Beaulieu C, Lavoie C, Proulx R. 2018. Bookkeeping of insect herbivory trends in herbarium specimens of purple loosestrife (Lythrum salicaria).

<p></p><p>The potential use of herbarium specimens to detect herbivory trends is enormous but largely untapped. The objective of this study was to reconstruct the long-term herbivory pressure on an invasive plant, purple loosestrife (<i>Lythrum salicaria</i>), by evaluating leaf damages over 1323 specimens from southern Québec (Canada). Historical trends suggest a gradual increase in hole feeding and margin feeding damages from 1883 to around 1940, followed by a period of relative stability. The percentage of specimens with window feeding damages did not begin to increase until the end of the 20th century, from 3% (2 ̶ 6%) in 1990 to 45% (14 ̶ 81%) in 2015. Temporal changes in the frequency of window feeding damages support the hypothesis of an increasing herbivory pressure by recently introduced insects. This study shows that leaf damages made by insects introduced for the biocontrol of purple loosestrife, such as coleopterans of the <i>Neogalerucella</i> genus, can be assessed from voucher specimens. Herbaria are a rich source in information that can be used to answer questions related to plant-insect interactions in the context of biological invasions and biodiversity changes.</p><p>