Andrea E. A. Stephens

Strength in numbers? Effects of multiple natural enemy species on plant performance

While plants are invariably attacked by numerous insects and pathogens, the consequences of multiple enemies for plant performance are poorly understood. In particular, a predictive framework is lacking for when to expect enemies to have independent versus non-independent effects on their host plant. This is problematic for weed biological control programmes where multiple enemies are frequently released with the possibility of antagonistic interactions that may reduce control. Here, we conduct an analysis of 74 unique plant–enemy–enemy combinations from 51 studies to determine the frequency of non-independent effects of natural enemies on host plant performance, and test a number of a priori predictions for determinants of independent and antagonistic effects of multiple enemies. For three-quarters of plant response measurements, enemies had independent effects on plant performance. In most of the remainder, multiple enemies led to less reduction in performance than that predicted from each enemy alone. Antagonistic effects occurred when enemies attacked the same plant part concurrently or attacked plant reproductive structures. These two predictors explained why antagonistic effects were particularly prevalent for weeds, plants in the family Asteraceae and enemies in the order Diptera. Our results suggest that a few simple rules about avoiding particular combinations of multiple enemies could improve biological control success.

Ant dominance in urban areas

A survey was conducted to determine the distribution of dominant ants and factors that may influence their dominance in New Zealand cities. A new method of active ant trapping combining aspects of pitfall trapping and attraction to food baits was used to capture a sample of all ant species that attended baits. Fifty eight percent of the ant species present in New Zealand were recovered from 2202 traps, with multiple species catches in 245 traps. There was a strong latitudinal relationship in the distribution of ant species, with the proportion of native to introduced species increasing in favour of the native species as latitude increased (south). The presence of Linepithema humile, the Argentine ant, a numerically dominant species was associated with a significant reduction in the number of other ant species captured. With increased urbanisation, providing refugia at times of cool temperatures for warm temperate-sub tropical introduced ant species, their range may extend into the higher latitudes, further displacing native ants from New Zealand cities.

Evaluation of lure dispensers for fruit fly surveillance in New Zealand

BACKGROUNDnFruit flies (Diptera: Tephritidae) represent a major biosecurity threat to the horticulture sector of New Zealand, which is entirely free of these invasive pests. A nationwide surveillance programme is conducted to ensure any incursion is detected as early as possible. A review of the lure dispensers used is reported here.nnnRESULTSnLure dispenser emission trials found that the currently used lure plugs release lure more slowly under New Zealand subtropical to temperate climates than wafer dispensers. Subsequent trapping experiments at high altitude in Hawaii (as a mimic of New Zealand meteorological and expected fruit fly ecological conditions) compared Lynfield traps baited with the existing lure plug dispensers and newer wafer dispensers. Catches of wild Oriental fruit flies, Bactrocera dorsalis (Hendel), were 9.5-fold higher with methyl eugenol wafers than with the plugs. Recaptures of sterile melon flies, Bactrocera cucurbitae (Coquillet), were 2.6-fold higher with cuelure wafers than with the plugs. Recaptures of sterile Mediterranean fruit flies, Ceratitis capitata Weid., were not significantly higher with trimedlure wafers than with the plugs.nnnCONCLUSIONSnRelease rate and trapping experiments found new lure dispensers differed in release rate characteristics from existing dispensers under temperate and subtropical conditions, and indicated some potential for improvement in surveillance efficacy.

Modelling the effects of inherited sterility for the application of the sterile insect technique

1u2002The sterile insect technique (SIT) involves the release of large numbers of sterile or partially‐sterile insects into a wild pest population to dilute the number of successful wild matings, with the eventual aim of eradication or area‐wide suppression. General population models, encompassing a wide range of SIT types, were used to derive principles for optimizing the success of SIT, with particular emphasis on the application of partial sterility leading to inherited sterility in the F1 population.

Influences of two life-history stages of the weevil, Larinus minutus, on its host plant Centaurea diffusa

1. We hypothesised that, for weed biological control, using species that feed as both adults and larvae would be advantageous. Here, we test the impacts of adult and larval feeding of Larinus minutus (Col.: Curculionidae), a successful biological control agent of diffuse knapweed, Centaurea diffusa (Asteraceae), in British Columbia, Canada.

Advance, retreat, resettle? Climate change could produce a zero‐sum game for invasive species

Climate change will alter the threats presented by invasive species. Increasing temperatures and changing precipitation regimes will likely simultaneously improve the suitability of a region for some species while decreasing it for others. We demonstrate the zero‐sum game nature of these changes by modelling the changes to the projected distribution of 13 tropical and subtropical Tephritidae species in cities in Australia and New Zealand using published CLIMEX models. Under current climate conditions, tropical and warm temperate cities were suitable for more species than arid or cool temperate ones. All New Zealand cities increased in suitability, while Australian cities show more variable responses. The changes that occur under climate change are in line with the expectation of species ranges moving into higher latitudes but are also influenced by changes to the precipitation regime. With climate change, the nature of biosecurity threats will alter, the range of species able to survive in cool temperate regions is likely to increase with decreases in species ability to survive in tropical regions. Biosecurity agencies will need to respond to changing geography of threats.