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

Authors: Halbritter, Dale; Wheeler, Gregory

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2021
Publication Date: 2/2/2021
Citation: Halbritter, D.A., Wheeler, G.S. 2021. Life history trade-offs of thrips reared on fertilized and unfertilized Brazilian peppertree with respect to changes in plant terpenoid profiles. Biological Control. 156 (2021) 104553. https://doi.org/10.1016/j.biocontrol.2021.104553.
DOI: https://doi.org/10.1016/j.biocontrol.2021.104553

Interpretive Summary: For biological control of invasive plants, large numbers of highly specialized insects (i.e., agents) are needed for field release to control the invasive target plant. Producing such numbers of insects in a laboratory environment can present problems if the plants used to raise the insects are not of optimum quality. Fertilizing plants results in larger, faster growing plants thereby ensuring a reliable quantity of food for the insect colony, but we considered whether fertilized plants are of the best quality for the insects. We investigated the impacts of fertilizing Brazilian peppertree (target plant) on the development and reproductive potential of the thrips agent. Brazilian peppertrees can produce defensive chemicals that affect their nutritional quality or deter insects from feeding on them and we examined how fertilization impacts these defensive chemicals. Results indicate that more thrips may survive on fertilized plants, while those that survive on unfertilized plants live longer and lay more eggs. Although thrips on fertilized plants don't live as long nor lay as many eggs, they grow larger and more of their eggs survive to hatch. There were differences in defensive chemicals between fertilized and unfertilized plants, which may contribute to the differences in thrips survival and reproduction we saw. Fertilizing plants for thrips colony production seems to be the best solution for ensuring sufficient quantities of plant material and providing suitable quality. Thrips are still able to perform well on unfertilized plants, suggesting they will do well once released into the field on wild plants.

Technical 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 2 wk: 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 higher quality eggs as more hatched. Differences in terpenoid profiles between damaged and undamaged low fertilizer plants and life history tradeoffs 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.