Plant Protection Quarterly VoI.6(4) 1991 181 ------France is at Valence, where the area of Systematics and biology of a predatory ( Mediterranean climate penetrates north­ ward up the Rhone valley. It extends sp_> introduced into Australia for biological control of along the eastern coast of Spain, inland as redlegged earth mite far as Za ragoza. It has been co llec ted once in Portugal, once at an unknown locality in Italy, and at several localities in Mo­ 0110 and RB. Halliday, CSIRO Division of Entomology, GPO Box 1700, J-e. rocco. Publi shed records of A. salicin us Canberra, ACT 2601, Australia. from central and northern Europe do not refer to Anyslis species A (e.g., those of Summary Collembola and . It was argued that Oudemans 1936). Aflystis species A was introduced from if Anystjs was introduced into Australia, The known distribution of AI1YStis spe­ France into Western Australia in 1965 to it might prey on both P. major and H. de­ ci es A was used to produce a bioclirnatic assist in the biological control of structor. It was eventually released in profil e of the species, using the climate redlegged earth mite, Hnlotydeus de­ Western Australia in 1965, and became es­ modelling program CLlMEX (S utherst smlctor (RLEM). It has previously been tablished there (Wallace 1981). The and Maywald 1985, Maywald and misidentified as A. snlici1Uls. Climatic present paper reports the resul ts of recent Sutherst 1991). The results are shown in modelling shows that Anystis species A work on the systematics and biology of Figure 2. Solid circles show loca tions is likely to occur in the eastern Mediter· this species of Allystis. where the species is likely to occur, and ranean, where it has not yet been col­ the size of the solid circle in each case is lected, and that it should spread to oc­ Systematics proportional to the climatic suitability of cupy large areas of southern Australia. When Wilson found Anystis in France, but that locality. Crosses show locations Under laboratory conditions it will eat a before the species had been identified, where the species is not likely to occur. wide variety of prey, and will preparatiOns were quickly made for its in­ Climates that appear to be suitable for also feed on artificial diets. It is capable troduction into Australia. [t was then Anystjs species A occur across the north of killing large numbers of RLEM, but identified in Europe as A. baccnrurtl (L.) coast of Africa and in the eastern Mediter­ does not do so when alternative food is sens u Oudemans (1936). This is the most ranean, in addition to its known areas of available, such as Cotlembola. Its eggs abundant and widespread species in the occurrence. It is no t known whether are laid on moist substrates and develop genus, and was already known to occur in Auystis species A occurs in these areas, in about 12 days to the prelarval stage. Australia (Womersley 1933, 1942). The since the required collecting surveys have They are then capable of withstanding proposed importation was therefore can­ not yet been conducted, but we predict dry conditions, but hatch quickly when celled (CSIRO correspondence, May that it will be found in the coastal strip of exposed to free water. 1938) . However, subsequentfield work in Algeria, Tunisia , Libya, Egypt, Israel, Australia cast doubt on this identification Turkey, Greece, and Italy, and on the Introduction (Wa llace 1981). The French species was Mediterranean islands. The redlegged earth mite (RLEM) known to be common in pasture, whereas The biodimatic profile of Anystis spe­ Halotydeus des tructor was described A. baccn ru11l in mainland Australia oc­ cies A derived from its European distri­ taxonomicall y by Tucker (1925). In his ac­ curred mainly in gardens and was un­ bution was then used to derive a pre­ co unt of the biology of the species, Tucker co mmon in pasture. The French species dicted distribution for the species in Aus­ noted that "no parasites were ever seen to was subsequently found not to be A. tralia, again using C LiMEX (Figure 3) . prey on these mites or to infest them". OO CCarlllll, but an undescribed species. The results suggest that this species Newman (1925), Anonymous (1929), and This species was eventually introduced should be able to establish populations in Swan (1934) repeated the observation that into Australia, under the name Allystis southwestern Western Australia, as well no effective natural enemies of H. des tTll c­ "species A" (Wallace 1981). It ca n be dis­ as in South Australia and large parts of lor had been observed. As ea rly as 1929, tinguished from A. bnccarum by the shape the southeastern mainland and northeast­ vigorous efforts were being made to find and ornamentation of the dorsal shield, ern Tasmania. It should be emphasized biologica l control agents (Newman, and by the shape of the peritreme. The that Figures 2 and 3 are extrapolations, 1929), and in 1930 CSIRO dispa tched misidentification of this species delayed based only on our limited knowledge of Herbert Womersley to South Africa for the biological control program by almost the natural geographic range of the spe­ that purpose (Womersley 1933). The re­ 30 years. cies, as shown in Figure 1. In particular, sult was a series of taxonomic studies of A recent taxonomic paper on the the species is well established at Miling, the predatory mites in the families included the statement that the which would appear to be only margin­ Bdellidae and Anystidae, which was initi­ species introduced into Austra li a was ally suitable climatica lly. Its ultimate dis­ ated by Womersley and continued by Anystjs salicilllls (L.) (Meyer and tribution in Australia could be predicted other authors. Ueckermann 1987). That name has since with more confidence if we knew more Womersley (1933) found that the blue been used elsewhere to refer to this spe­ about the actual limits of its native range, oat mite of New South Wales, Nolophal/"s cies (Holm and Wallace 1989, Gerson and and about its responses to specific climatic bicolor Froggatt 1921 , was the same as the Sm iley 1990, Michael el al. 1992). How­ va riables. Also, the distribution achieved European species Pellthniells major (Duges ever, this identifica tion too, is incorrect. by this species could be influenced by fac­ 1834) . He therefore argued that, since P. Allystis species A ca n be distinguished tors other than cl im ate, such as the pres­ major and H. destTllctor are closely related, from A. salicillils by a variety of morpho­ ence of competing predators, and the d is­ biologica I control agents for both pests logical criteria, most importantly the tribution of suitable prey species. might be found in the native range of P. shape of the dorsal shield (Otto 1992). Allen (1987) reported thatAllyslis mites major, in the southern Mediterranean re­ were being collected in France for im por­ gion of Europe. In 1937, the CS IRO's Geographic distribution tation into north-western Ta smania. Frank Wilson found a species of Anysfis The native range of Allystis species A is in However, this statement was inaccurate, preying on Pentimiell s major in southern the western Mediterranean areas of and no such importations have been ca r­ France (Wallace 1981). It was reported to France and Spain, and in north Africa ried out or are planned (J . lreson, personal be a general feeder, attacking a variety of (Figure I). The most northerly record in co mmunica tion 1991) . CLiMEX analysis 182 Plant Protec tion Quarterly Vo1.6(4) 1991 tra y to examine the behaviour of the mites. The most common prey for Anystis under these conditions was the juvenile a KMS 500 I I stages of sminthurids and other Collembola. The large adult stages of sminthurids were not attacked, and Hypogastrura and RLEM were a ttac ked only rarely. Further tests were then ca rried out in small plastic cages (15 x25 x25 mm), with r"" a moistened plaster substrate, in which ~' ~--' Anystis was offered a va riety of potential • o prey. Allystis could easily capture and kill RLEM in these small cages, but appeared reluctant to do so. Anystis moved rapidly around in the cages, and frequentl y en­ countered li ving RLEM . Its usual reaction was to touch the RLEM briefl y w ith its front legs and gna thosoma, apparentl y without infl ic ti ng any damage. RLEM was often attac ked, but in most cases was not killed but was released soon after be­ Figure 1. Collection records of Anystis species A (solid circles) and other ing ca ptured. RLEM were seen to escape without apparent injury even after being species of Anystis (open circles). Based on field work of M.M.H. Wallace. held by Anystis for as long as six minutes. x x Those RLEM that were killed were usu· ? KMS 590 ally not sucked completely dry. Instead, Anys tis fed fro m each specimen briefl y x before moving away to search for more x prey. In these small cages, Anystis fed readily on a variety of other food, incl uding Elltomobrya if they were freshly killed or anaesthetized by chilling. Anystis was tested w ith a range of other arth ropods, and was observed to feed on ant eggs, bushfly eggs, aphids (Metapolop/lillm x x x dirhodll m, Acyrthosipholl kO lldoi, A. pis ll m), x x o ther species of coll embola, and even arti­ x ficial diets such as egg-jam and suga r so­ x XX x x x x lution. Dead specimens as well as li ving x ones are taken as food. The Collem bola x x x were usually sucked completely dry, and Figure 2. Predicted distribution of Anystis species A in the Mediterranean appea red to be a preferred food. region. Is RLEM a preferred food fo r Allyslis? shows that Allystis species A is not likely established in planted pastures in the Preli minary observations on the whi te to succeed in north-western Tasmania. Western Cape Province, where it is exert­ tray showed th at specimens of All ystis The locations in France that show the best ing some control of RLEM (Meyer 1981, that had touched an RLEM and allowed it climate match for the towns of Burnie and Meyer and Ueckerm ann 1987). to escape, were often seen soon after feed­ Smithton are Cherbourg and Bourdeaux. ing on a dead collembolan. This sug­ Anystis species A does not occur in these Feeding and reproduction gested that RL EM is not a preferred food areas of northern France, so any introduc­ Specimens of Anystis species A were col­ for Anystis. Anystis was therefore offered tions fro m those areas would probabl y lec ted from Denmark and Coolup, both a choice of prey. Single An ystis were involve a different species of Anystis. WA , using a vacuum sa mpler, and were placed in small cages with 10 RLEM and The specimens introduced in to Aus­ used to examine a seri es of specific ques­ 10 Entomobrya (mainly E. tl11os trigata) . The tralia ca me from an abandoned pasture at tions about the species' feeding and repro­ experiment was replica ted 10 tim es, and Frejus, 25 km SW of Cannes, France. They duction. the numbers of living and dead prey were were released in May 1965 at four sites in counted after 43 hours. Western Australia - Miling, Yo rk, What does Anys!is feed all ? In control cages (without Anystis), ei­ Beverley, Pinjarra . The species became es­ Mul ti-species sa mples as co llected were ther 9 or 10 of the RLEM and Entomobrya tablished at Miling and Pinjarra, whence held before use in large (2 litre) glass jars survived the tri al period. In cages with it spread slow ly until 1976 (Waterhouse containing cut grass, moist ti ssue, and Anystis, the number of surviving RLEM 1978, Wallace 1981). Steps were then ta ken shredded paper. The cages included large ranged from 0 to 9 (mea n 4.4), and the to accelerate its spread by a program of numbers of RLEM and Collembola number of surviving Elltomobryn ranged collection and re-release (Johnston 1981, (Hyp:Jgastnl ra , Eu tomobrya, and unidenti­ from 8 to 10 (mea n 9.5). The number of Michael et af. 1992). Anystis species A has fied Sminthuridae), as well as several RLEM killed by Anystis is clearly grea ter also been introduced from southern hundred Anystis. Samples of this material than the number of En tomobryn ki lled. France into South Africa. It has become were ti pped out onto a fl at white pla stic This may be attributed to the fact that Plant Protection Quarterly Vo1.6(4) 1991 183 moist o r dry tissue paper suspended over salt solutions to regulate the atmospheric humidity. COllditions required for hatching Females collected from the field in No­ vember continued la ying eggs until late December. Eggs laid in November first x hatched to prelarvae on January 24th, and x x x x the first larva e merged five days later. x x x x Eggs kept at 22°C retained the ability to x x x x x x x x x hatch; those kept at 35°C did not. Eggs x x x x that had been kept in high relative humid­ x x x x ity (93%) directly after oviposition sur­ x x x x vived and hatched. In contra st, egg clus­ x x x x x x x x ters that were transferred to medium (ca. x x x x x 55%) or low (ca . 33%) humidity directly x x x x x after OViposition died. without producing • preiarvae . Eggs laid in June were kept in moist conditi ons (93% plus available water) un­ til they had developed inside the egg shell to the prelarval stage. They were then able o KMS I to survive exposure to low humidity (33%). It therefore appears that prelarvae are drought resistant but freshly-laid eggs are not, and an initial moist period is nec­ essary for development to the drought­ resistant stage. Figure 3. Predicted distribution of Allystis species A in Australia. The duration of the obligatory moist pe­ riod is not known for November eggs, but Elltomobryn was usually able to jump fered 50 RLEM eggs, but did not attack has been tested on eggs laid in June. away and escape w hen Anystis ap­ them, despite the lack of alternative prey. Freshly-laid June eggs were given condi­ proached. Anystis was sometimes seen With Anystis present, 43 and 46 RLEM tions of high humidity and available apparently chasing specimens of eggs survived 18 hours in two trials; in moisture for varying periods, and then Entomobrya, but was unable to catch them . controls without Anystis, 48 and 47 sur­ transferred to low humidity (33%) for a Freshly killed coUembola were usually vived. period of 13 da ys. They were then wa­ ta ken as soon as they were offered to these In choice experiments, single Anystis tered to initiate hatching. Eggs that had an Anystis. It appears that Entomobrya is a adults were each offered 50 RLEM eggs initial moist period of less than 12 days preferred food, but is not available as prey with ]0 small sminthurids as alternative died without hatching. This period of 12 because it is almost impossible to catch. prey. In three such trials, almost none of days represents the time required for de­ Anystis was then offered a choice of the sminthurids survived an 18 hour pe­ velopment to the prelarval stage (see RLEM and Folsomin calldidn (Collembola, riod (0 out of 10; lout of 10; 2 out of 10). below). It therefore appears that the fully­ from a laboratory culture). Seven Anystis The proportion of RLEM eggs surviving developed prelarva is the stage that is ca­ adults were placed in a cage with large the same period was very high - 45 out of pable of surviving low humidity. These num bers of both potential prey species. In 50; 40 out of 50; 39 out of 50. In each of observati ons are based only on small a period of 3.5 hours of constant observa­ three control cages, 47 outof the 50 RLEM numbers of egg clusters, and should be tion, the seven Anystis killed a total of 14 eggs, and all the srninthurids, survived for tested more extensively. Falsamin, but did not kill any of the avail­ the duration of these experim ents. When Egg clusters in which some of the eggs able RLEM. In another trial, seven Allystis a gro up of four Anystis was offered 50 had split were transferred o nto a dry protonymphs killed 21 Folsomin in 12 min­ RLEM eggs, 87 RLEM of mixed stages, substrate, and no further prela rvae ap­ utes, but did not kill any RLEM, when and 100 small sminthurids, they killed 29 peared, despite the fact that the atmos­ large numbers of both species of prey sminthurids in one hour of constant ob­ pheric humidity remained above 900/0. As were present. servation, but did not attack RLEM or soon as the eggs were placed back onto their eggs at all. mo ist substrate with liquid water avail­ Does Anystis feed 011 RLEM eggs? able, further prelarvae appeared. The A single tritonyrnph of Anystis was of­ Egg laying and development splittingof the egg shell therefore appears fered 30 RLEM eggs, and destroyed 28 of Anystis species A females readily Ja y eggs to require the uptake of free water, in ad­ them in 24 hours. Control eggs not ex­ on moist tissue paper. They were laid in dition to a high ambient humidity. The posed to the predator all survived intact. clusters of 13 to 47 eggs, interwoven with water required for hatching was provided This encouraging result was then exam­ transparent filaments. It has not yet been artificiall y by dropping water directly ined further. The same Anystis trito­ determined how many eggs a female is onto the eggs or the tissue paper on which nymph was transferred into a choice ex­ capable of laying. These egg clusters were they were resting. In one case, an egg clus­ periment with SO RLEM eggs and 20small exposed to a variety of environmental ter collected water in the form of dew, sminthurids. In an hour of constantobser­ conditions to examine their hatching re­ when the temperature was allowed to vation the Anystis killed and sucked dry quirements. Hatching of eggs may be rec­ drop overnight. This suggests that eggs four of the sminthurid s, but did no t attack ognized by the splitting of the egg shell, laid on moist soil in the field can easily any of the RLEM eggs. and the emergence of the legs of the obtain the moisture they need to initiate Two adult Anyslis were separately of- prelarva. Eggs were placed on either hatching. 184 Plant Protection Quarterly VoI.6(4) 1991 A series of eggs was exposed to high area where Anystis had been released. into the COImcii for Scientific and Industrial temperatures (up to 100"C) for over 1 experimental plots of pasture. This result Research 2, 244. hour, and was then transferred into a drop cannot be explained in terms of the cur­ Baker, W.V. (1967). Some observations on of water. These eggs absorbed water and rent laboratory observations, in which predation in an anystid mite. Entomolo­ split their shells to expose the legs of the Anystis does not prey heavily upon gist's Monthly Magazine 103,58-9. prelarva. The prelarvae were kept at 93% RLEM. A partial explanation could be Dug~s, A. (1834). Recherches sur I'ordre relative humidity, which is normally suit­ found in the fact that RLEM leaves its des Acariens. Al1l1ales des Sciences able for further development. However, feeding site and runs quickly down to the Natllrelles. Zoologie 2,18-63 + Plates 7, 8. instead of developing, the prelarvae shriv­ crown of its food plant in response to the Froggatt, W.W. (1921). The Blue Oat Mite elled and collapsed, and were obviously slightest disturbance, such as a physical (NotophalIlls bicoIor, n. sp.). Agricllltllral dead. The uptake of water by the eggs touch. It is possible that a rapidly moving Gazette of New SOllth Wales 32, 33-4 + 1 must therefore be a passive physical proc­ such as Auystis could cause sig­ Plate. ess that does not require the presence of a nificant disturbance to the feeding of Cerson, U. and Smiley, R.L. (1990). living embryo. RLEM, and thereby increase its mortality 'Acarine Biological Control Agents'. indirectly. Also, conditions in the field are (Chapman and Hall, London). p. 48. Is there all egg diapallse? much more complex than those in artifi­ Holm, E. and Wallace, M.M.H. (1989) . Egg clusters that were laid in June were cial laboratory cages, and there may be Distribution of some Anystid mites kept constantly moist, with free water other causes of mortality that have not yet (: Anystidae) in A ustralia and In­ available, and produced prelarvae 12 been identified. donesia and their role as possible preda­ days after ovipoSitjon, and larvae Develo pmental studies showed that to rs of the cattle tick Boophilils microplils emerged 4 - 5 days later. Eggs from one embryos complete their development (Acari: Ixodidae). Experimental and Ap­ egg cluster were transferred into low hu­ soon after oviposition in a moist environ­ plied Acarology 6, 77-83. midity for two days just before the ment. During this initial period, the em­ johnston, B.C . (1981) . 'Public and Private prelarvae were expected to appear. Sub­ bryo reaches a prelarval stage, and is then Interests in Government Funded Re­ sequently they were transferred back into able to withstand a period of drier condi­ search'. (Ph. D. thesis, Australian Na­ moist conditions. Prelarvae appeared the tions. The fully developed prelarval stage tional University). next day, and later developed. into living then remains inside the egg shell until a Lange, A.B., Drozdovskii, E.M. and larvae without any apparent breaks in de­ wet period caused by rain or dew triggers Bushkovskaya, L.M . (1974). The mite velopment. There is therefore no evidence its emergence. There does not appear to Allystis - an effective predator of small to suggest the existence of a diapause for be an obligatory egg diapause. The crack­ phytophages. Zashd.ita Rnstellii 1, 26-8. eggs laid in june. Eggs laid in November ing of the egg shell can be induced at any (In Russian). hatched and developed through to the time by the uptake of water, but only if Maywald, C.F. and Sutherst, R.W. (1991) . tritonymph stage over the summer, at a the embryo has developed for at least 12 User's guide to CLIMEX, a computer time when living mobile stages cannot be days. These laboratory results are consist­ program for comparing climates in collected in the field. This suggests that ent with observations from the field, in ecology. CSIRO Division of Entolllology there is no obligatory diapause in the which Anystis is first observed after the Report 48, 1-51. summer either, but this has yet to be first rains in autumn, but can appear after Meyer, M.K.P. (Smith) (1981). Mite pests tested experimentally. exceptional rainfall in summer (P . of crops in southern Africa. Science Bul­ Michael, personal communkation). It letin, Department of Agriculture and Fish­ Post-larval development therefore appears likely that eggs can be eries, Repllblic of SOllth Africa 397, 1-92. Mites collected in june were kept in large stored at 93% humidity but without free Meyer, M.K.P. (Sm ith) and Ueckermann, population cages for apprOXimately two water until required, and then induced to E.A. (1987). A taxonomic studyof some weeks and were then removed, leaving hatch by watering at any time when Anystidae (Acari : ). Ento­ their eggs behind. The first larvae ap­ predatory mites are re<:Juired . mology Memoirs, Department of Agricul­ peared in these cages on june 29th, and tllre and Water SlIppIy, Repllblic of SOllti. the first adults on july 27th, giving a first Acknowledgements Africa 68, 1-37. approximation of the larva to adult devel­ We would like to thank Murray Wallace, Michael, P.j., Dutch, M.E. and Pekin, c.j. opment time of 28 days, at 22' C. Detailed who was responsible for the early work (1992). Biological control of redlegged measurements of the duration of the im­ on Anystis species A and for the field earth mite, Halotydeus destructor, blue mature instars have not yet been com­ work in Europe, and Cunther Maywald oat mite, Penthnleus major, and lucerne pleted. for help with the CLlMEX analysis. The flea, Sminthurus viridis . In 'Pests of pas­ Collemhola were identified by Penny tures: weed, invertebrate and disease Discussion Greenslade, the aphids were generously pests of Australian sheep pastures' ed. The results of feeding trials indicate that donated by Peter Hart, and Phil Michael E.5. Delfosse (In press). Any,tis will attack RLEM adults and eggs supplied the living specimens of Anystis Newman, L.j. (1925). The Red Legged under some circumstances, but not in the without which this work would have Earth Mite Penthniells destrllctor (jack). presence of alternative food . Anystis sp. A been impossible. 10llrnal of the Department of Agricllltllre appears to be a general feeder attacking a of Western Australia (Second series) 2, wide variety of , as has been References 469-75. shown for other species of Anystis (Baker Allen, P.C. (1987). Insect pests of pasture Newman, L.j. (1929). Red Legged Earth 1967, Lange et al. 1974, Sorensen et al . in perspective. In 'Temperate pastures: Mite. 10llmal of the Department of Agri­ 1976). Anystis is likely to encounter a vari­ Their prod uction, use and manage­ culture of Western Australia 6, 449-52. ety of other prey in field conditions, and ment', eds j.L. Wheeler, c.j. Pearson, Otto, j.c. (1992). A new species of Anystis would not depend on catching RLEM. It and C.E. Robards (Australian Wool von Heyden compared with Anystis therefore appears unlikely thatAnystis sp. Corporation/CSIRO, Melbourne). p. salicin us (Linnaeus) (Acarina : A will kill large numbers of RLEM under 211. Anystidae). International Journal of fie ld conditions. Anonymous (1929). The Red Legged Acarology (In press). Wallace (1981) recorded a substantial Earth Mite in Western Australia Oudemans, A.C. (1936). Neues tiber decrease in the numbers of RLEM in an (Penthalell s destntetor, jack). 10llmal of Anystidae (Acari). Archiv fiir Plant Protection Quarterly VoI.6(4) 1991 185 Nalllrgeschichle 5,364-446. tllre, Ullioll of SOllih Africa 3, 21-36. Sorensen, J.T., Kinn, D.N., Doutt, R.L. and Wallace, M.M.H. (1981). Tackling the lu­ Cate, J.R. (1976). Biology of the mite, cerne flea and red-legged earth mite. Allystis agilis (Acari: Anystidae) : A !ollmal of Agriculture, Westerll Australia California vineyard predator. Annals of 22, 72-4. the Entomological Society of America 69, Waterhouse, D.F. (1978). Pasture pests 905-10. and biological control in A ustralia. Pro­ Sutherst, R.w. and Maywald, C.F. (1985). ceedings of the 2nd Australasian Con­ A computerized system for matching ference on Grassland Invertebrate Ecol­ climates in ecology. Agriculture, E.cosys­ ogy. eds. T.K. Crosby, and R.P.

tems and Environm ent 131 281-99. Pottinger (Government Printer, Wel­ Swan, D.C. (1934). The Red-Legged Earth lington, New Zealand). p. 12. Mite Halolydell' destruc/or (Tucker) in Womersley, H. (J 933). On some Acarina South Australia: With remarks upon from Australia and South Africa. Trans­ Pen/halell' major (Dug~s). TOIITllal of Ag­ actioll' of Ihe Royal Sociely of SOlllh Alls­ ricllltllre ofSolllh AII,tralia 38, 353-67. lralia 57, 108-12. Tucker, R.W.E. (1925). The Black Sand Womersley, H. (1942). The anystid mites Mite: Penthaleus destructor n. sp. Ento­ of Australia. Tran sactiolls of the Royal mology Memoirs , Department of Agriclll- Sociely of SOlllh A IIslralia 66, 15-22.

persist in any layerof natu_ral or semi-natu­ ral ecosystems but which are not particu­ larly aggressive and which cannot ordo not as monospecies dominate that layer or seri­ Letters to the Editor ously alter the vegetation or its functioning. although the accumulation o f several to many such species may do so. These are less serious environmental weeds and some may even be of benefit. Towards a rating schem e for environ­ semi-natura l ecosystem, thereby totally or 5. Ruderal weeds. Mostly annual plants mental weeds largely altering its nature and functioning. which are primarily weeds of cultivation The most serious environmental weeds are etc. and which are only able to invade and Dear Editor, in this group, which includes trees, aggres­ persist in severely and recently disturbed The need for a rating scheme for envi­ sive vines, thicket-forming shrubs and areas such as trackways. They sca rcely in­ ronmental weeds has become apparent dense herbs, all of which are able to domi­ vade or persist in established vegetation whilst preparing a database of Australian nate the ecosystems which they invade by and may have some value in stabilizing se­ environmental weeds with their distribu­ replacing or overtopping the natural verely disturbed areas and in retaining soil, tion and control. Marilyn Fox (this journal canopy. nutrients and organic matter. They are not Vol. 6 No.3 p. 109) has also considered the 2. Subcanopy dominanl weeds. Plants rea lly environmental weeds. need for such a scheme, suggesting that which can as monospecies dominate or re­ Each of these five levels can be used aggressiveness and life form are im portant place any subcanopy layer of a natural or alone to give a clear indication of the poten­ characteristics that should be considered as semi-natura l ecosystem, thereby prevent­ tial importance of an environmental weed, well as a weed's ability to act as a point ing or altering the course of replacement although intermediates will obviously oc­ source for further spread, its method of and natural regeneration and eventuall y cur and a plant may be in different catego­ propagule dispersal, and its reproductive seriously affecting its vegetational struc­ ries in different ecosystems or localities, potential. ture, integrity and functioning. These are Each main category can be expanded by To be of widespread use any such also serious environmenta l weeds. the use of letters to indicate its life form scheme should be widely acceptable to and 3. Special effect weeds. Plants which can (e.g., I (tree), v (vine), , (shrub), h (herb), supported by the range of workers in the as monospecies significantly degrade the im portance (e.g., p (point source), a (a ller­ field and should therefore be: developed by va lue or purpose for which a natural or genic), v (visual impact), or some other im­ people of different viewpoints and experi­ semi-natural ecosystem is valued without portant attribute. Broadleaf privet in moist ence; basically simple but capableof elabo­ necessarily dominating it or greatly alter­ basaltic woodlands of southeast Queens­ rationi and applicable across the full range ing its vegetational structure or function­ land would be a 1tp weed, and anyone can of ecosystems, ing. These are also serious environmental use or elaborate the scheme to rate their A Simple indicator of the aggressiveness weeds. Examples include weeds which ad­ own environmental weeds. and potential effect of the weed on the eco­ versely affect seal-pupping on islands, Suggestions for developing this or an al ­ system seems to be the dominant require­ compete with and replace similar native ternative rating scheme for environmental ment suggesting the following scheme plants and deplete the food source of an en­ weeds would be welcomed. which is put fOlWard as a starting point for dangered animal, damage historically im­ Dr. J.T. Swarbrick discussion. portant structures, are of high visual im­ University of Queensland, 1. Canopy dominant weeds. Plants which pact, or chemically irritate users of the area Ca tton College, can as monospecies dominate, replace or through allergens or stings. Catton, Qld 4343, Australia. overtop the natural canopy of a natural or 4. Minor weeds. Plants which invade and 18 November 1991