Do you find your Zebras like to lay on the tendrils of the plant? Many butterflies lay eggs off the foodplant deliberately. Some of the large fritillaries lay when the foodplant has disappeared...we have an English large fritillary species that lays all the eggs off plant on tree trunks...the cats hatch in the autumn and spend the winter in the bark crevasses...wait all winter having not fed on anything except their egg shell...and in the spring the cat walks down the trunk and searches for Violets on the forest floor. Butterflies don't usually make many mistakes..it's a matter of survival for them....where you see them laying off plant there is usually a good reason...many are fussy and lay only on one part of the plant...others right at the base near the ground...others on the stem. A good example a the Passifloras, which are often patrolled by ants which expect to find eggs to eat...so many Passiflora feeders (Heliconids) develop their own preferences on where they lay to give their eggs the best chance...and this often includes off plant laying.