The brown planthopper, Nilaparvata lugens, shows considerable geographic and temporal variability in its
response to varieties of cultivated rice. N. lugens has repeatedly ‘‘adapted’’ to resistant rice varieties; however,
the physiological changes underlying planthopper adaptation are poorly understood. Endosymbionts
within planthoppers, such as yeast-like endosymbionts (YLS) could play a role as they
produce essential amino acids for planthoppers. We used a full factorial study to determine how natal
rice variety, exposed rice variety, YLS presence, and the number of reared generations affected nymphal
development, planthopper total nitrogen content, and planthopper hydrolyzed amino acid profiles. Nymphal
development was strongly influenced by a four-way interaction between the exposed rice variety,
natal rice variety, number of reared generations, and YLS presence. While symbiosis improved nymphal
performance in the 8th generation, it appeared to be a drain on nymphs in the 11th generation, when the
aposymbiotic nymphs actually showed higher performance than the symbiotic nymphs. This suggests
that the symbiotic relationship may be acting beneficially in one generation while acting as a drain during
another generation. Aposymbiotic planthoppers reared for 11 generations had a higher proportional
concentration of rare amino acids than those reared for 8 generations, indicating that the planthopper
itself appears to improve its ability to acquire rare amino acids. Therefore, the change in amino acid composition
of planthoppers suggests an underlying change in protein expression or amino acid metabolism
over time.