Aphids are major crop pests that transmit more than half of all insect-vectored plant viruses responsible for high yield losses worldwide. Entomopathogenic fungi (EPF) are biological control agents mainly used by foliar application to control herbivores, including sap-sucking pests such as aphids. Their ability to colonize plant tissues and to interact with diverse plant pathogenic microorganisms have been reported. In our study, we evaluated the effectiveness of Beauveria bassiana ((Balsamo-Crivelli) Vuillemin) directly applied by contact or/and indirectly via endophytism in tobacco plants (Nicotiana tabacum L.) against the virus vector Myzus persicae (Sulzer) carrying the Potato leafroll virus (PLRV) or not. We found that both contact treatment and endophytic colonization of leaves significantly increased aphid mortality and decreased the fecundity rate when compared to control plants. In addition, on fungal-colonized leaves, viruliferous aphids were more negatively impacted than virus-free ones and nymph mortality was significantly higher than on fungal-free plants. Furthermore, we assessed PLRV transmission by M. persicae on tobacco plants inoculated with either B. bassiana or Metarhizium acridum ((Driver and Milner) JF Bischoff, Rehner, and Humber) as source or/and recipient plants. Myzus persicae was found to acquire and transmit PLRV regardless of the treatment. Nevertheless, the infection rate of endophytically colonized plants was lower at a seven-day incubation period and had increased to almost 100% after fifteen days. These results suggest that B. bassiana is effective against aphids, both by contact and via endophytism, and both B. bassiana and M. acridum delayed PLRV infection in tobacco.
Aphids (Hemiptera: Aphididae) cause significant damage and transmit viruses to various crop plants. We aimed to evaluate how the infectious status of aphids influences their interaction with potential hosts. Two aphid (Myzus persicae and Rhopalosiphum padi) and plant (Nicotiana tabacum and Triticum aestivum) species were used. The preferences of aphids towards healthy, virus-infected (Potato Leafroll Virus (PLRV) and Barley Yellow Dwarf virus (BYDV)), and endophytic entomopathogenic fungi (EEPF)-inoculated (Beauveria bassiana and Metarhizium acridum) plants were investigated in dual-choice tests. The headspace volatiles of the different plant modalities were also sampled and analyzed. Viruliferous and non-viruliferous aphids were more attracted to EEPF-inoculated plants compared to uninoculated plants. However, viruliferous aphids were more attracted to EEPF-inoculated plants compared to virus-infected plants, while non-viruliferous insects exhibited no preference. Fungal-inoculated plants released higher amounts of aldehydes (i.e., heptanal, octanal, nonanal and decanal) compared to other plants, which might explain why viruliferous and non-viruliferous aphids were more abundant in EEPF-inoculated plants. Our study provides an interesting research perspective on how EEPF are involved in behavior of virus vector, depending on the infectious status of the latter.
Climate change is a major environmental concern and is directly related to the increasing concentrations of greenhouse gases. The increase in concentrations of atmospheric carbon dioxide (CO2), not only affects plant growth and development, but also affects the emission of plant organic volatile compounds (VOCs). Changes in the plant odor profile may affect the plant-insect interactions, especially the behavior of herbivorous insects. In this study, we compared the foraging behavior of corn leaf aphid (Rhopalosiphum maidis) on barley (Hordeum vulgare L.) seedlings grown under contrasted CO2 concentrations. During the dual choice bioassays, the winged and wingless aphids were more attracted by the VOCs of barley seedlings cultivated under ambient CO2 concentrations (aCO2; 450 ppm) than barley seedlings cultivated under elevated CO2 concentrations (eCO2; 800 ppm), nymphs were not attracted by the VOCs of eCO2 barley seedlings. Then, volatile compositions from 14-d-old aCO2 and eCO2 barley seedlings were investigated by GC-MS. While 16 VOCs were identified from aCO2 barley seedlings, only 9 VOCs were found from eCO2 barley seedlings. At last, we discussed the potential role of these chemicals observed during choice bioassays. Our findings lay foundation for functional response of corn leaf aphid under climate change through host plant modifications.
