Life cycle, population dynamics

Eupoecialia ambiguella carries out two reproductive cycles per year regardless of the regions in France. 

• Its cycle begins in early spring (mid to late April), after bud break, with the emergence of adults from overwintering pupae. This beginning of 1st flight is characterized by the phenomenon of protandry, that is to say the appearance of males before females. This time lag can be spread over a week. The flight period will last over a month with a peak corresponding fairly well with the third to sixth leaf unfolding phenological stages.

• The habits (mating, egg-laying) of these butterflies are nocturnal and continue until dawn. The deposited eggs are 1st generation on the bracteoles of the flower buds, on the basis of the latter. It can also occur on the leaves. The eggs are laid in isolation, stuck by a mucus on their vegetable support. A female is capable of laying about fifty eggs during her life which will last about ten days. The egg will incubate between eight and fifteen days before hatching. 

• The caterpillar presents a wandering stage, known as the “wandering stage” of less than 24 hours after which it perforates a flower bud then the neighbors which it agglomerates by weaving a silky thread to form the “ glomerulus ”. This kind of nest will grow as the caterpillar grows larger, passing through five successive larval stages protected inside the glomerulus. The end of its development generally corresponds to the end of flowering. The caterpillar then emerges from its glomerulus and weaves its pupating cocoon nearby in the inflorescence or on the edge of a leaf. Pupation lasts ten to fifteen days.

• The adults of the 2nd flight emerge from the chrysalises at the end of June, ie after the "berries at the size of peas" phenological stage. The protandry phenomenon is reduced to a maximum of 2 days. The flight can last until the end of July. The adults mate and the females lay their 2nd generation eggs separately on the green berries being formed. After hatching and the wandering stage, the caterpillar perforates a bay to form a gallery under the epidermis, inside which it develops. It can attack neighboring berries thus forming a focus of several berries, often called "perforation". These foci are clearly visible at the end of development by the oxidation of the tissues consumed which take on a purplish hue, contrasting with the green one of the berries. It is during the formation of these foci and perforations in the berries that the budworm serves as a vector of Botrytis cinerea . At the end of August to September, the larvae emerge from the berries to pupate for the winter diapause. They form their pupation cocoon on the vines or in the soil. Sometimes, in very favorable weather conditions, a 3rd autumn flight can take place.

• Host plants : Cochylis is as polyphagous as eudemous (Table 1). On the other hand, few plants, except the vine, are common to both species. Mugwort naturally hosts cochylis caterpillars in large numbers. Buckthorn is also known to host cochylis in non-wine regions. This insect has never been observed on southern host plants colonized by eudemis (daphne, rosemary and olive). Mugwort is sometimes considered the original plant of cochylis.

Table 1: Assessment of cochylis ( host plants Eupoecilia ambiguella )

• Synoptic of Eupoecialia ambiguella development on vine (figure 1)