Using 1-min scans and stem height data in a post-release monitoring strategy for Galerucella calmariensis (L.) (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae), in Manitoba

The emergence of a North American classical biological control program against purple loosestrife has offered opportunities to develop post-release monitoring strategies providing objectively measurable results. The biological control agent Galerucella calmariensis, a leaf-feeding beetle, was released into a purple loosestrife (Lythrum salicaria) population in the Netley-Libau Marsh in southern Manitoba. A total of 578 adult beetles were released into a fixed monitoring station (FMS) between 1994 and 1995. The FMS was 10-m long by 5-m wide and divided into 1-m2 sampling quadrats. A 1-min visual scan was used to estimate the number of egg masses, adults, and larvae present in randomly selected 1-m2 sampling units. Similar data were also collected from 30 (3 in each of 10 quadrats) randomly selected stems. Data were collected about every 10 days from late May to September from 1996 to 2001. Heights of all stems in each 1-m2 sampling unit were measured in the fall of each year. Mean stem-height data derived from 30-tagged stems indicated that G. calmariensis had suppressed mean stem heights by 30%, while 56% of the all tagged stems were dead by late July by 1998 [4-years post-release (YRPR)]. By the fall of 2000 (6-YRPR), G. calmariensis herbivory resulted in eradication of all purple loosestrife stems. The results of this study indicated that: (1) simple 1-min visual scans employed every 10-days can be used for post-release monitoring to provide objective measures of G. calmariensis establishment and phenology, (2) using three randomly selected stems per quadrat or all stems in a quadrat can be used to measure plant performance, and (3) G. calmariensis can be used in a single-species release strategy against purple loosestrife.