58 Plant Protection Quarterly Vol.10(2) 1995 feeding on both plant and animal matter. Biological control of earth mites in pasture using The predatory anystid mite, Walzia australica, which is very commonly found endemic natural enemies in association with earth mites in south- ern New South Wales, is closely related David G. James, New South Wales Agriculture, Yanco Agricultural Institute, and very similar to the introduced PMB Yanco, New South Wales 2703, Australia. A. wallacei. There is little evidence to sug- gest that the introduced anystid is any more effective as a predator of earth mites Summary than the native anystid (Otto and Twenty endemic natural enemies (19 of the pest which expose inefficiencies of Halliday 1991, Michael et al. 1991, James predators, one pathogen) of redlegged native predators, parasites and patho- unpublished observations). All of the earth mite, Halotydeus destructor, and gens. Introduction of the predatory mites predators listed here have been observed blue oat mite, Penthaleus major, were (Anystis wallacei) in 1965 from France for either in the field or laboratory feeding on recorded in southern New South Wales control of redlegged earth mite was, how- earth mites. The importance and value of during 1989–94. Evidence is presented ever, not preceded by any such studies. It complexes of generalist natural enemies supporting the idea that this natural en- is now (belatedly) time to do these stud- has long been underrated due to the in- emy complex plays an important role in ies. herent difficulties of evaluating such spe- regulation of earth mite populations in In this paper, I examine some of the in- cies. However, research is now beginning unsprayed, established pasture. Integra- formation on endemic natural enemies of to indicate that biological control pro- tion of native biological control agents earth mites which has been obtained, gen- vided by generalist natural enemies can with selective insecticides could provide erally in the course of other work, over be highly effective and sustainable with- the basis of an IPM system for earth the past five years in southern New South out the instability often associated with mites in pasture. Wales. specialist natural enemies (Murdoch et al. 1985, McMurtry 1992). Introduction Endemic natural enemies of earth An entomophthoran pathogen, It is remarkable that virtually no attention mites: What are they? Neozygites acaracida, occurs commonly in has been paid to the complex of endemic Although no systematic survey has been earth mite populations in southern New natural enemies associated with earth conducted, at least 19 predators and one South Wales. Infection levels range from mites (redlegged earth mite (Halotydeus pathogen are known to attack earth mites 0–50% and the disease seems to be most destructor) and blue oat mite (Penthaleus in the Leeton-Narrandera district of prevalent among blue oat mites. Infected major)) in stable or semi-stable ecosys- southern New South Wales (Table 1). This mites are yellowish (H. destructor) or red tems such as roadsides, natural grass- is a conservative assessment and a rigor- (P. major) and become sterile before their lands and pastures. The identification of ous survey over the full earth mite range death which may take a week or two as components of this assemblage and would undoubtedly reveal many more the pathogen develops. The pathogen ap- evaluation of its impact on earth mite species. However, it is clear that no single pears to be most common during wet populations is a logical and essential step species of predator dominates the natural winters and may be the prime cause of the towards development of low-input man- enemy fauna associated with earth mites; frequently observed earth mite ‘popula- agement strategies. Biological control of rather, there is a characteristic complex of tion crashes’ in July-August. earth mites is a resource available in every species. The most important predators pasture, but one that we know little about appear to be those from the predatory Effectiveness of endemic natural and do not use in current chemical-based mite families Parasitidae, Bdellidae, enemies control strategies. It might be highly Erythraeidae, Anystidae and Cunaxidae. Data collected on H. destructor and preda- effective but remains an enigma; for ex- As far as is known, all the predator spe- tors during 1993 from a single long-term ample, it is common for neighbouring cies associated with earth mites are gen- (approximately 15 years) unsprayed pas- farmers to have contrasting earth mite eral feeders meaning they can feed on a ture paddock in Leeton provide a rudi- situations: one farmer has to spray every range of prey and in some cases on pollen mentary indication of population dynam- year, the other never has a problem. Ulti- and plant exudates. Some species such as ics which may be characteristic of undis- mately, biological control provided by Balaustium murorum may be omnivores turbed systems (Figure 1). On each date a endemic natural enemies will feature in whatever low-input management strat- Table 1. List of natural enemies observed causing mortality to redlegged egy we develop for earth mites. The use earth mite in the Leeton-Narrandera district of southern New South Wales of resistant clover varieties will help to 1987–1993. preserve natural enemy populations; bet- ter timing and reduction in use of chemi- Chrysopa spp. (Chrysopidae) cal sprays will do the same thing. To max- Hemerobius spp. (Hemerobiidae) imize the potential and use of this bio- Coccinella repanda, Harmonia conformis, resource, we must fully understand it. Diomus notescens (Coccinellidae) ‘Classical biological control’, used to de- Amblyseius victoriensis, Amblyseius messor, scribe the introduction of exotic natural Amblyseius masiaka, Amblyseius dieteri, enemies, monopolizes public awareness Typhlodromus occidentalis (Phytoseiidae) of biological control, but is in fact respon- Parasitus fimetorum (Parasitidae) sible for a minority of biocontrol solu- Walzia australica, Erythracarus sp. (Anystidae) tions. Most biological control occurs in Bdellodes affinis, Bdellodes lapidaria, unstudied or little studied but highly ef- Cyta latirostris (Bdellidae) fective indigenous systems which rarely Cunaxa sp. (Cunaxidae) receive any fanfare. Today, introductions Ledermuelleria sp. (Stigmaeidae) of exotic natural enemies are invariably Balaustium murorum (Erythraeidae) preceded by thorough ecological studies Neozygites acaracida (Entomophtharales) Plant Protection Quarterly Vol.10(2) 1995 59 vacuum sampler was used to collect ten likely that chemicals will remain an im- field applications of alphacypermethrin suction samples from 50 random loca- portant component of control for the fore- at 1.25 g a.i. ha-1 and significant survival tions in the paddock. The overall H. de- seeable future (James 1991). Modification of some species will also occur at 2.5 g a.i. structor population remained small and at of insecticide spray strategies (choice, ha-1. Field studies support these conclu- a level most farmers would not consider rate, amount and timing) currently offers sions (James unpublished data). Good worth spraying. Populations of predatory the greatest opportunity for improvement control of H. destructor in pasture is pro- mites and insects known to feed on earth of control efficacy and concomitant re- vided by alphacypermethrin at either of mites were an important part of the sys- duction in input. Integration of natural these rates (James unpublished data) sug- tem and comprised 8–76% of the organ- enemies with insecticides would also im- gesting that this chemical has potential as isms collected on each sampling date. prove earth mite control by using indig- an earth mite treatment within an IPM Combined data (all sampling dates) show enous biological control in overall man- program. Bifenthrin appears to be a less predators comprised 36% of the sampled agement which would in turn reduce in- likely candidate for incorporation in such biomass. Predators were dominated by secticide inputs. Very little is known a program. Data of the kind outlined anystid, bdellid, erythraeid and parasitid about the compatibility of natural en- above are needed for all chemicals used mites. On four occasions in August– emies of earth mites with insecticides in pastures and should be extended to in- September, there were more predators used in pasture. However, some data clude all natural enemy species in the sampled than H. destructor. Unfortunately from laboratory bioassays have been ob- complex associated with earth mites. no data were collected on earth mite and tained on the toxicity of alpha- predator populations in ‘chemically dis- cypermethrin and bifenthrin to five en- Conclusions turbed’ paddocks during the same sea- demic predators of earth mites. These two The preliminary data summarized here son. However, observational and anecdo- synthetic pyrethroids are likely to be reg- strongly support the idea that endemic tal evidence suggested earth mite istered for earth mite control in the near natural enemies play an important role in populations were generally considerably future. The predators differed consider- regulation of earth mite populations in larger than in the unsprayed paddock and ably in their susceptibility to these com- unsprayed, established pasture. This usually warranted insecticide treatment. pounds; one species, the bdellid mite, regulation is provided by a complex of Predators were present in much lower Cyta latirostris,