Spider mites of sugarcane in Australia: a review of grass-feeding Oligonychus Berlese (Acari: Prostigmata: Tetranychidae)

Abstract In many areas of the world, spider mites are significant pests of sugarcane. Australia is currently fortunate in lacking the most destructive species, and usually suffers only sporadic damage. Herein, we provide a key to the genera of spider mites associated with sugarcane, review the most significant genus, Oligonychus Berlese, and provide a key to the species of grass-feeding Oligonychus in the Australasian region. The species O. araneum Davis, O. digitatus Davis, O. grypus Baker and Pritchard, O. orthius Rimando, and O. oryzae (Hirst) are redescribed, while the Australian O. zanclopes sp. n. Beard and Walter from sugarcane and rice, O. turbelli sp. n. Beard and Walter, O. ephamnus sp. n. Beard and Walter and O. festucolus sp. n. Beard and Walter from other grasses, are newly described. Previous records of O. grypus in Australia appear to be misidentifications of what is described here as the new species O. zanclopes .     

Predation ofOligonychus pratensis [Aca.: Tetranychidae] byPhytoseiulus persimilis andAmblyseius californicus [Aca.: Phytoseiidae] under controlled laboratory conditions

The predator efficacy ofPhytoseiulus persimilis Athias-Henriot andAmblyseius californicus (McGregor) (Acarina: Phytoseiidae) when feeding on the Banks grass mite (BGM),Oligonychus pratensis (Banks) (Tetranychidae), was compared under controlled laboratory conditions. Predation byP. persimilis andA. californicus reduced the BGM densities by 60% and 28%, respectively. In general, phytoseiids preferentially fed upon the more abundant instars. Ovipositional rates forP. persimilis while feeding on BGM approximated rates when feeding onTetranychus spp. The use of a trade name is not an endorsement by Texas A&M University.     

Influence of aerial dispersal on persistence and spread of pesticide-resistant Metaseiulus occidentalis in California almond orchards

Aerial dispersal of the phytoseiid Metaseiulus occidentalis (Nesbitt) was evaluated as a component in managing pesticide-resistant populations established in California almond orchards. Peak dispersal occurred in late July and early August during 1982 and 1983. Most predators (and spider mites) left the orchards on the prevailing winds from the northwest. Within the orchard, the prevailing winds had less influence, and dispersal was usually random. Both spider mites and predators dispersed randomly with regard to height from the almond trees, but data obtained during one 24-h interval suggest they do not disperse randomly throughout the day. Most aerial movements occurred between 16–22 h when relative humidity and wind speeds increased and temperatures decreased. Spider mites and predators were trapped on panels located 200 m from the orchard. A survey of carbaryl resistance levels in M. occidentalis collected from almond orchards surrounding the release sites indicates that carbaryl-resistant M. occidentalis dispersed at least 800 m between 1981–83. However, growers wishing to use the resistant strains should release them in their orchards as natural dispersal appears to be too slow. Migration of native M. occidentalis into the release sites appeared to be sufficiently rare that dilution of carbaryl-resistant populations was minimal during a 2–4 year period.

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Résumé La dispersion aérienne du phytoseïdae, M. occidentalis (Nesbitt), a été estimée comme élément de la lutte contre les populations résistantes aux insecticides établies dans les vergers de Californie. La dispersion maximale s'est produite fin juillet et début a oût en 1982 et 1983. La plupart des prédateurs (et des acariens) quittent les vergers avec les vents dominants du nordouest. Dans le verger, les vents dominants sont moins importants et la dispersion est généralement au hasard. Tant les acariens que les prédateurs se dispersaient au hasard par rapport à la taille des amandiers, mais les relevés sur 24 heures laissent supposer qu'il n'y a pas une distribution aléatoire pendant la journée. La plupart des mouvements aériens se produisirent entre 16 et 22 heures quand HR et vitesse du vent augmentaient et température diminuait. Les acariens et prédateurs ont été piégés sur des panneaux à 200 m du verger.

     

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.

     

Behavioural response of spider mites (Tetranychus urticae) to induced resistance of cotton plants

ABSTRACT.

• 1 Spider mites (Tetranychus urticae Koch) given a choice between a cotton plant previously damaged by mites and an undamaged control preferentially moved to the control plant.
• 2 This host-choice behaviour was seen in adult female mites but not in immatures.
• 3 Adult females were not found to be significantly more fecund on control plants than on previously damaged plants, but the duration of this choice experiment precluded full assessment of effects on fecundity.
• 4 Mites responded very quickly, choosing previously undamaged plants without contacting or feeding on the test plants. This suggests that an olfactory response to a chemical substance(s) is involved.

     

Volatile spider-mite pheromone and host-plant kairomone, involved in spaced-out gregariousness in the spider mite Tetranychus urticae

ABSTRACT. From the host plant-spider mite complex Phaseolus lunatus—Tetranychus urticae Koch a volatile chemical is emitted that acts as a kairomone for the predatory mite Phytoseiulus persimilis Athias-Henriot (Sabelis et al. , 1984a). This kairomone is apparently a byproduct of a vital physiological process and/or it has a function in the biology of the spider mite as well.
The spider mite—host plant complex also emits a volatile spider-mite dispersing pheromone. This is shown in the present study where spider mites were introduced into an odour patch on a horizontal screen in a vertical airflow olfactometer. When spider-mite infested leaves of Lima bean are offered, the spider mites walk mainly straight and soon reach the edge of the screen. On the other hand, when clean Lima bean leaves are offered, the mites walk tortuously most of the time and reach the edge of the screen much later. Artificially damaged plants elicit the same response as undamaged plants. Differences in spider-mite behaviour are observed in the vertical airflow olfactometer when odour of either clean or spider-mite infested leaves is offered. A comparison of the behaviour in these two situations with that when no odour was offered suggests that Lima bean leaves emit a volatile kairomone that activates T. urticae and makes them return after losing the stimulus. A Y-tube olfactometer experiment confirms the existence of this kairomone.
At a low ratio of dispersing pheromone to plant kairomone, the spider mites behave as if only kairomone is present, walking mainly tortuously. At a high ratio they disperse. No aggregation-pheromonal effect is observed.
The possibility that the spider-mite dispersing pheromone acts as a kairomone for P. persimilis is discussed.     

Intraspecific competition in immature Amblyseius fallacis,Amblyseius andersoni,Typhlodromus occidentalis and Typhlodromus pyri (Acari: Phytoseiidae)

Intraspecific competition in immature Amblyseius fallacis, Amblyseius andersoni, Typhlodromus occidentalis and Typhlodromus pyri was examined in the laboratory using small cages at five different predator densities (two, four, eight, 16 and 32) in the absence and presence of prey 100 eggs of two-spotted spider mite, Tetranychus urticae (Koch), at 25 ± 1°C, 80% RH and 16L:8D photoperiod. In the absence of spider mite prey, some individuals of immature phytoseiids showed increased development and surival with increasing predator densities up to certain limits, but none survived to the adult stage, except for a single male each of A. andersoni and A. fallacis who completed development by cannibalizing on conspecifics at a density of 32 predators per cage. In the absence of spider mite prey, the mean immature survival time was independent of the initial predator density, but the variance of survival time increased with predator density. In the presence of prey, the proportion of immatures surviving to adulthood generally decreased with initial predator density and dropped sharply to almost none at the predator density of 32 for A. fallacis, eight for A. andersoni, 16 for T. occidentalis and four for T. pyri. The number of prey consumed per predator during the first day generally decreased with predator density in all four species, as prey available per predator decreased and the competition for food increased with predator density. Our data indicate that scramble competition is operating in these four species. Although cannibalism was occasionally observed, especially after the exhaustion of prey and in the generalist predators such as A. andersoni, the immatures of these phytoseiids were less influenced by the interference of conspecifics than by the increasing difficulty of finding food at high predator densities. The implications of this study for understanding phytoseiid population dynamics and their use in biological control are discussed.     

横断山地区叶螨三新种（蜱螨亚纲：叶螨科）

本文记述了发现于横断山地区的叶螨三新种:横断山苔螨Bryobia heng duanensis,矛拟细须螨Tenuipalpoides hastata和长裂爪螨Schizotetranychus elongatus,其中拟细须螨属在中国为首次报道。     

Positive association between thrips and spider mites in seedling cotton

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Mite Population Dynamics on Different Grape Varieties With or Without Phytoseiids Released (Acari: Phytoseiidae)

In a three-year study, mite populations were monitored in two vineyards, each having two grape varieties with different leaf hair density. In both vineyards native phytoseiids were present: Amblyseius andersoni in one vineyard, and Phytoseius finitimus in the other. The economically important predators Kampimodromus aberrans and Typhlodromus pyri were released in both vineyards in order to study their efficacy in controlling tetranychids and eriophyids and their persistence during periods of prey scarcity. In both vineyards, relative abundances of the mite species, especially phytoseiids, were found to differ on different varieties in the same vineyard. In the first experiment, A. andersoni reached higher densities and was more persistent on the variety with slightly pubescent leaf under-surface (Merlot). Typhlodromus pyri and K. aberrans releases were successful and the mites became more abundant on the variety with pubescent leaf under-surface (Verduzzo). In the second experiment, P. finitimus was more abundant on a variety with pubescent leaf under-surface (Prosecco) than with glabrous leaf under-surface (Riesling). The most interesting results of the present study concerned the interactions between native and released predators. In the first vineyard, different results were obtained when releasing T. pyri on the two varieties. On the variety with pubescent leaves, A. andersoni was rapidly displaced by T. pyri, whereas the former species persisted on the other variety throughout the three-year study, apparently becoming dominant during the last season. In contrast to T. pyri, interactions between K. aberrans and A. andersoni in this vineyard did not depend on variety. The results of the experiments carried out in the second vineyard stressed the importance of interspecific competition for phytoseiid releases. Typhlodromus pyri colonization failed on both varieties. Kampimodromus aberrans releases appeared to be more successful on Riesling than on Prosecco, where P. finitimus was more abundant. At the end of the experiments, K. aberrans displaced P. finitimus on both varieties.