History of introduction of salvinia Weevils in Okavango Delta

1. COLLABORATIVE EFFORTS IN BUILDING LOCAL CAPACITY FOR TOUR OPERATORS ON CONTROL OF SALVINIA IN OKAVANGO DELTA P/Bag 285 Maun E-mail: biokavango@orc.ub.bw Tel: 6817270 P/Bag 002 Maun E-mail: ckurungudla@gov.bw Tel: 686 0452 Background: Kariba weed or salvinia, Salvinia molesta is an aquatic alien invasive plant species. It is a floating water fern and considered as a major threat to our wetlands of Okavango Delta on northwest and Kwando/Linyanti/Chobe River systems on northeast of Botswana. The native range of the weed is South America. The species lacks co-evolved natural enemies in its introduced range, hence its invasiveness. Presence of nitrate and phosphate rich waters associated with eutrophication in the wide range of aquatic habitats in semi-arid climate, also favors invasiveness. Life cycle of Weevils: Average life period of adult weevils is 60 days. Life cycle of weevils has four stages: Eggs, Larvae, Pupae and Adult. Average of 1-2 eggs are laid for Every 2-5days. Eggs are deposited in the cavities of the rhizomes and leaves damaged by the adults, buds and roots. High nitrogen is required for larva and adults. Larval and pupation development decreases below 190C and optimum at 260C. Field tool: 1. Feeding damage by the salvinia weevils and larvae produce three types of colors on the weed. Severely damaged plants with dark brown foliage and very few green young leaves – Larval damage is higher than the adult damage. salvinia mat shows signs of sinking. 2. Moderately damaged plants have integrated mixture of chocolate brown and green foliage where egg incubation, larval and adults’ development is significant. 3. Healthy plants are green but have a few brown leaves indicating Weevils’ breeding and egg laying History of introduction of salvinia Weevils in Okavango Delta Control Methods: Salvinia is controlled by integrating physical and biological methods. The host specific biological control agent for salvinia is insect/weevil, Cyrtobagous salviniae (Figure 1), and has been in use in Okavango Delta since 1986. Responsible Institution: Aquatic Vegetation Control Unit, Department of Water Affairs, Maun and Kasane Biokavango Project:. The project is aimed at lifting barriers to mainstreaming biodiversity conservation objectives into three production sectors: water, tourism and fisheries. In the water sector, Salvinia molesta is a potential threat to the Okavango Delta’s biodiversity. Extensive weed spread could be detrimental to the ecological, hydrological and biochemical processes of the wetland system. This has the potential to adversely affect Delta water systems, livelihoods of rural communities and operations of private entrepreneurs. There is therefore a need to develop an integrated control and monitoring program for the weed, that is implemented by all key players in the Delta. Department of Water Affairs (DWA) : DWA has been managing the weed by physical and bio-control programs in the Delta for the past 25 years. Despite the significant progress made in the last ten years , the DWA has experienced several constraints in implementing the program. Control Mechanism: 1. C. salviniae larvae tunnel weed rhizome, causing the plant to collapse (Figure 3) 2. Adults feed more or less exclusively on the critical growth points such as apical buds and young leaves (Figures 2 and 3) Aim of Pilot Project: BIOKAVANGO Project and the DEPARTMENT OF WATER AFFAIRS identified TOUR OPERATORS AS KEY STAKEHOLDERS whose capacity need to be built in the control and monitoring of the spread of the salvinia weed. Five companies (Camp Moremi, Moremi Safaris, Splash Camp, Sandebi Camp and Khwai River Lodge) are engaged in implementing this intervention Intervention: 1. Develop infrastructure for breeding weevils at Pilot Sites. 2. Two Portapools are installed in each Camp 3. Train two guides per camp on maintenance of portapools and the introduction of weevils at infested sites 4. Monthly monitoring to determine the impact of weevils on infestations 5. AQUATIC VEGETATION CONTROL and BIOKAVANGO STAFF to oversee the implementation 1 2 3 PORTAPOOL How effective the salvinia bio-control weevil is! After successful control, Communities can now Harvest Water Lily Rhizomes in Wetland areas Thick infestation at Paradise Pools, Okavango Delta Successful control at Paradise Pools, Okavango Delta Outputs: 1. Knowledge transfer to tour operators on bio-control techniques of salvinia weed 2. Tour operators actively engaged in the protection of biodiversity within their concession areas 3. Pilot intervention replicated in other infested wetland areas of Botswana