Effect of the width of the herbicide strip on mite dynamics in apple orchards.

Herbicide strips are used in apple orchards to promote tree growth and survival, to increase yield and to reduce the risk of rodent damage to tree bark. However, herbicide strips, particularly wider ones, may cause problems including soil erosion, reduced organic matter, leaching of nitrates into ground water and increased incidence of plant diseases and pests, including two-spotted spider mites, Tetranychus urticae Koch. In this 2 year study we monitored mite dynamics in apple trees and used sticky bands on tree trunks to determine rates of T. urticae immigration into Nova Spy apple trees in plots with wide (2 m) or narrow (0.5 m) herbicide strips. Use of wider herbicide strips promoted two risk factors that could trigger outbreaks of tetranychid mites. First, concentrations of leaf N in apple trees were higher and those of P and K were lower with the wide strips. Such changes in nutritional quality of leaves would increase the potential for more rapid population growth of T. urticae, and to a lesser extent, the European red mite, Panonychus ulmi (Koch). Second, there were higher rates of T. urticae immigration from the ground cover vegetation into the trees. In 2006, and for most of 2007, densities of T. urticae were higher with wide herbicide strips, whereas densities of P. ulmi were not enhanced. However, by late August to early September in 2007, densities of both tetranychids were lower with wide herbicide strips. This is because both risk factors were counterbalanced, and eventually negated, by the enhanced action of phytoseiid predators, mostly Typhlodromus pyri Scheuten. From July through September 2006, ratios of phytoseiids to tetranychids were always several-fold lower with wide herbicide strips but in 2007, from mid-July onwards, predator-prey ratios were usually several-fold higher with wide strips. However, this numerical response of phytoseiids to prey density can only occur where the pesticide program in orchards is not too harsh on phytoseiids. Hence the impact of width of herbicide strip is contingent on the composition and size of the phytoseiid complex and the impact of pesticides on predation.

Influence of habitat structure and resource availability on the movements of Rhagoletis indifferens (Diptera: Tephritidae).

Habitat structure and resources availability may differentially influence movement between habitat patches. We examined fly movement decisions (stay or leave) at the scale of individual trees by measuring the response of marked Rhagoletis indifferens (Diptera: Tephritidae) to sweet cherry trees (Prunus avium) that were manipulated by changing the shape of the tree (structure treatment = normal or reduced) and the fruit load (fruit treatment = augmented, normal, or reduced). More than 600 observations were made at two field sites that differed in the average inter-tree distance: Senger site, 10.1 +/- 4.5 m; Tuemp site, 29.0 +/- 19.3 m. At the Senger site, flies were resighted most often in the normal structure-augmented fruit trees. At the Tuemp site, however, there were fewer transfers between trees, unusual tree preferences, and significant treatment interaction terms. Using a first principles diffusion model of attraction and by varying fly perceptual range to limit tree choice, we generated unusual tree preferences based on differential attraction to individual trees. Our results suggest that manipulating tree attractiveness may be a viable pest management strategy for closely spaced trees but not for dispersed trees. Further study into the relationship between the spatial arrangement of trees and the flies' ability to detect specific tree characteristics is warranted.

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.

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.

Microsatellite sequences are under-represented in two mite genomes.

Microsatellites are known to be a common feature of eukaryote genomes. Here we investigate the presence of microsatellite sequences in the genome of two mite species, Tetranychus urticae and Amblyseius fallacis, based on screening of both mite genomic libraries and Southern blots of these mites that we compare to two vertebrates. No signal with GT15 or a faint smear with CT10 were obtained in Southern analysis for the two mites, whereas both probes strongly bound with vertebrate DNA. Genomic libraries constructed in plasmid and lambda vectors were probed and only two CT microsatellites were isolated for T. urticae. Among eight trinucleotides probes tested, the strongest hybridization signal was detected for T. urticae with CAT and TGA probes. These two classes of repeats were also the most represented in genomic library screenings. However, only sequences with short numbers of units could be detected (

Response of male eye-spotted bud moth,Spilonota ocellana (Lepidoptera: Tortricidae), to different pheromone blends in north America and The Netherlands.

Response of male eye-spotted bud moth,Spilonota ocellana (Denis and Schiffermüller), to different ratios of synthetic sex pheromone components, (Z)-8-tetradecenyl acetate (Z8-14:OAc) and (Z)-8-tetradecenyl alcohol (Z8-14:OH), were compared in four North American locations and in one location in The Netherlands. In British Columbia, Nova Scotia, Michigan, and The Netherlands, a 99:1 blend ofZ8-14:OAc andZ8-14:OH captured significantly more maleS. ocellana thanZ8-14:OAc alone or binary blends containing 10-50%Z8-14:OH. In Ontario, where population sizes were low compared to the other four locations, trends in trap catches were similar, and there was no indication that maleS. ocellana responded differently to the tested pheromone blends. A 99:1 blend ofZ8-14:OAc andZ8-14:OH should be most effective in pheromone-based control programs ofS. ocellana in North America and in The Netherlands. Our results confirm earlier studies that a 99:1 blend ofZ8-14:OAc andZ8-14:OH captures significantly more maleS. ocellana thanZ8-14:OAc alone. However, our finding that a 99:1 blend ofZ8-14:OAc andZ8-14:OH is significantly more attractive than binary blends containing 10-50%Z8-14:OH differs from previous findings in Germany and Switzerland.