Influence of the number of hosts and the risk of predation on the foraging behavior of the parasitoid Eretmocerus eremicus

BACKGROUND

Parasitoids are natural enemies that can modify their behaviors as they search for hosts based on the characteristics of the sites in which they forage. Theoretical models predict that a parasitoid will stay for longer periods in high-quality sites or patches than in those of low quality. In turn, patch quality may be linked to factors such as the number of hosts and the risk of predation. In the present study, we sought to determine if the factors of the number of hosts, risk of predation, and their interaction influence the foraging behavior of the parasitoid Eretmocerus eremicus (Hymenoptera: Aphelinidae) as theory predicts. To do this, we evaluated different parameters of parasitoid foraging behavior, such as residence time, number of oviposition events, and attacks, in sites of different patch quality.

RESULTS

Our results show that when the factors, number of hosts, and, risk of predation, were evaluated separately, E. eremicus resided for longer periods and oviposited more frequently in patches with a high number of hosts and low risk of predation than in other patches. However, when both of these factors were combined, only the number of hosts influenced some aspects of the foraging behavior of this parasitoid, such as the number of oviposition events and attacks.

CONCLUSION

For some parasitoids like E. eremicus, theoretical predictions may be fulfilled when patch quality is linked to the number of hosts but will not be fully satisfied when patch quality is related to the risk of predation. Furthermore, at sites with different combinations of host numbers and risk of predation, host number appears to be more critical than predation risk. These results suggest that the performance of the parasitoid E. eremicus to control whiteflies will be mainly mediated by the levels of whitefly infestation and, to a small extent, by the risk of predation to which the parasitoid is subjected. © 2023 Society of Chemical Industry.

Activity of flonicamid on the sweet potato whitely Bemisia tabaci (Homoptera: Aleyrodidae) and its natural enemies

BACKGROUND

Flonicamid is a novel systemic insecticide that acts as a feeding blocker with potential use against whiteflies within IPM control tactics. Flonicamid efficacy against Bemisia tabaci Mediterranean populations from Crete was examined, as well as side effects on selected beneficials used extensively in current IPM schemes.

RESULTS

Low variability in adulticide activity was detected (<tenfold), while there was no resistance compared with a reference susceptible population. Flonicamid exhibited low to no insecticidal activity on eggs, emerging crawlers and second-instar nymphs at the maximum registered label rate (RLRmax ). In long-term cage experiments, flonicamid at the RLRmax (125 mg L(-1)) caused 95% mortality to whiteflies 10 days after treatment and delayed population growth by one generation (32 days). Flonicamid significantly delayed nymphal development by increasing the development time (DT50 ) of treated insects by 7.2 days. Flonicamid did not affect the survival of Eretmocerus eremicus adults, while lethal effects of an intermediate level were observed on Nesidiocoris tenuis adults and nymphs, Amblyseius swirskii adults and preimaginal stages of E. eremicus. Flonicamid reduced the feeding activity (consumption of B. tabaci eggs) of N. tenuis and A. swirskii by 28 and 37% respectively. Moreover, the fecundity of A. swirskii was reduced by 36% after exposure to flonicamid.

CONCLUSIONS

Flonicamid is an effective tool for the management of B. tabaci populations from Crete, and initial studies indicate that it could be combined with B. tabaci natural enemies.