Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
Literature review: Impact of Chilean needle grass ... - Weeds Australia
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species (Lawton and Schroder 1977 p. 138). Lawton and Schroder (1977) found evidencefor this relationship for monocot<br />
species (not including <strong>grass</strong>es) but not other plant groups they analysed in Britain.<br />
No published records have been located <strong>of</strong> invertebrates feeding on N. neesiana in <strong>Australia</strong> although a few species are known to<br />
feed on Nassella trichotoma. A most interesting recent development is the finding by Braby and Dunford (2006) <strong>of</strong> empty pupal<br />
cases <strong>of</strong> the endangered Golden Sun Moth Synemon plana Walker (Lepidoptera: Castniidae) protruding from N. neesiana<br />
tussocks, from which it was inferred to be a probable larval food plant (see further discussion below).<br />
Zimmerman (1993) recorded N. trichotoma and “some other <strong>grass</strong>es” as hostplants <strong>of</strong> the ground weevil Cubicorhynchus<br />
sordidus Ferguson (Coleoptera: Curculionidae: Amycterinae: Amycterini), evidently an identification <strong>of</strong> Howden’s (1986)<br />
“Cubicorrhynchus sp.” observed near Yass, NSW (see also May 1994), and noted that B.P. Moore had found both larvae and<br />
adults <strong>of</strong> the NSW species Phalidura abnormis (Macleay) (Amycterini) feeding on N. trichotoma, the native host plants being<br />
unknown. Larvae <strong>of</strong> P. elongata (Macleay) feed on underground parts <strong>of</strong> N. trichotoma, and other <strong>grass</strong>es (Zimmerman 1993),<br />
while adults consume N. trichotoma and pupae are also found in association with it (Howden 1986). Howden’s (1986) listing <strong>of</strong><br />
Phalidura assimilis Ferguson feeding on N. trichotoma near Yass are treated by Zimmerman as P. abnormis and May (1994)<br />
listed P. abnormis as the only known Phalidura N. trichotoma feeder. Adults and a larva <strong>of</strong> Cubicorhynchus calcaratus Macleay<br />
<strong>of</strong> eastern and southern <strong>Australia</strong> have been found in a clump <strong>of</strong> “Stipa” in South <strong>Australia</strong>, while Austrostipa nitida and A.<br />
nodosa along with other <strong>grass</strong>es are hosts <strong>of</strong> another eastern and southern species C. taurus Blackburn, with larvae found in the<br />
crowns and root masses (Howden 1986, Zimmerman 1993, May 1994). Other species in the genus also have <strong>grass</strong> hosts<br />
including Microlaena stipoides and “Stipa” for the Western <strong>Australia</strong>n C. bohemani (Boheman) (Zimmerman 1993) and<br />
unidentifed <strong>grass</strong> for C. crenicollis (Waterhouse) (May 1994). Howden (1986 p. 100) noted that all Cubicorhynchus species<br />
“collected to date have been associated with either native or introduced species <strong>of</strong> Poaceae”. Larvae “collected from the crowns<br />
<strong>of</strong> <strong>grass</strong> plants <strong>of</strong>ten regurgitated green material, indicating that they fed on underground stems and not the roots” (Howden 1986<br />
p. 100). Sclerorinus spp. (Amycterini) have been recorded from undetermined “Stipa sp.” (May 1994 p. 495). Amycterini are<br />
flightless ground-dwellers and most are confined to <strong>grass</strong>es, or other monocots, most larvae living underground in the root<br />
crowns and the adults eating leaves, evidently including, unusually, dry <strong>grass</strong> (Zimmerman 1993). Larvae are free living in the<br />
soil and eggs are deposited directly into the substrate, rather than a prepared site (Howden 1986, May 1994). Adults <strong>of</strong> the<br />
species that feed on wiry stems have stout, blunt mandibles and gular roll (‘lip’), while species that feed on s<strong>of</strong>t tissues have a<br />
different mouthpart morphology (Howden 1986). Themeda triandra and Austrodanthonia are not known hosts (not mentioned in<br />
Zimmerman 1993 or May 1994). Zimmerman (1993) considered the tribe to be Gondwanaland relics with no known closely<br />
related group in South America. “Over vast areas <strong>of</strong> the country the Amycterinae have been nearly exterminated by the clearing<br />
<strong>of</strong> vegetation, cultivation and the grazing <strong>of</strong> livestock, especially by the destructive activities <strong>of</strong> millions <strong>of</strong> sheep” (Zimmerman<br />
1993 p. 176).<br />
Gardener et al. (1996a) suggested that N. neesiana seed predation by ants appeared to be lacking, possibly due to the<br />
impenetrability <strong>of</strong> the lemma providing good protection to the edible caryopsis. However Gardener (1998) set up experiments in<br />
pasture in which de-awned seeds were placed on the soil surface or buried in soil at 1.5 cm depth and exposed for six weeks from<br />
late January to early March, or <strong>of</strong>ferred, along with de-awned Themeda triandra seed, in dishes arranged to prevent access by<br />
larger animals for 4 weeks in May. In the first experiment 99.5% <strong>of</strong> buried N. neesiana seeds were recovered but significantly<br />
fewer (71%) <strong>of</strong> the unburied seeds. In the second experiment 97.5% <strong>of</strong> the seeds <strong>of</strong> both species were recovered (“no seeds ...<br />
taken” Gardener 1998 p. 53). The experimental results were considered inconclusive: seeds in the first experiment may have<br />
been removed by other organisms, ants may have been inactive in the second experiment or not interested in the seeds. No<br />
identification was suggested for any ant species that may have been responsible.<br />
Absence <strong>of</strong> ant predation appears to be unlikely. On a world basis, Formicidae are amongst the most important granivores in<br />
desert ecosystems (Saba and Toyos 2003). Ants are the dominant seed predators in the Sonoita Plains <strong>grass</strong>land <strong>of</strong> Arizona,<br />
where they selectively remove seeds with awns, projections or significant pubescence (Pulliam and Brand 1975). The other main<br />
seed predators, sparrows and rodents, consume smaller amounts, selectively favour ‘smooth’ seeds, and have different seasonal<br />
foraging patterns, so have little dietary overlap with the ants. In the Monte Desert <strong>of</strong> northern Patagonia, Argentina, where the<br />
vegetation is a steppe dominated by Larrea divaricata Cav. and stipoid <strong>grass</strong>es, ants are the most important granivores in spring<br />
and summer, but remove little seed in other seasons (Saba and Toyos 2003). Ants are the dominant granivores in arid areas <strong>of</strong><br />
<strong>Australia</strong> (Morton 1985), although the dominant <strong>grass</strong>es in these areas rarely include stipoids. The <strong>Australia</strong>n fauna <strong>of</strong> seedharvesting<br />
ants is rich and the species are capable <strong>of</strong> causing severe seed losses: up to 90% <strong>of</strong> weed seeds in crops can be<br />
removed (Vitou et al. 2004). Ants are the dominant weed seed predators in agricultural landscapes in Western <strong>Australia</strong> and have<br />
preferences for particular weed species (Minkey and Spafford Jacob 2004). The few studies <strong>of</strong> ants in south-eastern <strong>Australia</strong>n<br />
native <strong>grass</strong>lands show that seed-harvesters are generally present (Coulson 1990 appendix 3, Miller and New 1997), one <strong>of</strong> them,<br />
Pheidole sp., being amongst the most abundant ants in Victorian Basalt Plains <strong>grass</strong>lands (Yen et al. 1994a). The seeds <strong>of</strong> N.<br />
neesiana are very similar to those <strong>of</strong> some Austrostipa spp., so it appears highly likely that they would be harvested by ants as a<br />
matter <strong>of</strong> course. Ant seed herbivory has been found to be higher for African <strong>grass</strong>es in Brazil compared to native savannah<br />
species (Klink 1996), so in <strong>Australia</strong> N. neesiana seeds may even by preferred.<br />
Apart from ants, Gryllidae and granivorous carabid ground beetles are the most important post-dispersal seed predators in<br />
temperate agro-ecosystems (Lundgren and Rosentrater 2007) and no doubt the seeds <strong>of</strong> N. neesiana must be destroyed by speices<br />
in these groups, although only one example seems to be on record. Slay (2001 p. 33) recorded that “field crickets” consumed<br />
shed N. neesiana seeds in a New Zealand pasture. The seeds were “hollowed out” and the insect “might well be implicated in<br />
reducing the numbers <strong>of</strong> recently shed seeds”. This is almost certainly the Black Field Cricket, Teleogryllus commodus (Walker)<br />
(Gryllidae), a recognised pasture pest in New Zealand (Heath 1968) and <strong>Australia</strong>, and a common native insect in south-eastern<br />
<strong>Australia</strong>n <strong>grass</strong>lands.<br />
A wide range <strong>of</strong> non-specific <strong>grass</strong> feeders including Orthoptera, Thysanoptera (thrips), Hemiptera (true bugs) and Noctuidae<br />
(Lepidoptera) are likely to be found to utilise N. neeiana in <strong>Australia</strong> (see the Appendix to this <strong>Literature</strong> Review).<br />
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