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Sublethal Effect of Plant Lower Nitrogen Level on Development and Feeding Preference of the Beet Armyworm, Spodoptera e

Sublethal Effect of Plant Lower Nitrogen Level on Development and Feeding Preference of the Beet Armyworm, Spodoptera exigua (Lepidoptera: Noctuidae). Yigen Chen and John Ruberson Dept. of Entomology, UGA. Importance of N for insects.  Many h erbivorous insects select high N plants.

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Sublethal Effect of Plant Lower Nitrogen Level on Development and Feeding Preference of the Beet Armyworm, Spodoptera e

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  1. Sublethal Effect of Plant Lower Nitrogen Level on Development and Feeding Preference of the Beet Armyworm, Spodoptera exigua (Lepidoptera: Noctuidae) Yigen Chen and John RubersonDept. of Entomology, UGA

  2. Importance of N for insects Many herbivorous insects select high N plants Efficiency of conversion of ingested food (ECI) is low when feeding on low N diets N affects plant direct defense N affects herbivore mortality incurred through natural enemies – plant indirect defense

  3. Study system  Plant: Cotton (Gossypium hirsutum)  Beet armyworm (BAW), Spodoptera exigua

  4. Questions? How do plant biomass and nutritional quality change in response to N? Is development of BAW affected by host plant quality? Is lifetime feeding damage per caterpillar affected by host plant quality? Can BAW distinguish host plants with different nutritional quality?

  5. Materials and Methods  Cotton plants (var. FiberMax 989)  Grown with peat moss and top soil in flower pot, fertilized with chemical solution 4-5 times weekly; 100 ml each time  Plants had 4-5 mature leaves for experiments  Cotton plant growing regimes 42, 112, 196, and 280 ppm N  Beet armyworm from lab colony

  6. Materials and methods — Question 1 ----How do plant biomass and nutritional quality change in response to N  Percentage of total N of dried leaf blade  Petiole NO3-N  Biomass measurement - Plants oven-dried and weighed

  7. Results — Question 1 ----How do plant biomass and nutritional quality change in response to N

  8. Results — Question 1 ----How do plant biomass and nutritional quality change in response to N

  9. Results — Question 1 ----How do plant biomass and nutritional quality change in response to N

  10. Materials and methods — Question 2 ----Is development of BAW affected by host plant quality?  Bioassay with neonate BAW caterpillars in Petri dish with excised leaves  Bioassay with 3-d-old caterpillars in caged plants which allow intra-plant movement

  11. Results — Question 2 ----Is development of BAW affected by host plant quality?  Bioassay with neonate BAW

  12. Results — Question 2 ----Is development of BAW affected by host plant quality?  Bioassay allowing intra-plant movement Note:Other variables such as pupa weight, % caterpillars pupated, and sex ratio were not affected by N treatment.

  13. Materials and methods — Question 3 ----Is lifetime feeding damage per caterpillar affected by host plant quality? • 3-d-old caterpillar caged on leaves attached to live plants with different N contents • Bioassay starts with leaf node 1, 2, and so on upward •  Measure leaf tissue eaten on D2, D4, D7, and after pupation

  14. Results — Question 3 ----Is lifetime feeding damage per caterpillar affected by host plant quality?

  15. Results — Question 3 ----Is lifetime feeding damage per caterpillar affected by host plant quality?

  16. Materials and methods — Question 4 ----Can BAW distinguish host plants with different nutritional quality? • Eight 5-d-old caterpillars released in the center • Bioassay on 3rd leaf

  17. Results — Question 4 ----Can BAW distinguish host plants with different nutritional quality?

  18. Summary Lower N decreases cotton plant biomass and nutritional quality for BAW caterpillars Low N level of host plants delays BAW development Low N level of host plants tends to increase BAW caterpillar lifetime feeding damage BAW caterpillars feed preferentially on high N plants

  19. Significance ? Trade-offs between low and high N cotton plants: Low N decreases plant biomass and suitability for BAW, but the reduced suitability may be compensated for by increased feeding by herbivores But lower N may tend to increase plant indirect defense through natural enemies - BAW may move more on low N plants to locate more suitable food, which would expose them to greater mortality Natural enemies may be more effective because BAW feeding on low N plants have prolonged developmental time

  20. Acknowledgments We thank Melissa Thompson for maintenance of BAW colony The project was financially supported by GA Cotton Commission and Cotton Incorporated

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