Monitoring of Larinus spp. (Coleoptera Curculionidae) infesting cardoon and development of a binomial sampling plan for the estimation of Larinus cynarae infestation level in Mediterranean conditions

The cultivation of cardoon, Cynara cardunculus var. altilis, for multi-purpose uses has increased substantially in recent decades. However, in some cardoon growing areas, the production of achenes is threatened by several insects, especially the weevils Larinus cynarae and Larinus scolymi. Due to the lack of specific monitoring and sampling programs for these pests, the aims of this work were to test the reliability of chromotropic traps for adult Larinus spp. monitoring and to develop binomial sequential sampling plans to assess the infestation level of L. cynarae in cardoon cultivations in a Mediterranean area. Field observations were conducted in two different cardoon growing areas in Sardinia (Italy) in 2019 and 2020. Purple- and red-colored cross-vane traps, placed at 1 m and 2 m above the ground, were utilized for monitoring Larinus spp. adults, and binomial sequential sampling plans were developed for L. cynarae based on the count of egg masses on flower heads for sample sizes of 30, 40, 50, 60, and 70 flower heads. The purple traps at 2 m above the ground were effective in monitoring L. scolymi, whereas red and purple traps were ineffective in monitoring L. cynarae adults at both 1 m and 2 m above the ground. Among different binomial sampling plans, a sample size of 70 flower heads is needed to obtain reliable estimates of L. cynarae infestations at or above 25% of infested flowers. Our findings constitute a baseline for the development of an integrated pest management program for the control of Larinus spp. infestations in cardoon-growing areas in Mediterranean environment.