Chinese Journal of Oceanology and Limnology Vol. 29 No. 1, P. 162-166, 2011 DOI: 10.1007/s00343-011-0101-z
Integrated biological control of water hyacinths, Eichhornia crassipes by a novel combination of grass carp, Ctenopharyngodon idella (Valenciennes, 1844), and the weevil, Neochetina spp.* GOPALAKRISHNAN Ayyaru1, RAJKUMAR Mayalagu1, 2, SUN Jun (孙军)2, **, PARIDA Ajay3, VENMATHI MARAN Balu Alagar4 1
Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai - 608502, Tamil Nadu, India
2
Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
3
M. S. Swaminathan Research Foundation, Third Cross Street, Institutional Area, Taramani, Chennai - 600 113, India
4
Takehara Marine Science Station, Graduate School of Biosphere Science, Hiroshima University, Minato machi 5-8-1, Takehara
725-0024, Hiroshima, Japan Received Dec. 18, 2009; revision accepted Apr. 1, 2010 © Chinese Society for Oceanology and Limnology, Science Press, and Springer-Verlag Berlin Heidelberg 2011
Abstract The efficacy of grass carp Ctenopharyngodon idella (Cyprinidae) and weevils Neochetina spp. (Curculionidae) to control the aquatic weed, water hyacinth, is investigated in a square net cage (happas) setting at a farm in Cuddalore District, South India. This novel combination of insects and fish is found to be superior to individual treatments for controlling the weed growth within 110 d. The biomass of the weed, number of plants, percentage of flowered plants and chlorophyll contents were studied. The weed biomass is reduced from 5 kg (day 1) to 0.33 kg (day 110) when exposed to grass carp and weevils. The number of plants is reduced to 0.75 in grass carp and weevil exposed happas, while it is 741.5 in the control. The mean number of leaves per plant is also reduced. In addition, the chlorophyll a and b are significantly reduced in happas exposed to the combination of fish and insects when compared to the other treatments. Based on the results of this study, we consider the combined use of grass carp and weevils to be more efficient and sustainable for managing water hyacinths than the use of these organisms individually. Keyword: water hyacinth; grass carp; weevil; biological control
1 INTRODUCTION The water hyacinth, Eichhornia crassipes (Pontederiaceae) (Mart. Solms), is recognized as the world’s most troublesome aquatic weed, causing environmental, economic, and social problems in many tropical and subtropical countries (Holm et al., 1991). The water hyacinth creates more problems, such as, choked waterways, starves the water of oxygen, create a prime habitat for mosquitoes, in temperate areas like the United States. For example, the annual cost of managing water hyacinth in the state of Florida alone is about US$ 5 million (Ochiel et al., 1999). In some parts of India, this floating plant forms dense impenetrable mats across waterways and stagnant water bodies such as ponds, which results in the blockage of irrigation canals and
interference with hydroelectric power projects and rice production (Gupta et al., 2007). Water hyacinths also suppress the growth of phytoplankton and other submerged plants in aquatic ecosystems (Gopal, 1987). However, the management of water hyacinths by physical, mechanical, and chemical methods is expensive and perpetual (Center et al., 1999). In 1991, several attempts to control the water hyacinth using weevils were made in South Africa (Cilliers, 1991). However, the weevil, Neochetina spp. Supported by the Chinese Academy of Sciences Research Fellowship for International Young Researchers to M. Rajkumar hosted by J. SUN, and the Knowledge Innovation Project of the Chinese Academy of Sciences (Nos. KZCX2-YW-QN-205, KZCX2-YW-213-2) to J. SUN Corresponding author:
[email protected]
No.1
GOPALAKRISHNAN et al.: Water hyacinth control by grass carp and weevils
(Coleoptera: Curculionidae), was not introduced on a larger scale to control the water hyacinths until 1996, when they were used in the Lake Victoria, African (Ochiel et al., 1999). The impact of weevils on water hyacinths has been successful and sustainable throughout the world (Gopal et al., 1981). Grass carp Ctenopharyngodon idella (Valenciennes, 1844) has also been used as a biological control method against submerged aquatic weeds because they can consume up to 18%–40% of their own body weight in a day (Gopal et al., 1981). However, their use against floating plants like water hyacinth has received little attention (Chilton et al., 1992). In contrast, a great deal of research has been conducted to evaluate the use and impact of the weevil on water hyacinths (Perkins, 1973; 1978; Deloach et al., 1976). Although biological control is a proven and sustainable method, there are no large scale programs in India for the control of water hyacinths. Therefore, this study was conducted to determine the efficacy of the novel combination of the weevil and the grass carp for control of the water hyacinth in India.
2 MATERIAL AND METHOD This study was conducted at a farm pond in the Village of Keelamanakudi, near Chidambaram (11°24N; 79°41E), Cuddalore District, South India from December 2006 to April 2007. The area of the pond was 30×30×1 m. The experimental design was a completely randomized block (CRD) with one control and three treatments (T 1–3) and five replications. In the control, water hyacinths were free from exposure to weevils or fish, while they were exposed to weevils in T-1, grass carp in T-2, and weevils and grass carp in T-3. Inside the pond, 20 happas (a square net cage) were erected to enclose an area 3 m long, 2 m wide, and 1 m deep using nylon fabric mesh (20 mm). The top of the happas were closed to prevent the movement of weevils from one to another. For the control and T-1, the bottoms of the happas were also closed to prevent grazing by grass carp; however, they were left open in treatments T-2 and T-3 to allow feeding by carp. Fresh water hyacinths were collected from a nearby irrigation canal. The hyacinths were sprayed with carboryl 100 wp (5 g/L) and then allowed to grow without exposure to weevils for one week. The weeds were then washed to remove the mud from the roots and leaves, after which they were allowed to dry on paddy straw for 10 min. Next, 5 kg (mean fresh weight) of hyacinths were placed into each happas. The mean number of plants per happas was
163
74.24 (±2.24). The farm pond had been stocked with Catla, Catla catla (Hamilton, 1822) (160) (Cyprinidae), which is a surface feeder that feeds on zooplankton, Rohu, Labeo rohita (Hamilton, 1822) (120) (Cyprinidae), which is a column omnivorous feeder, Mrigal, Cirrhinus mrigala (Bloch, 1795) (120) (Cyprinidae), which is a bottom detritus feeder, and grass carp, Ctenopharyngodon idella (50) (Cyprinidae), which feed on aquatic macrophytes in the pond. The stocking density of the farm pond was 0.5 fish/m2, which is the recommended stocking density for different carp species in this region (Gopal, 1987). The stock-sized fish (35 mm) were procured from a commercial carp nursery and stocked in the experimental pond on November 30, 2006 and the experiment was started on December 31, 2006 (after the fish were 61 d old). The size of the grass carp was between 13 and 15 cm. The weevils, Neochetina bruchi Hustache, 1926 and N. eichhorniae Warner, 1970 (Erirhinidae) were field collected from water hyacinths and released together into the designated treatment happas. The weevils were not separated by species due to difficulty in identifying them in the field. About 20 weevils per plant were inoculated into the T-2 and T-3 treatment happas. The water hyacinth biomass, number of plants and number of flowers were assessed every 10 d during the experiment for 110 d. The number of leaves per plant was assessed on the first day of the experiment and again on the 110th day. The chlorophyll content of the third leaf of ten plants was estimated using a standard acetone extraction method (Lichtenhaler, 1987). Data were subjected to one way ANOVA to identify significant differences between the control and treatments. The probability level used for the statistical analyses was P
