The study was carried out during 2012 and 2013 in the field and the laboratory of Vertebrate Pest Division, Bangladesh Agricultural Research Institute, Gazipur. Lesser bandicoot rat, Bandicota bengalensis was used as test animal. The animals were kept under the laboratory condition at least one week for acclimatization before starting the experiment. All the animals were starved for 6 hours before applying the treatments.
Observation of food consumption
All the baits were compared with standard bait (wheat grain). For each treatment 10 rats (5 males & 5 females) were used and they were individually caged. For all testing method 20 g of bait was provided in individual food cups and consumption rate was recorded to the nearest g on a daily basis for each rat to each food type presented. Paper was placed under each cage to recover spilled grain and to ensure accurate measurements of consumption. Daily food intake was determined by subtracting the spilled grain and the food remaining in the cup from the quantity originally given to each rat.
Preparation of zinc phosphide baits with different additives
For preparing 2% zinc phosphide bait with different additives, following combination of the ingredients were used such as powder milk (7.5%), sugar (20%), molasses (20%) dry fish (10%) mixed with wheat flour. The treatment combinations are –
T1 = Molasses + dry fish + powder milk + wheat flour, T2 = Sugar + dry fish + powder milk + wheat flour, T3 = Dry fish + powder milk + wheat flour, T4 = Molasses + dry fish + wheat flour, T5 = Molasses + powder milk + wheat flour, T6 = Molasses + wheat flour T7 = Powder milk + wheat flour, T8 = Dry fish + wheat flour, T9 = Sugar + wheat flour
Laboratory efficacy test
All the baits were compared with standard plain bait (wheat grain). The feeding test was conducted in the laboratory using acclimatized ten adults rats for each treatment. Two cups of bait were offered to each rat, one cup containing 20 g of plain wheat grain and another cup containing 20 g additive mixed Zn3P2 bait. The poison bait was supplied for three consecutive days and the plain wheat grains were provided up to the end of the experiment. Spilled bait material or wheat grains were collected in a paper placed beneath the cage and weighed for both the cups. Water was supplied at ad libitum. Consumption of bait additive, plain bait, mortality, and baits acceptance of the rats was recorded everyday. Tested bait acceptance was calculated using the EPPO (1982) modification equation.
Field Efficacy test
The experiments were carried out at farmer’s wheat fields in two different areas at Dinajpur and Rajshahi district of Bangladesh. In all the locations clear signs of rodent infestation were detected. Additive mix 2% zinc phosphide (Zn3P2) was used for this experiment. However, in the field test top ranking first six combinations along with wheat flour mixed with zinc phosphide were selected for the next test. So, The treatments combination are:
T1 = Molasses + dry fish + powder milk +wheat flour + Zn3P2, T2 = Dry fish + powder milk + wheat flour + Zn3P2, T3 = Molasses +dry fish + wheat flour + Zn3P2, T4 = Powder milk + wheat flour + Zn3P2, T5 =Dry fish + wheat flour + Zn3P2, T6 =Plain wheat + Zn3P2 (Standard poison bait).
Two methods were namely, the active burrow count method (El-Gawad and Ali 1982 b) and the foot tracks activity (using tracking tile) method (El-Sherbiny and Awad, 1987) were used to determine the population density in each location. Twenty active burrows/spots were used for each treatment. Before applying treatment all the active burrows were identified properly. Twenty tracking tiles (20 X 20 cm) for foot tact activity were used for each treatment. Foot tracts activity were taken for two nights for both pre and post treatment operation. The pre and post treatment rodent population were determined by using both of this method. Additives mixed zinc phosphide 10 g bait was placed near the burrow opening on a piece of paper. Bait was given in the evening and was collected in the next morning. Bait was placed for consecutive three days. Each treatment was replicated in three places in each location. Consumption was recorded everyday. Efficacy of the treatment was judged on the basis of rodent activity and percent reduction in population was calculated.
Data analysis
Daily consumption of each combination of additives mix diet was converted to gram. Additives mixed plain bait uptake was compare with Student t-test. The means with standard error were also calculated. Field data were analysis by one way analysis of variance and means were separated by LSD at 0.05% probability level. In all statistical test percentage data were transformed to arcsine to stabilize variance. STAR software version 2.0.1 (2014) was used to analyze the data.