Developmental disruption and midgut histopathology induced by β-isocostic acid in Aedes aegypti and Culex quinquefasciatus (Diptera: Culicidae)

Abstract

Background

Mosquito-borne diseases transmitted by Aedes aegypti and Culex quinquefasciatus pose major public health challenges worldwide. The emergence of resistance to synthetic insecticides, along with concerns about their ecological and health impacts, highlights the urgent need for novel, eco-friendly alternatives. This study investigates the larvicidal and growth-disrupting effects of β-isocostic acid, a sesquiterpene isolated from Sphaeranthus indicus, while considering its relevance for non-target safety and integrated vector control.

Methods

Larvae of Ae. aegypti and Cx. quinquefasciatus were exposed to β-isocostic acid at concentrations of 0.5, 1.0, and 1.5 mg/L. Developmental parameters—including larval, pupal, and adult durations were monitored. Growth index was calculated to assess developmental progression. Histopathological analysis of third-instar larvae was performed using hematoxylin-eosin staining to examine midgut alterations. Emergence quality and behavioural abnormalities in adults were also recorded.

Results

β-Isocostic acid significantly delayed larval and pupal development in both mosquito species. At 0.5 mg/L, Ae. aegypti larvae developed in 8.4 ± 1.0 days versus 6.0 ± 0.0 days in controls, while Cx. quinquefasciatus larvae required 7.5 ± 1.0 days compared to 6.2 ± 0.2 days. Growth index values confirmed reduced developmental rates. Histopathological changes included epithelial vacuolization, disruption of microvilli, and peritrophic membrane rupture. Deformities such as crumpled wings and sluggish behaviour were observed in emerging adults, indicating compromised viability.

Conclusion

β-Isocostic acid exerts potent, multi-stage developmental disruption in mosquito vectors through growth retardation and midgut damage. These findings support its potential as a botanical larvicide; however, further studies are warranted to evaluate non-target toxicity and feasibility for use in sustainable mosquito control strategies.