Seasonal abundance of Epilachna vigintioctopunctata on Solanum torvum in highland area of Sukarami, West Sumatra

The seasonal abundance of Epilachna vigintioctopunctata on Solonum torvum in highland area of Sukarami, West Sumatra has been studied. In a Sumatran highland (Sukarami, 928 m altitude, annual rainfall 2,900 mm, mean monthly temperature 20.8 - 21.4 ºC), the lady beetle species, E. vigintioctopunctata (hereafter abbreviated as EV) commonly occur on the solanaceous host plants such as egg plant and a weed Solanum torvum. EV frequently reached a high density to deplete the plants. Seasonal change in abundance and mortality of the EV populations was studied for nine consecutive years (1991 to 2000) in three sites of S. torvum fields in Sukarami. The census interval for checking EV was three to four days from the start of study until February 4, 1992 and then seven days until the end of study. The adult beetles found for the first time were sexed and their elytral spot patterns were recorded. Soon after individual beetles were marked in the field with color lacquer, they were immediately released on the same plant. The result of experiment show that: (1) The adult of EV fluctuated synchronously at three study sites; (2) The density index of EV adults on “old” and “new” plants combined varied from 0.13 to 1.25; 3) The fecundity index varied from 0 to 10.33; (3) The average Minimum Length of Residence (MLR) value for females and males was 9.7 days (range from 0 to 170 days, SE = 0.34) and 11.1 days (range from 0 to 161 days, SE = 0.34); (4) An intimate relation was found between changes of øi and Ni: dro‎p of øi was followed by decrease of Ni and rise of øi by increase of Ni; (5) The survival rate varied from 0.61 to 1.00, and (6) The immature stages also perform several high peaks.