General News

Biocontrol News and Information 27(4), 63N–79N pestscience.com General News David Greathead hoods. Both broom and tagasaste pods can be a seasonally important food source for kererū (an As this issue went to press we received the sad news endemic pigeon, Hemiphaga novaeseelandiae), par- of the untimely death of Dr David Greathead at the ticularly in regions where its native food plants have age of 74. declined. A previous petition for the release of G. olivacea into New Zealand was rejected by the New Besides being a dedicated and popular Director of Zealand Ministry of Agriculture and Forestry in CABI’s International Institute of Biological Control 1998 on the grounds that there was insufficient (IIBC), David was the driving force behind the estab- information to assess the relative beneficial and lishment and development of Biocontrol News and harmful effects of the proposed introduction. Information. He was an active member of its Edito- rial Board, providing advice and ideas right up to his As part of the submission to ERMA, Landcare death. Research quantified the expected costs and benefits associated with the introduction of additional biolog- We plan that the next issue will carry a full obituary. ical control agents for broom1. Due to uncertainties Please contact us if you would be willing to con- regarding the costs, a risk-averse approach was tribute information: commentary, personal adopted by assuming a worse-case scenario where memories or anecdotes on the contribution that tagasaste was planted to its maximum potential David made. extent in New Zealand (10,000 ha), levels of non- target damage to tagasaste were similar to those on Contact: Matthew Cock & Rebecca Murphy C. scoparius, and no pollen sources suitable for bee- Email: [email protected] / [email protected] keeping would replace broom stands. Due to uncertainties regarding the level of control that will be achieved, a single best estimate for overall bene- Figures Scotch Beekeeepers’ Fears fits of the proposed programme was estimated using an average of four potential biocontrol scenarios: no Potential non-target attack issues and beekeepers’ control, and 25%, 50% or 95% reductions in broom, fears are being brushed away as new Scotch broom weighted according to the success rate of past biolog- (Cytisus scoparius) biocontrol agents are approved ical control programmes against legume weeds for New Zealand. worldwide. Scotch broom is one of the worst invasive weeds in Even though a worse-case scenario was assumed, for New Zealand, affecting farming, forestry, conserva- costs, the benefits were estimated to outweigh costs tion and amenity values. An application to New by approximately 3:1, with an annual net benefit to Zealand’s Environmental Risk Management New Zealand of NZ$5.99 million. Using discounting Authority (ERMA) was recently made by the Canter- techniques over 50 years, an internal rate of return bury Broom Group (a collaborative stakeholder of 52%, and a net present value of $61.49 million was group, who contracted Landcare Research to prepare calculated at the 5% discount rate and $21.95 million the submission) seeking to import and release new at the 10% discount rate. These returns are robust to biological control agents for Scotch broom, namely, a significant overestimation of benefits and to signifi- chrysomelid leaf-beetle Gonioctena olivacea and an cant underestimation of costs. oecophorid stem-tying moth Agonopterix assimilella. The potential cost of mitigating non-target damage Both agents are narrowly oligophagous, with the to tagasaste (spraying plants with insecticide or potential to develop on a few closely related plant planting alternative species) was relatively minor for species within the tribe Genisteae, and both showed all scenarios. However, the annual cost of mitigating a clear preference for broom during specificity reduced pollen availability to beekeeping (moving testing. New Zealand has no native members of the hives or feeding pollen supplements or substitutes) Genisteae, so these agents pose little threat to native was estimated to reach $2.41 million if broom was New Zealand plants. Nevertheless, the application reduced by 95%. Landcare Research therefore con- was complicated because of the risk of non-target ducted additional work to investigate the potential damage to tagasaste (tree lucerne, Chamaecytisus impact of broom control on the beekeeping industry. palmensis), an introduced plant that is closely related to Scotch broom. In New Zealand, tagasaste Flowering broom stands were sampled fortnightly, is planted for soil stability on marginal hill country nationwide, over two flowering seasons. Broom and is a minor fodder crop, currently planted on only flowers have to be ‘triggered’ open for bees to gain c. 30–50 ha of summer-dry pastureland but with the access to pollen, which enabled the proportion of potential to be planted over 5,000–10,000 ha. In addi- flowers that had been pollinated at any one time to tion, broom is a good source of pollen for the be assessed. The overall proportion of triggered beekeeping industry and beekeepers were concerned flowers averaged c. 40% and ranged from 8 to 80% that a reduction in broom might affect their liveli- (peak fortnightly values ranged from 10 to 89%), Are we on your mailing list? Biocontrol News and Information is always pleased to receive news of research, conferences, new products or patents, changes in personnel, collaborative agreements or any other information of interest to other readers. If your organization sends out press releases or newsletters, please let us have a copy. In addition, the editors welcome proposals for review topics. 64N Biocontrol News and Information 27(4) indicating that the impact of reduced broom pollen 2Suzuki, N. (2003) Significance of flower exploding availability on bees is likely to vary according to site. pollination on the reproduction of the Scotch broom, However, it does appear likely that even a minor Cytisus scoparius (Leguminosae). Ecological reduction in broom abundance could result in periods Research 18, 523–532. of pollen shortage for bees at some sites. Neverthe- less, bees commonly foraged from previously 3Simpson, S.R., Gross, C.L. & Silberbauer, L.X. ‘triggered’ flowers, presumably because 25% of pollen (2005) Broom and honeybees in Australia: an alien remains after broom flowers are tripped for the first invasion. Plant Species Biology 7, 541–548. time2. Therefore, even at Lincoln, where a small (0.2 ha) patch of broom was surrounded by 16 beehives By: Quentin Paynter, Manaaki Whenua and a peak of 85% of flowers were pollinated, a 25% Landcare Research, Private Bag 92170, reduction in broom cover might not necessarily limit Auckland, New Zealand. pollen availability to bees. Email: [email protected] Fax: +64 9 574 4101 At two sites, Palmerston North and Lincoln, transects were set up during the broom flowering season and any bees encountered on regular patrols Natural Enemy Unleashed on Buddleia in New of these transects were followed and all their floral Zealand visits recorded. At Palmerston North honeybees were recorded only visiting broom and buttercup, Buddleja davidii (buddleia) was first introduced to Ranunculus sp., with the majority (c. 70%) of obser- New Zealand as an ornamental shrub and has since vations from broom. However, at Lincoln, there was become one of the biggest weed problems in North a greater diversity of pollen sources and only 18% of Island forests. A woody species with attractive floral visits were to broom flowers. A progression of purple flowers, it has fast growth rates, and out- other species was used: Sophora spp. and Chamae- standing ability to colonize bare ground. Originally cytisus palmensis were utilized alongside broom from China, buddleia is now considered to be an early in the season (October). While bees visited invasive weed in New Zealand, Australia and Teucrium fruticans heavily in early November, they Europe. visited flax Phormium tenax and white clover Trifo- lium repens almost exclusively when they came into Buddleia now costs the New Zealand forest industry bloom (mid-November). If these alternative pollen between NZ$0.5 and $2.9 million annually in control sources increase in abundance, should biological con- costs and lost production. Its capacity to out-compete trol of broom succeed, this would mitigate the young trees makes it a serious problem for forest impacts of a reduction in broom pollen availability owners, particularly in the Central North Island. For for honeybees. local and regional authorities in affected areas, buddleia has become a common weed along roadsides. It As broom is expected to decline gradually, bee- also represents a nuisance in open areas within keepers also have an opportunity to plant alternative native forest reserves, including slips and river beds. pollen sources to replace broom. Similarly, poten- New Zealand scientists at Ensis Forest Biosecurity tially negative effects to kererū could be also and Protection1 have recently unleashed a biological mitigated through appropriate planting of species control agent that could assist in managing this chosen to provide an alternative food source. serious weed problem. The leaf-eating weevil, Cleopus japonicus, was identified by Nod Kay as a Only two species of pollinator were recorded trig- potential biological control agent for buddleia and gering broom flowers: honeybees and bumblebees brought into New Zealand for testing in 1993. There Bombus terrestris, both of which were introduced followed a long and rigorous testing process enforced into New Zealand. Broom seed rain, which ranged 2 by the Environmental Risk Management Authority from 59 to 14,443 seeds/m , was very closely corre- (ERMA) to ensure that the introduction of this new lated to the rate at which honeybees pollinated 3 species would not have a negative impact on the New flowers, indicating that, as in Australia , broom Zealand environment. Extensive host testing studies invasion in New Zealand is being driven by intro- determined that the insect only eats buddleia and a duced pollinators.

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