Mite Eggs Research Articles

Allergenicity of house dust mite eggs

Allergenicity of house dust mite eggs

The entomopathogenic fungus Beauveria bassiana and its compatibility with triflumuron: effects on the twospotted spider mite Tetranychus urticae

Laboratory studies were conducted to determine the effects of the mycoinsecticide Naturalis-L ( Beauveria bassiana conidial formulation) on the twospotted spider mite Tetranychus urticae . Compatibility of B. bassiana with triflumuron (benzoylphenyl urea typically used as an insecticide, but also with acaricide effects), was also investigated in order to incorporate both in the control of this pest. For each juvenile stage, 180–22,800 viable conidia/mL on deutonymphs, 380–12,160 viable conidia/mL on protonymphs, and 712–7480 viable conidia/mL on larvae were evaluated. For the adult stage, the concentrations ranged from 213 to 54,720 viable conidia/mL. The mortality data used in the analysis were those accumulated after 5 days of treatment for deutonymphs and protonymphs, 7 days for larvae and 9 days for adults. The lethal concentration to kill 50% (LC 50 ) for the juvenile stages was 3184 viable conidia/mL (their probit-log concentration regression lines were the same), and 1949 viable conidia/mL for adults. No significant differences in mortality were observed among egg age classes (24-, 48-, 72-, and 96-h-old eggs) at the tested concentrations (1400–22,800 viable conidia/mL). When B. bassiana was combined with 0.25 g Alsystin (25% triflumuron as a wettable powder)/L, mite egg mortality decreased significantly. Triflumuron reduced mycelial growth but not conidial germination of B. bassiana . This fungus is a possible candidate to be included in integrated pest management programs with triflumuron of T. urticae . In such programs, the possible antagonist effects of triflumuron should be considered.

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator?2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips.3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside.4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.

Cellular immune responses to ovalbumin and house dust mite in egg-allergic children.

Although IgE-mediated food (egg) allergy is typically lost with age the underlying immune mechanisms are not understood, particularly in relation to the development of persistent IgE-mediated aeroallergen sensitivity. Lymphoproliferation and cytokine responses (IL-5, IL-10, IL-13 and IFN-gamma) to house dust mite (HDM) allergen and egg ovalbumin (OVA) were assessed using peripheral blood mononuclear cells (PBMC) from children aged 6 months to 5 years (n = 59) with acute IgE-mediated egg allergy (urticaria and angiedema or anaphylaxis), as confirmed by positive skin prick testing (SPT). Of these 46 had positive SPT on the day of blood collection and 13 had outgrown egg allergy (negative SPT and successful egg challenge). Where possible, responses were compared with previous data from nonallergic children of similar ages (n = 107). Transient lymphoproliferative responses to OVA were seen in both egg-allergic and nonallergic children, but were more marked and more prolonged in egg-allergic children. Younger egg-allergic children (< 18 months) showed a mixed Th0 cytokine response to OVA, with readily detectable IFN-gamma, IL-5, IL-13 IL-10. Although IL-13 and IL-5 responses (OVA) correlated in younger egg-allergic children, there was a dissociation of these Th2 responses with age. Loss of clinical reactivity to egg was associated with almost complete loss of IL-5 responses and OVA-specific lymphoproliferation. Although IL-13 levels tended to be lower with age, this was not significant. Strong IFN-gamma and IL-10 responses to OVA persisted in older children after loss of OVA-specific lymphoproliferation. Lymphoproliferative responses to HDM also developed earlier in egg-allergic children compared with nonallergic children. Th1 (IFN-gamma) responses to HDM were largely below detection prior to 18 months of age, but increased significantly with age. In egg-allergic children Th2 (IL-5, IL-13) HDM responses also progressively increased with age. At 3 years of age almost all egg-allergic children had positive SPT to HDM and positive lymphoproliferative responses to HDM, with strong Th1 and Th2 (Th0) cytokine production. IL-5 responses (rather than IL-13) responses most closely reflected clinical food allergy, with dissociation of IL-5 and IL-13 responses in older and egg-tolerant children. In this population, food and aeroallergen sensitivity was not associated with inability to produce IFN-gamma, but rather with mixed Th2 and Th1 (Th0) responses. Strong IL-10 and IFN-gamma responses where associated with the development of tolerance, suggesting persistent 'regulatory' populations of OVA-specific T cells, rather than clonal deletion of OVA responsive T-cells.

SELETIVIDADE DE CHLORFENAPYR E FENBUTATIN-OXIDE SOBRE DUAS ESPÉCIES DE ÁCAROS PREDADORES (ACARI: PHYTOSEIIDAE) EM CITROS

Com o uso de bioensaios, verificaram-se os efeitos residual de contato, ovicida e de persistência dos produtos chlorfenapyr e fenbutatin-oxide sobre duas espécies de ácaros predadores, Iphiseiodes zuluagai Denmark &amp; Muma e Euseius alatus DeLeon (Acari: Phytoseiidae), associados ao ácaro da leprose-dos-citros Brevipalpus phoenicis (Geijskes) (Acari: Tenuipalpidae). O efeito total sobre os adultos foi estudado por meio do método residual de contato com pulverização em superfície de vidro, conforme metodologia da IOBC. O efeito ovicida foi avaliado por meio de pulverização direta sobre os ovos dos ácaros predadores, também em superfície de vidro. A persistência dos produtos foi avaliada em laboratório, em arenas confeccionadas com folhas de laranjeira pulverizadas no campo, aos 0; 5; 15 e 30 dias após a aplicação. Os resultados obtidos mostraram que chlorfenapyr foi nocivo ao I. zuluagai e E. alatus e o fenbutatin-oxide foi levemente nocivo a E. alatus e inócuo a I. zuluagai. Nenhum dos produtos apresentou efeito ovicida. Fenbutatin-oxide apresentou baixa persistência para ambas as espécies de ácaros predadores, e chlorfenapyr, na dosagem de 31,3 ml, foi de baixa persistência, enquanto, na dosagem de 62,5 ml, foi moderadamente persistente. O fenbutatin-oxide apresentou-se inócuo e levemente nocivo aos ácaros predadores I. zuluagai e E. alatus, respectivamente, e de baixa persistência para ambas as espécies

Prey-Stage Preference in Generalist and Specialist Phytoseiid Mites (Acari: Phytoseiidae) When OfferedTetranychus urticae(Acari: Tetranychidae) Eggs and Larvae

We tested 13 species of phytoseiid mites for prey preferences between eggs and larvae of twospotted spider mite, Tetranychus urticae Koch. In general, oligophagous, specialized spider mite predators preferred eggs whereas more polyphagous, generalist predators showed no prey-stage preference or preferred larvae: Phytoseiulus macropilis (Banks), P. persimilis Athias-Henriot, Neoseiulus longispinosus (Evans), and Neoseiulus fallacis (Garman) preferred eggs; Kampimodromus aberrans (Oudemans), Galendromus occidentalis (Nesbitt), N. barkeri Hughes, N. californicus (McGregor), N. cucumeris (Oudemans), and Typhlodromus pyri Scheuten showed no prey-stage preference; and Amblyseius andersoni Chant, Euseius finlandicus (Oudemans) and E. hibisci (Chant) preferred larvae. When the ratio of spider mite eggs to larvae was altered, adult females of E. finlandicus, G. occidentalis, N. fallacis, and P. persimilis maintained relatively constant feeding ratios, resulting in slight negative prey-stage switching due mostly to the changes in prey-stage ratios offered. However, when offered a prey-stage ratio that was biased toward eggs, adult females of T. pyri exhibited positive switching, feeding disproportionately more on eggs than would be expected given the change in the ratio offered. There was no clear trend in the effect of starvation time on prey-stage preference for N. fallacis adult females. The egg preference of N. fallacis was also not affected when individuals were reared solely on eggs or larvae of T. urticae and subsequently tested as adult females. Individuals of field-collected strains of N. fallacis and P. persimilis showed no differences in prey-stage preferences when compared with individuals from long-term reared laboratory strains of the same species. However, individuals of one field-collected strain of G. occidentalis showed a stronger preference for eggs than individuals from three other strains (one laboratory and two field-collected) of the same species.

Quality Control of the Mass-Reared Predatory Mite, Amblyseius cucumeris (Acarina: Phytoseiidae)

Quantity, sex ratio, survival, fecundity, mobility, predation and feeding preference were investigated to assess the post-shipment quality of commercially available strains of Amblyseius cucumeris from 3 different companies supplying this product to growers in Canada. The quantity of live mites promised on the labelz was close to the number estimated from subsampling for companies A and C; whereas company B had provided only 66% of the number of mites on the label. The sex ratio of mites from company A was close to 1:1, whereas companies B and C had a greater proportion of females. All 3 products failed to meet the IOBC guideline of 7 eggs per female over 7 days at 22°C, although companies B and C were close to this standard. Survival of mites over 9 days was quite variable among companies. Only products B and C reached the IOBC standard of 80% survival over 5 days. Product A with only 58% survival on day 5 is unacceptable. Mobility of mites was good and similar for products B and C; whereas mites from product A were the least mobile. Predation tests indicated similar consumption of grain mite nymph in 24 hours for A. cucumeris from products B and C, whereas mites from product A consumed approximately 25% less nymphs in 24 hours. Feeding preference tests of adult predator mites from companies B and C indicated a preference for spider mite eggs rather than grain mite eggs.

Macrolophus caliginosus: Functional response to whiteflies and preference and switching capacity between whiteflies and spider mites

AbstractLaboratory experiments were performed with adult female Macrolophus caliginosus Wagner (Heteroptera: Miridae) at 22°C on bean plants to determine the functional response towards whiteflies, as well as the preference and switching capacity between the two prey species: whiteflies and spider mites. Predation of females presented with first instars of Trialeurodes vaporariorum Westwood (Homoptera: Aleyrodidae) was of a Type III functional response. The observed maximum predation was approximately 75 first instars at high prey densities within a 24‐h period. The preference of M. caliginosus females between eggs of T. vaporariorum and Tetranychus urticae Koch (Acarina: Tetranychidae) changed with the ratio of offered prey. The preference for T. vaporariorum eggs increased non‐linearly with increasing proportions of this prey type. The average maximum predation of whitefly and spider mite eggs were approximately 166 and 111 eggs per day, respectively, at the highest ratio of the two preys. The proportion of M. caliginosus females found on the test plants at the end of the experiment increased with prey density suggesting that this mirid spends more time in areas with high prey density. Macrolophus caliginosus females are voracious predators of eggs and first instars of T. vaporariorum as well as of spider mite eggs and may thus be a valuable addition to existing methods of biological control of T. vaporariorum and T. urticae.

Predatory mites avoid ovipositing near counterattacking prey.

Attacking prey is not without risk; predators may endure counterattack by the prey. Here, we study the oviposition behaviour of a predatory mite (Iphiseius degenerans) in relation to its prey, the western flower thrips (Frankliniella occidentalis). This thrips is capable of killing the eggs of the predator. Thrips and predatory mites - apart from feeding on each other - can also feed and reproduce on a diet of pollen. Because thrips may aggregate at pollen patches, such patches may be risky for oviposition by the predatory mites. We found that, in absence of thrips, predatory mites lay their eggs close to pollen, but further away when thrips are present. Predatory mite eggs near pollen were killed more frequently by thrips than when they were deposited further away. The oviposition behaviour of the predatory mite was also studied in absence of thrips, but in presence of the alarm pheromone of thrips. This pheromone is normally secreted upon contact with predators or competitors. When applied close to the pollen. predatory mites oviposited significantly further away from it. When the alarm pheromone was applied away from the food source, most eggs were found near the pollen. These results indicate that female predatory mites show flexible oviposition behaviour in response to the presence of their counterattacking prey.

Trichomes and spider-mite webbing protect predatory mite eggs from intraguild predation.

Predaceous arthropods are frequently more abundant on plants with leaves that are pubescent or bear domatia than on plants with glabrous leaves. We explored the hypothesis that for some predatory mites this is because pubescence affords protection from intraguild predation. In laboratory experiments, we tested whether apple leaf pubescence protected Typhlodromus pyri eggs from predation by western flower thrips, Frankliniella occidentalis. To investigate the effect of pubescence further, we added cotton fibers to trichome-free leaves. We also determined whether webbing produced by Tetranychus urticae protected Phytoseiulus persimilis eggs from predation by F. occidentalis. Predation by thrips on T. pyri eggs oviposited on field-collected pubescent "Erwin Bauer" apple leaves was significantly less than on glabrous "Crittenden" apple leaves. Phytoseiid eggs oviposited in the cotton fibers were preyed upon significantly less than those on the trichome-free bean disk. Increasing the cotton fiber density from 5 to 20 fibers only slightly further reduced predation by thrips on T. pyri eggs. Thrips fed upon significantly fewer P. persimilis eggs oviposited in Te. urticae webbing than eggs oviposited on a surface that differed only in the absence of Te. urticae web. We conclude that a complex leaf topography reduces intensity of intraguild predation in this system.

What omnivores eat: direct effects of induced plant resistance on herbivores and indirect consequences for diet selection by omnivores

Summary 1. Omnivory, where an animal crosses trophic boundaries, is thought to be common in natural and managed communities. Foraging theory predicts that omnivores will balance their diet as a result of nutritional needs, food quality and availability of alternate foods. We investigated diet selection of the western flower thrips [Frankliniella occidentalis (Pergande)], a herbivore under some circumstances, and a predator under other circumstances. 2. We demonstrate that induced plant resistance can indirectly affect diet selection by thrips. The density of herbivorous spider mites is reduced on induced plants compared to controls and is also positively correlated with the number of mite eggs that the thrips consume. 3. In choice tests, mite eggs from induced plants were less preferred by thrips than eggs from control plants. Mite egg size was also smaller on induced plants compared to controls. However, this alone did not explain the diet selection by thrips. In a field experiment, thrips avoided colonizing induced plants, but they were attracted to induced plants that we inoculated with mites. Thus, the presence of herbivorous prey on induced plants attenuated the negative effects of induced resistance on thrips colonization. 4. Feeding decisions of thrips can be influenced by several factors. We showed previously (Agrawal, Kobayashi &amp; Thaler 1999a) Influence of prey availability and induced host plant resistance on omnivory by western flower thrips. (Ecology, 80, 518–523.) that reducing plant quality can cause omnivores to shift towards relatively more predation than herbivory. We show now that on induced plants, reduced prey density and quality may antagonize this shift towards increased predation. 5. Induced plant resistance has negative effects on both the plant‐based food resource (direct effect) and the animal‐based food resource (indirect effect) of omnivorous thrips. Thus, variation in the quantity and quality of food items interact to determine the diet selection of omnivores.

The potential of Lagenaria rootstock to confer resistance to the carmine spider mite, Tetranychus cinnabarinus (Acari: Tetranychidae) in Cucurbitaceae.

Antibiosis and resistance of six Cucurbita and two Lagenaria accessions to the carmine spider mite, Tetranychus cinnabarinus Boisduval, were evaluated in the laboratory. Significant differences among accessions were observed three days after the inoculation of detached leaf discs. The Lagenaria accessions, Slawi and Sus, proved to be the most resistant to mites, with average populations of mite eggs, 87 and 95%, respectively less than that of the susceptible C. pepo accession, Orangetti. The Cucurbita accessions, Tace, Brava, Tetsukabuto, Phoenix and TZ-148 had mite egg totals 4, 9, 13, 26 and 40%, respectively, less than those of accession Orangetti. The Sus accession of Lagenaria was resistant to T. cinnabarinus from the four-leaf stage until fruit set in laboratory and field tests. Grafting the susceptible Brava onto Sus rootstock increased the resistance of the scion to the same level as that of non-grafted Sus. Grafting the susceptible Cucumis melo Noy Yizre'el on resistant or susceptible rootstocks of Cucurbita and Lagenaria accessions did not affect its susceptibility to T. cinnabarinus. The results indicate that resistance to T. cinnabarinus can be transferred by grafting from Lagenaria stocks to Cucurbita scions but not in the opposite direction.

INFLUENCE OF PREY AVAILABILITY AND INDUCED HOST-PLANT RESISTANCE ON OMNIVORY BY WESTERN FLOWER THRIPS

Theory predicts that the balance of nutritional needs, food availability, and the quality of particular food items are important factors in the feeding decisions of omnivorous animals. In this study we investigate factors that affect the feeding decisions of an omnivorous thrips (Frankliniella occidentalis) that eats both animal prey and plant foliage. In the presence of prey (mite eggs), adult and larval thrips consumed nearly half the amount of plant tissue as did thrips without prey. We manipulated host-plant quality by exposing plants to spider mite feeding. In the absence of prey, systemically induced plant responses following herbivory reduced the amount of feeding by thrips compared to that on uninduced control plants. In the presence of prey, induced responses caused a shift in the feeding preferences of thrips: thrips consumed half the amount of plant material and twice the number of prey on induced plants as did thrips on uninduced control plants. Our findings are relevant to understanding the complex factors that shape food-web interactions in nature. Variation in host-plant quality and availability of prey can exert a strong influence on the feeding preferences of omnivores. In addition, induced resistance may be a particularly useful biological-control strategy because it reduces herbivorous pest populations directly, and indirectly by causing a shift toward predation in naturally occurring omnivores.

Influence of Prey Availability and Induced Host-Plant Resistance on Omnivory by Western Flower Thrips

Theory predicts that the balance of nutritional needs, food availability, and the quality of particular food items are important factors in the feeding decisions of omnivorous animals. In this study we investigate factors that affect the feeding decisions of an omnivorous thrips (Frankliniella occidentalis) that eats both animal prey and plant foliage. In the presence of prey (mite eggs), adult and larval thrips consumed nearly half the amount of plant tissue as did thrips without prey. We manipulated host-plant quality by exposing plants to spider mite feeding. In the absence of prey, systemically induced plant responses following herbivory reduced the amount of feeding by thrips compared to that on uninduced control plants. In the presence of prey, induced responses caused a shift in the feeding preferences of thrips: thrips consumed half the amount of plant material and twice the number of prey on induced plants as did thrips on uninduced control plants. Our findings are relevant to understanding the complex factors that shape food-web interactions in nature. Variation in host-plant quality and availability of prey can exert a strong influence on the feeding preferences of omnivores. In addition, induced resistance may be a particularly useful biological-control strategy because it reduces herbivorous pest populations directly, and indirectly by causing a shift toward predation in naturally occurring omnivores.

Did dinosaurs come up to scratch?

The high specificity of bird ectoparasites has frequently been interpreted to mean that they have a long evolutionary history1. Either they were present as parasites before the main diversification of birds in the Cretaceous period2, or they evolved independently into avian parasites on several occasions. The recent discovery of dinosaurs with feathers3 suggests that birds may have inherited some of their ectoparasites from feathered theropod dinosaurs. We have now found microscopic egg-like structures on the surface of a fossil feather of approximately 120 million years old from the Crato Formation (Lower Cretaceous period) of northeast Brazil. They closely resemble the eggs of ectoparasitic feather mites and indicate an early origin for this specialized group of Acari.

Significance of mite prey in the diet of the onion thrips Thrips tabaci Lindeman (Thysanoptera: Thripidae)

Second‐instar larvae of the phytophagous thrips, Thrips tabaci, consumed significantly more spider mite (Tetranychus urticae Koch) eggs than did any other T.tabaci life stage. We supplemented two plant diets with mite eggs to assess whether the inclusion of prey could make up completely for dietary deficiencies in the host plant. Therefore, turnip weed (Rapistrumrugosum L.) floral tissue (a major breeding host of T.tabaci) and cotton vegetative tissue (a host on which T.tabaci populations dwindle) were compared. In both cases, prey in the diet reduced the developmental time from egg to adult and increased fecundity over that achieved on a host‐plant diet alone, but had no effect on immature mortality or adult life span. Females on turnip weed plus mite eggs produced more eggs than those on cotton cotyledons plus mite eggs. We discuss the role of facultative predation (or opportunism) in the ecology of T. tabaci.

Effects of Ozone on Reproduction of Twospotted Spider Mite (Acari: Tetranychidae) on White Clover

Twospotted spider mite, Tetranychus urticae Koch, is a significant pest of peanut, Arachis hypogeae L., that continues to present problems as an induced pest despite recent widespread implementation of IPM practices. Effects of ozone (O3) on reproduction of twospotted spider mites feeding on an O3-sensitive clone and an O3-resistant clone of white clover, Trifolium repens L., were investigated in a greenhouse in continuous-stirred tank reactor chambers. Mite eggs of narrow age distribution (approximately 6 h) were placed on white clover plants exposed to 5 treatment levels of O3. Constant amounts of O3 were added to charcoal-filtered air for 6 h per day to achieve 5 mean concentrations ranging from 10 to 112 nl per liter. Plants were exposed to O3 approximately 9 d before infestation with mites; daily exposures continued for approximately 20 d after mite infestation. The developmental stage of each mite was recorded at approximately 2-d intervals until females were sexually mature (approximately 10 d) and began ovipositing. Thereafter, the cumulative number of eggs produced per mite was recorded. After approximately 5 d of oviposition, each adult mite was removed and the percentage hatch of eggs remaining on each plant was measured for an additional 5 d. Ozone caused more chlorosis and necrosis on the O3-sensitive clover clone than on the O3-resistant clover clone. Increasing O3 levels caused a significant linear decrease in developmental period of the mites. Estimates of time to 1st oviposition decreased linearly with increasing O3. Estimates of time of 1st hatch of 2nd-generation eggs decreased linearly with increasing O3. Elevated O3 levels appear to decrease the time required for female mites to develop from egg to ovipositing adult, which may have a profound effect on the intrinsic rate of population increase. Different responses by mites feeding on resistant plants versus susceptible plants suggests that this is a plant-mediated response.

Leaf domatia and foliar mite abundance in broadleaf deciduous forest of north asia

Plant morphology may be shaped, in part, by the third trophic level. Leaf domatia, minute enclosures usually in vein axils on the leaf underside, may provide the basis for protective mutualism between plants and mites. Domatia are particularly frequent among species of trees, shrubs, and vines in the temperate broadleaf deciduous forests in north Asia where they may be important in determining the distribution and abundance of mites in the forest canopy. In lowland and montane broadleaf deciduous forests at Kwangn;akung and Chumbongsan in Korea, we found that approximately half of all woody species in all forest strata, including many dominant trees, have leaf domatia. Pooling across 24 plant species at the two sites, mites occupied a mode of 60% (range 20-100%) of domatia and used them for shelter, egg-laying, and development. On average, 70% of all active mites and 85% of mite eggs on leaves were found in domatia; over three-quarters of these were potentially beneficial to their hosts. Further, mite abundance and reproduction (expressed as the proportion of mites at the egg stage) were significantly greater on leaves of species with domatia than those without domatia in both forests. Effects of domatia on mite abundance were significant only for predaceous and fungivorous mite taxa; herbivore numbers did not differ significantly between leaves of species with and without domatia. Comparable patterns in broadleaf deciduous forest in North America and other biogeographic regions suggest that the effect of leaf domatia on foliar mite abundance is general. These results are consistent with several predictions of mutualism between plants and mites, and indicate that protective mutualisms may be frequent in the temperate zone.

European Red Mite Control with Pyramite in Apple Orchards, 1997

Abstract This study evaluates the effect of Pyramite on ERM when this compound is used to control white apple leafhopper (WALH), Thylocyba pomaria McAtee in apple orchards. A RCB design was used with three replications, each replicate consisting of a single standard sized apple tree. Treatments were evaluated by counting the number of mite eggs and motile forms on 10 leaves per replicate at different intervals after treatment. The leaves were selected randomly at shoulder height from each replicate. The treatments were applied on 23 Jun 1997. A Nobili (Molinella-Bologna, Italy) airblast sprayer was used. It was calibrated to deliver 107 gpa (1000 L/ha) at 150 PSI (1034.7 kPa).

Relative acute effects of low pH and high iron on the hatching and survival of the water mite (Arrenurus manubriator) and the aquatic insect (Chironomus riparius)

AbstractWe investigated the relative effects of low pH and high iron on a water mite, Arrenurus manubriator and an aquatic insect, Chironomus riparius. Eggs and active stages were exposed in static renewal toxicity tests to pH 6, 5, 4, 3, and 2, made by adding sulfuric acid to reconstituted soft water, or to iron levels of 200, 400, 600, 800, and 1,000 mg/L, made by adding ferrous sulfate to soft water at pH 4. Experiments were conducted at 22°C with a 16:8‐h photoperiod, and treatments were replicated three times with at least nine individuals per treatment. Data were analyzed with a logistic response function and one‐way ANOVA for pH and iron tests, respectively. Egg hatching was reduced at pH 2 for midges and at pH 3 for mites. Iron had no effect on hatching for either species. Survival of midge larvae was partially reduced at pH 4, and survival of mite deutonymphs, larvae, female and male adults was reduced at pH 3. Survival of midge larvae, and mite deutonymphs and male adults was reduced at 400, 200, and 1,000 mg Fe/L, respectively. Mite female adults and larvae were unaffected by iron. Higher metabolic requirements of unfed immature stages, the gelatinous covering of mite and insect eggs, the longer incubation period of mite eggs, and the greater osmoregulatory potential of adult mites may have contributed to the differences observed.