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December 2003, Volume 24 No. 4

 

General News

 

Testing Times for Testing

The high profile reporting of non-target impacts of a few classical weed biocontrol agents over the past few years highlighted one shortcoming of many, if not most, biocontrol programmes - related to not inadequate testing, but inadequate monitoring. In trying to answer the critics of biocontrol, its defenders could only point to the absence of reported problems for the overwhelming majority of the 1150 or more planned releases of weed biocontrol agents that have been made worldwide. An equally overwhelming absence of post-release surveys means that there is little concrete evidence about the non-target impact of most of these releases.

In New Zealand, Landcare Research has been dusting off old files and investigating the safety record of weed biocontrol there since the first biocontrol agent, cinnabar moth (Tyria jacobaeae), was released against ragwort (Senecio jacobaea) in 1929. This audit will alert the country's biocontrol community to any lurking dangers, and also identify past flaws that will help tighten up testing procedures for the future.

Landcare has been looking at some agents that are now common in New Zealand, checking what testing was done before each was released, and whether non-target attack has occurred - or might yet. Reporting results at the 11th Symposium on the Biological Control of Weeds in Canberra this year, Simon Fowler said that, overall, the reliability of host specificity testing in New Zealand in the past has been good although a few gaps have been identified.

The largest gap in testing probably occurred in some projects conducted between 1943 and 1982. Although early biocontrol projects included native species in specificity tests, during this period 13 introductions of natural enemies were made which relied heavily on testing in other countries, and New Zealand natives were not tested. In one case, thistles, the rationale was that there are no native thistles in New Zealand so there were no closely related native species to test. While there could have been problems where introductions were made against other targets with New Zealand relatives, no non-target impacts have been recorded on New Zealand native plants, and only one potential serious impact has emerged so far. Three agents were released against St John's wort (Hypericum perforatum) but they had not been tested against native Hypericum species. Hypericum japonicum and H. gramineum are uncommon plants and, although none of the agents has been recorded on them, they could be at risk. In many other projects during that period, and in all projects since 1990, it has been standard practice to test native plants so the omission of indigenous species from test plant lists should not occur now. However, this does not imply that selecting what plants to test is now always straightforward.

The first agent to be released in New Zealand, cinnabar moth, was tested against eight native species of Senecio before permission was given for its release against ragwort. However, when ragwort is defoliated the moth occasionally attacks two species of native Senecio (S. minimus and S. biserratus) which were not tested. Why were these two not included in the test plant list? They were in a different genus at the time. This is the only recorded instance of an introduced weed biocontrol agent attacking a native non-target species in New Zealand, but could such a testing omission happen again? It is unlikely. Plant systematics have clearly progressed since 1929 and if the testing were being conducted now, these two species would be included. However, even with the taxonomic relationships clarified, there is another source of uncertainty.

Alternanthera sessilis, a close relative of alligator weed (A. philoxeroides) was not included in host specificity tests in that biocontrol programme. Both are exotic species and indeed there are no native New Zealand plants in the family. But what was not foreseen was that A. sessilis would subsequently attain cultural importance as a new vegetable crop for some sectors of the community. Short of including a fortune-teller in the biocontrol project, this would have been hard to predict but Toni Withers (Forest Research), who has been working with Fowler and others on this project, believes that the current rigorous process for drawing up test plant lists means that a similar case would not now be overlooked. Of two agents introduced against alligator weed, one (the moth Arcola malloi) attacks other Alteranthera species, and although damage to A. sessilis has not been observed it remains a possibility.

The above rare instances of the failure of New Zealand's past testing procedures occurred because plants that might have been tested were not. There are just two recorded cases where plants were tested, but the testing failed to predict the non-target attacks that subsequently occurred. The broom seed beetle Bruchidius villosus and the gorse pod moth Cydia succedana have unexpectedly attacked seed of other exotic Fabaceae, although pre-release testing suggested that this would not happen. Investigations into both are continuing, but Fowler noted that a common link is that both use seasonally ephemeral resources (young pods) whose phenology in comparison to that of the agent differs slightly between Europe and New Zealand, potentially offering novel no-choice situations to agents in the field after release. This gives us a new concept to consider: Do agents introduced for discrete seasonal resources need more careful assessment? Should more rigorous no-choice testing be considered in these circumstances? Withers believes that the answer lies in our ability to accurately interpret the results of host specificity testing, something that retrospective analysis of the methods used in the past, combined with post release field assessment, will help us with.

The message is that if weed biocontrol is to win the confidence of its often vociferous sceptics, it is likely to require more sophisticated yet transparent interpretation of the host range testing carried out, and potentially will become more time-consuming and (therefore) more costly as a result. At a time when time and budgets are being cut this fills the biocontrol community with dismay. As a direct consequence of the greater cost some projects will not be undertaken, while the increased scrutiny is likely to raise the bar so high that potentially useful and harmless agents will be rejected.

Source: Hayes, L (ed) (2003) In retrospect. In : What's new in biological control of weeds. Annual review. Lincoln, New Zealand; Landcare New Zealand Ltd 2003, No. 25, pp. 7-9.

Contact: Simon Fowler,
Landcare Research, Private Bag 92170, Auckland, New Zealand.
Email: fowlers@landcareresearch.co.nz
Fax: +64 9 849 7093

Birch Sawflies Seen Off

An Old World birch leaf-mining sawfly, accidentally introduced to Alaska, is the subject of a classical biocontrol programme employing a natural enemy from neighbouring Canada. This programme, capitalizing on the successful biocontrol of birch leaf-mining sawflies in Canada, will also mark the first instance of a natural enemy being released as part of a major programme against an invasive alien species in the wild in Alaska.

Birches have a worldwide distribution in the North Temperate Zone, and some 12 native species are found in North America. They are an important component of the boreal forests that extend north to the treeline. A number of native and exotic species are highly valued and widely planted as ornamental and shade trees in town and cities. The wood from some birch species is used for wood pulp and timber and for a large variety of products, from furniture to canoes to ornaments. Birch sap is starting to find a niche as a non-timber forest product. In the harsh climate of the northern forests, birch buds, twigs, pollen catkins (flowers) and nutlets (fruits) are an important food source for birds, mammals and insects.

Since the early 1900s, North American birches have suffered the invasion of five leaf-mining sawflies, all of European origin. By mining the leaves, their larvae cause extensive discoloration that is unsightly and reduces amenity values. The annual destruction of the trees' photosynthetic capacity has long-term impact on their health, and severe attacks over several years can weaken them and make them susceptible to attack by other insects, diseases and drought. Application of systemic pesticides (dimethoate), the most common means of control for these pests in urban centres, has had significant monetary costs to the public, and an undoubtedly significant environmental cost.

The spread of the leaf miners across the continent was slow but unremitting. Two species, the birch leaf miner (Fenusa pusilla) and the amber marked leaf miner (Profenusa thomsoni), became particularly widespread and destructive. From their point of introduction on the east coast of North America, these two species spread across the intervening ca. 4000 km to the western Canadian province of Alberta by the 1960s and were soon causing alarm. Once populations were well established, most birch trees in urban centres had turned brown by midsummer, and this level of infestation continued year after year. The additive action of the species heightens the problem: attack begins with first generation F. pusilla in early- to mid-May, as the trees begin to break bud. This is followed by new waves of attack in June-July from the univoltine species, P. thomsoni , together with a second generation of F. pusilla. Although a third species, the late birch leaf edge miner, Heterarthrus nemoratus, is present in Alberta, it is very rare and causes little damage.

In the early 1990s, scientists were surprised to notice a dramatic drop in sawfly damage to birch trees in Edmonton, Alberta and even more surprised to find that a native parasitoid was responsible by reducing populations of one of the species, P. thomsoni. The parasitoid responsible, Lathrolestes luteolator, appears to be native to both Old and New Worlds. It had not previously been recorded from P. thomsoni, although it attacks sawflies in the genus Caliroa in Europe and North America, and Profenusa alumna on northern red oaks (Quercus rubra) in eastern Canada and the USA. It is not unusual to find native parasitoids switching to an exotic host, but they are generally not sufficiently efficient to exert effective control - indeed, it is an axiom of classical biological control that co-evolved natural enemies from the area of origin of the pest exert the most effective control because their life histories and population dynamics are most closely linked. However, there are a number of examples of such `new associations' providing useful levels of control (e.g. citrus leaf miner, Phyllocnistis citrella).

The control of F. pusilla followed more conventional classical biological control lines, utilizing two parasitoids, Lathrolestes nigricollis and Grypocentrus albipes, which are highly specific to F. pusilla in Europe. These parasitoids had previously been released against F. pusilla in eastern Canada in the 1970s and the northeastern USA in the 1980s, with excellent results, at least for L. nigricollis (G. albipes did not establish). Following on earlier successes, scientists from the Canadian Forest Service - Northern Forestry Centre (CFS-NoFC) teamed up with colleagues from the University of Alberta, and contracted CABI Bioscience (then the International Institute of Biological Control, IIBC) in Delémont, Switzerland to supply natural enemies from Austria. Lathrolestes nigricollis and G. albipes were shipped and released between 1994 and 1996, and both species became established although L. nigricollis was most successful. Since then, the wasp populations have increased rapidly and spread throughout the Edmonton area. In 2003, L. nigricollis was recovered from F. pusilla approximately 300 km from the release sites. It is now difficult to find the birch leaf-mining sawflies in Edmonton. As a result of the impacts of the parasitoids, the city curtailed its expensive (and sometimes controversial) policy of spraying its birch trees on public lands with dimethoate, and initiated a successful communication campaign to dissuade the public from applying insecticide on the grounds that it would disrupt biocontrol. Edmonton's success has been noted by authorities in areas still troubled by the sawflies, and NoFC is currently working with Northwest Territories and Alaska on control programmes.

Alaska remained free of alien birch leaf-mining sawfly pests until about the 1990s when the first damage to birch was noticed. Subsequently, birches in Anchorage began to sustain the greatest damage, which now extends over more than 14,000 ha in and around the city. The pest has also spread as far north as Fairbanks, east to Glennallen and south to Haines and Skagway. It was not until 2002 that the major culprit was positively identified as P. thomsoni; however, F. pusilla and H. nemoratus are also present in Anchorage but very rare. Birch is one of Anchorage's most common shade tree species, and the impact of them turning brown at the peak of the short summer is particularly dramatic. The rapid rate of spread of P. thomsoni, coupled with the failure of weekly trapping to find any evidence of the parasitoid, suggested that the sawfly has left behind the natural enemies that now control it farther east. A 3-year cooperative multi-agency programme has been initiated between CFS-NoFC and the US Department of Agriculture Forest Service (USFS) to study populations of P. thomsoni in Anchorage, locate populations of the parasitoid L. luteolator in Canada and introduce parasitoids to Alaska, in the expectation that it may re-enact its Canadian success and suppress P. thomsoni again. Of the known hosts of L. luteolator, only P. thomsoni and Caliroa cerasi occur in Alaska. No other members of these genera occur there so there is low risk of host switching. In 2003, baseline data were obtained on the ecology and mortality of P. thomsoni in Alaska, sources of L. luteolator were located in the Northwest Territories, parasitoids have been collected and are overwintering in Edmonton before being transported to Anchorage in the spring of 2004, and import permits have been secured to allow the releases to proceed.

While scientists are gaining the upper hand with P. thomsoni and F. pusilla, they are also keeping a close watch on two more recently introduced species that mine leaves of birch, Scolioneura betuleti and Messa nana. Both species are currently distributed only in eastern North America; S. betuleti has a localized distribution in Ontario and M. nana is widely distributed from Ontario to New Brunswick and in the northeastern USA. With its large range and propensity to cause high levels of damage, M. nana is a growing concern and warrants increased vigilance.

Sources: Anon. (2003) Science and nature give sawflies a one-two punch. Solutions (newsletter of the Canadian Forest Service) Fall/Winter 2002
www.nrcan.gc.ca/cfs/scf/national/what-quoi/Solutions

Anon. (2003) Forest Insect and Disease Conditions in Alaska - 2002. USDA Forest Service, Alaska Region, R10-TP-113, 62 pp.

Mason, P.G.; Huber, J.T. (2002) Biological control programmes in Canada, 1981-2000. Wallingford, UK; CABI Publishing, 608 pp.

Contact: David W. Langor,
Research Scientist - Insect Management & Biodiversity, Natural Resources Canada - Canadian Forest Service,
5320 - 122 Street NW, Edmonton,
Alberta, T6H 3S5 Canada
Email: dlangor@nrcan.gc.ca
Fax: +1 780 435 7359

Ed Holsten, Research Entomologist,
USDA Forest Service: Alaska Region;
S&PF, FHP & PNW, 3301 "C" St.,
Ste. 202, Anchorage, Alaska 99503, USA
Email: eholsten@fs.fed.us
Fax: +1 907 743 9453

End of the Road for the Cane Toad?

Cane toad (Bufo marinus), biocontrol's best-known disaster story, may become a model for developing a new form of biocontrol. According to a recent report*, the technical feasibility of producing a viral agent that can disrupt the development of cane toad looks extremely promising, but a number of other issues need to be addressed if the overall objective of producing an effective self-disseminating viral vector is to be achieved.

The report was the result of a review, funded by Department of the Environment and Heritage (DEH) through the National Heritage Trust, of the government-funded `Development of a cane toad biological control' project. The Australian Government is continuing its support for the approach through the DEH. In September it also announced that an additional A$ 200,000 of funds is being released by the DEH for new projects on short- and medium-term control techniques for cane toads in Australia.

Cane toads were introduced to Queensland in 1935 to control beetle pests in sugar cane, a job to which they proved singularly ill suited. Instead they became a pest themselves, preying on small animals and poisoning larger predators (including household pets) that try to eat them, and out-competing native reptiles and amphibians for habitat and food resources. They have spread beyond Queensland, with a range currently extending from northern New South Wales into the Northern Territory. They threaten the World Heritage Site of Kakadu National Park and are continuing to spread through the tropical north towards Western Australia. There are currently no control measures effective for anything but small, restricted areas.

Investigations into possible biocontrol solutions for cane toad began in 1990, with surveys for pathogens in the toad's area of origin in Venezuela and ecological studies of the pest there and in Australia. More recently, research has focused on investigating potential viral biocontrol agents. A stimulus for this work was rapid advances made in gene technology during the 1990s together with the progress made by CSIRO in genetic manipulation of viruses to interrupt animal development. While this approach fits with cultural pressure for `humane' control methods, it also needs to address public concerns about the safety of genetic modification. A project aimed at producing a recombinant viral agent was initiated in 2000, and was the subject of the recent review.

The report notes that, although there have been hitches in maintaining a healthy captive colony of cane toads for research purposes, excellent technical progress has been made and objectives have been met on time and on budget. It draws attention to the project's achievements and is encouraging about its prospects for success, while also pointing out areas that need to be addressed:

  • A recombinant ranavirus has been created, indicating that genetic modification is a technically feasible approach in this system.
  • Methods of attenuation (weakening the ability to cause disease) have been assessed. Attenuation by passaging was successfully demonstrated for a wild-type and a recombinant ranavirus in an Australian native frog, Litoria infrafrenata. Attenuation is fundamental to the production of a viral vector that does not endanger non-target species, and its reliability is vital for safeguarding native biodiversity. The report endorsed the need for further research to confirm results so far.
  • Genes critical to the development of cane toads have been identified using micro array technology, and potential for progress in this field is promising. Evidence indicates that developmental differences between cane toads and native frogs may be sufficient for a suitable gene to be identified.
  • The team has the skills and technology for moving the project forward to create a recombinant virus capable of acting as a biocontrol agent.

    The report highlights a number of gaps in the project so far and as planned:

  • A comprehensive plan for testing native species is needed to ensure that (a) the viral vector has been weakened successfully and (b) the genes selected to block cane toad development are specific to this species.
  • The scarcity of information on the proposed ranavirus vector needs remedying by targeted research.
  • Methods for containing the risk of the released virus escaping to other countries need to be considered.

    The report questions whether the project team can address these issues and, if not, calls for the Department of the Environment and Heritage to assess the implications of these gaps. The question appears somewhat rhetorical, insofar as the report describes the testing of the attenuated recombinant virus as "a major task that will need substantial expertise from outside the project team." While the report notes that is unlikely to be possible (or necessary) to test the 200 or more native frog species, it argues that the rationale for which species are to be tested, and why, needs to be explained (although this will be made more difficult because the phylogenetics of Australian frogs are not well established.) Factors to be considered include:

  • Impact of differences in ecology (e.g. habitat preferences and behaviour) between taxonomically closely related species on susceptibility.
  • Impact of an individual's health and environmental conditions on susceptibility.
  • Cost, feasibility and ethics of testing threatened species with few remaining wild populations, and whether to test species assumed extinct in the wild.
  • Necessity for testing other groups also susceptible to ranaviruses (reptiles, fish).

    The report calls for the development of a detailed strategy for comprehensively testing the success of attenuation in Australia's frogs, reptiles and fish, at various life stages, in advance of testing the recombinant attenuated virus. It suggests that the strategy should demonstrate that expertise has been sought from relevant experts in frog, fish and reptile biology, and ecology and virology.

    Most aspects of the ecology of ranaviruses, such as survival, mobility and pathogenicity, are little understood, yet would impinge on their success or otherwise as viral vectors. The report calls for research into their ecology, in particular to investigate key questions:

  • What is the status of ranaviruses in the Australian native fauna? (Only one in one species has been reported so far.)
  • What is their prevalence in wild cane toad populations? Ranaviruses are considered extremely robust in nature and readily transported through the environment. But if ranaviruses are present in wild cane toad populations as thought, why do they not have more impact, given the density of cane toad populations? Perhaps they are not present, or very prevalent? Or perhaps they are less robust, virulent or transportable in the natural environment?
  • Once (and if) ranaviruses have been shown to be present at appropriate levels in wild cane toad populations, more questions arise. How does environmental variation affect ranavirus prevalence, mobility, and capacity to infect? Do the wild type and attenuated viruses behave the same in the natural environment?

    The answers to these questions will confirm whether or not the ranavirus is a good choice of vector, and suggest whether additional dissemination mechanisms might be needed.

    The report praises the project team for ensuring that results are relayed to the public. However, it encourages them also to share results with scientists in other disciplines. It notes that the project will interest "a diverse range of scientists and practitioners from amateur herpetologists to ecologists and virologists" and suggests that they may be able to assist if kept informed of progress - and furthermore that keeping the entire community informed will tend to prevent a build up of concern that could develop in a vacuum of information.

    The potential for mutation and host range expansion in a virus being released into the environment is a natural cause of concern. Ranaviruses are considered stable and the likelihood of the one chosen for this project reverting back to its pathogenic form is described by the project team as close to zero. However, according to the report not all scientists share this confidence and they need to be presented with the evidence rather than reassurances. It stresses the importance of engaging the scientific community on the issue of safety, as dissent between scientific camps is likely to deepen public anxiety. The report makes the point that: "Confidence from the broader community will be essential if the virus is eventually to be released." Any such release would be controlled by the Office of the Gene Technology Regulator (OGTR), after an extensive programme of consultation with community groups.

    The report also discusses the issue of international commitments. National interests need to been weighed against those of other countries, which brings different elements of risk into consideration - some of the `plus' points at a national level may be negatively viewed by other countries. For example, ranaviruses can survive in the environment (i.e. outside the host) for extended periods under conditions of fairly high temperature and desiccation (which is good for agent dissemination). However, the virus could be transported by unwitting human agents (on boots or fishing equipment, for example) to another country, which may have (a) susceptible native species of amphibians, reptiles or fish that have not been tested under protocols designed to safeguard Australian native species and (b) native cane toads. With international travel and trade at unprecedented levels, these risks cannot be dismissed.

    Clearly this is an issue for quarantine authorities (although they are more used to keeping organisms out of, rather than within, a country's borders). The report states that no recombinant form of a ranavirus should be released unless it is feasible to contain it within Australia. This is not a limitation put on release of other, naturally occurring, biological control agents in Australia, and is likely to provoke protest (and counter-protest). The report also notes, however, that molecular techniques may be able to manipulate the virus, for example to reduce its survival outside the host without significantly compromising its effectiveness as a biocontrol agent, which could contribute to its safety from the quarantine perspective.

    Whether an attenuated recombinant self-disseminating ranavirus will prove to be the answer to the cane toad in Australia will take another 10 years to determine, according to this report - it does not pull its punches in laying out the of the size of the challenges ahead. In the meantime, the report calls for more resources to be provided for the complementary areas it asks to be researched, and for other avenues to be investigated to alleviate the cane toad problem in Australia in the short- to medium-term.

    In addition to evaluating the cane toad project, this report makes an important contribution to the debate on the future of disseminating viruses as biocontrol agents. It highlights the excellence of the research, the promise of the results so far, and the capabilities that Australia possesses, and is optimistic about the successful outcome of the technical aspects of the project. However, it also identifies obstacles to transferring this technology safely to the field and endorses the need for cooperation between scientists of different disciplines to overcome these. Above all, the report recognises the importance of perception over evidence-based argument in making judgments about risk, not only amongst the lay public but also within the wider scientific community.

    Effective safe control of cane toad would be welcome, not just in Australia, but throughout the world biocontrol community, for whom constant references to its introduction are a depressing reminder of the poor public perception of biological control's safety record. Experts and stakeholders, including members of conservation groups and research organizations, will attend a workshop early in 2004 to discuss how to take the research forward.

    *Hazell, D.; Nott, R.; Shannon, M.F. (2003) Review of the project `The development of a cane toad biological control'. Canberra, ACT; Department of the Environment and Heritage, National Heritage Trust, 18 pp.
    www.deh.gov.au/biodiversity/invasive/pests/canetoad

    Winning Water Lettuce War

    A project that has successfully controlled water lettuce (Pistia stratiotes) in a nature reserve in the Eastern Cape Province of South Africa has demonstrated the effectiveness of the control agent under some difficult conditions. Water lettuce, originally from South America, is a declared weed in South Africa. A leaf- and stem-feeding weevil, Neohydronomus affinis, was first released against it in 1985. It causes considerable damage and has controlled the weed in a number of situations. However, the Eastern Cape has a fairly temperate climate with cool winters and in addition the water bodies where control was achieved are highly eutrophic. Thus success under these conditions indicates that there really is no need to consider any other control methods.

    The Cape Recife Nature Reserve near the city of Port Elizabeth incorporates two water treatment settlement ponds that are also used extensively by birding enthusiasts as they attract many species of waterfowl. In 2001 one of these ponds was invaded by water lettuce, which by 2002 had covered the entire 1.5 ha pond and had also moved into the second pond. In August 2002, 240 adult N. affinis weevils were introduced to the first pond. A quantitative post-release evaluation was initiated at this site in January 2003 by the Department of Zoology and Entomology at Rhodes University, Grahamstown. Initially the plants were very large, averaging nearly 1 kg wet weight per plant. By March 2003 the mat of water lettuce had started to break up and the average wet weight of the plants had dropped to less than 100 g per plant - and there were on average 26 adult weevils per plant. The weevils also dispersed to the other pond. By June 2003, the entire mat had sunk and only a few scattered plants were found in the riparian vegetation. The evaluation will continue through the summer to document any reoccurrence of the weed.

    By: Martin Hill, Department of Zoology and Entomology, Rhodes University,
    Grahamstown, 6140, South Africa.
    Email: m.p.hill@ru.ac.za
    Fax: + 27 46 622 8959

    Donald Dahlsten

    Donald Dahlsten, a leading expert in biological control and forest entomology, and a professor of insect biology at the University of California, Berkeley died on 3 September 2003 at the age of 69.

    Over the course of his 40-year career, Dahlsten developed a reputation as one of the world's most respected leaders in biological control. His research focused on the development of ecologically sensitive methods for controlling insects that feed on trees in forests and in urban environments, which ultimately gave California a critical weapon in their fight against psyllid pests that were spreading fast through the state's eucalyptus trees. In the early 1990s, he found a species of Psyllaephagus wasp that effectively controlled the blue gum psyllid (Ctenarytaina eucalypti) infesting blue gum eucalyptus trees in nurseries throughout California. Two years after the parasitoid's introduction, it was hard to find any psyllids. It was a classical biocontrol success story.

    Dahlsten's expertise was called upon again when the red gum lerp psyllid (Glycaspis brimblecombei) began attacking and killing California's red gum eucalyptus trees in 1998. Following surveys in Australia, he imported another species of Psyllaephagus. The efficacy of this wasp is still being evaluated, but it has thus far been most successful in the state's coastal areas.

    In addition to his work on psyllids, Dahlsten distinguished himself with his research on the population dynamics of tree-killing bark beetles and the factors that attract their natural enemies. Other projects included research on how the methods used to control Pierce's disease, which affects grapevines and is spread by the glassy-winged sharpshooter (Homalodisca coagulata), affected riparian habitats, and on the ecological impact of the Sudden Oak Death pathogen, a fungus-like algae that has killed tens of thousands of oak trees throughout the state. Wide interests included ornithology (he maintained one of the largest databases of insectivorous birds in California's forests and riparian areas, and recently contributed a 20-page chapter on the biology of the chestnut-backed chickadee for `Birds of North America').

    An early career dedicated to football was blighted by polio but, undeterred, he shifted his career aspirations to science. He enrolled at UCLA (University of California, Los Angeles) before transferring to UC Davis, where he received his bachelor's degree in entomology in 1956. He continued his graduate studies at UC Berkeley, receiving his MSc and PhD degrees in entomology in 1960 and 1963, respectively. As a graduate student, he had worked as a research assistant in entomology at UC Berkeley. After he finished his studies, he taught at the Los Angeles State College for one year before coming back to UC Berkeley as an assistant entomologist. He worked his way up to a tenured faculty position by 1969, and from 1981 to 1988 served as chair of the former Division of Biological Control.

    Known as a dedicated educator, Dahlsten was appointed associate dean for instruction and student affairs at UC Berkeley's College of Natural Resources in 1996. He advised 39 graduate students during his tenure, but he also extended his enthusiasm for insects and education beyond the campus by developing and heading outreach programmes through the college and through the campus's Interactive University Project. In the CityBugs Program, for instance, Dahlsten and his students teamed up with teachers in the Oakland Unified School District to develop interactive lesson plans on insects. In the Environmental Leadership Outreach Program, Dahlsten also helped develop courses in urban environmentalism for Oakland public school students, particularly those in poor or politically disadvantaged communities.

    His more than 200 publications were a significant contribution to the field of biological control and he was a member of several professional societies. His efforts and outstanding contributions earned him earlier this year the UC Berkeley Distinguished Service Award and the College of Natural Resources Citation. Dahlsten received numerous other honours throughout his distinguished career, including the UC Berkeley College of Natural Resources Outstanding Teaching Award in 1995. For 2 years in a row, he was chosen to be a member of a research team visiting the People's Republic of China as part of an exchange programme in integrated pest management. One of Dahlsten's last honours will be given posthumously in November by the Western Forest Insect Work Conference - the 2003 Founder's Award - in recognition of his contributions to the field of forest entomology.

    David Rowney, a research associate at Dahlsten's lab and a friend for 32 years said, "Generations to come will benefit from the reduction in pesticide use that Don accomplished through his successful biological control efforts both in California and around the world."

 

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