Ch. kuesteri rearing experiments

Germann, Christoph, Geiser, Michael & Borer, Matthias, 2023, A review of the Chrysolina species - subgenus Stichoptera Motschulsky, 1860 - in Switzerland, with notes on distribution, conservation and preimaginal stages (Coleoptera, Chrysomelidae), Alpine Entomology 7, pp. 69-82 : 69

Ch. kuesteri rearing experiments

Note.

Six couples of Ch. kuesteri from Mont d`Orge (=Montorge Sion, Valais) collected in October 2020 were kept in plastic boxes. As its local host plant in Valais was not exactly determined (but presumed to be Linaria sp.), both adults and larvae were fed on Linaria purpurea , a readily available garden plant. Oviposition was observed on L. purpurea from November until January. In early February 2021 the first larvae were noticed (Fig. 5b ), which accepted L. purpurea without problems. The first moult took place in mid-February (Fig. 5c ), the second towards the end of the same month. In early March, more larval skins were found, suggesting a third moult. A fourth moult was observed in mid-March (Fig. 5d ), a fifth and final one in mid-April (Fig. 5e ). The first pale yellowish pupa (Fig. 5f, g ) was found on 30rd April. The larvae pupated at the bottom of the boxes, where some quartz sand had been added earlier. Further pupae followed in May. The first adult hatched on May 29th (Fig. 5h ). Part of the adults from autumn 2020 were still alive at that time (Fig. 6a ). In addition to those results in captivity (under environmental conditions in Rubigen, outside in the garden), 5th instar larvae were found in the field near Sion on March 22nd 2021 (Fig. 6c ), which shows a somewhat faster development at Mont d`Orge, a locality with exceptionally mild climatic conditions. Only later on, on 22nd March 2021, we found evidence of Veronica hederifolia L. acting as the host plant at Mont d d`Orge (Fig. 6b, c ).

Some insights into the development of Ch. kuesteri were already provided by Bourdonné et al. (2013), who also noted a larval development from October to May, in agreement with our observations and experiments. However, they noted a «quiescence» during the coldest season, which we did not observe. The same authors mentioned Linaria supina (L.) Chaz. and Antirrhinum majus L. as additional host plants. Rheinheimer and Hassler (2018) reported Linaria vulgaris P. Mill. and L. nivea Boiss. and Reut. and also quote an observation by Peter Sprick in Lower Saxony (Germany), confirming Veronica hederifolia as host plant, matching our field observations.

Figures

Figure 5. a-g. Preimaginal stages of Chrysolina kuesteri. a. Eggs shortly before hatching, late January; b. First larval instar; c. Larva after first moult in middle of February; d. Larva after fourth moult mid-March; e. Fifth (and last) larval instar, April; f, g. Pupa, lateral and ventral view; h. Freshly hatched adult, end of May (Photos: C. Germann).

Figure 6. a. Adult of Chrysolina kuesteri from Mont d'Orge in October; b. Habitat in the vineyards at Mont d'Orge; c. Fifth larval instar at the same locality in March 2021 feeding on Veronica hederifolia (Photos: C. Germann).