Optimizing insecticide timings for the grape mealybug, <i>Pseudococcus maritimus</i> (Hemiptera: Pseudococcidae) based on pheromone trap capture data

In agricultural systems, insect pest populations are often assessed using traps to survey adults, as adults are mobile and attracted to volatiles. While immature stages of insects (nymphs, larvae) are often most damaging, they can be difficult to sample, and management decisions targeting immatures must be based on adult sampling. For some insect pests, such as the grape mealybug (Pseudococcus maritimus), pheromone trap observations of adults occur too late to warn growers about pest risk, since overwintering first-instar nymphs are the dominant stage that transmits grape leafroll-associated viruses. Here, we propose a method to determine the time when insecticide applications will be most effective to control first-instar grape mealybug nymphs, based on the alignment between a modeled progression of life stages across degree days and pheromone trap capture data. We used literature to build a grape mealybug phenology simulation model and a 6-yr dataset of grape mealybug males captured in pheromone traps to infer the time when most virus-transmitting nymphs have hatched and are susceptible to insecticides. Our results show it is unlikely that most overwintering first-instar grape mealybugs occur in early spring, and that insecticides aimed at preventing grape leafroll-associated viruses transmission should occur by late autumn. Our study suggests that results from laboratory studies and field observations can be integrated to optimize insecticide application timing for a key vector pest species.