Effects of a pyralid pest on productivity of duckweeds in pond ecosystem

Abstract

There are numerous instances of plant-Animal relationships which are ecologically friendly and significantly useful to the humans. The aquatic plant Duckweed and its pest (The pyralid insect) bear of the same interactions. In this study different biotic aspects were examined to clarify critical interactions of this relationship. This was aimed to establish a technique to examine bioresources in pond ecosystem. The objectives of the study were selected to evaluate biomass development of duckweed (Spirodela Polyrhiza). Life cycle and behavioural activities of its insect pest (S occidentals) was examined. Abundance of adults and abundance of larval and pupal stage was also examined. Record was maintained in nature of injury caused by the insect pest on the duckweed productivity. Various procedures and the sampling methods were innovated by the EBBL were used to carry out the research work. The research stations was in the Mirzapur Kumudini Hospital Complex, in Tangail District (in PRISM farm). Some experiments have been conducted in the Zoological Garden, Carzon Hall, in Dhaka University campus. In the experiment, Duckweed biomass growth development, the result was vary significantly in inorganic and organic pond, and biomass was doubled in eight days in both ponds. Duckweed Biomass growth development were followed by the method used by (Khondoker 1993) Life cycle observation, incubation period for hatching varies form 4-7 days. Egg hatching was higher in summer and lower in winter. Larval period lasts twelve days to more than one month. Pupation occurred within a cocoon inside the case, pupation period lasted for 4-7 days. The adults emerge from the pupa (within 2-4 days).Life cycle observations were followed by the methods using by Tuskes (1977) Adult abundance was significantly high in August and October and lower in January in Inorganic pond and an adult abundance were more in April and less in January in Organic pond. Adult distribution were followed by the methods of Lavery and Costa (1973) Infestation was calculated both in the fronds and roots of the Duckweeds in both ponds. The infestation was significant on the roots but it was not significant on the fronds in Organic pond. In loss assessment of Duckweed growth, it was found that; growth rate was highly affected, in the Inorganic and Organic pond. Larval/Pupal case making process had significant impact on duckweed productivity. Measurements of the Duckweed infestation and loss estimation were followed by the method used by Denis. S. Hill (1997) Finding of the research will also play a significant role in augmentation of rural economy of Bangladesh. But it needs awareness regarding the use of Duckweeds by taking scientific care of its association in the aquatic ecosystem.