Variations in the Life Cycle of Legume Pod Borer, Maruca vitrata Fabricius (Lepidoptera: Crambidae) on Different Pulses

Legume or spotted pod borer, Maruca vitrata, is an important insect pest that causes severe economic damage in pulses. As the continuous mass culturing of this insect on different pulses is found to be difficult, comprehensive studies have not been done earlier. In keeping this, a comparison was made on its biology in different pulses viz., pigeon pea, green gram, black gram, cowpea, and lablab at the Department of Agricultural Entomology, Tamil Nadu Agricultural University, Coimbatore, during 2012–13. Maximum fecundity of M. vitrata was recorded (61.0 eggs) in lablab with a mean of 15.3 eggs/female/day in an oviposition period of 3.4 days followed by pigeon pea (14.0 eggs). The mean incubation period of the egg was minimum on pigeon peas (2.33 days) as against 3.07 days on lablab. Five larval instars were recorded with a mean developmental period of 2.19–2.47 days in different instars. The total larval period ranged from 10.76 days in cowpea to 13.19 days on the black gram with a mean of 11.81 days irrespective of the host studied. The pupal period ranged from 6.07 (green gram) to 6.67 days (lablab) with maximum pupation of 83.0% on pigeonpea. The total life cycle was minimum in cowpea (19.50 days) compared to 21.47 days on the black gram and the mean of 20.58 days irrespective of hosts studied. The mean longevity of females (3.64 days) was higher than male moths (3.15 days). The highest growth index of 7.45 was recorded on pigeonpea compared to 5.09 days on the black gram. The sex ratio (♂:♀) favoured females in all hosts and ranged from 1.0:2.13 in lablab to 1.0:2.34 on pigeonpea except on cowpea where it was male-biased (1.0:0.65). Hence, it is that clear the host preference was maximum on cowpea followed lablab, green gram, pigeon pea, and black gram. Lablab and cowpea found to be ideal hosts for quick development of M. vitrata.