The uncertainty surrounding the part played by the invasive North American seed bug, Leptoglossus occidentalis, in the observed decrease in seed production of the Mediterranean stone pine, Pinus pinea, is a limiting factor for its management and a concern to all stakeholders. Furthermore, the possibility of increasing cone production through irrigation and fertilization regimes is gaining interest among landowners, but its effects on insect pests are still unknown.
We carried out two field trials, an insect-exclusion trial and an insect-bagged trial, to evaluate the impact of this bug on young and mature cones of stone pine trees submitted to fertirrigation (FR) compared to trees with no treatment (C).
Protecting the branches with an insect exclusion bag resulted in a significant decrease in the mortality of second-year conelets, which dropped to 6% compared to 30% in exposed branches. Seed damage also decreased from 60% on exposed branches to 10% on protected ones.
The partial damage of the kernel can be a signature of L. occidentalis feeding, since such damage was not observed in exclusion bags. Additionally, another type of seed damage, showing a wholly shrunken and dry embryo without remaining endosperm, and a reduction in the number of extractable seeds may also be attributed to this seed bug. Overall, seed damage per mature cone reached up to 12% in bags with two adult bugs enclosed for a month, i.e., twice the seed damage in protected cones.
FR trees were more susceptible to both conelet mortality and seed damage. In the particular case of L. occidentalis, FR regime influenced the consumption positively by the nymphs but not by adults.
Farinha, A.C.O., Silva, J.E.P., Correia, A.C., Sousa, E.M.R., Roques, A. and Branco, M., 2018. Is Leptoglossus occidentalis entirely responsible for the high damage observed on cones and seeds of Pinus pinea? Results from a fertirrigation trial in Portugal. Forest Ecology and Management, 429, pp.198-206.