Biological control of Tetranychus urticae by Chrysoperla externa

Chrysoperla externa is an important biological control agent, whose performance may be influenced by the presence of trichomes. Although C. externa is registered for the control of Tetranychus urticae, limited information is available on its effectiveness, particularly under trichome conditions. This study evaluated the potential of C. externa to suppress T. urticae and examined the influence of trichomes. Laboratory bioassays assessed: the consumption of T. urticae by different predator instars and across mite developmental stages; the effect of trichomes on predator behavior using BORIS software; functional response of C. externa larvae; and predation in the presence of webbing. Under protected cultivation, were evaluated the effect of different release densities (0, 3, 6, and 10 larvae per plant) and releases performed on plants with one versus seven days of infestation. Analyses were conducted in R using GLMs (Poisson, Quasipoisson, and Negative Binomial) for laboratory data and GLMMs (Negative Binomial 1 and 2) for greenhouse trials, with trifoliate area as a random factor. All instars of C. externa consumed T. urticae, with higher consumption in later instars (p<0.001). Eggs and nymphs were consumed more than adults (p<0.001). Trichome presence increased the predation occurence (p<0.01). Larvae exhibited a Type II functional response (p<0.001). Webbing reduced consumption (p<0.001). In greenhouse trials, higher release densities resulted in greater mite suppression (p<0.001). Releases performed on plants with only one day of infestation provided superior control (p<0.001). Overall, C. externa showed potential as a natural enemy against T. urticae, and trichome presence may enhance its activity.