PROCEEDINGS OF THE FIFTH INTERNATIONAL WORKSHOP ON BIOLOGICAL CONTROL AND MANAGEMENT OF CHROMOLAENA ODORATA, DURBAN, SOUTH AFRICA, 23-25 OCTOBER 2000, ZACHARIADES, C., R. MUNIAPPAN AND L.W. STRATHIE (EDS). ARC-PPRI (2002) PP. 66-70 SUCCESSFUL BIOLOGICAL CONTROL OF CHROMOLAENA ODORATA IN GHANA: THE POTENTIAL FOR A REGIONAL PROGRAMME IN AFRICA J. A. Timbilla and H. Braimah Biological Control Unit, Crops Research Institute, P. O. Box 3785, Kumasi, Ghana Biological control of Siam weed, Chromolaena odorata, was revived in Ghana in 1989 after an initial failure in the 1970s. The arctiid moth Pareuchaetes pseudoinsulata was imported from Guam, USA in 1989 and, after quarantine studies, released in a pilot project in Kumasi in 1991. Establishment of P. pseudoinsulata was confirmed in Ghana in 1994. By 1999, the insect had spread to cover an area of about 81 501km2, representing about 57.9% of the total area infested by C. odorata in Ghana. In areas defoliated by P. pseudoinsulata, the C. odorata cover has decreased from a mean of 85.0% to 37.0% within a decade. Correspondingly, there is an increase in density of grass and other broad-leafed weed populations from 2 and 13.0% to 26.6 and 36.4%, respectively, thus increasing the fodder base for domestic and game animals. Plant species diversity following control of C. odorata increased from three to six species per unit area. Results obtained in 1999 indicate that P. pseudoinsulata causes significant damage in about 57.5% of the present distribution area of the insect. Considering the continued spread of C. odorata through many parts of Africa and the similarity of the threats posed by it there, the success achieved in Ghana raises hope for a regional programme for biological control of C. odorata. KEY WORDS: agent establishment and spread, biological weed control, impact on weed, Pareuchaetes pseudoinsulata, Siam weed INTRODUCTION After a decade of monitoring the performance of P. pseudoinsulata, results have shown that this insect Siam weed, Chromolaena odorata (L.) R.M. King and has the ability to reduce the C. odorata menace. H. Robinson (Asteraceae), was first discovered in This paper highlights research results since 1989 Ghana in 1969 (Hall et al., 1972). There are five and proposes an extension of the biological control schools of thought about its mode of introduction of C. odorata to other affected countries in Africa, into Ghana (Timbilla and Braimah, 1996). especially those within the West African sub-region. Biological control of C. odorata was initiated in Ghana in the early 1970s but failed due to the lack MATERIALS AND METHODS of sustained effort (Greathead, 1989). A nationwide survey by questionnaire was An international workshop was organized in Ghana conducted in 1991 to gather baseline information in 1988 by the Ghana committee of the African on the introduction, distribution and spread of Biosciences Network to examine the pest status of C. odorata. Parameters recorded included the the weed and propose strategies for effective history of introduction, common names, and integrated control while maintaining its usefulness diseases and pests known to be associated with as a medicinal plant (Frimpong, 1992). C. odorata. The importance of C. odorata to agricultural production in Ghana was also Subsequently, the Crops Research Institute of the determined. Another survey was conducted in 1993 Council for Scientific and Industrial Research to rate the most important weeds in the study area. initiated a biological control programme by importing the arctiid moth, Pareuchaetes The lifecycle of P. pseudoinsulata was studied in the pseudoinsulata Rego Barros (Lepidoptera: Arctiidae) laboratory using Kilner jars and wooden cages from Guam into Ghana in 1989. The objective of covered with grey-baft (30 x 30 x 30cm). Field the study was to reduce the competitiveness and releases of the control agent were done between further spread of C. odorata and to thereby enhance 18h00 and 20h00 in C. odorata fields. Subsequent biodiversity. Pareuchaetes pseudoinsulata was to the releases, monitoring was conducted to released in 1991, after two years’ quarantine for ascertain the field establishment and performance host-specificity and biological studies (Timbilla and of the insect. Braimah, 1991), and it had established by 1994 (Timbilla and Braimah, 1996). Using 5 x 5m2 quadrats, the percentage of C. odorata, grasses and other broad-leafed plants in 66 Timbilla and Braimah: Potential for a Regional Biocontrol Programme in Africa Navrongo • 700-1040mm Bolgatanga • • Wa B 1100-1250mm l a c k • Tamale 1125-1250mm V o l t a V O LA CÔTE D’IVOIRE L TOGO T 1300-1400mm A Sunyani L A K E Kumasi 4460-1750mm • Ho 500-1000mm ACCRA 750-2800mm Cape Coast Scale 1 : 4,000,000 Takoradi legend Land area infested by C. odorata Release sites of P. pseudoinsulata Distribution of P. pseudoinsulata 1999 Volta lake Figure 1. Map of Ghana showing release sites and distribution of Pareuchaetes pseudoinsulata in 1999. fields previously defoliated by P. pseudoinsulata was P. pseudoinsulata defoliation was also measured. estimated. The number of plant species per unit These measurements have been ongoing since area emerging from C. odorata fields after P. pseudoinsulata established in the fields. 67 Fifth International Workshop on Biological Control and Management of Chromolaena odorata RESULTS AND DISCUSSION Biology, Host-specificity Testing and Introduction of Pareuchaetes Weed Status and Economic Importance of pseudoinsulata into Ghana Chromolaena odorata in Ghana In 1989, the arctiid moth, P. pseudoinsulata, was In 1989 (20 years after the introduction of imported from Guam, USA by the Biological C. odorata), when the renewed effort to control Control Unit of the Crops Research Institute. C. odorata was initiated, in areas with optimal Preliminary investigations on the biology and host growth conditions the weed constituted about specificity of P. pseudoinsulata indicated that the 85.0% of the vegetation outside of cultivation, in insect completed a lifecycle within 35.5 days, with the form of dense thickets. The proportion of about 10 generations per year. None of 44 plant grasses and other broad-leafed weeds in the forest species of economic importance tested in Ghana regions of Ghana had been reduced by C. odorata to was defoliated by P. pseudoinsulata (Timbilla and about 2% and 13% respectively (Timbilla and Braimah, 1991). This resulted in field releases of Braimah, 1996). As a consequence, there was a P. pseudoinsulata in 1991 for the biological control reduction in fodder for domestic and game of C. odorata. animals, thereby impacting negatively on animal production. There was also a substantial reduction Establishment and Spread of Pareuchaetes of some native plant species such as Aspilia africana pseudoinsulata in Ghana (Pers.) C.D. Adams (Asteraceae) and Melanthera Initial field releases of P. pseudoinsulata were made scandens Schumach. (Asteraceae), which were in an experimental field of the Crops Research predominant fallow species before the introduction Institute at Fumesua, Kumasi in 1991, leading to of C. odorata. Thus C. odorata impacted negatively establishment in 1994 (Timbilla, 1996). Other on plant diversity. The damaging effects of releases were later made at Potrikrom and Assin C. odorata on plant diversity elsewhere have been Dadieso in 1997 (Fig. 1). A survey conducted in documented (Pickworth, 1976; Liggitt, 1983; 1999 on the distribution and spread of Macdonald, 1984; Erasmus, 1985, 1991; Byford- P. pseudoinsulata indicated that the insect had Jones, 1989). colonized an estimated 57.9% of the land area infested by C. odorata in Ghana (Fig. 1). Pareuchaetes By 1991 C. odorata had colonized about 60% of pseudoinsulata was observed to cause significant Ghana and was ranked as the most noxious weed in damage in an estimated 57.5% of this latter area. the forest regions (Timbilla and Braimah, 1996). In a study in 1992, C. odorata was ranked the most Impact of Pareuchaetes pseudoinsulata on important weed in the Forest Savannah Transition Chromolaena odorata and Resultant Zone (Timbilla et al., 1996). Effects on Biodiversity Following the establishment of the insect, Chromolaena odorata, however, is claimed to be of monitoring results have shown that use as a medicinal plant and in the improvement of P. pseudoinsulata is highly specific and an effective soil fertility in Ghana (Timbilla, 1998). This defoliator of C. odorata. Studies conducted in 1996 notwithstanding, the ecological damage caused by showed that the specificity and efficacy the weed necessitated its control. In 1987, the demonstrated by P. pseudoinsulata has reduced the government of Ghana signed an agreement for the competitiveness of C. odorata and species diversity biological control of the weed. This was in response has been enhanced. to an earlier international workshop resolution that there was the need for integrated control of Field studies conducted in 1998 indicated that, C. odorata, so that its usefulness could be exploited following the establishment of P. pseudoinsulata, the while its weediness was reduced. Biological control population of C. odorata had reduced from a mean was suggested as the most viable option to reduce 85.0% cover per unit area in infested fields to the competitiveness and spread of C. odorata while 36.4%. Grasses and other broad-leafed plants had maintaining its usefulness. In 1988, it was agreed increased from 2.0% and 13.0% in C. odorata- that approaches be made to FAO, WHO, UNDP and infested fields to 24.2% and 39.4% respectively. The other agencies to assist in funding research relating study also showed an increase in the number of to C. odorata. In 1992 the FAO sponsored a regional plant species per 1 x 1m2 area from three in survey on the introduction, distribution and spread previously colonized C. odorata fields to six in areas of the weed in western and central Africa. In 1993, where the insect has established and effected a proposal for funding was submitted to the African control of the weed.