STUDI SULLE LARVE DEI COLEOTTERI DITISCIDI III. Note morfologiche sul I e II stadio larvale di sei specie del genere Agabus Leach

Abstract

MORPHOLOGICAL NOTES ON THE FIRST AND SECOND LARVAL STAGE OF 6 SPECIES OF GENUS Agabus LEACH

The author relates about the morphological characters differentiating the first and the second larval stage of six species from the third larval stage of them. The third larval stage of this species is treated in a preceding paper (DE MARZO, 1973).

Because the morphology of the first stage is very different from the morphology of the third one, more space is devoted to the description of the main distinctive characters and similarities that the first stage of each of the six species shows respect to the other ones.

In the part regarding the second larval stage, whose morphology is similar to the third stage, some characters, useful for a specific identification of the single species, are given.

Two keys are proposed, to the first and second larval stages.

Finally it is noticed that the differences and similarities found comparing the first stage larvae of the six species validate (as it was found comparing the third larval stages) the present subdivision of these species in different subgenera (GUIGNOT, 1959). A preceding subdivision (GUIGNOT, 1931-33) is also justified because melanocornis (whose first stage larva, as the third stage, has peculiar characters) was separated from the other five species in a third subgenus.

The examined specimens were gathered in Southern Italy; their specific identification was verified with rearing, except for the first stage of A. brunneus F.; the specimens utilized to describe the first stage of this species were classified on the basis that their morphology showed differences and similarities to the first stage of A. dydimus 01. similar to the differences and similarities found comparing the third stages of brunneus and dydimus.

Vengono messi in evidenza i caratteri che differenziano le larve di I e II età delle sei specie esaminate dalle rispettive larve mature, già trattate dall'autore in una precedente nota; vengono, inoltre, rilevate le differenze e le affinità esistenti fra le larve del medesimo stadio di sviluppo. Alcuni dei caratteri più utili alla determinazione della specie sono ordinati in due tavole dicotomiche. Alcune considerazioni vengono fatte riguardo alla suddivisione in sottogeneri delle sei specie esaminate, alla luce delle differenze e delle affinità morfologiche riscontrate fra le loro larve di I e II età.