Study of the host-plant selection and colour attraction of Common Grass Yellow Caterpillar (Eurema hecabe)

Introduction

All insects start their life as eggs. As young insects grow and develop; their bodies change in a process called metamorphosis. In butterflies, complete metamorphosis is seen from caterpillar (larva) to adult body form. The Common grass yellow (Eurema hecabe ) was selected as the test species. This caterpillar is initially a uniform pale green in colour. Later instars are green with a white band along each side edged with yellow and are covered in short hairs. The caterpillar grow to a length of about 3 cm (about 1.18 in). For this research we collected this larvae from the areas in Western Province Sri Lanka .All 20 larvae was collected for this research. Mainly this research is based to study the colour preferences of Common Grass Yellow larvae and selection of host plant when it is with a non-host plans. All testing larvae are used to determine the colour attraction and the host-plant selection studies. All the 20 larvae are collected from leaves of Sesbania grandiflora. It is a quick growing perennial tree which tolerates a wide variety of soil and roots are heavily nodulated with root granules. 

Objective

To inspect there is a significant attraction for some selected colors. 

• To inspect there is a significant plant species that can attract Common grass yellow larvae.

Methodology

Larvae - all larvae are starved 2-4 hours before the experiments. Plants - fresh leaves from following plants 

• Sesbania grandiflora 

• Spinacia oleracea 

• Solanum Lycopersicon 

• Allium porrum 

• Acacia auriculiformis 

• Manihot esculenta 

• Aeschynomene 

• Caesalpinia pulcherrima 

Color attraction test –Experiments on color preference were made with 3-dimensional colored paper models since flat sheets of colored paper did not attract the larvae. Box of 5 cm X 5 cm X 5 cm is separated from 5cm long colorless passage. All trials are taken under the indirect sunlight with florescent lightning (LED lights). All experiments are were carried out at 30 C. Larvae who arriving on each model and those are staying in the intermediate space during 45 min were counted. Former larvae were removed from the color model after arrival on it. Tested colors are as follows – 

• Blue(7.5PB 3/22)

 • Green (2.5G 3/6) 

• Yellow-green(7.5GY 9/10)

 • Yellow(7.5Y 9/10) 

• Red(7.5R 4/12) 

• White(N9)

Plant species attraction test - The fresh leaves of two species of plants , were placed on a designed rectangular box ( 10 cm X 15 cm ). Twenty non-starved larvae were placed at the center of the box and the number on each leaf was recorded after a unit time (10 min).

Plant attraction experiments are done as 4 trials using 10 larvae. Following table shows the two plant species taken for each trial.

Color attraction test- A normality test was done for the experimental results shown in table 1. results as follows

This results shows larvae were mostly attracted to the Yellow green model, and equally attracted to green and yellow models, although larvae were least attracted to the white model. During the experiment first, larvae were attracted to the model although left after arriving the colored model. 

Plant selection test – First their behavior of host selection between the two species of plants was observed. When larvae placed between leaves of plants, the larvae were first attracted by color, after that equally attracted to the two types of plants. Although in some plants they were stayed for a long period of time and start to feed on them while in some plants they were departed quickly after arrived at the leaf. After doing 2 trials for each 2 plant species, these results were tabulated,

Conclusion

• Eurema hecabe larvae significantly attract to the Yellowish and greenish colors. 

• Eurema hecabe larvae mainly feed on plants which are belongs to Family Fabaceae. These results also shows there is a significantly higher number of larvae are attracted to Family Fabaceae plants.

Ending

This is a research done by myself in the period of level 1 as an undergraduate. Also this is a Individual study in the field of animal behavior. The final research was published as a e poster in a PDF format so I had to import the tabulated information in  picture formats because of the inability of making tables in this blog. Hope you all get some information as zoology enthusiasts. Thank you!