Leaf shape and the host-finding behaviour of two ovipositing monophagous butterfly species

Abstract. 1. Ovipositing Eurema brigitta (Wallace) and Eurema herla (W. S. Macleay) butterflies were followed in the field to determine the nature and extent of the pre-alighting discrimination shown by these insects towards their only host plant, Cassia mimosoides (L).
2. Both species tended to search in areas where plants with long, thin leaves (primarily grasses) were less common, on average, than in randomly placed quadrats. Both species were also more likely to alight on non-host plants with leaves of a similar size and shape to those of the host plant than on non-hosts with leaf shapes dissimilar to that of the host.
3. The search behaviour of these monophagous insects was not so specialized that the butterflies never alighted on non-hosts; in fact the majority of alightings were on non-host plants and the pre-alighting discrimination shown by these insects is clearly not the prime behavioural determinant of their monophagy.