Novel crop, novel pests: Assessment of insect damage to achenes of cardoon grown in a Mediterranean environment

Cardoon (Cynara cardunculus var. altilis) has gained interest as a novel crop for bioenergy, multipurpose uses, and industrial bio-based productions, also based on the achene yield. However, achenes can be affected by various insects, which are considered as minor pests in traditional Cynara crops. Nonetheless, very little information is available on these pests. The aim of this research was to identify the frequency of different insect species with particular regard to weevils, and to quantify the achene yields and losses caused by these spermophagous insects on cardoon. Field measurements were performed across three consecutive years in Sardinia (Italy). Mature cardoon heads of different insertion orders (primary, secondary, tertiary and quaternary heads, respectively) were manually harvested. For each head, the achenes were counted and weighed, and bare receptacles were scored in terms of damaged areas by weevil larvae (i.e., the percentage of total area). The results highlighted a higher frequency of Larinus scolymi (90%) compared to Larinus cynarae. The total number of achenes per head and the 1000-achene weight were markedly affected by head order. Actual achene yield ranged from 86.8 to 107.9 g per plant. The estimates of achene yield losses per plant due to Larinus weevils ranged from 36.3 in 2014 to 113.0 g per plant in 2015, corresponding to about 0.4 to 1.1 t per hectare, respectively. Our results showed that achene losses were caused mainly by L. scolymi, indicating that cardoon crop profitability could be jeopardised in the absence of insect controls. Based on the experimental data, appropriate strategies aimed at controlling weevil infestations are needed to preserve cardoon achene yields.