Dung was collected 1, 2, 4, 8 and 1 1 weeks aftez cattle were treated in the prescribed manner for nematode control in the spring with either an injection of 200 pg kg-I of avermectin B1 or a drench of levamisole hydrochloride. The avermectin B 1 treatment affected survival of the bushfly, Muscu vetustissimu Walker, and breeding of the introduced dung beetle, Onthophugus binodis Thunberg. No bush flies survived from egg to adult in dung collected from animals treated with avermectin B1 2 weeks earlier, but survival rates returned to normal 8 weeks after treatment. Adult survival of 0. binodis was not affected in dung of cattle treated with avermectin B 1 but oviposition was reduced and immature survival was zero in dung from animals treated one week previously, returning to normal 8 weeks after treatment. Dung from cattle treated with avermectin B 1 in summer and autumn would influence beetles little because most are not breeding then, but in spring when beetles are breeding the risk of harmful effects could be reduced by using an alternative treatment such as levamisole hydrochloride.
For the first time Halotydeus destructor has been laboratory-reared over the summer (October-May), on Trifolium subterraneum plants at fluctuating temperatures of 11-18 "C.The introduced redlegged earth mite, Halotydeus destructor (Tucker), occurs in areas of southern Australia with a mediterranean-type climate (wet winter/dry summer), where it causes severe damage to pasture legumes (Wallace 1970). The mite is only active from autumn to spring, during the cool moist period of the year, with aestivating eggs being retained in bodies of dead females during the dry summer (Norris 1950). Biological studies have been carried out on redlegged earth mite since the 1920s because of its economic importance, but it has not been successfully reared. The lack of a rearing method has limited the screening of pasture legumes for varietal resistance to H. destructor to 6 months of the year when the mites can be field-collected (Sandow and Gillespie 1987).Trifolium subterraneum L. cv. Junee was grown in well.fertilised sandy loam soil at 15 plants/pot (I5 cm diam. x 10 cm deep). When the plants were 3 weeks old, 200 miteslpot were added and enclosed by a clear plastic cover 1 I crn high with a lid, with steel gauze (0.125 mm aperture) side and top panels.The rearing room environment was: 1700-0700h; no light, 11 "C, 78% RH, and 0700-1700h; light from 16 l00W fluorescent tubes giving 300 pE/m'/s at the plants, I 8 T , 64% RH. Humidity around the mites was increased by occasional misting. The plants were watered once a week from saucers under the pots. Mites were counted twice a week. When the plants were 10 weeks old the progeny of the mites, usually of mixed stages, were transferred to new plants with a mouth-operated aspirator.For the first time H. destructor has been reared over the full seven months that diapausing eggs are the only stage in the field, passing through five generations without diapause. Tritonymphs were fieldcollected on three occasions in September and October 1990. Total abundance in all pots fell from 2400 mites initially to an average of 1930 mites through November and December, to 550 through January and February, probably associated with powdery mildew on older plants, and to 110 through March and April, following 3 weeks at a constant 15°C during equipment failure. On 21 May 1991 there were 660 mites alive. Now that rearing of H. destructor over summer is possible, a more systematic study of factors influencing its survival and fecundity will be undertaken to develop methods to mass-rear mites for use in experiments all year round.
Subterranean clover (Trifolium subterraneum L.) is the most widely sown pasture legume in southern Australia and resistance to important diseases and pests has been a major plant-breeding objective. Kabatiella caulivora, the cause of clover scorch, is the most important foliar fungal pathogen, and several cultivars have been developed with resistance to both known races. Screening of advanced breeding lines has been conducted to prevent release of cultivars with high susceptibility to other important fungal foliar disease pathogens, including rust (Uromyces trifolii-repentis), powdery mildew (Oidium sp.), cercospora (Cercospora zebrina) and common leaf spot (Pseudopeziza trifolii). Several oomycete and fungal species cause root rots of subterranean clover, including Phytophthora clandestina, Pythium irregulare, Aphanomyces trifolii, Fusarium avenaceum and Rhizoctonia solani. Most breeding efforts have been devoted to resistance to P. clandestina, but the existence of different races has confounded selection. The most economically important virus diseases in subterranean clover pastures are Subterranean clover mottle virus and Bean yellow mosaic virus, while Subterranean clover stunt virus, Subterranean clover red leaf virus (local synonym for Soybean dwarf virus), Cucumber mosaic virus, Alfalfa mosaic virus, Clover yellow vein virus, Beet western yellows virus and Bean leaf roll virus also cause losses. Genotypic differences for resistance have been found to several of these fungal, oomycete and viral pathogens, highlighting the potential to develop cultivars with improved resistance. The most important pests of subterranean clover are redlegged earth mite (RLEM) (Halotydeus destructor), blue oat mite (Penthaleus major), blue-green aphid (Acyrthosiphon kondoi) and lucerne flea (Sminthurus viridis). New cultivars have been bred with increased RLEM cotyledon resistance, but limited selection has been conducted for resistance to other pests. Screening for disease and pest resistance has largely ceased, but recent molecular biology advances in subterranean clover provide a new platform for development of future cultivars with multiple resistances to important diseases and pests. However, this can only be realised if skills in pasture plant pathology, entomology, pre-breeding and plant breeding are maintained and adequately resourced. In particular, supporting phenotypic disease and pest resistance studies and understanding their significance is critical to enable molecular technology investments achieve practical outcomes and deliver subterranean clover cultivars with sufficient pathogen and pest resistance to ensure productive pastures across southern Australia.
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