Cox proportional-hazards model: evaluation of Popillia japonica survival after insecticide treatments

Survival analysis is frequently used to assess the effectiveness of insecticide trials on insect survival. The target organism of this study isPopillia japonica, a pestcurrently causing considerable damage tovariousplant species in Northern Italy.Here, the effects of differentinsecticides,evaluatedon insectsby field trialsina peach orchard,wereexplored through non-parametric tests and semi-parametric marginal Cox proportional-hazard models. Adultinsects were confined on peach plants in net cages containing 25 individuals each. Five insecticides(Abamectin, Acetamiprid, Deltamethrin, Phosmet and Sulfoxaflor)plus untreated control were tested with four net cages per treatment, following a completely randomized design.The non-parametric tests, performed both for right-and interval-censored data, and the marginal Cox model led to the same inferential conclusions. All the insecticides, in particular Abamectin, Acetamiprid, Deltamethrin andPhosmet,resulted to be effective in killing insects if compared to the untreated control.