Specialist/generalist divergence: phylogenetic constraints on the correlation between allelochemical tolerance spectra and host ranges of herbivorous insects

Authors: DENG, ZHONGYUAN - Zhengzhou University; FANG, LIYING - Zhengzhou University; CHENG, LAN - Zhengzhou University; YANG, LIHONG - Chinese Academy Of Agricultural Sciences; ZONG, RUYI - Zhengzhou University; DING, QIAN - Zhengzhou University; WANG, LIXIANG - Zhengzhou University; Ni, Xinzhi; LI, XIANCHUN - University Of Arizona

Submitted to: Journal of Pest Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2025
Publication Date: 1/15/2026
Citation: Deng, Z., Fang, L., Cheng, L., Yang, L., Zong, R., Ding, Q., Wang, L., Ni, X., Li, X. 2026. Specialist/generalist divergence: phylogenetic constraints on the correlation between allelochemical tolerance spectra and host ranges of herbivorous insects. Journal of Pest Science. 99:10. https://doi.org/10.1007/s10340-025-02005-x.
DOI: https://doi.org/10.1007/s10340-025-02005-x

Interpretive Summary: Plant-feeding insects can be categorized as either generalists that feed on a wide range of host plants or specialists that feed on a limited group of host plants. The current study uses a specialist insect oriental tobacco budworm, and two generalists, old-world cotton bollworm and fall armyworm to conduct three unique comparisons of allelochemical tolerance profiles: 1) within-genus specialist / generalist (oriental tobacco budworm / old world bollworm) comparison; 2) within-family but across genus specialist / generalist (oriental tobacco budworm / fall armyworm) comparison; and 3) within-family but across genus generalist / generalist (old world bollworm / fall armyworm) comparison. The newly-hatched larvae of the three insect species were fed with 12 plant allelochemicals that are naturally encountered by the two generalists in their host plants. The results showed that the oriental tobacco budworm (a specialist) was more tolerant only to nicotine found in its favored host but less tolerant to other allelochemicals such as coumarin, capsaicin, quercetin, gossypol, rutin, xanthotoxin and flavone than its within-genus generalist, the old-world bollworm. At the same time, within-family but across genus comparisons found that the specialist (the oriental tobacco budworm), like its within-genus generalist (the old-world bollworm), was more tolerant to coumarin, I3C, capsaicin, 2-tridecanone, gossypol, xanthotoxin, nicotine and flavone, but less tolerant only to quercetin, chlorogenic acid and rutin than the across genus generalist, the fall armyworm. These results illustrate that the expected specialist/generalist divergence in allelochemical tolerance profiles only apply to corresponding species within a pest genus. The work provides critical basic information for developing strategies to simultaneously manage both generalist and specialist pests on a given crop.

Technical Abstract: Specialist insect herbivores are projected to be better adapted to a few allelochemicals in their specialized host plants than their generalist counterparts, which is at the expense of low tolerance to a broad range of other allelochemicals. It is unclear whether specialist / generalist differences in allelochemical tolerance spectrum are universally true or phylogenetically constrained. Thus, we used diet incorporation to test the tolerance spectrum of the neonate larvae of one specialist (Helicoverpa assulta) and two generalists (H. armigera, Spodoptera frugiperda) to 12 plant allelochemicals, including coumarin, indole-3-carbinol (I3C), capsaicin, quercetin, ferulic acid, 2-tridecanone, gossypol, chlorogenic acid, rutin, xanthotoxin, nicotine and flavone. Within-genus comparison found that, generalist H. armigera and the Solanaceae specialist H. assulta were equally tolerant to I3C, 2-tridecanone, chlorogenic acid and ferulic acid. But H. assulta was less tolerant to coumarin, capsaicin, quercetin, gossypol, rutin, xanthotoxin and flavone, and more tolerant only to nicotine found in its specialized host tobacco than H. armigera. In stark contrast, within-family but across genus comparisons showed that the Solanaceae specialist H. assulta and generalist H. armigera had the same level of tolerance to ferulic acid when compared with the across genus generalist S. frugiperda. The two Helicoverpa species were more tolerant to coumarin, I3C, capsaicin, 2-tridecanone, gossypol, xanthotoxin, nicotine and flavone, but less tolerant only to quercetin, chlorogenic acid and rutin than the across genus generalist S. frugiperda. The current study demonstrated that the predicted specialist/generalist divergence in allelochemical tolerance profiles only apply to corresponding pest species within a genus.