`Golden Delicious', `Delicious', and `York Imperial' apples (Malus ×domestica Borkh.) with various amounts of tufted apple bud moth (TABM) [Platynota idaeusalis (Walker)] feeding injury were evaluated for quality at harvest and following storage in air and controlled atmosphere. In addition, apples were artificially injured during two seasons to mimic TABM feeding injury. There was little or no effect of natural TABM injury on the quality of apples in many experiments. At harvest, firmness was not influenced by natural TABM injury, soluble solids concentration (SSC) was increased in three of 11 experiments, and starch levels decreased in two of 11 experiments. These results indicate a slight advancement of maturity of injured fruit. More severely injured fruit tended to have more decay after storage than fruit with less injury. Some injury, especially first brood injury, up to ≈7 to 10 mm2 surface damage, can be tolerated without compromising storage quality of processing apples. However, severe injury (>79 mm2) can increase decay. Second brood injury, whether caused by natural feeding of TABM or through artificial means, usually caused a higher incidence of decay than first brood injury. Artificial injury imposed close to harvest led to more decay in storage than did similar injury imposed earlier.
Cynthia L. Barden and Larry A. Hull
D.S. Achor, L.G. Albrigo, and C.W. McCoy
Upper surface leaf lesions on `Sunburst' mandarin [(Citrus reticulata Blanco × (C. paradisi Macf. × C. reticulate)] associated with feeding by the citrus rust mite [Phyllocoptruta oleivora (Ashm.)] are more severe than those on other citrus cultivars. Development of leaf lesions on `Sunburst' mandarin and two other cultivars were examined by light and electron microscopy. Damaged leaves treated with a fungicide confirmed that the anatomical changes on `Sunburst' are an enhanced wound periderm response to feeding injury by rust mite and not the result of fungal invasion.
David T. Handley and James E. Pollard
The tarnished plant bug (Lvgus lineolaris) is a serious pest of strawberries in North America, causing a severe malformation of the receptacle known as “apical seediness” or “buttoning”. Light and scanning electron microscopy were used to assess tarnished plant bug feeding on strawberries and to determine the nature of the injury. During early fruit development stages (anthesis to petal fall) the primary feeding sites were developing achenes. Feeding sites on more developed fruit changed to receptacle tissue, usually close to an achene. The “buttoning” malformation of strawberries associated with tarnished plant bug is most likely a result of the destruction of achenes during early fruit development stages. Feeding on receptacle tissue later in fruit development causes more localized damage, such as creases and indentations.
This study quantified how different shading levels alter the foliar nutrient, C:N ratio, chlorophyll content and key leaf characters in azalea `Delaware Valley White' Rhododendron mucronatum (Blume) (Ericales: Ericaceae), which influenced, in turn, feeding, oviposition, survival and development of the azalea lace bug, Stephanitis pyrioides (Scott) (Heteroptera: Tingidae). The mean contents of N, Ca, Fe, and Zn increased linearly with increases in the shading level, whereas P, K, B, Mn, and the C:N ratio of leaves were significantly decreased. Although injured leaves contained significantly less chlorophyll than uninjured leaves, the mean relative chlorophyll content of leaves increased linearly with the level of shading. Mean leaf area and moisture content of leaves increased linearly with increased degree of shading, while the mean trichome density decreased. The mean number of oviposited eggs and the percent of nymphs reaching adulthood increased linearly with the degree of shading. Azalea shoots suffered increased feeding injury as the season progressed, yet unshaded plants suffered more feeding injury than shaded plants. While the mean number of eggs laid, and the mean number of reared adults, were significantly and positively correlated with the mean leaf N, the mean feeding injury was negatively correlated with leaf N. Although these dependent variables were not correlated with K nor Ca, the mean number of eggs laid, and the mean number of reared adults were negatively correlated with the mean leaf P and with the mean C:N ratio. Mean feeding injury was positively correlated with leaf P and with the C:N ratio, but negatively correlated with N. This study shows that shaded plants are of better quality as hosts and that these plants can tolerate infestations by the lace bug.
Richard J. Campbell, Randolph L. Grayson, and Richard P. Marini
Scanning and transmission electron microscopy were used to investigate damage to strawberry (Fragaria ×ananassa Duch.) leaves caused by twospotted spider mite (Tetranychus urticae Koch.). Mites damaged epidermal cells on the lower leaf surface, but did not damage major vascular elements of the leaf. Mite-damaged spongy and palisade parenchyma cells had coagulated protoplasts, with some cells devoid of cellular contents. Mesophyll cells adjacent to damaged regions showed no ultrastructural distortion or disruption of chloroplasts.
George P. Opit, Greg K. Fitch, David C. Margolies, James R. Nechols, and Kimberly A. Williams
The effects of overhead and drip tube irrigation on twospotted spider mite (TSMs) (Tetranychus urticae Koch) and predatory mite (PMs) (Phytoseiulus persimilis Athias-Henriot) populations, as well as the biological control of TSMs by PMs, were investigated on Impatiens wallerana Hook. f. `Impulse Orange'. To determine the effects of the two irrigation methods on TSM populations, plants were inoculated with female TSMs 6 weeks after seeding. Plants were then irrigated twice every three days, and TSM counts were taken 3 weeks later. To assess the effects of irrigation method on PMs, plants were inoculated with TSMs 6 weeks after seeding, PMs were released 10 days later, plants were irrigated about once per day, and the number of predatory mites on plants was counted 3 weeks after release. To assess the effects of irrigation method on the biological control of TSMs by PMs, plants were inoculated with TSMs and PMs were released as before, but then plants were irrigated either three times every 2 days or three times every 4 days using either drip or overhead irrigation. The number of TSMs on plants and the number of leaves showing TSM feeding injury were measured 3 weeks after predator release. Overhead watering significantly reduced TSM and PM populations as much as 68- and 1538-fold, respectively, compared to drip irrigation with microtubes. Perhaps more important, overhead watering with or without predators significantly reduced the number of leaves sustaining TSM feeding injury as much as 4-fold compared to drip irrigation. These results confirm the common observation that TSM infestations and injury may be reduced by irrigation systems that wet plant foliage. However, predators still reduced TSMs even though overhead irrigation had a suppressive effect on predatory mites. Predators are particularly useful for reducing TSM injury when plants are watered infrequently. Overhead watering could be used in tandem with biological control as a component of an integrated crop management program for TSMs in ornamental greenhouses by rapidly lowering TSM population levels in hot spots before PMs are released.
D.S. Achor, H. Browning, and L.G. Albrigo
Young expanding leaves of `Ambersweet' [Citrus reticulata Blanco × C. paradisi Macf. × C. reticulata) × C. sinensis (L) Osb.] with feeding injury by third larval stage of citrus leafminer (Phyllocnistis citrella) were examined by light and electron microscopy for extent of injury and tissue recovery over time. Results confirmed that injury is confined to the epidermal layer, leaving a thin covering over the mine tunnel that consisted of the cuticle and outer cell wall. Wound recovery consisted of two possible responses: the production of callus tissue or the formation of wound periderm. The production of callus tissue developed within 3 days of injury when the uninjured palisade or spongy parenchyma below the injured epidermis produced callus tissue through periclinal or diagonal cell divisions. After 1 month, the entire epidermis was replaced by callus tissue. In the absence of secondary microbial invasion, this callus tissue developed a thick cuticle, followed by development of a covering of platelet wax after 4 months. Alternatively, wound periderm formed if the outer cuticular covering was torn before the cuticle had developed sufficiently to prevent the exposed cells from being desiccated or invaded by fungi, bacteria, or other insects. The wound periderm consisted of a lignified layer of collapsed callus cells, a suberized phellem layer, and a multilayered phelloderm-phellogen. Since there were always cellular collapse or fungi and bacteria associated with wound periderm formation, it was determined to be a secondary effect, not a direct effect of leafminer feeding.
Matthew R. Chappell*, Carol Robacker, Sherrod Baden, and Allen Byous
Azalea Lace Bug (ALB) is a significant pest on azalea species. ALB feeding injury causes a stippled appearance on the leaves of susceptible genotypes from late spring until leaf drop. To determine whether leaf surface lipids are a factor in determining resistance or susceptibility to ALB, epicuticular leaf wax was extracted from the leaves of eight azalea genotypes, half with resistance and half susceptible to ALB. Leaf wax from each genotype was extracted and re-suspended in an 2 ethanol: 1 water solution for application to all entries in a full diallel manner, including a control of solution only. Each treatment included three replications. The leaf wax solution was applied to each replication (single leaf) by painting the solution on one side of the midrib, on both abaxial and adaxial surfaces. By applying solution to one side of the leaf, the untreated leaf surface served as a control. Each leaf and two female ALB were placed in separate 50-mL sealed tubes at 24 °C and 12-hour daylength for 48 hours, at which time the number of live adults, frass spots, and eggs were counted. Frass and egg data were recorded separately for treated and untreated sides of each leaf. The application of leaf wax solution had an impact on the level of frass and egg deposition by ALB in all genotypes. The effect was most pronounced when solution of resistant genotypes was placed on susceptible genotypes, resulting in lower numbers of frass spots and eggs. The solution alone had little effect on frass or egg numbers. This research acknowledges that a major constituent of an azalea's resistance or susceptibility to ALB is via epicuticular wax components.
Eric Hanson, Steven Berkheimer, Annemiek Schilder, Rufus Isaacs, and Sasha Kravchenko
Seven primocane-fruiting and 15 floricane-fruiting raspberry varieties (Rubus idaeus) were compared for three fruiting seasons on a loamy sand soil in southwest Michigan. The earliest primocane-fruiting varieties (`Autumn Bliss', `Autumn Britten', `Polana') began ripening 3 weeks before the standard variety, `Heritage'. `Autumn Bliss' was the most productive early primocane-fruiting variety. `Caroline' and `Dinkum' ripened about 1 week earlier than `Heritage', and `Ruby' was 2 days later. `Caroline' was the most productive of this group and also had large fruit that were somewhat resistant to rot caused by Botrytis cinerea. `Caroline' also received the greatest leaf feeding from rosechafer beetles (Macrodactylus subspinosus). Most primocane-fruiting varieties were fairly resistant to leaf spot (Sphaerulina rubi), while `Dinkum' was highly susceptible to spur blight (Didymella applanata). Floricane-fruiting varieties were evaluated based on fruit production and quality as well as winter injury to canes, disease resistance, and feeding injury from two-spotted spider mites (Tetranychus urticae). The floricane-fruiting varieties showing minimal winter injury were `Boyne', `Killarney', `Latham', `Nova', and `Prelude'. `Canby', `Encore', `Glen Ample,', `Qualicum', `Reveille', `Titan', and `K 81-6' were moderately hardy; while `Tulameen', `Malahat', and `Lauren' were not hardy enough for this location. `Reveille', `Killarney', `Boyne', and `Prelude' were the most productive floricane-fruiting varieties. `Nova' and `Qualicum' had low levels of botrytis rot. `Nova' was most resistant to leaf spot and also had resistance to spur blight. Injury from mites was greatest on `Glen Ample' and lowest on `Malahat', `Prelude', `Qualicum', and `Tulameen'. `Caroline' (primocane-fruiting), `Prelude', and `Nova' (floricane-fruiting) were promising newer varieties.
Matthew Chappell, Carol Robacker, Sherrod Baden, and Allen Byous
Azalea lace bug (ALB) is a significant pest on azalea, with feeding injury causing speckling and discoloration on affected leaves. Feeding damage also results in a reduction of stomatal gas exchange and leaf chlorophyll content, postulated to diminish growth and flowering rates.
In azalea, specific lipid components of the plant cuticle have been implicated in ALB resistance of R. canescens. In this study, epicuticular leaf wax was extracted from the leaves of four azalea genotypes, divided into two groups: a resistant group including R. periclymenoides and `Fourth of July' and a susceptible group including R. austrinum and `My Mary'. Leaf wax was extracted and resuspended in solution for application to all entries in a full diallel manner, including controls of solution only and no treatment. Each genotype–solution treatment included 10 replications. The leaf wax solution was applied to each replication (leaf) by painting the solution on one side of the midrib, yet on both abaxial and adaxial surfaces. Two leaves attached to a stem and four female adult ALB were placed in separate 32-mL sealed cups. Experimental conditions were 24 °C and 12-hour daylength for 96 h, at which time the number of live adults, frass spots, and eggs were counted. Data revealed that application of leaf wax solution had an impact on the level of frass and egg deposition by ALB in both resistant and susceptible genotypes. The effect was most pronounced when a solution of resistant genotypes was placed on susceptible genotypes, as the application resulted in lower numbers of frass spots and eggs compared to the nil control. However, an increase in frass and eggs was observed when extract of susceptible genotypes was applied to resistant genotypes.