New Zealand Journal of Zoology abstracts

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^*Author for correspondence.
Z99029
Received 8 July 1999; accepted 1 August 2000

Biology of insects that feed in the inflorescences of Chionochloa (Poaceae) in New Zealand and their relevance to mast seeding

MARK J. MCKONE^*
DAVE KELLY
ANDREA L. HARRISON⁺
JON J. SULLIVAN^**
ANGELA J. CONE

Department of Plant and Microbial Sciences
University of Canterbury
Private Bag 4800
Christchurch 1, New Zealand

^*Present address: Department of Biology, Carleton  College, Northfield, Minnesota 55057-4025, USA.  Email: mmckone@carleton.edu

⁺Née Andrea L. Thom.

^**Present address: Landcare Research,

Private Bag 92170

Auckland, New Zealand

Abstract  Inflorescences of New Zealand Chionochloa species are attacked by at least three insects, two flies and a moth. There has been disagreement about the identity of various life stages of these insects. We followed the seasonal pattern of occurrence of the two fly species that fed in Chionochloa pallens inflorescences in a population on Mt Hutt, Canterbury. Eggs and larvae of Diplotoxa similis (Diptera: Chloropidae) appeared in the inflorescences as soon as they emerged. The larvae are principally flower feeders, and most D. similis individuals had pupated by the end of the flowering period. Diplotoxa similis adults emerged from the puparia at the end of the season, and probably overwintered as adults. The second fly was an undescribed cecidomyiid (Diptera: Cecidomyiidae). Eggs of the cecidomyiid are laid into the C. pallens florets at the time of flowering, and hatch into mobile, translucent, early-instar larvae. Late-instar larvae were less mobile and opaque orange, and probably dropped from the inflorescences late in the season. The third species, Megacraspedus calamogonus (Lepidoptera: Gelechiidae) has large mobile caterpillars which appear early in the season, but there is doubt about its egg morphology and oviposition sites. On two dates there was a negative correlation between densities of the two fly species among plants. Since D. similis appears first, it may be able to usurp resources and reduce densities of the cecidomyiid. A review of known occurrences of the three insects suggests that, compared to D. similis and M. calamogonus, the cecidomyiid (1) has a greater geographic range and (2) occurs on more Chionochloa species; however, these trends might be due to poor sampling of D. similis and M. calamogonus early in the season. The cecidomyiid appears to be less easily satiated than D. similis by masting in Chionochloa.

Keywords  Cecidomyiidae; Chionochloa (Poaceae); Diplotoxa similis (Diptera: Chloropidae); distribution; host range; insect flower feeding; mast seeding; Megacraspedus calamogonus (Lepidoptera: Gelechiidae); New Zealand grassland; predispersal seed predation; seasonal phenology

New Zealand Journal of Zoology, 2001, Vol. 28: 89-102
0301-4223/00/2801-0089 $7.00/0   (c) The Royal Society of New Zealand 2001



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