One is the loneliest number: The switch from group to solitary response in the cabbage looper, Trichoplusia ni.

Differences between solitary individuals and those who live in a group have been observed in many species. For example, solitary individuals may be more susceptible to predation or other mortality factors when compared to organisms living in a group. Behavioral adaptations in solitary organisms could provide self-defense or act as signals to others of potential risk. Previous studies in lepidopteran larvae show that regurgitation is more common in solitary individuals relative to those housed in groups. We have anecdotally observed this pattern of behavior in Trichoplusia ni (T.ni) by squeezing their abdomen to mimic a predation attempt. The purpose of this study is to determine how long it takes T.ni larvae to recognize a shift between group and solitary housing by using regurgitation as a behavioral measure of this social change. To test this, 15 larvae each were raised in two treatment groups (solitary vs group). In the last larval stage, five caterpillars from each treatment group were haphazardly selected. Those in the group-housed treatment were isolated into individual cups for four hours, then all 30 caterpillars were squeezed to elicit regurgitation. These methods allow us to determine the amount of time it takes T.ni larvae to develop a solitary response. Preliminary results suggest the time it takes for group-housed caterpillars to identify as solitarily-housed is as short as four hours. This study will further advance our understanding of behavioral plasticity in animals and may shed light on the role of secondary defenses in solitary individuals.