Greg English-Loeb

Host plant manipulation of natural enemies: leaf domatia protect beneficial mites from insect predators

Acarodomatia are small tufts of hair or invaginations in the leaf surface and are frequently inhabited by several taxa of non-plant-feeding mites. For many years, ecologists have hypothesized that these structures represent a mutualistic association between mites and plants where the mites benefit the plant by reducing densities of phytophagous arthropods and epiphytic microorganisms, and domatia benefit the mite by providing protection from stressful environmental conditions, other predaceous arthropods, or both. We tested these hypothesized benefits of domatia to domatia-inhabiting mites in laboratory and growth chamber experiments. In separate experiments we examined whether domatia on the wild grape, Vitis riparia, provided protection against drying humidity conditions or predaceous arthropods to two species of beneficial mite: the mycophagous species Orthotydeus lambi, and the predaceous species Amblyseius andersoni. For both taxa of beneficial mite, domatia significantly increased mite survivorship in the presence of the predatory bug, Orius insidiosus and the coccinellids Coccinella septempunctata and Harmonia varigata. There was no evidence for a protective effect of domatia with a third species of predatory arthropod, lacewing larvae Chrysoperla rufilabris. In contrast, there was no evidence for either species of beneficial mite that domatia provided any protection against low humidity. Thus in this system the primary mechanism by which domatia benefit beneficial mites is by protecting these organisms from other predatory arthropods on the leaf surface.

Influence of flowering cover crops on Anagrus parasitoids (Hymenoptera: Mymaridae) and Erythroneura leafhoppers (Homoptera: Cicadellidae) in New York vineyards

Abstract 1 We tested the hypothesis that providing nectar‐producing cover crops will enhance the biological control of grape leafhoppers (Erythroneura spp.) by Anagrus wasps in commercial vineyards in New York, U.S.A.

Mycophagous mites and foliar pathogens : Leaf domatia mediate tritrophic interactions in grapes

Acarodomatia are small structures found on the underside of the leaves of many woody plant species. Several taxa of nonphytophagous mites are frequently associated with these small tufts of hair or invaginations of the leaf surface. Botanists, and more recently ecologists, have hypothesized that these structures mediate a mutualistic association between the plants and predaceous and microbivorous (microbe-feeding) mites. We examined the influence of domatia on the abundance of a tydeid mite, Orthotydeus lambi, on the riverbank grape, Vitis riparia, and its impact on a key fungal pathogen, grape powdery mildew, Uncinula necator. In two field experiments, we manipulated domatia (by blocking them with glue or using clones that varied in domatia size) and O. lambi densities on V. riparia vines that we had inoculated with mildew. Mite densities were significantly higher on plants with intact domatia than on plants with blocked domatia (38% and 200% greater in experiments 1 and 2, respectively). In addition, clones with larger domatia had significantly more mites than clones with smaller domatia. In the first experiment, the greater number of mites on plants with domatia relative to plants without domatia did not translate into reduced incidence of mildew; mites reduced mildew to very low levels in both treatments. In the second experiment, plants with intact domatia had a significant 48% reduction in leaf area covered with mildew relative to plants with blocked domatia. In addition, clones with larger domatia (and thus more O. lambi) had less mildew than clones with smaller domatia. This study represents the first experimental evidence that acarodomatia benefit plants through increased abundance of a mycophagous mite, which resulted in decreased severity of a plant disease.

Testing the resource concentration hypothesis with tarnished plant bug on strawberry: density of hosts and patch size influence the interaction between abundance of nymphs and incidence of damage

Abstract. 1. Attributes of patches with strawberry plants were manipulated experimentally to assess the impact of patch size and host density on the abundance of tarnished plant bug (Hemiptera: Miridae) and incidence of fruit damage.

Behavioral and population consequences of acarodomatia in grapes on phytoseiid mites (Mesostigmata) and implications for plant breeding

We examined the influence of acarodomatia in the riverbank grape Vitis riparia Michaux (Vitaceae) on the distribution and abundance of predatory mites (Phytoseiidae) and their interactions with herbivorous mites. Acarodomatia are tufts of nonglandular trichomes or pits located in major leaf vein axes of many species of woody perennial plants and are often occupied by predatory and mycophagous mites. In common garden plantings of different accessions of V. riparia we found a significant positive relationship between size of domatia and the abundance of naturally occurring predatory mites. Behavior of adult predatory mites may explain this positive association, in part. In separate laboratory experiments, gravid females of Typhlodromus pyri Scheuten and Amblyseius andersoni Chant spent more time and deposited more eggs on half of a V. riparia leaf with accessible domatia versus the other half in which access to domatia was blocked with pruning tar. Domatia also had population consequences. In an outdoor experiment using potted grapevines, population size of T. pyri and A. andersoni mites was greater on V. riparia with open domatia compared to V. riparia in which domatia were blocked with pruning tar. Population size of predatory mites was also greater on V. riparia with domatia than on Vitis vinifera L., whether their axils were blocked or not. Since V. vinifera have very small domatia, these results indicate that the presence of domatia is important, not just access to vein axils. Elevated predatory mite populations in response to domatia, however, did not translate into differences in the abundance of European red mite Panonychus ulmi (Koch), an important pest of grapes.

Impact of Strawberry Cultivar and Incidence of Pests on Yield and Profitability of Strawberries under Conventional and Organic Management Systems

ABSTRACT Yield, incidence of pests, and profitability of strawberries under conventional and organic management systems were measured through four fruiting seasons, using three cultivare widely grown in the northeastern United States (dayneutrals [Tribute or Tristar], Earliglow and Honeoye). Fruits were more abundant in conventional than in organic plots, but the average weight of fruit was not affected by management system. Of all strawberry cultivare tested in this study, Honeoye was the most productive, both in terms of number and weight of harvested fruits. Incidence of tarnished plant bug damage by was much higher than for grey mould or slugs. Density of nymphs and proportion of fruits damaged by plant bugs were higher in organic than in conventional plots, and for Honeoye than dayneutrals or Earliglow. In contrast, management system and strawberry cultivar did not affect to a great extent the incidence of damage by grey mould or slugs. Productivity of strawberry plants was negatively correlated with incidence of damage by plant bugs, and positively with incidence of grey mould. Weed biomass was greater in organic than in conventional plots. Economic analysis indicated that a lack of reliable, effective measures for managing pests of strawberries without synthetic pesticides, especially weeds and plant bugs, may severely constrain yield and profitability of organic strawberries in the northeastern United States. Due to its high productivity and low susceptibility to plant bugs, Honeoye was by far the most profitable cultivar in this study, and appeared highly suitable for organic management.

Biological Control of Grape Powdery Mildew Using Mycophagous Mites

We evaluated the efficacy of a mycophagous tydeid mite, Orthotydeus lambi, in controlling grape powdery mildew on mature vines of nine different grape cultivars and one unnamed hybrid grown in an experimental vineyard over a 3-year period. O. lambi became well established on all vines where they were released. However, some cultivars supported higher densities than others, depending on, among other factors, the presence and abundance of leaf trichomes in vein axils (domatia). The establishment of O. lambi substantially reduced powdery mildew on foliage and fruit, although the magnitude of disease suppression was greater on some grape genotypes than others, depending on mite density and innate susceptibility to grape powdery mildew. Treatments where O. lambi was used alone were as effective as fungicide. Significantly better disease control was found in treatments with both mites and fungicides. The mass of pruning material and leaf photosynthetic rates were significantly greater for vines with O. lambi, fungicide, or a combination of mites and fungicide compared with untreated vines. The combination of mites and fungicide resulted in significantly greater yield than mites or fungicide alone. Our results illustrate the potential of O. lambi for biological control of grape powdery mildew but also highlight limitations related to differences among grape genotypes in innate susceptibility to mildew and suitability for mites.

Impact of Reflective Mulch on Yield of Strawberry Plants and Incidence of Damage by Tarnished Plant Bug (Heteroptera: Miridae)

Abstract The current study investigated the impact of reflective mulch on yield of strawberry plants and incidence of damage by tarnished plant bugs, Lygus lineolaris (Palisot de Beauvois), for three strawberry cultivars: ‘Honeoye’, ‘Earliglow’, and two sibling Dayneutrals (‘Tribute’ and ‘Tristar’, herein considered as one cultivar). Of all cultivars tested, Honeoye was the most productive and least susceptible to tarnished plant bug. For Earliglow and Honeoye, reflective mulch enhanced productivity of strawberry plants and suppressed density of nymphs per flower cluster and proportion of damaged fruits, but did not significantly impact numbers of nymphs or damaged fruits per hectare. Results with Dayneutrals were not consistently significant. Both in the presence or absence of reflective mulch, proportion of damaged fruits increased with increasing density of nymphs per flower cluster and with decreasing number of fruits harvested per row section, suggesting that planting productive strawberry cultivars or maintaining cultural practices that promote high yield may provide an effective line of defense against tarnished plant bug. These results also suggest that reflective mulch may suppress incidence of damage by tarnished plant bug both directly, by reducing number of nymphs per flower cluster, and indirectly, by enhancing productivity of strawberry plants. Economic analyses evaluating costs and benefits of using reflective mulch, as well as studies investigating mechanisms that underlie the impact of reflective mulch on yield and incidence of damage by tarnished plant bug, are still needed before reflective mulch can be implemented as a management strategy in commercial strawberry fields.

Impact of Insecticide Application and Mass Trapping on Infestation by Strawberry Sap Beetles (Coleoptera: Nitidulidae)

The impact of insecticide application and mass trapping on the level of infestation by the strawberry sap beetle, Stelidota geminata Say (Coleoptera: Nitidulidae), was assessed in cultivated strawberry. In total, more than 17,000 adults were captured in traps baited with whole wheat bread dough. Early in the season, captures were similar for traps at the periphery of and within the strawberry field, whereas captures were lowest within the field after fruits had begun to ripen. The presence of peripheral traps slightly increased captures of adults within the strawberry planting, suggesting that mass trapping of adults with food-baited traps may not be a viable management strategy. Applications of fenpropathrin at dusk or mid-day, between the appearance of ripe fruits and the first harvest, reduced infestation of fruits by sap beetle larvae. Fruits located on the ground were more heavily infested by sap beetles than fruits in the plant canopy, which either is due to foraging movements of adults on the groun...

Lack of trade‐off between direct and indirect defence against grape powdery mildew in riverbank grape

Abstract 1. The hypothesis that plants that invest more in an indirect defence will invest less in direct mechanisms was tested using genotypes of the riverbank grape Vitis riparia that varied in expression of acarodomatia, tufts of non‐glandular trichomes on underside of leaves that are frequently occupied by mycophagous mites. Mycophagous mites in this system have been shown to protect vines from grape powdery mildew caused by the fungus Uncinula necator.