Seed preference of Milkweed Bugs ( fasciatus) (: ) in Trinidad

Kathryn M. Alvarado

Abstract- Oncopeltus fasciatus, commonly known as Milkweed bugs, are specialized seed feeders that use a proboscis for piercing and sucking. Milkweed seeds are a critical part of their diet and provide sustenance for each instar into adulthood. Little information is known about the seed preferences of Milkweed bugs which is mainly due to lack of research. This study serves to provide additional research and information regarding Oncopeltus sp. and their feeding behaviors as well as seed preferences. A total of 40 bugs were collected at two different collection sites. Three types of seed- bearing fruits were experimentally tested over three time periods during each day. Balata and cashew seeds were more commonly preferred over other seed choices. The bugs were seen actively feeding during the evening hours more often than morning or afternoon hours. Additionally, this specific species was observed engaging in cannibalistic acts. The overall purpose of this experiment was to determine seed preferences and time of feeding activity for the Oncopeltus species. Through this experiment, Milkweed bugs are better understood and researchers are able to use this information to conduct further research regarding their diets in accordance with seed preference.

Introduction

Oncopeltus fasciatus is a member of the Lygaeidae family that is comprised of more than 60 genera of seed feeding . This specific species undergoes incomplete with five different instars before reaching adulthood. Milkweed bugs in Trinidad have not been widely researched. However, several studies have been conducted in the United States in regions such as Texas, Georgia, and Missouri discussing coloration and wing span in relation to gender and size (Davis 2009). There have been fewer studies discussing their diets, seed preference, and feeding habits. The Milkweed bug relies on seed flowering plants to obtain nutrition and complete their lifecycle. Oncopeltus sp. preference for milkweed plants stems from natural selection and higher evolutionary fitness. Chemical properties in the milkweed plant species produce bright coloration in Milkweed bugs and in turn warn predators of their toxicity (Chaplin 1980). Milkweed plants are among the few toxic plants with the chemical steroid, cardenolide. In Toco, Trinidad milkweed, cashew, and balata are all toxic plants containing the same chemical steroid known to be extremely toxic if consumed raw. Upon field observations, Milkweed bugs were seen feeding from these three plants. Interestingly enough, they were all set to have the same chemical the insects need in order to increase the chances of survival through bright red-orange coloration. In order to further study the observations obtained in the field, a research experiment was conducted to analyze the seed preferences of Oncopeltus fasciatus in a lab setting. The purpose of this experiment was to contribute to the already known information about this and open up other questions about the outcome of this experiment. Once a species is widely studied, it is easier for them to be understood and their behaviors more easily explained.

Materials & Methods

Collecting Specimens Adult and nymphal Milkweed bugs were collected by hand from two sites in Toco, Trinidad during the summer months of May and June 2019. The first site was located on a hill at Jammev Beach Resort while the second site was at a creek off the roadside near Jammev Beach Resort. Both sites were previously scouted for the presence of Milkweed bugs. The bugs were spotted climbing around the stems and leaves of milkweed plants. Milkweed bugs were taken from about two to three plants from both sites during the morning and afternoon hours. All bugs were collected by hand and placed in small plastic collection jars for proper transport. Both sites were visited twice per day until a total of 40 specimens were reached in order to ensure that there was an even number of bugs from both locations.

Data Collection After collection, the specimens were evenly placed in two 6-quart plastic lidded containers with proper air flow, a water-soaked cotton ball, foliage cover, food, and a cotton nesting area. The Milkweed bugs were allotted three days in order to get acclimated to a new habitat and setting. All three types of seeds (balata, cashew, and mango) were left out freely during the acclimation period. The seeds were removed the night before the start of the experiment. In the morning at 9:00 AM, the specimens in both containers were given one of each type of seed; balata, cashew, and mango seeds. Their activity was recorded with a digital timer for twenty-five minutes. Only active feeding was recorded which means that the bug’s proboscis needed to be seen feeding on the seeds in order to count as a data point. All data was recorded and written in a journal during the twenty-five minutes. Following the twenty- five minutes, the seeds were collected and placed separately in plastic containers. The next trial was performed in the exact same manner but at 12:00 PM and then again at 9:00 PM for a total of three trial times per day. The same steps were repeated for a series of four more days. A total of thirty trials were performed and all data and observations were recorded in a journal.

Results

A total of 40 various (males, females, adults, and nymphs) Milkweed Bugs were collected and placed into artificial habitats for data collection over a span of 9 days. Observations showed that the time of day the bugs were most actively feeding was during the night with 70% feeding activity. Morning hours consisted of 20% feeding activity while the afternoon hours resulted in 47.5% feeding activity. The Balata and Cashew seeds were chosen equally over the total time by 25 bugs each. Mango seeds were chosen the least amount of times during feeding with only 5 bugs total during the duration of the experiment. An additional food source observed was carcass matter which was chosen by a total of 13 Milkweed bugs.

Activity of consumption by time of day 30

25

20

15 28

10 19 AMOUNT AMOUNT OF BUGS 5 8 0 AM (9:00) NOON (12:30) PM (9:00) TIME OF DAY

Figure 1.1 Time of day milkweed bugs fed on seeds. Three times of the day are shown along with the number of bugs actively eating seeds. The number within the graph represents the exact number of bugs feeding.

Seed Preference 30

25 25 25 20

15

10 13 AMOUNT AMOUNT OF BUGS 5 5 0 Balata Cashew Mango Other SEED TYPE

Figure 1.2 Three seed types are shown with the amount of milkweed bugs feeding on each specific seed type. The ‘Other’ variable denotes carnivorous feeding activity. The exact numbers of each are displayed within the variables.

The Milkweed bugs were divided into two evenly split groups and differences in the bugs were quite prominent. Group 1 exhibited no signs of carnivorous activity while Group 2 displayed numerous signs with a total of 32.5 % carnivorous feeding. Group 1 had the highest quantity of bugs feeding on actual seeds (36 bugs) while Group 2 had 20 bugs feeding on seeds and 13 feeding on other organic material (cannibalistic feeding). Within Group 1, balata seeds were most preferred in the morning while cashews were favored in the afternoon and evening hours. For Group 2, cannibalistic feeding took place more often in the morning. The bugs in Group 2 preferred balata seeds during the afternoon and equally fed on balata and organic material (cannibalistic feeding).

Group 1: Seed Preference per Time Period 12

10

8

6

4

AMOUNT AMOUNT OF BUGS 2

0 Balata Cashew Mango Other SEED TYPE

AM NOON PM

Figure 2.1 Trial Group 1 findings are displayed in relation to seed type and time of day. Lack of color signifies a quantity of 0 for certain variables.

Group 2: Seed Preference per Time Period 7 6 5 4 3 2

AMOUNT AMOUNT OF BUGS 1 0 Balata Cashew Mango Other SEED TYPE

AM NOON PM

Figure 2.2 Trial Group 2 results are outlined along with the seed type preference in relation to time of day. The key denotes what color responds to a certain time period. Colorless variables indicate a quantity of 0 for that specific group.

Figure 3.1 Habitat display for Milkweed bugs.

Figure 3.2 Adult and Milkweed bugs feeding on balata seed.

Discussion

This study was the first known experiment pertaining to Oncopeltus fasciatus and their specific feeding habits or more specifically their seed preferences in Toco, Trinidad. Results of this study indicated that Milkweed bugs prefer to feed off balata and cashew seeds as opposed to mango seeds and matter (Figure 1.2). During this study, it was also evident that the Milkweed bugs’ optimal feeding activity time was during evening hours around nine o’ clock (Figure 1.1). It is commonly known that the milkweed plant, Asclepias, is the main diet of Milkweed bugs but it is less commonly known that these bugs feed off other material beside milkweed and can still be reproductively successful. Through this research, it was evident that the bugs chose to feed off of toxic plants related to the milkweed plant. Cashew and balata trees, much like the milkweed, contain milky latex derivatives that are poisonous to other and cause the bright red-orange coloration to detract predators. This could be the main reason why Milkweed bugs are attracted to balata and cashew seeds when milkweed is no longer a food source option. There was not much correlation as to why the Milkweed bugs were more actively feeding during the night time hours. This could have something to do with the climate as the bugs were seen hiding under the leaves during the morning and afternoon hours. Little information is known about their various activity throughout the day. An aspect that was rather surprising during this study was the fact that some of the Milkweed bugs were carnivorous. The carnivorous actively was solely seen in Group 2 due to the fact that all specimens in Group 1 were still alive. Since the adult lifespan is about 6 weeks, the insects most likely died due to natural causes or stress from a new environment. Oncopeltus species is not known to be predatory, but there have been instances where they were seen feeding on insect matter (Richardson 2010). During field work and specimen collection, a Milkweed bug was observed carrying an ant up a leaf and feeding on it after a while. This aspect is extremely interesting since they are predominantly seed feeding insects and known to be non-carnivorous. In order to understand more about these seed feeding insects, research has to be done in order to answer specific questions. Following the outcome of this research study, further investigation into the cannibalistic side of Oncopeltus fasciatus should be conducted. Extensive research about their life cycle, daily life, and toxicity levels should be investigated in order to gain a better understanding about Milkweed bugs.

Acknowledgments

Dr. Adrienne Brundage and Dr. Kevin Conway provided guidance, advise, and revision help for this paper. Dr. Adrienne Brundage provided inspiration and collection assistance. Dr. Kevin Conway provided the necessary permits for specimen collection and freezing. My colleagues, Marisa Guerrero and Sadie Arguello aided through specimen collection and support throughout the paper.

Literature Cited

Chaplin, S. J. (1980). An energetic analysis of host plant selection by the , Oncopeltus fasciatus. Oecologia,46(2), 254-261.

Davis, A. K. (2009). Gender- and Size-based Variation in Wing Color in Large Milkweed Bugs (Oncopeltus fasciatus) in Georgia. Southeastern Naturalist,8(4), 723-732.

Iowa State University. (2018, September 20). Family Lygaeidae - Seed Bugs. Retrieved from https://bugguide.net/node/view/129

MBG Press. (n.d.). Milkweed bugs. Retrieved from http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home- gardener/advice-tips-resources/pests-and-problems/insects/plant-bugs/milkweed-bugs.aspx

Richardson, M. L., Mitchell, R. F., Reagel, P. F., & Hanks, L. M. (2010). Causes and Consequences of Cannibalism in Noncarnivorous Insects. Annual Review of Entomology,55(1), 39-53.