Back To BNI Home
Back to BNI Available Issues

December 1998, Volume 19 No. 4

General News

RHD after One Year in New Zealand

Last year BNI [18, 100N-101N] reported on the illegal introduction of the rabbit calicivirus disease RCD (now reverted to its original name of Rabbit Haemorrhagic Disease or RHD) into New Zealand. Readers will recall that in July 1997 the Ministry of Agriculture had declined an application to import the virus as a biological control for rabbits, largely because of the lack of certainty about its benefits and risks. The virus was imported by persons unknown, probably before the Ministry decision had been made, and released and spread by farmers in late August 1997 using a variety of bait concoctions. This blatant breach of New Zealand's border biosecurity system caused considerable anger in government agencies and among many members of the public, exacerbated by the cavalier attitudes of some farmers. However, I am happy to report that the initial stand-off between farmers and government reported in the earlier article has been ameliorated somewhat by their common need to find out how the disease has worked. Everyone wanted to know whether RHD, rabbits, and conventional control could be managed, or at least the outcomes of the disease predicted, so that benefits could be maximized and risks minimized.

New Zealand has major exotic vertebrate pest problems and invests about NZ$100 million a year on their control and on research. However, most of the impacts of these pests remain unresolved and biological control offers the only sustainable widespread solution for many of these problem animals. The use of RHD is the first modern attempt in New Zealand at biological control of a vertebrate pest, and it would be a great pity if the unfortunate way it was introduced blighted future consideration of other biocontrol agents. This, and the need to understand how it has worked, has overridden some of the anger at its origin and brought many of the stakeholders together in a common cause.

The Foundation for Research, Science and Technology, the Ministry of Agriculture and Forests, and regional governments initiated a research programme in August 1997. The programme is led by Landcare Research working on the field epidemiology of RHD, but includes a consortium of other research agencies (AgResearch, the Rural Futures Trust, and Massey, Auckland and Lincoln universities) investigating virology, vector behaviour, predation effects, epidemiology and modelling. Some results of Landcare Research's work to date are described here.

Status of RHD in New Zealand

The disease has been spread, by people and naturally, over most of the country with variable effects on the rabbits. Mortality rates, where measured, have varied from zero to 94% with reductions of around 60-70% being common. Generally, natural epidemics have been more consistently successful than the various attempts at using RHD on baits. Largely to avoid the haphazard use of concoctions of virus obtained from dead rabbits in the field, a known lethal strain of the virus is now commercially available to farmers in New Zealand.

Field Epidemiology of RHD

We compared the behaviour of RHD at two sites in Central Otago, one where RHD was released by mass aerial baiting (biociding), and the other where it arrived naturally. Indices of rabbit abundance declined by 67% (from 68 and 35 rabbits per spotlight kilometre, respectively) on both sites during the spring 1997 epidemic. Rabbit abundance remained static for the next three months and then declined at a rate greater than expected for that time of year to a low of ten and three rabbits per spotlight kilometre, respectively, in June 1998. Numbers have begun to increase again with the start of a new breeding season, and reached 16 and five per kilometre in August 1998.

At the biocided site, the daily death rate (indicated by the presence of fresh rabbit carcasses along fixed transects) peaked three days after the biociding, and few new carcasses were found after 40 days. Carcasses were found over the whole baited area soon after the baiting. At the natural epidemic site, the daily death rate peaked at day 20 and new carcasses were still being found up to 80 days after the first death was recorded.

Sera from shot rabbits were tested for antibodies to RHD using a competitive ELISA test developed in Italy1. We used a 1:40 dilution and assumed `inhibition' levels above 50% indicated immunity to RHD. No rabbits (out of 60) were immune on the natural site before the epidemic, but this increased to 31% (n = 62) immediately after the epidemic. Eight per cent of rabbits (n = 60) were immune on the biocide site before the epidemic (presumably because the farmer did some spot baiting before mass biociding) and this increased to 43% (n = 60) immediately after. There were no differences in the levels of immunity between these two sites, but other studies have shown higher levels of immunity after biociding than after natural epidemics. The proportion of antibody-positive rabbits among the cohort that was alive before the spring 1997 epidemics has since declined on both sites, although the levels of antibodies in those that were positive remained high. One explanation for this might be that rabbits that survive infection have higher mortality rates than rabbits that were never infected, i.e. the disease is not without cost even if the animal lives. Challenge trials indicate that loss of antibodies does not necessarily mean loss of immunity to further challenge.

Fresh rabbit carcasses appeared in a down-wind direction on both sites, at a rate of about 100 m/day. A number of fly species were carrying RHD virus, and preliminary work by AgResearch showed some rabbits became infected and died when exposed to flies2. Scavengers presumably play a role in disseminating virus by opening carcasses and exposing infected tissues to flies. More fresh rabbit carcasses were scavenged during the natural epidemic (41%, n = 157) than during the biocide (18%, n = 127). Predicting the timing and intensity of epidemics will partly depend on understanding the role of vectors.

A unique symptom among seropositive survivors, observed only in New Zealand, is that a small proportion have lost their ears.

Antibody Status of Other Species

Feral cats, ferrets, harrier hawks, and to a lesser extent hedgehogs, use rabbits as a food source either by scavenging or predation. By eating rabbits that have died of, or are infected with, RHD they may produce antibodies in response to the virus, as occurs in foxes3. Our objective was to determine whether any predators, scavengers, or hares produced an antibody response when exposed to rabbits with RHD.

We collected serum samples from predators and scavengers, from an area of mass biociding and from spot-baited areas, during February and May 1998. The samples were tested for RHD antibodies using the competitive ELISA test at 1:40 dilution. We found that: 53% (n = 51) of cats, 10% (n = 51) of ferrets, 11% (n = 18) of hawks and 3% (n = 30) of hedgehogs were seropositive (those with greater than 50% inhibition); there was a bimodal distribution of antibody levels for all animals except cats; the proportion of seropositive animals was higher in February than in May; although about equal numbers of male and female ferrets were sampled, only female adults were seropositive. No juveniles were seropositive, which suggests ferrets had to be alive during the epidemic and that RHD was not active at these sites in 1998; no hares (n = 34) from the Mackenzie Basin, where RHD had occurred, were seropositive; and in areas where RHD had apparently not occurred, no predators or scavengers were seropositive.

Pre-existing Viruses

A non-pathogenic rabbit calicivirus, thought to be the ancestor of RHD, has been identified in Europe4, and it appears to impart immunity to the pathogenic virus5. Before the arrival of RHD in New Zealand, the New Zealand Applicant Group conducted a serological survey of wild rabbits using various ELISA tests some of which showed high titres of `factor x', and they concluded that this was evidence of a benign calicivirus being already present in a high proportion of wild rabbits6. The questions remain (a) whether this conclusion is correct, and, if so, (b) whether the factor is similar to the European non-pathogenic virus, and (c) whether it imparts any immunity to rabbits challenged with RHD virus.

In March 1998, we captured 64 rabbits from areas of New Zealand where RHD had not been reported. Serum from each was taken at capture, and one and six months after challenge with RHD. Each sample was tested at four dilutions (1:10, 1:40, 1:160 and 1:640) using both the competition ELISA specific for RHD and a less-specific indirect `sandwich' ELISA used by the Applicant Group to measure the presence of any caliciviruses. All rabbits were orally dosed after the first sample of serum was taken and the survivors again after six months. Each dose was 50 LD50s of the Czech-strain of RHD virus, obtained from the Elizabeth MacArthur Institute in Victoria.

We found that: 14 rabbits survived challenge including one that was seropositive before the first challenge and one that did not sero-convert at the first challenge but died at the second challenge; all but one of the survivors were positive to `factor x', the negative survivor was a juvenile; all adult rabbits, both survivors and victims of the challenge, were positive to `factor x', but only six of 22 juvenile rabbits, i.e. those born in the previous breeding season, were positive to `factor x'.

`Factor x' clearly does not guarantee immunity to RHD, which means that it will not affect the outcomes resulting from the presence of RHD virus - unless it is a calicivirus and recombines with RHD virus. Lack of cross-immunity is not unexpected given the high prevalence of `factor x' in the Applicant Group's survey yet high mortality rates during the initial RHD epidemics in New Zealand. The question remains whether `factor x' is a calicivirus descended from the benign rabbit calicivirus.

Ecological Consequences of RHD

Rabbits are the main food of three predator species (ferrets, cats, and harrier hawks). Increased consumption of native prey of secondary importance in predators' diets is commonly observed after declines in rabbit abundance. This is corroborated by studies of predation on banded dotterels in braided riverbeds. The proportion of banded dotterel eggs lost to predators was 52% 7% shortly after the rabbits were controlled with baits poisoned with sodium monofluoroacetate (Compound 1080)7. This compared with only 23% 4% egg loss (averaged from 12 sites) during subsequent breeding seasons when no rabbit control was conducted. Preliminary data from the breeding season during the 1997 RHD epidemic indicated that 56% 10% (averaged from four sites) of eggs were lost to predators where rabbit abundance was originally high (up to 50 rabbits per spotlight kilometre) and population declines were pronounced (up to 90%). This is a similar predation rate to that reported after rabbit poisoning. The longer-term implications for dotterel populations, and for other native prey, are unknown. Continued monitoring during subsequent breeding seasons will quantify the longer-term effects of RHD on these native bird populations.

References

1 Capucci, L.; Frigoli, G.; Rønsholt, L.; Lavazza, A.; Brocchi, E.; Rossi, C. (1995) Antigenicity of the rabbit hemorrhagic disease virus studied by its reactivity with monoclonal antibodies. Virus Research 37, 221-238.

2 Barratt, B. I. P.; Ferguson, C. M.; Heath, A. C. G.; Evans, A. A.; Logan, R. A. S. (in press) Can insects transmit rabbit haemorrhagic disease virus? Proceedings of the 51st New Zealand Plant Protection Society.

3 Leighton, F. A.; Artois, M.; Capucci, L.; Gavier-Widen, D.; Morisse, J.-P. (1995) Antibody response to rabbit viral hemorrhagic disease virus in red foxes (Vulpes vulpes) consuming livers of infected rabbits (Oryctolagus cuniculus). Journal of Wildlife Diseases 31, 541-544.

4 Capucci, L.; Fusi, P.; Lavassa, A.; Pacciarini, M. L.; Rossi, C. (1996) Detection and preliminary characterization of a new rabbit calicivirus related to rabbit hemorrhagic disease virus but nonpathogenic. Journal of Virology 70, 8614-8623.

5 Chasey, D.; Trout, R. C.; Sharp, G.; Edwards, S. (1997) Seroepidemiology of rabbit haemorrhagic disease in wild rabbits in the UK and susceptibility to infection. In: Chasey, D.; Gaskell, R. M.; Clarke, I. N. (eds) Proceedings of the 1st International Symposium on Caliciviruses, pp. 156-162.

6 Lough, R. S. (1998) Factors which may limit the long term effectiveness of rabbit calicivirus disease in New Zealand. Unpublished report to the New Zealand RCD Applicant Group, 12 pp.

7 Rebergen, A.; Keedwell, R.; Moller, H.; Maloney, R. (1998) Breeding success and predation at nests of banded dotterel (Charadrius bicinctus) on braided river beds in the central South Island, New Zealand. New Zealand Journal of Ecology 22, 33-41.

By: John Parkes, RHD Research Programme Leader, Landcare Research, PO Box 69, Lincoln, New Zealand
E-mail: Parkesj@landcare.cri.nz 

 

 

Mikania Weed Broadens its Range

The tropical world is awakening to the creeping threat of the invasive weed mikania, Mikania micrantha. A perennial vine in the New World tribe Eupatoriaceae, which contains many other well-known weed species such as Siam weed (Chromolaena odorata), Crofton weed (Ageratina adenophora) and mistflower (A. riparia), it is now recognized as one of the world's most serious tropical weeds. Originating from Central and South America, mikania is widespread in tropical Asia, including India, Malaysia, Thailand and Indonesia, and has recently been reported from Nepal. It also occurs in Papua New Guinea, the Solomon Islands, the Philippines, Christmas Island in the Indian Ocean and Pacific Ocean islands including Fiji and Western Samoa. Earlier this year it was recorded for the first time from Australia, and subsequent investigations suggested it may have been in north Queensland for as long as ten years.

In India, mikania occurs in the northeast and southwest of the country. One major route of entry was its introduction as a cover crop and purportedly as camouflage for airfields in the 1940s in northeastern India where it has since become naturalized. It is now causing substantial yield losses in smallholder agroforestry systems, in tea, oil palm, rubber, teak and sal (Shorea robusta) plantations, and in many crops including bamboo, reed, plantains and pineapples. It has also invaded natural evergreen, semi-evergreen and moist deciduous forests and is threatening biodiversity in national parks, for example the Royal Chitwan National Park in Nepal. However, in its natural habitat mikania is a component of aquatic ecosystems such as marshes and riverbanks and is rarely seen outside of these. Surveys conducted in Karnataka and Kerala States by Kerala Forest Research Institute (KFRI) (in collaboration with CABI Bioscience) in 1997-98 indicated that the range of the weed is much greater than previously supposed; it is very variable in form and, in many areas, is extremely invasive. Its climbing habit enables it to reach and smother the canopy of small trees. Mikania can grow from the smallest of cuttings and almost any node touching the ground will root. It has a rapid growth rate and produces copious quantities of wind-borne seed from small, creamy-white, mildly scented tubular florets whose pollen and nectar attract large numbers of bees, wasps, flies and butterflies.

The damage caused by mikania's smothering growth characteristics may be compounded by allelopathic properties. Anecdotal evidence of this abounds, but the only firm evidence comes from studies on its impact in rubber in Malaysia, where the weed retarded plant growth through the production of allelopathic substances.

In the 1980s, the possibility of using insect agents for biocontrol of the weed was investigated, but these efforts were dogged by problems of predation of the agents after introduction. However, the potential of co-evolved exotic pathogens is now being recognized, and in particular there are exciting prospects for a highly specific neotropical rust fungus, Puccinia spegazzinii, collected during surveys in Trinidad and Brazil. Studies conducted by CABI Bioscience and Viçosa University (Minas Gerais, Brazil) have shown this species to be highly pathogenic to the Indian biotypes of the weed, and host specificity tests indicate that it is restricted to M. micrantha and does not extend its range to even closely related species within the genus Mikania. It thus has great potential for use in mikania's adventive range as a classical biocontrol agent.

In Australia, mikania is one of the primary target weeds of the Northern Australia Quarantine Strategy and is a prohibited weed on Commonwealth and State lists. It is a threat to the narrow wet tropical coastal belt of northern Australia which includes prestigious national parks such as Kakadu. Some argue that its potential Australian distribution covers a broader area. However, at present mikania exists as a very small infestation (20-30 m perhaps) and a few garden specimens around Mission Beach, north Queensland, where the climate is ideal for its establishment. The authorities are in the process of attempting total eradication. Most of the infestation has already been removed by the Department of Natural Resources (DNR). It is now a matter of monitoring the site and removing all the small plants that are regrowing from fragments - the plant is not easy to find especially while small.

Information on mikania, particularly in relation to the threat to Australia, can be found on the Internet at:
http://www.dpie.gov.au/aqis/homepage/public/industry/milemin.html

Further information on the Australian mikania infestations, plant identification, and some predictions for its spread are at:
www.agric.wa.gov.au/progserv/plants/weeds/climate/mikania.htm

Contact: Sean Murphy, CABI Bioscience UK Centre (Ascot), Silwood Park, Buckhurst Road, Ascot, SL5 7TA, UK.
E-mail: s.murphy@cabi.org
Fax: +44 1491 829123

For Australia: Reece Luxton, Land Protection Officer, Qld Dept of Natural Resources, C/ Centre for Wet Tropics Agriculture, PO Box 20, South Johnstone, Qld. 4859, Australia.
E-mail : LuxtonRX@dnr.qld.gov.au
Fax: +61 7 4064 2249

 

 

Eradication of White-spotted Tussock Moth in New Zealand

A two-year campaign costing US$12 million has resulted in the eradication of the white-spotted tussock moth (Orgyia thyellina) in New Zealand.

Native to Japan, Korea, Taiwan and China, the moth was found infesting Auckland's eastern suburbs in April 1996. Little biological information was available on the insect which is only occasionally a pest in its home range. Quarantine populations reared at Forest Research in Rotorua were used for life cycle studies, host determination, toxicity testing, pheromone development - and for rearing a field monitoring population. Feeding trials demonstrated that the caterpillars had a strong preference for members of the Rosaceae, including pip and stone fruit, and also maple, birch and willow. Given the history of destruction inflicted by other lymantriids (gypsy moth and Douglas fir tussock moth) and the unpredictability of exotic insects in new environments, it was considered to be a serious threat to New Zealand's forests and trees - with amenity, shelter and garden trees primarily at risk, but horticulture and forests also threatened.

A response strategy was developed. As the infestation was confined to an area of 300 ha, which with a buffer zone gave an operational area to be treated of some 4000 ha, it was agreed that eradication should be attempted. Codenamed `Operation Evergreen', this began in spring 1996. The insect over-wintered as egg masses during 1996 on plants, fences, houses and outdoor furniture. These eggs were expected to hatch in the spring and the first generation of caterpillars to pupate producing flight-capable female and male moths. These would then give rise to two further generations over the summer, the final generation of flightless female adults laying over-wintering eggs.

Bacillus thuringiensis var. kurstaki (Btk) was found to be effective against the caterpillar, particularly instars I-III. However, the height of the trees meant that aerial application was necessary. The initial operational strategy was to treat the entire 4000 ha area with up to six aerial applications of Btk (as Foray 48B at 5 litres/ha) spaced a week apart and beginning soon after egg hatch. The aim was to ensure that all caterpillars were exposed to at least three applications of Btk before they entered the fourth instar. However, a protracted egg hatching period and the survival of some first generation larvae led to nine sprays by aircraft over the operational area, with a further 14 helicopter applications to the infested 300 ha area, finishing in April 1997. In addition, weekly ground spraying of more than 200 properties was carried out.

Spraying had an immediate impact on population levels, and ground searching for residual infestations became less and less effective. This problem had been foreseen, and a search for a more effective monitoring system had been given priority. Commercially available lymantriid pheromones proved ineffective, so efforts focused on the development of a synthetic pheromone. A pheromone was developed by collaborative work involving New Zealand and Canadian (Simon Fraser University) scientists, but this was too late for the 1996-97 spray programme, and monitoring during this season involved the use of live caged females. In the period December 1996 - January 1997, 68 first generation males were caught in 46 out of 250 traps, and these were all contained within the known infested area. A further six moths were caught in April, arguably late second/early third generation individuals. Monitoring continued into late June but no further moths were caught.

No spraying was conducted in the 1997/98 season, given the level of spraying the previous year and the absence of live moths since the previous April. Instead, 7000 synthetic pheromone traps were deployed over 2000 properties and risk sites, and these were inspected every fortnight from late December until mid June. No male moths were caught, and white-spotted tussock moth was declared eradicated from Auckland's eastern suburbs in June 1998.

The management of a programme which included aerial spraying in a populated area as an essential component was complex. It included features such as advanced flight control, mapping and aircraft monitoring techniques so that the public could be warned just minutes before aircraft passed over. Extensive health monitoring was also implemented. Above all, the programme was characterized by teamwork and collaboration - between researchers, operations people, policy specialists, communications staff, contractors and the Aucklanders.

Source: Hosking, G. (1998) White-spotted tussock moth - an aggressive eradication strategy. Aliens 7, 4-5.

Contact: Gordon Hosking, Ministry of Agriculture and Forestry, P. O. Box 2526, Wellington, New Zealand.
Fax: +64 7 345 6861

 

 

Fire Ant Update

Last year we described how decapitating phorid flies were being released in the USA against the imported red fire ant, Solenopsis invicta [BNI 18(2), 23N-24N]. Here, we give more details of that work and also outline work behind the release of the first pathogen against S. invicta in the USA.

Off With Their Heads

The phorid now being released in Florida, Pseudacteon tricuspis, was one of eight species of fire ant decapitating flies studied in and around the Embrapa National Research Centre for Environmental Monitoring and Impact Assessment in Jaguariúna, Sao Paulo State in Brazil between January and June 1996. These flies are widely distributed, host specific, and also interfere with fire ant foraging, so were identified as promising prospective agents for a biological control programme. Seven of the species were reared from egg through to the adult stage, and all of them were found to pupate inside the head capsule of their host. Pupae and sexes of the species could not be distinguished morphologically at the pupal stage, except that females consistently emerged from larger hosts. Males of P. tricuspis readily mated with females while they were ovipositing in fire ant workers, but mating in the other species was not observed, so rearing methods were able to be developed only for P. tricuspis. However, P. tricuspis and P. litoralis were both sufficiently abundant to be exported to the US Department of Agriculture - Agricultural Research Service (USDA-ARS) in Florida from the Brazilian Quarantine Laboratory for host specificity testing.

Further studies (1996-98) in Brazil and Florida showed that damp conditions are needed for pupation, and that total development time is 4-10 weeks, depending on temperature. Adults emerge in the morning, and are ready to mate and parasitize new hosts by midday. With current rearing methods, about 70% of larvae emerge as adults, and in Florida at the moment some 400-600 flies are being reared per day, with a growth of 30-40% in each generation. During 1997, flies were released in Florida at three sites near Gainesville (800 flies in July, 1200 in September and 1500 in September-October). Many first-generation flies were found at two sites, but they only appear to have been permanently established at the third site where they have been collected monthly since October 1997. So far, these flies have survived a winter and a summer drought. Observations indicate that about half the fire ant colonies at this site are attacked. The flies do not yet appear to have expanded out of the initial release area. Releases for 1998 are continuing at four additional sites.

Checking the Queen

Now USDA-ARS scientists have released fire ant brood infected with a microsporidian, Thelohania solenopsae, at sites in nine states (Arkansas, Oklahoma, Mississippi, Louisiana, Tennessee, South Carolina, Alabama, Georgia and North Carolina), following test releases in Florida. Originally identified in Brazil in 1973, it is the most common pathogen in fire ants in South America. It was discovered in the USA by ARS scientists in 1996 in fire ant colonies in Florida, Mississippi and Texas. This is the first micro-organism to be evaluated in South America as a potential biological control agent of the fire ant in the USA.

The pathogen infects fire ant colonies and chronically weakens them. Workers transmit the pathogen to the queen via food exchange. The disease slowly reduces her weight. She lays fewer and fewer eggs, all infected with the pathogen. Field work in Argentina indicated that fire ant mounds were less dense in a Thelohania-infested area, infected colonies had smaller mounds, and sexual brood was present less frequently than in uninfected colonies. It was also found that infection increased the mortality rate and shortened the longevity of fire ant colonies reared under laboratory conditions. Although colony elimination can take from nine to 18 months, infected colonies were found to be smaller than healthy colonies after only three months. The development of better infection techniques and methods to mass produce the microsporidian is now underway.

Contact: [for phorids]: Luiz Alexandre Nogueira de Sá, Laboratório de Quarentena "Costa Lima", Embrapa Meio Ambiente, Caixa Postal 69, CEP 13820-000 Jaguariúna, SP, Brazil.
E-mail: lans@cnpma.embrapa.br
Fax: +55 19 867 8740
Internet: http://www.bdt.org.br/bdt/biocontrol/
[or] Sanford Porter, USDA-ARS, CMAVE, PO Box 14565, Gainesville, FL 32604, USA.
E-mail: sdp@nervm.nerdc.ufl.edu
Fax: +1 352 374 5818
[for microsporidians] David Williams or David Oi, USDA-ARS CMAVE, PO Box 14565, Gainesville, FL 32604, USA.
E-mail: dfw@nervm.nerdc.ufl.edu  or doi@gainesville.usda.ufl.edu
Fax: +1 352 374 5984
[or] Juan Briano, USDA-ARS, SABCL, Agr. Couns. ARS Lab, US Embassy Buenos Aires, Unit 4325 APO AA 34034-0001, Argentina.
E-mail: jabriano@mail.retina.ar

For a new Internet manual, `Microsporidia (Protozoa): a handbook of biology and research techniques' see:
http://www.ars-grin.gov/ars/
SoAtlantic/Gainesville/location.html

 

 

Root-knot Nematodes: Could Biocontrol Replace Methyl Bromide?

It has been known since the early 1980s that some nematode pests can be controlled effectively by nematophagous fungi and bacteria. The most studied case of natural control concerns the cereal cyst nematode in cereal monocultures in northern Europe where two species of fungi, Nematophthora gynophila and Verticillium chlamydosporium, effectively control this widespread pest. These agents provide the most sustainable method of nematode management in intensive agriculture and today plant breeders no longer incorporate cyst nematode resistant genes into elite cultivars. However, such natural control is slow to establish and difficult to exploit.

Work continues at IACR-Rothamsted in the UK with V. chlamydosporium but with an isolate that is active against root-knot nematodes. All species of these major pests are found to be susceptible to the fungus which destroys the eggs and may reduce fecundity. The fungus is very variable and isolates which do not colonize the rhizosphere do not provide control. The host plant has a major effect on the efficacy of the fungus, affecting both the amount of fungus able to develop in the rhizosphere and the multiplication of the nematode. Verticillium chlamydosporium is most effective on plants which support extensive growth in the rhizosphere and on plants which are relatively poor hosts for the nematode and produce only small galls in response to nematode attack. The fungus is confined to the rhizosphere and on highly susceptible crops too many egg masses remain embedded in the large galls produced and so escape parasitism. A biomanagement strategy has been developed in which the fungus is applied to specific poor hosts in the cropping cycle to enhance their efficiency in reducing nematode infestations before the next susceptible crop.

This strategy is being compared with the use of methyl bromide and an integrated control strategy using granular nematicides for the control of root knot nematodes on vegetable crops in southern Europe The programme is funded by the European Commission and includes laboratories in Crete, Italy, Portugal, Spain and the UK. Details of the programme can be found on the Internet at:
www.area.ba.cnr.itreO85acOl/bkfair3444.html

The programme began in March 1998 and a Workshop Manual has been produced which covers the methods used for working with V. chlamydosporium. The manual includes methods for the isolation, selection and evaluation of isolates in laboratory and field tests and describes studies on risk assessment and visualising the fungus in the rhizosphere. It is anticipated that the manual will be published by the International Organization for Biological Control (IOBC).

By: Brian Kerry, Entomology and Nematology Department, IACR-Rothamsed, Harpenden, Hertfordshire AL5 2JQ, UK.
E-mail: brian.kerry@bbsrc.ac.uk
Fax: +44 1582 760981

 

 

News from India

Progress at PDBC

Highlights of research work conducted at the Project Directorate of Biological Control (PDBC) in Bangalore and at its 16 coordinating centres spread over different parts of India in 1997-98* included devising an acrylic, multicellular rearing unit for Helicoverpa armigera. The unit, which provides 80-90% larval survival, is transparent, durable, amenable to surface sterilization and made of indigenous materials.

Advances were also made in identifying and investigating organisms with potential for biocontrol in a range of systems. This included the description of new predatory coccinellids in the genera Pseudoscymnus and Serangium, and the development of an endosulfan-tolerant strain of Trichogramma [for details of this see: BNI 19(3), 74N-75N].

Entomophilic nematodes (Steinernema spp.) were isolated from elevations of 107-2200 m above sea level and were found to be predominant in sandy loam and clay loam soils. One isolate (PDBCEN 6.11) caused the death of Plutella xylostella and Opisina arenosella larvae within a day of inoculation, and of H. armigera, Spodoptera litura and Corcyra cephalonica within two days.

A number of microbial agents were shown to have promising activity. Pseudomonas putida PDBC No. 19 was found to completely inhibit growth of Sclerotium rolfsii in dual culture. From a number of Trichoderma and Gliocladium isolates tested, T. harzianum isolate PDBC TH2 and G. virens gave greatest inhibition of mycelial growth in S. rolfsii. Gliocladium virens isolate Pl 1 (GV) was found to be a potent antagonist in vitro against Fusarium oxysporum f. sp. gladioli, which causes gladiolus corm rot and yellows.

The disease antagonist T. harzianum PDBC TH2 along with T. koningii, G. virens and G. deliquescens were all effective against the nematode Meloidogyne incognita, causing 94.5% mortality. Finally, seed germination and the seedling vigour index of parthenium weed were greatly reduced at different concentrations of culture filtrates of G. virens.

Around the Regions...

In cotton in Andhra Pradesh, Biointensive Integrated Pest Management (BIPM) excelled due to the significant role played by the beneficial insects, which increased through intercropping with groundnut. The seed cotton yield obtained through the BIPM strategy was highest at 1.827 t/ha. The incremental cost-benefit ratio (IBCR) in BIPM was high (10.07) compared to farmers' practice (1.55) and judicious use of insecticide (1.59).

In Gujarat, bud and boll damage, damage to locules and populations of sucking pests were significantly lower in BIPM modules compared with a control. Parasitism due to Agathis spp. was very high. The yield in BIPM plots was significantly higher and also gave a higher ICBR than insecticidal treatments and the control. Intercropping of maize with cotton enhanced the activity of Cheilomenes sexmaculata in BIPM blocks. Studies revealed that maize, Cassia occidentalis, parthenium weed, castor, sunnhemp, marigold, tobacco, etc., harbour various parasitoids/predators of cotton pests.

At Bangalore, an entomopathogenic fungus, Paecilomyces farinosus, was isolated from the spiralling whitefly Aleurodicus dispersus. The green lacewing Mallada astur was predominant on guava and about 230 nymphs of spiralling whitefly were consumed by a single larva in 10-12 days. The efficacy of Cryptolaemus montrouzieri in controlling the green shield scale Chloropulvinaria psidii on guava was demonstrated at Kestur village near Bangalore.

In Assam, successful control of water hyacinth was achieved by the exotic weevils Neochetina eichhorniae and N. bruchi in Disangmnukh area of Sibsagar district and less flowering was observed in the remaining water hyacinth areas of Sibsagar district.

In Kerala, Orthogalumna terebrantis has established over all the release sites giving partial suppression of water hyacinth.

Golden Jubilee Celebration

The Project Directorate of Biological Control celebrated 50 years of India's Independence by organizing monthly seminars, cultural programmes, group discussions and exhibitions running from 15 August 1997 to 15 August 1998. The seminars covered varied topics including: `Success of biological control' [in Hindi], `Management of agricultural research', `Special statistical techniques', `Cultural programmes', `Pest management in horticultural crops', `Entomophilic nematodes', `Biological suppression of plant diseases, phytoparasitic nematodes and weeds using disease antagonists', `Predatory mites' and `A hundred years of Cryptolaemus in India'.

*PDBC (1998) Annual Report (1997-98). Bangalore, India; Project Directorate of Biological Control, 167 pp.

By: Dr S. P. Singh, Project Directorate of Biological Control (ICAR), P. B. No. 2491, H. A. Farm Post, Bellary Road, Bangalore - 560 024, India.
E-mail: pdblc@x400.nicgw.nic.in
Fax: +91 80 3411961

 

 

Assessing Agent Risk

The ERBIC (Evaluating Environmental Risks of Biological Control) project was set up as a consequence of a workshop organized by the European Plant Protection Organisation (EPPO) and IIBC in 1996, which recognized that the new European guidelines for pest control did not take into account the risks of using exotic natural enemies, and proposed a new set of European guidelines which is now being developed by an EPPO panel. Both the EPPO-IIBC workshop and the EPPO panel stressed the urgency of needing scientific methods to evaluate the risks of introduced natural enemies to indigenous non-target species - EPPO already has pest risk analysis methods agreed and established for European plant protection services, into which new protocols for evaluating the safety of biological control agents could be fitted.

Coordinated by Professor Heikki Hokkanen (University of Helsinki) in collaboration with teams led by him and Dr Franz Bigler (Swiss Federal Research Station for Agroecology and Agriculture), Dr Jeff Waage (CABI Bioscience), Professor Giorgio Celli (University of Bologna) and Professor Joop van Lenteren (Wageningen Agricultural University), the project is focusing on the exotic biological control agents most widely used in Europe today. In-depth case studies and population modelling will be used to evaluate these. The effect of alien generalist and specialist predators and parasitoids will be studied on local non-target organisms, particularly key beneficial species. The effects of microbial natural enemies will also be evaluated.

The overall objective of this project is to facilitate the development of sustainable, biologically based production systems, in line with the commitments of many EU governments to reduce use of chemical pesticides. The specific objectives, which aim to ensure that the introduction and use of biological control agents for pest control - a key component of sustainable agriculture - is done in a way which does not put at risk non-target organisms are: (1) to determine the negative and positive effects of different types of biological pest control for agriculture, the environment and biodiversity in Europe, (2) to develop rapid and reliable methods to assess the potential risk of import and release of biocontrol agents in Europe and (3) to design specific European guidelines to ensure that biological control agents which are to be introduced are environmentally safe.

Contact: Professor Heikki Hokkanen, Department of Applied Zoology, Latokartanonkaari 5, Box 27, FIN-00014, University of Helsinki, Finland.

Back To BNI Home
Back to BNI Available Issues