A four-year survey on insecticide resistance and likelihood of chemical control failure for tomato leaf miner Tuta absoluta in the European/Asian region

Tuta absoluta is an invasive destructive pest that is currently posing a major threat for tomato production worldwide. Insecticides are a key component of typical pest management schemes. Resistance to diamides, the most recently introduced class of insecticides, was recently reported in Italy. Monitoring of insecticide efficacy is the basic tool for proactive evidence-based resistance management. Here, we report the findings of a 4-year survey performed at the Euro-Asian region. A total of 35 populations were collected between 2012 and 2016 from Greece, Italy, Spain, Israel and UK. The response of these populations was evaluated through laboratory bioassays with the main insecticides used for T. absoluta control: chlorantraniliprole, indoxacarb, emamectin benzoate and spinosad. Analysis of the results indicated six cases of low/moderate resistance to the emamectin benzoate (resistance ratio (RR) > 15-fold), a single case of resistance to spinosad (RR: 33-fold) and five cases of resistance to indoxacarb (RR: 13- to 91-fold). Likelihood of control failure was detected for indoxacarb, but reports of poor field performance were absent. Resistance to chlorantraniliprole, after 2015, was widespread in Italy and Greece with high RR (>64-fold) and significant likelihood of control failure in most cases. Chlorantraniliprole resistance was also detected in Israel (RR: 22,573-fold) but not in Spain and UK (RR < twofold). The absence of diamide resistance in tomato leaf miner populations in Spain is most likely linked to a recently established integrated pest management program including non-chemical measures and the rotational use of insecticides of different mode of action classes.