Abstract
These studies were conducted in the field at Multan, Pakistan to investigate the population trend of the aphid, Aphis gossypii and the ladybeetle, Coccinella septempunctata on brinjal, Solanum melongena, during the 2013-14 and 2014-15 crop seasons. Brinjal varieties Round Black, Dilnasheen, Black Beauty, Hybrid Shilpa, Bemisal and Nirala were used in the experiment. The number of aphids and ladybeetles were recorded at weekly intervals from October 15 to March 1, both years. Aphid numbers were recorded on three leaves per plant and four plants per plot and averaged per leaf. Numbers of ladybeetles were recorded from the whole plant by sampling three plants per plot. Seasonal mean number of aphids per leaf was at the maximum on the variety Black Beauty and lowest on Nirala, during the 2013-14 growing season. During the 2014-15 season the maximum number of aphids per leaf was recorded on the variety Round Black and lowest on Nirala. When sampling dates were compared, the highest and lowest aphid numbers/leaf was noted on February 1 and March 1, respectively, during 2013-14. However, the maximum and minimum number was recorded on February 1 and January 1, respectively during 2014-15. The number of ladybeetles per plant was highest on December 1 and lowest on October 15, during both growing seasons. A significant positive correlation was found between aphid and ladybeetle populations during 2013-14, and correlation was positive but non-significant during the 2014-15 season. Findings from our study indicate that there exists a positive correlation between the two populations, but is not always significant. A positive correlation is expected between prey (aphid) and predator (ladybeetle). However, it's strength and consistency needs to be further investigated by repeating the study for more seasons and at more locations to clearly see the trend of the two populations.