Oviposition behaviour and distribution of egg masses of the European leaf roller,Archips rosanus (L.), on citrus trees

The citrus leaf roller (CLR), Archips rosanus, a threatening pest of leaves and fruitlets on fruit trees, which in recent years has led to considerable damage to different citrus trees in some parts of the Mazandaran province of Iran. Insect activity on citrus trees causes the growth of buds and leaves to stop and foliage to dry. Pest oviposition as egg masses occurs on the host tree’s trunk. Eggs spent a year in the hibernation stage and, in the following spring, hatched the first instar larvae that fed on the opened buds. The distributions of CLR egg masses, deposited in 2015–2016, were evaluated on the Thomson novel cultivar (Citrus sinensis L.) in the northern region of Iran. The results showed that the numbers of egg masses laid on the trees at different height ranges of 0–50, 50–100, 100–150 and 150–200 cm were, respectively, 38.65, 33.78, 18.54 and 9.03%. The mean number of A. rosanus eggs per mass, however, was not significant at different heights of the tree. Also, most of the egg masses were laid in the north and south directions in comparison with the west and east directions, with no significant difference in mean number in different geographical directions.     

Contribution to the biology of the citrus bud mite, Aceria sheldoni (Ewing) (Acarina: Eriophyidae)*

In laboratory studies mites of Aceria sheldoni were reared on citrus fruit peels, beneath coloured cellophane hoods, to cater for their thigmotaxis and sensitivity to light of particular wave lengths. Hatching was most successful at 25°C and 98% r.h. but was reduced by low humidities (35–40% r.h.), when abnormal dwarf larvae emerged. The eggs hatched in 3–14 days; the length of a generation (egg to egg) was 12–33 days. The threshold of embryonic development was 9 °C and that for completion of the life cycle, egg to egg, was 12.5 °C. The average number of eggs laid per female was six (4–8). It increased to twelve (5–19) if the mite, during its larval stages, had been fed on buds. The vitality of both the eggs and the mature mites was tested by exposure to extreme low and high temperatures (below 0 °C, 39 °C): 50% of mites died after 30 min at 30 °C; 50% died after 30 min at –15 °C or lower.     

The life-history of the eriophyid mite Aculus schlechtendali on apple in South-east England

During 1975–77 the life-history of Aculus schlechtendali was studied in apple orchards. The morphology of the mite and its development at a range of temperatures were studied in the laboratory.
Deutogynes of A. schlechtendali hibernated mainly in small permanently dormant buds and under loose bark on spurs and around buds on 1-yr shoots, and moved into fruit buds between the bud burst and pink but stages and into vegetative buds as the buds began to swell. Populations on leaves reached a peak in August and mite feeding at high density caused browning of the under surfaces. The return to hibernation sites began in July.
The developmental stages of the mite are described. A generation took c . 39, 16 and 10 days at 10, 16 and 22 C, respectively. Protogynes laid totals of 67–102 eggs at a rate of 1.7, 2.4 and 2.8 eggs/day at 10, 16 and 22 C: deutogynes laid 21–47 eggs after hibernation at a rate of 1.3 and 1.6 eggs/day at 10 and 16 C. The species was found only on cultivars and species in the genera Malus and Pyrus .     

Control of tomato grey mould on unheated crops using non- systemic fungicide sprays

High volume sprays of dichlofluanid (0.1 % a.i.) reduced total fruit numbers but gave better control of Botrytis cinerea infections of tomato stems, leaves and fruit than sprays at 0.05 or 0.025% a.i. Surface residues from the sprays at 0–1, 0.05 or 0.025% a.i. were respectively 5.4, 1.6, 0.7 μg/g fresh weight of ripe fruit at harvest. Tank-mixed zineb (0.12% a.i.) and captan (0.2% a.i.) were less effective and increasing the spray intervals from 1 wk to 2 and 3 wk reduced the fungitoxicity of captan and zineb more than that of dichlofluanid. Harvest residues on ripe fruit were 7.1, 2.8 or 2.4 μg/g when dichlofluanid (0.1 % a.i.) sprays were applied at 1, 2 and 3 wk intervals respectively. Good control of B. cinerea was achieved if the whole plant was sprayed initially with dichlofluanid as soon as the second truss was flowering and subsequent sprays were restricted to the upper section of stem including the four or five youngest trusses of buds, flowers and fruit. When used as a post-infection spray there was a period of c. 8 wk before dichlofluanid markedly reduced the incidence of grey mould. Tank-mixed zineb (0.12% a.i.) controlled Botrytis fruit spotting but not leaf and stem infections. Botrytis stem lesions extended more rapidly on zineb-sprayed plants than on unsprayed plants or on plants treated with captan or dichlofluanid.     

Behavioural response and winter survival of mated and unmated diapausing females of the Tetranychus atlanticus-urticae complex (Acari, Tetranychidae)

Behavioural responses were studied in mated and unmated females of a Dutch strain of the spider mite Tetranychus urticae which were destined to enter diapause. Observations were confined to the period between acquirement of the winter coloration by the females (a few days after the last moult) and their entering of artificial hibernation sites offered to the mites on the host leaves. Unmated females were found to stay longer on the leaf surface than mated females; they entered the hibernation sites significantly later than mated females. The delay in the search for hibernation sites shown by unmated females may be seen as a behavioural adaptation to enhance the chance of being fertilized before hibernation. Winter survival of mated and unmated diapausing females of the same strain of mites was studied both in the laboratory at a constant temperature of 2±1°C and outdoors under natural climatic conditions in Amsterdam during the winter of 1990–1991. Survival was high under both conditions for mated as well as unmated females; no significant differences in survival were found between both types of female. Observations on post-diapause females of Tetranychus atlanticus (a mite belonging to the T. urticae complex) sampled from strawberry fields near Moscow in spring, showed that at most 10% of the females of this natural spider mite population were unmated. Both mated and unmated females had survived winter temperatures of -28 to -30°C.     

Increased susceptibility of black-currant bushes to the gall-mite vector (Phytoptusribis Nal.) following infection with reversion virus

Healthy black-currant bushes (var. Wellington XXX) and others infected systemically with a virulent strain of reversion virus were exposed equally to infestation by the gall-mite vector (Phytoptus ribis Nal.). Shoots with malformed leaves caused by mites feeding at the stem apices were virtually restricted to the virus-infected bushes. Buds infested with mites became rounded galls, which were far fewer and more localized on shoots of healthy bushes than on infected ones. Similar results were obtained in further experiments with Wellington XXX and seven other varieties. Bushes infected systemically with an avirulent strain of reversion virus developed more galls than healthy bushes, but fewer galls than bushes infected with a virulent strain. The young buds of virus-infected bushes were 170 times more susceptible to dispersing mites than those of healthy bushes. The axillary buds of healthy bushes resisted infestation and the apical meristems were virtually inaccessible to mites, whereas the axillary and apical buds of virus-infected bushes were invaded readily. An experiment with bushes var. Cotswold Cross that were either healthy or partially or completely infected with reversion virus was retained for two years. Each year there was a relationship between symptom expression and mite infestation; only shoots with chronic virus symptoms developed mite-affected leaves and numerous galls. Virus infection increased the vulnerability and accessibility of the apical and axillary buds by decreasing the density of hairs on the stems and leaves. Infected bushes also presented a greater catchment area to dispersing mites and more shoots and buds were available for colonization than on healthy bushes. The interactions between virus, host and vector are discussed, together with their implications in nature, in experimental design and in disease control.     

The aetiology and development of damage in young fruit trees infested with fruit tree red spider mite, Panonychus ulmi (Koch)

Infestations of fruit tree red spider mite, Panonychus ulmi (Koch) altered the growth of young plants of plum and apple. At first, damage to the leaves from mite feeding did not affect their photosynthetic rates. The effects on other processes depended on the density of the infestation. Densities of 1–2 mites/cm² of leaf decreased the rate of shoot extension of Brompton plum, but about 0.5 mite/cm² increased it. Less dense infestations apparently caused no damage. The rate of growth of the leaf area of a plant relative to that of the mite population on it determined changes in the mite density, and therefore the effects of infestation. The growth of the root system was decreased before that of the shoots. Later, when some leaves were severely damaged photosynthesis was decreased. The onset and severity of this phase probably depended on the number of mites and days of feeding on individual leaves. The later-formed leaves were smaller, and sometimes fewer on infested plants. Some plants were infested with too low a density of mites to decrease shoot extension, but grew less in dry weight because of decreased photosynthesis later in the season. The initial effects are ascribed to an imbalance in the growth controlling substances caused by feeding. Radioactivity was detected in the growing regions of plants remote from mature leaves on which ¹⁴C-labelled mites were confined.     

Host Selection by the Herbivorous Mite Polyphagotarsonemus latus (Acari: Tarsonemidae)

This study examined the host-selection ability of the broad mite Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae). To make long-distance-shifts from one host plant patch to another, broad mites largely depend on phoretic association with whiteflies. However, the host plants of whiteflies and broad mites are not necessarily the same. We determined the host-preference and acceptance of free-moving and phoretic broad mites using two behavioral bioassays. We used a choice test to monitor host selection by free-moving mites. In the case of phoretic mites, we compared their rate of detachment from the phoretic vector Bemisia tabaci placed on leaves taken from various host plants. The suitability of the plant was further determined by monitoring mite’s fecundity and its offspring development. We compared the mites’ responses to young and old cucumber (Cucumis sativus cv. ‘Kfir’) leaves (3rd and 8–9th leaf from the apex, respectively), and two tomato (Solanum lycopersicum cvs. ‘M82’ and ‘Moneymaker’). Free-moving mites of all stages and both sexes preferred young cucumber leaves to old cucumber leaves and preferred young cucumber rather than young tomato leaves, demonstrating for the first time that broad mites are able to choose their host actively. As for phoretic mated females, although eventually most of the mites abandoned the phoretic vector, the rate of detachment from the whitefly vector was host dependent and correlated with the mites’ fitness on the particular host. In general, host preference of phoretic female mites resembled that of the free-moving female. Cues used by mites for host selection remain to be explored.     

Threshold‐based spraying decision programmes for the red spider mite Tetranychus marianae on eggplant

The red spider mite, Tetranychus marianae McGregor (Acari: Tetranychidae), has been an important pest of eggplant Solanum melongena L. (Solanaceae) and other vegetables in the Mariana Islands. The damage due to T. marianae has been severe and caused huge economic losses. Because no threshold levels are available for T. marianae, many growers are applying up to 12 chemical applications per eggplant cropping period. This is not only expensive, but also results in lower yields because of extensive foliar damage and development of resistance in mites to chemicals. To diminish the calendar‐based chemical applications and to preclude damage to foliage and fruit quality, this study was undertaken for the development of a threshold level for optimum timing of chemical applications for T. marianae. In the direction of this aim, an attempt was made to generate different threshold levels by applying chemical spray (Sun‐spray 6E, 5 ml/l) within 12 h after reaching the threshold levels at 2, 4, 6, 8 and 10 mites/leaf, as well as current recommended calendar‐based sprays and non‐sprayed control in a replicated block design for the dry and wet seasons of 2010 at two locations (Yigo and Inaranjan) in Guam (USA). Based on T. marianae‐infested leaves, incidence of T. marianae and yield levels, the plots sprayed at 2 or 4 mites/leaf in the dry season and 2–8 mites/leaf during the wet season had significantly lower leaf damage and incidence of T. marianae compared with a greater number of mites/leaf in calendar‐based sprays and control plots. At the greater threshold levels, the mean yield was significantly reduced in comparison with the mean yield obtained when plots were sprayed at a threshold of 2–8 mites/leaf. Therefore, it is concluded that the optimum threshold chemical spray for T. marianae on eggplant is 4 mites/leaf during the dry season and 8 mites/leaf in the wet season.     

The timing of sprays for the protection of terminal buds on apple shoots from powdery mildew

Post-blossom sprays of fungicides, repeated at 10-day intervals until leader (syn. extension) shoots had stopped producing new leaves, provided the best protection of terminal buds against Podosphaera leucotricha on the apple cv. Lane's Prince Albert. Spraying was most effective in early summer, although many of these buds were not invaded until later, when the rate of shoot growth declined; applications from July to September did not compensate for the enhanced infection which followed interruptions of the post-blossom programme between late May and early July. This early period was critical because most leaf infections occurred then, and because this phase of the epidemic on foliage determined the eventual intensity of mildew on terminal leaves, and hence the inoculum available for infecting terminal buds. Also, many lateral shoots ceased growth early and their apices were directly protected by sprays applied in June. Applications after early June were too late to protect newly formed fruit buds on spur branches.     

Heat tolerance of strawberry tarsonemid mite Phytonemus pallidus

The heat tolerance of the strawberry tarsonemid mite Phytonemus pallidus ssp. fragariae was studied in northern Sweden by treating adult mites in hot water at temperatures 44°C, 46°C and 48°C. During the summer, the shortest exposure times required to kill all adult mites at these temperatures were 6, 2.5 and 1.25 min, respectively. It is concluded that hot‐water treatment of strawberry runners for 6.5 min at 46°C would suffice to kill all tarsonemid mites on infested runners. This exposure time includes the time needed to raise the temperature of the plant material to that of the water bath. In the autumn, from the middle of September and later, the mites became successively much more heat tolerant as they prepared for hibernation. It is expected that longer exposure periods are needed to kill mites on frigoplants.     

Dispersal of Acalitus essigi to blackberry (Rubus fruticosus agg.) fruit

The eriophyoid mite, Acalitus essigi (Hassan), is hypothesised to be responsible for redberry disease of blackberry (Rubus fruticosus L. agg.) fruit. Infested fruit ripen unevenly with affected drupelets becoming hard, inedible and bright red, whereas unaffected drupelets ripen evenly. As a first step toward possible control of this disease, the method and timing of dispersal of A. essigi onto developing blackberry fruit was examined. No mites were found on unopened flower buds or open flowers. However, infestation of fruit was found to commence during the green stage of fruit development and significantly increase during the red fruit stage. Although redberry symptoms were not observed, experimental exclusion of A. essigi to prevent the mite moving up the pedicel of open flowers by a sticky barrier significantly reduced A. essigi populations within the resultant fruit by over five fold that of control fruit. Although very low levels of aerial dispersal onto fruit cannot be discounted it was concluded that non-aerial or crawling dispersal via the fruit pedicel was the dominant method of blackberry fruit infestation.     

Within-plant and within-leaf dispersion pattern of two-spotted spider mite,Tetranychus urticae Koch (Acari: Tetranychidae) on okra

Tetranychus urticae distribution on spatial scale both within leaf and within plant was assessed by the index of dispersion (Id), Lloyd's mean crowding index (Imc), Lloyd's patchiness index (Ip) and Morisita's index (I _δ). Id values in all leaves and leaf parts promised aggregated distribution regardless of leaf position and leaf areas. The values of Imc estimated were all larger than the mean. The value of Ip and I _δ  also indicated increased degree of aggregation and clumping in all leaves and leaf areas. While pattern of distribution is same in all the leaves and leaf parts, population estimated is high in young fully opened top leaves than the grown-up middle and bottom leaves. Within the young leaf, top area of upper side of the leaf housed relatively increased number of T. urticae than bottom area of upper side of the leaf. Because young fully opened leaves consistently contained major proportion of mites (48.33%), particularly the top leaf area (79.62%), these leaves and leaf areas can be used as sampling unit for population estimation to minimise the time spent on sampling. However, it warrants future research for predictive models to associate a number of mites of top leaf to other leaves and top area to other areas. Further, releasing predators in young fully opened leaves may increase predator efficiency if supplementary studies on predator–prey relationship on spatial scale are triggered.     

Gene note. Mdh3 encoding a Phalaenopsis 039-like homeodomain protein expressed in ovules of Malus domestica

A cDNA clone, Mdh3, was isolated from young fruit of Malus domestica Borkh. The Mdh3 gene is closely related to the Phalaenopsis 039 homeobox gene, which is involved in ovule development in orchids. Mdh3 mRNA was expressed in young apple leaves, flower buds and young fruit. In situ hybridization of flower buds showed that Mdh3 mRNA accumulated in the ovules, suggesting that Mdh3 may be involved in apple ovule development.     

Do domatia mediate mutualistic interactions between coffee plants and predatory mites?

Many plant species possess structures on their leaves that often harbour predatory or fungivorous mites. These so‐called domatia are thought to mediate a mutualistic interaction; the plant gains protection because mites decimate plant pathogenic fungi or herbivores, whereas the mites find shelter in the domatia. We tested this hypothesis using two species of coffee (Coffea spp.) plants that posses domatia consisting of small cavities at the underside of the leaves, and which often harbour mites. We assessed densities of domatia, of the predatory mite Iphiseiodes zuluagai Denmark and Muma (Acari: Phytoseiidae) and of herbivorous mites Oligonychus ilicis (McGregor) (Acari: Tetranychidae) and Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae) on Coffea arabica L. (Rubiaceae) and Coffea canephora Pierre in the field. Over a period of 50 days, C. arabica harboured on average 7.5 times more predatory mites and 0.4–0.66 fewer prey mites than C. canephora. Hence, the higher density of predatory mites on C. arabica could not be explained by higher densities of prey. However, the density of domatia on C. arabica was on average 1.65 times higher than on C. canephora, and within each species, leaves with higher densities of domatia also harboured more predators. This suggests a positive effect of domatia on predatory mites. In the laboratory, survival of adult female predatory mites on leaves of C. arabica with open domatia was indeed significantly higher than on leaves with closed domatia. Hence, predatory mites benefited from the domatia. However, plants with higher densities of domatia did not harbour fewer herbivores. Taken together, our study only provides partial evidence for a mutualistic interaction between coffee plants and predatory mites, mediated by domatia.     

The spatial and temporal distribution of predatory and phytophagous mites in field-grown strawberry in the UK

Extensive sampling of strawberry plants in everbearing and June-bearing strawberry plantations and on potted plants showed that different species of mites were spatially separated. Of the two phytophagous species recorded, Tetranychus urticae was most abundant on old leaves and Phytonemus pallidus on folded leaves and flower/fruit clusters. Predatory phytoseiid mites were found on all plant parts but different species were spatially separated; Neoseiulus cucumeris and N. aurescens were found mostly on folded leaves and clusters, and N. californicus and Phytoseiulus persimilis on old and medium aged leaves. No Typhlodromus pyri were found in the field plantations. These patterns of distribution did not change over sampling dates in summer and early autumn. An understanding of this within-plant zonation of mite species is important when studying predator–prey interactions and when designing sampling strategies for strawberry. A programme to sample the entire mite system on strawberry should be stratified to include all the above mentioned parts of the plant. Different sampling protocols, as appropriate, are required for sampling different pest species and their associated predators.     

Chemical Diversity and Antimicrobial Activity of Volatile Compounds from Zanthoxylum zanthoxyloides Lam. according to Compound Classes,Plant Organs and Senegalese Sample Locations

The chemical diversity of Zanthoxylum zanthoxyloides growing wild in Senegal was studied according to volatile compound classes, plant organs and sample locations. The composition of fruit essential oil was investigated using an original targeted approach based on the combination of gas chromatography (GC) and liquid chromatography (LC) both coupled with mass spectrometry (MS). The volatile composition of Z. zanthoxyloides fruits exhibited relative high amounts of hydrocarbon monoterpenes (24.3 – 55.8%) and non‐terpenic oxygenated compounds (34.5 – 63.1%). The main components were (E)‐β‐ocimene (12.1 – 39%), octyl acetate (11.6 – 21.8%) and decanol (9.7 – 15.4%). The GC and GC/MS profiling of fruit essential oils showed a chemical variability according to geographical locations of plant material. The LC/MS/MS analysis of fruit oils allowed the detection of seven coumarins in trace content. The chemical composition of fruit essential oils was compared with volatile fractions of leaves and barks (root and trunk) from the same plant station. Hexadecanoic acid, germacrene D and decanal were identified as the major constituents of leaves whereas the barks (root and trunk) were dominated by pellitorine (85.8% and 57%, respectively), an atypic linear compound with amide group. The fruit essential oil exhibited interesting antimicrobial activities against Staphylococcus aureus and Candida albicans, particularly the alcohol fraction of the oil.     

Seasonal prevalence and susceptibility to agrochemicals of Tyrophagus similis (Acari: Acaridae) in spinach buds and agricultural soil under greenhouse conditions

Seasonal prevalence of Tyrophagus similis was investigated from 1997 to 1998 in two spinach greenhouses in central Japan. Susceptibility of T. similis to agrochemicals was also tested in the laboratory. Tyrophagus similis density in the soil was low during the high temperature period from May to August. The density rapidly increased in late autumn and remained at a high level during the cool season from December to February. The number further increased in April and then rapidly decreased in May. The high temperatures in the greenhouses from spring to early autumn are considered the main causes of population decrease. Mites on spinach buds increased the number after those on and in the soil increased. Mites attacked spinach buds mostly in late autumn and early spring. Dichlorvos did not reduce the number of mites in either greenhouse even though it was highly toxic under laboratory condition. This discrepancy suggests that the mites in both the soil and spinach buds had little direct contact with the chemicals. These data suggest that once crop damage by mites is detected, it is usually too late to use chemicals, and that mites that live in the buds are protected from agrochemicals. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fungal Endophytic Communities in Healthy and Declining Quercus robur L. and Q. cerris L. Trees in Northern Italy

Healthy and declining English oak (Quercus robur) and Turkey oak (Q. cerris) in north‐western Italy, in a plain oak forest showing decline for oak puzzle disease, were tested to assess possible variations in the composition of their fungal endophytic communities and their relation to the health status of trees. Samples collected in spring (buds) and in autumn (leaves, annual shoots and twigs) were surface‐sterilized, cut into fragments and placed on potato dextrose agar for a month; 26 fungal species were isolated, the most frequent being Tubakia dryina, Dendrodochium sp., Eutypella sp. and a sterile mycelium. Correspondence analysis showed significant qualitative differences between assemblages inhabiting twigs and herbaceous tissues that were due to the low frequency of Tubakia dryina in twigs and its higher frequency in buds, leaves and shoots. Tubakia dryina was isolated more frequently from leaves of declining oaks and from buds of healthy oaks; Monochaetia monochaeta showed a preference for healthy trees, especially leaves and buds. According to the Shannon–Wiener index, endophytic fungal communities of leaves, twigs and buds of declining English oak were poorer than those of declining Turkey oak, but there were no significant differences between healthy hosts.     

VEGETATIVE REGROWTH FOLLOWING CUTTING IN THE SHRUB BACCHARIS PILULARIS SSP. CONSANGUINEA (DC) C. B. WOLF

The resprouting ability following cutting of the chaparral shrub Baccharis pilularis ssp. consanguinea (DC) C. B. Wolf was investigated following the felling of individuals of various ages. Numbers of resprouts and resprout biomass were low in 1-yr-old shrubs, increased to a maximum in shrubs 3–4 yr old, and declined to zero in shrubs <8 yr old. Numbers of leaves produced were also lower in 1-yr-old shrubs. The results are interpreted on the basis of the internal origin of resprout buds and the increasing extent of the shrub's root system as it matures.