| Abstract | Rice is the principal crop and chief dietary ingredient for the people of Bangladesh The hot and humid climate of Bangladesh is highly conducive for easy proliferation of a multitude of pest problems. Rice hispa (Dicladispzz armigera, Olivier; Chrysomelidae: Coleoptera) is one
of the most damaging rice pests in Bangladesh. The current hispa management strategies heavily depend on chemical means. The chemicals not only increase the cost of production but
also manifest many fold problems of non-point pollution of rice ecosystem, residual toxicity to the consumers, disproportionate killing of the natural enemies, ih_\'i1U health hazards to the users and many more. ln this context, the current study was done to formulate acceptable hi spa management practices in the light of integrated pest management (IPM) principles. The main objective of the study was to investigate the key elements of the field ecology
and pest status of rice hispa to develop efficient management practices for the farmers of Bangladesh. More specifically, trends of hispa infestation in Bangladesh and its correlation with temperature and rainfall, and the extent of crop damage caused by hispa under field conditions, were studied. The other objectives were the identification of natural enemies of rice
hispa prevailing in the Bangladesh rice ecosystem and their effectiveness, effects of insecticide on hispa population and their natural enemies, overwintering of hispa during the winter after harvest of Aman crop, documentation of current hispa management practices and an assessment of their efficacy and suggesting efficient and effective management practices.
A detailed survey and field experiment was conducted at the Agricultural Training
Institute (AT1), Daulatpur, Khulna, Bangladesh, from late 1994 to early l997. The survey was conducted in 18 southern districts, which are the most hispa prone areas of the country. Recommended and commonly grown rice varieties, namely BRl 1: BR23 and BR3O, were grown for the experiments. Sampling was done by using sweep nets and ‘farm cop‘. Surveys
were carried out in seven hispa infested lhanas (sub-districts) of six districts. 70 randomly selected farmers were interviewed by pre-set questionnaires. Data were also collected through personal visits to hispa prone areas, including river banks, to study possible over wintering of hispa. A special study trip was made inside the Sundarban (the single largest mangrove forest of the world) by a motor boat to investigate the rice hispa overwintering.
At the onset of the experiments hispa was extremely rare in Bangladesh. Therefore
hispa specimens had to be collected from different locations of the country and reared in net- caged pot plants and later in big (4 rn x 2 m = 8 m2) net cages in the experimental fields. Continuous observations were made for predation and parasitization of hispa at all its life
stages. Suspected natural enemies were collected, studied and the unidentified ones were preserved in 70% ethyl alcohol for later identification. The efficiencies of some of the natural enemies were studied inside field cages. Cold tolerance of hispa was studied in the laboratory by putting hispa in a refrigerator at a set temperature for a definite period. It was revealed from the study of the 12 years of hispa infestation, rainfall and temperature data of l8 hispa prone districts of Bangladesh that the e.\'tent of hispa infestation varied greatly from location to location and within a location. According to the recorded data.
sometimes the infestation was lower when the rainfall was high but sometimes it showed an opposite trend. The infestation data also shows that a similar type of hispa infestation was prevailing in consecutive two years or more in some of the districts under study with totally different quantum and distribution of rainfall. Although hispa infestation prevailed almost throughout the year, there were fluctuations in the extent of infestation. No regular trend of hispa infestation could be detected from the available information (temperatures and rainfall). It was found through a farmers‘ survey that hispa infestation can start from as early as 25 DAT (Days after transplpnting) and can continue up to 85 DAT. But in the experimental fields it was observed differently, i.e., infestation started at seedling stage and continued up to
maturity of the crop. The damage of the crops in most cases was proportional to the duration of the infestation. Local rice varieties were less able to recover from hispa attack than the high yielding varieties Perhaps severe infestation of hispa in the early stages and during the crops‘
reproductive period caused more yield loss. Current management practices are mainly the use of chemicals and limited use of some mechanical methods. Applications of insecticides do not seem to be a good solution to control the hispa problem. They kill the adult hispa as well as the natural enemies of hispa and this disrupts the ecological balance which ultimately help
building the hispa population in the subsequent seasons from the remaining eggs, larvae and immigrant population. Control of hispa by sweep net collections, destroying larvae by cutting the mined leaves and conserving natural agents by avoiding chemical applications, appeared to
be ecologically, economically and environmentally sound.
An undescribed species of Trio/iogramnm was found and observed to be quite effective as an egg parasite (60-99%). This parasite was not equally available and active everywhere throughout the rice growing seasons and was absent on the first hispa eggs in early spring. Some other natural agents were also found actively parasitising eggs or larvae, or predating on
hispa at different stages of its life.
The prevailing notion about overwintering of rice hispa inside the Sundarb an area of
Bangladesh was found to be unt-rue. lt appeared from a thorough investigation during the study period that hispa overwinters on ratoons, straws, stubbles and weeds, specifically in the hispa
prone areas. Overwintering hispa adults were found to be highly tolerant to cold surviving up to 9 consecutive days at 6 to 9 CC even without consuming any food.
The best possible control strategy would be to manage the hispa adults during the
period between T. aman and bot-0 crop, a bridging time, as they do not lay eggs during this period. This may be done by emphasising hispa collection for money or other incentives such as food for work. Conservation and development of natural biological agent populations should
be strengthened by preventing application of broad-spectrum chemicals. A1-tempts should also be made to develop methods for large scale rearing of biological agents.
Frequent field visits, collection and killing of adults at first sight, clipping leaves with
larvae. keeping fields free from ratoons. weeds and stubbles after mnaii harvest. cutting crops close to the ground, planting legume crops on dikes, gradual flooding of the land before puddling the soil for transplanting are the possible effective, economic and eco-friendly
management practices suggested for the farmers of Bangladesh. And all these are in addition to with-holding agrochemicals.
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