Treating Scots pine seedlings with the herbicide atrazine does not affect shoot chemistry or feeding and oviposition by Lygusrugulipennis

Polyphagous Lygus (Heteroptera: Miridae) bugs, which have one of the widest documented host-plant ranges, have accepted nursery-grown conifer seedlings as host plants only recently. One explanation for this adaptation to the conifer nursery environment could be the increased attractiveness of conifer seedlings due to herbicide treatments. In three laboratory experiments, we tested whether atrazine treatments (2 or 4 kg•ha−1) affected shoot chemistry of pine seedlings and the feeding and oviposition behaviour of the European tarnished plant bug, Lygusrugulipennis Popp. Shoot growth of the pine seedlings was decreased by the atrazine treatment (2 kg•ha−1) in only one experiment. The number of feeding lesions caused by Lygus bugs and the number of eggs laid per seedling were not affected by herbicide treatments, nor was the proportion of seedlings damaged. Concentrations of total amino acids were not affected by the herbicide in any of the experiments. In one experiment, the level of lysine was increased in the atrazine treatment. Terpenes and resin acids were analysed only in one experiment, and total concentrations of these defence compounds were not affected by atrazine. Dominant monoterpenes were α-pinene and 3-carene, the latter varying strongly between individual seedlings. Abietic acid and neoabietic acid were the dominant abietane and pimarane resin acids. The results suggest that applications of atrazine are not likely to reduce the resistance of pine seedlings to Lygus bugs. Herbicides may have an indirect effect by reducing the availability of alternative host plants for bugs. Other potential causes for increased numbers of Lygus bugs on nursery-grown conifer seedlings are discussed.