Here, we present a protocol to investigate the pupation preference of mature larvae of Ectropis grisescens in response to soil factors (e.g., substrate type and moisture content) using choice bioassays. We also present a protocol of no-choice bioassays to determine the factors that affect the pupation behaviors and survivorship of E. grisescens.
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Method Article
Choice and No-Choice Bioassays to Study the Pupation Preference and Emergence Success of Ectropis grisescens
In This Article
Summary
Abstract
Many insects live above the ground as larvae and adults and as pupate below the ground. Compared to the above-ground stages of their life cycles, less attention has been paid on how environmental factors affect these insects when they pupate within the soil. The tea looper, Ectropis grisescens Warren (Lepidoptera: Geometridae), is a severe pest of tea plants and has caused huge economic losses in South China. The protocols described here aim to investigate, through multiple-choice bioassays, whether mature last-instar E. grisescens larvae can discriminate soil variables such as the substrate type and moisture content, and determine, through no-choice bioassays, the impact of the substrate type and moisture content on pupation behaviors and the emergence success of E. grisescens. The results would enhance the understanding of the pupation ecology of E. grisescens and may bring insights into soil-management tactics for suppressing E. grisescens populations. In addition, these bioassays can be modified to study the influences of various factors on the pupation behaviors and survivorship of soil-pupating pests.
Introduction
Compared to the larval and adult stages of insects, the pupal stage is highly vulnerable due to the limited mobile ability of pupae, which cannot rapidly escape from dangerous situations. Pupating below the ground is a common strategy used by diverse groups of insects (e.g., in the orders Diptera1,2,3,4, Coleoptera5, Hymenoptera6, Thysanoptera7, and Lepidoptera8,9,10
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Protocol
1. Moisture-choice Bioassays to Determine Pupation Preference of E. grisescens
- Obtaining mature last-instar larvae of E. grisescens
- Cut fresh shoots (30 - 40 cm in length) of tea plants (Camellia sinensis L.). Insert 25 - 30 shoots into a 250 mL triangular flask. Fill the flask with tap water. Put 3 - 4 flasks (with tea shoots) in a plastic basin (upper side: 51 cm in diameter; bottom side: 40 cm in diameter; height: 16 cm).
- Release 1,000 - 2,000 larvae (second to fifth instar) of the laboratory colony of E. grisescens onto the leaves of the tea shoots in each basin. Maintain thes....
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Results
The moisture-choice bioassays showed that significantly more E. grisescens individuals pupated on or within the 5%- and 35%-moisture sand compared to the 80%-moisture sand (Figure 2a). However, significantly more individuals preferred to pupate on or within the soil (sandy loam 1 and 2 and silt loam) that had an intermediate moisture content (Figures 2b - 2d).
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Discussion
Pupation preferences responding to different soil variables have been studied in a few pests6,9,22,23. For example, to study the preference of mature larvae of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) among different soil moisture conditions, Hulthen and Clarke22 set a 3 x 3 Latin-square design containing 9 containers filled with soil at either 0%, 75.......
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Disclosures
The authors have nothing to disclose.
Acknowledgements
We thank Yuzhen Wen, Shiping Liang, Shengzhe Jian, and Yanjun Li (College of Forestry and Landscape Architecture, South China Agricultural University) for their help in the insect rearing and experimental set-up. This work was funded by the National Natural Science Foundation of China (Grant No. 31600516), the Guangdong Natural Science Foundation (Grant No. 2016A030310445), and the Science and Technology Planning Project of Guangdong Province (Grant No. 2015A020208010).
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Materials
| Name | Company | Catalog Number | Comments |
|---|---|---|---|
| Triangular flask | Bomex Chemical (Shanghai) Co., LTD | 99 | 250 mL |
| Plastic basin | Chahua, Fuzhou, China | 100 | upper side: 51 cm in diameter; bottom side: 40 cm in diameter; height: 16 cm |
| Zip lock bags | Glad, Guangzhou, China | 126/133 | |
| Polypropylene containers | Youyou Plastic Factory, Taian, China | 139/155/160/161/190 | upper side: 20.0 cm [L] × 13.5 cm [W], bottom side: 17.0 cm [L] × 10.0 cm [W], height: 6.5 cm |
| Waterproof polyviny chloride sheet | Yidimei, Shanghai, China | 141 | |
| Tape | V-tech, Guangzhou, China | VT-710 | |
| Oven drier | Kexi, Shanghai, China | KXH-202-3A | |
| Environmental chamber | Life Apparatus, Ningbo, China | PSX-280H |
References
- Dimou, I., Koutsikopoulos, C., Economopoulos, A. P., Lykakis, J. Depth of pupation of the wild olive fruit fly, Bactrocera (Dacus) oleae (Gmel.) (Dipt., Tephritidae), as affected by soil abiotic factors. Journal of Applied Entomology. 127 (1), 12-17 (2003).
- Chen, M., Shelton, A. M. Impact of soil type, moistur....
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