gillessanmartin's Journal

The distinction between Henosepilachna angusticollis and Henospilachna argus regularly causes problems here on iNaturalist and is intrinsically difficult. I don't feel very confident in identifying these species for observations from southern Europe and I have never seen H.angusticollis. Very few good representations of these species are available in the literature or online (with certain identification).
I have just gathered here the information I could find in the literature. Any comments or additions are welcome !

Both species can be present in Spain, Portugal and southern France on the same host plants. Elsewhere, H.argus is the only species present. Chnootriba (=Henosepilachna) elaterii has a wider distribution in Southern Europe, but this species is easy to distinguish.

Henosepilachna angusticollis (vs H.argus):

• In dorsal view, more elongated shape, the tip of the elytra looks more pointed (all authors). The widest part of the elytra stands in their anterior third in angusticollis but close to their middle in argus (Vincent Nicolas, online discussion). Good illustration: Eizaguirre (2015) plate p.506 (see below)
• In lateral view, the shape is more flat, less convex (Eizaguirre 2015)
• Pronotum less wide relative to the base of the elytra (Reiche 1862, Nedved & Djuric 2022) and pronotum less wide relative to its length, less "transverse" (Reiche 1862), Width/Length ratio < 2 (vs >=2 in H.argus) (Migeon et al. Comm Pers)
• The shape of the pronotum is different, according to Reiche (1862) and Eizaguirre (2015), but difficult to find a good illustration or a clear explanation. Stronger lobe in the middle of the posterior margin (Reiche 1862). The anterior angles (of the pronotum) are rounded and projecting forward, while the posterior angles are attenuated (Eizaguirre 2015)
• Pilosity on the elytra shorter and more dense (Eizaguirre 2015).
• Eizaguirre (2015) describes differences in the male genitalia that seem to be very weak and without illustration.
• Limited to the Mediterranean basin (Spain, Portugal, Southern France) and maybe Malta and Crete (Nedved & Djuric 2022)
• Host plants cited in the literature : various cucurbitaceae. H.argus only on Bryonia dioica in Northern Europe but can probably be found on other cucurbitaceae more in the South.

Note that most of the differences concern the general shape, which might be difficult to appreciate in photographs as the angle of view and the lens might distort the apparent shape.

Sources :

• Eizaguirre S. 2015. Fauna ibérica Vol. 40: Coleoptera, Coccinellidae. Madrid: Editorial CSIC Consejo Superior de Investigaciones Científicas. p.189-194 + plate p 506
• Nedvĕd O, Djurić M. 2022. Ladybirds of Europe: Field Guide. HabiProt.
• Reiche L. 1861. Espèces nouvelles de coléoptères appartenant à la faune circa-méditerranéenne. Annales de la Société entomologique de France 4:539–546. - Original description available here : https://gallica.bnf.fr/ark:/12148/bpt6k6341439k/f99.item

• Criterion about the widest part of the elytra taken from this online discussion :
  https://www.insecte.org/forum/viewtopic.php?t=147710

My protocol for microscopic slide mounting of Coccoidea (scale insects) and many other insects (inspired by various sources but mostly Kondo & Watson). Total time ~ 1 hour (but you can prepare several specimens in parallel)

• Clearing: KOH 10%. Pierce the back with a needle (not necessary for small Diaspididae). Duration: a few minutes (if heated) to a few hours, then crush the scale insect with a spatula to evacuate the body contents. If you wait long enough, the contents will become liquid and will drain easily.
• Rinsing: 80% alcohol 4-5 drops + glacial acetic acid 1-2 drops → aim = to rinse and neutralise KOH to facilitate the next staining step. Squeeze the insect with a spatula to remove any bubbles or remaining body content
• Staining: acid Fuchsin in lactic acid (10mg powder in 10ml lactic acid). A few minutes (until the specimens are sufficiently colored).
• Rinsing off excess stain: return to the 80% alcohol + acetic acid bath for a few minutes: aim = to remove excess dye + dehydration. NB : If maceration lasts too long, the dye tends to fade.
• Dehydration: 99% alcohol (+ 1 drop of glacial acetic acid?) for a few minutes. The acetic acid helps fix the stain. NB : some people use pure glacial acetic acid at this stage.
• Final clearing: clove oil for a few minutes. In theory, not necessary if you are using Euparal but I usually do it anyway. Purpose = to evacuate alcohol but also the rest of the greasy contents, oils, waxes, etc. You can also conserve the specimens for longer in clove oil
• Mounting: Euparal : less sensitive to incomplete dehydration, and solvents maybe less toxic (?) than Canada balsam

Misc :

• Spatulas are essential for moving specimens from one bath to another and for squeezing out specimens. Made from entomological needles, flattened with a hammer, bent and cut to the desired shape with scissors, then attached to a mandrel. Alternative : nylon wire flattened with pliers : advantage = transparency, disadvantage : less thin and less rigid.
• The staining step varies greatly between protocols, especially in terms of duration (from a few seconds to several hours). I think this is due to the fact that acid fuschin can be prepared in different ways (e.g. in lactic acid, in water) and at different concentrations. If the stain is too concentrated, I tend to lose the sample in it... 10mg powder in 10ml lactic acid 80% (= 0.1% solution) seems to work well for me.
• Leucaspidini (Diaspidinae) need an extra dissection step (e.g. at the KOH step) to extract the female body from its external protection (skin of the last larval stage).
• For very waxy species you may need a bath with a detergent such as Decon 90, Histoclear,... Some people do this at the beginning, others at the end...