Bidirectional Predation Between Larvae of the Hoverfly Episyrphus balteatus (Diptera: Syrphidae) and the Fall Armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae)

Evaluation of the biocontrol potential of Episyrphus balteatus (Diptera: Syrphidae) on wheat aphids in northern China

Marmalada hoverfly, Episyrphus balteatus De Geer (Diptera: Syrphidae), is a cosmopolitan fly species providing pest control and pollination services. As wheat aphids cause significant losses to global wheat production, a systematic evaluation of the predatory potential and biocontrol service functions of E. balteatus in wheat ecosystems was undertaken. The daily maximum prey consumption of third instar E. balteatus on the adult of Rhopalosiphum padi Linnaeus, Schizaphis graminum Rondani, and Sitobion miscanthi Takahashi (Hemiptera: Aphididae) were 250, 500, and 100 individuals/third instar larvae, respectively. The S. graminum population decline rates in cages after release of the third instars at ratios of 1:100 and 1:200 were 100% and 94.17%, respectively, 72-h after exposure. Feeding assays involving R. padi, S. graminum, and S. miscanthi showed a DNA detectability half-life of 4.17, 6.44, and 4.83 h, respectively, in third instar larvae of E. balteatus. Using multiplex polymerase chain reaction-based gut content analysis to detect prey DNA remains, we confirmed that E. balteatus larvae preyed upon R. padi, S. graminum, S. miscanthi, and Metopolophium dirhodum Walker (Hemiptera: Aphididae) in the field experiments during 2022 to 2024. A significant positive correlation was also found between corrected prey detection rate and aphid population dynamics. These results provide an entry point for understanding the ecological service function of E. balteatus and developing the biological control strategy of the wheat aphid management.

Can the Generalist Predator Calosoma chinense Kirby Be Effectively Employed in the Biological Control of Spodoptera frugiperda (J. E. Smith)?

Calosoma chinense Kirby, a generalist predator, consumes a variety of pests. To better understand its predatory behavior and capacity, particularly against Spodoptera frugiperda (J. E. Smith), we identified the field species and investigated the predation capacity of the third-instar larvae and adults of both sexes against the first- to sixth-instar larvae, pupae, and male and female adults of S. frugiperda. The predation preference for different developmental stages of S. frugiperda was further examined. Our results indicated that C. chinense can prey on S. frugiperda in various stages, including larvae and adults, demonstrating robust predatory abilities. Among them, female adults of C. chinense exhibited the strongest predatory ability against first-instar larvae of S. frugiperda, with the highest daily consumption of 38.90 ± 0.79 individuals. The first-instar larvae of C. chinense also showed a certain predatory ability towards S. frugiperda, with a daily consumption of 6.95 ± 0.88 individuals per predator. The predation ability of C. chinense larvae increased with larval growth, especially for the first to third instar of S. frugiperda larvae, and C. chinense female adults had the strongest predation ability, followed by male adults and then third-instar larvae. However, there was no significant difference in predation capacity against fourth- to sixth-instar larvae and male and female adults of S. frugiperda, nor between adults of both sexes and third-instar larvae of C. chinense. The predation choice experiment revealed that the third-instar larvae and male and female adults of C. chinense showed a positive preference for S. frugiperda larvae from the first to fourth instars, while for the fifth- to sixth-instar larvae, they exhibited a negative preference. Overall, C. chinense exhibited a strong ability to prey on S. frugiperda. Our study indicates that C. chinense has the potential for application in the biological control of S. frugiperda.

The invasive Spodoptera frugiperda (J.E. Smith) has displaced Ostrinia furnacalis (Guenée) as the dominant maize pest in the border area of southwestern China

BACKGROUND

The invasive fall armyworm (FAW) Spodoptera frugiperda (Lepidoptera: Noctuidae) has widely colonized the tropics and subtropics of Asia. However, the impact on the succession of the Asiatic corn borer (ACB) Ostrinia furnacalis (Lepidoptera: Pyralidae), a perennial dominant stemborer of maize in these areas, remains elusive. Here we analyzed the predation relationship, mimicked population competition, and surveyed the pest populations in the border area of Yunnan (southwestern China).

RESULTS

Laboratory assays revealed that the 2nd to 6th instar larvae of FAW preyed on ACB, and only the 4th and 5th instar larvae of ACB preyed on FAW (1st instar larvae only, 50% predation rate). The 6th instar FAW preyed on the 1st to 5th instar ACB with a theoretical maximum of 14.5-58.8 ACB individuals (per maize leaf) and 4.8-25.6 individuals (per tassel). When maize plants were infested with eggs of either FAW or ACB in field cage trials, maize damage was 77.6% and 50.6%, respectively, compared with 77.9% and 2.8% upon co-infestation. In field surveys conducted in 2019-2021, FAW density was significantly greater than that of ACB, which took a great impact on maize growth.

CONCLUSION

Our findings indicate that FAW can outcompete ACB at both the individual and population levels, which may result in FAW becoming the dominant pest. These results provide a scientific basis for further analysis of the mechanism by which FAW invades new agricultural areas and offers early-warning strategies for pest management. © 2023 Society of Chemical Industry.

Hoverflies provide pollination and biological pest control in greenhouse-grown horticultural crops

Beneficial insects provide pollination and biological control in natural and man-made settings. Those ecosystem services (ES) are especially important for high-value fruits and vegetables, including those grown under greenhouse conditions. The hoverfly Eupeodes corollae (Diptera: Syrphidae) delivers both ES, given that its larvae prey upon aphid pests and its adults pollinate crops. In this study, we investigated this dual role of E. corollae in three insect-pollinated and aphid-affected horticultural crops i.e., tomato, melon and strawberry within greenhouses in Hebei province (China). Augmentative releases of E. corollae increased fruit set and fruit weight of all three crops, and affected population dynamics of the cotton aphid Aphis gossypii (Hemiptera: Aphididae). On melon and strawberry, E. corollae suppressed A. gossypii populations by 54-99% and 50-70% respectively. In tomato, weekly releases of 240 E. corollae individuals/100 m²led to 95% fruit set. Meanwhile, releases of 160 hoverfly individuals per 100 m²led to 100% fruit set in melon. Also, at hoverfly/aphid release rates of 1:500 in spring and 1:150 in autumn, aphid populations were reduced by more than 95% on melon. Lastly, on strawberry, optimum levels of pollination and aphid biological control were attained at E. corollae release rates of 640 individuals/100 m². Overall, our work shows how augmentative releases of laboratory-reared hoverflies E. corollae can enhance yields of multiple horticultural crops while securing effective, non-chemical control of resident aphid pests.