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