Population dynamics of aphids and their natural enemies on lucerne in western Maharashtra

Studies on seasonal abundance of aphids and their natural enemies in relation to the climatic factors were undertaken on lucerne (Medicago sativa) during 2005-07. During the study, 3 aphid species viz., pea aphid (Acyrthosiphon pisum Harris), spotted aphid (Therioaphis maculate, Buckton) and cowpea aphid (Aphis craccivora Koch.) were found predominant on lucerne. Infestation of pea aphid was noticed from December,2005 to middle of March, 2006 and middle of Nov.,2006 to 2nd week of February, 2007 with maximum population in 4th week of January, 2007 (57.80 aphids/tiller). Whereas, cowpea aphid was found from January, 2006 to 2nd week of February, 2007 and last week of Dec., 2006 to 2nd week of February, 2007. During this period, peak infestation noticed in 3rd weekof January, 2007 (23.50 aphids/tiller). However, spotted aphid showed two population peaks from December, 2005 to end of February, 2006 and 2nd week of July, 2006 to 1st week of August, 2006 with maximum population built up in the month of January (73.90 aphid/tiller). Infestation of pea aphids showed negative correlation with minimum temperature and positive correlation with evening relative humidity. However, spotted aphids and cowpea aphids showed negative correlation with maximum and minimum temperatures. Predators, Coccinellid, Chrysoperla carnea, syrphid and spiders showed highly significant positive correlation with aphids.