Variation in Host Use at Individual and Population Levels in Green Tortoise Beetles (Cassida viridis) and Conservation Insights for Threatened Cassida Species
(2025) BION02 20232Degree Projects in Biology
- Abstract
- Phytophagous insects, comprising over half a million species, depend on plants for survival and are broadly categorised as specialists or generalists based on the range of host plants they exploit. Host plant selection is shaped by environmental factors, such as local plant availability, and ecological pressures, including competition and predation. While patterns of specialisation and generalisation have been extensively studied across species, relatively little attention has been paid to intraspecific variation in host use — an important consideration for conservation planning, particularly for specialist species. This thesis investigates host-use variation in adult green tortoise beetles (Cassida viridis) at both population and... (More)
- Phytophagous insects, comprising over half a million species, depend on plants for survival and are broadly categorised as specialists or generalists based on the range of host plants they exploit. Host plant selection is shaped by environmental factors, such as local plant availability, and ecological pressures, including competition and predation. While patterns of specialisation and generalisation have been extensively studied across species, relatively little attention has been paid to intraspecific variation in host use — an important consideration for conservation planning, particularly for specialist species. This thesis investigates host-use variation in adult green tortoise beetles (Cassida viridis) at both population and individual levels across three populations in southern Sweden. The influence of beetle age and host plant availability on host use, and how these factors vary within and between populations, were explored. The results revealed significant differences in host use between populations, with beetles in Häckeberga and Nöbbelöv exhibiting higher frequencies of host plant switching. However, most individuals within each population demonstrated strong specialisation, with over 70% utilising only one host plant species. While the majority specialised on the most common host plant, some individuals specialised on less abundant species. Older beetles were more likely to switch between host plants, a trend observed consistently across populations. Although host plant availability influenced host use, its effect was less pronounced than expected, suggesting that additional ecological factors play a substantial role. These findings highlight the importance of recognising individual-level specialisation in host use when developing conservation strategies for Cassida species with multiple known host plants. Furthermore, this thesis discusses the implications for conservation efforts targeting threatened Cassida species in Sweden, integrating insights from both the literature and the findings of this study. (Less)
- Popular Abstract
- Host plant use by green tortoise beetles
How do green tortoise beetles decide which plants to call home? Do they simply settle for the most common plants in their environment, or are there other factors influencing their choices? And do all beetles in a population behave the same way, or do individual beetles have unique preferences or adaptations?
The green tortoise beetle (Cassida viridis) is a striking insect found in south-western Europe, often near ponds, streams, or other wet habitats. These herbivorous beetles are easy to recognize by their shield-like shell, which extends to cover their entire body—leaving only their antennae and feet visible when viewed from above. Completely dependent on their host plants for survival,... (More) - Host plant use by green tortoise beetles
How do green tortoise beetles decide which plants to call home? Do they simply settle for the most common plants in their environment, or are there other factors influencing their choices? And do all beetles in a population behave the same way, or do individual beetles have unique preferences or adaptations?
The green tortoise beetle (Cassida viridis) is a striking insect found in south-western Europe, often near ponds, streams, or other wet habitats. These herbivorous beetles are easy to recognize by their shield-like shell, which extends to cover their entire body—leaving only their antennae and feet visible when viewed from above. Completely dependent on their host plants for survival, green tortoise beetles spend every stage of their lives—egg, larva, pupa, and adult—closely tied to the surface of these plants. Their preferred hosts include various species in the mint family (Lamiaceae), such as mints (Mentha spp.), marsh woundwort (Stachys sylvatica), and gypsywort (Lycopus europaeus).
Previous research has shown that the availability of host plants influences how herbivorous insects use them. My study aimed to dig deeper, examining how host plant availability shapes the choices of green tortoise beetles and how these choices differ both between and within populations. Using a mark-recapture method, I collected data from three populations to uncover these patterns.
Does availability determine host plant use?
Surprisingly, the availability of host plants didn’t fully dictate how they were used. While the most common host plant was generally the most used, the usage of less abundant plants didn’t follow the expected patterns. Interestingly, the host plants preferred varied between populations, and older beetles showed a broader use of host species compared to younger beetles.
On a population level, all available host plants were used to some extent. However, a closer look at individual beetles revealed that more than 70% of them stuck to just one host plant species during their lifetime—even when multiple options were available.
Why does this matter?
These findings underscore the importance of looking beyond population averages to consider individual behaviour in specialized species. This perspective can be crucial for conservation efforts, particularly for threatened species, and for understanding population dynamics in greater detail.
Future research is needed to uncover why most individuals stick to a single host plant. Is it due to individual specialization, personal preference, or other factors shaping these choices? Understanding these details could shed light on the delicate balance between insects and their environments.
Master’s Degree Project in Biology 45 credits 2024
Department of Biology, Lund University
Advisors: Maja Tarka, Kristina Karlsson Green & Erica Winslott (Less)
Please use this url to cite or link to this publication:
http://lup.lub.lu.se/student-papers/record/9184987
- author
- Alveteg, Sofie
- supervisor
-
- Maja Tarka LU
- Erica Winslott LU
- Kristina Karlsson LU
- organization
- course
- BION02 20232
- year
- 2025
- type
- H2 - Master's Degree (Two Years)
- subject
- language
- English
- id
- 9184987
- date added to LUP
- 2025-02-12 14:39:10
- date last changed
- 2025-02-12 14:39:10
@misc{9184987,
abstract = {{Phytophagous insects, comprising over half a million species, depend on plants for survival and are broadly categorised as specialists or generalists based on the range of host plants they exploit. Host plant selection is shaped by environmental factors, such as local plant availability, and ecological pressures, including competition and predation. While patterns of specialisation and generalisation have been extensively studied across species, relatively little attention has been paid to intraspecific variation in host use — an important consideration for conservation planning, particularly for specialist species. This thesis investigates host-use variation in adult green tortoise beetles (Cassida viridis) at both population and individual levels across three populations in southern Sweden. The influence of beetle age and host plant availability on host use, and how these factors vary within and between populations, were explored. The results revealed significant differences in host use between populations, with beetles in Häckeberga and Nöbbelöv exhibiting higher frequencies of host plant switching. However, most individuals within each population demonstrated strong specialisation, with over 70% utilising only one host plant species. While the majority specialised on the most common host plant, some individuals specialised on less abundant species. Older beetles were more likely to switch between host plants, a trend observed consistently across populations. Although host plant availability influenced host use, its effect was less pronounced than expected, suggesting that additional ecological factors play a substantial role. These findings highlight the importance of recognising individual-level specialisation in host use when developing conservation strategies for Cassida species with multiple known host plants. Furthermore, this thesis discusses the implications for conservation efforts targeting threatened Cassida species in Sweden, integrating insights from both the literature and the findings of this study.}},
author = {{Alveteg, Sofie}},
language = {{eng}},
note = {{Student Paper}},
title = {{Variation in Host Use at Individual and Population Levels in Green Tortoise Beetles (Cassida viridis) and Conservation Insights for Threatened Cassida Species}},
year = {{2025}},
}