Analysis of prey preference in phytoseiid mites by using an olfactometer,predation models and electrophoresis

Prey preference of three phytoseiid species,Typhlodromus pyri Scheuten,Amblyseius potentillae (Garman) andA. finlandicus (Oudemans) which occur in Dutch orchards, was analysed with respect to two economically important phytophagous mites, the European red spider mitePanonychus ulmi (Koch), and the apple rust miteAculus schlechtendali (Nalepa). Two types of laboratory experiments were carried out: (1) olfactometer tests to study the response when volatile kairomones of both prey species were offered simultaneously; and (2) predation tests in mixtures of the two prey species and comparison with calculated predation rates, using a model provided with parameters estimated from experiments with each prey species alone. In addition, the diet of field-collected predators was analysed using electrophoresis. For each predator species the results of the different tests were consistent, in thatT. pyri andA. potentillae preferredP. ulmi overA. schlechtendali, whereasA. finlandicus preferredA. schlechtendali overP. ulmi.     

Assessment of Amblyseius fallacis (Acari: Phytoseiidae) for biological control of tetranychid mites in an Ontario peach orchard

We introduced a mass-reared pyrethroid-resistant strain of the predatory phytoseiid mite Amblyseius fallacis (Garman) into an Ontario peach orchard in an attempt to control populations of the phytophagous mites Panonychus ulmi Koch and Tetranychus urticae Koch (Acari: Tetranychidae). Releases of 1,000 and 2,000 mites per tree were made, at three different times. The release of 2,000 mites per tree in June and in July resulted in significantly higher phytoseiid densities than was observed on control trees. However, densities of P. ulmi or T. urticae were not significantly affected by any release rate or by timing. The release of 1,000 A. fallacis per tree, or of any density in August, did not significantly increase phytoseiid abundance. In the following year, population dynamics of both phytoseiid and phytophagous mites were not significantly affected by the previous year's release. Amblyseius fallacis can be a useful predator in some fruit orchards. However, further research is necessary into the timing and rate of release, modified spray programmes, and with different crops, in order to clarify the role of this species for biological control in Ontario peach orchards.     

Factors affecting biological control of apple mites by mixed populations ofMetaseiulus occidentalis andTyphlodromus pyri

Metaseiulus occidentalis (Nesbitt) andTyphlodromus pyri Scheuten have complementary features/ traits that enable them to control effectively plant-feeding mites on apple. Populations of both predators gave as good or better biological control of the apple rust mite (Aculus schlechtendali Nalepa), European red mite (Panonychus ulmi Koch) and two-spotted spider mite (Tetranychus urticae (Koch)) than single-predator populations. With mixed predators,M. occidentalis provided better control of spider mites the first season after release, butT. pyri gave better control in the second season. Several factors affected the ability of predators to provide biological control: When prey were dense,M. occidentalis rapidly increased during the warm mid-summer, whileT. pyri provided greater predation when it was cool at the start or end of the growing season. When few prey were present, searching byM. occidentalis was more confined on individual apple leaves, but it migrated between leaves and trees more often. Pollen feeding, cannibalism and interspecific predation were more common byT. pyri. In fall, oviposition byM. occidentalis stopped sooner and in the following spring,T. pyri reproduced beforeM. occidentalis. Research needs and management of mixed-predator populations are discussed.     

The effect of an alternative food supply on the relationship between two Typhlodromus species and Panonychus ulmi (Koch) (Acarina)

Using seedling plants in an insectary, populations were recorded of two species of Typhlodromus (Phytoseiidae) when provided with known numbers of Panonychus ulmi (Koch) (Tetranychidae) and/or large numbers of Aculus fockeui (Nal.) (Eriophyidae). T. pyri Scheut. and T. finlandicus (Oudms.) both maintained P. ulmi at a low level compared with populations where Typhlodromus was not present, and whether or not A. fockeui was also available. Both species of Typhlodromus increased more rapidly when provided with A. fockeui as well as P. ulmi, and under these conditions T. pyri reduced P. ulmi to a lower level than where A. fockeui was not provided.

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Zusammenfassung Der Versuch sollte zeigen, ob die Raubmilbe Typhlodromus spp. (Phytoseiidae) die Spinnmilbe Panonychus ulmi (Koch) (Tetranychidae) weiter niederhalten könnte, wenn gleichzeitig eine andere günstige Beute angeboten würde. Es wurden getopfte Prunus-Sämlinge in einem Gewächshaus benutzt, die zur Hälfte mit einer großen Anzahl von Aculus fockeui (Nal.) (Eriophyidae) infiziert wurden, bevor bekannte Anzahlen von P. ulmi und Typhlodromus pyri Scheut. oder T. finlandicus (Oudms.) auf ihnen angesetzt wurden. Während eines Zeitraumes von 8 Wochen wurden in annähernd wöchentlichen Abständen einzelne, als Wiederholungen angesetzte Pflanzen jeder Versuchsvariante entnommen und ihre Milbenpopulationen ausgezählt. Bei Abwesenheit der Raubmilben stieg die P. ulmi-Population schneller auf Pflanzen an, die von A. fockeui frei, als auf solchen, auf denen sie vorhanden waren. Sowohl T. pyri wie T. finlandicus hielten P. ulmi auf einem vergleichsweise niedrigen Niveau, gleichgültig ob A. fockeui gleichfalls vorhanden war oder nicht. Beide Typhlodromus-Arten vermehrten sich rascher, wenn ihnen neben P. ulmi zusätzlich A. fockeui zur Verfügung stand, und unter diesen Bedingungen reduzierte T. pyri die P. ulmi-Population auf ein niedrigeres Niveau als bei Abwesenheit von A. fockeui. Diese Ergebnisse zeigen, daß die Gegenwart von A. fockeui die Bekämpfung von P. ulmi durch Typhlodromus spp. nicht beeinträchtigt, daß sie aber eine günstige Beute darstellt und eine erhöhte Vermehrungsrate der Raubmilben bewirkt.

     

The effect of pyrethroid lambdacyhalothrin applications on the spatial distribution of phytophagous and predatory mites in apple orchards

The spatial distribution of three phytophagous mites,Panonychus ulmi (Koch),Tetranychus urticae Koch andAculus schlechtendali (Nalepa), and two predacious mites,Zetzellia mali (Ewing) andAmblyseius fallacis (Garman), and the effect of pyrethroid lambdacyhalothrin applications on mite spatial dispersion were investigated over a 3-year period in an apple orchard in Ontario. The index of dispersion and the slope of Taylor's power law were used to evaluate dispersion patterns of mites. Panonychus ulmi showed that between-tree spatial variation decreased with an increase of population densities, whereas between-leaf variation increased with population densities. With all other four species it appeared that between-tree variation is much greater than between-leaf variation at all field population density levels. The values ofb by Taylor's power law suggested that all five species of mites are aggregated, but that in generalP. ulmi andT. urticae (b=1.427–1.872) are more aggregated than their predators (b=1.254–1.393). Taylor's regression technique suggests that pyrethroid applications causedP. ulmi, T. urticae, Z. mali andA. fallacis to be less aggregated whileA. schlechtendali was more aggregated. The impact of changes in mite spatial distribution following pyrethroid applications on sampling plans is discussed.     

Hierarchical structure in kairomone preference of the predatory mite Amblyseius potentillae: dietary component indispensable for diapause induction affects prey location behaviour

ABSTRACT.

• 1 The phytoseiid predator Amblyseius potentillae (Garman) responded to volatile kairomones emitted from leaves infested by the two-spotted spider mite (Tetranychus urticae Koch), the apple rust mite (Aculus schlechtendali (Nalepa)) or the thrips Frankliniella pallida (Uzel), only when the predators had been reared on a carotenoid-free diet. In contrast A.potentillae responded to the European red spider mite (Panonychus ulmi (Koch)) both when the predators had been reared on a carotenoid-containing and a carotenoid-free diet.
• 2 Carotenoid-deficient predators did not respond to odour emitted from a host plant that was infested by larvae of the fruit-tree leaf roller (Adoxophyes orana (F.v.R)), a carotenoid-containing phytophage, that cannot be preyed upon by A.potentillae.
• 3 Carotenoids are indispensable for diapause induction in A.potentillae. Hence, carotenoid-deficient predators can increase their fitness by feeding from a carotenoid source. This may explain the response of carotenoid-deficient predators to the kairomones of the two-spotted spider mite, F.pallida and the apple rust mite (all containing ingestible carotenoids). As the fruit-tree leaf roller cannot serve as prey and thus as a carotenoid source, it makes sense that the predators lacking carotenoids do not respond to the kairomone of this phytophagous insect.
• 4 Two-choice experiments in a Y-tube olfactometer showed that the kairomone preference of A.potentillae has a hierarchical structure: the kairomone of the European red spider mite is the most preferred one, followed by that of apple rust mite, whereas the kairomone of the two-spotted spider mite is the least preferred of these three.

     

Synomone-induced suppression of take-off in the phytoseiid mite Phytoseiulus persimilis Athias-Henriot

Plant-inhabiting predatory mites in the family Phytoseiidae are known to disperse passively on air currents. In this article ww analyse observations on the behaviour that initiates aerial dispersal, the so-called take-off behaviour. When starved for 24 hours at 25°C and 35% RH, about 80% of the females of Phytoseiulus persimilis Athias-Henriot became airborne during 10 minute exposure to wind velocities of 2 ms^-1 or higher. However, take-off was suppressed when females were exposed to volatile chemicals emanating from leaves that had been infested by two-spotted spider mites (Tetranychus urticae Koch) during one day preceding the experiments. This result is the first unambiguous proof that phytoseiid mites exert control over take-off. Interestingly, the females of the predator strain under study did not show the characteristic upright posture that was hypothesized to be important for take-off in two other species of phytoseiid mites (Amblyseius fallacis Garman and Metaseiulus occidentalis (Nesbitt)). These observations shed new light on the behaviour involved in controlling take-off. It is suggested that take-off control is exerted mainly via the grasp of the claws and the adhesive empodia in a way reminiscent of that described for aphids.     

Do phytoseiid mites select the best prey species in terms of reproductive success?

Optimal foraging theory predicts that predators prefer those prey species that are most rewarding in terms of reproductive success, which is dependent on prey quality and prey availability. To investigate which selection pressures may have moulded prey preference in an acarine system consisting of two prey species and three predator species, we tested whether prey preference of the predators is matched by the associated reproductive success.The predators involved areAmblyseius finlandicus (Oudemans),Am. potentillae (Garman) andTyphlodromus pyri Scheuten. The prey species are the apple rust mite (Aculus schlechtendali (Nalepa)) and the fruit-tree red spider mite (Panonychus ulmi (Koch)).Reproductive success was assessed in terms of intrinsic rate of increase and for one predator also in terms of diapause induction. All three predator species reached highest reproductive success on the same prey species: apple rust mite. This was most pronounced for the predatorAm. finlandicus, because its larval stage suffered severe mortality when feeding onP. ulmi.An independent study on prey preference of the three predator species (Dicke et al., 1988) revealed thatAm. finlandicus prefersAc. schlechtendali toP. ulmi, whereas the other two predator species have the reverse preference.Thus, on the basis of current data, prey preference ofAm. finlandicus can be understood in terms of reproductive success. However, this is not so for prey preference ofT. pyri andAm. potentillae. Investigations needed for a better understanding of prey preference of the last-named two predator species are discussed.     

Adaptations and responses of Dasymutilla occidentalis (Hymenoptera: Mutillidae) to predators

The mutillid wasp Dasymutilla occidentalis possesses several adaptations and exhibits a number of responses wich appear to be of defensive value: a long mobile sting with powerful venom; a strong, rounded and slippery cuticle; an ability to run very rapidly and evasively; an aposematic warning coloration pattern; and the ability to respond to an attack by making stridulatory sounds and by releasing a chemical secretion or both. The effectiveness of these defenses is supported by tests utilizing various vertebrate and arthropod predators. The raison d'être of the multiple lines of defense possessed by D. occidentalis and the relative value of each line of defense are discussed. It is postulated that aposematic coloration, audible stridulation, and a volatile defensive exudate all function primarily as part of an early warning system enabling a predator to recognize this wasp-with its very algogenic venom-as unpalatable and potentially dangerous.

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Zusammenfassung Die Mutillide Wespe Dasymutilla occidentalis besitzt verschiedene Anpassungen und zeigt eine Anzahl von Reaktionen, die für die Verteidigung von Wert sind: ein langer, beweglicher Stachel mit starkem Gift, eine starke, runde und glatte Kutikula, die Möglichkeit, sehr schnell und ausweichend zu laufen sowie ein aposematisches Warn-Farben-Muster. Desweiteren ist sie fähig, einem Angriff mit einem knisternden Ton entgegenzutreten sowie ein chemisches Sekret abzugeben oder auch beides. Im Labor durchgeführte Zusammenstöße zwischen vertebraten und invertebraten Räubern und D. occidentalis beweisen klar den Wert der ganzen Anzahl von Verteidigungsmechanismen für die Wespe.Diese Zusammenstöße liefern auch einen Einblick in die raison d'être der vielseitigen Verteidigung. die stärkere Kutikula und ihre Glätte, Haupteigenschaften zum überleben gegen Räuber, funktionieren gleichzeitig mit dem Stich zum Schutz gegen Vertebraten und mit schneller Fluchtmöglichkeit zum Schutz gegen die meisten Invertebraten. Das akustische Geräusch scheint eine Hilfsverteidigung zu sein wenigstens gegen einige Spinnen und vermutlich auch gegen einige Vertebraten. Die chemische Sekretion, die hauptsächlich aus 4-methyl-3-heptanon besteht, scheint möglicherweise direkten Verteidigungswert gegen einige Eidechsen zu haben und funktioniert höchstwahrscheinlich hauptsächlich im Zusammenhang mit der roten und schwarzen aposematischen Färbung und dem knisternden Ton als vielseitiges Warnsystem, das fähig ist, durch Signalisieren allen potentiellen vertebraten Räubern mitzuteilen, daß dieses Insekt ungenießbar ist.

     

Genetic and biochemical comparisons of organophosphate resistance between strains of spider mites (Tetranychus species: Acari)

The results of genetic and biochemical studies of resistance to parathion in strains of Tetranychus urticae are presented. Included in the study is the well-known Leverkusen-R strain, as well as two resistant strains from New Zealand. For the toxicological part of the genetic investigation, a topical application technique is employed. Both genetically and biochemically, the resistances of the two independent New Zealand strains appear identical to the Leverkusen resistance, viz., due to the same major dominant gene which lowers the inhibition rate of the cholinesterase enzyme. Comments are made upon the universal significance of this basic resistance mechanism.

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Genetische und biochemische vergleiche der organophosphatresistenz von verschiedenen spinnmilben-stämmen (Tetranychus-species: Acari)

Zusammenfassung Die Ergebnisse genetischer und biochemischer Untersuchungen der Resistenz gegenüber Parathion an Stämmen von Tetranychus urticae Koch werden dargestellt. In die Untersuchung waren sowohl der wohl bekannte Leverkusener R-Stamm als auch zwei resistente Stämme von Neuseeland einbezogen. Im toxikologischen Teil der genetischen Untersuchungen wurde eine topische Applikationstechnik angewendet. Genetisch wie biochemisch scheint die Resistenz der zwei voneinander unabhängigen Neuseeländer Stämme mit der Resistenz des Leverkusener Stammes identisch, d.h. von dem gleichen dominanten Hauptgen verursacht zu sein, welches die Hemmungsrate der Cholinesterase-Enzyme senkt. Bemerkungen über die universelle Bedeutung dieses grundlegenden Resistenzmechanismus werden angefügt.

     

Further studies on the reproductive isolation of geographical strains in the Tetranychus telarius complex

Cross breeding experiments with British and North American colour forms of the mites included in the Tetranychus telarius complex suggest that T. urticae Koch is the correct name for the green form, and T. cinnabarinus Boisd. for the reddish form. Different strains, with different degrees of incompatibility, occur in each species.

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Zusammenfassung Es würden Kreuzungsversuche durchgeführt, um die Verwandtschaft zwischen britischen und nordamerikanischen Farbformen des sogenannten T. telarius Komplex zu prüfen.Paarungen zwischen Vertretern der grünen Form ergaben F₁ Hybriden, die voll fortpflanzungsfähig waren, obgleich sie unterschiedliche Grade von Unverträglichkeit zeigten.Solche zwischen den rötlichen Formen ergaben vollständige Unverträglichkeit; die F₁ Weibchen waren steril oder hatten sehr geringe Fruchtbarkeit. Wenn Nachkommen von derartigen Weibchen erzeugt wurden, waren sie männlichen Geschlechts.Die unterschiedlichen Verwandtschaftsverhältnisse, die zwischen Farbformen verschiedener geographischer Verbreitung bestehen, werden besprochen, und es wird daraus geschlossen, dass alle Angehörigen einer jeden Farbgruppe als gleiche Arten betrachtet werden müssen. Es wird vorgeschlagen, dass T. urticae Koch der korrekte Name ist, der jetzt für die grünen Formen angewendet werden sollte, und T. cinnabarinus Boisd. für die rötlichen Formen beizubehalten.

     

Effect of temperature on the developmental rate of preimaginal stages of Aphidoletes aphidimyza (Diptera, Cecidomyiidae)

The duration of preimaginal stages of Aphidoletes aphidimyza Rond. is determined mainly by temperature.The lower threshold temperatures for egg, larva, pupa and total preimaginal development are 10.1°, 4.3°, 5.7° and 6.2°; the sums of effective temperatures are 25.0 day degrees, 110.9 day degrees, 154.1 day degrees and 280.2 day degrees, respectively. Equations for the dependence of duration of preimaginal stages on constant temperature were calculated.The larval feeding period is only 20% of the total preimaginal development period. Overlapping generations should therefore be maintained to assure a permanent preying activity and thus an effective biological control in glasshouses.

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Die wirkung der temperaturen auf die präimaginalen studien von Aphidoletes aphidimyza (diptera, cecidomyiidae)

Zusammenfassung Die Entwicklungsdauer der präimaginalen Studien von Aphidoletes aphidimyza Rond. ist hauptsächlich von der Temperatur abhängig. Zwei Charakteristiken—die untere Temperaturschwelle und die Summe der wirksamen Temperaturen—sind wichtig für die Verwendung der aphidiphagen Gallmücke gegen Blattläuse in Glashäusern. Diese Charakteristiken wurden von uns erstmals festgelegt.Die unteren Temperaturschwellen für die Embryonal-, Larven-, Puppen- und für die ganze Präimaginalentwicklung von A. aphidimyza sind 10.1°, 4.3°, 5.7° und 6.2°; die Summe der wirksamen Temperaturen 25.0, 110.9, 154.1 und 280.2 Gradtage.Die Zeit, während der sich die Larve ernährt und Blattläuse vernichtet, entspricht nur 20% der gesamten Präimaginalentwicklung. Für eine ununterbrochene Aktivität der Larven und damit für eine hohe Wirksamkeit der biologischen Blattlausbekämpfung in Glashäusern ist deshalb unbedingt eine Ueberlappung der Gallmückengenerationen erforderlich.

     

How larvae of Thrips tabaci reduce the attack success of phytoseiid predators

Neoseiulus barkeri (= Amblyseius mckenziei) and Amblyseius cucumeris (Acari:Phytoseiidae) are used as control agents of Thrips tabaci (Insecta:Thripidae) in greenhouse crops. Their success in capturing prey larval stages is related to both the feeding state of the predators and to the size of the larvae. When starved, predators are more successful in seizing larvae. Upon contact with a starved predator second stage prey larvae incur a lower death risk than first stage larvae. The larvae of T. tabaci reduce the attack success of their predators by jerking the abdomen and by producing a drop of rectal fluid. When this defensive behaviour is prevented by anaesthetising the larvae with CO₂, predator attack success increases. Anaesthesia does not, however, level out the difference in death risk of the two larval stages. Conceivable causes for this discrepancy are discussed.Availability of suitable prey is dependent on the dynamics of the age structure of the prey population and, hence, may be lower than total thrips density suggests. If so, alternative food sources may be important to maintain the predator population.

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Zusammenfassung Neoseiulus barkeri (= Amblyseius mckenziei) und Amblyseius cucumeris (Acari: Phytoseiidae) werden zur Bekämpfung von Thrips tabaci (Insecta: Thripidae) in Gewächshauskulturen eingesetzt. Sowohl der Ernährungszustand der räuberischen Milben als auch die Grösse der Thripslarven haben Einfluss auf das Ausmass der Beutenahme. Die Prädatoren sind erfolgreicher, wenn sie eine Zeitlang ohne Nahrung gehalten wurden. Beim Zusammentreffen mit einer ausgehungerten Raubmilbe besteht für Thripslarven des zweiten Stadiums ein geringeres Risiko erbeutet und gefressen zu werden als für Larven des ersten Stadiums. T. tabaci Larven mindern den Angriffserfolg der Prädatoren durch kräftiges Hin- und Herschlagen des Abdomens und durch Abgabe eines Tropfens Rektalflüssigkeit. Wird dieses Abwehrverhalten der Larven durch Anaästhesie mit CO₂ verhindert, erhöht sich der Angriffserfolg der Prädatoren. Anästhesie nivelliert jedoch nicht das für beide Larvenstadien unterschiedlich hohe Risiko erbeutet zu werden. Mögliche Ursachen für diesen Unterschied werden diskutiert.Die Verfügbarkeit geeigneter Beutetiere hängt ab von der zeitlichen Entwicklung der Altersstruktur ihrer Population. Das Angebot an wirklich geeigneten Beutetieren kan also unter Umständen geringer sein, als dies die Gesamtthripsdichte zunächst vermuten lässt. Ist das der Fall, dürften alternative Nahrungsquellen für die Ernährung der Prädatorenpopulation wichtig sein.

     

Interspecific competition and predation between immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

Interspecific competition and predation in immature Amblyseius fallacis (Garman), Amblyseius andersoni Chant, Typhlodromus occidentalis (Nesbitt) and Typhlodromus pyri Scheuten were examined in small cages at three egg densities (0, 20 and 80) of two-spotted spider mite, Tetranychus urticae Koch, in the laboratory at 25±1°C,80% RH and 16L: 8D photoperiod. For the six possible between-species comparisons, the large polyphagous A. andersoni always outcompeted the other three predator species, which were either smaller and/or less polyphagous; the small oligophagous T. occidentalis was always eliminated by the other three predator species, which were either larger and/or more polyphagous. The small and polyphagous T. pyri tied with the large and oligophagous A. fallacis. The outcome of the interaction was generally similar at the three prey densities except in (1) the A. fallacis-A. andersoni system where the advantage of A. andersoni over A. fallacis was reduced when 20 or 80 eggs per cage were present at the start of the interaction and (2) the A. fallacis-T. occidentalis system where the advantage of A. fallacis over T. occidentalis increased with prey density. This study indicates that predator size, predator degree of polyphagy and prey density can affect the competitiveness of immature phytoseiids.     

Walking,feeding and intraspecific interaction of larvae of Metaseiulus occidentalis,Typhlodromus pyri,Neoseiulus fallacis and Amblyseius andersoni held with and without eggs of Tetranychus urticae

Larvae of Metaseiulus occidentalis (Nesbitt), Typhlodromus pyri Scheuten, Neoseiulus fallacis (Garman) and Amblyseius andersoni Chant exhibited different activity levels when held on apple leaf or on tile arenas and given or not given eggs of Tetranychus urticae Koch and water (tiles only). M. occidentalis larvae held without prey exhibited high levels of walking (includes searching) during 24 hours of evaluation, whereas M. occidentalis larvae held with prey fed quickly and then became less active. Fed larvae of M. occidentalis were less active on leaves than tile. Larvae of T. pyri on leaves had a very low frequency of walking, almost never fed and quickly assumed a resting position during development. While much less active than M. occidentalis, fed and unfed T. pyri larvae walked more on tiles than leaves before resting. Larvae of N. fallacis and A. andersoni fed at low rates and were similarly active on tiles and leaves. Free water increased walking by M. occidentalis, A. andersoni and T. pyri on tile but not N. fallacis. M. occidentalis larvae interacted 5–7 times more often than larvae of the other three species. Cannibalism or scavenging was rarely seen and then only for M. occidentalis larvae. Larvae of all four mites walked, fed and interacted much more in the first 12 hours than the second 12 hours of tests, except unfed M. occidentalis. Unfed M. occidentalis larvae did not molt to protonymphs but unfed larvae of the other three species did. Unfed and fed protonymphs of all four species walked more at 4 hours after molting than larvae at 12–24 hours. Unfed and fed protonymphs of T. pyri or A. andersoni had similar walking frequencies, but unfed protonymphs of N. fallacis were more active than fed ones. Trends in larval activities are discussed relative to the life history of each species.     

Intra- and interspecific predation on four life stage groups by the adult females of Metaseiulus occidentalis, Typhlodromus pyri, Neoseiulus fallacis and Amblyseius andersoni

Do adult females of oligophagous species such as Neoseiulus fallacis (Garman) and Metaseiulus occidentalis (Nesbitt) show less intra- and interspecific predation on phytoseiids when other foods are scarce than polyphagous species such as Amblyseius andersoni Chant and Typhlodromus pyri Scheuten? We caged single adult females of each species without food with ten of their own eggs or larvae, with ten eggs or larvae of the other species or with ten nymphs or adult females of M. occidentalis (T. pyri for M. occidentalis). We assessed the ambulatory activity, survival time, egg levels and prey loss in each test. Polyphages (in particular T. pyri) lived longer than oligophages (in particular N. fallacis) without food. The small T. pyri detected its own stages and benefited most by feeding on small active stages of other species. Amblyseius andersoni, the largest mite, fed and gained the most of any species when held with nymphs and female adults. Metaseiulus occidentalis fed on eggs of all four species to enhance survival. The large hyperactive N. fallacis gained the least from these behaviours. Each mite seemed uniquely adapted to survive conditions of scarce prey and these behaviours may explain their roles in phytoseiid mite complexes. Overall, oligophagous adult females fed less and gained less by feeding on phytoseiids than did polyphagous adult females.     

Karyotypes and sex-determination in spider mites (Tetranychidae)

The chromosomes of 13 species of spider mites (Tetranychidae) are determined using the aceto-orcein squash technique in order to establish the haplo-diploid sex-determination. 12 species showed the existence of haploid and diploid eggs:Neotetranychus rubi (Trägårdh) with 7 and 14 chromosomes;Eurytetranychus buxi (Garman) with 5 and 10;Bryobia sarothamni (Geijskes),Eotetranychus tiliarium (Joh. Hermann) andE. carpini (Oudemans) with 4 and 8;Panonychus ulmi (Koch),Schizotetranychus schizopus (Zacher),Oligonychus ununguis (Jacobi).Tetranychus hydrangeae Pritch. & Baker, T.pacificus McGregor,T. urticae Koch andT. cinnabarinus (Boisduval) with 3 and 6 chromosomes.The progeny of virgin females in 7 different species consisted of eggs with the haploid complement. One species was shown to be thelytokous, viz.Tetranycopsis horridus (Canestrini & Franzago), having a diploid number of 4 chromosomes. Some eggs of an inbred line ofT. urticae showed a patchwork quilt of odd polyploidy in embryonic tissue.     

The Transfer of Typhlodromus pyri on Grape Leaves for Biological Control of Panonychus ulmi (Acari: Phytoseiidae, Tetranychidae) in Vineyards in Ontario, Canada

The phytophagous mite Panonychus ulmi Koch has become a significant problem in Ontario vineyards. We attempted to introduce and establish populations of the predatory mite Typhlodromus pyri Scheuten for P. ulmi biological control. Grape leaves were transferred from a vineyard containing T. pyri in early summer 1998, by picking leaves from a donor vineyard and attaching them onto leaves in the release vineyard where T. pyri were extremely rare. Two release treatments were used with rates of 8.5 (1×) and 25.5 (3×) mobiles per vine. In the first season, T. pyri established in similar densities in both release treatments, which were significantly higher than controls. However, there were no differences among treatments in P. ulmi densities in 1998 as a result of predator release. During summer 1999, significantly fewer P. ulmi mite-days were observed in release plots compared to the control. Amblyseius fallacis (Garman) was common throughout the release vineyard in 1998 and in 1999, but appeared on the vines too late in the season to maintain low P. ulmi densities. T. pyri appeared to out-compete A. fallacis in 1999 because A. fallacis densities were significantly lower in plots where T. pyri had been released than in control plots. We conclude that T. pyri can be effective for P. ulmi biological control in Ontario vineyards and may be introduced by transferring leaves. In Europe, transferring prunings has been the standard method of inoculating T. pyri into new vineyards. Here we show that transferring leaves is another practical method.     

Some insectary experiments with predacious mites to determine their effect on the development of Metatetranychus ulmi (Koch) populations

Summary As field spraying experiments give results which are difficult to resolve in terms of individual predator species, a series of experiments has been carried out in an insectary to find out what effect predacious mites of various species have upon populations of Metatetranychus ulmi (Koch), in the absence of other prey. Known numbers of each mite species were placed on seedling plants, and the development of the resulting populations followed.In one experiment, where initial numbers of 5, 25 or 50 M. ulmi females were placed on a plant, together with five females of Typblodromus tiliae Oudms., the M. ulmi population in every case remained throughout the following three months at a density of less than one mite per leaf, which was less than a total of 50 mites per plant. Where the same numbers of M. ulmi started in the absence of T. tiliae, a rapid increase of M. ulmi resulted in populations of over 3000 mites per plant in up to eleven weeks.It was also found that both the size of the host plant, and the initial ratio of M. ulmi and T. tiliae, had an effect on the development of the T. tiliae populations.Of other predacious species, T. finlandicus was similar to T. tiliae in its effect on M. ulmi. Although T. umbraticus itself increased steadily, it exerted little effect on the M. ulmi population, nor did T. tiliarum which, however, did not develop well under these conditions. Phytoseius macropilis (Banks) was also slow to increase and had little effect on the M. ulmi population.

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Zusammenfassung Man hat aus Freilandversuchen gefolgert, daß gewisse Typhlodromus-Arten eine wichtige Rolle bei der Bekämpfung von Metatetranychus ulmi (Koch) spielen können, obwohl die Beurteilung der. Ergebnisse nach der Anwendung von Chemikalien und in Gegenwart räuberischer Insekten oft erschwert ist. Um diese Komplikationen auszuschalten, wurden Versuche in einem Insektarium durchgeführt, wo die Wirkung von Typhlodromus auf M. ulmi in Abwesenheit anderer Beute geschätzt werden kann.Wenn Ausgangszahlen von 5, 25 oder 50 M. ulmi-Weibchen zusammen mit 5 Weibchen von Typhlodromus tiliae Oudms. an kleine Pflanzen gesetzt wurden, blieb die M. ulmi Population während der folgenden drei Monate in jedem Fall niedrig und überstieg die durchschnittliche Dichte von einer Milbe pro Blatt oder eine Summe von 50 Milben pro Pflanze nicht. Wenn die gleichen Anzahlen von M. ulmi-Weibchen in Abwesenheit von T. tiliae angesetzt wurden, so ergab sich ein jäher Anstieg zu Populationen von über 3000 Milben je Pflanze im Zeitraum bis zu 11 Wochen und bald folgte Bronzefärbung der Blätter.Die Größe der Wirtspflanzen beeinflußte die Entwicklung der T. tiliae-Populationen ebenso wie das Ausgangsverhältnis von M. ulmi zu T. tiliae. Sowohl größere Wirtspflanzen wie höhere M. ulmi-Werte führen zu größeren T. tiliae-Zahlen.Von anderen räuberischen Arten hat Typhlodromus finlandicus (Oudms.) eine ähnliche Wirkung auf M. ulmi wie T. tiliae. Obwohl Typhlodromus umbraticus Chant sich selbst stetig vermehrte, übte er einen geringen Einfluß auf die M. ulmi-Populationen aus; ebenso wenig Typhlodromus tiliarum Oudms., welcher sich jedoch unter der gegebene Bedingungen nicht gut entwickelte. Auch Phytoseius macropilis (Banks) zeigte nur langsames Wachstum und hatte wenig Wirkung auf die M. ulmi-Population.So wurde nachgewiesen, daß T. tiliae unter etwas begrenzten Bedingungen und in Abwesenheit irgendeiner anderen Beute fähig ist, Populationen von M. ulmi auf einer relativ niedrigen und gleichbleibenden Dichte zu halten, woraus sich eine Stütze für die Theorie ergibt, daß das auch unter Obstgartenverhältnissen zutrifft.

     

Effect of host plant nitrogen fertilization on the biology of the two-spotted spider mite, Tetranychus urticae

Females of Tetranychus urticae Koch were reared on leaf discs of apple trees and bush beans grown at different N concentrations (0.6–75 mM NO _inf3 ^sup- ). N-deficiency increased pre-imaginal development time, preoviposition period, and decreased female weight, fecundity and oviposition rate of the mites. N, water, amino acid, and sugar content of the apple leaves were positively correlated with weight and egg production and negatively correlated with development time and pre-oviposition period. The reverse correlations were found with total phenol content of the leaves and above mite parameters. A reduction of leaf N by 50% was related with a tenfold decline in fecundity on apple leaves. The stress mainly affected the oviposition rate and to a lesser extent the oviposition period. On apple leaves the net reproductive rate (av. no. offspring per , R_o), mean length of a generation (T), and innate capacity for increase (r_m) were R_o=40.3, T=17.1, and r_m=0.22 for the standard N concentration, and 4.7, 25.0, and 0.06 for strong N-deficiency, respectively.

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Zusammenfassung Die polyphage Gemeine Spinnmilbe ist ein wirtschaftlich bedeutender Schädling. Die Rolle einzelner Nährstoffe bei der Milbenvermehrung wurde schon von einigen Autoren mit unterschiedlichen Ergebnissen untersucht. Der Stickstoff scheint aber einer der Hauptfaktoren zu sein.Ueber Gewebekulturen klonierte Apfelbäume sowie aus Samen gezogene Buschbohnen wurden in Nährlösungen mit verschiedenen N-Angeboten kultiviert. Aus solchen Pflanzen wurden Blattscheiben ausgestanzt und mit Weibchen von T. urticae besetzt. Gemessen wurden die tägliche Eiablage bis zum natürlichen Tod, die Entwicklungsdauer und das Weibchengewicht. Mit dem bei N-Mangel abnehmenden N, Aminosäuren- und Zuckergehalt (v.a. Sorbit) im Blatt korrelierend nahmen auch Gewicht, Ablagerate und Fekundität ab, bzw. die Entwicklungsdauer und Praeovipositionsperiode zu. Die umgekehrte Wirkung auf diese Milbenparameter hatte der Gesamtphenolgehalt. Eine Reduktion des N-Gehalts der Blätter auf die Hälfte (1.5% N) bewirkte auf Apfelblättern eine Abnahme von Fekundität und Ovipositionsrate um das zehnfache, bzw. eine Zunahme der Präovipositionsperiode um mehr als das dreifache. Der Stress beeinflusste v.a. die Maxima der Ablageverläufe und weniger die Lebensdauer. Der Wassergehalt war ebenfalls mit der Fekundität positiv korreliert.Auf Bohnenblättern legten die Tiere mehr Eier und erreichten ein höheres Gewicht als auf Apfel, dies bei gleichem N-Gehalt beider Pflanzen. Es wirken somit noch andere Faktoren auf die Reproduktion der Spinnmilben.Die Populationsparameter wurden ebenfalls sehr stark beeinflusst. Auf Apfelblättern ergab sich bei der Kontrolle eine Nettoreproduktionsrate R_o von 40.3 und bei starker N-Defizienz 4.7. Die mittlere Generationsdauer T sowie die spezifische natürliche Wachstumsrate r_m betrugen für die Kontrolle 17.1 Tage, bzw. 0.22 und für starken N-Mangel 25.0 Tage, bzw. 0.06.Die Ergebnisse zeigen, dass sich bereits kleinere Unterschiede im Stickstoffgehalt und damit zusammenhängend im Zucker- und Phenolgehalt stark auf die Populationsdynamik der Gemeinen Spinnmilbe auswirken können.