Development of a multiple biological control of the invasive species Bagrada hilaris (Burmeister) aimed to the caper bush safeguard

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is an invasive pest bug native to Africa and Asia that infests more than 70 agriculturally significant crops worldwide. In Italy, it has been recorded exclusively on the island of Pantelleria, where its control relies mainly on synthetic pesticides. The economic and environmental drawbacks of these treatments, along with the emergence of insecticide resistance, highlight the urgent need to identify targeted and more effective control techniques. The purpose of this study was to investigate the effectiveness of the Sterile Insect Technique (SIT), in combination with Classical Biological Control, as a sustainable strategy for managing B. hilaris. Previous research has shown promising effects of irradiation (through γ rays) on newly emerged B. hilaris adults. For practical implementation, however, field-collected specimens must be irradiated; hence, the effects of irradiation were also investigated for other life stages (mature adults and fifth-instar nymphs). Subsequently, the “optimal” irradiation dose -balancing sterility, longevity and competitiveness- was defined by examining the sperm competition and sexual behavior of the species, comparing the irradiated males with unirradiated controls. The study of sperm competition suggested that B. hilaris female do not discriminate among sperm from different mates, indicating the presence of sperm mixing. This result was also confirmed in males irradiated at 60 and 80 Gy, indicating that, in the event of release, they would have the same sperm competition potential as their wild counterparts. These findings were corroborated by observational tests on mating duration and frequency under choice and no choice conditions, suggesting that the 80 Gy dose ensures a good level of sterility (95 %) and sexual performance comparable to that exhibited by untreated individuals. Additionally, feeding damage appears to be caused predominantly by B. hilaris females, reducing concerns about collateral effects if sterile males are released into the environment. The ideal ratio of sterile to wild males (overflooding ratio) was estimated, showing that a 1:5 ratio (non-irradiated:irradiated males) is sufficient to significantly reduce the population’s fertility. Finally, the synergy between SIT and Classical Biological Control was explored to maximize the chance of controlling this target species. To test the suitability of this oviposition substrate, the oophagous parasitoid Gryon aetherium (Talamas) was confined with sterile eggs laid by females mated with males irradiated at 80 Gy (SIT eggs). Gryon aetherium successfully exploited these eggs, producing numerous viable offspring. Moreover, the use of irradiated eggs (at 24, 32, and 40 Gy) as “sentinel eggs” was tested for field monitoring of parasitoids, effectively minimizing the risk of unintentional releasing new B. hilaris nymphs. The parasitoid demonstrated successful parasitism at all doses tested, with an extremely low host hatching rate. Overall, the identification of the optimal irradiation dose and the compatibility of SIT strategy with a specialized biocontrol agent provide solid basis for semi-field studies, particularly in geographically confined areas such as Pantelleria Island. These results offer promising prospects for the development of integrated control programs that reduce dependence on synthetic insecticides.