Controllo sostenibile dei fitofagi in colture ornamentali e innovative in serra

This thesis aimed to identify biological control agents for managing Aphis nerii populations on the ornamental crop Mandevilla. This challenge is heightened by the close plant-herbivore relationship between A. nerii and Mandevilla, as the aphid sequesters toxic compounds from Apocynaceae plants, affecting the food chain and complicating biological control efforts. The first step of the research was to evaluate the abilities to exploit A. nerii as prey or host. Through a series of experiments, we evaluated the survival, fecundity, and effectiveness of seven natural enemies commonly employed in the biological control of aphids in reducing A. nerii populations. This initial screening demonstrated that Micromus angulatus Stephens (Neuroptera: Hemerobiidae), Sphaerophoria rueppellii Wiedmann (Diptera: Syrphidae), Propylea quatuordecimpunctata L. (Coleoptera: Coccinellidae), and Micromus variegatus Fabricius (Neuroptera: Hemerobiidae) were able of surviving, preying on A. nerii, and effectively reducing its infestations. The other natural enemies tested proved unable to prey on or parasitize A. nerii, nor to reduce its density. Moreover, in semi-field and greenhouse experiments, S. rueppelli and M. angulatus, reduced the density of A. nerii, suggesting their potential as biological control agents against this pest. The success of a biological control strategy based on generalist predators can be affected by diet quality, which can be related to plant-herbivore-predator relationships. In a laboratory study, we assessed the effects of three diets (1: A. nerii + Mandevilla; 2: Myzus persicae Sulzer + Mandevilla; 3: M. persicae + sweet pepper) on the survival and fecundity of M. variegatus and P. quatuordecimpunctata. Survival probability was not influenced by diet. Propylea quatuordecimpunctata produced no eggs, while a reduction in M. variegatus fecundity occurred with the A. nerii + Mandevilla diet compared to the other diets. These results highlight the predation capacity of M. variegatus on A. nerii and, in particular, the capacity of the predators to overcome the limitation posed by the cardenolides-mediated effect. The effectiveness of predators in crops depends on life history traits such as development, survival, and fecundity, which are critical for generalist 9 predators that may feed on suboptimal prey. In laboratory conditions, we evaluated the effects of a lowquality diet based on A. nerii and a high-quality diet based on M. persicae on the life-table parameters of M. angulatus and M. variegatus. Micromus angulatus completed its life cycle on A. nerii, though larval development, adult longevity, and fecundity were slightly reduced compared to a diet of M. persicae. This confirms its potential as a biological control agent for A. nerii. Conversely, none of the M. variegatus larvae developed to adulthood on the A. nerii diet, indicating that A. nerii is likely an unsuitable prey for this species. Predatory efficiency is crucial for evaluating a predator's potential in pest control. In laboratory experiments, we assessed predation rates and functional responses of C. carnea, M. angulatus, and P. quatuordecimpunctata on A. nerii. Micromus angulatus showed the highest predation rates, while C. carnea showed the lowest aphid consumption rate. Both M. angulatus and P. quatuordecimpunctata exhibited a Type II functional response, with M. angulatus demonstrating superior predation capacity due to a higher attack rate and shorter handling time. In contrast, C. carnea did not show a significant response to varying densities of A. nerii. Overall, our study highlighted that while several predators manifested potential in controlling A. nerii infestations, the best performance was achieved with the brown lacewing M. angulatus, suggesting that releases of this predator may help growers control populations of this pest.