The almond blossom weevil: the pest that works in winter
Savvas Pastopoulos, Agronomist MSc, Pastopoulos Agronomics, Neos Mylotopos, Pella, Greece
The almond blossom weevil, Anthonomus amygdali Hustache, destroys flower buds during the winter, long before the orchard shows the slightest visible sign. The Italian literature records bud losses reaching 83% on individual trees, while the Greek data is very thin. What follows gathers what is documented, states explicitly which figures come from foreign conditions, and shows exactly where the two windows lie in which the insect is reachable.
The approvals discussed in this article are those of the Greek Ministry of Rural Development and Food and are valid in Greece only. They say nothing about what is approved in any other country. Readers outside Greece must check their own national register.
In Greek, at least two unrelated stone fruit insects are called "anthonomos". This article deals only with Anthonomus amygdali of almond, which eats buds and flowers. It does not deal with Furcipus rectirostris, the cherry stone weevil, whose larva develops inside the stone of the cherry and whose cycle and damage are entirely different.
1. Why a serious pest goes unnoticed
The weevil leaves nothing visible during the season when anyone actually looks at the orchard. It works from November to February, when the trees are bare and visits are infrequent. Its damage shows up as buds that simply fail to open, and in practice that is almost always attributed to something else: to frost, to insufficient chilling hours, to poor fruit set, to blossom blight.
There is a second reason the pest escapes notice. The infested bud falls. The mature larva jerks its body inside the bud and increases the chance of abscission [3]. The evidence of attack therefore ends up on the ground rather than on the tree, which is exactly where nobody is looking.
The result is a pest that, when it has been measured systematically, was found to destroy half the bloom, and that nevertheless rarely appears in Greek advisory bulletins as a cause.
2. Recognising it in the field
The adult is a small weevil of the family Curculionidae, 3 to 4.2 mm long including the rostrum, dark chestnut in colour [3]. The rostrum is long with lateral grooves, the antennae are elbowed with a clubbed tip, the pronotum is reddish with a whitish longitudinal band, and the head is almost black. The elytra carry three transverse bands, grey in males and yellowish in females.
The larva lives inside the bud and cannot be seen unless the bud is opened. It eats the primordia of the stamens and the pistil. If the bud has not opened, it also eats the petal primordia. If the bud has begun to open, it eats the inside of the calyx [3].
The three signs worth looking for
- November, on the scaffolds. Buds with small erosions from adult feeding, before oviposition begins.
- Winter, on the ground under the canopy. Fallen buds. Opened with the tip of a knife, they contain the larva or the pupa.
- Spring, at bloom. Dry buds that never opened, scattered among normal flowers, without the grey mycelium of blossom blight and without the characteristic bending of an infected shoot.
3. The cycle, month by month
The insect has one generation per year. The fullest description of its cycle remains the monograph by Monaco, published in 1967 and based on four years of observation in almond orchards of Apulia [1].
The table reproduces data from Apulia in the 1960s, supplemented by Greek technical literature [3] [4]. It is the sequence of stages that transfers, not the exact dates. Apulia corresponds climatically to southern Greece. For Macedonia and northern Greece every stage is expected later, and the difference can reach three to six weeks, as it generally does between the Greek climatic zones.
| Period | Stage | What happens |
|---|---|---|
| June to November | Adult in diapause | Adults shelter under loose bark, in trunk cracks, in plant debris and in the soil. Shelters have been found on other trees too, not only on almond |
| Late November to December | Emergence and feeding | Adults leave the shelters and settle on the almond trees. They feed mainly on flower buds, removing the internal tissues. Feeding lasts about two weeks before oviposition begins |
| Second half of December to March | Oviposition | The female bores a hole with her rostrum and lays one egg in each flower bud. In total 35 to 45 eggs. The peak runs from late January through February, and laying stops when the late cultivars come into bloom |
| January to March | Larva | Incubation takes 15 to 20 days and larval development 16 to 18 days. Early larvae in January destroy almost all the bud tissue. Late larvae prevent the blossom from opening |
| March | Pupa | Pupation takes place inside the infested bud or the closed flower, which has often already fallen to the ground. It lasts 11 to 14 days, or 20 to 25 days when March is very cold |
| Mid March to early May | Emergence of new adults | The first adults appear in mid March, the peak is in April and the last emerge in early May. They leave through an exit hole cut by the insect itself |
| April to the first half of June | Supplementary feeding | The new adults feed on the leaves, causing small erosions, and then withdraw into their summer shelters |
The observation that matters for management is that the insect is exposed in only two windows. The first is the adults of November and December, before mass oviposition begins. The second is the new adults of spring, before they enter diapause. In between, from January to March, it is inside the bud and out of reach.
4. The damage and its magnitude
The damage is twofold. Adults eat buds during their winter feeding, and larvae erode buds from within. The infested bud dries without opening and eventually drops [3] [6].
The only quantitative data that exist come from Monaco's four year record in Apulia [1].
| Year | Flower bud loss | Maximum on individual trees |
|---|---|---|
| 1962 | 25 to 40% | 83% |
| 1963 | 50 to 60% | 76 to 78% |
| 1964 | 50 to 60% | 76 to 78% |
| 1965 | 20 to 35% | about 61% |
In 1965 a further loss of up to 20% of the young fruitlets was recorded. Infestation recurred every year, but with wide variation between neighbouring trees of the same cultivar. That last point has a practical consequence: sampling one or two trees says nothing about the orchard.
They are measurements from Apulia, in cultivars and under growing conditions of the 1960s. They show what the insect is capable of when left alone, not what is happening today in a Greek almond orchard. What transfers is the magnitude of the risk, not the percentage.
Bud loss does not translate one to one into yield loss. Almond sets far more flowers than it can carry, and natural fruit drop is heavy. In a year with normal bloom, a 20% bud loss may not show at harvest at all. In a year with frost or insufficient chilling hours, the same loss is added to an already reduced bloom and becomes decisive.
5. What holds for Greece and what is not known
Its presence is certain
The insect occurs in Greece, and this is established in two independent ways. First, the approvals register of the Greek Ministry of Rural Development and Food contains approvals of plant protection products on almond with Anthonomus amygdali as an explicit target [7]. An approval is not granted for a target that does not occur in the country. Second, the pest is named in a bulletin of a Regional Plant Protection Centre [5].
In the EPPO database the species is registered under the code ANTHAM, with Anthonomus ornatus as a synonym [8]. The distribution table lists no countries, so Greek presence does not follow from there, but from the two Greek sources above.
The hosts
The main host is almond. Peach, apricot and plum are reported as secondary hosts in some regions [3] [6]. The Greek approvals register, however, contains no approval against this weevil on peach, apricot or plum, only on almond [7]. That is an indication that in practice the pest is treated as an almond problem.
The search of the Greek sources found no published phenology study, no recorded percentage of infested buds, and no numerical intervention threshold. The bulletins place the intervention wherever the adult population is dense [4] [5], without "dense" ever being defined in numbers. None of this means the insect is unimportant, it means it has not been measured. The difference is substantial, and confusing the two is why a pest capable of losses in the order of 50% is absent from most Greek crop protection programmes.
The nearest data that exist
The only modern systematic population record from our neighbourhood comes from southeastern Turkey. A three year survey in almond orchards of the Diyarbakır, Elazığ and Mardin provinces found four Anthonomus species, with A. amygdali dominant [2]. Adult flight was recorded from April to June, with the following peaks in individuals per 100 branch beats.
| Location | Peak | Date |
|---|---|---|
| Ergani, Diyarbakır | 154 individuals | 26 May 2003, the highest of the three years |
| Gezin, Elazığ | 36 individuals | 22 May 2002 |
| Ömerli, Mardin | 25 individuals | 12 May 2003 |
The three provinces lie in southeastern and eastern Anatolia, in a continental climate with a cold winter and a very hot dry summer, at altitudes and in cultivars that do not correspond to Greek lowland orchards. The method transfers intact, meaning branch beating and expression as individuals per 100 beats. The dates and the counts do not. They serve as an order of magnitude for what a high population means, and as evidence that spring is the season in which this insect is easy to measure.
6. Monitoring
Because no Greek action threshold exists, monitoring serves two purposes at once. It shows whether the pest is present in the particular orchard, and it builds, year by year, the data that is missing today.
The various methods for detecting the insect
- Branch beating, spring. The method of the Turkish study [2]. A branch is struck over a white cloth or tray, the adults that drop are counted, and the result is expressed per 100 beats. Repeated on fixed trees at fixed intervals from mid March to June.
- Sticky trapping, throughout the active period. Insect glue or double sided sticky tape on the trunk collar and on the scaffolds [3]. It catches adults as they climb up from their shelters, and gives a picture of the settling period.
- Bud inspection, November and spring. In November, a search for eroded buds on the scaffolds. In spring, a count of buds that failed to open, on a fixed number of shoots per tree [3].
Monaco recorded wide variation between neighbouring trees of the same cultivar [1]. A tree with 60% infestation can stand next to one with 10%. Sampling fewer than ten trees per orchard produces a number without meaning.
7. The intervention window and the approvals
The biology yields two windows, as described in section 3. The Greek and the Italian literature agree on this.
The autumn window
The first window opens when the adults leave their summer shelters and move up into the almond trees, from late November through December. During those weeks the insect sits on the shoot and not inside the bud, and feeds for about two weeks before oviposition begins [1]. That is where the importance of the moment lies. Once oviposition is under way, the egg and the larva are inside the flower bud, they cease to be reachable, and the damage for that season has already been done.
The Greek technical sources give not a single date but a sequence. The first intervention is placed in November, before leaf fall, and a second follows after about three quarters of the leaves have fallen and on through January, wherever the population is dense [4]. Another Greek source places one to three interventions between 10 November and the end of December [3]. The two formulations do not conflict, because both put the weight on the same interval and leave the number of interventions to be decided by the density of the population.
The point that needs care is that leaf fall is used as an indicator and not as a date. In a mild and late season defoliation is delayed, and the right moment is delayed with it. The criterion is therefore the condition of the tree and the presence of adults on it, established through the checks of section 6, and not the calendar.
The spring window
The second window opens when the new adults emerge. The first appear in mid March, emergence peaks in April and the last come out in early May [1]. From then until the first half of June the adults feed on the leaves and leave small erosions, and afterwards they withdraw to their summer shelters [1]. The intervention is placed within that interval, in April and May, before the insect enters diapause, while the adults are on the foliage [3] [6].
Its logic differs from that of the autumn. In November the aim is to prevent the damage of the current season. In spring the damage has already been done, and the aim is to reduce the population that will return the following winter. It is an investment in the next season rather than a rescue of the current one, and that changes how its worth is judged.
Two practical points favour it. The first is that the moment is located through the branch beating of section 6, which is exactly the method by which emergence was recorded in the Turkish study [2], so no blind estimate is needed. The second is that the intervention coincides in time with the one against the almond seed wasp, so in an orchard that already monitors the seed wasp the moment is known and no separate pass is added.
The dates of both windows come from Apulia and from Greek technical sources that do not state a region. For Macedonia every stage is expected later, and the difference can reach three to six weeks, as explained in section 3. The date therefore does not transfer unchanged. The sequence transfers, and confirmation comes from observation within the orchard itself.
What applies in Greece today
The current list of products approved against Anthonomus amygdali on almond, with the rates, the growth stages and the pre harvest intervals, is in the approvals register of the Greek Ministry of Rural Development and Food, at fyto.plantprotect.gr [7], which is in Greek and valid in Greece only. It changes over time, and for that reason it is not copied here.
The choice of product and of moment is always made within the limits of the label and of the approval decision, which prevail over any other information, including this text and the international literature. Where the approved growth stage does not cover one of the two windows, management rests on the cultural measures of the next section.
Older Greek and foreign texts on this weevil name active substances such as azinphos methyl, chlorpyrifos, diazinon, methomyl, phosalone and phosmet [6], while the Italian monograph of 1967 describes trials with dieldrin and DDT [1]. None of these is approved in the European Union today. Those texts retain historical and biological value, not practical value. The current picture is always in the Greek Ministry approvals register, at fyto.plantprotect.gr, which is in Greek and valid in Greece only.
8. Cultural measures and natural enemies
The shelters are the weak link
For the whole summer and part of the autumn the insect lies motionless under loose bark, in trunk cracks, in plant debris and in the soil [1]. Trunks and scaffolds free of loose bark and cracks offer fewer shelters. So does a clean trunk collar.
Mass trapping
Greek technical literature reports mass trapping with insect glue or double sided sticky tape on the trunk collar and the scaffolds, from early April to early November [3]. The rationale is that adults move on foot between the tree and their shelters. No published evaluation of its efficacy exists, Greek or foreign, and it is therefore reported here as a practice under trial, not as a method with documented performance.
Natural enemies
Two parasitoids were found in Apulia, Syrrhizus distinguendus of the family Braconidae and Scambus pomorum of the family Ichneumonidae. Both were judged negligible because they were uncommon [1]. There is no record at all of natural enemies of this weevil in Greece.
The spring window of this weevil coincides with the critical stage of the almond seed wasp, and the shelters under the bark are the same ones used by other pests. The overall picture of the pests and diseases of the crop, with a diagnostic tool working from symptoms, is in the article Almond pests and diseases. For the wood borer that shares the same shelters, see Capnodis tenebrionis.
9. Sources
The numbers in the text refer to the list below.
- [1] Monaco, R. (1967). Studi sui Coleotteri Curculionidi I. Anthonomus amygdali Hust. Entomologica (Bari) 3:1-83. Source for the entire life cycle, the number of eggs per female, the durations of incubation, larval and pupal development, the bud loss percentages in Apulia from 1962 to 1965, the two parasitoids and the historical trials with dieldrin and DDT. The abstract and the publisher page were used, not the full 83 page text.
- [2] Bolu, H. and Özgen, İ. (2007). Determination of Anthonomus species on almond trees in the Diyarbakır, Elazığ and Mardin provinces and population changes of Anthonomus amygdali Hustache. Türkiye Entomoloji Dergisi 31(3):189-202. Source for the four Anthonomus species on almond, the dominance of A. amygdali, the April to June flight period and the three population peaks in individuals per 100 branch beats. The abstract was used, not the full text.
- [3] Anthonomos, the insect that feeds on almond buds. Farmacon, technical crop protection articles, in Greek. Source for adult morphology including the 3 to 4.2 mm length and the colour differences between the sexes, for larval feeding, for the secondary hosts, for the monitoring methods using sticky surfaces, for mass trapping from April to November, and for the recommendation of one to three interventions between 10 November and the end of December.
- [4] Almond blossom weevil, spraying before leaf fall. Elliniki Georgia, in Greek. Source for the single annual generation, the start of adult activity in early November, oviposition from December to the end of February, and the recommendation to spray in November before leaf fall with a repeat after three quarters of the leaves have dropped.
- [5] Almond, control of the blossom weevil and of Phomopsis. Reproduction of a bulletin of the Regional Centre for Plant Protection, Quality and Phytosanitary Control of Volos, 2 February 2022, in Greek. Source for the official Greek mention of the pest in an agricultural warning bulletin, and for the wording of the recommendation without dates and without a numerical threshold.
- [6] Pests and diseases of stone fruit. Undergraduate thesis, School of Agricultural Technology, Department of Crop Production, Hellenic Mediterranean University, dspace repository, in Greek. Source for the classification of this weevil among the secondary pests of stone fruit, for peach and apricot as hosts, and for the list of old active substances formerly cited as control. An undergraduate thesis does not stand alone for a quantitative claim and was not used for one.
- [7] Register of approved plant protection products of the Greek Ministry of Rural Development and Food, data version 7 October 2026, in Greek, valid in Greece only. Source for the existence of approvals against Anthonomus amygdali on almond, for the approved growth stage BBCH 71 to 89, and for the absence of any approval with the same target on peach, apricot and plum. The list changes over time and the register itself is always the reference.
- [8] EPPO Global Database, Anthonomus amygdali (ANTHAM). Source for the EPPO code, the synonym Anthonomus ornatus and the taxonomic position. The distribution table lists no countries, so Greek presence is not established from there.
This content is general technical information and not individualised agronomic advice. Plant protection products are used solely on the basis of the approvals of the Greek Ministry of Rural Development and Food, which are valid in Greece only, and of the label instructions, which prevail over any other information, including this text. Readers in other countries must consult their own national register. The register figures relate to the stated data date and change over time.
The dates and percentages quoted come, where this is expressly stated, from non Greek conditions and do not transfer unchanged. They are not a prediction for any particular orchard.
Every intervention is carried out under the responsibility of the user, following on site assessment by a licensed agronomist. Pastopoulos Agronomics accepts no liability for the use of this information.
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