C. M. Ferguson

Predicting the Risk from Biological Control Agent Introductions: A New Zealand Approach

Since the publication of Silent Spring (Carson 1963) there has been increasing demand to reduce the amount of agricultural pesticides used. This need has been further supported by the development of increasing levels of pesticide resistance, and the market advantages for products from “sustainable” agricultural systems. Classical biological control, where a predator, parasite, or pathogen is imported to control a weed or pest, is one obvious alternative to pesticides and has often been promoted as environmentally safe (e.g., DeBach and Rosen 1991).

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand II. Nematodes

Abstract Soil samples were taken from around the base of tussock plants and paired areas of inter‐tussock vegetation at four native tussock grassland sites across New Zealand, in three consecutive summers. Seventy nematode taxa were identified with the plant associated nematode trophic group being the most abundant at three of the four sites. Of the plant parasitic nematodes, Criconema, Pratylenchus, and Helicotylenchus spp. were found at all sites, with Hemicycliophora, Longidorus, a putative Punctodera, and Rotylenchus found at only one site each. The observation of mermithid nematodes at three of the four sites, coupled with absence of insect parasitic Steinernema or Heterorhabditis sp. from microscopic observations and soil baiting suggests that the insect parasitism niche is occupied largely by mermithids in the tussock grassland habitats studied. A range of community indices were calculated, with Shannon‐Weiner (2.10–2.39), Simpson dominance (0.129–0.205), Maturity Index (2.67–2.92), and Structure Index (67.7–87.5) being significantly different among sites. Total nematode abundance was significantly greater beneath tussock than inter‐tussock vegetation, but the number of nematode taxa and species richness were significantly greater from inter‐tussock samples. This suggests that tussocks may provide a more productive habitat but that the increased diversity of the vegetation in inter‐tussock areas is reflected in some measures of nematode diversity. Comparisons are made and discussed with other studies of native grassland nematodes in New Zealand and worldwide.

Effect of Fire on Microarthropods in New Zealand Indigenous Grassland

Abstract Indigenous tussock grassland in New Zealand has a history of extensive pastoralism, and burning has been used to remove litter to improve establishment of aerially oversown pasture species and to promote palatable tussock growth for livestock. In recent years, considerable areas of tussock grassland have been retired from grazing and formally protected. Conservation land managers, as well as farmers, require information on the impacts of both managed burns carried out in spring and accidental fires that usually occur in warmer, drier conditions in summer. This study investigated the impact of spring and summer tussock grassland burning on the predominant soil microarthropods, Collembola and Acari, at 2 sites in Otago, in the South Island of New Zealand. Quantitative sampling was carried out before and for up to 26 months after burning replicated 1-ha plots. Total density of microarthropods in unburnt plots covered a similar range at both sites with an average over 3 years of about 18 000–20 000·m−2 at each site. Both sites shared a dominance of Mesostigmata and Oribatida (Acari) and Isotomidae (Collembola). Burning in spring reduced densities of Oribatida after treatment at both sites for the duration of the study. However, after initial postburn reductions in density, populations of Isotomidae and Poduroidea (Collembola) recovered in the second year after burning. Prostigmata (Acari) appeared to be unaffected by fire. The effects of spring and summer grassland fires on microarthropod densities were rarely different. It was concluded that longer-term sampling would be required to observe the full recovery period for microarthropod populations after fire but that results from this study indicate rapid recovery of some microfaunal populations after fire, which is not strongly influenced by seasonal effects.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island of New Zealand I. The macro‐invertebrate fauna

Abstract This contribution introduces a short series of papers on biodiversity of indigenous tussock grassland at four sites in New Zealand. A survey of invertebrates of tussock grassland sites was carried out in summer of 3 successive years, 2001–03. The sites included two in Otago in snow tussock grassland at Deep Stream and Mt Benger, a site at Cass in inland Canterbury, and one at Tukino in the central North Island. Sampling was carried out by taking turf samples from each site, and extracting the invertebrates with heat extractors. The invertebrates were divided into 30 major groups. This quantitative sampling method allowed the densities of invertebrate groups to be calculated. Total macro‐invertebrate density for all sites ranged between c. 1600 and 5600 m–2. Total invertebrate abundance was highest at the central North Island site, but this was very much dominated by Formicidae. Across all sites, Formicidae, Coleoptera, and Pseudococcidae were consistently the most abundant groups represented.

Using Models to Estimate Parasitoid Impacts on Nontarget Host Abundance

Abstract A method is described for estimating the impact of a parasitoid on the abundance of a nontarget host, using the intrinsic rate of host increase, the average abundance of the host in the presence of parasitism, and the estimated mortality caused by the parasitoid. The method is applied to the braconid Microctonus aethiopoides Loan, introduced to New Zealand to control Sitona discoideus Gyllenhal in lucerne but also attacking native weevils Irenimus spp. and Nicaeana spp. The nontarget host population was modeled using discrete Ricker or continuous logistic models, tuning the models to host population data in the presence of parasitism, then removing parasitism and determining the increase in predicted equilibrium host density. In an area where up to 30% parasitism of a nontarget host population has been recorded, the model estimated an 8% reduction of the nontarget host. In another area, where the parasitoid has not established, the method was applied in reverse to predict the parasitoid’s impact if it did establish. In this case, the model predicted a 30% suppression of population density. The host’s intrinsic rate of increase, rm, accounts for this difference in predicted impact, which was small in the low altitude area where rm was high, and the impact was larger in the higher altitude site where rm was smaller.

Field Parasitism of Nontarget Weevil Species (Coleoptera: Curculionidae) by the Introduced Biological Control Agent Microctonus aethiopoides Loan (Hymenoptera: Braconidae) over an Altitude Gradient

Abstract The parasitoid, Microctonus aethiopoides Loan (Hymenoptera: Braconidae) was introduced into New Zealand in 1982 to control the alfalfa pest, Sitona discoideus Gyllenhal (Coleoptera: Curculionidae). Studies have shown that a number of nontarget weevil species are attacked in the field by this parasitoid. A field study was carried out to investigate nontarget parasitism by M. aethiopoides over an altitudinal sequence from the target host habitat (alfalfa) into native grassland. Three locations were selected for the study, and at each, the alfalfa growing in the valley floor was sampled annually for parasitism of the target pest that ranged between 17 and 78%. At progressively higher altitudes, three further grassland sites at each location were sampled monthly during spring to autumn for up to 6 yr. Weevil densities were estimated, species identified, and dissections carried out to determine reproductive status and parasitism. Almost 12,000 weevils were collected during the study, which were identified as 36 species in total from the three locations. Eight weevil species were found to be parasitized, including S. discoideus, the target host that was found at all sites. Parasitism of nontarget species was ≈2% overall but varied with location, site, and season. Substantial nontarget parasitism was found at only one of the locations, with up to 24% parasitism of a native weevil, Nicaeana fraudator Broun (Coleoptera: Curculionidae), recorded. Another species, Irenimus egens (Broun) (Coleoptera: Curculionidae), was also found at this location at similar population densities but was attacked far less by M. aethiopoides. Results are discussed in relation to weevil phenology.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the Central North Island of New Zealand VI. Coleoptera biodiversity, community structure, exotic species invasion, and the effect of disturbance by agricultural development

Abstract The diversity of Coleoptera communities in tussock grassland at two sites in Otago, one in Canterbury and one in the central North Island, was compared. The impact of agricultural disturbance on the communities was compared between native tussock, tussock oversown with exotic pasture species and cultivated sown pasture. Coleoptera were heat-extracted from turf samples taken in summer in two consecutive years. In native and oversown treatments, Staphylinidae and Curculionidae predominated in abundance at three of the four sites, and in species richness at all sites and treatments. Carabidae were more species-rich than Curculionidae in cultivated treatments at most sites. The mean density of Coleoptera in native tussock treatments ranged between 654/m2 and 97/m2. Carnivores were the predominant trophic group followed by herbivores. Species diversity was higher in the native or oversown treatments and the Otago sites were the most diverse overall, and the least disturbed. A total of 19 exotic species were found but there was no relationship with treatment, although their density was higher in cultivated treatments. There was no evidence to suggest that modified vegetation provides a source of exotic Coleoptera species to invade native tussock.

Effect of native weevils (Coleoptera: Curculionidae) on white clover establishment and yield in tussock grassland

Abstract A trial was carried out in unimproved tussock grassland on the East Otago Plateau of the South Island of New Zealand to investigate the impact of native broad-nosed weevils (Coleoptera: Curculionidae) feeding on survival, establishment, and yield of oversown white clover. The trial consisted of 20 sites 1 km apart where two plots were established in each of 5 consecutive years. At each of the sites in each year, one of the plots was sprayed with parathion at 2-weekly intervals from September to December to allow seedlings to establish in “insect-free” conditions. The other plot was left untreated. The plots were sown in October and, by late December, seedlings suffered on average 40 and 6% mortality in the untreated and sprayed plots respectively. Sublethal insect feeding reduced nodulation on average by 46% and final established plant density by 39% in the unsprayed plots. Despite identical treatment of the two plots after the initial 3 months, white clover yields were significantly higher in th...

Seed coating with insecticide to improve oversown white clover (Trifolium repens L.) establishment in tussock grassland

Abstract Laboratory and field‐screening experiments were carried out to evaluate a range of systemic insecticides for protection of white clover (Trifolium repens L.) seedlings from native broad‐nosed weevil (Curculionidae: Brachycerinae) feeding damage, and for compatability with rhizobia. A laboratory bioassay showed that acephate, carbosulfan, oxamyl, thiodicarb, triaziphos, isofenphos, and lindane could reduce weevil feeding damage and increase seedling survival. When evaluated in the field, carbosulfan and isofenphos improved early seedling establishment more effectively than lindane and acephate. A commercially available white clover seed treatment, furathiocarb, increased seedling survival, and yield for up to 13 months after sowing. In the laboratory, carbosulfan, or its liquid carrier, caused rapid mortality of rhizobia whereas isofenphos and furathiocarb caused no significant mortality of rhizobia.

Biodiversity of indigenous tussock grassland sites in Otago, Canterbury and the central North Island. V. Penicillia and aspergilli

Abstract In the course of a series of investigations into the biodiversity of indigenous tussock grasslands, penicillia and aspergilli were isolated from soil samples from four locations: Deep Stream and Mt Benger in Otago, Tukino in the central North Island and Cass in Canterbury. Samples were collected in the summers of 2003 and 2005 and, at each locality, were taken from sites under indigenous tussock grassland, under oversown tussock grassland and under pasture cultivated from tussock grassland. Isolations were made on potato‐glucose‐chlortetracycline agar plates inoculated with soil suspensions. Thirty‐six Penicillium species were recovered, all cosmopolitan, and of the 12 most common, 10 species: P. canescens,P.janthinellum,P.janczewskii,P.jensenii,P. lividum, P. loliense, P. melinii, P. miczynskii, P. sclerotiorum and P. simplicissimum were isolated from samples from all four locations but P. montanense and P. novae‐zeelandiae were not recovered from Deep Stream or Mt Benger. P. lividum and P. sclerotiorum were recovered mainly from samples from indigenous sites and P. jensenii from oversown or cultivated sites. In other countries, some of these species have been associated with forest‐grassland rather than grassland soils and it was thought possible that they were relics associated with pre‐human forest vegetation which may have covered the localities. At the subgenus, not species, level, however, the pattern was typical of grassland, not forest, soils, with the subgenus Furcatum dominant. Six of the common species are known to have the potential to produce tremorgens, neurotoxins known to cause incoor‐dination when ingested by mammals but with little investigated effects on invertebrates. Aspergillus cervinus was the only Aspergillus species recovered, only from Tukino and principally from samples from the indigenous sites.