Bulb Mite Research Articles

6Pgdh polymorphism in wild bulb mite populations: prevalence, environmental correlates and life history trade-offs

Genetic polymorphism in key metabolic genes plays a pivotal role in shaping phenotypes and adapting to varying environments. Polymorphism in the metabolic gene 6-phosphogluconate dehydrogenase (6Pgdh) in bulb mites, Rhizoglyphus robini is characterized by two alleles, S and F, that differ by a single amino acid substitution and correlate with male reproductive fitness. The S-bearing males demonstrate a reproductive advantage. Although the S allele rapidly fixes in laboratory settings, the persistence of polymorphic populations in the wild is noteworthy. This study examines the prevalence and stability of 6Pgdh polymorphism in natural populations across Poland, investigating potential environmental influences and seasonal variations. We found widespread 6Pgdh polymorphism in natural populations, with allele frequencies varying across locations and sampling dates but without clear geographical or seasonal clines. This widespread polymorphism and spatio-temporal variability may be attributed to population demography and gene flow between local populations. We found some correlation between soil properties, particularly cation content (Na, K, Ca, and Mg) and 6Pgdh allele frequencies, showcasing the connection between mite physiology and soil characteristics and highlighting the presence of environment-dependent balancing selection. We conducted experimental fitness assays to determine whether the allele providing the advantage in male–male competition has antagonistic effects on life-history traits and if these effects are temperature-dependent. We found that temperature does not differentially influence development time or juvenile survival in different 6Pgdh genotypes. This study reveals the relationship between genetic variation, environmental factors, and reproductive fitness in natural bulb mite populations, shedding light on the dynamic mechanisms governing 6Pgdh polymorphism.

Fertility loss under thermal stress: males have lower fertility limits but no evidence of sex differences in sensitivity

Climate change models predict that the frequency and intensity of heatwaves are likely to increase, therefore understanding population responses to these extreme climatic events will be key in mitigating biodiversity loss. Here, using the male dimorphic bulb mite, Rhizoglyphus robini, we investigate and compare the impact of experimental heat stress on survival and fertility between females and male morphs that differ in the expression of a sexually selected weapon. We show that lethal limits are similar among all individuals, but find clear sex differences, although no difference between morphs, in sub‐lethal temperatures causing sterility: female fertility remains high close to lethal limits, whereas both male morphs suffer fertility loss at more than 2.5°C below their lethal limits. Contrastingly, when thermal stress was lower the sexes and morphs do not differ in their thermal sensitivity and declines in reproductive output are comparable. These declines appear to be additive as we observe the greatest declines when both sexes were exposed to thermal stress. In addition, during assays we included an extra treatment that allowed individuals two extra days to recover and found that fertility loss was almost fully recovered when thermal stress was low, but only partially recovered under the most extreme temperatures. The impact of heat stress on fertility therefore appears to be temporary with individuals rapidly recovering: whether recovery can negate negative population level effects remains to be investigated. Our experiments reveal the impact of heat stress on survival and fertility, finding sex‐specific fertility loss under the most extreme thermal conditions.

What determines whether to scramble or fight in male bulb mites

What determines whether to scramble or fight in male bulb mites

Saffron Bulb Mite Rhizoglyphus robini (Claparede) Its Occurrence, Biology and Chemical Intervention Tactics on Saffron Corms in Kashmir, India

Saffron corms are attacked by a wide variety of arthropod pest species and mites are one of them. Among Arachnida class bulb mite causes considerable damage to saffron crop and presence of this pest is a regular feature in its cultivation. To record the occurrence of saffron bulb mite, field study was conducted at different saffron growing areas of Kashmir. For biology of the pest, laboratory study was conducted at Department of Entomology, Faculty of Horticulture, Sher-e-Kashmir University of Agricultural Sciences and Technology, Shalimar. The mean percent infestation of saffron bulb mite from all the locations revealed highest and lowest percent mite infestation of 25.83 and 12.50 recorded from Dhussu and Saffron research station respectively. Passing through five active stages viz., Egg, Larva, Protonymph, Tritonymph and adult completed the life cycle of Rhizoglyphus robini. The heteromorphic deutonymph or hypopal stage is sometimes produced for phoresis when population is overcrowded, but this stage was not observed during the study. The results revealed that the females laid their eggs on the corms. The average incubation period of egg was observed to be of 6.16 ±0.78 days while as other developmental periods Larva, Protonymph, and Tritonymph were of 5.22 ±0.68, 5.76 ±0.52, and 7.00 ±0.91 days at 25± 50C respectively. The longevity of adult male and female were 27.9 ±0.44 and 22.9 ±0.69 days respectively. The efficacy of different doses of acaricides against Saffron bulb mite revealed that drenching the soil with chlorpyrifos 20 EC + foliar spray with cyenopyrafen 30 SC showed best results with 4.23 percent leaves with stunted growth and chlorosis, 97.34 percent flower emergence and 2.23 percent bulb rot.

Garlic Mite, Aceria tulipae (Acarida: Eriophyidae): A Review

Garlic (Allium sativum), belonging to the family Amarylidaceae, is a bulbous plant which is widely used as a condiment for its pungent flavour. India holds second position in garlic production after China. It is attacked by many insect pests. The most hazardous pest is Garlic mite (Aceria tulipae). This mite is also known as dry bulb mite or onion mite. It attacks in both field and storage condition. In field condition a typical pig tail appearance is seen in infected plants. In storage condition reddish brown spots appear on the garlic cloves due to the feeding of this mite. This article accrued different aspects of Aceria tulipae, viz., host range and host specificity, invasive history and distribution, morphology, taxonomic confusion, dispersal, biology and relationship with abiotic factors, population dynamics, damage symptoms in field and storage and its management.

Small-scale genetic structure of populations of the bulb mite Rhizoglyphus robini.

Bulb mites are an economically significant pest of subterranean parts of plants and a versatile laboratory animal. However, the genetic structure of their populations remains unknown. To fill this gap in our knowledge of their biology, we set up a field experiment in which we allowed mites to colonize onion bulbs, and then determined the genetic structure of colonisers based on a panel of microsatellite loci. We found moderate but significant population structure among sites separated by ca. 20m (FST range 0.03-0.21), with 7% of genetic variance distributed among sites. Allelic richness within some bulbs was nearly as high as that in the total population, suggesting that colonisation of bulbs was not associated with strong population bottlenecks. The significant genetic structure we observed over small spatial scales seems to reflect limited dispersal of mites in soil.

Attraction of Tetranychus urticae to garlic treated with chlorfenapyr to control dry bulb mite, Aceria tulipae

Attraction of Tetranychus urticae to garlic treated with chlorfenapyr to control dry bulb mite, Aceria tulipae

A sexually selected male weapon characterized by strong additive genetic variance and no evidence for sexually antagonistic polyphenic maintenance.

Sexual selection and sexual antagonism are important drivers of eco-evolutionary processes. The evolution of traits shaped by these processes depends on their genetic architecture, which remains poorly studied. Here, implementing a quantitative genetics approach using diallel crosses of the bulb mite, Rhizoglyphus robini, we investigated the genetic variance that underlies a sexually selected weapon that is dimorphic among males and female fecundity. Previous studies indicated that a negative genetic correlation between these two traits likely exists. We found male morph showed considerable additive genetic variance, which is unlikely to be explained solely by mutation-selection balance, indicating the likely presence of large-effect loci. However, a significant magnitude of inbreeding depression also indicates that morph expression is likely to be condition-dependent to some degree and that deleterious recessives can simultaneously contribute to morph expression. Female fecundity also showed a high degree of inbreeding depression, but the variance in female fecundity was mostly explained by epistatic effects, with very little contribution from additive effects. We found no significant genetic correlation, nor any evidence for dominance reversal, between male morph and female fecundity. The complex genetic architecture underlying male morph and female fecundity in this system has important implications for our understanding of the evolutionary interplay between purifying selection and sexually antagonistic selection.

Nutrient-dependent allometric plasticity in a male-diphenic mite.

Male secondary sexual traits often scale allometrically with body size. These allometries can be variable within species and may shift depending on environmental conditions, such as food quality. Such allometric plasticity has been hypothesized to initiate local adaptation and evolutionary diversification of scaling relationships, but is under‐recorded, and its eco‐evolutionary effects are not well understood. Here, we tested for allometric plasticity in the bulb mite (Rhizoglyphus robini), in which large males tend to develop as armed adult fighters with thickened third legs, while small males become adult scramblers without thickened legs. We first examined the ontogenetic timing for size‐ and growth‐dependent male morph determination, using experimentally amplified fluctuations in growth rate throughout juvenile development. Having established that somatic growth and body size determine male morph expression immediately before metamorphosis, we examined whether the relationship between adult male morph and size at metamorphosis shifts with food quality. We found that the threshold body size for male morph expression shifts toward lower values with deteriorating food quality, confirming food‐dependent allometric plasticity. Such allometric plasticity may allow populations to track prevailing nutritional conditions, potentially facilitating rapid evolution of allometric scaling relationships.

Genomic evidence that a sexually selected trait captures genome-wide variation and facilitates the purging of genetic load.

The evolution of costly traits such as deer antlers and peacock trains, which drove the formation of Darwinian sexual selection theory, has been suggested to both reflect and affect patterns of genetic variance across the genome, but direct tests are missing. Here, we used an evolve and resequence approach to reveal patterns of genome-wide diversity associated with the expression of a sexually selected weapon that is dimorphic among males of the bulb mite, Rhizoglyphus robini. Populations selected for the weapon showed reduced genome-wide diversity compared to populations selected against the weapon, particularly in terms of the number of segregating non-synonymous positions, indicating enhanced purifying selection. This increased purifying selection reduced inbreeding depression, but outbred female fitness did not improve, possibly because any benefits were offset by increased sexual antagonism. Most single nucleotide polymorphisms (SNPs) that consistently diverged in response to selection were initially rare and overrepresented in exons, and enriched in regions under balancing or relaxed selection, suggesting they are probably moderately deleterious variants. These diverged SNPs were scattered across the genome, further demonstrating that selection for or against the weapon and the associated changes to the mating system can both capture and influence genome-wide variation.

A Review of Prospective Biocontrol Agents and Sustainable Soil Practices for Bulb Mite (Acari: Acaridae) Management

Mites of the genus Rhizoglyphus (Acari: Acaridae) are serious pests of plants belonging to the orders Liliales and Asparagales such as onions, garlic, lilies, and tulips. Their control by synthetic pesticides is becoming problematic as a result of resistance development in these mites and environmental and health issues. New pest control methods thus need to be developed. This review provides an overview of studies related to bulb mite management. Entomopathogenic fungi and generalist predatory mites are prospective agents for biological control of these pests while entomopathogenic nematodes and the metabolites of their symbiotic bacteria seems to be less effective. There are, however, many more organisms in the soil that might play important roles in biological control of bulb mites as well as other soil pests of these bulbous plants. Therefore, a holistic approach based on the understanding of food webs in the soil environment and their ecological services is essential for developing effective control of bulb mites. For the rehabilitation and conservation of soil biodiversity supporting these ecosystem services, emphasis must be placed on sustainable soil management (e.g., ensuring green coverage, minimal soil disturbance and high content of organic matter).

Evaluation of the entomopathogenic fungusMetarhiziumbrunneumand thepredatory miteStratiolaelaps scimitus against Rhizoglyphus robini under laboratory conditions.

Rhizoglyphus robini Claparède (Acari: Acaridae) is a pest of bulbs, corms and tubers of several economically important crops. The biological control of R. robini has yet to be fully explored as an alternative to chemical pesticides. Entomopathogenic fungi in the genera Metarhizium (Hypocreales: Clavicipitaceae) are used for the biological control of several agricultural pests. The soil-dwelling predatory mite, Stratiolaelaps scimitus (Womersley) (Acari: Acaridae) is also frequently used alone or in combination with other biological control agents. There are few reports on the use of M. brunneum or S. scimutus against R. robini. The objectives of this research were to investigate the in vitro effect of different predatory mite ratios of S. scimitus on R. robini mortality and the combined use of a M. brunneum-based granule with S. scimitus as potential strategies to manage this pest. Mortality of R. robini in Petri dishes containing predators was significantly higher than without predators. When soil-filled containers containing R. robini were treated with both M. brunneum granules and S. scimitus, the lower densities of the bulb mite were obtained with the highest ratio of predator/prey mites. The number of bulb mites in the containers treated with only M. brunneum was significantly lower than the untreated control. These results demonstrate the potential for releasing of S. scimitus alone and in combination with M. brunneum granules to manage R. robini.

A modified method for mass production of generalist predatory edaphic mite Gaeolaelaps aculeifer as a candidate for biological control of the saffron corm mite

ABSTRACT Gaeolaelaps aculeifer (Canestrini) (Acari: Laelapidae) is an edaphic predator of several agricultural pests. Development of simple and low-cost innovative mass rearing techniques and the use of this predator to control soil pests have high importance. For the mass production of G. aculeifer, three growth environments were evaluated. Saffron corms and layered potatoes were used to feed mites, and the mixture of “cocopeat + perlite and saffron chaff” was used to maintain more moisture and to prepare the environment for more ventilation and more porosity, increase hiding places, and provide shelter for the predatory mites to lay eggs. In each treatment, 40 male and female adults of G. aculeifer were released. To feed the predators, approximately 500–800 bulb mites were added to each unit, weekly. The results showed a 27-fold increase in G. aculeifer populations within 30 days. After 60 days, the rate of predator population decreased. Saffron is an expensive plant with abundant benefits and diverse uses. The bulb mite Rhizoglyphus robini is a potentially serious pest damaging saffron corms. This method gives saffron growers the choice to improve the biological control of bulb mites in their saffron fields.

Toward an understanding of the chemical ecology of alternative reproductive tactics in the bulb mite (Rhizoglyphus robini)

BackgroundUnder strong sexual selection, certain species evolve distinct intrasexual, alternative reproductive tactics (ARTs). In many cases, ARTs can be viewed as environmentally-cued threshold traits, such that ARTs coexist if their relative fitness alternates over the environmental cue gradient. Surprisingly, the chemical ecology of ARTs has been underexplored in this context. To our knowledge, no prior study has directly quantified pheromone production for ARTs in a male-polymorphic species. Here, we used the bulb mite—in which males are either armed fighters that kill conspecifics, or unarmed scramblers (which have occasionally been observed to induce mating behavior in other males)—as a model system to gain insight into the role of pheromones in the evolutionary maintenance of ARTs. Given that scramblers forgo investment into weaponry, we tested whether scramblers produce higher quantities of the putative female sex-pheromone α-acaridial than fighters, which would improve the fitness of the scrambler phenotype through female mimicry by allowing avoidance of aggression from competitors. To this end, we sampled mites from a rich and a poor nutritional environment and quantified their production of α-acaridial through gas chromatography analysis.ResultsWe found a positive relationship between pheromone production and body size, but males exhibited a steeper slope in pheromone production with increasing size than females. Females exhibited a higher average pheromone production than males. We found no significant difference in slope of pheromone production over body size between fighters and scramblers. However, scramblers reached larger body sizes and higher pheromone production than fighters, providing some evidence for a potential female mimic strategy adopted by large scramblers. Pheromone production was significantly higher in mites from the rich nutritional environment than the poor environment.ConclusionFurther elucidation of pheromone functionality in bulb mites, and additional inter- and intrasexual comparisons of pheromone profiles are needed to determine if the observed intersexual and intrasexual differences in pheromone production are adaptive, if they are a by-product of allometric scaling, or diet-mediated pheromone production under weak selection. We argue chemical ecology offers a novel perspective for research on ARTs and other complex life-history traits.

Screening and evaluation of acaropathogenic fungi against the bulb mite Rhizoglyphus robini

• Fungal isolates effective in controlling bulb mites ( Rhizoglyphus robini ) were screened. • The selected fungal isolates have high virulence and thermotolerance. • Three Metarhizium anisopliae were determined to be the most suitable for bulb mite control. Bulb mites ( Rhizoglyphus robini ) damage the bulbs, corns, and tubers of garlic, shallots, and onions. Bulb mites have recently become a serious problem because of the continuous use of acaricides, which has resulted in resistance among bulb mite populations. Thus, there is a need to find alternative control methods to suppress bulb mite populations. Here, we report the results of screening pathogenic fungi for the control of R. robini . The initial screen was performed using 342 isolates of entomopathogenic fungi from soils from South Korea. As a result, 57 isolates of putative acaropathogenic fungi were selected from cadavers of bulb mites supporting fungal sporulation. However, 11 isolates were finally selected for further study through a re-evaluation of the pathogenicity of the isolates. These isolates were identified as two isolates of Metarhizium pemphigi , two isolates of Metarhizium pingshaense , and seven isolates of Metarhizium anisopliae by a microscopic examination and sequence analysis of the ITS region and EF-1α gene. The virulence, thermotolerance and UV-B tolerance of the 11 isolates were further evaluated and compared. Eight isolates showed more than 80% mortality and three isolates showed 100% mortality at 7 days after treatment. The thermotolerance of conidia showed a large difference depending on the fungal isolate, and five isolates showed a conidial germination rate of approximately 60% or more even after 2 h of heat treatment. On the other hand, the UV-B tolerance was very low in all the isolates, and only one isolate showed more than approximately 80% tolerance to 0.1 J cm −2 , but the other isolates showed a conidial germination rate of less than 30%. Based on all of the above results, three isolates, M. anisopliae 4–3-2, 4–8-1, and 4–31-2, were the most effective isolates in controlling bulb mites and could be considered promising biological control agents against bulb mites.

Development and reproduction of Rhizoglyphus robini Claparéde (Astigmata: Acaridae), an emerging pest in Indonesia, on six host plants

ABSTRACT The bulb mite, Rhizoglyphus robini Claparède, is an important pest of plants with bulbs, corms or tubers. The mite is ubiquitously found infesting subterranean organs of crops in fields, greenhouses, and storage facilities. Although the mite is of economic and biosecurity importance, the information about its biology is still obscure. In this current study, the development and reproduction of R. robini on carrot, taro corm, ginger rhizome, shallot bulb, garlic clove, and onion bulb were studied under laboratory conditions. The intrinsic rate of increase (rm ) of the mite was estimated by an equation relating the mite reproduction rate to its pre-reproductive time. The results showed that the development, fecundity, and rm of the mite were significantly affected by the host plant variability. The mite development lasted for 9.80 to 12.56 days, the fecundity was 45.05 to 242.00 eggs per female, and the rm was 0.210 to 0.271. The higher rm values of R. robini on carrot, shallot, garlic, and onion alarms the potential of the mite to become a new threat to those commodities. The biological information of R. robini obtained in this study can be applied to evaluate the differential susceptibility of the tested host plants.

Efficacy of soil isolates of entomopathogenic fungi against the bulb mite, Rhizoglyphus robini (Acari: Acaridae)

The bulb mite, Rhizoglyphus robini, is a serious pest of garlic, onion and other crops. The mite is usually found in association with dangerous fungal pathogens such as Fusarium spp. Control of this pest has relied upon the use of synthetic acaricides but chemical control of the bulb mite is difficult because it is able to develop resistance quickly. Thus, alternative control methods, e.g. biological control, need to be developed and implemented. The aim of this study was to assess efficacy of selected strains of entomopathogenic fungi (EPF) against adult females of R. robini under laboratory conditions. New EPF strains were isolated from soil samples collected in onion and garlic fields in the Czech Republic and Israel using soil elution and cultivation on selective media. Fungal species were determined using macroscopic, microscopic and molecular markers. The efficacy against R. robini females was tested in 17 isolated and 3 reference strains of EPF. Results revealed high variability among species and strains. The highest efficacy against R. robini mites was found in strains of Metarhizium anisopliae isolated from soil samples collected in the Czech Republic which caused mortality up to 99.3%, and a Metarhizium indigoticum strain from Israel causing 98.3% mortality after four days of bioassay. Isaria fumosorosea strains did not caused mortality higher than 40%. The lowest virulence was found in Beauveria spp. strains causing mortality of mites between 5 and 25%. Median lethal time (LT50) and median lethal concentration (LC50) in the three most virulent strains ranged between 2 and 4 days and between 1.01×104 and 2.36×105 spores/ml, respectively. The concentration-response models indicated that the M. indigoticum strain is more lethal than M. anisopliae strains. The present study showed that some strains of entomopathogenic fungi, especially from the genus Metarhizium, could be perspective biocontrol agents against R. robini.

<p class="Body"><strong>Acute toxicity and sublethal effects of metal oxide nanoparticles against the bulb mite</strong></p>

Crocus sativus L. (Iridaceae) known as saffron is the most commercially important medicinal food product in Iran and worldwide because of its significance for exporting commercial. However, the health of this plant is adversely threatened by abiotic and biotic stress. Bulb mite Rhizoglyphus robini Claparede (Acari: Acaridae) as abiotic stress is oligophagous and the main pest of tuber plants, commonly found in all the cultivated saffron producing areas could decrease saffron economic value. The mites tunnel through corms allowing the entry of fungal and bacterial pathogens. The widespread use of commercial pesticides in modern agriculture to protect crops from pests has caused significant public concern because of their side impacts on the environment and non-target species. Nanotechnology has been used in the production, processing, storage, packaging, and transport of agricultural products. Newly, oxide nanoparticles have been introduced as novel pesticides against pests and fertilizer. This study was conducted as an effective and environmentally-friendly method to control the growth of Rhizoglyphus robini. The lethal and sublethal effects of metal oxide nanoparticles (MNPs) including nano copper oxides (nano-CuO), nano magnesium oxide (nano-MgO), nano zinc oxide (nano-ZnO), nano titanium dioxide (nano-TiO2), and nano iron oxide (nano-Fe2O3) which their lethal concentrations ranged between 159.2 and 1036.4 mg L-1 were studied on Rhizoglyphus robini adult females. The contact effect of the tested MNPs was evaluated using the corm dip bioassay method. Assays showed that the contact toxicity of the nano-CuO treatment (229.1 mg L-1) was higher than other MNPs. To assess the sublethal effects of the MNPs, adult females were exposed to the LC25 concentration of MNPs, and life history and life-table parameters of the surviving Rhizoglyphus robini were investigated. The exposure to sublethal concentrations of the tested MNPs prolonged the egg incubation, larval period, and nymphal period significantly when compared to the control mites. Compared to other MNPs or control mite, nano-MgO and nano-TiO2 led to the longest duration of the total immature stages (11.32 and 11.32, respectively). The net reproductive rate (R0), the intrinsic rate of increase (rm), the finite rate of increase (λ), and the generation time (T) were significantly different between control and MNP treatments. The population exposed to ZnO-, MgO-, and TiO2-nanoformulations had a much lower rm value (0.164, 0.164, and 0.171 d-1, respectively) compared to the control population (0.231 d-1) and those exposed to Fe3O4- and CuO-nanoformulations (1.19 and 1.19 d-1, respectively). According to our findings, all tested MNPs, especially CuO-, ZnO-, and MgO-nano formulations, have a potential application for use in the management of Rhizoglyphus robini.

A modeling exercise to show why population models should incorporate distinct life histories of dispersers

AbstractDispersal is an important form of movement influencing population dynamics, species distribution and gene flow between populations. In population models, dispersal is often included in a simplified manner by removing a random proportion of the population. Many ecologists now argue that models should be formulated at the level of individuals instead of the population level. To fully understand the effects of dispersal on natural systems, it is therefore necessary to incorporate individual‐level differences in dispersal behavior in population models. Here, we parameterized an integral projection model, which allows for studying how individual life histories determine population‐level processes, using bulb mites, Rhizoglyphus robini, to assess to what extent dispersal expression (frequency of individuals in the dispersal stage) and dispersal probability affect the proportion of successful dispersers and natal population growth rate. We find that allowing for life‐history differences between resident phenotypes and disperser phenotypes shows that multiple combinations of dispersal probability and dispersal expression can produce the same proportion of leaving individuals. Additionally, a given proportion of successful dispersing individuals result in different natal population growth rates. The results highlight that dispersal life histories, and the frequency with which disperser phenotypes occur in the natal population, significantly affect population‐level processes. Thus, biological realism of dispersal population models can be increased by incorporating the typically observed life‐history differences between resident phenotypes and disperser phenotypes, and we here present a methodology to do so.

A standardized method for rearing Rhizoglyphus robini (Astigmata: Acaridae)

Rhizoglyphus robini Claparede (Acari: Astigmata: Acaridae) is a mite infesting crop such as saffron corms, onions, garlic, leeks and lilies. Bulb mites were observed associated with diseased saffron corms in Vermont research sites, confirming their pest status in New England. To assess the efficacy of different IPM and biological controls a standard method to rear bulb mites in the laboratory was essential. This study focused on developing an efficient laboratory medium to rear R. robini. Bulb mites were extracted from infected saffron corms in Vermont (USDA plant-hardiness zone 5a [− 20° to − 15 °F]). A bulb mite culture was first established on potato dextrose agar (PDA) medium with an average moisture content of 67% at the Entomology Research Laboratory, University of Vermont. Bulb mite species identification and R. robini separation were done, and bulb mites were incubated in a dark chamber at 25 °C. While establishing the R. robini laboratory culture, contamination of microbial disease restricted populations. Experiments were conducted to determine the most suitable growth medium that supported bulb mite population and minimized microbial disease. Three treatments were tested: 1. antibiotics (chloramphenicol) + fungicide (dodine) + PDA, 2. antibiotics + PDA and 3. PDA only. The results showed significantly (P ≤ 0.05) larger populations of R. robini in Petri dishes containing PDA with antibiotics compared to other treatments. The greatest number of bulb mites was observed 14 to 20 days after introduction on the growth media.