Abstract
Scholarly opinion exists that nutrition can play a vital role in the development and growth of hornworms. The current research analyzed this hypothesis using four food types for the purposes of comparison. The researchers exposed the hornworm larvae to tobacco, tomato, and radish plants, and to the solid food. After this, the researchers monitored the daily weight changes in larvae exposed to every type of nutrition, and made the conclusion that the most efficient food type for the hornworms was the solid food.
Concerning the plant food types, their effectiveness was highly doubted, while the tobacco plants in particular proved to even reduce the weight and functioning of hornworm larvae. This was supposed to be the result of greater maturity of tobacco plants and larger concentrations of nicotine in their leaves. After discussing these findings, the researchers suggested directions for further studies in the topic and analyzed the implications of the current research findings for the overall topic development.
Introduction
The issues surrounding the development of living forms on Earth have always been of crucial importance for human beings. Drawing from this, scholars take their time to investigate the conditions of development of this or that animal species, bird, or insect in laboratory environment to be able to project the results to actual environment settings. The current paper also focuses on the topic that presents crucial interest, i. e. the growth of tobacco hornworms under the conditions of feeding them by tobacco, tomato, and radish plants and solid food. Accordingly, the major purposes of this work include to study the process of hornworms’ growth in the laboratory conditions using the above mentioned feeding materials and to react to the null hypothesis that the solid food facilitates faster and more essential growth of hornworms in laboratory conditions.
Materials and Methods
Materials Used
The research process required the substantial numbers of Tobacco Hornworms to be delivered to the laboratory. Therefore, the first step in acquiring the necessary research materials was the order of the hornworms that were later delivered from two major locations, i. e. the Mulberry farms and the Carolina Biological Supply. Of course, the research required the plants and the solid food for the purposes of hornworm feeding.
Accordingly, the Brown University provided the tobacco plants grown in its greenhouse, while the Carolina Biological Supply helped the researchers with the seeds for tomato and radish plants that were further grown in a specially equipped greenhouse-trailer. Such an approach provided the researchers with the guarantee of objectivity and uniformity of data, as any results of the study could be attributed to hornworms’ reactions to various feeding sources, but not to the differences in those sources. The solid food for the experiment was developed directly by researchers.
The plants were cultivated using potting soil and the Shultz fertilizer, while their photoperiod was 12 hours, usually from 7a.m. to 7p.m. The process of plants growing was accompanied by replacement of some of them. In particular, tomato and radish plants were replaced once or twice a day, depending on the level of defoliation, while tobacco plants were not replaced at all. The latter fact was conditioned by the interest in potential effects of more mature tobacco plant leaves on tobacco hornworms, as Jackson et al. (2000, p. 15) argue that the mature tobacco leaves might not only facilitate the hornworm growth but also change their chemical structure and affect their functional capabilities and living cycle.
Methodology Implemented
The major methodological approach used during the experiment was focused on feeding the tobacco hornworms in two main ways: using the tobacco, tomato, and radish plants, and using the solid food. The contents of the latter included in particular the powder of Mulberry leaves, corn meal, agar, beet powder, and 1% of soy flour. After the two different types of nutrients for hornworms were prepared, the experiment entered its next stage, i. e. the development of aquaria in which the tobacco hornworms were later placed together with either solid food or tobacco, tomato, and radish plants. This stage of the experiment was divided into two weeks, with each week dealing with either solid food usage or feeding the tobacco hornworms with the above mentioned plants.
Week 1 was the time when the researchers designed aquaria to place four larvae of tobacco hornworms and the dose equaling 20gr of solid food. After being in the aquaria for specified periods of time, the hornworm larvae were subsequently transferred to the freezer (for the time of 48 hours) and then placed into the drying oven, where they were located during 24 hours at the temperature of 35oC. This process allowed the researchers to monitor the dynamics of weight change in hornworm larvae in both the wet and the dry states. Finally, this stage allowed calculating the conversion factor that equaled 0.149.
Week 2 included the procedures associated with two placing larvae in each of the aquaria provided with the specified quality of tobacco, tomato, and radish plants. Here, the plants were replaced similarly to the way they were replaced during their growing. During both weeks, hornworm larvae from both categories of aquaria were collected and weighted twice a day to get the average weight for the day and to include a certain day data into the comprehensive list of weight change dynamics.
Results
General Notions
The overall results of the experiment proved that the process of feeding of hornworm larvae brings more promising results when it is carried out through the use of solid food rather than tobacco, tomato, and radish plants. The main reason for such a consideration is the fact that the weight, or mass, change rates for hornworm larvae fed by solid food display almost no negative figures and their meanings are higher than the ones observed in the rates of mass change of larvae fed by the mentioned types of plants. As the results show, only the rates of growth provided by the tomato plant feeding can be compared in their efficiency to the ones represented by the rates of growth of larvae fed by solid food.
Daily Mass Change
One of the main factors to prove that solid food feeding proved to be the most effective one is the comprehensive analysis of the average meaning of mass change rates observed daily in larvae fed by solid food and by the mentioned plants:
Fig. 1 Weight change dynamics for larvae fed by solid food.
Thus, Figure 1 reflects the changes of weight in hornworm larvae during Week 1 when they were fed by the solid food. If compared to the weight changes in hornworm larvae fed by tobacco, tomato, and radish plants, the meanings from figure 1 reflect the greater effect of solid food on hornworm growth than the plant effects as presented in Figure 2
Fig. 2 Weight change dynamics for larvae fed by tobacco, tomato, and radish plants.
So, Figure 2 reflects the assumption that the solid food is more effective for the purpose of growth of hornworms. Although occasionally, the average meanings of the growth rates for larvae feed by plant are higher then those of larvae fed by solid food, the average effectiveness on the whole is higher, and ANOVA tests are used to illustrates this point.
ANOVA
On the whole, ANOVA tests are used to compare and analyze means of various t-tests carried out using two variables, while ANOVA itself usually implements three or more variables (Leopold and Layalle, 2006, p. 1318). However, in this research ANOVA is applied to every single type of food, and after this the joint ANOVA for the four is provided. So, the ANOVA results for the tomato plants are shown in Figure 3:
Fig. 3 ANOVA for tomato plants.
The means from Figure 3 show that tomato plants are also rather effective type of food for hornworm larvae feeding, and ANOVA analyses for tobacco and radish plants prove that those two types of food are less effective in increasing the larvae weight and facilitating their growth. So, Figure 4 represents the means of tobacco plants as researched during the reported study:
Fig. 4 ANOVA for tobacco plants.
So, one can see that such a vital component of ANOVA as the coefficient is much higher for tomato plants than for tobacco ones, although the P-value of the latter is obviously greater.
Fig. 5 ANOVA for radish plants.
Figure 5 proves that radish plants also have coefficients and P-values lower than tomato plants, and by far lower than solid food results. On the whole, from the above presented figures one can see that tomato plants display the greatest efficiency in hornworm larvae growth is contrasted against other plant food types used. However, Figure 6 proves that the solid food provides the best results as far as the values of its major parameters, like P-value and the coefficient outweigh the values of all the plant food types considered as a single whole:
Fig. 6 ANOVA for solid food.
Dry Weight Conversion
If the wet weight of hornworm larvae is converted into the dry weight using the conversion x factor at the value of 0.149, the figures again prove that the solid food in the best way to feed the larvae to facilitate their growth. Due to certain reasons, the hornworm larvae, even the ones that weighed less than others, start growing faster and become larger than others if they are fed by the solid food suggested for this research.
Figure 7 illustrates the comparative dry weight of the hornworm larvae before and after feeding them with tomato, tobacco, and radish plants, and solid food respectively:
Fig. 7 Compared dry weights of larvae before and after feeding.
So, Figure 7 reveals that solid food provided for the steady growth of larvae even if they weighed less than other larvae, while the ones fed by plant food types often displayed even the reduction of weight as a result of such feeding.
Scatter Plot and Linear Regression Lines
Obviously, a scatter plot of the relations between the values of plant types and solid food for the hornworm larvae will illustrate the dynamics of the larvae growth and the associations of this dynamics with the food types used. Figure 8 represents the comparative picture of linear regression lines placed into the comprehensive scatter plot. The latter contains the points of weight growth and reduction for all four food types, with tomato plants in red, tobacco in black, radish in blue, and solid food I green:
Discussion
Analysis of Results
A brief theoretical background should start the analysis of the obtained results. The point here is that scholars like Leopold and Layalle (2006) and Mechaber et al. (2002) have argued several years before the current research, that nutrition can seriously affect the existence, development, and functioning of insects on the whole and hornworms, or Manduca sextas, in particular. The word affect in this respect can have both positive and negative coloring as nutrition can either facilitate or stop and reduce the development of hornworm larvae (Leopold and Layalle, 2006, pp. 1317 – 1318; Mechaber et al., 2002, p. 3). The results of the current research prove this point rather specifically, as far as they show how one way of nutrition can enhance growth and how some other ways can reduce of stop it.
In particular, the results of the research allow confirming the null research hypothesis, according to which there is a direct connection between the hornworm larvae growth and their nutrition by the solid food. More specifically, the scatter plot of the dry weight meanings for the hornworm larvae fed by the four various food types proves that only in the larvae fed by the solid food considerable growth was observed. Three other nutrition types not only failed to facilitate growth, but obviously also conditions the reverse process. To visualize the comparison, let us see that the hornworm larvae fed by tobacco plants lost weight for almost 90%, while those fed by the solid food experienced approximately 100% weight increase (the mass of the larvae grew from 0.5 up to -0.4 and from 0 to 1.1 respectively).
Implications for the Topic
The implications of such findings for the whole topic of the development and growth of the hornworm larvae are rather considerable. First of all, the results obtained in the discussed research allow proving the research hypothesis and assuming that, at least for the studied sample of the hornworm larvae, the nutrition of these moths by the solid food is considerably more effective than feeding them with such plant types as tobacco, tomato, and radish plants. Accordingly, these findings allow the researchers to agree with Leopold and Layalle (2006, p. 1317), Hermsmeier (2001, p. 687), and Mechaber et al. (2002, p. 4) who also advocate the role of nutrition in the development and functioning of the hornworm larvae.
Further on, the researchers have managed to also support one of the minor ideas of the current study. As the tobacco plants were more mature and originated from sources other than the rest of plants, it was supposed that the hornworms fed by those tobacco plants would experience the negative consequences of the higher concentrations of nicotine in the tobacco plants’ leaves. The results of the research prove this point, also argued about by Jackson et al. (2000, p. 11), Baldwin (2001, p. 1451), and Kessler (2004, pp. 641 – 642), and allow stating that the use of ANOVA analyses and scatter plots for all the food types used during the experiment facilitated the successful confirmation of the research hypothesis.
Accordingly, the implications of the current research results for the whole topic of hornworms development include the additional experimental evidence to the already formulated ideas, the development of new aspects of the latter, and the provision of directions for further research works in this area.
Future Research Suggestions
In more detail, the suggestions for future research in the topic might have at least three major focus areas. First of all, scholars might want to go into more detail concerning the process of growth and development of the hornworm larvae on the whole, not making any specific emphasis on the issues of nutrition. Among the possible ideas to consider in this focus area, there are the proper conditions that would facilitate hornworm appearance and development as well as negative environments that would make their growth and functioning impossible even in spite of the proper nutrition.
The second possible focus area in the topic is the consideration of other nutrition alternatives for hornworms. In particular, future scholars might use the data of this research, as well as of previous ones, to consider some more plants or other nutrition strategies against the solid food to see if the latter is genuinely effective compared to all nutrition types or only in contrast to the tobacco, tomato, and radish plants. Finally, the third interesting focus area for future research is the study of conditions, at least theoretically, that would make the proper solid food nutrition insufficient and ineffective for hornworms’ growth.
Conclusion
Drawing from the above presented considerations, it is possible to conclude that the research, results of which are presented and discussed in this paper, has considerable scholarly and ecological importance. From the scholarly point of view, the discussed research is a well-documented paper in which the topic is properly introduced, the adequate methodology is selected, and research results are presented and analyzed in order to handle the research hypothesis and answer the research questions. Moreover, this paper meets the ideas of numerous prior scholars, which evidences that the current research is developed in a proper way.
As for the ecological value of this study, it is also obvious because the research copes with the task of defining the most efficient ways to feed and develop the populations of hornworms in cases of necessity. Finally, the current study suggests three directions for future research in the topic, which might also be beneficial for the ecology by their results.
Works Cited
Baldwin, Ian. “An Ecologically Motivated Analysis of Plant-Herbivore Interactions in Native Tobacco.” Plant Physiology 127 (2001): 1449 – 1458. Print.
Hermsmeier, David et al. “Molecular interactions between the specialist herbivore Manduca sexta and its natural host Nicotina attenuate.” Plant Physiology 125 (2001): 683 – 700. Print.
Jackson, Michael et al. “Survival and development of tobacco hornworm larvae on tobacco plants grown under elevated levels of ozone.” Journal of Chemical Ecology, 26, 1(2000): 1 – 19. Print.
Kessler, Andre. “Herbivore-induced plant vaccination. Part I. The orchestration of plant defenses in nature and their fitness consequences in the wild tobacco Nicotina attenuate.” Plant Journal 38 (2004): 639 – 649. Print.
Leopold, Pierre and Sophie Layalle. “Development Biology: Linking Nutrition and Tissue Growth.” Science 312. 5778 (2006): 1317-1318. Print.
Mechaber, William et al. “Behavioral responses of adult female tobacco hornworms, Manduca sexta, to hostplant volatiles change with age and mating status.” Journal of Insect Science 2.3 (2002): 1 – 5. Print.