Response of Neoseiulus fallacis Garmen and Galendromus occidentalis Nesbitt (Acari: Phytoseiidae) to Tetranychus urticae Koch (Acari: Tetranychidae)-Damaged Hop Humulus lupulus (L.) (Urticales: Cannabaceae)

Abstract 1 The response of Neoseiulus fallacis Garmen and Galendromus occidentalis (Acari: Phytoseiidae) to Tetranychus urticae Koch (Acari: Tetranychidae)‐damaged and undamaged hop, Humulus lupulus (L.), plants was tested using a Y‐tube olfactometer. 2 Neoseiulus fallacis but not G. occidentalis was attracted to volatiles from T. urticae‐damaged hop plants when paired with undamaged plants. 3 The response of N. fallacis to these volatiles was stronger for plants severed at the soil surface than for intact plants. 4 There was no difference in the response of N. fallacis to severed or intact hop plants that had no spider mite damage, indicating that artificial wounding by severing alone does not elicit the production of attractive volatiles detectable to N. fallacis. These results are consistent with the existence of cross‐talk between signalling pathways initiated by feeding damage and artificial wounding that result in elevated levels of predator‐attracting volatiles.     

Jerking in predaceous mites (Acari: Phytoseiidae) with emphasis on larvae

Jerking, a behavior involving a pronounced and often repeated lunging of the body, was studied in larvae among seven species of phytoseiid mites, Euseius finlandicus, Galendromus occidentalis, Neoseiulus californicus, Neoseiulus fallacis, Phytoseiulus macropilis, Phytoseiulus persimilis and Typhlodromus pyri, and in the nymphal stages of N. fallacis. This behavior was observed in larvae of six of the seven species and in all active immature stages of N. fallacis. Jerking was usually triggered by direct contact with a con- or heterospecific mite, although jerking occurred occasionally without direct contact in N. fallacis larvae. The larval jerking tendency (the mean fraction of contacts resulting in jerking) of a species was significantly correlated with a tendency to congregate with conspecifics. Congregated larvae often probed their immediate area and each other with the front legs, repeatedly jerking in response to contact with neighboring larvae. Species with larvae having higher jerking tendencies also jerked more repeatedly per jerking event. Among species, there was no consistent relationship between jerking tendency and larval age. Larvae of N. fallacis had a higher tendency to jerk than protonymphs and deutonymphs, and they had both the highest jerking and congregating tendencies among larvae of all species studied. An individual was more likely to jerk when approached by another mite than when it initiated contact, and when observed in N. fallacis larvae that initiated contact, jerking was sometimes aggressive. Jerking N. fallacis larvae experienced fewer and shorter periods of probing by the mouthparts and fewer attacks from cannibalistic adult females than anesthetized larvae that were unable to jerk.     

Some effects of pre-release host-plant on the biological control of Panonychus ulmi by the predatory mite Amblyseius fallacis

Amblyseius fallacis Garman has been selected for pyrethroid resistance and mass reared for experimental release as a biological control agent for tetranychid mites on a number of crops in Canada. Several releases of this predator onto apple and peach trees have failed to result in the establishment of A. fallacis, or in the biological control of Panonychus ulmi Koch. Here, we test the hypothesis that the change of host-plant at the time of release is a critical factor in the establishment of A. fallacis for biological control of P. ulmi. Functional and numerical response studies were undertaken on two populations of A. fallacis: a wild strain collected from the canopy foliage of an apple orchard near Vineland, Ontario; and a second strain reared on bean plants in a commercial insectary with Tetranychus urticae as prey. Each population consumed significantly more P. ulmi and produced significantly more eggs when on leaf disks from the plant species they were reared on, than on leaf disks from the novel host plant. A further experiment was conducted to determine if establishment and biological control of mass-reared A. fallacis could be affected by rearing a population for a short term on apple leaves prior to release on apple trees. Three release treatments were made into potted apple trees in a glasshouse, using predators commercially mass-reared on bean and T. urticae: A. fallacis released directly; A. fallacis reared in the laboratory for four weeks on bean and T. urticae; A. fallacis reared on apple leaves and T. urticae for four weeks. They were compared with a control treatment lacking predator release. Contrary to results of the functional and numerical response studies, no difference was observed between release treatments. All release treatments adding A. fallacis resulted in a similar, if limited, degree of biological control of P. ulmi. These results indicated that there may be short-term effects of host plant on the establishment of A. fallacis and biological control of P. ulmi, which in our study were observed as an initial reduction of the predatory response. However, in a test, the predators appeared to overcome these short-term effects and successfully established on the new host-plant to control P. ulmi.     

Effects of humidity on eggs and immatures of Neoseiulus fallacis,Amblysieus andersoni,Metaseiulus occidentalis and Typhlodromus pyri (Phytoseiidae): implications for biological control on apple,caneberry, strawberry and hop

The lethal humidity (LH₅₀) responses at 20°C of eggs of two strains of Neoseiulus fallacis (Garman) were 71.6 and 69.7%; of three strains of Amblyseius andersoni (Chant) were 62.9, 62.0 and 62.4% and of one strain each of Typhlodromus pyri Scheuten and Metaseiulus occidentalis Nesbitt were 55.0 and 28.4%, respectively. Eggs of three genetically distinct strains of A. andersoni from Oregon, the Netherlands and Italy did not respond differently from one another nor did eggs of freely hybridizing N. fallacis from Michigan and Oregon. Mortality of larvae through development to early protonymphs at 50% RH, 20°C. was 91.9, 82.3, 46.2 and 31.0% for fed mites and 98.1, 83.2, 67.0 and 89.7% for unfed mites of Oregon strains of N. fallacis, A. andersoni, T. pyri and M. occidentalis, repectively. Fed larvae-protonymphs of M. occidentalis and T. pyri were more tolerant of low humidity than fed larvae-protonymphs of N. fallacis and A. andersoni. Mortality was less for fed than unfed larvae-protonymphs of M. occidentalis and T. pyri, but there were no differences for A. andersoni and N. fallacis. Levels of feeding by predator larvae on T. urticae and cannibalism by phytoseiid protonymphs contributed to species differences. Responses to humidity are discussed in relation to geographic and host plant distributions and biological control by single or mixed species populations of phytoseiids.     

Effects of acaricides,pyrethroids and predator distributions on populations of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> in apple orchards

We sampled mites in three apple orchards in Nova Scotia, Canada, that had been inoculated with pyrethroid-resistant Typhlodromus pyri and had a history of Tetranychus urticae outbreaks. The objective of this study was to monitor populations of T. urticae and phytoseiid predators on the ground and in trees and to track dispersal between the two habitats. Pesticides were the chief cause of differences in mite dynamics between orchards. In two orchards, application of favourably selective acaricides (abamectin, clofentezine) in 2002, coupled with predation by T. pyri in trees and Neoseiulus fallacis in ground cover, decreased high T. urticae counts and suppressed Panonychus ulmi. By 2003 phytoseiids kept the tetranychids at low levels. In a third orchard, application of pyrethroids (cypermethrin, lambda-cyhalothrin), plus an unfavourably selective acaricide (pyridaben) in 2003, suppressed phytoseiids, allowing exponential increases of T. urticae in the ground cover and in tree canopies. By 2004 however, increasing numbers of T. pyri and application of clofentezine strongly reduced densities of T. urticae in tree canopies despite high numbers crawling up from the ground cover. Another influence on T. urticae dynamics was the distribution of the phytoseiids, T. pyri and N. fallacis. When harsh pesticides were avoided, T. pyri were numerous in tree canopies. Conversely, only a few N. fallacis were found there, even when they were present in the ground cover and on tree trunks. Low numbers were sometimes due to pyrethroid applications or to scarcity of prey. Another factor was likely the abundance of T. pyri, which not only competes with N. fallacis, but also feeds on its larvae and nymphs. The scarcity of a specialist predator of spider mites in trees means that control of T. urticae largely depends on T. pyri, a generalist predator that is not particularly effective in regulating T. urticae. The Canadian Crown's right to retain a non-exclusive, royalty-free licence in and to any copyright is acknowledged.     

Neoseiulus fallacis: dispersal and biological control of Tetranychus urticae following minimal inoculations into a strawberry field

In three separate tests, 100 adult female Neoseiulus fallacis (Garman) (plus immatures) were released at five point locations across 1.6-m rows of strawberries to control twospotted spider mites, Tetranychus urticae Koch. Beginning in April, during 6–12 weeks, predators controlled pests locally and dispersed downwind by 20–30 m. Up to 100 m² around each release point was colonized, and the entire 2.5 ha field was covered by predators by September. Distances dispersed by N. fallacis were similar within and across rows, suggesting that dispersal was primarily by aerial rather than by ambulatory means. Factors that affected dispersal were temperature, wind direction, density of spider mites, and mowing and flailing of foliage. An exponential model of dispersal was fitted to the data. On average, the area dispersed by N. fallacis doubled every 70 degree-days. From these results, a strategy of minimum release is suggested. To establish N. fallacis over a field in a single season, ca. 100 adult females per 1–2 m of row can be released before 1 July, after T. urticae have achieved 2–5 female adults per leaf. Releases should be 50 m apart and to the upwind side of the field. Selective sprays may be needed to suppress spider mites until predators gain control and disperse over the field.     

Toxicity of organophosphorus systemic pesticides to predator mites and prey

Three systemic OP insecticides, Di-Syston^®, Meta-Systox-R^® and Systox^® were added at six concentrations (0.002–0.032% active ingredient) to nutrient solutions in which bean plants were cultured. On all concentrations the materials were less toxic to the two-spotted spider mite,Tetranychus urticae Koch feeding on the plant than toNeoseiulus fallacis (Garman) preying on theT. urticae. Of the three, Di-Syston was the least toxic to both mite species. WhenT. urticae were cultured on detached bean leaves, placed on cellucotton in nutrient solutions containing the same pesticide concentrations, their eggs were also toxic toN. fallacis. Longevity studies in conjunction with³²P labelled foliage showed thatN. fallacis are incapable of feeding directly on bean leaves.

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Zusammenfassung Drei systemische Phosphorinsektizide, Di-Syston^®, Meta-Systox^® und Systox^®, wurden, in sechs Konzentrationen (0,002–0,032% Wirkstoff) zu Nährstofflösungen hinzugefügt, in denen Bohnenpflanzen kultiviert wurden. Für die SpinnmilbeTetranychus urticae, die an den Bohnenblättern saugte, waren die drei Insektizide in sämtlichen Konzentrationen weniger toxisch als für die RaubmilbeNeoseiulus fallacis, die sich vonT. urticae ernährte. Es ergab sich demnach keine ökologische Selektivität. Von den drei geprüften Mitteln war Di-Syston für die beiden Milben am wenigsten toxisch. Wenn manT. urticae auf abgetrennten Bohnenblättern, die sich auf Cellucotton in Nährstofflösungen mit den genannten Insektizidkonzentrationen befanden, züchtete, wurden ihre Eier fürN. fallacis ebenfalls toxisch. Lebensdauer-Versuche mit Blättern, die³²P enthielten, zeigten, daßN. fallacis nicht fähig ist, sich direkt von Bohnenblättern zu ernähren.

     

Ambulatory dispersal behavior ofNeoseiulus fallacis (Acarina: Phytoseiidae) in relation to prey density and temperature

Ambulatory dispersal behavior ofNeoseiulus fallacis (Garman) was studied in the laboratory to evaluate within-plant movement in relation to temperature and prey density. Adult femaleN. fallacis were confined in 2.5-cm-diameter arenas on the abaxial surface of excised corn leaves. Four temperatures (23, 28, 33, and 39° C) and prey densities ranging from 0 to 55 spider mite eggs per cm² were used. The walking paths of these mites were traced, digitized and used to calculate turning angles, walking speeds and turning rates. A computer simulation of walking behavior used this information to model mite ambulatory behavior and predict dispersal rates.Neoseiulus fallacis behavior while on whole corn leaves was quantified to verify the results of the simulation. The results showed thatN. fallacis will follow a leaf or arena edge (edge-walking) at all temperatures and prey densities. In addition, this behavior was used to the exclusion of the other types of behavior such as resting, and random-walk type search when prey egg density was less than 4 eggs per cm². The exclusion of edge-walking behavior from the model caused the model to underestimate substantially the dispersal rates leaves. These data suggest that there are at least two recognizable types of ambulatory search used byN. fallacis—the random-walk type, which is used when prey density is high (searching within prey patches), and the edge-walking behavior, which is used when prey density is low. This behavior allows the mite to travel rapidly from leaf to leaf in search of new prey patches.     

Overwintering and effects of autumn habitat manipulation and carbofuran on Neoseiulus fallacis and Tetranychus urticae in peppermint

The percentages of Neoseiulus fallacis (Garman) in four subhabitats of peppermint fields in November were 37% on dead leaves, 45% in debris below dead leaves, 3% in hollow stems and 15% on live foliage. In December, the percentages were 36, 39, 7 and 18%, respectively, for these same sites. The values were 40, 37, 18 and 5% and 6, 80, 14 and 0% for January and February, respectively. By April, 95% of all predators were on new foliage feeding on Tetranychus urticae Koch, while the rest were still in debris. Augmenting plots with debris increased overwintering survival of N. fallacis compared to the natural condition while removal of debris decreased it. An autumn carbofuran (Furadan 4F) treatment completely eliminated overwintering N. fallacis, thus leading to outbreaks of T. urticae the following spring. The results of these overwintering studies are discussed in relation to improved biological control and spider mite management.     

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.     

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.     

Research advances on pesticide resistance in natural enemies

Recent research on the factors governing resistance development among arthropod natural enemies is reviewed, including selection studies of resistance development in the predatory miteAmblyseius fallacis (Garman) andTetranychus urticae Koch and patterns of toxicity to pesticides and mixed function oxidase activity in a group of pests, predators and parasites. New areas of resistance development in the speciesPhytoseiulus persimilis A. H. andTyphlodromus pyri Scheuten are discussed as are genetic studies of resistance inP. persimilis and the toxicology of resistance inA. fallacis. Lastly, the widespread documentation of resistance inA. fallacis, a predator of plant-feeding mites, the cecidomyidAphidoletes aphidimyza (Rond.), a predator of aphids and 2 parasites of leafhopper in orchards of North America, is discussed relative to the long-term use of organophosphate-based insecticides and programs of integrated pest control.

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Résumé Les récentes recherches sur les facteurs déterminant le développement d'une résistance aux pesticides chez les arthropodes ennemis naturels des ravageurs sont rappelées, y compris les études sur la sélection pour cette résistance de l'acarien prédateur,Amblyseius fallacis (Garman) et deTetranychus urticae Koch, ainsi que les types de toxicité des pesticides pour un ensemble de ravageurs et de leurs parasites et prédateurs. De nouveaux domaines dans les phénomènes de la résistance chezPhytoseiulus persimilis A.H. etTyphlodromus pyri Scheuten sont discutés, telles que les études génétiques de la résistance chezP. persimilis et la toxicologie de la résistance chezA. fallacis. Enfin la très abondante documentation sur la résistance deA. fallacis, prédateur d'acariens phytophages, deAphidoletes aphidimyza (Rond), cecidomyie prédatrice de pucerons et de deux parasites de cicadelles en vergers en Amérique du Nord, est discutée en fonction de l'utilisation prolongée d'insecticides à base d'organophosphorés et de programmes de lutte intégrée.

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Published as article No. 8498 of the Michigan Agricultural Experiment Station, Michigan State University, East Lansing, Michigan 48824.     

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.     

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.     

Nutritional benefits of intraguild predation and cannibalism among generalist and specialist phytoseiid mites

1. Intraguild predation and cannibalism are common among predaceous phytoseiid mites (Acari, Phytoseiidae) but the nutritional benefits gained by these processes are poorly understood. 2. The study reported here addressed the questions of whether cannibalism and intraguild predation provide different nutritional benefits and whether the ability to utilise cannibalism and intraguild predation is linked to the diet specialisation of phytoseiid mites. Specialists tested were Phytoseiulus macropilis, Galendromus occidentalis, and Neoseiulus longispinosus; generalists tested were Amblyseius andersoni, Neoseiulus cucumeris, and Neoseiulus fallacis. 3. All generalists and the specialist P. macropilis were able to complete juvenile development with both con‐ and hetero‐specific prey. Juvenile development of generalists was shorter with heterospecific prey than with conspecific prey, whereas development of the specialist P. macropilis did not differ between prey types. Only a few N. longispinosus and G. occidentalis, both specialists, reached adulthood by cannibalism but none reached adulthood by intraguild predation. 4. All generalists were able to sustain oviposition by intraguild predation. Neoseiulus cucumeris and A. andersoni laid more eggs with heterospecific prey than with conspecific prey, whereas N. fallacis had similar oviposition rates with both prey types. No specialist sustained oviposition by intraguild predation or cannibalism. 5. Overall, generalists gained equal or more nutritional benefits by intraguild predation than by cannibalism and were able to utilise phytoseiid intraguild prey as an alternative food source. Specialists gained equal or more nutritional benefits from cannibalism than from intraguild predation. For specialists, con‐ and hetero‐specific phytoseiids may be considered only a supplemental food.     

Genomic constitution and variation in five partial amphiploids of wheat–<Emphasis Type="Italic">Thinopyrum intermedium</Emphasis> as revealed by GISH,multicolor GISH and seed storage protein analysis

Genomic in situ hybridization (GISH) and multicolor GISH (mcGISH) methodology were used to establish the cytogenetic constitution of five partial amphiploid lines obtained from wheat × Thinopyrum intermedium hybridizations. Line Zhong 1, 2n=52, contained 14 chromosomes from each of the wheat genomes plus ten Th. intermedium chromosomes, with one pair of A-genome chromosomes having a Th. intermedium chromosomal segment translocated to the short arm. Line Zhong 2, 2n=54, had intact ABD wheat genome chromosomes plus 12 Th. intermedium chromosomes. The multicolor GISH results, using different fluorochrome labeled Th. intermedium and the various diploid wheat genomic DNAs as probes, indicated that both Zhong 1 and Zhong 2 contained one pair of Th. intermedium chromosomes with a significant homology to the wheat D genome. High-molecular-weight (HMW) glutenin and gliadin analysis revealed that Zhong 1 and Zhong 2 had identical banding patterns that contained all of the wheat bands and a specific HMW band from Th. intermedium. Zhong 1 and Zhong 2 had good HMW subunits for wheat breeding. Zhong 3 and Zhong 5, both 2n=56, possessed no gross chromosomal aberrations or translocations that were detectable at the GISH level. Zhong 4 also had a chromosome number of 2n=56 and contained the complete wheat ABD-genome chromosomes plus 14 Th. intermedium chromosomes, with one pair of Th. intermedium chromosomes being markedly smaller. Multicolor GISH results indicated that Zhong 4 also contained two pairs of reciprocally translocated chromosomes involving the A and D genomes. Zhong 3, Zhong 4 and Zhong 5 contained a specific gliadin band from Th. intermedium. Based on the above data, it was concluded that inter-genomic transfer of chromosomal segments and/or sequence introgression had occurred in these newly synthesized partial amphiploids despite their diploid-like meiotic behavior and disomic inheritance.     

Do leaf domatia mediate intraguild predation and host plant resistance to Oligonychus aceris (Shimer) on Red Sunset Maple (Acer rubrum)?

The predatory mites Neoseiulus fallacis (Garman) (Acarina: Phytoseiidae) and Zetzellia mali (Ewing) (Acarina: Stigmaeidae) have the potential to suppress populations of Oligonychus aceris (Shimer) (Acarina: Tetranychidae) on maple cultivars under field conditions. Red Sunset red maples (Acer rubrum) are more resistant to O. aceris than ‘Autumn Blaze’ Freeman maple (Acer × fremanii). Examination of leaves indicated that the mite resistant Red Sunset trees had more leaf domatia than those from Autumn Blaze. Laboratory assays found that maple cultivars did not affect rates of O. aceris consumption by N. fallacis or Z. mali in a 24 h period. Each predator exhibited distinct preferences for O. aceris life stages. N. fallacis consumed significantly more protonymphs and adults of O. aceris, whereas Z. mali consumed more eggs. In contrast, maple cultivars significantly influenced rates of intraguild predation between phytoseiids and stigmaeids. Adult N. fallacis consumed more immature stages of Z. mali on Autumn Blaze than on Red Sunset maple, but adult Z. mali consumed the same numbers of N. fallacis nymphs on both cultivars. These findings provide a potential mechanism to explain the resistance of Red Sunset maples to O. aceris. On Red Sunset maples, where domatia provide Z. mali with refugia from predation by N. fallacis, both predators can contribute to the mortality of O. aceris. In contrast on Autumn Blaze maples Z. mali have no place to hide from N. fallacis, so the contribution of this stigmaeid to O. aceris mortality is greatly diminished. Thus, differential susceptibility of these cultivars to spider mites may be mediated by the capacity of leaf domatia to influence rates of intraguild predation among phytoseiid and stigmaeid predators.     

Larval survival and feeding by immature Metaseiulus occidentalis,Neoseiulus fallacis,Amblyseius andersoni and Typhlodromus pyri on life stage groups of Tetranychus urticae Koch and phytoseiid larvae

When 20 newly hatched larvae either of Metaseiulus occidentalis (Nesbitt), Neoseiulus fallacis (Garman), Amblyseius andersoni Chant or Typhlodromus pyri Scheuten were held in arenas without food at 95% RH and 20°C, the percentages of mites surviving to protonymphs were 5.0, 81.3, 86.3, and 83.8%, respectively. Unfed M. occidentalis larvae starved within 2–3 days, while immatures of the other three species lived up to 12–14 days, with some becoming adults by cannibalizing and/or scavenging. Phytosciid larvae given eggs, larvae/protochrysalis/protonymphs (L/P), deutochrysalis/deutonymphs (D) or teleiochrysalis/female adult (T/A) of Tetranychus urticae Koch, fed at different incidences during 6 h tests. Larvae of T. pyri never fed, but almost all larvae of M. occidentalis fed on eggs and L/Ps and 60–70% of M. occidentalis larvae fed on Ds and T/As. N. fallacis and A. andersoni larvae fed at incidences from 20–75% depending on the stage of spider mite given. Larvae fed more commonly on eggs and L/Ps than Ds and T/As for M. occidentalis and N. fallacis but not A. andersoni. Protonymphs and deutonymphs of all four species, readily fed on T/As after 3 h of exposure, but incidences were higher for A. andersoni and T. pyri. Feeding on phytoseiid larvae by protonymphs and deutonymphs also was more common for A. andersoni and T. pyri. Except for M. occidentalis, deutonymphs fed more than protonymphs on phytoseiid larvae. Results are discussed in relation to individual species life histories and the value of these traits in predicting a species role in a biological control system.     

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.     

X-ray treatment of Oenothera chromosomes

Summary The fertilisation of untreated ovules ofOenothera blandina by pollen subjected to doses of X-rays resulted in F₁ generations consisting of normal plants with no pollen sterility, normal plants with about 50% or more pollen sterility and variant plants usually with 50% or more bad pollen.The pollen-sterile normal plants included seven with segmentally interchanged chromosomes, the remainder examined having only normal chromosomes. Five plants had one ring of four chromosomes, one had one ring of six chromosomes and one had two rings of four chromosomes. The inheritance of the interchanges was traced in several cases. Some of them were not transmitted because they were lethal to pollen carrying them and also failed to form embryo sacs.Most of the variant plants appeared cytologically normal, having seven ring pairs at metaphase 1. Three plants had interchanges, two of them having a chain of four chromosomes as the maximum catenation. The F₂'s of the variant plants consisted of normalblandina with the exception of the narrow leaved one that had a ring of four chromosomes.It is concluded that the variant plants, the pollen sterile normals and the interchange normals in which the interchange was not transmitted through the pollen were all defectives, resulting from deletions produced in the parental pollen by the action of the X-rays.Some indications of a quantitative relationship between X-ray dosage and percentage numbers of variants, pollen steriles and interchange heterozygotes respectively could be traced.