Mite Density Research Articles

Mite density, not diversity, declines with biomass removal in Patagonian woodlands

Belowground biodiversity loss from anthropogenic causes is far less addressed and quantified than aboveground biodiversity loss. Soil fauna supports soil productivity and biogeochemical cycles, and their decline needs further research. We tested the effects of a woodland harvest gradient (0, 30, 50, and 70% biomass removal) on litterfall, mesofauna density, and Oribatida diversity in three sites of northwestern Patagonia (Argentina). Sites contrasted in plant community structure and productivity. Acari from litter and soil were compared. Annual litter production showed a 58% decline at the highest harvest intensity level, which was constant across sites. Litter structural α- diversity decreased with the highest intensity harvest only at the high productivity site. The density of soil-inhabiting Acari did not change with increasing harvest intensity, while the density of Acari inhabiting the litter decreased by 65% at the highest harvest intensity. Within Acari, Oribatida inhabiting the litter had the most significant density decline with increasing harvest intensity. Oribatida richness and α- diversity only differed among sites, suggesting resistance to increasing biomass removal despite shifts in litter production and litter structural diversity. Prostigmata did not respond to increasing biomass removal either in soil or litter. Our study is the first to assess Acari response to an aboveground biomass removal gradient in southern woodlands. Applying high biomass removal to low productivity sites can compromise micro detritivore density and thus, impair its functional role. Site productivity should be considered in management plans entailing conservation of soil fauna in southern woodlands.

A Promising Predator-In-First Strategy to Control Western Corn Rootworm Population in Maize Fields

Western Corn Rootworm is a pest of maize that mostly damages roots. Many alternative strategies have been explored to control this species, with little or non-lasting success, and it remains a threat to maize production worldwide. Gaeolaelaps aculeifer, a soil-dwelling predatory mite that inhabits the first few centimeters of the soil, showed high predatory potential against WCR larvae in the laboratory. In this study, we explored the efficiency of G. aculeifer against WCR in more realistic contexts. First, we infested maize plants isolated in pots in a greenhouse with WCR, and tested the impact of different densities of mites on plant protection. Using standard indicators of WCR population presence and impact, we confirmed that G. aculeifer has the potential to control WCR at densities starting from 100 mites/plant. Then, considering that the release of a large amount of biocontrol agents at WCR emergence might be too costly and constraining for large-scale implementation, we tested the efficiency of a predator-in-first strategy in a maize field infested by WCR. The goal was to introduce fewer G. aculeifer combined with Aleuroglyphus ovatus eggs as an alternative food source in order to let the mite population grow in the field and reach sufficient density at the critical stage for protection. This strategy gave comparable results to pesticide on all indicators examined in our field trial, highlighting the potential to sustainably manage this pest.

CORRELATION BETWEEN HOUSE DUST MITE DENSITY WITH HEALTHY HOUSE CRITERIA AND ASTHMA STATUS IN PEDIATRIC PATIENTS

Abstract Background: Asthma is a chronic respiratory disease most often found in children and has the highest prevalence in developing countries. House dust mites are the second most common trigger of asthma whose habitat is influenced by the criteria for a healthy.Objective: Understanding the correlation between sleep density and asthma status in pediatric patients and criteria for a healthy house.Methods: This study was an analytical observational method with a cross sectional study design that took place from June to October 2020. It involved 25 respondents of children with asthma patients aged 3-11 years. There is a confounding variable, namely the criterion score for a healthy house. Dust samples were collected in the bedroom of the respondent diagnosed with bronchial asthma. The identification process using the floating method was carried out at the Parasitology Laboratory, Faculty of Medicine, Diponegoro University, Semarang Indonesia. Respondent data were analyzed using statistical software programs. Non-parametric test with lambda correlation test.Results: The mean of house dust mite’s density in the respondent's house was 3.68 ± 2.32. House dust mite’s density was associated with the criteria for a healthy house (p <0.05), but house dust mite density was not related to the asthma status of pediatric patients (p> 0.05).Conclusion: There is no correlation between pediatric asthma status and house dust mite density.

Seasonal Activity and Sensitivity of Some Tomato Cultivars to Tetranychus urticae Koch.

The results of the current study showed that the first appearance of Tetranychus urticae on the leaves of tomato plants in the field was on 7/14/2020 and that the highest average number of mites was on 17/8/2020 (371.78) individuals/10 leaves, while the lowest average for these numbers was recorded on 5 /10 (23.19 individuals), and the highest average of these numbers was on the Nabaa variety (240.05 individuals), while the lowest average of these numbers was recorded on the local variety (102.26 individuals). The correlation was positive and significant between the number of mites and the average weekly temperature (0.750) * and significant negative (0.685 * -) with the relative humidity. The lowest mean of infestation was on the tomato cultivars Sandra (69.97%) and GS (63.05%). Based on the criteria of % of infested leaves and mite population density, the tomato cultivars GS and local were the least sensitive to infection, respectively. The correlation values were insignificantly negative between of the affected leaves and the content of these leaves of proteins (-0.262), carbohydrates (-0.476) and flavonoids (-0.221), while it was significant positive with phenols (0.751) and insignificantly positive with alkaloids (0.432).

Varroa mite and deformed wing virus infestations interactively make honey bees (Apis mellifera) more susceptible to insecticides

Varroa mite is one of the major adverse factors causing honey bee population decline. In this study, Varroa destructor-infested and uninfested honey bee colonies were established by selective applying miticide (Apivar® amitraz). Mite population was monitored monthly (April–October 2016), and deformed wing virus (DWV) loading was detected seasonally (April, July, and October). Four immunity- and two physiology-related gene expressions, natural mortality, and susceptibility to five insecticides were comparatively and seasonally examined in field-collected honey bee workers. Results showed that Apivar-treated bee colonies had minor or undetectable mite and DWV (using RT-qPCR) infestations in whole bee season, while untreated colonies had substantially higher mite and DWV infestations. In untreated colonies, Varroa mite population irregularly fluctuated over the bee season with higher mite counts in Jun (318 ± 89 mites dropped in 48 h) or August (302) than that (25 ± 4 or 34) in October, and mite population density was not dynamically or closely correlated with the seasonal shift of honey bee natural mortality (regression slope = −0.5212). Unlike mite, DWV titer in untreated colonies progressively increased over the bee season, and it was highly correlated (R2 = 1) with the seasonal increase of honey bee natural mortality. Significantly lower gene expressions of dor, PPO, mfe, potentially PPOa and eat as well, in untreated colonies also indicated an association of increased DWV infestation with decreased physiological and immunity-related functions in late-season honey bees. Furthermore, bees with lower mite/DWV infestations exhibited generally consistently lower susceptibilities (contact and oral toxicities) to five representative insecticides than the bees without Apivar treatment. All of these data from this study consistently indicated an interaction of Varroa/viral infestations with insecticide susceptibilities in honey bees, potentially through impairing bee's physiology and immunity, emphasizing the importance of mite control in order to minimize honey bee decline.

Safety and Efficacy of Topical Lotilaner Ophthalmic Solution 0.25% for the Treatment of Demodex Blepharitis: A Pilot Study.

Purpose Evaluate safety and efficacy of topical lotilaner ophthalmic solution, 0.25% for the treatment of Demodex blepharitis. Patients and Methods. 15 patients with Demodex blepharitis, defined as >10 collarettes on the upper lid, lid margin erythema, and Demodex density of ≥1.5 mites/lash on microscopy, were treated bid for 28 days with lotilaner ophthalmic solution, 0.25%. Contact lens wear, artificial eyelashes, and lid structural abnormalities were among the exclusion criteria. No other antibacterial, antiparasitic, or anti-inflammatory treatment or lid hygiene products were permitted. Patients were assessed on Days 7, 14, 28, 60, and 90. Outcome measures were changes in collarette grade and mite density on Day 28. Adverse events and changes in intraocular pressure (IOP), corrected distance visual acuity (CDVA), and slit-lamp biomicroscopy were assessed. Results Mean collarette grade (upper lids) improved from 3.07 ± 0.21 to 0.79 ± 0.19 on Day 28; the change was statistically significant for both upper and lower lids from Day 14 on. Mean mite density per lash decreased from 2.28 ± 0.16 at baseline to 0.14 ± 0.05 at Day 28 (p < 0.0001). Mite eradication (0 mites) was documented in 57.1% of eyes. The effects were durable through Day 90. There were no adverse events and little to no change in CDVA or IOP. The drop was well tolerated, with no discontinuations due to ocular irritation. Conclusion Topical lotilaner ophthalmic solution, 0.25% for 4 weeks, showed promising efficacy for the treatment of Demodex blepharitis. This novel treatment appears to be safe and well tolerated. Randomized controlled studies are needed to confirm the results.

Abundance of domestic mites in dwellings of children and adolescents with asthma in relation to environmental factors and allergy symptoms

Exposure to house dust allergens, mainly from domestic mites, is an important cause of allergic reactions in sensitized asthmatic patients. A total of 63 dust samples were collected from 16 flats in Bytom (south Poland); in each flat a person (age 4–17 years) suffering from bronchial asthma lived with his/her family. Mite density was calculated as the number of specimens per g of dust. The results were compared with household features and the data were statistically analyzed. In total 566 mite specimens were isolated, including 526 members of the family Pyroglyphidae (93%). The dominant species were Dermatophagoides pteronyssinus (60% of the total count) and Dermatophagoides farinae (32%). Pyroglyphids were found in all mite positive samples (68%) of which 35% also contained non-pyroglyphids, including glycyphagids, cheyletids and gamasids. The results suggest associations between the density of some mite taxa (per g of dust) and the following indoor environmental factors: presence of pets, number of inhabitants, coal-stoves as a type of heating, cleaning frequency, higher relative humidity, presence of flowers and PVC windows. The severity of asthma seems to be associated with the numbers of D. farinae, total domestic mites and live mites per g of dust.

Population dynamics and biological aspects of Tetranychus urticae on three squash (Cucurbita pepo) varieties

Squash (Cucurbita pepo L.) is a popular plant in Egypt, field study was carried out to evaluate the susceptibility of three squash varieties, i.e. Eskandarani, Hytech and Miletto infestation with two spotted spider mite Tetranychus urticae. Temperature and humidity played a strong role in the T. urticae infestation on squash varieties where there is a positive relationship between the population of T. urticae and temperature while negative between the population and humidity. Also, temperature plays an important role on biology of T. urticae where they completed their development and reproduced at all tested temperatures (20, 25, 30ºC).Also developmental time, oviposition period, adult longevity and life span decreased with increasing temperatures, while daily oviposition rate and fecundity increased with increasing temperatures. Therefore 30 ºC is the ideal degree in which all stages of growth are shortened. On the other hand the susceptibility of squash varieties to the T. urticae infestation attributable to phytochemical contents which varied from variety to another, and affect mite density levels. A positive relationship was found between mite infestations and squash leaf contents i. e. total carbohydrates, total protein and total lipids in squash leaves, while a negative one found with alkaloids and total phenolic compounds, total flavonoids and total carotenoids and chlorophyll (a&amp;b).Thus temperature and humidity and phytochemical contents of plant leaves has an important effect on infesting squash by T. urticae.

Development and population growth of the two-spotted spider mite (Tetranychus urticae Koch) on strawberry fertilized with different doses and sources of organic fertilizers

ABSTRACT This study deals with the evaluation of the biological parameters and population growth of TSSM in strawberry fertilized with different doses and sources of organic fertilizers. Plants were grown in a greenhouse where the treaments were: Bokashi compost, Penergetic®, boiled chicken manure solution at 2.5%, 5%, 7.5%, and 10% concentrations; and control (unfertilized plants). The immature duration, adult females longevity, number and viability of eggs were determined through mite rearing on leaf disks taken from the treated plants. Populations of TSSM adult females on strawberry leaves were also recorded in greenhouse. In addition, the levels of nitrogen, potassium and phenolic compounds were determined in leaves. Shorter immature period, higher female longevity, higher number and viability of eggs were obtained for TSSM reared on Bokashi fertilized plants. Denser adult TSSM population was also found on Bokashi fertilized plants in greenhouse. A moderate and positive correlation was observed between nitrogen foliar levels and egg numbers, adult female longevity, as well as between potassium foliar amount and mites density. The leaf content in phenolic compounds was correlated positively with the deutonymph duration and negatively with population density recorded in greenhouse.

Counting phoretic Varroa destructor mites dislodged from honey bees (Apis mellifera) sampled under the escape board: a simple, precise and rapid method

In order to control infestation of the parasitic mite Varroa destructor infestation, it is essential to determine mite density in a colony. In daily practice, the beekeeper needs a simple, reproductive, safe and fast method. We have developed a new technique of sampling under the escape board to count dislodged mites from bees and compared it with the measure on brood - which is considered as the "Gold Standard." On average, the number of mites measured under the escape board was 60% lower compared to the number of mites measured on brood and the ratio escape board/brood was proportional to the number of mites counted on brood with a narrow dispersion around the predicted value (the 95% limits of agreement around the bias were ± 23%). This new method is simple, rapid and safe, inasmuch as dislodging and counting mites from sampled bees can be performed later on.

Safety and efficacy of lotilaner ophthalmic solution, 0.25% for the treatment of blepharitis due to demodex infestation: A randomized, controlled, double-masked clinical trial

PurposeTo evaluate the safety and efficacy of lotilaner ophthalmic solution, 0.25% for the treatment of blepharitis due to Demodex infestation compared to vehicle control. MethodsIn this phase II, randomized, controlled, double-masked clinical trial, 60 eligible participants with Demodex blepharitis were randomly assigned in a 1:1 ratio to receive either topical lotilaner ophthalmic solution, 0.25% (Tarsus Pharmaceuticals, Inc., Irvine, CA) (study group) or the vehicle without lotilaner (control group) bilaterally twice a day for 28 days. Participants were followed at Days 7, 14, 28, 60 and 90. The efficacy parameters were change in collarette grade and Demodex density at Day 28. Safety parameters were adverse events, changes in corrected distance visual acuity (CDVA), intraocular pressure (IOP) and slit-lamp biomicroscopy. ResultsThe study group showed a statistically significant decrease in collarette grade compared to the control group beginning at Day 14 (p = 0.003) in the upper eyelid and at Day 28 (p = 0.003) in the lower eyelid. Decreases in both lids were maintained through Day 90 (p < 0.001). At Day 28, mite eradication was achieved in 66.7% and 25.9% of eyes in the study and control group (p = 0.005); at Day 90, these proportions were 68.2% and 18.5% (p = 0.001), respectively. No serious adverse events or clinically significant changes in CDVA and IOP were observed. ConclusionFor Demodex blepharitis, treatment with lotilaner ophthalmic solution, 0.25% for 4 weeks is safe and effective. The improvement in collarette grade and mite density observed during the treatment period persisted for at least two months following treatment cessation.

No influence on population dynamics of spider mites in cotton fields of intercropping with walnut, a poor-quality host

Intercropping is a common agricultural practice used to improve crop yields and profits; however, the intercrop species and its quality as a host for the main crop's key pests can affect the pests' population dynamics under intercropping conditions. Fruit trees - cotton intercropping systems are commonly applied in Xinjiang of China, and previous studies have confirmed that intercropping of cotton with species (e.g., jujube and apple) that are good spider mite hosts can increase the spider mite density in cotton. In this study, the effect of intercropping cotton with walnut, which is a poor host for the key spider mite pest Tetranychus truncatus, was examined. For this spider mite, feeding on walnut leads to significantly longer development time for larvae + nymphs and a short oviposition period which leads to a lower total fecundity, lower survival rate and lower intrinsic growth rate (rm) compared to cotton. Correspondingly, in the two-year, multiple-scale field study, we found that the population dynamics of spider mites in cotton did not significantly differ in the field plots between a walnut-cotton intercropping system and monocultural cotton. Similar trends of spider mite density were also observed in commercial fields. Based on previous work and the current study on fruit tree-cotton intercropping systems, we concluded that while intercropping cotton with intercrop species that are suitable spider mite hosts increase the spider mite population in intercropped cotton, the use of a poor host plant such as walnut has no significant effect on spider mites populations in cotton. Hence, our study results improved the understanding of pest management and monitoring in intercropped cotton systems.

Demodex infestation as a cause of sensitive skin in a dermatology outpatient clinic.

Sensitive skin is subjective cutaneous hyperreactivity to environmental factors. Demodicosis is a skin disorder caused by Demodex mites. There may be a link between demodicosis and sensitive skin. This study aimed to examine facial Demodex mites density and other factors associated with sensitive skin in patients. A total of 349 randomly selected patients presented to the dermatology department. The research data were collected using a questionnaire form that included the participants' sociodemographic and lifestyle characteristics, a sensitive skin questionnaire, the Dermatology Life Quality Index (DLQI), and European Health Interview Survey (EHIS). Patients underwent standardized superficial skin surface biopsy of 4 areas of the face. D.folliculorum count greater than 5mites/cm2 was considered positive. In relation to Demodex, there was an increase in skin sensitivity with higher Demodex density (p=0.04). There was a statistically significant, weak positive correlation between skin sensitivity and DLQI score (r=0.33, p=0.00), and there was also a significant but very weak negative correlation between skin sensitivity and EUROHIS (r=-0.164, p=0.002). Skin sensitivity was more common in patients with a concomitant dermatological disease (p=0.01) and increased with more frequent cosmetic use (p=0.00). Alongside other risk factors, for the patients presenting with complaints of sensitive skin, investigating Demodex population density may help alleviate sensitive skin symptoms with appropriate therapies and preventive measures.

Pests of Florida Hops: Preliminary Observations

Surveys of arthropods associated with hops at the University of Florida's Gulf Coast Research and Education Center, Wimauma, Florida, USA, from 2016 to 2020 reveal that spider mites are the primary pest of the crop. Lepidoptera and lace bugs also were observed causing occasional damage to the crop. Whiteflies and thrips have been observed on the crop in low numbers. The tall (5.5 m) canopy of the hops trellis creates a challenge to applying insecticides with adequate coverage. Sampling data indicate that spider mite densities tend to be higher in the upper canopy than at ground level. Efforts to control spider mites with releases of the commercially available predator Phytoseiulus persimilis showed promise. Naturally occurring spider mite predators observed on hops at Gulf Coast Research and Education Center include Stethorus sp., Neoseiulus sp., Orius sp., and trash bugs.

The Biocontrol Agent Pyemotes zhonghuajia Has the Highest Lethal Weight Ratio Compared with Its Prey and the Most Dramatic Body Weight Change during Pregnancy.

Simple SummaryTo explore the biocontrol potential of Pyemotes zhonghuajia, we studied the paralytic process, time to lethality, efficiency, reproductive development, and the ability to search for Spodoptera litura larvae. We found that one newly emerging P. zhonghuajia female could kill a third instar larva greater than 680,000 times her own body weight. An individual P. zhonghuajia adult female was able to kill S. litura eggs and first to third instar larvae. Pyemotes zhonghuajia could develop on eggs, first to sixth instar larvae, and pupae, but only produced offspring on the eggs and pupae. The presence of 50 or 100 P. zhonghuajia resulted in significantly higher mortality rates of first, second, and third instar S. litura larvae in a 2 cm searching range compared with other searching ranges (4.5 and 7.5 cm). Therefore, P. zhonghuajia could potentially be used to control S. litura.Pyemotes spp. are small, toxic, ectoparasitic mites that suppress Coleoptera, Hemiptera, and Lepidoptera plant pests. To explore their potential use as a biocontrol agent, we studied the reproductive development, paralytic process, time to lethality and mortality, and searching ability of Pyemotes zhonghuajia on different developmental stages of the oriental leafworm moth, Spodoptera litura. Pyemotes zhonghuajia gained 14,826 times its body weight during pregnancy. One single P. zhonghuajia female could rapidly kill one S. litura egg and first to third instar larvae, but not fourth to sixth instar larvae, prepupae, or pupae within 720 min. Pyemotes zhonghuajia could develop on eggs, first to sixth larvae, and pupae, but only produced offspring on the eggs and pupae. A single P. zhonghuajia female (an average weight of 23.81 ng) could paralyze and kill one S. litura third instar larvae (an average weight of 16.29 mg)—680,000 times its own weight. Mites significantly affected the hatch rate of S. litura eggs, which reduced with increasing mite densities on S. litura eggs. Releasing 50 or 100 P. zhonghuajia in a 2 cm searching range resulted in significantly higher mortality rates of S. litura first instar larvae within 48 h compared to second and third instar larvae in searching ranges of 4.5 and 7.5 cm within 24 h. To the best of our knowledge, this is the first study to reveal that P. zhonghuajia undergoes the greatest changes in weight during pregnancy of any adult female animal and has the highest lethal weight ratio of any biocontrol agent.

Immunological detection in indoor environments of house dust mite allergens using avian antibodies - IgY: An innovative tool

IgY technology has emerged as an alternative for antibody production with immunodiagnostic purposes. Recently, we produced avian antibodies (IgY) against group-1 dust mite allergens of Dermatophagoides sp (Dsp) and Blomia tropicalis (Bt). These allergens are important sensitizing agents that contribute to the pathophysiology of allergy rhinitis and asthma in patients living in tropical areas. The purpose was to explore the utility of IgY for detecting dust mite allergens in indoor environments. We collected 100 samples of dust from mattresses of asthmatic individuals living in two cities on the Colombian Caribbean coast. We used an in-home indirect enzyme-linked immunosorbent assay (ELISA) to detect the mite allergens using two IgYs (IgY-PO2 and IgY-PO4). We determined the IgY detection limit using whole body extracts of Dsp and Bt; likewise, IgY specificity was probed against one crude extract of cockroach, as well as the precision and accuracy of measurements. Both antibodies recognized allergens in the mite extracts, even at the lowest tested concentration (0.05 µg/mL); none reacted with the cockroach extract demonstrating their specificity for mite allergens. On the other hand, IgY-PO4 showed the best precision (intra-assay: CV &lt; 6.99%; inter-assay: CV ≤ 8.71%) and an accuracy: 80.62 – 100.39%. Allergen levels detected were consistent with the mite density present in the dust samples. We confirmed the usefulness of IgY-PO2 and IgYPO4 for detecting dust mite pollution in indoor environments.

Demodex folliculorum and Demodex brevis (Acari: Demodecidae) and their association with facial and non-facial pathologies

ABSTRACT The mites Demodex folliculorum (Simon) and Demodex brevis Akbulatova are part of the regular human skin fauna, found in the pilosebaceous unit, and their infestations might cause the disease known as demodicosis. Inflammatory response is triggered by this interaction in patients, causing the appearance of several facial dermatoses. In the present revision, mites will be characterized and their association with dermatological diseases shall be discussed, as well as diagnostic methods, immune response to their infestations, and the major treatments used for Demodex-related cases. Demodex infestations both in hair follicles (D. folliculorum) and in sebaceous glands (D. brevis) might lead to the aggravation of dermato-facial pathologies, and trigger a local inflammatory reaction in many cases, associated with mite density and their potential as vectors of pathogenic microorganisms. The treatments for these Demodex-associated pathologies have proven to be effective, particularly in decreasing density, and consequently, in mitigating symptoms and the overall patient clinical condition.

Effects of botanical acaricides on Raoiella indica and Oligonychus sp. and their toxicity on two species of phytoseiid predatory mites

In this study, three commercial botanical acaricides (BA) were evaluated on two species of phytophagous mites, the red palm mite (Raiella indica) and the papaya mite (Oligonychus sp.). The toxicity of the BA on the predatory mites Neoseiulus californicus and Phytoseiulus persimilis was also assessed. For R. indica, CinnAcar and EPA-90 caused more than 90% decrease in the population density in the laboratory. In field trial, CinnAcar was the most effective in suppressing the mite population density. For Oligonychus sp., CinnAcar and EPA-90 caused up to 88.5 and 95.2% mortality in the laboratory. In greenhouse trial, EPA-90 caused more than 90% decrease in the population density of motile stages. Residual exposure showed that EPA-90 had moderate toxicity to the phytoseiid predators, causing 48% mortality in N. californicus and 55% mortality in P. persimilis, whereas CinnAcar and NeemAcar produced 22 to 32% mortality.

Phenology and abundance of date palm mite Oligonychus afrasiaticus (McGregor) (Acari: Tetranychidae) in Riyadh, Saudi Arabia.

In the present study, we evaluated the effect of management practices, fruit season, host habitats (young and old fronds, date fruits and grasses), and temperature on the phenology and abundance of the date palm mite (DPM). The study was conducted in two date palm orchards (two plots each): a managed and an unmanaged plot. The phenology of DPM was assessed based on adult cumulative mite days (ACMDs), while mean mite density was used to assess the mite abundance on different host habitats. The ACMDs and mean mite density were significantly different between managed and unmanaged plots on different host habitats in both fruiting and off-seasons. The date fruits had highest ACMDs during fruiting season. While young fronds had significantly higher ACMDs than on old fronds an grasses during both seasons in both plots.. The temperature and season type significantly affected the mean density of DPM eggs and adults. There was a significant effect of host habitats mean density of DPM eggs and immatures. Based on the adult phenology and abundance of DPM, the mite overwinters in young fronds and aerial offshoots of infested date palm trees. These overwintering DPM caused the seasonal date fruit infestation, each year. Additionally, different phytophagous and predatory mites, which co-occur with DPM, and were found on different host habitats affected the phenology and abundance of DPM. Moreover, the change in DPM body color was related to the host habitat that they fed in. Exceptionally, the brown color of females collected during the winter season could be due to physiological changes due to low temperature. In DPM males collected from different host habitats throughout the study, some morphological variations in the width of the knob, height of the hook, and the angle between the knob axis and dorsal margin of the shaft were also recorded. The results of this study suggest that young fronds and grasses are the suitable sites for DPM survival and overwintering. Hence, the management practices, early in the fruit season and/or during off fruit winter months, should be directed towards these habitats. These could provide efficient reduction in seasonal infestation of DPM.

Economic injury level for Tetranychus urticae Koch on parthenocarpic cucumber under protected environment in north-western Indian Himalayas

Damage potential of two-spotted spider mite, Tetranychus urticae Koch (Tetranychidae), on parthenocarpic cucumber, Cucumis sativus Linnaeus, under naturally ventilated polyhouse was assessed by artificially releasing of different mite densities (2, 4, 8 and 16 mites/leaf) at 4, 6 and 8-weeks after transplanting (WAT) coinciding with early, mid and late crop stage. Mites were restricted to feed for 4-weeks (limited feeding duration) as well as throughout crop growth (unlimited feeding duration). Injury inflicted to leaves by mite feeding increased significantly with the advancement in duration of infestation. Tetranychus urticae infestation exhibited varying levels of stunting effects on plant growth. Crop yield under limited feeding duration increased over unlimited feeding duration from 10.7 to 22.4, 6.4 to 15.4 and 0.6 to 2.2% for the infestation initiated in early, mid and late crop stages, respectively, with the loss in marketable yield to vary from 7.4 to 53.3%. Relationship deduced between reduction in yield and cumulative mite days (CMDs) revealed one mite day feeding reduced the yield up to 0.112 g/plant. Whereas, on initial mite density basis, reduction in yield varied from 12.87 to 51.95 g/plant/mite at different plant growth stages. The economic injury level (EIL) determined was very low (0.83 mites/leaf) for the infestation initiated in early stage, whereas, for the infestation initiated in later part of plant growth (6 and 8-WAT), EIL of 1.25 and 3.33 mites/leaf were established.