Bud Mite Research Articles

Forecasting emergence and movement of overwintering hazelnut big bud mites from big buds

Eriophyoid big bud mites are key pests of hazelnut throughout the world, but they are difficult to control with chemicals or other methods because they are protected inside the bud. The most effective time for control is during the relatively short emergence period which is difficult for growers to predict. The key objectives of this study were to monitor mite emergence from big buds in spring, determine the phenology of mites in relation to tree phenology and weather, and identify the optimum timing for control measures. Mite emergence was found to occur between early and late spring in Canterbury, New Zealand. Mite emergence and movement occurred when daily maximum temperatures were >15 degrees C and when mean temperatures were >9 degrees C, with mite emergence increasing with temperature. The developmental status of new buds during mite emergence was a crucial factor in the infestation of new buds. An accumulated heat sum model (DD), starting at Julian date 152 and using a lower threshold temperature of 6 degrees C, predicted the onset of emergence on two cultivars and at two sites at approximately 172 DD. A regression model based on leaf number, bud length, bud width, DD and Julian date provided a more satisfactory prediction of percent accumulated mite emergence. It is recommended both peak mite emergence and the developmental status of hazelnut buds be used to optimise the time to apply control measures. The optimum time to apply a control was predicted to be before buds measure 0.5 x 0.5 mm (width x length), are enclosed within the axil, and have a rounded tip, or, when 50% accumulated mite emergence has occurred, whichever occurs first.

Relationship between rust mites Calepitrimerus vitis (Nalepa), bud mites Colomerus vitis (Pagenstecher) (Acari: Eriophyidae) and short shootsyndrome in Oregon vineyards

Short Shoot Syndrome (SSS) causes severe crop losses in Oregon vineyards due to bunch necrosis during the early part of the season. Other symptoms include malformed leaves, unusually short and angled shoots, scar tissue and bronzed leaves close to harvest time. This work shows that SSS found in Oregon vineyards is closely associated with grape leaf rust mite, Calepitrimerus vitis (Nalepa) infestations. Very few bud mites, Colomerus vitis (Pagenstecher), were found in the vineyards during the current year and no relationship could be found between SSS symptoms and this species. During winter, rust mites are dormant and no evidence of direct bud damage from rust mites was found inside undeveloped buds. Tissue damage from mites was first observed between bud break and the two-leaf stage in mite infested vineyards. Rust mite colonies were found under outer bud scales and bark of canes close to the buds. Crop losses as high as 23.7% were directly linked to rust mite infestations and SSS from several vineyards sampled in Oregon.

SUSCEPTIBILITY OF SOME MANGO VARIETIES TO THE BUD MITE ERIOPHYES MANGIFERAE (SAYED) AND MAL-FORMATION DISEASE AND THE RELATION OF MITE INFESTATION TO MALFORMATION DISEASE

In field study, Eleven mango varieties, (Mangiferae indica L.) at Sharkia, Ismailia, and Fayoum Governorates, were examined to estimate the population fluctuation of the bud mite Eriophyes mangiferae Sayed, their susceptibility to mite infestation, the relation between the mite infestation and chemical contents of mango buds and the correlation between the bud mite and malformation disease. The highest population occurred during Sept. to Jan. or Feb. and the lowest population was existed during Mar. to Jun. Temperature and relative humidity had no significant effect on the mite population. The highest level of mite infestation was recorded at Sharkia followed by Fayoum and Ismailia Governorates. Mango varieties were differed in their susceptibility to E. mangiferae infestation. Zebda, Taimour, Ewais and Arnaba were the most susceptible varieties, while Mabrouka, Company, Excellent Succari and White Succari were the least susceptible ones. On the other hand Mesk, Geolck and Alphonse varieties showed moderate susceptibility to mite infestation. Buds of some high susceptible varieties possessed a lower values of total carbohydrates and total soluble sugars than some moderate or susceptible varieties to mite infestation. Phenol contents recorded a higher levels in the most of susceptible varieties while a lower levels were found in the most of moderate and low susceptible varieties. The total soluble proteins and amino acids recorded a higher values in some susceptible varieties. The susceptible characteristic was positively correlated with total soluble proteins and amino acids while negatively correlated with the total carbohydrates and total soluble sugars. However the phenol content showed no clear trend. Obtained results also revealed that mango varieties had varying degrees of floral malformation, Company, Alphonse and Geolck were the most susceptible varieties, while Zebda var. was the most resistant one. Statistical analysis showed a negative correlation between the eriophid bud mite and the incidence of malformation disease. Zebda var. harboured the highest number of mites but exhibited the lowest percentages of malformation, whereas the opposite trend was observed with company var

Life History of Kampimodromus aberrans as a predator of Phytoptus avellanae (Acari: Phytoseiidae, Phytoptidae)

The biology of Kampimodromus aberrans (Oudemans), a predator of the big bud mite, Phytoptus avellanae Nalepa, was studied under laboratory conditions. All experiments were conducted on hazelnut leaf discs in an incubator at 25 +/- 1 degrees C, with 16:8 h L:D, at an average daily relative air humidity of 76%. Observations were made twice daily for the immature stages and daily for the adults to determine developmental time, survival and fecundity. The mean developmental time for females was 6.90 days and for males was 7.10 days, and mean adult longevity for females was 11.67 days. The mean total and daily egg production were 12.67 and 1.85 eggs, respectively. The net reproduction rate (R0) was 7.09 females/female, intrinsic rate of increase (rm) was 0.153 female/female/day and mean generation time (T0) was 12.80 days. The mortality rate of immature stages was 0.66% and the sex ratio was 0.51 female.

Eriophyoid mite damage in Vitis vinifera (grapevine) in Australia: Calepitrimerus vitis and Colomerus vitis (Acari: Eriophyidae) as the common cause of the widespread ‘Restricted Spring Growth’ syndrome

Leaf and shoot distortions and retarded shoot growth in Vitis vinifera L. prevalent in Australian vineyards in early spring, were investigated in replicated field experiments over 3 yrs. Leaf distortion and retarded shoot growth were identified as damage due to feeding of extremely high populations of over-wintered deutogynes of Calepitrimerus vitis (Nalepa) (grape rust mite). This damage was hitherto known in Australia as 'Restricted Spring Growth' (RSG), a syndrome comprising several growth abnormality symptoms, none with a clearly identified cause or a successful treatment. A successful treatment against C. vitis was used to selectively eliminate RSG, while C. vitis numbers were recorded using a validated trapping technique; intercepting deutogynes migrating from winter shelters in the wooden vine structure, to emerging green tissues. Severe leaf distortion was associated with > 400 C. vitis deutogynes per spur, while > 1000 per spur had the added effect of severely retarding shoot growth. A 43.0-47.2% shoot length reduction was recorded for Cabernet Sauvignon, 27.1-32.8% for Sauvignon Blanc, when 4-6 leaves were separated. Symptoms were most prominent up to 8-9 separated leaves, however 24.7-30.4% shoot length reduction was still evident at flowering, and 12.8% circa fruit set. C. vitis effect on vine fruitfulness, and yield parameters at fruit set, were also studied. Once successfully treated to prevent C. vitis damage, poor bud burst remained evident in some vineyards. Surveys of unburst buds from such vineyards revealed presence of Colomerus vitis (Pagenstecher) (grape bud mite). When Col. vitis numbers in unburst buds reached 100-500 per bud, apical meristems of primary, and commonly also secondary buds were dead, preventing bud burst. The remaining living scale tissue was distinctly scarred. Bud and associated shoot damage were documented. Retarded shoot growth and leaf distortion, previously attributed to RSG, are misdiagnosed C. vitis spring feeding damage. Clustered high infestations of Col. vitis can cause bud-axis necrosis, bud burst failure, shoots with short basal internodes, and short, thin, zigzagged shoots with absent fruit clusters; all previously considered RSG.

Biology and phenology ofCecidophyopsis psilaspis(Acari: Eriophyidae) on Pacific yew (Taxaceae)

AbstractThe biology and phenology of the yew big bud mite,Cecidophyopsis psilaspis(Nalepa, 1893), were studied on Pacific yew,Taxus brevifoliaNutt., in British Columbia, Canada. The mite showed the typical life cycle of eriophyoids on evergreen hosts, with all stases being present throughout the year. The numbers ofC. psilaspis, which colonized both vegetative and reproductive buds, peaked in May to August, with the lowest numbers in March and October and the highest numbers in June. Mite numbers differed among bud types, with averages following the sequence terminal buds = lateral buds > male reproductive buds > axillary buds > female reproductive buds > latent buds. Very few mites were found in latent buds except during bud formation, when other vegetative buds were unavailable. Reproductive buds were colonized mostly from May to July. There was no evidence of arrhenotoky inC. psilaspis, as the proportion of mites that were females ranged from 54% to 100%. Temperature and predation were considered the likely factors that determine population fluctuations. It was hypothesized thatC. psilaspisabundance increased following favorable spring temperatures and new food resources, whereas predation by other mite species and lower temperatures, which prolonged development, were responsible for the low numbers in March and October.

Hazelnut Pollenizers `Gamma', `Delta', `Epsilon', and `Zeta'

‘Gamma’ has incompatibility alleles S 2 and S 10 , but only S 10 is expressed in the pollen because of dominance (Mehlenbacher, 1997a). The trees set many catkins, and pollen is shed in midseason, at about the same time as ‘Daviana’. The pollen-shedding period is short, and thus ‘Gamma’ should not be the sole pollenizer in an orchard. It is a suitable pollenizer for ‘Lewis’ (S 3 S 8 ) and ‘Barcelona’ (S 1 S 2 ), but sheds pollen too early for ‘Clark’ (S 3 S 8 ) and ‘Ennis’ (S 1 S 11 ). It is incompatible on its parent ‘Casina’ (S 10 S 21 ). Nuts and kernels resemble those of ‘Casina’ but are slightly larger (Table 1). Nut maturity is a few days before ‘Barcelona’, and about 80% of the nuts fall free of the husk at maturity. The frequency of moldy kernels is very low. The original seedling tree was vigorous and moderately productive. Bud mite ratings are intermediate. ‘Delta’ has incompatibility alleles S 1 and S 15 ; both are expressed in the pollen. The trees set many catkins, and shed copious amounts of pollen in late midseason with ‘Hall’s Giant’. It is a suitable pollenizer for ‘Lewis’ and for early-emerging females of ‘Clark’, but is incompatible on ‘Barcelona’, ‘Ennis’ (S 1 S 11 ), and ‘Willamette’ (S 1 S 3 ). The nuts are slightly larger than those of ‘Casina’ (Table 1) and mature a few days later than ‘Barcelona’. About 85% of the nuts fall free of the husk at maturity, while a few remain attached to the husk at the edge of the basal scar. The original seedling tree was ‘Gamma’, ‘Delta’, ‘Epsilon’ and ‘Zeta’ are four new hazelnut (Corylus avellana L.) pollenizer cultivars. They were released by the Oregon Agricultural Experiment Station in February 2002. They shed pollen at different times during the fl owering season, spanning the time that female infl orescences of most cultivars are receptive. They have complete resistance to eastern fi lbert blight caused by Anisogramma anomala (Peck) E. Muller. ‘Gamma’ and ‘Delta’ carry resistance from ‘Gasaway’, while ‘Epsilon’ and ‘Zeta’ carry resistance from ‘Zimmerman’. The traditional pollenizers ‘Daviana’ and ‘Butler’, and four selections (VR4-31, VR11-27, VR20-11, and VR23-18) previously released as pollenizers for ‘Barcelona’, express incompatibility allele S 3 in their pollen (Mehlenbacher and Thompson, 1991). Although compatible on ‘Barcelona’ females (S 1 S 2 ), their pollen is incompatible on females of recently released ‘Lewis’ and ‘Clark’ (both S 3 S 8 ) (Mehlenbacher et al., 2000, 2001). ‘Gamma’, ‘Delta’, ‘Epsilon’, and ‘Zeta’ provide growers with additional pollenizer options for recently released and standard cultivars.

Species status and population genetic structure of grapevine eriophyoid mites

AbstractBud mite, blister mite (Colomerus vitis Pagenstecher), and rust mite (Calepitrimerus vitis Nalepa) (Acari: Eriophyoidae) are recognized grapevine pests. Much of the biology and ecology of these pests is poorly understood. We used two types of molecular markers to gain further insight into the breeding biology and population structure of these mites, using individuals collected from sites around south‐eastern Australia. Patterns of genetic variation observed using PCR‐RFLP of ITS 1 (Internal Transcribed Spacer 1) confirmed the separate species status of the rust mite, and resolved the species status of bud and blister mites, revealing two closely related but distinct species. Microsatellite markers revealed extensive genetic differentiation between bud mite populations and blister mite populations even at micro‐geographical levels, suggesting low movement in these species. The findings indicate that separate control strategies are needed against bud and blister mites, and that localized control strategies are likely to be effective given their limited dispersal.

Potential Acaricides for Management of Blueberry Bud Mite in Michigan Blueberries

The goal of this study was to evaluate potential alternatives to endosulfan for control of the blueberry bud mite (Acalitus vaccinii), because the availability of this acaricide may be restricted in the future. Laboratory evaluations of potential acaricides showed that endosulfan and a combination of abamectin plus oil provided 97% and 100% control, respectively. Pyridaben and fenpropathrin were less effective, reducing mite survival by 49% and 57%, respectively. Further laboratory evaluation of the abamectin plus oil treatment showed that each component applied alone provided a high level of control of blueberry bud mite. Field trials in Michigan on a mature highbush blueberry (Vaccinium corymbosum) planting were conducted to compare control of this pest by postharvest applications of endosulfan, delayed-dormant application of oil, or a combination of both treatments. The oil provided a 40% reduction in mite scores, while endosulfan was more effective (48%) and similar to the combination of endosulfan and oil (52%). A separate field trial using a multifan/nozzle sprayer that applied the pesticide in 233.8 L·ha-1 (25 gal/acre) of water suggested that the level of control from one application of endosulfan was not as effective as two applications. Results are discussed in relation to developing future bud mite control programs in blueberry and the need to address gaps in our understanding of the biology of blueberry bud mite. Endosulfan (Thiodan 50 WP), Endosulfan (Thiodan 3 EC), Abamectin (AgriMek 0.15 EC), Fenpropathrin (Danitol 2.4 EC), Pyridaben (Pyramite 60 WP).

Ecology and Control of Eriophyid Mites Injurious to Fruit Trees in Japan

Studies on the damage, biology, natural enemies and management of the economically important eriophyid mites: persimmon bud mite, Aceria diospyri, ficus mottle mite, Aceria ficus, peach silver mite, Aculus fockeui, and pink citrus mite, Aculops pelekassi in Japan are reviewed. A. diospyri and A. pelekassi mainly cause damage to the fruits of host plants. The rust symptom on persimmon fruits by A. diospyri differs among varieties. A. ficus causes economic loss in fig with leaf mosaic, leaf malformation, fruit mosaic, and fruit drop. A. fockeui injures peach leaves, reduces the sugar content of the fruit, and the damaged trees have lower vigor due to post-harvest defoliation. These mites overwinter in buds of host plants as adults. Overwintered mites begin to reproduce on the leaves after late May or mid-April. Fruit infesting mites, A. diospyri and A. pelekassi, migrate to and infest fruits after June. Since the density of overwintered A. ficus is high in large dormant fig buds, cutting of the big buds is effective to reduce mite damage in the next season. Several acaricides, insecticides and fungicides are effective against the eriophyid mites. A. pelekassi populations with dithiocarbamate-fungicide resistance were confirmed in the early 1990's and outbreaks of the mite sometimes cause severe damage to citrus fruits. It was found that some phytoseiids, a tydeid and a stigmaeid feed on these eriophyids. Phytoseiidae mites play an important role in the control of A. diospyri, A. ficus and A. fockeui populations in low densities. A marked resurgence in A. fockeui populations occurs after synthetic pyrethroids are sprayed, because they have no effect on A. fockeui but are harmful to the predators, such as phytoseiid mites.

'Rosita' Ornamental Hazelnut

Received for publication 26 Dec. 2001. Accepted for publication 18 Mar. 2002. Oregon Agricultural Experiment Station Technical Paper no. 11849. E-mail: mehlenbs@bcc.orst.edu ‘Rosita’ is a new red-leafed hazelnut (Corylus L. hybrid) cultivar for the ornamental market. It was released by the Oregon Agricultural Experiment Station in Apr. 1999. Compared to other red-leafed ornamental hazelnut cultivars, ‘Rosita’ has a more desirable upright but compact growth habit and darker leaf color, and the leaf edges have a ruffled appearance. ‘Rosita’ produces few catkins and nuts. It has moderate resistance to eastern filbert blight (EFB) caused by Anisogramma anomala (Peck) E. Muller and big bud mites (primarily Phytoptus avellanae Nal.). ‘Rosita’ is the first ornamental cultivar to be released by the Oregon State Univ. (OSU) hazelnut breeding program.

Challenges facing Chamaecyparis nootkatensis seed orchards: low seed production, pollen-cone abortion, self-pollination, and accelerated embryo development

Seed orchard production of Chamaecyparis nootkatensis (D. Don) Spach seed faces several challenges including low seed production, pollen-cone abortion, self-pollination, and accelerated reproductive development. In a seed orchard study in 1988 and 1989, approximately eight seeds were produced per cone, but only one to three seeds per cone contained viable embryos. Pollen-cone abortion in 21 clones ranged from 6 to 87% in 1989–1990 and from 0 to 6% in 1990–1991. A bud mite, identified as Trisetacus chamaecypari Smith, was consistently associated with pollen-cone abortion in two orchard locations. This mite may be the cause or simply a symptom of unhealthy pollen cones. In a pollination study involving wind, self, and cross pollinations on five clones, self-pollinated cones had significantly fewer seeds containing embryos (4%) compared with the other treatments (28–33%). Pollen-cone development at a seed orchard occurred in July and August 1990 and was comparable with natural stand phenology. However, embryo development was significantly accelerated, with embryos at a seed orchard substantially larger than embryos at the natural stand at comparable times.

Some biological and morphological differences between gall and vagrant forms of Phytoptus avellanae Nal. (Acari: Phytoptidae)

The big bud mite (Phytoptus avellanae Nal.), one of the most important pests of hazelnut (Corylus spp., Corylaceae), has two forms - a gall form and a vagrant form. The gall form lives inside big buds. It has a simple life cycle and a single nymphal type. The vagrant form lives on vegetative and generative organs and inside the big buds. It has a different and rather complex life cycle and two nymphal types. In this study the gall and vagrant forms of P. avellanae were examined biologically and morphologically. Biological studies were performed at 20 ± 1°C and 70% R.H. in the laboratory and mites were reared on leaf discs and the duration of the different stages was determined. The gall form did not survive on the leaf disc after the first instar nymphal stage, whereas the vagrant form survived on the leaf disc. The latter had two nymphal types, one with the normal two nymphal stages, but the other with three nymphal stages. This condition is unknown in any other eriophyoid. Morphological comparisons showed that the gall and vagrant forms were significantly different from each other in size, shape and color.

Observations on intraplant distribution and life history of eriophyoid mites (Acari: Eriophyidae, Phytoptidae) inhabiting evergreen cypress,Cupressus sempervirens L.

Two species of eriophyoids, bud mite Trisetacus juniperinus (Nalepa) and vagrant mite Epitrimerus cupressi (Keifer) (new record), were commonly found on evergreen cypress (Cupressus sem-pervirens L.) in Italy. The distribution and biology of these mites were studied in a seed orchard on two groups of half-sib plants with common mother. Both groups and crown height affected the severity of T. juniperinus infestations. The mite prefered the apical bud of the plant where it developed throughout the year. On the contrary, only time of year significantly affected E. cupressi infestations, which seemed evenly distributed on plants with the lowest population in winter, when only females, with same features of the spring-summer females, were found. The two species showed a weak negative association. Infestations of T. juniperinus under artificial conditions, as in young plantations and nurseries, can become particularly destructive to the plants while E. cupressi seems harmless.

Environmental management and biological aspects of the two eriophyoid fig mites Aceria ficus (Cotte) and Rhyncaphytoptus ficifoliae Keifer in Egypt

Abstract: Mites associated with abandoned fig trees in Egypt were observed during a 2‐year study. This study included species diversity and seasonal fluctuations as well as some biological aspects of common eriophyoid species. Three phytophagous species consisted of the fig bud mite Aceria ficus (Cotte), the fig leaf mite Rhyncaphytoptus ficifoliae Keifer and the two‐spotted spider mite Tetranychus urticae Koch, representing a basic trophic level, were fed upon by three of predacious mites (Pronematus ubiquitus (McGregor), Amblyselus swirskii Athias‐Henriot, Agistemus exsertus Gonzalez). Population abundance of the injurious mites were affected by the prevailing climatic conditions, action of predators and leaf age. A control measure of one summer pesticide (abamectin) application throughout the year seemed to be the most successful management of harmful mites. Life table parameters showed that the population of A. ficus multiplied 28.52 times in a generation time of 17.90 days, while R. ficifoliae population increased 16.50 times in a generation time of 14.61 days. Field and laboratory studies indicated that the viviparity is a typical character in the reproduction of R. ficifoliae.

Citrus Bud Mite (Acari: Eriophyidae): an Economic Pest of California Lemons?

The citrus bud mite, Aceria sheldoni (Ewing), has a reputation as being a serious pest of lemons in California, although recent studies failed to reveal a consistent economic impact. To resolve some previous inconsistencies, we evaluated the economic value of treatments to suppress citrus bud mite populations on a commercial scale over 3 yr. Experiments were conducted in 6 groves and included 2 treatments of 100 trees each. In 1 treatment (treated), trees were managed according to conventional commercial practices and included 1-2 annual applications of narrow-range oil to suppress citrus bud mite populations. In the other treatment (untreated), experimental trees were managed identically as treated trees, except that oil spray applications for citrus but mite were withheld. Bud mite density and incidence on experimental trees were monitored monthly, as were the number of fruit and the proportion of distorted fruit. Fruit from all 100 trees in each treatment per grove were commercially harvested, graded and packed. Crop volume, grade, size distribution, and value were compared across treatments. Although oil sprays effectively suppressed citrus bud mite populations, this yielded no consistent benefit to crop volume, grade, or value. For all groves the value of fruit from treated trees was not significantly greater than that from untreated trees, even, before the cost of oil sprays was subtracted. In 4 of 6 cases, crop value was numerically lower in the treated treatment. Results suggest that the oil sprays themselves may have had deleterious effects on fruit initiation and abortion. The potential phytotoxicity of oil sprays, although long known, may not be fully considered in contemporary treatment decisions for the citrus bud mite.

SUSCEPTIBILITY OF CERTAIN MANGO VARIETIES TO THE BUD MITE- ACERIA MANGIFERAE (SAYED) (ERIOPHYIDAE: ACARI) AND ITS CONTROL

Ten mango cultivars were evalauated for their susceptibility to the bud mite, Aceria mangiferae (Sayed) during March May, 1997. The varieties viz., Rumani, Sappattai, Peter and Neelum had more number (74 mites per leaf) of mites than Malgoa (2.0), Baneshan (8.7) and Bangalora. Dicofol at 0.03% recorded a minimum of 10.1 mites/bud, resulting in 64.3 per cent reduction over control followed by monocrotophos at 0.07% (57.5%) and neem seed kernal extract at 10% (53.7%) whereas, neem oil at 3.0% was least effective (32%).

MORPHOLOGY, ONTOGENY, AND INTRASPECIFIC VARIABILITY OF THE YEW BIG BUD MITE,CECIDOPHYOPSIS PSILASPIS(ACARI: ERIOPHYIDAE)

AbstractAll ontogenetic stases of the yew big bud mite,Cecidophyopsis psilaspis(Nalepa), from British Columbia were studied by scanning electron and light microscopy and were compared with an English population of this species. The species was redescribed from the two populations, which were found to be quite similar in general appearance and in most of the morphometric data analyzed. Spermatophores in this species are similar to those observed in other Eriophyoidea. Details of a male spermatophoric organ are described and illustrated for the first time in an eriophyoid mite. Moulting inC.psilaspisis shown to be prodehiscent. The data reported here neither support nor reject the alternative hypothesis that the first active stase is larval versus nymphal. However, to account for the ontogenetic evidence, the first active stase is herein considered larval.

Rearing Eriophyes insidiosus Keifer and Wilson (Acari: Eriophyoidea), a fastidious bud mite

Eriophyes insidiosus Keifer and Wilson is a fastidious bud mite which reproduces only inside buds of its host. These buds provide microenvironmental and physical conditions that are difficult to reproduce artificially. In this study, rearing of E. insidiosus was attempted on peach (Prunus persica Batsch, Rosaceae) cuttings generated by tissue culture, by rooting infested peach cuttings, and on peach trees that were infested naturally or manually. Manual infestation of buds, soon after dormancy ended, was the most successful technique, providing large numbers of mites. Availability of this methodology will contribute to the progress of studies on the relationships between bud-mite vectors and the viruses they transmit.

Increase in Flower and Young Fruit Abscission Caused by Citrus Bud Mite (Acari: Eriophyidae) Feeding in the Axillary Buds of Lemon

During the course of a 3-yr field study on lemons, 8,467 unopened flowers were tagged, rated for severity of floral distortions caused by citrus bud mite, Aceria sheldoni (Ewing), and monitored weekly to determine if they developed a fruit or abscised without developing a fruit. Each fruit developing from these flowers was rated for severity of distortions caused by citrus bud mite and monitored weekly to determine if the fruit persisted beyond the June-drop period or abscised before or during the June-drop period. Abscission rates of both flowers and fruit increased significantly with increasing bud mite-caused distortion. Distortion rating of fruit was correlated significantly with the distortion rating of the flowers from which they developed. The possibility that the increased rates of abscission of flowers and young fruit may be caused by previously observed decreases in auxin activity and other biochemical changes in bud mite-infested axillary buds is discussed.