Evaluation of modified collection drums and light emitting diode bulbs for trapping the edible long-horned grasshopper, ruspolia differens (serville) in Uganda

Abstract

The long-horned grasshopper (Ruspolia differens) is a delicacy in Uganda and many African countries. It is traditionally trapped at night during the swarming seasons using mercury bulbs that consume a lot of electric energy and pollute the environment. In addition, the collection drums used in the traditional trapping technique are non-selective, trapping non-target insects, some of which are allergenic to humans. Further, these traps are inefficient in retaining the insects. The International Centre of Insect Physiology and Ecology designed a modified R. differens collection drum by fitting a funnel to minimize escape of R. differens catches; and partitioning the drum into three compartments using meshes of varying sizes to filter bigger non-target insects at the top, R. differens in the middle and smaller insects at the bottom. The mercury bulbs traditionally used in attracting R. differens to the trap were replaced with LED bulbs to save electric energy and prevent the release of mercury into the environment. The objectives of this study were (i) to determine the effect of collection drum design and light source on the quantity of R. differens trapped in Masaka, (ii) determine the effect of collection drum design and light source on the number of non-target insects trapped along with R. differens in Masaka and (iii) carry out a cost-benefit analysis of using improved traps and the traditional traps for trapping R. differens. The study was conducted in Nyendo town Masaka district during April – May and repeated in November – December swarming seasons of 2019. Experiments were set at four trapping sites of commercial trappers and trapping was done for a total of fourteen effective nights which were spread out over the two swarming seasons. Experiments were overlaid with existing setups of commercial trappers which consisted of 16 to 20 traditional drums. Six drums were randomly selected from each site as experimental units, of which three were used as controls (3 replicates) and the other three were replaced with modified R. differens collection drums. Measurements of R. differens and counts of non-target species were taken from the three modified drums and three selected traditional drums from each site per night. Thirty randomly selected commercial trappers were interviewed to collect data on capital expenditures, operating costs and returns of the traditional technique; and these costs and returns were also estimated for the improved technique. Results show that the modified drums collected a comparable quantity of R. differens as the traditional drums, but with significantly reduced contamination from non-target insects (Achaea sp., Haritalodes sp., Heteronychus sp. and Paederus sp.) which were xiv smaller than R. differens. Most importantly, 85% of Paederus sp. (Nairobi fly) which is the most hazardous non-target insect was eliminated. The bottom wire mesh was found effective at filtering off non-target species smaller than R. differens to the bottom compartment. However, the upper wire mesh was not effective at filtering non-target species which were of the same size or bigger than R. differens. Light Emitting Diode bulbs of 400 W trapped a comparable quantity of R. differens as mercury bulbs of the same wattage, but the LED bulbs consumed less than half of the electric power compared to the mercury bulbs. Trapping R. differens using modified drums with LED 400 W bulbs was more profitable than the traditional drums with mercury 400 W. The improved technique comprising the modified drums and LED 400 W bulbs is therefore recommended as a better alternative for trapping cleaner R. differens while saving energy.