Earth Mite Research Articles

Antixenotic resistance of subterranean clover cotyledons to redlegged earth mite, Halotydeus destructor

AbstractThe short‐term response of redlegged earth mite, Halotydeus destructor (Tucker) (Acarina: Penthaleidae) to cotyledons of different varieties of subterranean clover (Trifolium subterraneum subsp. subterraneum L.) was assessed by means of paired choice tests, and no‐choice tests. H. destructor had lower numbers and fed less on detached cotyledons of resistant than susceptible varieties, yielding a correlation between the numbers of mites and feeding damage to the cotyledons during a three hour test period. For a number of resistant and susceptible varieties, there was a negative correlation between cotyledon deterrence in the three hour choice test and feeding damage to seedlings after a two week period. Since the response of the mites to different subclover varieties occurred within three hours, it is concluded that the resistance is based on antixenosis.No evidence was obtained for antifeedant activity in organic solvent extracts from the variety DGI007 (resistant) in comparison with those from the variety Dalkeith (susceptible). Water soluble compounds from DGI007 cotyledons were preferred by mites, in feeding tests in terms of numbers, over those from Dalkeith (susceptible). Squeezed sap from the cotyledons of both varieties showed the same effects on mites as 5% glucose and were more phagostimulatory than water extracts. Mechanically damaged cotyledons of Dalkeith and DGI007 attracted more mites than the undamaged counterparts. The toughness of cotyledons in 17 varieties of T. subterraneum subsp. subterraneum was measured with a manual penetrometer. Results showed a negative correlation between toughness values and mite feeding damage scores (r2 = 0.752) for all varieties except S3615D (resistant). This implies a likely involvement of epidermal toughness as a contributor in the antixenotic resistance of these varieties. Other mechanisms may be involved in the resistance of S3615D.

Assays for the effects of volatile compounds from artificially damaged cotyledons of subterranean clover on the redlegged earth mite, Halotydeus destructor

The effects on the redlegged earth mite (Halotydeus destructor) (Acarina: Penthaleidae) of volatile compounds released from artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.), a host plant, were investigated with different assays. Mites were repelled by the volatile compounds in flask tube and in trimmed cotyledon disc tests. No differences could be shown between different tissue amounts and between resistant and susceptible varieties. When a membrane sachet was used containing either 2-(E)-hexenal, a compound produced by damaged subclover cotyledons, or the total volatile compounds collected from damaged cotyledons of Dalkeith (susceptible) admixed with 1% glucose, mites gathered to low but were deterred by high concentrations of the compounds. Volatile compounds collected from the resistant variety DGI007 were more deterrent than those from the susceptible Dalkeith. Membrane sachets containing 30 p.p.m. of 2-(E)-hexenal and 1% glucose were less preferred than cotyledons of Dalkeith (susceptible) but were not different from DGI007 (resistant). By increasing the glucose concentration to 5%, the membrane sachets with 30 p.p.m. of 2-(E)-hexenal were preferred to cotyledons of either variety. The results indicate that the membrane feeding technique provides a sensitive way of assaying volatile compounds from damaged subclover cotyledons against the mite.

Correlation of 1-octen-3-one with antixenotic resistance in subterranean clover cotyledons to red-legged earth mite,Halotydeus destructor (Acarina: Penthaleidae)

Artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.) released several volatile metabolites, including 1-octen-3-one, arising from lipid peroxidation. The amount of 1-octen-3-one produced was negatively correlated with feeding damage caused by the red-legged earth mite (Halotydeus destructor) in nine out of 10 resistant and susceptibleT. subterraneum varieties tested. The EC50 of this compound in deterring mites from feeding in a membrane bioassay was 50 ppm. Cotyledon toughness was also involved in resistance. The resistant variety, S3615D, which has the lowest toughness value among the resistant varieties, produced the highest amount of 1-octen-3-one recovered from the headspace in 1 hr. Artificially damaged cotyledons of both susceptible Dalkeith and resistant DG1007, growing in shade, showed lower toughness, but had enhanced production of C8 volatile compounds and were avoided by mites during a 3-hr feeding test. When both 1-octen-3-one content and cotyledon toughness value were taken as cofactors in resistance, the resultant multiplication value yielded a more significantly negative correlation with mite feeding damage scores within the 10 varieties than either factor alone. We conclude that 1-octen-3-one has a role in resistance of subclover cotyledon to the mite.

A method to test compounds for feeding deterrence towards redlegged earth mite (Acarina: Penthaleidae)

SummaryA bioassay, based on a membrane sachet technique, has been developed to identify antifeeding compounds affecting the redlegged earth mite, Halotydeus destructor (Acari: Penthaleidae). The method consists of counting H. destructor numbers on membrane sachets in choice experiments, which was quicker and more efficient than weighing the mites. Five per cent aqueous glucose solution was used as a feeding stimulant, with Tween 80® at 5% concentration as a solubilising agent for water‐insoluble compounds. (+)‐Catechin, rutin, biochanin A, formononetin, chlorogenic acid, and gramine acted as feeding deterrents at 1% concentration. Quercetin (1 %) and azadirachtin (100 ppm) had no significant effect. At lower concentrations (0.01%), compounds showed antifeeding (gramine), phagostimulating (quercetin and chlorogenic acid), or no effects on mite numbers. Dose‐dependent deterrent effects of plant extracts were demonstrated with the bioassay, which could be used for other mites.

Genetic structure of Halotydeus destructor and Penthaleus major populations in Victoria (Acari: Penthaleidae)

The redlegged earth mite (Halotydeus destructor) and the blue oat mite (Penthaleus major) are major pests of pastures and crops in southern Australia. Reproductive modes, migration rates and levels of differentiation between populations were investigated using allozyme electrophoresis. Collections were made throughout Victoria and a sample was also obtained from Western Australia. Three enzyme loci were polymorphic in H. destructor (Mdh-1, Mdh-2 and Idh). Genotype frequencies of these loci did not differ between phenotypic males and females, providing no evidence for haplodiploidy. Allele frequencies were in Hardy-Weinberg equilibrium, indicating that H. destructor is diploid and sexual. This was confirmed via crosses between males and females. Allele frequencies differed between Victorian sites, although F statistics indicated little differentiation over all loci. A sample from Western Australia did not differ in allele frequencies from the Victorian sites. Four polymorphic loci were found in P. major (Mdh-1, Mdh-2, Idh and Gpi). Only a few multilocus genotypes occurred in a sample, indicating that P. major is parthenogenic. No male P. major were found in this study. A number of colour morphs were also identified and a genetic association between genital plate colour and clonal type was found in one population of P. major. Two different body colour morphs were associated with different clonal types.

Molecular genetic analysis of subterranean clover-microbe interactions

Trifolium subterraneum (subterranean clover) is of considerable economic importance to the Australian rural industries as a pasture legume. In addition to its commercial value, it has a number of specific attributes—such as small seed size, diploidy, self-fertilization, the ability to be transformed and small genome—which make it a prime target for the modern techniques of molecular genetics. We report genetic and physiological factors that control the production and excretion of the lipooligosaccharide molecules formed by Rhizobium leguminosarum bv. trifolii in the formation of the symbiosis with subterranean clover. These molecules, synthesized by the products of the nodulation ( nod) genes, are a major determinant of nodule occupancy and the strain selection imposed by the host plant. In addition, we have investigated which plant genes and proteins are activated in subterranean clover when they are either physically wounded, infected with Rhizobium, or attacked by red-legged earth mites. To analyse these interactions more precisely, we have cloned plant genes involved in the phenylpropanoid pathway and used their promoters to construct transgenic subterranean clover plants. Our studies provide an insight into the nature and consequences of the chemical exchange between plants and invading microbes.

Responses and feeding damage of redlegged earthmite (Acarina: Penthaleidae) to seedlings of resistant and susceptible subterranean clover varieties

Responses of redlegged earth mite (Halotydeus destructor) to seedlings of three resistant and four susceptible varieties of subterranean clover (Trifolium subterraneum) were measured after 7 or 14 days in pot experiments in the glasshouse. With a single variety/pot, mites on resistant varieties (DGI007, EP145SubD and Rutherglen B) produced 45% of the progeny that were produced by mites on the susceptible varieties (89838G, Dalkeith, Junee and 70088B). Number of stages completed and survival were little affected by varieties. Feeding damage (silvering of cotyledons) on resistant varieties averaged 45% of that on susceptible varieties with a single varietylpot. H. destructor fed less on resistant varieties in choice than in single variety experiments. On Junee and 89838G seedlings, feeding damage was similar to that on other susceptible varieties, but there were about half as many H. destructor progeny as on Dalkeith and 70088B. Mites laid more eggs on soil away from Junee plants, compared to the other three susceptible varieties. Different factors adversely affected the number of progeny produced on resistant varieties and on Junee.

Host plant species and carbohydrate supplements affecting rate of multiplication of redlegged earth mite

The effects of young plants of different legume species on the rate of multiplication of Halotydeus destructor (Tucker)(Acarina: Penthaleidae) were examined in one, two or four week experiments in the laboratory. Rates of multiplication of H. destructor were substantially greater on Vicia sativa (common vetch), Phaseolus vulgaris (dwarf bean) and Pisum sativum (snow pea), than on subterranean clover, Trifolium subterraneum; cultivars Dalkeith, Geraldton and Junee. Levels of soluble carbohydrate and soluble nitrogen were greater in vetch, bean and pea, than in the subclovers. Concentrations of 20 amino acids were not associated with differences in mite performance; pea contained higher levels of glutamine and homoserine than the other plants, which may have adversely affected mite multiplication. In further experiments a carbohydrate supplement caused a fourfold increase in rate of multiplication on subclover cv Junee, but had no effect on rate of multiplication on vetch cv Blanchefleur. The carbohydrate supplement did not cause the rate of multiplication on subclover to equal that on vetch. Subclover is not an optimum host plant for H. destructor nutritionally. The nutritional value of host plants is one factor affecting mite multiplication.

A grower survey of diseases, invertebrate pests, and pesticide use on potatoes grown in South Australia

In 1991, a survey was distributed to 251 potato growers in South Australia to determine major diseases, insect and other invertebrate pests, and chemicals used to control them. The overall response rate was 48%, but of these, 24 individuals were no longer growing potatoes. The results were summarised for the State and by district (Adelaide Hills, Adelaide Plains, Murray Lands, South East). The most prevalent diseases encountered by respondents in all districts were target spot caused by Alternaria solani, and rhizoctonia canker caused by Rhizoctonia solani. Other diseases of concern to growers included late blight caused by Phytophthora infestans, seed piece decay caused by various pathogenic and saprophytic microorganisms, common scab caused by Streptomyces scabies, and leaf roll caused by potato leaf roll virus. The most commonly used fungicides for disease control were chlorothalonil (33-42% of respondents), mancozeb (30%), and cupric hydroxide (11-13%). The most commonly used seed treatments for control of seed piece decay were mancozeb (51 % of respondents), tolclofos methyl (24%), and lime (20%). Green peach aphid (Myzus persicae), potato aphid (Macrosiphum euphorbiae), potato moth (Phthorimaea operculella), and jassids and leafhoppers (Jassidae, Cicadellidae) were the pests of greatest concern to the growers. Others included Rutherglen bug (Nysius vinitor), redlegged earth mite (Halotydeus destructor), and thrips (Thripidae). The most commonly used insecticides were ethamidophos (40% of respondents), monocrotophos (22-28%), and dimethoate (7-13%).

Effect of aphids and mites on herbage and seed production of subterranean clover (cv. Daliak) in response to superphosphate and potash

The dry matter production (DM) and seed yield of subterranean clover (Trifolium subterraneum L. cv. Daliak) were reduced by infestations of redlegged earth mite (Halotydeus destructor Tucker) and blue-green aphid (Acyrthosiphon kondoi Shinji) during spring growth, flowering and burr burial. The dominance of these pests varied with season. The effects of spraying with insecticides on the DM and seed yield responses to superphosphate and potassium chloride fertilisers were measured. Responses to superphosphate were described by Mitscherlich functions for each of 3 levels of potassium chloride, except for seed yields with pest sprays. At optimum levels of superphosphate and potassium chloride, controlling pests increased DM by up to 150% (from 4.37 to 6.52 t/ha). For all levels of superphosphate, spraying to control pests where no potassium chloride was applied significantly increased DM over that on unsprayed plots that were fertilised with potassium chloride. The maximum DM response to superphosphate application was achieved at 15-20 kg P/ha. With optimum superphosphate, the value for DM depended on the combination of spraying for pests and amount of potassium chloride applied, generating a series of Mitscherlich response curves for superphosphate application with differing maximum yields. With optimum superphosphate applied, the least DM recorded within a season was 3.47 t/ha (pests not sprayed, nil potassium chloride), and the most was 6.52 t/ha (pests sprayed, 120 kg potassium chloride/ha), an increase of about 180%. At optimum levels of superphosphate and potassium chloride, controlling pests increased seed yield by up to 380% (from 290 to 1100 kg/ha). With optimum superphosphate, seed yield within a season ranged from 210 (pests not sprayed, nil potassium chloride) to 1100 kg/ha (pests sprayed, 120 kg potassium chloride/ha), an increase of 524%. With pests sprayed, seed yield declined with superphosphate applications >20 kg P/ha; the relationship was best described by a quadratic function. With pests not sprayed, seed yield did not decline with increasing amounts of superphosphate, and the relationship fitted a Mitscherlich function.

Effects of early defoliation on the seedling growth of subterranean clover

Two experiments were conducted in an open-sided glass shelter at Perth during winter. Subterranean clover (Trifolium subterraneum, L.) seedlings were grown in shallow seed boxes at low plant densities, 2 4 and 2 0 plants/dm2. The effects of a single defoliation involving mainly the removal of cotyledons only, on shoot growth and leaf production were measured at harvest, c. 5 weeks after sowing. Total shoot dry weights were reduced by 15-30% when 40-60% of the leaf area was removed by single defoliations from days 7 to 19 after planting. However, the growth was reduced by almost 70% when both cotyledons were removed (days 7 to 9) before emergence of the unifoliate leaf, i.e. when all of the leaf area was removed. In general, the relative reduction in growth largely depended on the percentage of leaf area removed, rather than on time of removal. Defoliation also reduced the size of trifoliate leaves, and total numbers of trifoliate leaves at harvest. There was a linear relationship between total leaf numbers and shoot dry weights. In the field, these findings are probably of more relevance in terms of insect damage, especially from redlegged earth mites, than for grazing by sheep.

Using omethoate insecticide and legume inoculant on seed

Omethoate, an organophosphorus insecticide used for early control of redlegged earth mite on legume seed, was toxic to some Rhizobium strains on direct contact when diffused through agar seeded with these bacteria or mixed in broth cultures containing the bacteria. Omethoate mixed with peat-based legume inoculant and applied to seed of subterranean clover or lucerne significantly (P<0.05) reduced the number of nodules formed over 3 weeks on seedlings grown in pots of sand, compared with inoculated controls. Most nodules were immature and located on lateral roots, and plant dry matter at 4 weeks was significantly (P<0.05) less for lucerne. Significantly (P<0.05) fewer rhizobia were recovered from seeds and seedlings of lucerne when seed was treated with omethoate. When subterranean clover seed was pretreated with omethoate 16 h before inoculation and sown into moist sand, there were no significant differences in the mean numbers of rhizobia, mean numbers of nodules or dry matter compared with inoculated controls. With lucerne, the number of nodules formed following omethoate pretreatment was significantly less than on inoculated controls at day 21 but not at day 30, and the dry matter at day 30 was not adversely affected. Rhizobia numbers were reduced less than by mixing omethoate and inoculant, so more taproot nodulation occurred and more of the nodules were functional (i.e. N2-fixing) at 3 weeks. In a field trial with pea, white clover and murex medic, seed pretreatment with omethoate before inoculation had no effect on nodule number 9-11 weeks after sowing, compared with inoculated controls.

Emergence and early establishment of Chondrilla juncea L. (skeleton weed) in the Western Australian wheatbelt

AbstractWhen sown over consecutive years at two sites in the Western Australian wheatbelt, a maximum of 34.5% of viable Chondrilla juncea seeds gave rise to emerged seedlings. During the early winter months at one site, waterlogging on a duplex soil type led to an almost complete failure of emergence. Very low levels of seed persistence (maximum 3.1%) between years were noted.The protection provided by stubble enhanced the survival of C. juncea seedlings which emerged during May, but for seedlings which emerged later, the effects of stubble upon seedling survival were strongly dependent upon the abundance of the red‐legged earth mite (Halotydeus destructor) At the observed densities of winter annuals, the presence of seedlings and young plants appeared to reduce seedling mortality in C. juncea.Young plants of C. juncea were highly susceptible to simulated cultivation practices until 12 weeks following emergence. It is argued that seedling establishment of C. juncea is most likely to occur during the pasture phase of crop/pasture rotations in the Western Australian wheatbelt and that pastures immediately following cropping years are most prone to invasion.

The distribution of Halotydeus destructor and Penthaleus major (Acari : Eupodidae) in Australia in relation to climate and land use

The red-legged earth mite, H, destructor, is restricted to the southern parts of Australia having a Mediterranean-type climate, with warm dry summer and cool wet winter. The northern or inland distribution agrees closely with the 205-mm isohyet for the growing season May-October inclusive. The eastern distribution is limited by the quantity of midsummer (December-March) rainfall and agrees closely with the 225-mm isohyet for this period. Other limitations to distribution within these isohyets are imposed by high summer temperatures (mean monthly maximum of hottest month, 33�C). The blue oat mite, P. major, can tolerate a drier climate, reaching a May-October isohyet of about 190 mrn, and a higher proportion of summer rain. This enables it to survive on the south coast of New South Wales and on the northern tablelands of New South Wales as far as southern Queensland, but not in north coastal areas where the midsummer rainfall exceeds about 500 mm. On the evidence available, the likely future movements of these mites both within Australia and overseas are discussed. Vigilance will be needed to prevent H. destructor from becoming a pest in the Americas and in the Mediterranean region.

Diapause in the aestivating egg of Halotydeus destructor (Acari : Eupodidae)

The occurrence of an aestivating diapause in the eggs of the red-legged earth mite, H. destructor, is established. The production of diapause eggs in females is influenced by the increasing maturity of food plants in the spring. Morphogenesis is resumed following exposure to early summer conditions for 4-6 weeks in the field. In the laboratory, diapause development was achieved by exposing the eggs to various combinations of temperature and relative humidity. The most effective treatment was exposure for 32 days to 52DC and 50% R.H., although diapause development occurred within the temperature range 15-70DC and relative humidity range 10-100%, and even when the eggs were completely immersed in water. It was most successfully promoted in atmospheres having vapour pressures of about 40 mmHg, at all temperature and humidity combinations. At 20% R.H., diapause development was relatively slower than at humidities above and below this, whereas tolerance to high temperatures was greatest at this humidity. Diapause eggs were not harmed either by complete immersion in water or by periodical desiccation and re-moistening.

Carbamate and organophosphorus sprays as alternatives to DDT to control red-legged earth mites (Halotydeus destructor and Penthaleus major)

Four experiments, two conducted in 1962 and two in 1963, are described. Low volume applications of two carbamates, eight organophosphorous compounds, and a quinoxaline miticide were tested for their value in controlling the two species of red-legged earth mites, Halotydeus destructor (Tucker) and Penthaleus major (Duges) alongside the standard DDT treatment of four ounces active ingredient an acre. Two of the organophosphorous compounds, namely azinphos ethyl and 'Imidan' applied at half an ounce active ingredient an acre, were shown to give effective control of both mite species for at least five weeks and can now be recommended as alternative mite control treatments that would eliminate the risk of contamination of meat or animal products by undesirable residues. Since DDT at 2 oz active ingredient an acre gave very effective mite control, this lower dosage may- be useful in lessening the residue risk.

Treatment of pastures with granular phorate to control the lucerne flea (Sminthurus viridis) and the red legged earth mite (Halotydeus destructor)

Ten per cent phorate ('Thimet') granules were broadcast on to pastures to control the lucerne flea, Sminthurus viridis (L.) and the red-legged earth mite, Halotydeus destructor (Tuck.). A rate of one ounce of active ingredient an acre gave effective control of both pests, principally by fumigant action. Biscirus lapidarius Kramer, a useful bdellid mite preying upon the lucerne flea, was reduced in numbers by this treatment. Rain during or immediately after application inhibited the fumigant action. Changes in population density after treatment provided indirect evidence of the mechanisms of density regulation in these pests.

The effect of insecticide treatment on the yield and botanical composition of sown pastures in Western Australia

The yield and botanical composition of established, sown pastures were measured after applying insecticides to control the red-legged earth mite. Halotydeus destructor (Tuck.), the lucerne Flea, Sminthurus viridis (L.) and the webworm, Talis spp. The response to treatment depended upon the pest involved, the numbers present, and the vigour of the pasture. Control of H. destructor resulted in an average response of 3.9. cwt an acre of extra dry matter in the spring. To consume this, it is sugested that stocking rate should be increased by about 1/4 sheep per acre. This could be raised to 1/3 sheep per acre by careful selection of treatment areas. Slightly greater responses, up to perhaps 1/4 sheep per acre, can be expected when S. viridis is plentiful. Heavy webworm attack reduced carping capacity on average about one sheep per acre. The economics of insecticide treatment are examined in the light of these results. A formula is given whereby the farmer can calculate the likely return from treatment on his own property. It is concluded that in a large number of cases treatment is near the borderline of profitability. Farmers should make certain that insecticide treatment is the best way of spending their money. Having decided to use insecticides they should (a) treat only those areas where obvious damage is being done and avoid any blanket spraying programme and (b) ensure that some positive use is made of the increased herbage following treatment.

Seed treatment with systemic insecticides for the control of red-legged earth mite (Halotydeus destructor)

Successful control of the red-legged earth mite, Halotydeus destructor (Tuck.) (Acarina : Eupodidae) was achieved by treating subterranean clover, vetch, and pea seed with systemic insecticides before sowing. The most satisfactory measure of dosage was the quantity of insecticide per unit area of seed surface. Residual action in peas for up to one month after sowing was achieved with dimethoate, metyl demeton, phorate powder, and phorate liquid at dosages of 0.3, 1.0, 2.0 and 5.0 grams per .square metre of seed surface respectively. A t these dosages, seedling emergence of peas was reduced by two to seven per cent. Phorate inhibited the germination of cereals to a greater extent than it did legumes. These insecticides may kill the nodulating bacteria of legumes and this is a potential difficult in their use. Dimethoate appeared to be less toxic than either methyl demeton or phorate. Stimulation of bacterial growth can also occur at certain dosages. This problem needs further investigation.

Halotydeus destructor . [Distribution map

Abstract A new distribution map is provided for Halotydeus destructor (Tucker) (Acarina, Penthaleidae) (Red-legged Earth Mite (Australia), Black Sand Mite (South Africa)) Hosts: Pasture plants (notably clover) cereal and other field and market-garden crops. Information is given on the geographical distribution in AFRICA, Southern Rhodesia, Union of South Africa, AUSTRALASIA, Australia, New Zealand.