Comparison ofTetranychus evansi andT. urticae [Acari: Tetranychidae] as prey for eight species of phytoseiid mites

Eight phytoseiid species were tested to evaluate and compare their potential as predators ofTetranychus evansi Baker & Pritchard andT. urticae (Koch). The study was conducted using arenas of excised nightshade (Solanum douglasii Dunal) and Lima bean (Phaseolus vulgaris L.) leaves infested with eitherTetranychus species. When the prey wasT. evansi, the predatorsAmblyseius californicus (McGregor) andPhytoseiulus persimilis Athias-Henriot from Ventura, California, showed the highest oviposition rates. However, those rates were 4 to 6 times lower than rates for the same predators feeding onT. urticae. OnlyA. californicus and the strain ofP. persimilis from Beni-Mellal, Morocco, had survivorship higher than 50% 8 days after the beginning of the experiment. The results indicated thatT. evansi is an unfavorable prey for all the phytoseiids tested.

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Résumé Huit espèces d'Acariens phytoseiides étaient testées en vue de comparer leurs potentialités prédatrices vis-à-vis deTetranychus evansi Baker & Pritchard et deTetranychus urticae (Koch). L'étude était réalisée sur des feuilles détachées deSolanum douglasii Dunal et dePhaseolus vulgaris L. Les feuilles avaient été infestées avec l'une ou l'autre des espèces deTetranychus. Amblyseius californicus (McGregor) etPhytoseiulus persimilis Athias-Henriot, de Ventura, ont donné les taux d'oviposition les plus élevés avecT. evansi, mais ces taux étaient 4 à 6 fois inférieurs à ceux obtenus lorsque la proie étaitT. urticae. SeulsA. californicus et la souche deP. persimilis de Beni-Mellal avaient une survie supérieure à 50%, 8 jours après le début du test. Les résultats indiquent queT. evansi n'est pas une proie favorable pour toutes les espèces testées.

     

Laboratory Evaluation of a Laboratory-selected Organophosphate-resistant Strain of Amblyseius finlandicus (Acari: Phytoseiidae) for Possible Use in Finnish Apple Orchards

The survival of adults and immatures, and reproduction at rates of 150, 300 and 900 ppm a.i. of azinphosmethyl were compared among four types of Amblyseius finlandicus females and their offspring; a laboratory-selected colony (SEL16) resistant to azinphosmethyl, an unselected base colony (Tuorla), reciprocal F1 females from crosses between SEL16 and a very susceptible colony (Hiekkaharju). The SEL16 and reciprocal F1 females had a higher survivorship than the unselected Tuorla base colony after 2 and 4 days on leaves treated with the three concentrations of insecticide. Azinphosmethyl decreased oviposition by the surviving females of all types, but the decrease was smaller in the SEL16 strain than in the base colony. The survivorship of immatures of SEL16 on fresh azinphosmethyl residues after 6 days was low at all three concentrations, but no survivors were found in the base colony at any of the concentrations. Females deposited significantly more eggs on the untreated areas of the leaves. The importance of this behavior for biological control is discussed. There were no significant differences in developmental rate, ovipositional rate, sex ratio and ovipositional period between the SEL16 and unselected base colony on untreated leaf substrates, suggesting that resistance was not associated with decreased fitness. A mode of inheritance study indicated that azinphosmethyl resistance was incompletely dominant. This was also suggested by the results of bioassays, where the reciprocal F1 females performed nearly as well as the SEL16 strain on leaves treated with field rates of azinphosmethyl.     

Does prey preference change as a result of prey species being presented together? Analysis of prey selection by the predatory mite Typhlodromus pyri (Acarina: Phytoseiidae)

Summary Prey-selection behaviour of the phytoseiid mite Typhlodromus pyri Scheuten was analysed with a Markovtype model of feeding-state dynamics and feeding-state dependent searching behaviour (Sabelis 1981, 1986, 1989; Metz and Van Batenburg 1985a, b). All behavioural characteristics of the predator which are independent of the feeding state were represented by one parameter. The remaining feeding-state dependent characteristics were represented by a function of the feeding state, with one parameter. The best parameter values to describe a predator-prey interaction were determined by fitting the model to the predation rates in monocultures. Under the assumption that the parameter values are not dependent on the composition of prey species supply, the diet of the predators in mixed cultures was predicted from parameters estimated in monoculture experiments.Two prey types, apple rust mite (Aculus schlechtendali (Nalepa)) adults and European red spider mite (Panonychus ulmi (Koch)) larvae were studied. A large discrepancy was observed between calculated and experimentally determined predation rates of T. pyri in mixed cultures: the predators actually killed 3–7 times more P. ulmi larvae than was predicted by the model.The large difference between observed and predicted predation rates in mixed cultures cannot be explained by changes in the behaviour of the prey species as a result of being together. Therefore, it seems likely that the prey selection behaviour of the predator was different when prey species were presented together than when presented singly. Apparently the predatory mite T. pyri prefers P. ulmi to S. schlechtendali.     

中国北方植绥螨二新种和二新纪录（蜱螨亚纲：植绥螨科）

本文记述采自中国北方滨海地区植绥螨二新种及二新纪录种。单毛盲走螨Typhlodromus,monosetus sp.nov.采自吉林长自山;凹胸盲走螨T.concavus sp.nov.采自山东省泰山。山葡萄钝绥螨Amblyseius vineaticus Wainstein及柞钝绥螨A.quaesitus Wainsteia et Begliarov均采自长白山,为中国新纪录。首次描述千山盲走螨T.qianshanensis Wu雄螨。     

中国西北地区钝绥螨属五新种和一新纪录(蜱螨亚纲:植绥螨科)

本文报道了作者在我国西北地区采集的植绥科钝绥螨属5个新种和1个新记录种。对新种作了详细的形态描述,分别与其近似种进行了比较并绘图说明。标本保存于广东省昆虫研究所。     

Direct and indirect adverse effects of tomato on the predatory mite Neoseiulus californicus feeding on the spider mite Tetranychus evansi

Plants may defend themselves against herbivores via morphological traits, chemical traits, or a combination of both. Herbivores that overcome the defensive mechanisms of a plant tend to specialize on this plant due to enhanced protection from natural enemies. Well‐known examples of plants possessing a suite of defensive mechanisms are found in nightshades (Solanaceae), especially in the tomato genus Lycopersicon. The spider mite Tetranychus evansi Baker and Pritchard (Acari: Tetranychidae) is specialized on solanaceous plants and is an invasive pest of tomato in Europe and Africa. Biological control of T. evansi with currently available natural enemies, such as the predatory mites Phytoseiulus persimilis Athias‐Henriot and Neoseiulus californicus McGregor (both Acari: Phytoseiidae), is unsuccessful, with the underlying mechanisms only vaguely known. We hypothesized that T. evansi is a key pest of tomato because this host plant provides a two‐pronged protection from natural enemies. Direct adverse effects of tomato on predators may arise from morphological traits and/or trichome exudates, whereas indirect effects are prey‐mediated through the accumulation of toxic plant compounds. Using a 2 × 3 factorial design, we assessed and separated direct and indirect effects of tomato on the life history of N. californicus feeding on two strains of T. evansi (reared on bean or tomato) on three substrates (tomato leaf, bean leaf, and an artificial cage). Developmental time and oviposition rate of N. californicus were both directly and indirectly negatively affected by tomato whereas offspring sex ratio and survival of juveniles and adult females were unaffected. The direct and indirect, prey‐mediated adverse effects of tomato on N. californicus with T. evansi prey had similar magnitudes and were additive. We conclude that T. evansi per se is a suitable prey species for N. californicus and discuss the results with respect to the potential use of N. californicus as biological control agent of T. evansi on tomato and other host plants.     

Practical placement improves the performance of slow release sachets of Neoseiulus cucumeris

This research investigated factors that affect the performance of Neoseiulus cucumeris (Oudemans) (Acari: Phytoseiidae) slow release sachets, focusing on dispersal in environments with non-continuous canopies and high exposure to greenhouse environmental conditions. When released from a central plant in a tray, the distribution of N. cucumeris across all other plants was uneven with the majority of mites recovered at the release point. Shading by a plant canopy reduced the mean internal temperature of the sachets, temperature peaks were less pronounced and the relative humidity was higher than in exposed sachets. Most N. cucumeris left the exposed sachets in the first week, followed by reduced emergence and no signs of breeding were observed in the sachets. Sachets in a plant canopy had low emergence during the first week, increasing thereafter. Overall, plant canopy sachets released more N. cucumeris than exposed sachets. Emergence patterns of N. cucumeris from sachets under greenhouse and ideal conditions were variable, with sachets generally performing better under ideal conditions. Even under constant ideal conditions, the number of N. cucumeris released from sachets varied among batches and some produced a suboptimal number of predators. Results demonstrate that exposed greenhouse conditions can seriously affect the performance of N. cucumeris sachets and that good coverage is needed to compensate for limited dispersal in non-continuous plant canopies.     

Host plant specificity in several species of generalist mite predators

1. Species in the genus Neoseiulus are considered to be generalist predators, with some species used in biological control programmes against phytophagous mites and insects. 2. A general survey of Neoseiulus species in inland Australia indicated that different species are associated with particular tree species. This pattern of host plant use was investigated for four Neoseiulus species (N. buxeus, N. cappari, N. brigarinus, N. eremitus) by means of a sampling programme through time and across space. 3. Each species of Neoseiulus was collected entirely or mostly from one species of tree; little or no overlap was detected despite the tree species growing in well‐mixed stands. Host plant specificity thus appears to be strong in this genus. 4. Species in two other genera (Pholaseius and Australiseiulus), also considered to be predatory, showed a similar association with particular tree species. 5. The implications for the use of these predators in biological control are considerable. In particular, phytoseiid species with specific needs in terms of host plants may not be suitable for use as general purpose predators. Meeting the needs of phytoseiids through the modification of host plant attributes may be a step towards enhancing their efficacy as biological control agents.     

Discrimination of three Typhlodromalus species (Acari: Phytoseiidae) using random amplified polymorphic DNA markers

We compared the random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) banding patterns obtained from four laboratory cultures representing three phytoseiid mite species (Typhlodromalus limonicus (Garman and McGregor), two cultures of Typhlodromalus manihoti (de Moraes) and Typhlodromalus tenuiscutus (McMurtry and de Moraes). The RAPD-PCR was conducted on the pooled DNA from five adult female mites. For each culture, three samples of five females were analysed with each of eight RAPD-PCR primers. Five of the eight primers could be used individually to distinguish the species. To quantify the within- and between-species variation, genetic distances were calculated based on the proportion of shared scorable bands. The within-species genetic distances (0.072-0.186) were much lower than the between-species genetic distances (0.407-0.656). We believe that this technique could be used effectively to identify other cryptic mite species.     

Are herbivore-induced plant volatiles reliable indicators of herbivore identity to foraging carnivorous arthropods?

Plants that are damaged by herbivorous arthropods provide carnivorous enemies of the herbivores with important information. They emit an induced volatile blend that is highly detectable to the carnivores from a distance. Such detectable signals that indicate herbivore presence are important for the carnivores because herbivores themselves are under strong selection not to expose themselves. In addition, carnivores would benefit from a specificity of the induced plant volatiles. Whether herbivore-induced plant volatiles are reliable indicators of herbivore identity, however, has not been resolved unambiguously. Some studies support the reliability of herbivore-induced plant volatiles, while others do not. Different approaches have been used such as chemical analysis, behavioural analysis or a combination of the two. Based on the total of chemical studies one might conclude that in most cases herbivore-induced plant volatiles are not very specific for the herbivore that damages the plant. However, arthropod chemosensors are much more sensitive than the detectors of analytical instruments. Therefore, chemical analyses are not suitable to demonstrate whether or not herbivore-induced plant volatiles are reliable indicators of herbivore identity to carnivores. Behavioural studies should provide this information. In analysing carnivore behaviour it should be realised, however, that arthropod behaviour can be highly variable. Arthropod foraging decisions are affected by external and internal factors such as (a) abiotic environmental factors, (b) presence of competitors or enemies, (c) deprivation of food or oviposition sites, (d) specific deprivation of certain nutrients or (e) learning. In this paper their effect on discrimination of carnivores between volatile blends emitted by plants infested by different herbivores is reviewed. This provides testable hypotheses of why discrimination was not found in some studies. The ability of carnivores to discriminate is likely to be more common than is clear to date, which should invoke functional studies of the conditions that influence the occurrence of this discrimination.