Pauline Syrett

The invertebrate fauna on broom, Cytisus scoparius,in two native and two exotic habitats

This study quantifies the invertebrate fauna found on broom, Cytisus scoparius, L. (Link), in two countries where it grows as a native plant (France and England) and two countries where it grows as an alien plant (New Zealand and Australia). The data are used to test three hypotheses concerning the predicted differences in invertebrate community structure in native versus exotic habitats: (1) Are generalist phytophages dominant in exotic habitats and specialist phytophages dominant in native habitats? (2) Are there empty phytophage niches in exotic habitats? (3) As a plant species accumulates phytophages, do these in turn accumulate natural enemies? The broom fauna was sampled at five sites in each country by beating five broom bushes per site. The sampling efficiency of beating was quantified at one field site and it was shown to collect 87 % of invertebrate abundance, 95 % of invertebrate biomass and 100 % of phytophagous species found on the branches. Generalist phytophages were dominant on broom in exotic habitats and specialists dominant on broom in the native habitats. Thus, the two countries where broom grows as a native plant had higher numbers of total phytophage species and a higher abundance of specialist phytophages per bush. There was no significant difference in the average abundance of generalist phytophage species found per bush in native and alien habitats. Phytophages were assigned to seven feeding niches: suckers, root feeders, external chewers, flower feeders, seed feeders, miners and pollen feeders. Empty niches were found in the exotic habitats; species exploiting structurally specific parts of the host plant, such as flowers and seeds, were absent in the countries where broom grows as an alien plant. The pattern of niche occupancy was similar between native and exotic habitats when just the generalist phytophages were considered. As phytophage abundance and biomass increased, there were concomitant increases in natural enemy abundance and biomass. Thus, it appears that as plants accumulate phytophages, the phytophages in turn accumulate natural enemies and a food web develops around the plant. Moreover, in the native countries, the history of association between the natural enemies and their prey has been sufficient for specialist predators and parasitoids, feeding on the specialist phytophages, to have evolved.

Arthropod introductions for biological control of weeds in New Zealand, 1929 - 1995

A number of arthropod species exotic to New Zealand have been purposefully introduced for biological control ofweeds. A smaller number of specialist weed-feeding insects have arrived accidentally and established here. These introductions have been beneficial to New Zealand through their deleterious impact on exotic weedy species. Recent purposeful introductions of new species have been made to contribute towards biological control of seven weed species, and four more weeds are currently the subject of investigations to identify suitable control agents.

Predicting the impact of the biocontrol agent Aulacidea subterminalis (Cynipidae) on growth of Hieracium pilosella (Asteraceae) under differing environmental conditions in New Zealand.

A gall wasp, Aulacidea subterminalis, was released into the field in New Zealand in 1999 for biocontrol of the grassland weed Hieracium pilosella. To predict its likely impact in the field, the effect of the gall wasp on plant growth was measured under stress-free conditions in a shade house trial with potted plants. Plants with galls showed a reduction in stolon length of 75%. They had slightly lower total dry matter and reduced root weight. In a glasshouse experiment to measure the impact of water stress, nutrient stress, and plant competition on growth of H. pilosella and performance of the gall wasp, the number and mean diameter of gall clusters were not significantly different between treatment and control plants. However, galled plants produced more, but shorter, stolons in all stress treatments, and stolons that were more branched in nutrient- and water-stressed plants, than ungalled plants. Under the plant competition treatment, total stolon length relative to biomass was greater with, than without, wasps, indicating that stolons were thinner. Galling by A. subterminalis is likely to reduce vegetative reproduction of H. pilosella whether or not the plants are stressed, indicating that the wasp may be a successful biocontrol agent.

Host range of Cheilosia urbana (Meigen) and Cheilosia psilophthalma (Becker) (Diptera: Syrphidae), candidates for the biological control of invasive alien hawkweeds (Hieracium spp., Asteraceae) in New Zealand

Abstract Four Eurasian Hieracium spp. (Asteraceae) are noxious weeds in New Zealand and targets for biological control. Cheilosia urbana (Meigen) and Cheilosia psilophthalma (Becker) (Diptera, Syrphidae) are univoltine, sympatric hoverflies from Central Europe which have been screened to determine their safety as biological control agents. Females of both species oviposit on Hieracium pilosella L. rosettes in April and May but their larvae occupy different feeding niches. C. urbana larvae move into the soil where they feed externally on the roots, making small holes, whereas C. psilophthalma larvae remain on and feed on the aboveground plant parts. During no-choice larval-transfer tests, neonate C. urbana larvae fed and completed development to the adult stage on eight of nine Hieracium spp. tested, whereas C. psilophthalma larvae completed development to the adult stage on all nine Hieracium spp. tested. Neither C. urbana nor C. psilophthalma developed on species from genera other than Hieracium. A successful method was developed to conduct single-choice oviposition tests with both species. Two critical test plant species outside the genus Hieracium were each offered to gravid C. urbana females in the presence of the target weed H. pilosella but none of the nontarget test plants were accepted for oviposition. The screening results indicated that both species of hoverflies are sufficiently host specific for release in New Zealand where no native Hieracium species exist. Invasive hawkweeds of Eurasian origin are also considered serious weeds in North and South Americas, where in contrast to the situation in New Zealand, native Hieracium spp. are also present. Thus, additional host specificity tests with native Hieracium species and other American Asteraceae will be necessary to determine the experimental host range of both hoverflies within the genus Hieracium and to examine whether other plant species would be at risk.

Can sibling species explain the broadening of the host range of the broom seed beetle, Bruchidius villosus (F.) (Coleoptera: Chrysomelidae) in New Zealand?

Following introduction into New Zealand for biological control of Scotch broom, Cytisus scoparius, the broom seed beetle, Bruchidius villosus, was found utilising tagasaste, Chamaecytisus palmensis, which was not predicted by host range testing. Historical and more recent records of the host range of B. villosus are inconsistent. One possible explanation for these inconsistencies is that more than one species is included within the current concept of B. villosus. Sequence data from the mitochrondrial gene COI was used to determine whether there was genetic support for B. villosus as a single genetic entity with a broad host range within the Genisteae, or whether the nominal species is composed of two or more sibling species each with narrower host ranges. Samples of B. villosus collected from eight countries and five plant species were analysed. Results showed a low level of sequence polymorphism (0.8%) between individuals of B. villosus compared with the divergence between B. villosus and its congeners B. lividimanus and B. seminarius (8 and 12% respectively). This suggests that B. villosus is a single species with a broader host range than was predicted by host range tests.

Feeding range of Sitona regensteinensis Hbst. (Coleoptera: Curculionidae), a potential agent for biological control of Cytisus scoparius (L.) link (Broom) in New Zealand

The weevil Sitona regensteinensis is being considered for biological control of Cytisus scoparius in New Zealand. Adult feeding tests demonstrated that while foliage of C scoparius was preferred, weevils fed also on Chamaecytisus palmensis and Lupinus arboreus. Tests with the root‐feeding larval stage have yet to be completed.

Predicting possible negative impacts of weed biocontrol by artificially suppressing invasive hawkweed in New Zealand's tussock grasslands

To test the theory that successful biocontrol of invasive hawkweeds (Pilosella and Hieracium spp.) would increase bare ground and accelerate erosion, small areas of hawkweed were suppressed with herbicide in a nine-year study. An increase in bare ground resulting from the treatments was maintained throughout. No new invasive species were recorded, and apart from a temporary increase in a perennial grass, no existing exotic species moved into the gaps created. Indigenous plants did not respond either, although at one site where mat plants were prevalent, treatments slowed their decline. As recovery of existing vegetation was minimal, it is likely that invasion of hawkweed is a consequence of degradation rather than the reverse, and if biocontrol is successful, degraded grasslands may suffer further damage, especially in areas that are grazed. The effect may be ameliorated since biocontrol agents are predicted to perform less well under conditions of low fertility and low moisture. Our results emphasize the importance of pre-release ecological studies to clarify the role of invasive plants proposed for biocontrol.

A new species of Zecicindela Larochelle & Larivière (Coleoptera: Carabidae: Cicindelinae) from the Mackenzie Basin, New Zealand

ABSTRACT Zecicindela tekapoensis sp. nov. (Coleoptera: Carabidae: Cicindelinae) is described. It is placed in the endemic genus Zecicindela Larochelle & Larivière, even though it is the only known species in the genus with a tridentate labrum. The specimens were found on a very dry, barren terrace surface near the Tekapo River, in the Mackenzie Basin.

Implications of individual variation in insect behavior for host specificity testing in weed biocontrol

This study shows that individual behavioral variation is an under-recognised source of error that may affect the outcome of host range tests in a stenophagous species. Original specificity testing of the broom seed beetle, Bruchidius villosus (F.) (Coleoptera: Chrysomelidae: Bruchinae), a biocontrol agent for Scotch broom, Cytisus scoparius (L.) Link (Fabaceae: Genisteae), failed to detect its ability to oviposit in the field on a congeneric non-target plant, the exotic Cytisus proliferus L.f. (Fabaceae: Genisteae). These tests were repeated using individual beetles from the original UK collection sites and from New Zealand, 15 generations post release. In the original tests, low replication of small batches of females masked high levels of individual variation in oviposition preference. Although most beetles showed strong preference for the target weed, there was some indication that New Zealand beetles showed higher preference for the non-target than UK beetles.