Literature review: Impact of Chilean needle grass ... - Weeds Australia

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