STUDI SUI COLEOTTERI CURCULIONIDI I. ANTHONOMUS AMYGDALI HUST.

Abstract

Sono descritti l'adulto (femmina e maschio) e gli stadi preimmaginali dell'Anthonomus amygdali Hust (Coleopt. - Curculionidae) ed è esposta la la biologia dello stesso, seguita in Puglia negli anni 1962-1966.
Gli adulti dopo aver trascorsa l'estate e parte dell'autunno riparati sotto le cortecce dei mandorli e di altre piante, si portano in novembre e in dicembre sui rami dei mandorli; si nutrono perforando preferibilmente le gemme a fiore; in queste le femmine depongono le uova (uno per gemma) dalla seconda metà di dicembre a marzo. Dopo 15 - 20 giorni di incubazione si ha la nascita delle larve, che in 16 - 18 giorni compiono il loro sviluppo a spese dei tessuti teneri delle gemme, delle varie parti dei bocci fiorali o, le più tardive, anchedei frutticini da poco allegati. Tutte le gemme, i bocci fiorali e i frutticini attaccati dall'insetto cadono al suolo. Nelle stesse gemme o nei frutticini più o meno svuotati le larve si trasformano in pupa. Questa normalmente dopo 11 - 14 giorni
 (o anche dopo un maggior numero di giorni, fino a 20 - 25, se si verificano in marzo temperature molto basse) dà l'adulto, che si porta sulle foglie di mandorlo. I primi adulti compaiono verso la metà di marzo; il massimo sfarfallamento si ha in aprile. Gli adulti si nutrono del parenchima fogliare producendo piccole erosioni nel lembo o al margine delle foglie; nella prima quindicina
di giugno si trasferiscono in ricoveri, rappresentati dalle cortecce sollevate
degli stessi mandorli o di altri alberi per trascorrervi l'estate e parte dell'autunno.
Le intestazioni si verificano in  Puglia ogni anno con intensità: nel 1962
sono andate perdute a causa dell'Antonomo il 25-40% delle gemme (con punte massime del 63 e d ell'83% ); nel 1963 e 1964 il 50-60% delle gemme (con massimi del 76-78%), nel 1965 il 20-35 % delle gemme (con massimi del 43 e del 61% ).
L'azione svolta da due parassiti, il Syrrhizus distinguendus Sarra (? = Syrrhizus delusorius Foerst) (Braconide) e lo Scambus pomorum Ratz. (Icneumonide), è di importanza trascurabile perchè le due specie sono poco frequenti.
La lotta artificiale può essere attuata con trattamenti di cloroderivati organici (Dieldrin, DDT), in gennaio, nel periodo di massima presenza degli adulti di Antonomo sulle piante.

The author in the present paper refers about morphology, ethology and life cycle of the Anthonomus amvgdali Hust. (Col. Curculionidae, Calandrinae).

In the morphological study the various stadia of the insect have been de scribed, underlining especially those characters of greater sistematic impor- tance. In the biologica! study observations carried out in Puglia during the years 1962-1966 are reported.

This weevil lives mainly on the almond-trees (Amygdalus communis and A. communis, var. amara). A. amygdali spends summer and part of autumn under the barks of the trunk of the a1mond-trees, olive-trees, or in other natura! refuges. Such refuges are left from the second half of November and, gradually, also in December; practically at the end of this month all adults of the Antho- nomus have settled on the leaves of the almond-trees. The highest number of adults on the plants is observed in January. The adults after the autumnal appearance feed principally on flower buds, of which they remove part of the internai tissues; in negligible measure they feed on vegetative buds. The number of female in this species is slightly higher to that of male. 

Every female lays between 35-45 eggs, which are inserted singly into each flower bud. Rarely one happens to find 2 or also 3 eggs in the same bud; in this case they bave been laid at different times and by different females.

The egg-deposition starts in the second half of December; it is at its maxi- mum at the end of January and during the whole February, and it ends with the blossoming of the latert (March) varieties of almond-trees.

Not later than March all the adults, which carne on the plants in autumn, die.

The incubation lasts 15-20 days.

As the egg-deposition takes place during a fairly long period, the buds of the almond-trees, at the time when the small larva is born within them, can be more or less developed, so that the larval ethology results rather dif- fcrent in its first stages.

The first larvae which are born (in January) almost completely consume the tissues at their disposal, because the buds which give them hospitality are still quite small, latent, and they bave recently taken up again their vegetative activity.

The larvae born later, in gemmae which are rather enlarged and now can be called flower buds do not destroy all the tender tissues which they bave at their disposal. Nevertheles the opening of the blossom itself is always inhi- bited because of the destruction of the ovary and the excision of the bundles, which are under it, with the consequent interruption of the afflux of the sap.

EspeciaUy in March a great number of the eggs of the insect batch in buds nearing the anthesis, so that the latter develops in a more or Iess nor- mal way. The larva, therefore, after the petals bave fallen, starts to attack the small fruit, which is stopped in its growth and is emptied from the interior part before it can reach a diameter of 5 - 6 millimetres.

All the gemmae, the flower buds and the small fruits, attacked by the insect fall to the ground.

The larva, in the buds and the small fruits fallen to the ground, by its violent jerks, can make its shelter jump l - 2 centimetres high.

The pupation takes place on the ground, in the buds, whose cavity, pro- duced by the feeding larva, is lined with excrements.

In the second half of March we bave the first emergence of the adults, the last at the beginning of May, with maxima in April.

After the emergence which took place on the ground, the adults of the Anlhonomus move to the leaves of the almond-trees, they feed on the most tender leaves, making few millimetres wide, erosions in separate points or cutting the leaf border marginally.

Such manner of feeding goes on until the first half of June, when the weevil moves to the refuges for the summer-autumn diapause.

The damages caused by this insect consist in the loss of the buds, both pierced while feeding and ruined, by the larvae. We must add to this the loss of the small fruits, which has amounted up to 20% in 1965.

The quantity of buds infested with larvae of Anthonomus, as measured on samples of flower buds picked up a short time before the anthesis, in zones situated along the Adriatic coast and the interior, has been the following:

1962 between 25 - 40%, with a maximum of 83%

1963-64 » 50- 60%, with a maximum of 78%

1965   >>   25 - 35%, with a maximum of 61,3%.
From these data we notice that the infestation repeats itself every year, more or Jess seriously. Although all the plants are attacked, often we observe that the infestation varies on different plants, even if near each other and of the same variety.

The different period of flowering of each variety does not affect the intensity of the infestation; the adults of the Anthonomus are present on the almòndtrees during the whole winter, and when they cannot lay any more eggs in the flower buds of the earlier varieties, since these start to bloom, they pass on plants of those varieties which are yet in an earlier stage of flowering. In this way the weevil can pass from earlier cultivars to later cultivars until the latter varieties bave started flowering.
The Anthonomus is attacked in Puglia by 2 parasitic Hymenoptera: the Syrrhizus distinguendus Sarra (? = S. delusorius Foerst) (Braconidae) and the Scambus pomorum Ratz. (lchneumonidae), both of negligible importance because not too frequent.

Chemical control of the Anthonomus can be conducted with the use of chlorinated hydrocarbons applied in the period of highest presence of the weevil on the plants, that occurs in January.
In 1963 and 1964 some insecticides were applied to plants at the end of December to ascertain the sensibility of the weevil towards chemical.

Emulsifìable concentrates of DDT (200 gr of p.a. for hl of water), Dieldrin (125 gr of p.a. for hl of water) and E.C.E. '(200 gr of p.a. for hl of water) were employed.
DDT and Dieldrin were more effective than E.C.E.; Dieldrin was a slightly more effective than DDT.
The action of Dieldrin resulted so persistent, that though after 3 and 6 weeks a certain reinfestation was verifìed, the number of weevils present on the untreated plants was always found to be, in each trial, about 8-10 times higher than that found on the treated plants.