Bionomics of tortoise beetle, Cassida circumdata Herbst: An emerging pest of water spinach in northern and eastern India

Abstract

The present study records the occurrence of tortoise beetle, Cassida circumdata Herbst on water spinach (Ipomoea aquatica) from the northern and eastern region of the country. Both the grubs and adults prefer to feed the chlorophyll of the leaf lamina and thereby creating shot holes on it. Affected leaves often failed to fetch the good market price. The seasonal incidence and biology of this pest were studied at Varanasi region, Uttar Pradesh during 2017-18. The pest occurred thorough out the year with peak during 34th and 48thstandard meteorological weeks (SMW) i.e., third week of August and last week of November, respectively when almost 50% of leaves were severely damaged. With the onset of summer in the region the population was declined. C. circumdata had life-cycle of 38.5 – 70.25 days under laboratory conditions. The incubation period varied from 2.5 to 6 days with an average of 4.25±1.25 days. There were five larval instars. The first, second, third, fourth and fifth instar larval period ranged from 2.75 to 3.50, 2.75 to 4, 2.50 to 3.25, 2.50 to 3.50 and 4 to 5 days, respectively. The pre-pupal and pupal stages lasted for 1.5–4.75 and 5–7.25 days, respectively. Adults survived for 15 to 33 days with an average of 23.20±7.69 days.