Putting pests on a diet? Changing crop production practices to reduce plant susceptibility to pests and improve biocontrol success

Abstract: Control of greenhouse floriculture pests is best done using a systems approach,
combining biological control and plant resistance with the manipulation of environmental and crop production practices. Studies suggest that high fertilizer levels stimulate pest reproduction by providing them with more organic nitrogen, such as amino acids and proteins, present in plant tissues. In his project, we looked at western flower thrips (Frankliniella occidentalis), infesting several varieties of potted chrysanthemum. We hypothesized that lowering fertilizer input could reduce the suitability of a host plant for thrips without compromising plant quality. In addition, a variety of biostimulants (beneficial fungi and bacteria) were tested to determine if any of them were able to reduce the impact of low fertilizer on potted chrysanthemum quality and marketability. Finally, we analyzed leaf biochemistry to identify changes in the concentrations of metabolites related to insect feeding and plant defenses. We found that lowering fertilizer rates significantly changed the concentrations of certain plant defense compounds, defense signaling hormones, and nutrient content of chrysanthemum plants with corresponding effects on thrips oviposition and some reduction of thrips population growth. However, the required low fertilizer rates affected plant quality and biostimulants did not compensate for this effect. In the end, the greatest differences in plant metabolites and thrips oviposition were correlated to chrysanthemum variety, not fertilizer level. Thus, by identifying some of the underlying causes for thrips outbreaks, we greatly increase the resilience of the production system against this pest.