# Defense Responses of Cucumber and Cowpea to Frankliniella occidentalis Infestation Influence the Growth, Development, and Host Preferences of the Pest

## TL;DR

Cucumbers and cowpeas respond to thrips infestation by strengthening their cell walls, but thrips still prefer cowpeas even though they reproduce better on cucumbers.

## Contribution

The study reveals how plant defense mechanisms and thrips adaptability interact through molecular pathways and host selection.

## Key findings

- Cucumbers and cowpeas both attract F. occidentalis, but thrips reproduce better on cucumbers.
- Thrips infestation activates plant defense pathways like jasmonic acid and lignin biosynthesis.
- F. occidentalis adjusts its host preference and reproduction to overcome plant defenses.

## Abstract

Frankliniella occidentalis (Pergande) is a globally invasive pest that inflicts significant damage on economically important vegetable crops such as cucumbers (Cucumis sativus L.) and cowpeas (Vigna unguiculata L. Walp). To elucidate the interactions between host plants and F. occidentalis and to support the development of sustainable management strategies, this study evaluated the host selectivity and life history parameters of F. occidentalis living on these plant species to assess its adaptability. Transcriptome–metabolome profiles and associated metabolites were analyzed in healthy plants and in those infested by F. occidentalis for 48 h to characterize the defense responses of both host species. The results showed that both plant species are attractive to F. occidentalis, with a stronger preference observed for cowpeas. However, the reproductive output of F. occidentalis was significantly higher on cucumbers (16.99 ± 0.43 eggs/female) than on cowpeas (12.00 ± 0.38 eggs/female) plants, indicating a mismatch between host preference and performance. Feeding by F. occidentalis strongly induced the brassinolide and jasmonic acid signaling pathways, activated the phenylpropanoid metabolic pathway, increased the accumulation of the lignin precursor sinapyl alcohol, and promoted lignin biosynthesis, thereby enhancing cell wall rigidity as a physical defense barrier. These findings demonstrate that cucumbers and cowpeas coordinately regulate lignin synthesis through hormone–metabolism crosstalk as a defensive strategy against thrips attack. In response, F. occidentalis adjusts its host selection and reproductive investment to overcome plant defenses, reflecting an adaptive counter-strategy in host–herbivore interactions. This study provides new insights into the molecular mechanisms underlying plant–thrips interactions and supports the development of environmentally friendly pest control approaches.