Acronicta tridens vs psi (Dark/Grey Dagger)
Acronicta tridens (Dark Dagger)
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Acronicta psi (Grey Dagger)
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These two are indistinguishable on external features. Both are bivoltine and can be found May to October throughout GB.
They require genital dissection to identify to species.
Information on separating these two species and on separating them from the very similar European species A.cuspis (Large Dagger) can be found at Difficult Species Guide and all three are illustrated in MBGBI10 p135.
They require genital dissection to identify to species.
Information on separating these two species and on separating them from the very similar European species A.cuspis (Large Dagger) can be found at Difficult Species Guide and all three are illustrated in MBGBI10 p135.
Male genitalia:
In A.tridens apex of the sacculus is produced into a point while in A.psi it is blunt. In both species there are two subapical teeth; in A.tridens the produced apex makes a third tooth (‘tridens’ = ‘three teeth’).
In A.tridens apex of the sacculus is produced into a point while in A.psi it is blunt. In both species there are two subapical teeth; in A.tridens the produced apex makes a third tooth (‘tridens’ = ‘three teeth’).
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Female genitalia: Both species have an appendix at the junction of the ductus bursae with the corpus bursae (at the apex of which the ductus seminilis enters). According to the Difficult Species Guide, this appendix is larger in A.tridens and smaller in A.psi. This relative difference is fairly apparent with a direct comparison of similar preparation, but can be difficult to judge when direct comparison is not available; and its appearance can be altered by variations in the preparation eg degree of rotation of the corpus relative to the ductus bursae. From my own observations I would suggest that a more absolute means of distinguishing females comes from the density of sclerotisation of the posterior pole of the corpus bursae and the extent to which this sclerotisation enters the appendix. In A.tridens the sclerotisation is dense (the sclerotised stipples are broader than the spaces between them) and it clearly extends into the appendix; in A.psi the sclerotisation is less dense (the sclerotised stipples are smaller than the spaces between them) and it hardly enters the appendix.
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Page published 15/11/2021
