plant preferences of heliothis virescens kira white, marple newtown high school
DESCRIPTION
Plant preferences of Heliothis virescens Kira White, Marple Newtown High School Dr. Mark Mescher , Dr. Consuelo De Moraes , Mr. Tom Bentley, Pennsylvania State University. Beginning of Feeding Choice experiment. H. Virescens being parasitized by Microplitis croceipes. Hypothesis: - PowerPoint PPT PresentationTRANSCRIPT
Plant preferences of Heliothis virescensKira White, Marple Newtown High School
Dr. Mark Mescher, Dr. Consuelo De Moraes, Mr. Tom Bentley, Pennsylvania State University
Hypothesis:1. If Heliothis virescens is given the choice between Nicotiana tabacum variety K326 and
Nicotiana noctiflora, then the Heliothis virescens will eat more of the Nicotiana tabacum variety K326.
2. If Heliothis virescens is given the choice between Nicotiana tabacum variety K326 and Nicotiana longiflora, then the Heliothis virescens will eat more of the Nicotiana tabacum variety K326.
3. If Heliothis virescens is given the choice between Nicotiana longiflora and Nicotiana noctiflora, then the Heliothis virescens will eat more of the Nicotiana longiflora.
4. If Heliothis virescens are given only Nicotiana noctiflora or Nicotiana longiflora, then the Heliothis virescens on the Nicotiana noctiflora will increase in weight more than the Heliothis virescens on the Nicotiana longiflora.
Methods and MaterialsFeeding Choice Bioassay
The Nicotiana tabacum variety K326, Nicotiana longiflora, and Nicotiana noctiflora used in the experiment were 10 weeks old. Second instar Heliothis virescens were used in the feeding choice bioassay. The bioassay lasted for 20 hours. For the bioassay, H. virescens were placed in separate discs with a diameter of 32 mm in a plastic container with 6 discs. In each disc, the H. virescens was given the choice between two 12 mm circles of different Nicotiana species leaves. There were three groups of six H. virescens each with one leaf disc of N. noctiflora and N. longiflora, N. noctiflora and N. tabacum variety K326, and N. longiflora and N. tabacum variety K326. To analyze the results, sigmascan was used to find the area of the leaf disc that remained and a paired t-test was used with these values.
No Choice Feeding Growth Bioassay
For the growth assay, H. virescens were weighted before and after the test. Six H. virescens each were given one leaf disc of either N. noctiflora or N. longiflora. The test lasted 72 hours, and every 24 hours the leaf discs were removed, analyzed, and replaced with fresh discs of the same species. To analyze the results of the growth bioassay, the percent difference of the weight of the H. virescens at the beginning and end of the test was used. A two sample t-test was used to see if the results were statistically significant.
9.150%
50.469%
N. tabacumN. noctiflora
13.775%
47.019%
N. longifloraN. noctiflora
23.313%
26.883%
N. tabacumN. longiflora
Results
Percentage of Leaf Disc Eaten by H. virescens
Mean (% change in mass)
Standard Deviation
N. noctiflora 0.054 0.391
N. longiflora -0.335 0.126
IntroductionIn previous research, it was found that when herbivores attack plants, it causes a change in the chemicals emitted by the plants.1 These chemicals, called herbivore-induced plant volatiles, are specific to the herbivore and allow parasitic insects to located their hosts from a distance.
A study in 1996 investigated the interactions between Cardiochiles nigriceps (a parasitic wasp), H. virescens (an herbivore), and many Nicotiana species (tobacco). Three species of tobacco were particularly interesting:2
1. N. tabacum variety K326 – large population of H. virescens, few C. nigriceps2. N. noctiflora – few H. virescens, large population of C. nigriceps3. N. longiflora – average number of H. virescens and C. nigriceps
Effects of Plant Chemistry4. Nicotiana species contain pyridine alkaloids which decrease growth in H.
virescens3
5. There are differences in the concentrations of these chemicals between species of Nicotiana and parts of the plants
References1DeMoraes, C. M.; Lewis, W. J.; Paré, P. W.; Alborn, H. T.; Tumlinson, J. H. Herbivore-infested plants selectively attract parasitoids. Nature, 393, 570-573 (1998).2Jackson, D. M.; Nottingham, S. F.; Schlotzhauer, W. S.; Horvat, R. J.; Sisson, V. A.; Stephenson, M. G.; Foard, T.; McPherson, R. M. Abundance of Cardiochiles nigriceps (Hymenoptera: Braconidae) on Nicotiana species (Solanaceae). Environmental Entomology, 25, 1248-1255 (1996).3Jackson, D. M.; Johnson A. W.; Stephenson, M. G. Survival and development of Heliothis virescens (Lepidoptera: Noctuidae) larvae on isogenic tobacco lines with different levels of alkaloids. J. Econ. Entomol., 95, 1294-1302 (2002).
AcknowledgementsPennsylvania Govenor’s School for Agricultural Science: for making this amazing experience possibleMr. Tom Bentley: for helping me with all of my problemsDr. Mark Mescher and Dr. Consuelo De Moraes: for the use of the entomology lab
Figure 1: N. tabacum variety K326 Figure 2: N. noctiflora Figure 3: N. longiflora
DiscussionFeeding Choice Assay
It was expected from previous studies that the H. virescens would prefer the N. tabacum to the N. longiflora and the N. noctiflora, and prefer N. longiflora to N. noctiflora. However,
1. H. virescens consumed a statistically significant percent more of the N. noctiflora than the N. tabacum (p=0.000) and the N. longiflora (p=0.011)
2. The difference in the amount of leaf disc consumed between the N. tabacum and the N. longiflora was not statistically significant (p=0.492)
No Choice Growth Assay
This test was a follow-up to the feeding choice assay. Since the results were unexpected, the purpose of this test was to determine a reason for the H. virescens preference of N. noctiflora
3. H. virescens on the N. noctiflora experienced a statistically significant greater percent weight gain (p=0.012)
4. However, during the experiment, it was expected that all of the H. virescens would gain weight, but the H. virescens on the N. longiflora lost an mean of 33.5% of their weight.
Conclusions
Feeding Choice Assay1. Possible explanation for the disproportionate numbers of H. virescens and C. nigriceps found in the 1996
study• H. virescens could have been on the N. noctiflora, which would have attracted the C.
Nigriceps• Once H. virescens are parasitized, they usually fall to the ground, so none
would have been found on the N. noctiflora• Once N. noctiflora is damaged, it changes its chemical composition, making it less appealing
to H. virescens• This experiment used leaf discs from undamaged leaves, which would not
have altered chemicals in response to attack by H. virescens
No Choice Growth Assay2. One reason for the preference of H. virescens for N. noctiflora as found in the feeding choice assay could
be that the H. virescens gain a greater percent of weight while feeding on the N. noctiflora as compared with the N. longiflora. Source of error:
• Leaf discs from undamaged plant• Leaf discs that dried out might be less attractive to H. virescens• On average, the H. virescens on the N. longiflora lost weight
Further Research3. Use leaf discs from Nicotiana species damaged by H. virescens4. Use leaves still connected to a plant to control the variable of change in plant chemistry resulting from
damage
H. Virescens being parasitized by Microplitis croceipes
Beginning of Feeding Choice experiment
Results of one feeding choice group