Citrus Rust Mite Research Articles

Antagonistic effects of the endophytic fungus Meira geulakonigii on the citrus rust mite Phyllocoptruta oleivora

The fungus Meira geulakonigii has been shown to reduce populations of citrus rust mite (CRM; Phyllocoptruta oleivora) on citrus leaves and fruits, in both the field and laboratory. However, attempts to isolate the fungus from leaves and fruits have been unsuccessful. The aims of this study were therefore to determine whether M. geulakonigii is a citrus endophyte, and to assess possible mechanisms involved in its mite-antagonist activity. A quantitative real-time PCR and regular PCR approaches were developed to detect M. geulakonigii in both the field and laboratory. The fungus was detected throughout. Different methods revealed that M. geulakonigii is an endophyte, which colonizes both the peel of grapefruits. Applications of conidia protected the grapefruits against CRM, and fungal secretions extracted from growth media caused 100% CRM mortality. Meira geulakonigii is a beneficial endophyte of grapefruits that colonizes the fruit's peel, and protects it from CRM. Findings from this study demonstrate the endophytic nature of M. geulakonigii in its interaction with grapefruits. In addition, a molecular approach was developed to specifically detect the fungus inside the grapefruit peel. This approach can be used to assess the natural occurrence of M. geulakonigii in grapefruit.

Development of <I>Iphiseiodes quadripilis</I> (Banks) (Acari: Phytoseiidae) on Pollen or Mite Diets and Predation on <I>Aculops pelekassi</I> (Keifer) (Acari: Eriophyidae) in the Laboratory

Development and reproduction of Iphiseiodes quadripilis (Banks) were evaluated on single food diets of pollen (Malephora crocea Jacquin [ice plant] or Quercus sp. [oak]), spider mites, [Eutetranychus banksi (McGregor) or Panonychus citri (McGregor) (Acari: Tetranychidae)], or the citrus rust mite Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae). Experiments were conducted in an environmental chamber at 28 degrees +/- 1 degrees C, 14:10 (L:D) daylength, and 45% RH. I. quadripilis completed development and laid viable eggs that subsequently hatched on diets of either ice plant or oak pollen or eggs and motile stages of E. banksi. P. citri was acceptable as prey, but survival of larvae to adults was only 36%, whereas survival on E. banksi, ice plant pollen, and oak pollen was 48, 60, and 68%, respectively. The webbing produced by P. citri seemed to inhibit foraging behavior of I. quadripilis larvae and nymphs. Larvae of I. quadripilis developed only to the second nymphal instar on a diet of P. oleivora alone or water alone. Starved I. quadripilis females and deutonymphs were observed preying on the pink citrus rust mite, Aculops pelekassi (Keifer) (Eriophyidae). During 4-min observation trials, two series of I. quadripilis fed on 1.8 +/- 0.47 and 3.5 +/- 0.45 A. pelekassi motile stages after being starved for 6 and 24 h, respectively. I. quadripilis females did not prey on P. oleivora in arenas containing both rust mite species.

Development of Iphiseiodes quadripilis (Banks) (Acari: Phytoseiidae) on Pollen or Mite Diets and Predation on Aculops pelekassi (Keifer) (Acari: Eriophyidae) in the Laboratory

Development and reproduction of Iphiseiodes quadripilis (Banks) were evaluated on single food diets of pollen (Malephora crocea Jacquin [ice plant] or Quercus sp. [oak]), spider mites, [Eutetranychus banksi (McGregor) or Panonychus citri (McGregor) (Acari: Tetranychidae)], or the citrus rust mite Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae). Experiments were conducted in an environmental chamber at 28° ± 1°C, 14:10 (L:D) daylength, and 45% RH. I. quadripilis completed development and laid viable eggs that subsequently hatched on diets of either ice plant or oak pollen or eggs and motile stages of E. banksi. P. citri was acceptable as prey, but survival of larvae to adults was only 36%, whereas survival on E. banksi, ice plant pollen, and oak pollen was 48, 60, and 68%, respectively. The webbing produced by P. citri seemed to inhibit foraging behavior of I. quadripilis larvae and nymphs. Larvae of I. quadripilis developed only to the second nymphal instar on a diet of P. oleivora alone or water alone. Starved I. quadripilis females and deutonymphs were observed preying on the pink citrus rust mite, Aculops pelekassi (Keifer) (Eriophyidae). During 4-min observation trials, two series of I. quadripilis fed on 1.8 ± 0.47 and 3.5 ± 0.45 A. pelekassi motile stages after being starved for 6 and 24 h, respectively. I. quadripilis females did not prey on P. oleivora in arenas containing both rust mite species.

Binomial Sampling to Estimate Rust Mite (Acari: Eriophyidae) Densities on Orange Fruit

Binomial sampling based on the proportion of samples infested was investigated for estimating mean densities of citrus rust mite, Phyllocoptruta oleivora (Ashmead), and Aculops pelekassi (Keifer) (Acari: Eriophyidae), on oranges, Citrus sinensis (L.) Osbeck. Data for the investigation were obtained by counting the number of motile mites within 600 sample units (each unit a 1-cm2 surface area per fruit) across a 4-ha block of trees (32 blocks total): five areas per 4 ha, five trees per area, 12 fruit per tree, and two samples per fruit. A significant (r2 = 0.89), linear relationship was found between ln(-ln(1 -Po)) and ln(mean), where P0 is the proportion of samples with more than zero mites. The fitted binomial parameters adequately described a validation data set from a sampling plan consisting of 192 samples. Projections indicated the fitted parameters would apply to sampling plans with as few as 48 samples, but reducing sample size resulted in an increase of bootstrap estimates falling outside expected confidence limits. Although mite count data fit the binomial model, confidence limits for mean arithmetic predictions increased dramatically as proportion of samples infested increased. Binomial sampling using a tally threshold of 0 therefore has less value when proportions of samples infested are large. Increasing the tally threshold to two mites marginally improved estimates at larger densities. Overall, binomial sampling for a general estimate of mite densities seemed to be a viable alternative to absolute counts of mites per sample for a grower using a low management threshold such as two or three mites per sample.

Biological control of citrus insect pests in Turkey.

Abstract The usage and acceptability of biological control methods are set to increase in agriculture in the future because of food safety and pesticide residue issues. Biological control implementation in Turkey started with control of cottony cushion scale Icerya purchasi (Homoptera: Margarodidae) through the introduction and release of Rodolia cardinalis (Coleoptera: Coccinellidae) in citrus plantations. Currently, the key pests of citrus, i.e. citrus mealybug ( Planococcus citri (Homoptera: Pseudococcidae)), citrus rust mite (Phyllocoptruta oleivora (Acarina: Eriophyidae)) and California red scale ( Aonidiella aurantii (Homoptera: Diaspididae)), can be suppressed by biological control, a specific acaricide and summer oil applications, respectively. As a main pest, the citrus mealybug infested area is approximately 100 000 ha in total on the East and West Mediterranean coasts of Turkey. Until now, biological control for citrus mealybug has been implemented on only 3000 ha (3.5%) of the citrus growing area. However, the small-scale nature of biological control applications in relation to the size of infested area is set to change as public awareness will lead to an increase in the area over which biological control is implemented in the future.

Assaying three new fungi against citrus mites in the laboratory, and a field trial

The Basidiomycotine fungi Meira geulakonigii, Meira argovae and Acaromyces ingoldii were assayed in the laboratory against five species of herbivorous mites: Phyllocoptruta oleivora (Eriophyidae), Panonychus citri, Eutetranychus orientalis, Tetranychus urticae and Tetranychus cinnabarinus (all four Tetranychidae). All fungi caused significantly high mortality rates (as compared to controls) after 14 days, some after 1 week. Phyllocoptruta oleivora was the most susceptible, showing >80% mortality even after 1 week. In a field trial, grapefruits sprayed either once a month or once a season with M. geulakonigii had significantly fewer P. oleivora and less damage than unsprayed fruit. These results suggest that M. geulakonigii may protect grapefruits against the injurious P. oleivora.

Genetic diversity in Hirsutella thompsonii isolates based on random amplified polymorphic DNA analysis

Hirsutella thompsonii Fisher is a host-specific fungal pathogen of the diverse group of arthropods known as the Acari. It particularly affects eriophyid mites, and the identification of its isolates is a difficult task due to its pleomorphic nature. Seven isolates of H. thompsonii var. thompsonii and H. thompsonii var. synnematosa collected from various agro-climatic regions of India were subjected to PCR analysis using random decamer primers to differentiate between them. Random amplified polymorphic DNA analysis revealed that all of the isolates from the citrus rust mite, Phyllocoptruta oleivora Ashmead (Acari: Eriophyidae), clustered together, with the exception of one, HtCRMB. The only isolate of H. thompsonii from Aceria guerreronis keifer (Acari: Eriophydae), HtPDBC, clustered separately.

TWO SPECIES OF CECIDOMYIIDAE PREDACIOUS ON CITRUS RUST MITE, PHYLLOCOPTRUTA OLEIVORA, ON FLORIDA CITRUS

Larvae of two undescribed species of Cecidomyiidae (Diptera) were found preying upon Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae) on Florida citrus. Identifications to genus were made from adults reared in the laboratory. The two species had distinctive larval coloration. One larval type was completely yellow and was identified as Feltiella n. sp., while the second larval type had an orange color with a transverse white band close to the mouthparts. The latter cecidomyiid was identified as belonging to a genus near Lestodiplosis in the broad sense. Feltiella n. sp. (n = 17) and the species near the genus Lestodiplosis (n = 12) consumed 33.8 ± 4.6 (mean ± SEM) and 43.0 ± 6.4 citrus rust mite eggs; 14.2 ± 1.4 and 15.0 ± 2.0 citrus rust mite nymphs, and 3.0 ± 0.4 and 5.6 ± 0.9 citrus rust mite adults/10 min., respectively. There were no significant differences (P > 0.05) in the consumption rates of either predator on any rust mite life stage. These data indicate that Feltiella n. sp. and the species near the genus Lestodiplosis are both efficient predators of P. oleivora eggs, larvae, and nymphs.

Beauveria Bassiana Pathogenicity to the Citrus Rust Mite Phyllocoptruta Oleivora

The pathogenicity of Beauveria bassiana to one of the major pests of citrus crops, Phyllocoptruta oleivora, was assessed by inoculating mites with different concentrations of conidia (1 x 10(6), 5 x 10(6), 1 x 10(7), 5 x 10(7) and 1 x 10(8)). Treated mites were kept at controlled conditions (25 +/- 0.5 degrees C, 12 h photoperiod and 98% relative humidity) and mite survivorship was evaluated daily. Mortality was found to increase in time and was dependent on the conidia concentration, with values ranging from 24 to 91% for the lowest and highest conidia concentration, respectively. The calculated LC50 on the fifth day was 4.23 x 10(6) conidia/ml. Mean lethal time was 3.98, 9.79, 3.09 and 2.74 days for 5 x 10(6), 1 x 10(7), 5 x 10(7) and 1 x 10(8) conidia/ml, respectively. Conidia were found to adhere all over the mite body surface, especially at the anal region, where vegetative mycelium was found entering the mite body. We noticed the formation of small crystals inside the mite's body that were produced during colonization of the body cavity by the fungus. This is the first report of B. bassiana pathogenicity for this species.

Effects of Reducing Sample Size on Density Estimates of Citrus Rust Mite (Acari: Eriophyidae) on Citrus Fruit: Simulated Sampling

The consequence of reducing sample size on the accuracy and precision of estimates of citrus rust mite, Phyllocoptruta oleivora (Ashmead), densities on oranges was investigated. The sample unit was a 1-cm2 surface area on fruit. Sampling plans consisting of 360, 300, 200, 160, 80, 48, 36, or 20 samples per 4 ha were evaluated through computer simulations by using real count data from 32 data sets of 600 sample units per 4 ha. The original and reduced sampling plans were hierarchical with different numbers of sample areas per 4 ha, trees per area, fruit per tree, and samples per fruit. Individual estimates (n=100 simulations per data set) using each plan were sometimes considerably below or above target densities. In an original set of count data with a mean of six mites per cm2, simulations of 36 samples per 4 ha produced individual estimates ranging from one to 16 mites per cm2, whereas 80 samples per 4 ha produced estimates ranging from two to 10 mites per cm2. The plans consisting of 36 or more samples were projected to provide precision levels of 0.25 (SEM/mean) or better at densities of five or more mites per cm2 based on log-data, a projection that needs to be verified under real-grove situations. Each plan consistently provided mite detection in these sampling simulations except those consisting of 20 or 36 samples, which sometimes failed to detect mites when the target density was less than five mites per cm2. The study provided insight into the probable precision, accuracy and detection thresholds for eight candidate sampling plans varying from relatively low to high resource input.

Larval Cryptothelea gloverii (Lepidoptera: Psycidae), an arthropod predator and herbivore on Florida citrus

The orange bagworm (OBW), Cryptothelea gloverii (Packard) (Lepidoptera: Psychidae) was previously reported feeding on citrus fruit and foliage and preying upon the camphor scale Pseudaonidia duplex (Cockerell) (Homoptera: Coccidae). In this study using laboratory assays, OBW preyed upon citrus rust mite, Phyllocoptruta oleivora (Ashmead) (Acari: Eriophyidae) and consumed eggs and adults of both P. oleivora and Panonychus citri (McGregor) (Acari: Tetranychidae), two important pest mites on Florida citrus. OBW was also observed to feed on the purple scale, Lepidosaphes beckii (Newman) (Homoptera: Diaspididae) and on a fungus (Penicillium sp.). OBW fed on orange and grapefruit leaves by starting from the border and eating part of the leaf, by chewing holes, or consuming the outer epithelium of either the axial or abaxial surface of the leaf without penetrating through the leaf. OBW was observed in orange orchards in association with fruit extensively russeted by P. oleivora feeding. Laboratory assays revealed that OBW larvae preferred to feed on oranges infested with P. oleivora rather than on clean fruits that were free of mite feeding damage. Feeding damage to citrus fruit by OBW larvae results in one to several holes being eaten into the rind or albedo, without damage to the fruit sacs.

A new fungus with dual biocontrol capabilities: reducing the numbers of phytophagous mites and powdery mildew disease damage

The fungus Meira geulakonigii Boekhout, Scorzetti, Gerson & Sztejnberg (Basidiomycota: Ustilaginomycetes) was assayed against three species of phytophagous mites and against cucumber powdery mildew, Sphaerotheca fusca (Fr.) Blumer. The corrected mortality of the citrus rust mite, Phyllocoptruta oleivora (Ashmead), came to almost 100%, whereas that of the citrus red mite, Panonychus citri McGregor, and that of the carmine spider mite, Tetranychus cinnabarinus (Boisduval), was around 80%. The coverage of cucumber leaves by the powdery mildew was significantly lower on detached cotyledons and on growing plant foliage sprayed with Meira geulakonigii and cucumber fruit yield was significantly higher. These leaves also carried fewer carmine spider mites. The novelty of these results and their practical application are discussed.

DISTRIBUCIÓN ESPACIAL Y FLUCTUACIÓN POBLACIONAL DE PHYLLOCOPTRUTA OLEIVORA (ASHMEAD) (ACARI: ERIOPHYIDAE) EN CÍTRICOS DE GÜEMEZ, TAMAULIPAS

El presente trabajo de investigación se realizó en el municipio de Güemez, México, en el periodo de Junio de 1998 a Octubre de 1999. Se determinó la distribución espacial y fluctuación poblacional del arador de los cítricos Phyllocoptruta oleivora (Ashmead). Esta investigación se realizó en 10 árboles de naranjo de la variedad Valencia, seleccionados al azar en una superficie de una hectárea. Cada árbol se dividió en 7 áreas de muestreo y se realizaron muestreos cada 14 días, tomando como unidad de muestra las hojas. En total se registró la población en 700 hojas por fecha de muestreo. De los datos obtenidos se realizaron análisis para determinar la distribución espacial que presenta el ácaro en la zona de estudio, utilizando para ello 8 índices de muestro. Se registró la fluctuación poblacional y posibles factores climáticos que pudieran limitar la densidad poblacional. Los índices de Lexis, Charlier, David y Moore, Green y el parámetro K de la binomial negativa indicaron una distribución agregada en todas las fechas de muestreo donde se detectó la presencia de ácaros. Los valores de Morisita, Iwao y la ley de poder de Taylor mostraron disposición aleatoria en dos, dos y tres de las fechas de muestro respectivamente, en las demás se presentó disposición agregada. En todos los muestreos se encontró mayor cantidad de ácaros en el estrato medio seguido del estrato inferior y superior respectivamente. Se detectaron tres picos poblacionales; el 27 de marzo, el 21 de agosto y el 25 de septiembre con promedios de 3.8, 2.9, y 4.5 ácaros por hoja respectivamente. De los factores climáticos evaluados, la temperatura fue el que presentó el coeficiente de correlación mas alto (r=0.69916).

Identification and evaluation of potential predators of the citrus rust mite, Phyllocoptruta oleivora, in Israel

Damage caused by citrus rust mite (CRM), Phyllocoptruta oleivora (Ashmead), is usually negligible in minimally to unsprayed isolated groves located in the central coastal plain of Israel. Assuming that resident natural enemies were responsible for this situation, we monitored the pest’s potential predators in five unsprayed citrus plots, and concurrently determined their feeding habits in the laboratory. In the field Iphiseius degenerans (Berlese) and Amblyseius swirskii Athias-Henriot were the main predators found, the former being dominant during the critical winter and spring months, the period of low pest populations. In the laboratory, when solely CRM was offered, the decline in pest numbers was similar in leaf arenas containing either phytoseiid or the stigmaeid Agistemus cypriusGonzalez. Only I. degenerans, however, seemed to kill fewer CRM in the presence of pollen. While the cessation of pesticide applications during two years was insufficient for reducing CRM populations, observations suggest that a three year break from broad spectrum pesticides would be the turning point for the reestablishment of I. degenerans, the postulated more important predator. Our field and laboratory data suggest that a complex of indigenous, generalist predators could be responsible for the control of CRM in isolated, unsprayed citrus groves on the central coastal plain of Israel.

Economic Analysis of Aldicarb on Citrus in the Indian River Area in Southeastern Florida

Aldicarb is a pesticide used on several crops to control citrus rust mite (Phyllocoptruta oleivors), citrus nematode (Tylenchulus semipenetrans) and other citrus pests. Analysis of previous research experiments indicates that this pesticide is beneficial to both orange (Citrus sinensis) and grapefruit (Citrus parasisi) production and that both cost savings and higher yields can be experienced in many types of groves. Actual grove data shows that net returns for mature grapefruit that receive aldicarb can be $500/acre ($1235/ha) greater than net returns for identical acreage that uses other pest control options. Also, based on grove reset data, it is shown that with an application of aldicarb the resulting increased yields for 3-year-old trees more than cover the additional cost of applying the aldicarb.

Diel periodicity of emergence of adult citrus rust mites in central Florida.

Emergence of adult citrus rust mites, Phyllocoptruta oleivora (Ashmead) from the imagochrysalis occurred with a diel periodicity that peaked between mid morning and early afternoon. The pattern of emergence did not differ for mites reared from eggs held under different photoperiod regimes. The transition of nymphs to the imagochrysalis stage also showed a diel periodicity, occurring in the evening. The average duration of the imagochrysalis stage at 28 degrees C was 14-15 h. Wetting by rain or dew was simulated by immersing fruit in water each night, but the transition to the imagochrysalis stage or the subsequent emergence pattern of adults was not affected. Adult mites reared from eggs laid during two, consecutive 12-h periods emerged at the same time of day, but the peaks of emergence were separated by 24 h. Eclosion of larvae from eggs laid during two, consecutive 12-h periods did not show a diel periodicity. Eggs continuously immersed in water during their development did not hatch, whereas there was a small, but significant, reduction in the viability of eggs immersed in water each night. These results are discussed in relation to external cues that may entrain the diel patterns of development and adult emergence, and to the adaptive responses of citrus rust mite to cyclic fluctuations of key environmental variables in central Florida.

Rearing, release and establishment of imported predatory mites to control citrus rust mite in Israel

Citrus rust mite, Phyllocoptruta oleivora (Ashmead), is a major pest of citrus in Israel. Five species of predatory mites: Amblyseius herbicolus Chant, Euseius victoriensis (Womersley), Euseius elinae (Schicha), Typhlodromus rickeri Chant and Euseius stipulatus (Athias-Henriot), were imported to improve the biological control of the pest. Mite rearing and sampling methods were developed and improved, and the predators were released. Recovery in some citrus orchards was recorded, but only E. victoriensis became established in the north of Israel.

Ecology and Aerobiology of Dispersing Citrus Rust Mites (Acari: Eriophyidae) in Central Florida

Aerial dispersal of citrus rust mite, Phyllocoptruta oleivora (Ashmead), in central Florida showed a diel periodicity peaking between late morning and early afternoon. The abiotic factors that best described the dispersal pattern were solar radiation, time, and leaf wetness; whereas wind speed, humidity, temperature, and rainfall had minimal effect. The longevity of adult mites removed from fruit was inversely related to constant temperatures between 25 and 35°C. The longevity of mites removed from fruit at 2-h intervals between 0700 and 1300 hours and exposed to ambient temperature and humidity outdoors was inversely related to the time of removal from the host. There was a linear relationship between the number of mites captured in traps and population density on fruit. Mites left fruit harboring extremely low populations and some fruit supporting dense populations yielded hundreds of dispersing mites per day. Mites were readily carried on air currents between adjacent citrus groves. Nearly all of the mites captured in dispersal traps were adult females, and were found in greater proportions in traps than would be expected from the sex ratio of mites on fruit. Studies using isolated fruit in the laboratory showed that a single virgin or inseminated female could initiate a local population through oedipal mating and sibmating. The data are discussed in relation to the selective forces that may shape the dispersal behavior of citrus rust mite and to the potential impact of aerial dispersal on mite management and the development of acaricide resistance.

A Method for Harvesting and Shipping Live Citrus Rust Mites (Acari: Eriophyidae)

Field populations of citrus rust mite, Phyllocoptruta oleivora Ashmead in Florida have shown resistance to dicofol (Omoto et al. 1994) and shifts in susceptibility to abamectin (Bergh et al. 1999). Resistance monitoring of eriophyid mites has not been widely practiced, limiting the availability of reference strains and technical expertise. This study was prompted when a company expressed interest in testing the susceptibility of citrus rust mite populations from Texas to their acaricide. Under normal conditions, citrus rust mites do not live long off of the host (J. C. B., unpublished data), and importing them into Florida on citrus fruit or foliage requires quarantine. However, importing mites off of host plant tissue reduces the risk of introducing a new pest or plant pathogen and does not require their quarantine. Our objective was to develop methods for removing large numbers of citrus rust mites from their host and shipping them live to other locations. Toward this end, we capitalized on two aspects of their biology. First, mites disperse by leaping from the plant and are borne away on air currents (Bergh and McCoy 1997). This behavior also occurs on excised pieces of citrus leaf as the tissue deteriorates (Omoto et al. 1994). Second, rust mites in Florida are regularly submerged in rain or dew and can withstand extended periods of immersion, remaining motionless until dried (J. C. B., personal observation). Mites were harvested from 'Sunburst' mandarin leaves from seedlings maintained in a greenhouse at the Citrus Research and Education Center (CREC), Lake Alfred, FL. To examine the effect of temperature on the harvest of mites, heavily infested leaves were cut into 2 x 2 cm pieces, which were randomly assigned to 4 groups. Each piece of leaf was impaled on an insect pin and the pin was inserted into the side of a rubber stopper. Five stoppers with leaf pieces were placed in each of four translucent plastic boxes lined with wet paper towel. Each piece of leaf was positioned about 1.5 cm above the center of a filter paper disk (Whatman No. 50, 38 mm diam.) placed on the wet paper towel. The boxes were covered and placed in lighted environmental cabinets at 20, 25, 30, and 35?C. The filter paper disks were replaced at 2-h intervals from 09:00 to 17:00 hours, and the mites on each were counted using a dissecting microscope at 20x. The mean number of mites harvested on each of three days was compared among temperatures using PROC GLM of SAS (SAS Institute 1985) and the Tukey multiple range test at the 5% probability level. To examine the effect of light on the harvest of mites, rubber stoppers with impaled leaf pieces were placed in uncovered boxes in chambers set at 30?C, with bright, overhead lights and continuous darkness. The filter paper disks were replaced at 2-h intervals from 08:00-16:00 hours and the mites were counted as described above. The t-test was used to compare the mean number of mites harvested in constant light and dark conditions on each of three days.

Phytophagous mite populations on Tahiti lime, Citrus latifolia, under induced drought conditions.

In the north-western region of Venezuela, Phyllocoptruta oleivora, Tetranychus mexicanus and Brevipalpus phoenicis are common plant-feeding mites on leaves, fruits and branches of Tahiti lime, Citrus latifolia. The population dynamics of these herbivores are affected by many factors, such as weekly treatments with wettable sulphur, particularly during the wet season, maintenance pruning of plants, irrigation with microsprinklers, induction of water stress by withholding irrigation and biotic and abiotic environmental factors. During October 1994-January 1995, 31 trees in a commercial orchard were sampled weekly in order to describe population fluctuations of plant-feeding mites (mean number of mites per leaf or fruit), before (4 weeks) and after (4 weeks) a period of 6 weeks of drought stress (no irrigation). The population density of P. oleivora increased progressively during the last 3 weeks of the irrigation period and reached a maximum of 24 mites per fruit. In contrast, the populations of the other two species, T. mexicanus and B. phoenicis, remained at the same low density as before the withholding-irrigation period. After 6 weeks without irrigation, only T. mexicanus increased, to a high mean value of 11 mites per leaf. The withholding-irrigation practice appears to affect the population size of P. oleivora towards the end of this period and that of T. mexicanus at the beginning of the re-establishment of the water supply. The highest proportion of trees (32%) was infested by T. mexicanus after the withholding-irrigation period, when irrigation was resumed, whereas the highest levels of infestation of trees by P. oleivora and B. phoenicis were 16 and 10%, respectively, during the last week of the water-stress period. Although factors affecting the dynamics of the mites in the orchard are likely to be complex, irrigation management apparently plays an important role.