Bruchids - Secret Seed Eaters


.BRUCHIDS - secret seed eaters

N. Keals 1, D. Hardie 2 and R. Emery 2

1. Centre for Legumes in Mediterranean Agriculture, The University of Western Australia, Nedlands 607 Western Australia

2. Agriculture Western Australia, Locked Bag 4 Bentley Delivery Centre Bentley, Western Australia

Abstract

The seeds of nearly all legume species are vulnerable, both in the field and in storage, to attack by bruchids (seed-beetles). There are at least 200 species of seed-beetles around the world which are pests of temperate crop, pasture and tree legumes. Legume species suited to Mediterranean areas are becoming an important component of the farming systems of Western Australia, but seed-beetles are a potential risk to these industries. There are several species of seed-beetles already present in Western Australia and there is a danger of other species being introduced. This highlights the need for surveys to determine the risk to industry.

One problem facing bruchid pest research in Australia is the lack of current identification keys. This prohibits accurate identification and risk assessment. This paper reports on surveys of Western Australian farms and quarantine imports which are currently underway. These surveys will facilitate the development of pest management programs and recommendations for changes to state and national protocols. Treatments to control bruchids at all life stages will also be investigated.

This work will reduce the likelihood of new pests becoming established. However, should this happen, the project will enable immediate response via a pest management plan to identify, control, contain and in some instances, eradicate the pest. The benefit to Australia in financial terms is difficult to assess, although our reputation as an exporter of "clean and green" grain cannot be understated.

Introduction

The seeds of all legume species are vulnerable to attack by seed-beetles, both in the field and in storage. Around the world, temperate crop, pasture and tree legumes may be infested by at least 200 species of bruchid. The identified economic bruchid pests come from six key genera: Bruchus, Bruchidius, Callosobruchus, Acanthoscelides, Zabrotes and Caryedon. Callosobruchus spp. and Acanthoscelides obtectus are the main pests of stored legume seed. They are highly adaptive and have an increasing geographical distribution from seed movement via humans. Only five seed-beetles (Acanthoscelides obtectus; Bruchus pisorum; Callosobruchus chinensis; C. maculatus; C. phaseoli) have been identified as pest species of temperate legumes in Australia to date. Other species may be present but not yet detected possibly because the host plant has not yet been utilised as an economic species or the seed-beetles have not been identified as pests owing to the lack of systematic produce surveys and inadequate identification keys. Most of the useful keys for economic species are not in english or out of-date or difficult to use except by specialists. There are real dangers that new pest species may be introduced in imported seed especially with the increasing national and international trade in legume seed and related commodities.

Legume species suited to Mediterranean areas of Australia farming are becoming an increasingly important component in Western Australia. Legume crops represent an environmentally friendly way to improve yield and grain protein content. Before 1970, field peas were the only broadacre legume crop of any significance grown in southern Australia. Since then, grain legume production in Australia has increased more than 50-fold from less than 25,000 ha to over 2 million ha in 1995/96 (Pulse Australia Yearbook 1997/98). Within Western Australia there has been a parallel interest in the use of forage legumes, both in species diversity and the area sown. The area under pasture legumes has increased dramatically with 8.4 million ha sown to pastures. Of this, the main pasture complex includes sub-clovers, with an increase in medics, rose clover, serradella and lucerne (WA Year Book 1997).

Pulse legumes are used mostly as a rain-fed winter crop grown in rotation with cereals in southern Australia. There are several pulse legumes grown in Western Australia and work is being conducted to further increase the number of species and varieties. The pulses currently grown include faba beans, lentils, chickpeas, dry (field) peas and lupins, with research being conducted on other genera including Vicia. With this increased interest in pulse production the seed-beetle in Western Australia has re-emerged as an important pest. The pea weevil (Bruchus pisorum) reduces crop yield, seed quality (direct damage and as a produce contaminant) and the amount of viable seed for sowing in the following season.

Forage legumes are grown in rotation either with cereal grains or as complete pastures. With the introduction of new forage varieties of medic (Medicago sp.) and clover (Trifolium sp.) as well as new species such as Vetch (Lathyrus sp.) and Bisurulla (Bisurulla sp.), the risk of accidentally introducing new species of seed-beetle’s to Western Australia increases further. This scenario has developed because both State and Commonwealth Quarantine protocols and procedures are not designed to cope with the seed-beetle menace. This was illustrated in 1996 with the detection of Acanthoscelides macrophthalmus in Leucana seed grown in Queensland (AQIS BULLETIN August 1996). This species has been recorded from Mexico, El Salvador and Texas. The eggs or larvae of this species may have arrived via necklaces, place mats or seed inadvertedly or deliberately brought through quarantine infested with the seed-beetle. Another, potentially disastrous introduction was averted when pasture researchers at Agriculture Western Australia voluntarily heat treated Trifolium and Medicago seed imported from Sardinia. This treatment successfully killed the seed-beetle Bruchidius trifolli which had been found in imported medicago seed. In Sardinia B. trifolli has been shown to reduce the seed carry-over in trial plots by 50%. This practise is still in place and will remain until State quarantine protocols can be changed.

To date there have been no reports of on-farm damage in legumes from storage bruchids in Western Australia. This could be a result of the small amount of on-farm storage for susceptible commodities, environmental factors associated with this type of storage or just good luck. Whatever the reason there are certainly some seed-beetle species already present in Western Australia that, given the right conditions, have the potential to be as damaging as some of the true weevils and beetles that attack stored cereals in this country.

The pulse industry in Western Australia has been urged to focus more on quality to maximise returns and ensure access to markets that discriminate on quality. All the processors and marketers are developing informal Quality Assurance programs. Pulse Australia’s Quality Assurance programme is currently a voluntary process, beginning with farmers but directed at all aspects of the pulse industry (Pulse Australia Year Book 1997/98:14). Pulse Australia’s Quality Assurance system (PAQAS), based on the SQF 2000 program developed by Agriculture Western Australia was keenly viewed by the processors and marketers. With the new PAQAS in place and its own SQF 2000 program Agriculture Western Australia would make an increased investment in pulse quality research and work more closely with pulse traders and grower groups to develop and implement practical quality assurance systems.

The potential of seed-beetles to damage legumes commodities in Australia can be best illustraed by being aware of what happens in other countries. C. maculatus infests nearly all species of legumes grown in Africa. To help control this beetle in Africa measures include; shelling soon after harvest, fumigation with phosphine under polythene protected sacks (T. Ajibola Taylor:1981). In the United States of America similar control measures are used along with fumigation in sealed silos.

Another problem facing countries that produce pulse and forage legumes is in the area of exporting agricultural produce to discerning markets. This is evident in Japan, which has a list of prohibited bruchids on the phytosanitory certificate lists. A recent development in Western Australia has been to compile a list of insects and diseases that attack and infest Phaseolus species.

CLIMA’s bruchid project

As part of initiatives related to the emerging pulse industries, a joint project of Agriculture Western Australia and the Centre for Legumes in Mediterranean Agriculture is looking at the taxonomy and control of bruchids, which is being funded by the Grains Research and Development Corporation. The project is driven by three aims;

The over-riding theme is to improve the quality of seed produced by the Western Australian pulse industry and reduce the risks associated with new pulse and forage legumes.

Bruchid taxonomy is being reviewed and documented for existing and potential pulse and forage legumes. Type specimens and taxonomic keys have been obtained from taxonomic specialists around the world. These sources include the Washington State University, University of Idaho, Royal Hollaway at the University of London, Overseas Development Natural Resources Institute, Institute of Biological Sciences at the University of Biological Sciences, Northern Arizona University, Agriculture Western Australia, Istituto Sperimentale Per Le Colture Foraggere Sezione Operativa Periferica Di Cagliari, Proyecto Biomasa Dinot-Uni, Hacettepe University Turkey and CSIRO. Others also include the Australian National Insect Collection and the Missouri Museum for samples of pest bruchids and quarantine intercepts. As many of the seed-beetle keys require translation. The translation and amalgamation of the bruchid identification keys has begun with several Spanish, Russian and Hungarian papers translated with a number in Portugese, French and German to be translated.

Once translated the taxonomic keys main characters are combined and entered into an interactive taxonomic key programme (Delta-Key). This will allow the development of printed and interactive identification keys designed for use by both specialists and extension officers. The assistance of key personnel in the use of the Delta programme and selection of key Bruchid characteristics is vital in the development of the taxonomic keys. It is envisaged that the Delta keys can be taken to at least genus level and will include photographic images of most pest bruchid’s that will be incorporated into online interactive keys over the internet and extension publications.

In-conjunction with the taxonomic work and aided by the increased interest in residual-free produce, work is being pursued to investigate non-chemical methods of seed-beetle control in infested legumes. This work is taking place at the Stored Grain Laboratory at Agriculture Western Australia. Cultures of C. maculatus, C. phaseoli (two strains) and Acanthoscelides obtectus have been obtained for the control phase of the project. A further culture of C. chinensis will be imported from Queensland and evaluated in a quarantine insectary. Preliminary phosphine and heat treatment trials have been conducted. The effects of these two different control methods on seed germination and beetle survival are being conducted on the cultured beetles.

The final aim of the project is to identify Western Australian quarantine anomalies and provide alternative quarantine protocols which will minimise the chances of bruchid pests entering Australia. Currently the quarantine responsibility is undertaken by the Western Australian Quarantine Inspection Service (WAQIS) in-conjunction with Agriculture Western Australia and the Australian Quarantine Inspection Service (AQIS). At times this can cause confusion as the WAQIS regulations can be more strict than the AQIS regulations. With this comes problems with international and national trade agreements which puts pressure on importers and exporters. Another problem is unsatisfactory compliance with phytosanitory certificates, in Australia and overseas. Information on the number of interceptions in Australia has not been collected and collated until now. The increasing importation into Australia of legume seed for research purposes will provide an opportunity to quantify the risk posed by exotic species of seed-beetles. Some of the quarantine anomalies that have been identified so far include a lack of experience in dealing with seeds (no seed specialist at AQIS), while WAQIS has their own seed inspector. Another quarantine problem that has been identified so far is that only 15% of all registered mail is inspected. Hence quarantine surveillance ends up being passive rather than active surveillance.

A pest interactions database is being developed to help identify key pests and various plant hosts. This database currently holds information on 250 species of seed-beetles, giving over 700 pest host interaction. This database will provide a valuable tool to extension officers, researchers, grain storage facilities and farmers who are looking to identify pests on economic crops and will eventually be accessible via the internet. A list of temperate grain and pasture legume species of economic importance to Australia is being compiled. This will enables a complete list of bruchid species of economic interest to temperate Australia to be gathered.

Conclusion

The project based at CLIMA and funded by the GRDC will be completed by 2000. At that time all key results available for public release with interim updates being presented at conferences and workshops. There are a dwindling number of people with the skills and expertise to identify potential pest species that will affect the pulse industry and how these products are stored. Continued work funded by the GRDC and agribusiness will enable the viable future of the agriculture industry and allow for new industries to develop and become successful, as the risks and problems are identified.

"There are no such things, there can be no such things as stored product insects, but there are insects which can invade and infest stored products" (Labeyrie 1981:3).

 

References

Horrigan, B (1996) Unwelcome Guests Under Investigation in AQIS Bulletin – August 1996:8

Labeyrie, V (1981) Ecological problems arising from weevil infestation of food legumes in The Ecology of Bruchids Attacking Legumes (Pulses), Dr. W. Junk Publishers, London.

Pulse Australia (1998), Pulse Australia Year Book 1997/98

Taylor, T.A., (1981) Distribution, ecology and importance of bruchids attacking grain legumes and pulses in Africa in The Ecology of Bruchids Attacking Legumes (Pulses), Dr.W. Junk Publishers, London.

Western Australian Year Book (1997), Western Australian Government Press