Zoology - Theses
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ItemEffect of vegetation diversity on natural enemy abundance in two agricultural contexts( 2012)Vegetation diversity has long been known to enhance natural pest control at both the local and landscape level. However little is known about the characteristics of this vegetation that promote/shelter more natural enemies and suppress pests. The main aim of this thesis was to examine how characteristics of common non-crop vegetation influence the abundance, diversity and association of natural enemies residing in two different agricultural systems (canola fields and vineyards). These crops were chosen to contrast annual and perennial cropping systems. Canola, grown directly after a pasture phase of a field, is Australia’s most important oilseed crop. Pressure on invertebrates may be greater due to level of disturbance; in contrast, vineyards are often surrounded with various types of vegetation which may enhance invertebrate abundance. To explore this aim, the effect of within crop, non-crop vegetation (grass strips within canola crop) on abundance of pests and natural enemies in the crop was examined. Invertebrates were collected across grass-canola transects in two fields planted to canola with unsown grass strips at intervals. Sampling with pitfall traps and vacuum sampling was completed to collect ground dwelling fauna during two sampling periods: post sowing and post emergence of canola seeds. Invertebrates collected were categorized mainly into two groups: pests and natural enemies. Abundant pests in the canola fields were red legged earth mite, Halotydeus destructor; blue oat mites, Penthaleus spp. and lucerne flea, Sminthurus viridis. Natural enemies considered were spiders (Araneae), predatory mites (Acari), predatory beetles (Coleoptera) and parasitoids (Hymenoptera). In general more predators and parasitoids were found in the unmown grasses of grass strips and more pests in mown sections of the grass strips and overall pests were more abundant in the crops than in grass strips. Vegetation types may have different influences on the biota that reside within them. Thus the effectiveness of different vegetation types in promoting conservation biological control was assessed at vineyards with two types of non-crop habitat: adjacent- grass with and without trees. Invertebrates were sampled in the canopy with sticky traps and on the ground with pitfall traps at 40 sites from six different vineyards at Yarra Valley (Victoria) for five consecutive months from bud burst to harvest (October through February). Collected invertebrates were classified as natural enemies and other invertebrates since none of the invertebrates collected are considered as pests in vineyards. The most abundant natural enemies were generalist predators (spiders and predatory beetles Coleoptera: Carabidae and Staphylinidae) and parasitoids (Hymenoptera), lacewings (Neuroptera), hover flies (Diptera: Syrphidae) and other predatory Diptera (Asilidae, Empididae and Tachinidae), predatory thrips (Thysanoptera), predatory Hemiptera, and ladybird beetles (Coleoptera: Coccinellidae). Other invertebrates analyzed included several other beetle families, thrips (Thysanoptera) and several herbivore families of Hemiptera. Overall no effect of vegetation diversity was identified in this study though a significant vineyard effect was revealed for most of the natural enemies and other invertebrates.