A Generalist Feeding on Brassicaceae: It Does Not Get Any Better with Selection

Area of Science:

• Plant-insect interactions
• Chemical ecology
• Insect toxicology

Background:

• Brassicaceae plants produce toxic isothiocyanates from glucosinolates for defense against herbivores.
• Lepidopteran insects, including specialists and generalists, frequently feed on Brassica plants.
• Helicoverpa armigera, a polyphagous moth, is a noted pest on some Brassicas.

Purpose of the Study:

• To investigate the role of artificial selection in enhancing Helicoverpa armigera performance on Brassicas.
• To determine if improved performance contributes to the pest status of H. armigera on Brassica crops.
• To compare H. armigera performance on different Brassica species (cabbage and kale).

Main Methods:

• Artificial selection was applied to Helicoverpa armigera for 2, 21, and 29 generations to improve performance on Brassicas.
• Larval growth rate, development time, and pupal weight were measured.
• Behavioral assays were conducted after 50 generations of selection.
• Performance was compared between selected and parental strains on cabbage, kale, and an artificial diet.

Main Results:

• No significant differences in larval growth rate, development time, or pupal weight were observed between parental and selected H. armigera strains after multiple generations of selection.
• Behavioral assays also showed no differences between strains after 50 generations.
• Helicoverpa armigera exhibited better performance on kale than on cabbage, though both were comparable to other crop hosts where the species is a major pest.

Conclusions:

• Artificial selection is not a primary driver for the pest status of Helicoverpa armigera on Brassica crops.
• Plant quality, specifically differences between Brassica species like kale and cabbage, significantly influences herbivore performance.
• Factors beyond direct performance enhancement likely contribute to the "pest" status of H. armigera.