Flue-cured tobacco, Nicotiana tabacum (L.) is often attacked by various pests such as aphids, whiteflies, and tobacco budworms. Insecticide application has been the primary method in managing these pests in Yunnan province. However, it is necessary to look for more sustainable strategies that can help control pests. In this context, conservation biological control is a highly promising alternative, involving the cultivation or conservation of flowering plants within the agricultural ecosystem to attract and support natural enemies. The objective of this study was to evaluate the potential of alyssum, Lobularia maritima (L.) Desv. in attracting natural enemies and managing pests in flue-cures tobacco cultivation. The study conducted two field experiments over successive years, each with two treatments and three replicates, arranged in a completely randomized design. The treatments were (1) tobacco monoculture, and (2) tobacco intercropped with alyssum flower strips. The population density of natural enemies and pests was monitored weekly throughout the study period. The results showed that the presence of alyssum flowers in the tobacco + alyssum treatment significantly increased the abundance of generalist predators such as syrphids, rove beetles, carabids, Orius sp., and spiders during both experiments. This increase in predator population led to a substantial reduction in tobacco pests, particularly aphids. Intercropping alyssum with tobacco can serve as an effective strategy for managing pests specific to the Nicotiana plant, as well as addressing the limited availability of approved insecticides for this crop. This approach may help to mitigate pest-related issues and reduce the reliance on insecticides in tobacco cultivation, contributing to more sustainable pest management practices.

Arthropods sampling and collection

To comprehensively evaluate the impact of border flower strips on main pest populations and natural enemies in flue-cured tobacco fields, we conducted at weekly intervals sampling throughout the entire lifecycle of the border flower strips, from seedling to fruit maturity. In 2022, a total of twelve samplings were conducted at weekly intervals, starting on May 30^th and ending on August 15^th, covering the tobacco seedling and flourishing stages. In 2023, a total of seventeen samplings were conducted at weekly intervals between May 1^st and August 21^st. In case of rainy weather, the investigations were postponed.

The main methods used to investigate arthropod species and quantities on flower and tobacco strips are visual observation, sweeping net, and beating tray (Ribeiro and Gontijo, 2017). Similarly, methods employed to study arthropod types and quantities in tobacco fields include visual observation, pitfall traps, and walking inspections (Song et al., 2010; Ribeiro and Gontijo, 2017). Specific survey methods are as follows:

(1) Visual observation, sampling time is from 8:00 to 18:00.

a. 5 flowers (bunch) were randomly selected at each point, and each point was observed by naked eye to attract the species and quantity of flower-visiting insects on the flowers of plants.

b. In flue-cured tobacco fields, each plot has 5 rows of tobacco plants (2022) to 8 rows (2023). Randomly survey 5 rows from each plot, inspecting 5 plants marked with red string at specified locations in each row, and record all diurnal arthropods observed visiting the tobacco plants. Additionally, during the flowering period of the tobacco plants, visually survey and record the diurnal arthropods visiting the tobacco flowers. Before the flowering period, only observe the arthropods on the front and back of the tobacco leaves from top to bottom and record their types and quantities.

(2) Sweeping net, at each point, 20 nets were swept in the flowers with an insect-catching net (the insect-catching net was waved back and forth once for 1 net), and the flower-visiting insects caught in the net were collected, and their species and quantity were recorded.

(3) Beating tray involves randomly selecting 5 flowers (bunch) from each plot and gently tapping them into a porcelain tray. Insect pests and natural enemies that fall from the flowers are then counted. To prevent the flying specimens from escaping quickly, the bottom of the tray is filled with 10-20 mL of water containing a few drops of detergent before each tapping.

(4) Pitfall traps (Supplementary Fig. 1). Use a disposable plastic cup (9.50 cm in height and 6.30 cm in diameter at the cup mouth) as a container to bury it underground in the tobacco field, with the cup mouth flush with the ground. And the plastic cups were filled with 40 mL of water containing several drops of detergent to break the superficial tension. Each plot is equipped with a total of 3 traps. Collect arthropods that fall into trap cups every 7 days.

(5) Walking inspection. At night, a walking inspection method is used in each plot, which involves investigating a total of 3 rows along the tobacco planting belt. While walking, the types and quantities of arthropods on the tobacco and its planting belt are observed, recorded, and collected.

All sampled arthropods were stored in a 70% ethanol solution and identified in the laboratory using a stereo dissecting microscope (model Olympus SZ 51, produced by Puhe Optoelectronics (Shanghai) Technology Co., Ltd). In the case of species that cannot be identified, prepare specimens, number them uniformly, and ask relevant taxonomic experts to identify them.

The count of adult parasitoids and parasitized insect pests was evaluated in the second experiments using the aforementioned methodology, which included visual observation and laboratory identification for counting adult insects and mummies, as well as the use of beating trays for counting adult insects on flower strips. Through field observation and laboratory identification of adult insects and mummies, it was determined that the parasitoids belong to A. gifuensis Ashmead.

Statistical analyses

The totals of arthropods sampled in each replicate were calculated based on their types (aphids, thrips, tobacco caterpillars, whiteflies, generalist predators, adult parasitoids, and mummified aphids), as well as the date of sampling. This sum includes data from all types of sampling methods used. Therefore, as the type and quantity of samplings were standardized across treatments and dates, each sum mentioned above represents a single measurement of pest or natural enemy density per experimental unit (three per treatment).

The population density of pests and natural enemies data were analyzed by SPSS software (version 25.0; SPSS, Chicago, IL, USA). The differences in the effects of the different treatments (tobacco + alyssum and tobacco + tobacco strips) and sampling time on the population density of pests and natural enemies were analyzed using a two-way analysis of variance (ANOVA). The least significant difference (LSD) test was used to analyze the differences in population densities of insect pests and natural enemies between different treatments (P < 0.05).

Differences in population densities of insect pests (aphids, thrips, tobacco caterpillars, whiteflies) and natural enemies (not including those sampled on alyssum flowers) between treatments were assessed using two-way repeated measures analyses of variance (PROC GLM) for each experiment’s data. The least significant difference (LSD) test was used to analyze the differences in population densities of insect pests and natural enemies between different treatments under the same sampling time (P < 0.05). All images were drawn in Gradpad Prism v8.0.2 (GraphPad Software Inc., USA).

References

Ribeiro, A. L., & Gontijo, L. M. (2017). Alyssum flowers promote biological control of collard pests. BioControl, 62(2), 185-196. DOI: 10.1007/s10526-016-9783-7

Song, B. Z., Wu, H. Y., Kong, Y., Zhang, J., Du, Y. L., Hu, J. H., & Yao, Y. C. (2010). Effects of intercropping with aromatic plants on the diversity and structure of an arthropod community in a pear orchard. BioControl, 55(6), 741-751. DOI: 10.1007/s10526-010-9301-2

Usage notes

Microsoft Excel or LibreOffice can be used to view Populationofmainpestsandnaturalenemiesinflue_curedtobaccofieldsunderdifferenttreatmentandsamplingtimes_Data.csv and Otherpredatorssampledatdifferentinvestigationdate_Data.csv