Many lepidopteran larvae spend virtually all of their time, from hatching until close to pupation, in direct association with their host plants. There they rest, feed, defecate, and in some cases manipulate the leaves, e.g., to counter plant defenses or to construct larval shelters. Species-specific host plant characteristics, as well as the developmental stage of both leaf and larva, influence the time larvae allocate to different activities, which in turn can influence their performance and survival. Using both direct observations and time-lapse video footage, we conducted a series of laboratory assays to compare the time that E. clarus larvae of different instars spent feeding and constructing shelters on the foliage of six different leguminous host plants. In addition, for one host (kudzu) we tested the ability of E. claruslarvae to construct shelters on leaves of different ages that varied markedly in trichome density.
Time spent feeding (frequency and duration of feeding bouts) varied significantly across the six host plants for fourth and fifth instar larvae. Notably, larvae on the highest quality host (soy) spent approximately 60% more time feeding than did larvae on the lowest quality host (wisteria). Fourth instars tended to feed more frequently but for shorter amounts of time than did fifth instar larvae. Additionally, first, second, and third instar larvae varied in time needed to initiate or complete construction of a leaf-and-silk shelter on leaves of the six host plant species, with host plant, larval instar, and the interaction between the two all having significant effects on construction time. On wisteria, first instar larvae took approximately half as long to complete their shelters as did third instar larvae, while the opposite pattern was true on soy. Finally, fourth instar larvae did not construct shelters on young, expanding kudzu leaves, but readily did so on larger, older leaves with lower trichome density. Interactions amongst larval stage, host plant identity, and leaf characteristics therefore all play important roles in shaping patterns of larval host use activity, with important implications for insect fitness.