Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densities.     

Potential of the predatory mite Phytoseius finitimus (Acari: Phytoseiidae) to feed and reproduce on greenhouse pests

Phytoseiid mites of the genus Phytoseius are natural enemies of tetranychid and eriophyid herbivorous mites mostly found on hairy plants where they feed on prey, as well as on pollen. Nevertheless, the nutritional ecology and the role of these predators in biological pest control are only rarely addressed. In the present study, we evaluated the potential of Phytoseius finitimus to feed and reproduce on three major greenhouse pests, the two-spotted spider mite, the greenhouse whitefly and the western flower thrips. Additionally, we estimated the effect of cattail pollen when provided to the predator alone or in mixed diets with prey. Contrary to thrips larvae, both spider mite larvae and whitefly crawlers sustained the development of P. finitimus. In addition, females consumed more spider mite eggs and larvae, as well as whitefly crawlers than thrips larvae, but laid eggs when feeding on all prey. When provided alone, cattail pollen sustained the development and reproduction of the predator. The addition of pollen in mixed diets with prey reduced prey consumption, though it increased the predator’s egg production. We discuss the implications of our findings for biological pest control.     

Intraguild predation among plant pests: western flower thrips larvae feed on whitefly crawlers

Omnivores obtain resources from more than one trophic level, and choose their food based on quantity and quality of these resources. For example, omnivores may switch to feeding on plants when prey are scarce. Larvae of the western flower thrips Frankiniella occidentalis Pergande (Thysanoptera: Thripidae) are an example of omnivores that become predatory when the quality of their host plant is low. Western flower thrips larvae usually feed on leaf tissue and on plant pollen, but may also attack eggs of predatory mites, their natural enemies, and eggs of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), one of their competitors. Here, we present evidence that western flower thrips larvae prey on Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), another competitor for plant tissue. We tested this on two host plant species, cucumber (Cucumis sativa L.), considered a host plant of high quality for western flower thrips, and sweet pepper (Capsicum annuum L.), a relatively poor quality host. We found that western flower thrips killed and fed especially on whitefly crawlers and that the incidence of feeding did not depend on host-plant species. The developmental rate and oviposition rate of western flower thrips was higher on a diet of cucumber leaves with whitefly crawlers than on cucumber leaves without whitefly crawlers, suggesting that thrips do not just kill whiteflies to reduce competition, but utilize whitefly crawlers as food.     

Cross‐resistance of chrysanthemum to western flower thrips,celery leafminer,and two‐spotted spider mite

Chrysanthemum [Chrysanthemum × morifolium Ramat. (Asteraceae)] is one of the economically most important greenhouse ornamentals worldwide. A major constraint in chrysanthemum production is adequate pest management, requiring the use of different tactics, such as improving host plant resistance, in the framework of an integrated pest management (IPM) approach. In this study, we investigated cross‐resistance of chrysanthemum to its three major pests: western flower thrips [Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)], celery leafminer [Liriomyza trifolii (Burgess) (Diptera: Agromyzidae)], and two‐spotted spider mite [Tetranychus urticae Koch (Acari: Tetranychidae)]. We quantified resistance to each pest by performing greenhouse bioassays with a broad range of chrysanthemum types from commercial germplasm provided by Dutch breeding companies. Considerable variation was detected among the chrysanthemum cultivars in thrips silver damage and growth damage, leafminer damage, measured as number of mines and pupae, and spider mite numbers and damage. We observed significant positive correlations between thrips damage (both silver and growth damage) vs. leafminer numbers (both mines and pupae), and between leafminer numbers (both mines and pupae) vs. spider mite numbers. Our results indicate an overlap in resistance to all three herbivores. The important implications of this result for chrysanthemum breeding are discussed.     

Positive association between thrips and spider mites in seedling cotton

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Testing for non-target effects of spiromesifen on <Emphasis Type="Italic">Eretmocerus mundus</Emphasis> and <Emphasis Type="Italic">Orius laevigatus</Emphasis> under greenhouse conditions

Spiromesifen is a novel insecticide/acaricide belonging to the new chemical class of spirocyclic phenyl-substituted tetronic acids, and it is especially active against whiteflies and tetranychid spider mite species. In the biologically based integrated pest management (IPM) programs in vegetable crops in southeastern Spain, the key natural enemies include the parasitoid Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) for sweetpotato whitefly control, and the minute pirate bug, Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) for western flower thrips control. Side effects of spiromesifen on E. mundus and O. laevigatus, were evaluated by laboratory studies and field trials in commercial greenhouses under IPM programs. Results indicate that spiromesifen had favourable selectivity to O. laevigatus and E. mundus and would complement biological control of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) by E. mundus. Handling editor: Patrick De Clercq     

Effectiveness of imidacloprid (ProAgro 100 SL) in the control of glasshouse whitefly (Trialeurodes vaporariorum) and western flower thrips (Frankliniella occidentalis) on tomato under cover

In 2002 a glasshouse experiments were carried out on the effectiveness of ProAgro 100 SL in the control of glasshouse whitefly and western flower thrips on tomato cv. Perkoz. Strict observation of the basic prophylactic rules such as introducing in to glasshouse only healthy seedlings, uninfected by whitefly and thrips as well as isolation of tomato plants, especially the seedlings from ornamental plants are important to the limit of the pest population. During the vegetation period the population of whitefly and thrips may be limited by the insecticide application. The glasshouse experiments on the performance of ProAgro 100 SL in the control of mentioned above pest species were carried out at the Research Institute of Vegetable Crops in Skierniewice. The ProAgro 100 SL was applied in the concentration of 0,1%. The standard treatment was Juventox 040 SL (acetamiprid) in the concentration of 0.05%. The obtained results allow to find that ProAgro 100 SL in the rates of 0.1% performed well in the limiting population of whitefly and western flower thrips on glasshouse tomato.     

Evaluation of phytoseiid predators for control of western flower thrips on greenhouse cucumber

Ten predatory mite species, all phytoseiids, were evaluated for control of western flower thrips (WFT), Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), on greenhouse cucumber. This study was done to further improve biological control of thrips on this crop. Neoseiulus cucumeris (Oudemans) is at present used for biological control of thrips in greenhouses. Compared to this species, Typhlodromalus limonicus (Garman & McGregor), Typhlodromips swirskii (Athias-Henriot) and Euseius ovalis (Evans) reached much higher population levels resulting in a significantly better control of thrips. T. limonicus was clearly the best predator of WFT. Also Euseius scutalis (Athias-Henriot) increased to higher populations levels than N. cucumeris, but without controlling the thrips, probably because of an unequal distribution of this predator on the plant. Iphiseius degenerans (Berlese), Neoseiulus barkeri (Hughes), Euseius finlandicus (Oudemans) and Typhlodromus pyri (Scheuten) did not establish better than N. cucumeris. A non-diapausing exotic strain of N. cucumeris did not differ from the North European strain. The best performers in this study were all of sub-tropical origin. T. limonicus, T. swirskii and E. ovalis have good potentials for controlling not only thrips but also whiteflies. Factors affecting the efficacy of phytoseiids on greenhouse cucumbers are discussed.     

Host-plant-mediated interaction between populations of a true omnivore and its herbivorous prey

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are competitors with twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), for plant resources and potential predators on spider mites when the opportunity arises. Which interaction predominates may depend on relative population densities and individual species’ responses to the plants on which they co‐occur. We examined interactions between populations of thrips and spider mites on several cultivars of two bedding plants: impatiens (Impatiens wallerana Hook.f) cultivars ‘Impulse Orange’ and ‘Cajun Carmine’, and ivy geranium [Pelargonium peltatum (L.) L’Her ex Aiton] cultivars ‘Sybil Holmes’ and ‘Amethyst 96’. Four combinations of thrips and mite numbers were studied: thrips alone, mites alone, and two densities of thrips and mites together. We compared population numbers after 4 weeks. Overall, mite numbers increased more rapidly than thrips did, but both species increased more rapidly on impatiens than on ivy geraniums. Between impatiens cultivars, thrips and mites increased more slowly on ‘Cajun Carmine’ (i.e., it was more resistant) than on ‘Impulse Orange’. On ivy geraniums, spider mites increased more slowly on ‘Sybil Holmes’ than on ‘Amethyst 96’ but the reverse was the case for thrips. Regardless of plant species or cultivar, thrips had a strong negative effect on spider mites whenever they co‐occurred, suppressing mite population growth by around 50% compared to when mites were alone. However, the effect of spider mites on western flower thrips depended on the quality of the plant species. On impatiens, thrips co‐occurring with spider mites increased slightly more than thrips alone did, while on ivy geranium mites had a small negative effect on thrips. Contrary to expectations, thrips had a larger negative impact on spider mites on plants that were more susceptible to thrips than they did on plants more resistant to thrips. We suggest that host plants mediate the interaction between an omnivore and its herbivorous prey not only by altering individual diet choice but by changing the relative population dynamics of each species.     

Insecticidal properties of a Chenopodium-based botanical

The emulsifiable concentrate UDA-245 based on an essential oil extract from Chenopodium ambrosioides variety near ambrosioides, a North American herbaceous plant, was compared with commercially available pesticides for their effectiveness to control green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae), western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), and greenhouse whitefly, Trialeurodes vaporariorium (Westwood) (Homoptera: Aleyrodidae). Side effects on the whitefly parasitoid Encarsia formosa Gahan (Hymenoptera: Aphelinidae) also were determined. With green peach aphid, UDA-245 at 0.5% concentration was significantly more effective than the control (water) treatment in a laboratory bioassay and significantly more effective than neem oil and the control treatment and as effective as insecticidal soap in a greenhouse assay. With the western flower thrips, UDA-245 at 0.5% was significantly more effective than neem oil, insecticidal soap and the control treatment in a laboratory bioassay, whereas in a greenhouse assay, UDA-245 at 1.0% was the only treatment that maintained control of the western flower thrips 2 wk after the last treatment period. UDA-245 at 0.5% (laboratory bioassay) was significantly more effective in managing greenhouse whitefly than neem oil, endosulfan, and the control treatment and as effective as insecticidal soap. Insecticidal soap proved to be toxic to the parasitoid E. formosa (71.9% mortality), whereas UDA-245 at 0.5% was not significantly more toxic than the control (11.2 and 4.6% mortality, respectively). Our results suggest that a greenhouse integrated pest management (IPM) program using a botanical such as UDA-245 could effectively control infestations of major pests present while having a negligible effect on biological control agents.     

Selection for non-diapause inAmblyseius cucumeris andAmblyseius barkeri and exploration of the effectiveness of selected strains for thrips control

In Europe and North America the western flower thrips,Frankliniella occidentalis, is an important pest in various greenhouse crops, such as sweet pepper and cucumber. Two species of predatory mite are commercially applied for biological control of this pest:Amblyseius cucumeris andA. barkeri. Thrips control is generally successful from March onwards. During winter, however, thrips control by these predatory mites is less effective. An important reason for this is that the commercially applied strains of both mite species enter reproductive diapause under short-day photoperiods, whereas the western flower thrips does not enter diapause. In this paper we report on selection experiments for non-diapause in strains of both mite species, aimed at obtaining predators that do not enter diapause under light- and temperature conditions prevailing in winter. Additional experiments were done to estimate the potential of the selected lines as control agents ofF. occidentalis. Selection for non-diapause proved highly successful in both predatory mite species. In a New Zealand strain ofA. cucumeris diapause incidence decreased from 41% to 0% in about ten generations; in a Dutch strain ofA. barkeri diapause incidence decreased from 67% to 0% in about six generations. Furthermore, selection for non-diapause had no influence on predator performance, measured as predation rate and oviposition rate on a diet of first instar thirps larvae. Rates of predation and oviposition were the same for selected and unselected lines in both species; rates of predation and oviposition were higher forA. cucumeris than forA. barkeri. After 18 months under non-diapause conditions, no less than 92% of a sample of the selected non-diapause line ofA. cucumeris did not enter diapause when tested under diapause-inducing conditions. This indicates that ‘non-diapause’ is a stable trait in these predatory mites. Finally, a small-scale greenhouse experiment in a sweet pepper crop showed that the selected non-diapause line ofA. cucumeris established successfully under diapause-inducing short-day conditions.     

东亚小花蝽对西方花蓟马和二斑叶螨的捕食选择性

多食性天敌对猎物的捕食选择性及猎物密度对天敌捕食的干扰作用直接影响到天敌对不同猎物的控制作用.在实验室条件下研究了东亚小花蝽对西方花蓟马和/或二斑叶螨不同虫态的捕食选择性,以及两猎物中一种猎物的密度变化对小花蝽取食另一种猎物的影响.结果如下:东亚小花蝽5龄若虫和成虫对西方花蓟马2龄若虫的捕食选择性均强于对其成虫,对二斑叶螨的选择性为雌成螨>若螨>幼螨.实验中西方花蓟马2龄若虫是东亚小花蝽最喜好的虫态.二斑叶螨雌成螨密度固定为60头/19.63cm2,西方花蓟马若虫密度从10增加到60时显著地减少了东亚小花蝽对二斑叶螨的取食.反之,固定西方花蓟马同样密度,增加二斑叶螨密度却没有显著改变小花蝽对西方花蓟马的取食.此结果进一步表明,西方花蓟马是东亚小花蝽更喜好的猎物.     

新疆棉区主要害虫的演替及其机理分析

阐述了新疆棉区主要害虫的演替及其机理。1950～1960年主要害虫为黄地老虎、牧草盲蝽象、烟蓟马、苜蓿蚜为主;1970～1980年以棉铃虫、烟蓟马、棉长管蚜、棉红蜘蛛为主;从1990年开始以棉铃虫、棉蚜、棉红蜘蛛为主。导致这一演替的主要原因为作物布局、耕作制度、栽培方法、管理技术的变化和农药化肥的过量施用。     

Biological control of thrips and whiteflies by a shared predator: Two pests are better than one

We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator–two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.     

Pest response in packed table grapes to low temperature storage combined with slow-release sulfur dioxide pads in basic and large-scale tests

The effect of low temperature storage combined with slow release sulfur dioxide pads was determined in basic laboratory and large-scale commercial tests on western flower thrips, Frankliniella occidentalis Pergande; grape mealybug, Pseudococcus maritimus (Ehrhorn); Pacific spider mite, Tetranychus pacificus McGregor; twospotted spider mite, Tetranychus urticae Koch; and omnivorous leafroller, Platynota stultana Walshingham. Temperatures within the foam containers among the packed clusters decreased from ambient to 2 degrees C within approximately 1 d and ranged from 0.4 to 1.7 degrees C in all tests. Sulfur dioxide concentrations in the foam containers ranged between 0.2 and 1.6 ppm during the 1- to 6-wk storage period in basic tests and 0.5-1.1 ppm during the 1- to 8-wk storage period in the large-scale test. Western flower thrips was completely controlled by a > or =1-wk exposure. Grape mealybug mortality was > or =93% after 2-5 wk exposures and 100% after a 6-wk exposure in basic tests. Pacific spider mite and twospotted spider mite mortality was 98.0 and 99.6%, respectively, after a 6-wk exposure. Mortality of grape mealybug and twospotted spider mite increased significantly at > or =3-wk exposures and Pacific spider mite mortality increased significantly at > or =4-wk exposures. Mortality of the spider mites in general was directly related to the duration of exposure. An 8-wk exposure to low temperature storage combined with slow release sulfur dioxide pads in the large-scale test resulted in 100% mortality of western flower thrips, twospotted spider mite, and omnivorous leafroller. The treatment resulted in <8% survival of grape mealybug and <1% survival of Pacific spider mite in the large-scale test. The combination treatment offers an economical method to attain quarantine control of certain insects and mites.     

Modified atmosphere treatments as a potential disinfestation technique for arthropod pests in greenhouses

Incidental transport of arthropods on plant material can be a significant mode of pest entry into greenhouses. We evaluated the use of controlled atmosphere treatments as a potential way to eliminate arthropod pests on plant propagules (i.e., cuttings or small rooted plants). Lethal exposures to CO2 or N2 were determined for common greenhouse pests including fungus gnat larvae, Bradysia sp.; green peach aphid, Myzus persicae (Sulzer); sweetpotato whitefly, Bemisia sp.; twospotted spider mite, Tetranychus urticae Koch; and western flower thrips, Frankliniella occidentalis (Pergande). We also studied the effect of pest species, life stage, and presence or absence of plants on efficacy of modified atmosphere treatments. Finally, effects of modified atmospheres on plant quality were evaluated for several bedding plant species including begonia, Begonia semperflorens-cultorum Hort. 'Cocktail Series', chrysanthemum, Dendranthema grandiflora Tzvelev., geranium, Pelargonium X hortorum L.H. Bailey, and impatiens, Impatiens wallerana Hook f., and among cultivars of geranium and chrysanthemum. Exposure for 12-18 h to >99% N2 or CO2 caused complete mortality of aphids, mites, thrips, and whiteflies. Fungus gnat larvae were more tolerant of hypoxic conditions. Adult mites and eggs were equally susceptible. For most pests, there was no difference in response to atmospheres modified by CO2 or N2. However, there was variation in response among plant species and cultivars, with effects ranging from delayed flowering to mortality. Despite the possibility of adverse effects on some plants, this work indicates that use of modified atmospheres has potential to eliminate arthropod pests on plant propagules before they are introduced into greenhouses.     

Influence of diet on life table parameters of <Emphasis Type="Italic">Iphiseius degenerans</Emphasis> (Acari: Phytoseiidae)

Studies on the reproduction, longevity and life table parameters of Iphiseius degenerans (Berlese) were carried out under laboratory conditions of 25 ± 1 °C, 75 ± 5% RH and 16L:8D h. As food sources for the predatory mite, Ricinus communis L. pollen, all stages of the spider mite Tetranychus urticae Koch, Frankliniella occidentalis (Pergande) larvae, and Ephestia kuehniella Zeller eggs were selected. All diets were accepted as food by the adult mites. Female longevity ranged from 29.5 to 42.4 days, the highest value was recorded on a diet of Ephestia eggs. The highest percentage of females escaping the experimental arena was observed on the diet consisting of thrips larvae. The highest oviposition rate (1.9 eggs/female.day) was recorded when the predator was fed on spider mites on an artificial substrate. For other diets, oviposition rates ranged from 1.0 to 1.3 eggs/female.day. The intrinsic rate of natural increase (r _m) of I. degenerans varied between 0.015 and 0.142 females/female.day. The diet consisting of castor bean pollen resulted in the highest population growth whereas the diet on spider mites brushed off onto a bean leaf arena resulted in the slowest population growth. This can be explained by the inability of the predator to cope with the webbing of T. urticae, and the high escape rate of the progeny when reared on spider mites. The percentage of females in the offspring ranged from 40 to 73%.This revised version was published online in May 2005 with a corrected cover date.     

Efficacy of Silwet L-77 against several arthropod pests of table grape

Silwet L-77, an organosilicone surfactant, was applied to several arthropod pests of California table grapes. Eggs of grape mealybug, Pseudococcus maritimus (Ehrhorn), and omnivorous leafroller, Platynota stultana Walsingham, were tolerant to 0.1, 0.25, and 0.5% treatment solutions; however, eggs of Pacific spider mite, Tetranychus pacificus McGregor, were highly susceptible with mortality >99.4% (0.1% Silwet L-77). Mortality of immature and adult stages of cotton aphid (Aphis gossypii Glover), Western flower thrips (Frankliniella occidentalis Pergande), and Pacific spider mite (Tetranychus pacificus McGregor) was > or = 93.8, > or = 98.5, and > or = 99.4% for 0.1, 0.25, and 0.5% Silwet L-77, respectively. Grape mealybug crawlers had 100% mortality when treated with 0.5 and 1.0% Silwet L-77 solutions; however, mortality was only 6.7% when 0.1% Silwet L-77 was applied. 'Thompson Seedless' table grapes were not damaged when treated with up to 1% Silwet L-77; however, grapes treated with the 0.5 and 1.0% solutions appeared wet after removal from cold storage because of the effect of the surfactant spreading the water condensation. Grapes dried with the normal bloom on the berries when they reached room temperature.     

Odour-mediated responses of phytophagous mites to conspecific and heterospecific competitors

Plants under herbivore attack produce volatiles, thus attracting natural enemies of the herbivores. However, in doing so, the plant becomes more conspicuous to other herbivores. Herbivores may use the odours as a cue to refrain from visiting plants that are already infested, thereby avoiding competition for food, or, alternatively, to visit plants with defences weakened by earlier attacks. We investigated the response of one species of herbivore (the spider mite Tetranychus urticae) to odours emanating from cucumber plants infested by conspecific or heterospecific (the western flower thrips, Frankliniella occidentalis) herbivores. Olfactometer experiments in the laboratory showed that spider mites have a slight, but significant, preference for plants infested with conspecifics, but strongly avoid plants with thrips. These results were substantiated with greenhouse experiments. We released spider mites on the soil in the centre of a circle of six plants, half of which were infested with either conspecifics or heterospecifics (thrips), whereas the other half were uninfested. It was found that 60–70% of the mites were recaptured on the plants within 5 h after release. Results of these experiments were in agreement with results of the olfactometer experiments: (1) significantly fewer spider mites were found on plants infested with thrips than on uninfested plants and (2) more mites were found on plants with conspecifics than on clean plants (although this difference was not significant). From a functional point of view it makes sense that spider mites prefer clean plants over thrips-infested plants, since thrips are not only competitors, but are also known as intraguild predators of spider mites. Possible reasons for the slight attraction of spider mites to plants infested with conspecifics are discussed. Received: 22 June 1996 / Accepted: 29 September 1996     

Functional response of the predator <Emphasis Type="Italic">Scolothrips takahashii</Emphasis> to hawthorn spider mite, <Emphasis Type="Italic">Tetranychus viennensis</Emphasis>: effect of age and temperature

A leaf disc bioassay was employed to examine the effects of temperature and predator age on functional response of an acarophagous thrips, Scolothrips takahashii Priesner, to hawthorn spider mite, Tetranychus viennensis Zacher, in the laboratory. The results indicated that the predatory thrips exhibited type-II functional responses against the mites under various temperatures, and that females are more voracious than males. Analysis showed that temperature had significant effects on the predatory capacity of adult thrips over the range of 20–35 °C. Attack rate in females linearly increased with temperature while in males it was independent of temperature. Handling times in both males and females decreased linearly with increasing temperature. Extended response models describing the functional response with temperature incorporated as a parameter were developed, yielding an estimated maximum numbers of prey attacked at four temperatures were 38.38, 55.06, 71.74 and 88.42 eggs per day for females, and 15.11, 26.11, 37.11 and 48.01 eggs per day for males, respectively. The age of predator affected both the type of the functional response shown and the magnitude of predation by S.␣takahashii on the spider mite. Females of various ages exhibited Type-II functional responses with similar attack rates, but handling time prolonged linearly as age increased: the handling times in 15- and 18-d-old females were significantly longer than in 6-d-old thrips. However, Type-I functional responses were determined for males aged 12 d or more; the maximum number of prey eaten in 24 h decreased as age increased. The implications of the results for the management of hawthorn spider mite are discussed.