Meeting Abstract

73.2  Saturday, Jan. 5  Low plant nitrogen content and high population density enhance migratory characters in a polyphenic locust CEASE, AJ*; ELSER, JJ; HAO, S; HARRISON, JH; University of Sydney; Arizona State University; Institute of Zoolog, Chinese Academy of Sciences; Arizona State University arianne.cease@sydney.edu.au

Locusts present an impressive and well-studied example of phenotypic plasticity in which population density regulates a variety of behavioral, morphological, and physiological traits that often culminate in migratory swarms. Oedaleus asiaticus, a north Asian locust, has outbreaks and migratory swarms comprised predominantly of brown morphs. Heavy livestock grazing promotes outbreaks by lowering plant nitrogen content and likely lowering the protein:carbohydrate ratio to the optimal range for this locust. However, it is unclear if a change in plant quality can modulate the effect of density on phase characteristics. We found that locusts reared at high population density and fed low-N plants (i.e. plants that are high quality for O. asiaticus) had the most enhanced migratory characteristics while locusts fed high-N plants (i.e. deleterious for this locust) consistently had decreased expression of migratory characters. These results do not support existing paradigms that poor-quality resources increase the expression of migratory phenotypes. We then compared feeding habits of the brown (outbreak) and green (non-outbreak) morphs. There was no difference in plant preference nor protein:carbohydrate intake target ratio; however, when confined to diets extreme in their protein:carbohydrate ratios, green locusts decreased consumption and brown locusts maintained a similar consumption rate on all diets. From these results we infer that the green morph strategy may be most beneficial for sedentary insects confined to limited food choices to avoid long-term deleterious effects of consuming an unbalanced diet, while the brown morph strategy of being more willing to consume suboptimal foods may be most beneficial for roaming insects.