Corn Pollen Research Articles

Comparison of Corn Pollen and Natural Fine Particulate Matter Transport in Streams: Can Pollen Be Used as a Seston Surrogate?

The transport of fine particulate organic matter (FPOM) in streams is an important process that links stream reaches, but until recently little was known about the distances traveled by fine particles in streams or the mechanisms governing their transport, deposition, and resuspension. Within the past decade, a number of studies have measured FPOM transport distances using either natural stream particles or a variety of artificial particles as FPOM surrogates. The purpose of our study was to compare estimates of FPOM transport distances in streams using: 1) radioactively labeled natural FPOM, and 2) corn pollen as an FPOM surrogate. We compared the particle types with simultaneous releases at 3 locations in Bloomington Creek, Idaho, and in a streamside flume in Pennsylvania. Mean transport distances in the stream and in the flume ranged from 49 to 637 m for corn pollen, compared with 23 to 1164 m for natural FPOM. Particle deposition velocities, which adjust for the effects of water depth and velocity on ...

Impact of cysteine proteinase inhibition in midgut fluid and oral secretion on fecundity and pollen consumption of western corn rootworm (Diabrotica virgifera virgifera)

Cysteine proteinases predominate in the midgut fluid (MF) and oral secretion (OS) of adult western corn rootworm (WCR) based on their mild acidic pH optima (pH 6.0), enhanced activities after treatment with thiol reducing agents, and inhibition by selective cysteine proteinase inhibitors (PIs). Four cysteine PIs including E-64, calpeptin, calpain inhibitor II, and leupeptin (also a serine PI) strongly inhibited azocaseinolytic activity in a dose-dependent manner in both the MF and OS. The most significant effect on adult female WCR of cysteine PI consumption with corn pollen was the reduction in fecundity, but female survival was not apparently affected. Mean fresh weights for all PI-fed females were also lower than control groups. All PI-fed groups [E-64, calpain inhibitor I (Cal I) and leupeptin] had a significantly lower daily egg production than respective corn pollen-fed controls. E-64 was more potent than leupeptin and Cal I on inhibiting fecundity, which correlates with their relative anti-proteinase potency in vitro. E-64, Cal I, and leupeptin at 1.5-2 nmol/beetle/day reduced fecundity down to 25-45% of control values. Reduced egg production by PI-fed beetles results from a combination of the direct inhibition of protein digestion and a post-ingestive negative feedback mechanism, which reduces food intake. The supplement of ten essential amino acids into the E-64-treated pollen enhanced up to 3.7-fold the number of eggs laid compared to the E-64-fed group without these amino acids, suggesting that egg production is dependent on the supply of essential amino acids from corn pollen proteolysis.

Assessment of Corn Pollen as a Food Source for Two Tephritid Fruit Fly Species

The melon fly, Bactrocera cucurbitae (Coquillett) is a serious pest of cucurbit crops. Although melon fly females oviposit in cucurbit crops, both males and females are frequently associated with a range of nonhost plants, including both crops such as corn (Zea mays C. Linnaeus) and wild plants such as castor bean (Ricinus communis C. Linnaeus) that occur within the cropping area or along the crop borders. This association with nonhost plants has been used for control purposes through the technique of spraying protein baits incorporating a toxicant on these nonhost plants. Association of melon flies to corn has not been reported to be tied to any phenological stage of corn. We report field studies that show that melon flies, as well as oriental fruit flies, B. dorsalis (Hendel), may show increased population levels in corn at the time of, and subsequent to, flowering and pollen shed and suggest that this population increase may be tied to pollen consumption. Before this, pollen had not been reported to be an important food source for the tropical Bactrocera spp.

Effects of dietary transgenic Bt corn pollen on larvae of Apis mellifera and Galleria mellonella

SUMMARYThe effects of dietary transgenic Bt corn pollen on 4–5–day-old honey bee worker larvae were examined. We measured larval and pupal mortalities, pupal weight, and haemolymph protein concentration of newly emerged adults after they were fed (as larvae) various pollens (mixed bee pollen, non-transgenic corn pollen, Cry1A(b) or Cry1F corn pollen). There were no significant differences in all the parameters tested between larvae fed transgenic Bt corn pollen Cry1 A(b) or Cry1 F and non-transgenic corn pollen. We also evaluated Bt corn pollen as a potential control for wax moth larvae in a laboratory study. We fed first instar wax moth larvae three types of pollen: non-transgenic corn pollen, Cry1 A(b) corn pollen, and Cry1F corn pollen. We found that the mortality of larvae fed Cry1 F corn pollen was significantly greater than the mortality of larvae fed Cry1 A(b) corn pollen or non-transgenic corn pollen (P < 0.05). In each trial Cry1 F fed larvae showed 100% mortality. Our studies suggest that transgenic Bt corn pollen does not pose a threat to honey bee larval development and has the potential to serve as an alternative control for wax moth.

Antifeedant effects of proteinase inhibitors on feeding behaviors of adult western corn rootworm (Diabrotica virgifera virgifera).

Low-molecular-weight peptidyl proteinase inhibitors (PIs) including leupeptin, calpain inhibitor I, and calpeptin were found to be potent antifeedants for adult western corn rootworm (WCR) against the phagostimulation of cucurbitacin B (Cuc B) or a corn pollen extract (CPE). Leupeptin was the strongest (ED50 = 0.36 and 0.55 nmol/disk for Cuc B and CPE, respectively) among PIs tested with an antifeedant potency much stronger than the steroid progesterone (ED50 = 2.29 and 5.05 nmol/disk for Cuc B and CPE, respectively), but slightly less than the reference alkaloid, strychnine (ED50 = 0.17 and 0.37 nmol/disk for Cuc B and CPE, respectively). All active PIs contain a di- or tripeptidyl aldehyde moiety, indicating that PIs exert their antifeedant effects by covalent interaction with putative sulfhydryl (SH) groups on taste receptors as do these PIs with cysteine proteinases. However, opposite inhibition potency against Cuc B versus CPE by two thiol-group reducing agents, DTT and L-cysteine, and the results with other cysteine-modifying reagents obscure the net functional role of SH groups at WCR taste chemoreceptors. Surprisingly, the model phagostimulant for diabroticites, Cuc B, was more easily counteracted by these feeding deterrents than the stimulants present in CPE. Three-dimensional structure-antifeedant relationships for the PIs suggest that a novel taste chemoreception mechanism exists for these peptidyl aldehydes or that they fit partially into a strychnine binding pocket on protein chemoreceptors. Favorable economic benefit may be achieved if PIs are discovered to be useful in adult WCR control, since both pre- and postingestive sites would be targeted.

Coleopteran-specific Cry3Bb Toxin from Transgenic Corn Pollen Does Not Affect the Fitness of a Nontarget Species,Coleomegilla maculataDeGeer (Coleoptera: Coccinellidae)

Coleomegilla maculata DeGeer is a polyphagous predator that is important for suppressing pest populations in corn. We evaluated the impact of Cry3Bb-expressing transgenic corn pollen (event MON863) on C. maculata fitness parameters in the laboratory. C. maculata larvae were fed mixtures of pollen containing 0, 25, 50, 75, or 100% transgenic pollen, aphids, or were not fed; and the duration of each instar and pupal weight were compared among treatments. In a second trial, other C. maculata larvae were reared on one of the pollen mixtures or artificial diet; and the duration of larval and pupal stages, pupal weight, adult mobility, adult survivorship, and female fecundity were compared among treatments. There were no differences in any of the fitness parameters among C. maculata in the treatments fed different mixtures of pollen. Beetles in the pollen mixture treatments had faster larval development times, greater larval survivorship, and greater pupal weight than the beetles fed only aphids or an artificial diet. We conclude that we did not detect any effects on the fitness of C. maculata that ingested pollen from event MON863. However, these results do not necessarily apply to other transgenic crops expressing toxins specific to Coleoptera.

Settling speed of corn ( Zea mays) pollen

The settling speed of corn pollen is fundamental for determining the distance that corn pollen can be transported in the atmosphere and for determining its probability of being deposited on plants and the ground. The settling speed, v S, and the corresponding volume-equivalent diameter, D e, of corn pollen grains were measured at various times after pollen was released from the anther. The geometric size of pollen grains decreased with increasing time after release from the anther due to loss of water during drying. The density of corn pollen ranged from 1.25 g cm −3 when freshly collected to 1.45 g cm −3 when dry. Values of v S ranged from 21 cm s −1 for pollen grains with D e of 76– 80 μm to 32 cm s −1 for pollen grains with D e of 103– 106 μm . Over a wide range of pollen sizes (76– 106 μm ), which included pollen collected from two hybrid varieties and one inbred line, v S was described well ( P<0.000001) by theoretical values based on the size, shape, and density of the pollen and using an aerodynamic drag coefficient given by c d=24 Re −1(1+0.158 Re 2/3).

Evaluation of dietary effects of transgenic corn pollen expressing Cry3Bb1 protein on a non‐target ladybird beetle, Coleomegilla maculata

AbstractA transgenic corn event (MON 863) has been recently developed by Monsanto Company for control of corn rootworms, Diabrotica spp. (Coleoptera: Chrysomelidae). This transgenic corn event expresses the cry3Bb1 gene derived from Bacillus thuringiensis (Berliner), which encodes the insecticidal Cry3Bb1 protein for corn rootworm control. A continuous feeding study was conducted in the laboratory to evaluate the dietary effect of MON 863 pollen expressing the Cry3Bb1 protein on the survival, larval development, and reproductive capacity of the non‐target species, Coleomegilla maculata DeGeer (Coleoptera: Coccinellidae). First instar C. maculata (less than 24 h old) and newly emerging adults (less than 72 h old) were fed individually on a diet mixture containing 50% of MON 863 pollen, non‐transgenic (control) corn pollen, bee pollen (a component of normal rearing diet), or potassium arsenate‐treated control corn pollen. In the larval tests, 96.7%, 90.0%, and 93.3% of C. maculata larvae successfully pupated and then emerged as adults when fed on MON 863 pollen, non‐transgenic corn pollen, and bee pollen (normal rearing) diets, respectively. Among the larvae completing their development, there were no significant differences in the developmental time to pupation and adult emergence among the transgenic corn pollen, non‐transgenic corn pollen, and bee pollen diet treatments. All larvae fed on arsenate treated corn pollen diet died as larvae. For tests with adults, 83.3%, 80.0%, and 100% of adult C. maculata survived for the 30 days of the test period when reared on diets containing 50% of MON 863 pollen, non‐transgenic corn pollen, and bee pollen respectively. While the adult survival rate on MON 863 pollen diet was significantly less than that on the bee pollen diet, there was no significant difference between the MON 863 and non‐transgenic corn pollen treatments. During the period of adult testing, an average of 77, 80, and 89 eggs per female were laid by females fed on the MON 863 pollen, control corn pollen, and bee pollen, respectively; no significant differences were detected in the number of eggs laid among these treatments. These results demonstrate that when offered at 50% by weight of the dietary component, transgenic corn (MON 863) pollen expressing Cry3Bb1 protein had no measurable negative effect on the survival and development of C. maculata larvae to pupation and adulthood nor any adverse effect on adult survival and reproductive capacity. Relevance of these findings to ecological impacts of transgenic Bt crops on non‐target beneficial insects is discussed.

GM crops go walkies

Two recent reports revive concerns about the implications of large-scale use of genetically modified (GM) crops. The Mexican government announced that GM DNA could be detected in seeds collected from endogenous corn varieties at 15 different locations, the New York Times reports. So far, it's unclear what the source of the DNA is, but experts think it likely that transgenic ‘Bt’ corn has interbred with local plants. Bt corn carries a bacterial toxin gene that protects the plant from the European corn borer pest. Considering that Bt corn, or indeed any GM crop, cannot be grown in Mexico, the findings suggest that geography and plant variety impose smaller barriers for transmission of transgenes than previously anticipated. Bt corn was also a focus of attention in six papers published on-line in PNAS on 14 September (Zangerl et al., Sears et al., Hellmich et al., Pleasants et al., Stanley-Horn et al., Oberhauser et al.). Previous work had indicated that, under laboratory conditions, Bt toxin not only killed European corn borers but also harmless black swallowtail caterpillars. Here, the authors report that Bt corn pollen can contaminate neighboring plants with doses high enough to kill the swallowtail caterpillars. However, the studies also show that Bt toxin rarely exceeds lethal doses in the fields and poses only a minor threat to the ecosystem. Moreover, the harmful Bt corn variant Bt176 is only a prototype – new Bt corn variants are not harmful, and Syngenta, the producer of Bt corn, has already taken Bt176 off the market. J.d.B.

Bt versus monarchs, part II

Two years ago, researchers provided evidence that corn transgenic for Bt, the pesticide from Bacillus thuringiensis, was harmful to monarch butterfly larvae. Now US researchers from the private and public sectors respond with their own studies that show that there is little if any risk from Bt corn pollen. Six studies appeared in the Proc. Natl. Acad. Sci. U. S. A. (published online 14 September 2001; http://www.pnas.org), that, in general, agree that Bt corn has a low risk. One author, Mark Sears (University of Guelph, Ontario, Canada), told reporters, ‘there is less than a 1 or 2% risk of a monarch caterpillar being exposed.’ One biotech critic, Jane Rissler (Union of Concerned Scientists, Cambridge, MA, USA; http://www.ucsusa.org), noted that one Bt corn variety was harmful to monarch larvae, but that for unrelated reasons, the variety is being discontinued. [Vorman, J. (2001) Reuters, 11 September] TS

Bt or not Bt: is that the question?

Recent public concerns over the transgenic (genetically modified) plants and nontarget impacts such as those from Bt-toxin expressing corn pollen on the monarch butterfly populations have escalated, despite good pest management intentions and good science (1–9). Plant resistance to insect pests has evolved naturally over many millions of years and involves (i) both constitutive and inducible phytochemical and morphological mechanisms in plants, (ii) counteradaptations to plant defenses by the herbivores, and (iii) biotic interactions of the multitrophic level communities of insect pathogens, parasites, and predators (10–13). The outcomes of such complex biotic interactions are sometimes determined by local mosaics of abiotic environmental conditions or regional climate changes that directly influence the component participants and their behavioral, physiological, and genetic adaptations (14–16). The intentional selection and breeding of insect and/or pathogen-resistant plant genotypes such as corn (Zea mays) has resulted in slow, but steady, progress against stalk-boring larvae such as the European corn borer and other such species, and host plant resistance in general has significantly reduced the need for broad-spectrum insecticides across agroecosystems and forests (17, 18).

Corn pollen deposition on milkweeds in and near cornfields.

The density of corn pollen on leaves of milkweed plants inside and outside of cornfields was measured in several studies from different localities. The purpose was to obtain a representative picture of naturally occurring pollen densities to provide a perspective for laboratory and field studies of monarch larvae feeding on milkweed leaves with Bt corn pollen. Pollen density was highest (average 170.6 grains per cm(2)) inside the cornfield and was progressively lower from the field edge outward, falling to 14.2 grains per cm(2) at 2 m. Inside the cornfield, and for each distance from the field edge, a frequency distribution is presented showing the proportion of leaf samples with different pollen densities. Inside cornfields, 95% of leaf samples had pollen densities below 600 grains per cm(2) and the highest pollen density observed was 1400 grains per cm(2), which occurred in a study with a rainless anthesis period. All other studies had rainfall events during the anthesis period. A single rain event can remove 54-86% of the pollen on leaves. Leaves on the upper portion of milkweed plants, where young monarch larvae tend to feed, had only 30-50% of the pollen density levels of middle leaves.

Temporal and spatial overlap between monarch larvae and corn pollen.

To assess the likelihood that monarch larvae will be exposed to Bacillus thuringiensis (Bt) pollen, we studied milkweed and monarch densities in habitats which comprise much of the land available to breeding monarchs, e.g., cornfields, cornfield edges, other agricultural fields, and nonagricultural areas, in four regions of the monarch breeding range. We found that monarchs use milkweed in cornfields throughout their breeding season, and that per plant densities are as high or higher in agricultural habitats as in nonagricultural habitats. As a result of the prevalence of agricultural land, most of the monarchs produced in the upper Midwest are likely to originate in cornfields or other agricultural habitats. There was a greater temporal overlap between susceptible monarchs and corn anthesis in the northern than the southern part of the summer breeding range, because of earlier pollen shed in the south. The importance of agricultural habitats to monarch production suggests that, regardless of the impact of genetically modified crops, agricultural practices such as weed control and foliar insecticide use could have large impacts on monarch populations.

Assessing the impact of Cry1Ab-expressing corn pollen on monarch butterfly larvae in field studies.

Survival and growth of monarch larvae, Danaus plexippus (L.), after exposure to either Cry1Ab-expressing pollen from three Bacillus thuringiensis (Bt) corn (Zea mays L.) events differing in toxin expression or to the insecticide, lambda-cyhalothrin, were examined in field studies. First instars exposed to low doses ( approximately 22 grains per cm(2)) of event-176 pollen gained 18% less weight than those exposed to Bt11 or Mon810 pollen after a 5-day exposure period. Larvae exposed to 67 pollen grains per cm(2) on milkweed leaves from within an event-176 field exhibited 60% lower survivorship and 42% less weight gain compared with those exposed to leaves from outside the field. In contrast, Bt11 pollen had no effect on growth to adulthood or survival of first or third instars exposed for 5 days to approximately 55 and 97 pollen grains per cm(2), respectively. Similarly, no differences in larval survivorship were observed after a 4-day exposure period to leaves with 504-586 (within fields) or 18-22 (outside the field) pollen grains per cm(2) collected from Bt11 and non-Bt sweet-corn fields. However, survivorship and weight gain were drastically reduced in non-Bt fields treated with lambda-cyhalothrin. The effects of Bt11 and Mon810 pollen on the survivorship of larvae feeding 14 to 22 days on milkweeds in fields were negligible. Further studies should examine the lifetime and reproductive impact of Bt11 and Mon810 pollen on monarchs after long-term exposure to naturally deposited pollen.

Monarch larvae sensitivity to Bacillus thuringiensis- purified proteins and pollen.

Laboratory tests were conducted to establish the relative toxicity of Bacillus thuringiensis (Bt) toxins and pollen from Bt corn to monarch larvae. Toxins tested included Cry1Ab, Cry1Ac, Cry9C, and Cry1F. Three methods were used: (i) purified toxins incorporated into artificial diet, (ii) pollen collected from Bt corn hybrids applied directly to milkweed leaf discs, and (iii) Bt pollen contaminated with corn tassel material applied directly to milkweed leaf discs. Bioassays of purified Bt toxins indicate that Cry9C and Cry1F proteins are relatively nontoxic to monarch first instars, whereas first instars are sensitive to Cry1Ab and Cry1Ac proteins. Older instars were 12 to 23 times less susceptible to Cry1Ab toxin compared with first instars. Pollen bioassays suggest that pollen contaminants, an artifact of pollen processing, can dramatically influence larval survival and weight gains and produce spurious results. The only transgenic corn pollen that consistently affected monarch larvae was from Cry1Ab event 176 hybrids, currently <2% corn planted and for which re-registration has not been applied. Results from the other types of Bt corn suggest that pollen from the Cry1Ab (events Bt11 and Mon810) and Cry1F, and experimental Cry9C hybrids, will have no acute effects on monarch butterfly larvae in field settings.

Impact of Bt corn pollen on monarch butterfly populations: a risk assessment.

A collaborative research effort by scientists in several states and in Canada has produced information to develop a formal risk assessment of the impact of Bt corn on monarch butterfly (Danaus plexippus) populations. Information was sought on the acute toxic effects of Bt corn pollen and the degree to which monarch larvae would be exposed to toxic amounts of Bt pollen on its host plant, the common milkweed, Asclepias syriaca, found in and around cornfields. Expression of Cry proteins, the active toxicant found in Bt corn tissues, differed among hybrids, and especially so in the concentrations found in pollen of different events. In most commercial hybrids, Bt expression in pollen is low, and laboratory and field studies show no acute toxic effects at any pollen density that would be encountered in the field. Other factors mitigating exposure of larvae include the variable and limited overlap between pollen shed and larval activity periods, the fact that only a portion of the monarch population utilizes milkweed stands in and near cornfields, and the current adoption rate of Bt corn at 19% of North American corn-growing areas. This 2-year study suggests that the impact of Bt corn pollen from current commercial hybrids on monarch butterfly populations is negligible.

Effects of Corn Plants and Corn Pollen on Monarch Butterfly (Lepidoptera: Danaidae) Oviposition Behavior

The oviposition behavior of adult insects can have a major impact on the level of exposure of their offspring to natural and artificial toxins. Pollen from Bt-corn hybrids represents a novel toxin and very little is known regarding its detection and possible avoidance by ovipositing females. The effect of corn plant proximity and corn pollen presence on the oviposition behavior of the monarch butterfly, Danaus plexippus (L.), was assessed in cage and flight chamber studies. The proportions of monarch eggs oviposited on milkweed plants dusted pollen from with a Bt-corn hybrid, an untransformed hybrid, gravel dust, and undusted control plants were recorded from a cage study. None of the treatments differed significantly in the relative proportion of eggs found. The effect of Bt and untransformed corn plant proximity and corn pollen presence was also assessed in a flight chamber. A significantly higher proportion of eggs (96%) were recovered from patches of milkweed plants not surrounded by corn plants, and a significantly higher proportion of eggs (nearly 70%) were recovered from patches of milkweed plants not dusted with corn pollen. There were no significant differences in the effects of Bt corn plants or corn pollen compared with untransformed plants or pollen. These results may have important implications for the level of exposure of monarch larvae to Bt-corn pollen.

Stochastic dynamic population model for northern corn rootworm (Coleoptera: Chrysomelidae).

A stochastic dynamic population model for the complete life cycle of northern corn rootworm, Diabrotica barberi Smith & Lawrence, is described. Adult population dynamics from emergence to oviposition are based on a published single-season model for which temperature-dependent development and age-dependent advancement determine adult population dynamics and oviposition. Randomly generated daily temperatures make this model component stochastic. Stochastic hatch is 50+/-8%. A stochastic nonlinear density-dependent larval survival model is estimated using field data from artificial infestation experiments. A regional model of corn phenology is estimated to incorporate the effect of dispersal on adult mortality. Random daily weather is generated using parameters for Brookings, SD. Model performance is evaluated with deterministic simulations, which show that the population converges to zero unless adult mortality is reduced by the availability of corn pollen from the regional model of corn phenology. Stochastic model performance is evaluated with stochastic daily weather, egg hatch, and larval survival in various combinations. Sensitivity analysis is conducted to evaluate model responsiveness to each parameter. Model results are generally consistent with published data.

Pollen Drift fromBacillus thuringiensisCorn: Efficacy Against European Corn Borer (Lepidoptera: Crambidae) in Adjacent Rows of Non-Bt Corn

Commercial non-Bacillus thuringiensis (Bt) corn was planted adjacent to Bt corn to determine the effects of Bt corn pollen falling on non-Bt plants for control of European corn borer larvae, Ostrinia nubilalis (Hubner). Field plots in Iowa and Kansas consisted of two center rows of Bt corn with eight rows of adjacent non-Bt corn on each side. In mid-September 1996 and 1997, we counted European corn borer larvae and larval tunnels in the stalk and ear shank. There were no significant differences in European corn borer numbers across non-Bt rows and the slope of the regression line was not significantly different from zero. In a single plot in Iowa, however, fewer tunnels were observed in rows of corn that were closer to Bt corn. This site was isolated from natural infestations and probably does not reflect a typical field situation. Our results suggest that Bt pollen has minimal or no control of European corn borer larvae in adjacent rows of non-Bt corn under natural conditions. Bt pollen drifting onto adjacent non-Bt plants should not increase the risks related to resistance management.

Biology of Euseius yousefi (Acari: Phytoseiidae) Life Tables and Feeding Behaviour on Different Diets

Effects on development, survivorship and reproduction of Euseius yousefi Zaher and El-Borolossy were studied in the laboratory using four different diets: the tetranychid mite Tetranychus urticae koch, the eriophyid mite Eriophyes dioscoridis Soliman and Abou-Awad, date palm pollen Phoenix dactylifera (L.) and sweet corn Zea mays L. pollen. The total development time ranged between 6.25 and 7.27 days for the adult female on animal diets and date palm pollen. In contrast, sweet corn pollen prolonged the developmental time and a higher nymphal mortality occurred. A total of 63.8, 50.5 and 57.6 eggs per female were obtained when eriophyid and tetranychid mites as well as date palm pollen, were provided, respectively. A diet of T. urticae provided the shortest generation time (T) and female longevity as well as the highest intrinsic rate of natural increase (rm = 0.294). A diet of E. dioscoridis resulted greatest female longevity and mean total fecundity which resulted in the highest net reproductive rate (Ro) value, intrinsic rate of increase (rm = 0.231) and finite rate of increase (e r m = 1.260) per day for E. yousefi. A diet of date palm pollen showed a close values of (T), (rm), (e r m) and total eggs per female with a diet of eriophyid mite. The sex ratio of E. yousefi was strongly female biased (♀/total ranged 0.73-0.82). Sweet corn pollen was the least favorable food source, with shortest adult longevity and without reproductive activity.