Showier plants host more larvae: distribution and movement of generalist caterpillars among plants in the field

Abstract

1. Host recognition and movement among plant species is widely studied in adult insects. These behaviours are rarely considered in juveniles despite evidence that they also move between plants.2. This study investigated what may influence caterpillars of a generalist moth Helicoverpa punctigera to move among individual plants and whether caterpillars gravitate towards more vigorously flowering plants in the field.3. This study tested caterpillar behaviour towards potted plants of a primary and secondary host species. The plants were inserted into the ground 50 cm apart. Caterpillars were placed, alone, onto either the primary or secondary host and left for 24 h before recording their final position. Individual caterpillars were also placed on the ground equidistant from each plant species, and their orientation behaviour was filmed.4. Caterpillars placed on either a primary or secondary host plant for 24 h moved to the other plant species a quarter of the time.5. They mostly moved to the primary host when placed at equal distance from each plant species and appeared to track volatiles by raising and swaying their heads.6. In field surveys of two native daisy hosts at multiple field sites, the number of flower heads on each plant or stand was recorded along with the number of Helicoverpa larvae. Almost all caterpillars were on the primary host species, and 76% were on plants with more flower heads than the median.7. This study concludes that H. punctigera caterpillars approach plants with attractive volatiles but wander from both attractive and less attractive plants (Restlessness hypothesis). They therefore gravitate towards vigorously flowering primary hosts.