Combination of semiochemicals and entomopathogenic fungi for the control of Frankliniella occidentalis

Abstract: Thrips (Thripidae) are phytophagous insects with Frankliniella occidentalis
(Western flower thrips or WFT) and Thrips tabaci (Onion thrips) recognized as the most
damaging species to crops. They feed by piercing and sucking on the plant tissues, causing both direct damage through feeding and indirect damage by transmitting viruses. Thrips can develop resistance to phytosanitary products quickly, amplifying their negative impact on agriculture. Hence, investigating biological alternatives, such as biopesticides, is imperative to mitigate the impact on non-target populations, consumers, and to suppress resistance development. Entomopathogenic fungi (EPF) emerge as promising biopesticides. As the application of EPF through inundative spraying for WFT control requires a substantial inoculum that results in high treatment costs, an alternative approach would be to attract WFT by a semiochemical into a trap containing EPF spores, facilitating the infection of conspecifics. Therefore, it is crucial to identify the attractive compounds of WFT, that are compatible with the fungal strains. This study aimed to lay the groundwork for the development of autoinoculation of EPF against WFT. Highly pathogenic fungal strains for thrips were exposed to semiochemicals to assess the fungal growth inhibition. Fungistatic capacities were observed for all of tested molecules, except panisaldehyde 10 % and verbenone 1 %. Geraniol, nerol, and linalool exhibited pronounced deleterious effects at 10 %. Verbenone, p-anisaldehyde, methyl isonicotinate, and neryl (S)-2-methylbutanoate were weak inhibitors of fungal growth, particularly on isolates of Akanthomyces lecanii (Bb1), Metarhizium anisopliae (10.1), and Beauveria bassiana (11.4). Visual assessments indicated that B. bassiana isolate (2.1) and M. anisopliae isolates (32.1, 33.1, and 34.2) displayed the greatest mean inhibitions. Notably, the proprietary isolate Bb1 caused a statistically significant population decrease. This study has successfully identified semiochemical molecules with a weak fungistatic effect against fungal strains suitable for controlling F. occidentalis and also identified a fungal strain with potential utility in WFT control.