggs of the spider mite, Tetranychus urticae Koch, by the predatory mite Phytoseiulus persimilis Athias-Henriot was examined on cut stems of chrysanthemums. Three levels of leaf hairiness (trichome density) were obtained using two different chrysanthemum cultivars and two ages within one of the cultivars. The number of prey consumed by P. persimilis was inversely related to trichome density. At low prey densities (less than ten eggs per stem), prey consumption did not differ in a biologically meaningful way between treatments. The effect of prey spatial arrangement on the predation rate of P. persimilis was also examined. Predation rates were higher in prey patches on leaves adjacent to the release point of P. persimilis, but significantly greater numbers of prey were consumed in higher density prey patches compared to low density patches. The predators exhibited non-random searching behaviour, spending more time on leaves closest to the release point. The implications of these findings for biological control and predator-prey dynamics are discussed.     

Interactions in a tritrophic acarine predator-prey metapopulation system V: Within-plant dynamics of Phytoseiulus persimilis and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

To investigate the relative contributions of bottom-up (plant condition) and top-down (predatory mites) factors on the dynamics of the two-spotted spider mite (Tetranychus urticae), a series of experiments were conducted in which spider mites and predatory mites were released on bean plants. Plants inoculated with 2, 4, 8, 16, and 32 adult female T. urticae were either left untreated or were inoculated with 3 or 5 adult female predators (Phytoseiulus persimilis) one week after the introduction of spider mites. Plant area, densities of T. urticae and P. persimilis, and plant injury were assessed by weekly sampling. Data were analysed by a combination of statistical methods and a tri-trophic mechanistic simulation model partly parameterised from the current experiments and partly from previous data. The results showed a clear effect of predators on the density of spider mites and on the plant injury they cause. Plant injury increased with the initial number of spider mites and decreased with the initial number of predators. Extinction of T. urticae, followed by extinction of P. persimilis, was the most likely outcome for most initial combinations of prey and predators. Eggs constituted a relatively smaller part of the prey population as plant injury increased and of the predator population as prey density decreased. We did not find statistical evidence of P. persimilis having preference for feeding on T. urticae eggs. The simulation model demonstrated that bottom-up and top-down factors interact synergistically to reduce the density of spider mites. This may have important implications for biological control of spider mites by means of predatory mites.     

Relative toxicity of nC24 agricultural mineral oil to Tetranychus urticae Koch (Acari: Tetranychidae) and Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseiidae) and its possible relationship to egg ultrastructure

The relative toxicity (LC₅₀ values based on µg oil/cm²) is evaluated of aqueous n C24 agricultural mineral oil (AMO) emulsions to the egg, six-legged nymph (larva), eight-legged protonymph and adult stages of two-spotted mite ( Tetranychus urticae ) and its predator, Phytoseiulus persimilis , on French bean leaf discs, using a Potter spray tower to apply of the oil. The egg of P. persimilis was the least susceptible stage (LC₅₀ 444.84) and its LC₅₀ was significantly higher than all other stages tested of either P. persimilis or T. urticae . The LC₅₀ for adult female T. urticae (LC₅₀ 63.89) was significantly lower than the larva (LC₅₀ 93.86); however, there was no significant difference in response between the protonymph (LC₅₀ 70.44) and the larva, which were both higher than T. urticae eggs (LC₅₀ 17.55). LC₅₀s for P. persimilis larva (LC₅₀ 43.87), protonymph (LC₅₀ 41.55) and adult female (LC₅₀ 53.34) were similar. Scanning electron microscopy showed that the egg surface of T. urticae is usually well covered with fine silk that may trap more oil and increase AMO efficacy. Other possible differences in AMO efficacy between T. urticae and P. persimilis may be due to differences in egg size, egg incubation period, egg surface structure and the presence of vulnerable respiratory cones in T. urticae eggs. Dose of 0.2–0.3% (w/w) is considered to be the most appropriate for n C24 AMOs use against T. urticae in combination with P. persimilis in integrated pest management programs.     

Functional response of Neoseiulus californicus (Acari: Phytoseiidae) to Tetranychus urticae (Acari: Tetranychidae) on strawberry leaves

Neoseiulus californicus (McGregor) is a predatory mite employed for biological control of the agricultural pest Tetranychus urticae (Koch). We explored whether environmental differences, in this case the trichome densities of abaxial leaf surfaces of strawberry cultivars (‘Maehyang’ and ‘Sulhyang’ varieties) affect the functional response of adult female N. californicus preying on immature stages (egg, larva and nymph) of T. urticae. We also evaluated the functional response of N. californicus to eggs of T. urticae at different temperatures (15, 20, 25, 30 and 35°C). We conducted a logistic regression of the proportion of prey consumed as a function of initial prey density to identify functional response types, and used nonlinear least‐squares regression and the random predator equation to estimate attack rates and handling times. The functional response of adult female N. californicus to T. urticae was not influenced by non‐glandular trichomes on abaxial leaves but was affected by temperature. Overall, adult female N. californicus exhibited a type 2 functional response to T. urticae. The handling time of N. californicus was highest (1.9970 h) against T. urticae nymphs. The attack rate did not change much at 15–30°C, but was significantly higher at 35°C. The handling time decreased significantly with increasing temperature at 15–35°C. At 35°C, the attack rate was highest (0.2087) and the handling time was lowest (0.9511 h).     

Prey stage preference and functional response of Euseius hibisci to Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, and (c) estimate the functional response of E. hibisci when pollen of Ligustrum ovalifolium was present as well. We conducted experiments on excised pieces of strawberry leaf arenas (Fragaria ananassa) under laboratory conditions of 25 ± 2 °C, 60 ± 5% RH and 12 h photophase. Our results indicated that the predator consumed significantly more prey eggs than other prey stages. Consumption of prey deutonymphs and adults was so low that they were excluded from the non-choice functional response experiments. The functional response on all food items was of type II. The two parameters of the functional response were estimated for each prey type by means of the adjusted non-linear regression model. The highest estimated value a (instantaneous rate of discovery) and the lowest value of T_h (handling time, including digestion) were found for the predator feeding on prey eggs, and a was lowest and T_h highest when fed protonymphs. Using the jack-knife method, the values for the functional response parameters were estimated. The values of a and T_h produced by the model were similar among all prey types except for the eggs, which were different. Using pollen simultaneously with prey larvae decreased the consumption of the latter over the full range of prey densities The suitability of this predator for biological control of T. urticae on strawberry is discussed.     

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.     

The Effects of Prey Patchiness, Predator Aggregation, and Mutual Interference on the Functional Response of Phytoseiulus persimilis Feeding on Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The spatial distributions of two-spotted spider mites Tetranychus urticae and their natural enemy, the phytoseiid predator Phytoseiulus persimilis, were studied on six full-grown cucumber plants. Both mite species were very patchily distributed and P. persimilis tended to aggregate on leaves with abundant prey. The effects of non-homogenous distributions and degree of spatial overlap between prey and predators on the per capita predation rate were studied by means of a stage-specific predation model that averages the predation rates over all the local populations inhabiting the individual leaves. The empirical predation rates were compared with predictions assuming random predator search and/or an even distribution of prey. The analysis clearly shows that the ability of the predators to search non-randomly increases their predation rate. On the other hand, the prey may gain if it adopts a more even distribution when its density is low and a more patchy distribution when density increases. Mutual interference between searching predators reduces the predation rate, but the effect is negligible. The stage-specific functional response model was compared with two simpler models without explicit stage structure. Both unstructured models yielded predictions that were quite similar to those of the stage-structured model.     

Interactions in a trirophic acarine predator-prey metapopulation system: effects of Tetranychus urticae on the dispersal rates of Phytoseiulus persimilis (Acarina: Tetranychidae, Phytoseiidae)

The dispersal behaviour of the predatory mite Phytoseiulus persimilis Athias-Henriot between bean plants was studied in a greenhouse. The aim of the study was to estimate the rate of predator emigration affected by different densities of Tetranychus urticae Koch and different numbers of between-plant connections (bridges). The results show that predators emigrate from a plant almost exclusively as a response to the local prey density whereas the loss rate (the per capita rate at which predators disappear from the system) also depends on the prey density on the surrounding plants, provided they are connected to the central plant by bridges. © Rapid Science Ltd. 1998     

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.     

Distribution of Tetranychus evansi and its predator Phytoseiulus longipes (Acari: Tetranychidae, Phytoseiidae) in southern Brazil

Tetranychus evansi is an important pest of tomato in several countries. The predatory mite Phytoseiulus longipes has been found in association with it in Uruguaiana, State of Rio Grande do Sul, Brazil. The objective of this study was to evaluate the distribution of those two species in Uruguaiana region. Bi-weekly samples of plant parts were taken between January 28 and April 30, 2007 in Uruguaiana and five neighboring counties. Tetranychus evansi was found in all counties, but P. longipes was only found in Uruguaiana, mainly in the urban area. It is conceivable that such restricted distribution of P. longipes is due to its recent introduction to the region. Alternatively, unfavorable winter conditions could prevent its persistence, except in protected places. Buildings and vegetation characteristics of the urban area of Uruguaiana could moderate strong winds, intense rainfall and low temperatures that commonly occur in the area.     

Spatial distribution and coincidence of Neoseiulus californicus and Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) on strawberry

In strawberry greenhouses in La Plata (Buenos Aires, Argentina), Tetranychus urticae is a major pest and Neoseiulus californicus is its most important established phytoseiid predator. The purpose of this study was to determine the spatial distribution and coincidence of N. californicus and T. urticae on strawberry. T. urticae populations exhibited density variations that were followed, with some temporal delay, by those of the predator. In general terms, N. californicus exhibited lower aggregation than T. urticae. The index of dispersion (I) of T. urticae had values significantly greater than 1 in 100% of the sampling dates. The percentage of infested leaflets increased with prey density in a curvilinear way, ranging from 80 to 100% when density was higher than 100 individuals/leaflet. N. californicus had values of I higher than unity in 86.7% (G1) and 53.8% (G2) of the cases. TaylorÕs b and IwaoÕs values were greater than 1 for both populations, this indicating aggregation. IwaoÕs results showed larger aggregation units of T. urticae (=53.24) than of N. californicus (=3.61), probably due to its higher fecundity and oviposition behaviour of laying eggs in clumps. Both populations were overdispersed, although in general terms, N. californicus exhibited lower aggregation than T. urticae. This would create refuges for the prey, thus increasing the persistence of the system. Index of coincidence of predator (Ic) was high most of the time even at low densities of both populations, decreased abruptly at the end of an interaction cycle and was similar at greenhouse and plant spatial scales. The high spatial coincidence of N. californicus with T. urticae suggests an important dispersal capacity of the predator and a high ability to detect leaflets with prey. The refuge index for the prey decreased with predator density and was higher at greenhouse scale than at plant scale, both at similar predator densities. At greenhouse scale and despite high predator density, the prey had a 10%-refuge, which would lead to the system persistence. Results of the present study suggest that N. californicus is a promising established natural enemy for controlling T. urticae on strawberry.     

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。     

Field evaluation of Beauveria bassiana efficacy for the control of Tetranychus urticae Koch (Acari: Tetranychidae)

Trials with eggplants were conducted to evaluate field efficacy of Beauveria bassiana (Bb) applications against Tetranychus urticae, during spring of 2006 and 2007. In the 2006‐Trial, a rate of ca. 0.7 × 10¹² conidia/ha was sprayed onto plants at intervals. In the 2007‐Trial, the rates of ca. 0.8 × 10¹² and 1.6 × 10¹² conidia/ha were sprayed at 1‐ or 2‐week intervals. Based on population densities of mites and leaf damage assessed throughout the trial, the Bb sprays with 1‐ or 2‐week interval showed better control than those of 3 or 4 weeks. In both trials there was no statistical difference between 1‐week and 2‐week spray interval for all parameters measured. Furthermore, the higher rate performed significantly better than the lower rate, regardless of the intervals. No interaction was found between the spraying interval and the applied rate. Ultimately, to suppress the population density of T. urticae and prevent the eggplant damage in spring, the higher rate applied at 2‐week interval was effective.     

Optimum release times for biological control of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) by Phytoseiulus persimilis Athias-Henriot (Acari: Phytoseidae) on the strawberry in greenhouses

The effectiveness of the predatory mite Phytoseiulus persimilis Athias‐Henriot (Acari: Phytoseidae) in controlling the two‐spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae) was evaluated in commercial strawberry greenhouses in two areas of Korea. Optimum release times for P. persimilis were investigated by case studies. Control effects of the two‐spotted spider mite by release of the predatory mite were shown. There was mostly good control by the release of P. persimilis when there were fewer than 0.9 T. urticae per leaf. We recommend it would be ideal to release P. persimilis twice in December and once in February for very early strawberry harvest, and three times from February to March (after overwintering) for early harvest.     

Temperature‐dependent development of Neoseiulus barkeri (Acari: Phytoseiidae) on Tetranychus urticae (Acari: Tetranychidae) at seven constant temperatures

Abstract The effect of seven constant temperatures of 15, 20, 25, 27, 30, 35 and 37°C on developmental time of Neoseiulus barkeri Hughes were determined in laboratory conditions under 65%± 5% RH and a photoperiod of 12 : 12 (L : D) h on nymphal stages of Tetranychus urticae Koch. Total developmental time of females (from egg to adult emergence) at the above‐mentioned temperatures was 26.59, 14.43, 6.32, 5.64, 4.59, 3.98 and 4.67 days, respectively. Developmental rate of the N. barkeri increased as temperature increased from 15 to 35°C, but declined at 37°C. A linear and two nonlinear models were fitted to developmental rate of immature stages of N. barkeri to predict the developmental rate as a function of temperature, as well as to estimate the thermal constant (K) and critical temperatures (i.e., T_min, T_opt and T_max). The estimated values of the T_min and K for total developmental time using the linear model were 12.07°C and 86.20 degree‐days (DD), respectively. The T_min and T_max estimated by the Sharpe‐Schoolfield‐Ikemoto (SSI) model were 11.90°C and 37.41°C, respectively. The estimated T_opt for overall immature stage development of N. barkeri by the Lactin and SSI models were 33.89°C and 24.51°C, respectively. Based on the biological criteria of model evaluation, the linear and SSI models were found to be the best models for describing the developmental rate of overall immature stages of N. barkeri and estimating the temperature thresholds.