The Effect of Food Type on the Development Rate of the Danaid Eggfly Sharmaine L
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Journal of Young Investigators RESEARCH ARTICLE The Effect of Food Type on the Development rate of the Danaid Eggfly Sharmaine L. Miller1*, Benjamin Mensah2, and Daniel Wubah3 Butterflies are important components of community trophic structure because they serve as food for mammals, lizards, birds, other insects, and spiders (Schreiner, 1997). Furthermore, certain species of butterfly are also valued pollinators and herbivores; therefore, butterflies are important in maintaining ecosystem biodiversity (Hammer, 2014). Individual butterflies are vulnerable as larvae because they are small and slow. They are also immobile as pupae or cocoons. A shortened larval and/or pupal period should decrease the chances of being ingested or attacked by predators and increase the probability of surviving to adulthood. Therefore, efforts to identify food types effective at increasing the development rates of threatened butterfly species may be useful. The purpose of this study was to determine whether different food types affect the rate of development of Hypolimnas misippus, also known as the Danaid eggfly. Two experimental groups with twenty larvae each were used in the study. One half was fed Portulaca oleracea and the second half was fed Portulaca quadrifida, both of which are common food plants for H. misippus. To determine if growth rate depended on food type, the number of days from egg to pupa, the pupal weight, and the number of days from pupa to adult were recorded. Short period of days between stages and a high pupal weight would indicate a fast growth rate. The findings revealed a difference in the larval period between the two groups (p=1.0 x 10-5) with the P. oleracea group having a shorter larval period in comparison to the P. quadrifida group. However, there was no difference in the pupal weight and pupal period between the two groups (p=0.684 and p=0.199 respectively). These results suggest P. oleracea may increase the development rate, specifically the larval period of H. misippus. This would allow this species of butterfly to reach adulthood faster and increase their population size. INTRODUCTION There are 860 different species of butterflies in Ghana. One such maintaining biodiversity (Schreiner, 1997). An example of a species is the Hypolimnas misippus or the Danaid eggfly specific predator of H. misippus is Lanius collaris, a fiscal (Gordon, 2010). H. misippus eats a variety of different food shrike, which was observed to feed on larvae in a prior study plants from several plant families such as Convolvulaceae, conducted by Mensah. It can be predicted that if the population Malvaceae, and Portulacaceae (Mensah and Kudom, 2011). The of H. misippus declines, then it is likely the population of fiscal primary food type of H. misippus is Portulaca oleracea, which shrikes could also decline as a consequence. belongs to the Portulacaceae family; however, H. misippus is Schreiner (1997) describes the four stages of the life cycle of also known to consume Portulaca quadrifida, another member of a butterfly: egg, larva, pupa, and adult. First, the adult butterfly the Portulacaceae family (Mensah and Kudom, 2011). lays its eggs on the appropriate host plant. Then, the eggs hatch The H. misippus species was specifically chosen for this and small larvae emerge. The larval stage is subdivided into study because females have had no problems laying eggs in different phases called instars, and as the instar stage progresses, research settings. Also, the species appears to be in decline since the larvae grow larger (Benrey and Denno, 1997). Subsequently, June 2009 in some areas in Cape Coast, Ghana as indicated by after sufficient food is obtained and converted into energy, the Mensah and Kudom (2011). The species still remained to be larvae then transform into pupae. Inside the pupae, the larva form scarce as this study was conducted during the summer of 2012. It disintegrates and reorganizes itself into the adult form. After is also important to note a species survey is to be conducted at a about a week, the pupa opens and the butterfly emerges later date to determine if H. misippus is endangered. In the (Schreiner, 1997). meantime, however, the concept and results of this study will still The goal of this study was to determine if a particular food benefit future butterfly conservation research. type affected the growth rate of H. misippus. If a food type Efforts should be made to conserve H. misippus or positively affected the growth rate of the Danaid eggfly, then butterflies in general because they are critical players in researchers would need to work towards conserving that particular species of plant. By having a faster growth rate, H. 1 Towson University, 8000 York Rd, Towson, MD 21252, misippus would be able to avoid being eaten and being attacked USA by predators at such early stages of development, therefore having a higher probability of surviving to adulthood when they 2 Department of Entomology and Wildlife, University of Cape can escape predators easily by utilizing flight. Coast, Cape Coast, Ghana Conversely, according to the slow-growth, high-mortality 3 Washington and Lee University, Lexington, VA 24450, USA hypothesis, individuals that feed on a poor quality food would develop slowly and would therefore have a larger window of *To whom correspondence should be addressed: vulnerability to predation and thus an increased risk of mortality [email protected] (Cornelissen and Stiling, 2012). In a similar study, researchers varied the development rates of butterfly larvae by rearing 39 JYI | June 2014 | Vol. 26 Issue 5 © 2014 Journal of Young Investigators Journal of Young Investigators RESEARCH ARTICLE individuals on different food plants (with variations in the and released into the box with the mesh siding. A heat lamp, to amount of protein) and also by altering the temperature simulate sunlight (H. misippus is active during the day), was conditions, both of which affect the development rate (Benrey placed adjacent to this set-up and pointed down towards the tin and Denno, 1997). It was observed that larvae with fast containing the P. quadrifida. The female was taken out of the development rates had fewer incidents of parasitism than larvae mesh box daily to be fed with 10% (weight/volume) sucrose with slow development rates (Benrey and Denno, 1997). This sugar solution. was because the window of vulnerability to predation or parasitism was much smaller for larvae with faster development Experimental Design rates than larvae with slow development rates (Benrey and Once the eggs hatched into small black larvae, the box apparatus Denno, 1997). was removed. The tin of P. quadrifida, a large magnifying glass, In a more recent study conducted by Mensah and Kudom a paint brush, 50 plastic cups, large amounts of mesh, and filter (2011), they studied whether different food plants, P. oleracea, paper were transferred to the UCC lab (for better lighting to P. quadrifida, and Asystasia gangetica, in the Cape Coast area transfer the larvae to the cups). Once a larva was identified with affected the development rate of H. misippus (Mensah and the magnifying glass, it was then transferred carefully with the Kudom, 2011). The number of days from egg to pupa (larval paintbrush. 25 larvae were chosen haphazardly and were fed P. period), pupal weight, and the number of days from pupa to adult oleracea (20 in the experimental group, 5 in the extra or back-up (pupal period) were determined and also the nutritional content group). A second set of 25 larvae were chosen haphazardly and of each plant was analyzed (Mensah and Kudom, 2011). A fed P. quadrifida (20 in the experimental group, 5 in the extra or shortened larval and pupal period and heavy pupae would back-up group). Each cup was approximately 200mL and indicate a fast development rate. It was determined that H. contained a filter paper (for waste collection) at the bottom along misippus had the fastest larval development rate and heaviest with a handful of food plant. The cup was covered with mesh and pupae when fed P. oleracea, but similar pupal development rates was rubber banded closed. Food plant was not weighed before when fed on any of the three plants (Mensah and Kudom, 2011). placing in each cup because the subjects were fed ad libitum. Other similar studies involving different food types affecting the Thus, large quantities or handfuls of food were placed in the cups development rate of H. misippus were difficult to find. daily and food was given more often as the larvae changed In this study, two food plants from the Portulacaceae family instars. were focused on to distinguish whether there is a difference in There were 25 replications for each food plant. All cups the species of Portulacaceae itself (P. oleracea versus P. were placed together in the UCC lab under a constant quadrifida) on the development rate of H. misippus. In addition temperature of 26ºC with a lighting of 12L:12D. Therefore, to this, food intake was focused on, rather than nutritional temperature was not a confounding factor and would have not content, to determine whether the species had a preference for affected the development rate. In sum, the experimental and extra either food type. This could be analyzed by determining the food groups were fed for a maximum of 18 days. type that is replaced more often as a result of higher consumption Materials such as filter paper, tweezers, rubber bands, by larvae. Lastly, this study contributes to the very few studies napkins, a petri dish (with a cover) and a paintbrush were looking at whether specific food type affects the development gathered to replace food every morning. First, each larva was rate of H. misippus (Gordon, 2010). removed from their cup by brushing them with a paintbrush into a petri dish.