Interactions among phytophagous mites, and introduced and naturally occurring predatory mites, on strawberry in the UK

In choice test experiments on strawberry leaf disc arenas the phytoseiid mites Neoseiulus californicus and N. cucumeris were more effective than Typhlodromus pyri as predators of the phytophagous mites Tetranychus urticae and Phytonemus pallidus. There were no preferences shown for either prey by any of these predators. In multiple predator leaf disc experiments both Phytoseiulus persimilis and N. cucumeris significantly reduced numbers of T. urticae eggs and active stages; this effect was seen when the two species were present alone or in combination with other predator species. Neoseiulus californicus was less effective at reducing T. urticae numbers, and T. pyri was not effective; no interaction between predator species was detected in these experiments. When T. urticae alone was present as prey on potted plants, P. persimilis and N. californicus were the only phytoseiids to significantly reduce T. urticae numbers. These two predator species provided effective control of T. urticae when P. pallidus was also present; however, none of the predators reduced numbers of P. pallidus. There were no significant negative interactions when different species of predators were present together on these potted plants. In field experiments, releases of both P. persimilis and N. cucumeris significantly reduced T. urticae numbers. However, there was a significant interaction between these predator species, leading to poorer control of T. urticae when both species were released together. These results show the importance of conducting predator/prey feeding tests at different spatial scales.     

Biological control of strawberry tarsonemid mite Phytonemus pallidus and two-spotted spider mite Tetranychus urticae on strawberry in the UK using species of Neoseiulus (Amblyseius) (Acari: Phytoseiidae)

Two species of Neoseiulus, N. californicus and N. cucumeris, showed potential for biocontrol of phytophagous mites on strawberry. N. californicus controlled Tetranychus urticae on potted strawberry plants in a gauze-sided glasshouse at temperatures comparableto early summer in the UK (8–20°C). Both species of phytoseiid reducednumbers of the tarsonemid Phytonemus pallidus on potted strawberry plants under glasshouse conditions (15–23°C). In several experiments reductions in the range of 71–81% in numbers of tarsonemid active stages and eggs, compared to non-release plants, were obtained. The importance of establishing a suitable predator: prey ratio at an earlystage was demonstrated in an experiment where an initial ratio of 1 N. cucumeris: 10 P. pallidus gave a greater degree of controlthan 1:20 or 1:40.     

Predator avoidance in phytophagous mites: response to present danger depends on alternative host quality

We studied whether volatiles released by putative host plants affect the antipredator response of an herbivorous mite, Tetranychus urticae, when the patch was invaded by Phytoseiulus persimilis. Tetranychus urticae laid a lower number of eggs on tomato leaves than on lima bean leaves, suggesting that lima bean is a preferred host food source for T. urticae. In addition, T. urticae preferred lima bean plant volatiles to tomato plant volatiles in a Y-tube olfactometer test. To investigate the antipredator response of T. urticae, we examined the migration of T. urticae from a lima bean leaf disc to a neighbouring leaf disc (either a tomato or lima bean leaf disc) when ten predators were introduced into the original lima bean disc. A Parafilm bridge allowed for migration between the leaf discs. No migrations occurred between leaf discs when there were no predators introduced to the original leaf disc. However, when predators were introduced migrations did occur. When the neighbouring leaf disc was upwind of the original disc, the migration rate of the mite from original lima bean leaf disc to a neighbouring tomato leaf disc was significantly lower than that to a neighbouring lima bean leaf disc. By contrast, when the neighbouring leaf disc was downwind of the original leaf disc, there was no difference in the migration rates between lima bean leaf discs and tomato leaf discs. The number of T. urticae killed by P. persimilis for each treatment was not different, and this clearly shows that the danger was the same in all treatments regardless of the decision made by T. urticae. From these results, we conclude that T. urticae change their antipredator response by evaluating the difference in host plant volatiles in the patch they inhabit.     

Life-history of predatory mites Neoseiulus californicus and Phytoseiulus persimilis (Acari: Phytoseiidae) on four spider mite species as prey, with special reference to Tetranychus evansi (Acari: Tetranychidae)

The commercially available strains of Phytoseiulus persimilis Athias-Henriot, the biological control agent of Tetranychus urticae Koch, perform poorly in the Western Mediterranean, probably because they are not well adapted to local climatic conditions. For that reason, efforts are being focused on the development of a biological control programme using native phytoseiid mites. Four species of red spider mites can be found in vegetable crops in eastern Spain: T. urticae, Tetranychus turkestani Ugarov and Nikolski, Tetranychus ludeni Zacher and the recently introduced Tetranychus evansi Baker and Pritchard. To evaluate their potential role as biological control agents, the present study evaluates the life-history of local populations of Neoseiulus californicus (McGregor) and P. persimilis when fed on T. urticae, T. turkestani, T. evansi, and T. ludeni in the laboratory. Results indicate that N. californicus and P. persimilis are able to feed and complete their development on the four tested red spider mite species. The predators may exhibit a particularly high capacity for population increase when fed on T. urticae, T. turkestani, and T. ludeni, thus may be able to provide effective control of these species in the field. When fed T. evansi, however, predator performance was poor; significant increase in development and preoviposition times, and a reduction in oviposition period and fecundity were recorded. The resultant low capacity for population growth suggests poor ability of the two tested predators to suppress T. evansi populations on commercial crops. It is unlikely therefore that P. persimilis and N. californicus, now being widely used to control T. urticae in greenhouse crops in Central Europe, will be able to halt any spread of T. evansi to greenhouse crops in temperate areas.     

Survival, horizontal distribution, and economics of releasing predatory mites (Acari: Phytoseiidae) using mechanical blowers

The predatory mites Phytoseiulus persimilis and Amblyseius cucumeris are commonly used in commercial greenhouses for augmentative biological control of spider mites and thrips, respectively. One disincentive for growers to use biological control is the cost of manually distributing predators. Therefore, we tested the efficiency of two types of mechanical blowers for dispensing predatory mites. One blower had a metering device to control the flow of material (MBWMD); the other had no metering device (MBWOMD). Predator survival was measured at various distances after dispensing them with blowers. Survival also was compared with a manual-sprinkling method. When blowers were held horizontally, the distribution of predators was uneven for both blowers. For P. persimilis, 77% were found at 1.52 and 2.44 m with the MBWOMD, whereas 75% were located at 2.44, 3.35, and 4.27 m with the MBWMD. For A. cucumeris, 97% were found at 1.52, 2.44, and 3.35 m with the MBWOMD, while 81% landed at 2.44 and 3.35 m with the MBWMD. Percentages of live P. persimilis found using the MBWMD, MBWOMD, and manual-sprinkling were 31 ± 4, 49 ± 3, and 68 ± 8%, respectively. For A. cucumeris, percentages of survival were 61 ± 4, 79 ± 4, and 83 ± 7%, respectively. The MBWOMD dispensed P. persimilis 22 and 44 times faster than the MBWMD and manual-sprinkling, respectively. Mechanical blowers have the advantage of better coverage, substantially less labor, and estimated total costs to growers that are approximately half that of the manual release method.     

Photographic sampling: a photographic sampling method for mites on plants

A photographic sampling method for mites on plants was evaluated using Tetranychus urticae and Phytoseiulus persimilis on pepper plants. It was found to be 92% accurate for T. urticae eggs and 98% accurate for P. persimilis eggs at densities up to 45 eggs per cm² for T. urticae, and up to 3 eggs per cm² for P. persimilis. The motiles of the two species were not confused, nor were they confused with exuviae or other matter.     

Comparative toxicity of some acaricides to the predatory mite, Phytoseiulus persimilis and the twospotted spider mite, Tetranychus urticae

The relative toxicity of someacaricides to the predatory mite, Phytoseiulus persimilis and the twospottedspider mite, Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae) wasevaluated in laboratory. Five of theacaricides tested, including bifenazate,acequinocyl, chlorfenapyr, flufenoxuron andfenbutatin oxide, were much less toxic to adultfemales and immatures of P. persimilisthan to those of T. urticae, and adultfemale predators treated with these fiveacaricides produced 84±96% as many eggs as didcontrol females. Etoxazole did not seriouslyaffect the survival and reproduction of adultfemale predators but caused high mortalityrates in eggs and larvae of P.persimilis. Milbemectin and fenazaquin werevery toxic to adult females and immatures ofP. persimilis. Adult female predatorssurvived on a diet of spider mites treated withbifenazate, acequinocyl, chlorfenapyr,flufenoxuron and fenbutatin oxide, and theirfecundity, prey consumption and the sex ratioof the progeny were not substantially affected. Based on the results, bifenazate, acequinocyl,chlorfenapyr, flufenoxuron and fenbutatin oxideappeared to be the promising candidates for usein integrated mite management programs whereP. persimilis is the major naturalenemy.     

Comparative life-history traits of three phytoseiid mites associated with Tetranychus urticae (Acari: Tetranychidae) colonies in clementine orchards in eastern Spain: implications for biological control

The management of Tetranychus urticae, a key pest of clementine trees, is mainly based on the use of acaricides. However, more environmentally safe measures, such as biological control, are being encouraged. Life-history traits of the three most abundant phytoseiid mites associated with T. urticae on this crop (Euseius stipulatus, Phytoseiulus persimilis and Neoseiulus californicus) were studied. The experiments were performed under laboratory conditions (25°C, 80 ± 5% RH and 16:8 h (L:D)) on clementine leaves and T. urticae as prey. Euseius stipulatus could not complete its life cycle, whereas P. persimilis and N. californicus completed it satisfactorily. The estimated intrinsic rate of increase (r _m) was significantly higher for P. persimilis (0.344 day⁻¹) than for N. californicus (0.244 day⁻¹) and both were higher than the r _m value of T. urticae on clementine leaves. Implications of these results for the biological control of T. urticae in this crop are discussed.     

Neoseiulus Californicus (Acari: Phytoseiidae) as a Potential Control Agent of Tetranychus Urticae (Acari: Tetranychidae): Effect of Pest/Predator Ratio on Pest Abundance on Strawberry

Neoseiulus californicus (McGregor) is a promising agent for successful Tetranychus urticae Koch control through conservation techniques, in strawberry crops in La Plata (Buenos Aires, Argentina). In prey–predator interaction, initial relative densities have an important effect on system dynamics. The economic threshold level (ETL) used for this pest in the present study was 50 active mites per leaflet. In our laboratory experiments, initial T. urticae to N. californicus ratio had a significant effect on the population abundance of T. urticae at a 7-day period. When pest/predator ratio was 5/1 (at initial pest densities from 5 to 15 females/leaflet) the final number of active T. urticae/leaflet was significantly lower than the ETL, while at 20 females/leaflet this number did not differ from the ETL. At 7.5/1 ratio, the final number of active T. urticae/leaflet, at initial pest densities from 5 to 15 females/leaflet, reached the ETL without surpassing it. At 10/1 and 15/1 ratios, pest densities exceeded the ETL only at 15 initial T. urticae/leaflet. Most greenhouse and field observations were consistent with the predictions of a graphical model based on experimental results. This predator was very effective in limiting pest densities at a 7-day period and within the range of pest–predator ratios and absolute densities used in this study. Conservation of N. californicus promoting favorable pest/predator ratios may result in early control of T. urticae.     

Effect of pollen supplement on intraguild predatory interactions between two omnivores: The importance of spatial dynamics

Arthropods often engage in complex trophic interactions such as intraguild predation (IGP), true omnivory (i.e., feeding on plants and prey), and apparent competition. Theoretical treatments of the effects of such interactions on herbivore populations have been concerned almost entirely with equilibrium conditions. Yet these interactions are common in non-equilibrium settings such as agroecosystems, where they are likely to have a strong influence on pest populations. We therefore tested short-term effects of IGP and food supplementation on interactions between two predators (the phytoseiid mite Neoseiulus cucumeris and the anthocorid bug Orius laevigatus) and their shared prey, Frankliniella occidentalis, on strawberry plants. All three consumers feed on strawberry pollen, both mites and bugs prey on thrips, and the bug also feeds on the mites (IGP). Strong IGP on mites (IG prey) by the bugs (IG predator) was recorded in structurally-simple arenas. In a more complex setting (whole-plants), however, the intensity of IGP differed among plant structures. Likewise, pollen supplementation reduced both IGP and predation on thrips in a structurally simple setting. In the whole-plant experiment, IGP was more intense on pollen-bearing than pollen-free flowers. The study illustrated how spatial dynamics, generated when consumers track food sources differently in the habitat and possibly when herbivorous and IG prey alter their distribution to escape predation, led to site-specific configuration of interacting populations. The intensity of resulting trophic interactions was weakened by food supplementation and by increased complexity of the habitat.     

引种捕食螨胡瓜新小绥螨在中国的适生区分布预测

胡瓜新小绥螨(Neoseiulus cucumeris)是一种商业化的广食性生防天敌,可以防治多种农业害螨和害虫,具有重要的经济和生态价值。但是作为一种外来引种的捕食螨,它在我国的适生区域分布以及气候变化对其分布的影响尚不明确。根据胡瓜新小绥螨的现有分布点和19个生物气候因子,利用刀切法评估关键气候因素的重要性,并采用Maxent生态位模型分别预测了目前和未来气候条件下它在中国分布情况,分析了其在中国的潜在适生区域的变化。结果表明模型预测得到的受试者工作特征曲线ROC曲线下的面积AUC(Area under curve)值为0.87,表明模型的准确度好。最冷季节的降水量(Bio_19)、等温性(Bio_3)和气温季节性(Bio_4)是影响胡瓜新小绥螨适生性的最重要的环境因子, 对模型的贡献率分别为36.2%、25% 和18.1%。目前胡瓜新小绥螨的适生区面积约占我国陆地面积的60%,在未来气候条件下,其适生区域有进一步扩大的趋势,在2050年其中高度适生区域扩张至63%。不同时期胡瓜新小绥螨的分布中心比较稳定,均分布于四川省内,但有向东北迁移的趋势。本研究明确了胡瓜新小绥螨在中国适宜的释放区域及可能定殖的区域,为该引种天敌的合理利用提供了理论依据。     

Ultrastructural changes in strawberry leaves infested by two-spotted spider mites

Ultrastructural changes in strawberry leaves after different periods of feeding by Tetranychus urticae were studied. Electron micrographs indicate that the first detectable changes in cells directly punctured by the mites usually occurred after 3 days of feeding and were confined to the chloroplasts. These organelles show instability of the lamellae and the thylakoid membrane system as well as the envelope. Longer times of mite feeding (6–9 days) caused severe alterations, not only within chloroplast. In heavily injured tissues, misshapen cells contain homogeneous protoplasts in which only remains of necrotic chloroplasts were visible. Mesophyll cells adjacent to directly punctured tissues also exhibited subcellular alterations. Possible mechanisms of plant-tissue responses to mite feeding are discussed.

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Zusammenfassung Ultrastrukturelle Veränderungen wurden in Erdbeerblättern nach verschiedenen Perioden Saugtätigkeit von Tetranychus urticae Koch gesucht. Elektronenmikroskopische Aufnahmen zeigen, dass die ersten sichtbaren Veränderungen in direkt von Milben angestochenen Zellen meist nach 3 Tagen Saugen auftraten und auf die Chloroplasten beschränkt waren. Diese Organellen zeigen eine Instabilität der Lamellen, des Thylakoidmem-bransystems sowie der Umhüllung. Ein längere Zeit dauerndes Saugen der Milben (6–9 Tage) verursachte schwere Veränderungen und zwar nicht bloss in den Chloroplasten. In schwer geschädigten Geweben enthalten deformierte Zellen homogene Protoplasten, in denen nur Reste nekrotischer Chloroplasten sichtbar waren.Mesophyllzellen in der Nachbarschaft von direkt angestochenem Gewebe zeigte ebenfalls subzelluläre Veränderungen. Mögliche Mechanismen der Reaktion des Pflanzengewebes auf Milbensaugen werden diskutiert.

     

Local and distant prey-related cues influence when an acarine predator leaves a prey patch

Over relatively long distances, the predatory mite Phytoseiulus persimilis is able to detect volatiles produced by bean plants that are infested by its prey, Tetranychus urticae, the twospotted spider mite. Our investigation examined the separate and combined effects of prey, their products, and prey-induced plant volatiles on when P. persimilis left a potential prey host plant. In wind tunnels, we assessed the relative importance of and interaction among local and distant prey-related cues. The examination of local cues included: (1) all local cues (prey eggs, webbing, and prey-induced plant volatiles), (2) food (prey eggs) and webbing only, (3) plant volatiles only, and (4) no prey-related cues. The examination of distant cues involved the presence or absence of prey-induced plant volatiles from upwind plants. External volatile cues, produced by placing prey-infested plants upwind in the wind tunnel, resulted in more predators leaving downwind plants, and leaving sooner, than when clean plants were upwind, regardless of the availability of prey or prey-related cues on the local plant. However, local cues, especially the presence of food/webbing, had a greater effect than distant cues on timing of predator leaving. Predators remained in larger numbers and for longer times on prey-infested plants. However, the presence of either locally-produced plant volatiles or food/webbing alone still reduced the number of predators leaving a plant in the first hour compared to clean plants. After the first hour, the number of predators leaving was primarily driven by the presence of food/webbing. When no food/webbing was available, predators left plants rapidly; if food/webbing was available, some predatory mites remained on plants at least 24 hours. Even if no food/webbing was available, predators presented with local volatiles remained on plants for several hours longer than on clean plants without local volatiles. These small changes in leaving rates may lead to differences in local population dynamics, and possibly regional persistence, of the predator-prey interaction in patchy environments.     

Effects of temperature on the establishment potential of the predatory mite Amblyseius californicus McGregor (Acari: Phytoseiidae) in the UK

Amblyseius californicus was introduced into the UK in the early 1990s as a biocontrol agent against glasshouse red spider mite Tetranychus urticae. This study investigated the effects of temperature on the establishment potential of A. californicus in the UK in the light of recent reports of their successful overwintering outside of glasshouse environments. The developmental thresholds were 9.9 and 8.6 °C respectively using simple and weighted linear regression. Using the day-degree requirement per generation calculated by weighted regression (143 day-degrees) in combination with climate data, it was estimated that up to seven generations would be possible annually outdoors in the UK. Non-diapausing adult females froze at −22 °C, with 100% mortality after reaching their freezing temperature. Up to 90% of mites died before freezing after short exposures to low temperatures. Significant acclimation responses occurred; 90% of acclimated individuals survived 26 days exposure at 0 °C and 11 days at −5 °C (acclimated mites were reared at 19 °C, 6L:18D followed by 1 week at 10 °C, 12L:12D). Non-diapausing adult females survived over 3 months outdoors in winter under sheltered conditions and oviposition was observed. The experimental protocol used in this study is discussed as a pre-release screen for the establishment potential of other Amblyseius species, and similar non-native biocontrol agents.     

Factors affecting the distribution of a predatory mite on greenhouse sweet pepper

The predatory mite Neoseiulus cucumeris is used for biological control of phytophagous mites and thrips on greenhouse cucumber and sweet pepper. In a previous study, N. cucumeris provided effective control of broad mite but was only rarely found on the sampled leaves, raising questions about the factors affecting N. cucumeris distribution. To determine the distribution of N. cucumeris, leaves of pepper plants were sampled three times per day: just after sunrise, at noon and just before sunset for two years and throughout a 24 h period in one year. The presence of other mites and insects was recorded. Biotic (pollen) and abiotic (temperature, humidity) factors were monitored from the three plant levels. The effect of direct and indirect sunlight on the mites was assessed. N. cucumeris was found primarily in flowers; however, the mite’s distribution was affected by other predators (intraguild predation); in the presence of the predatory bug Orius laevigatus virtually no mites occurred in the flowers. Whereas temperature and humidity varied from the top to the lower level of the plants, apparently neither these factors nor the presence of pollen outside the flowers influenced mite distribution. N. cucumeris was found to be negatively phototropic; therefore N. cucumeris were pre-conditioned to light by rearing under light conditions for 4 months before being released. The light-reared mites were initially more numerous during the noon sampling period, however, rearing conditions caused only a temporary and non-significant change in distribution.     

Threat-sensitive anti-intraguild predation behaviour: maternal strategies to reduce offspring predation risk in mites

Predation is a major selective force for the evolution of behavioural characteristics of prey. Predation among consumers competing for food is termed intraguild predation (IGP). From the perspective of individual prey, IGP differs from classical predation in the likelihood of occurrence because IG prey is usually more rarely encountered and less profitable because it is more difficult to handle than classical prey. It is not known whether IGP is a sufficiently strong force to evolve interspecific threat sensitivity in antipredation behaviours, as is known from classical predation, and if so whether such behaviours are innate or learned. We examined interspecific threat sensitivity in antipredation in a guild of predatory mite species differing in adaptation to the shared spider mite prey (i.e. Phytoseiulus persimilis, Neoseiulus californicus and Amblyseius andersoni). We first ranked the players in this guild according to the IGP risk posed to each other: A. andersoni was the strongest IG predator; P. persimilis was the weakest. Then, we assessed the influence of relative IGP risk and experience on maternal strategies to reduce offspring IGP risk: A. andersoni was insensitive to IGP risk. Threat sensitivity in oviposition site selection was induced by experience in P. persimilis but occurred independently of experience in N. californicus. Irrespective of experience, P. persimilis laid fewer eggs in choice situations with the high- rather than low-risk IG predator. Our study suggests that, similar to classical predation, IGP may select for sophisticated innate and learned interspecific threat-sensitive antipredation responses. We argue that such responses may promote the coexistence of IG predators and prey.     

Response of predatory mites with different rearing histories to volatiles of uninfested plants

The behavioural response of the predatory mite Phytoseiulus persimilis to volatiles from several host plants of its prey, spider mites in the genus Tetranychus, was investigated in a Y-tube olfactometer. A positive response to volatiles from tomato leaves and Lima bean leaves was recorded, whereas no response was observed to volatiles from cucumber leaves, or leaves of Solanum luteum and Solanum dulcamara.Different results were obtained for predators that differed in rearing history. Predators that were reared on spider mites (Tetranychus urticae) on Lima bean leaves did respond to volatiles from Lima bean leaves, while predators that had been reared on the same spider mite species but with cucumber as host plant did not respond to Lima bean leaf volatiles. This effect is compared with the effect of rearing history on the response of P. persimilis to volatile allelochemicals of prey-infested plant leaves.     

Morphology of the olfactory system in the predatory mite Phytoseiulus Persimilis

The predatory mite Phytoseiulus persimilis locates its prey, the two-spotted spider mite, by means of herbivore-induced plant volatiles. The olfactory response to this quantitatively and qualitatively variable source of information is particularly well documented. The mites perform this task with a peripheral olfactory system that consists of just five putative olfactory sensilla that reside in a dorsal field at the tip of their first pair of legs. The receptor cells innervate a glomerular olfactory lobe just ventral of the first pedal ganglion. We have made a 3D reconstruction of the caudal half of the olfactory lobe in adult females. The glomerular organization as well as the glomerular innervation appears conserved across different individuals. The adult females have, by approximation, a 1:1 ratio of olfactory receptor cells to olfactory glomeruli.     

Effects of fenvalerate and azinphosmethyl on two-spotted spider mite and phytoseiid mites

The pyrethroid fenvalerate showed significantly faster activity against adult two-spotted spider mite Tetranychus urticae Koch c.f. azinphosmethyl using broad bean leaf discs sprayed in a Potter tower. LC₅₀s for fenvalerate were similar at 24 and 48 hr (0.056 and 0.051g AI/1) while LC₅₀s for azinphosmethyl were significantly different at 24 and 48 hr (0.72 and 0.38g AI/1, respectively). Mortality was partitioned to run-off and direct mortality. Fenvalerate showed an increasing contribution to mortality by run-off with increasing concentration. Increasing concentrations of azinphosmethyl had no effect on the proportion of T. urticae running off the discs. Fenvalerate inhibited egg production c.f. azinphosmethyl (60% and 20% inhibition respectively c.f. control after 24hr). The effect was not permanent. Carbaryl showed no acaricidal or inhibitory effects at 1g AI/1. T. urticae detected fenvalerate residues as reflected by choice of oviposition sites on untreated halves of leaf discs c.f. treated halves. Azinphosmethyl had no effect on oviposition preference. Phytoseiid mites were highly sensitive to fenvalerate residues. Predators moved off the test arena into sticky barriers after feeding on fenvalerate-treated eggs or walking on glass slides treated at 0.00005g AI/1.

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Résumé Les insecticides pyrethroïdes ont été utilisés pour lutter contre les pullulations d'araignées rouges. Cette note examine les réponses de Tetranychus urticae Koch et des prédateurs phytoseiidés résistants aux organo-phosphorés, Amblyseius fallacis Garman et Typhlodromus occidentalis Nesbitt, au fenvalerate (pyrethroïde) et à l'azinphosmethyl (organophosphate). Quelques essais avec du carbaryl sont indiqués.Une femelle adulte de T. urticae est placée sur une rondelle de feuille de Phaseolus vulgaris L. pulvérisée dans une tour de Potter.Les résultats sur la mortalité en fonction de la dose obtenus montrent une activité plus rapide du fenvalerate que de l'azinphosmethyl. Les DL₅₀ du fenvalerate (0,056 et 0,051g AI/I) sont les mêmes à 24 et 48 h, tandis que l'azinphosmethyl montre une activité plus lente (DL₅₀ de 0,72 et 0,38g AI/I à 24 et 48 h). La mortalité se partage entre la sortie de la rondelle et la mortalité in situ.Le fenvalerate provoque une plus forte répulsion que l'azinphosmethyl. Contrairement à l'azinphosmethyl le fenvalerate inhibe la production d'oeufs 60% et 20% d'inhibition à DL50 au bout de 24 h par rapport au témoin. Cette inhibition n'est pas permanente. Le carbaryl n'a pas d'effets inhibiteur ou acaricide à 1g AI/l.Les femelles adultes de T. urticae décèlent les résidus de fenvalerate sur les rondelles et pondent leurs oeufs sur les moitiés non traitées ou traitées à l'azinphosmethyl.Les Phytoseiides sont très sensibles aux résidus de fenvalerate. Après consommation d'oeufs traités, A. fallacis est incapable d'éviter des bandes gluantes. T. occidentalis décèle des traitements à 0,00005g AI/l en quittant les lames traitées par les bandes gluantes.

     

Prey-related odor preference of the predatory mites Typhlodromalus manihoti and Typhlodromalus aripo (Acari: Phytoseiidae)

Typhlodromalus manihoti and Typhlodromalus aripo are exotic predators of the cassava green mite Mononychellus tanajoa in Africa. In an earlier paper, we showed that the two predators were attracted to odors from M. tanajoa-infested cassava leaves. In addition to the key prey species, M. tanajoa, two alternative prey mite species, Oligonychus ossypii and Tetranychus urticae also occur in the cassava agroecosystem. Here, we used a Y-tube olfactometer to determine the attraction of the predators to odors from O. gossypii- or T. urticae-infested cassava leaves and their prey-related odor preference. T. aripo but not T. manihoti was slightly attracted to odors from O. gossypii-infested leaves. Both predator species showed a stronger response to odors from cassava leaves infested by M. tanajoa over odors from cassava leaves infested by O. gossypii. Neither predator species was attracted to odors from T. urticae-infested leaves and the predators preferred the odors from M. tanajoa-infested leaves over those from T. urticae-infested leaves. When O. gossypii was present together with M. tanajoa on the same leaves or on different sets of leaves offered together as an odor source the two predators were attracted. In contrast, after mixing non-attractive odors from T. urticae-infested leaves with attractive odors from M. tanajoa-infested leaves, neither T. aripo nor T. manihoti was attracted. Ecological advantages and disadvantages of the predators’ behavior and possible implications for biological control of M. tanajoa are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.