Life history trade-offs of thrips reared on fertilized and unfertilized Brazilian peppertree with respect to changes in plant terpenoid profiles

Abstract

Mass rearing is a critical component of a successful biological control program and is strongly dependent on the diet agents consume. We investigated the impact of fertilizing the target Brazilian peppertree, Schinus terebinthifolia, on plant terpenoids and the phenology, fecundity, and morphometrics of the thrips agent, Pseudophilothrips ichini. Plants in 3.8 L pots were fertilized (24N-8P-16K) at one of three concentrations every two weeks: Low (0 g/L), Medium (1.8 g/L), or High (3.6 g/L). To examine fertilizer impacts on life history, cohorts of 20 thrips eggs were reared in containers on stem cuttings from the potted plants. Terpenoid profiles were characterized using gas chromatography-mass spectrometry from potted plants grown at each fertilizer level, half of which experienced 72 h of thrips feeding. The fewest thrips reached the pre-pupa on Low fertilizer plants, but those thrips developed the fastest, lived longer as adults, and laid more eggs. Thrips on plants at either Medium or High fertilizer levels took longer to develop, had shorter adult lifespans, laid fewer eggs, but adults were larger, and they produced potentially higher quality eggs. Differences in terpenoid profiles between damaged and undamaged Low fertilizer plants and life history trade-offs suggest fertilizing may have minimal impacts on thrips; however, fertilized plants grow faster and larger, thereby ensuring a reliable supply of host material for mass rearing. Moreover, these results suggest that although thrips may have reduced survival, they will perform well following field releases when fed wild, unfertilized Brazilian peppertrees.