This study examined the effects of various levels of nitrogen inputs (optimal, insufficient and excessive) and water inputs (optimal, low drought and high drought) to tomato plants (Solanum lycopersicum) on survival and development of an invasive tomato leafminer, Tuta absoluta (Meytick) (Lepidoptera: Gelechiidae). Plant growth i.e. plant height and the number of nodes declined under insufficient or excessive nitrogen treatment. Compared to optimal N, insufficient N treatment decreased leaf N content and increased the carbon/nitrogen ratio (C/N) whereas an excess of N had no effect on both leaf N content and leaf C/N ratio. Sub-optimal nitrogen supplies, water treatments and their interactions, significantly reduced the leafminer survival rate and slowed down its development. Together with the findings from three recent companion studies, we assumed that a combination of changes in nutritional value and chemical defense could explain these observed effects. Furthermore, our findings supported both the “Plant vigor hypothesis” and the “Nitrogen limitation hypothesis”.

Soil abiotic factors and plant traits are able to trigger bottom-up effects along the tri-trophic interaction plant-herbivore-natural enemy. The consequences could be useful for controlling the insect herbivores. The South American tomato pinworm Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), a devastating invasive pest on tomato and other Solanaceae plants, is currently threatening the tomato production worldwide. Recent knowledge on bottom-up effects on this pest has been gained, with fertilization, irrigation, plant traits, as well as their interactions being the major sources of these effects. Evidence is now emerging on how they impact on the performances of the moth from the perspective of tri-trophic interactions. In this review, we summarize the essential experiments studying the bottom-up effects on T. absoluta and discuss the implications of those findings for the integrated pest management programs. Future promising research directions are then proposed.

Prescribed burning (PB) is gaining popularity as a low-cost forest protection measure that efficiently reduces fuel build-up, but its effects on tree health and growth are poorly understood. Here, we evaluated the impact of PB on plant defenses in Mediterranean pine forests (Pinus halepensis and P. nigra ssp. laricio). These chemical defenses were estimated based on needle secondary metabolites (terpenes and phenolics including flavonoids) and discussed in terms of chlorophyll fluorescence and soil nutrients. Three treatments were applied: absence of burning (control plots); single burns (plots burned once); and repeated burns (plots burned twice). For single burns, we also explored changes over time. In P. laricio, PB tended to trigger only minor modifications consisting exclusively of short-lived increases (observed within 3 months after PB) in flavonoid index, possibly due to the leaf temperature increase during PB. In P. halepensis, PB had detrimental effects on physiological performance, consisting of (i) significant decreases in actual PSII efficiency (ΦPSII) in light-adapted conditions after repeated PB, and (ii) short-lived decreases in variable-to-maximum fluorescence ratio (Fv/Fm) after single PB, indicating that PB actually stressed P. halepensis trees. Repeated PB also promoted terpene-like metabolite production, which increased 2 to 3-fold compared to control trees. Correlations between terpene metabolites and soil chemistry were found. These results suggest that PB impacts needle secondary metabolism both directly (via a temperature impact) and indirectly (via soil nutrients), and that these impacts vary according to species/site location, frequency and time elapsed since last fire. Our findings are discussed with regard to the use of PB as a forest management technique and its consequences on plant investment in chemical defenses.