# Evaluating the Influence of Trap Type and Crop Phenological Stage on Insect Population Diversity in Mediterranean Open-Field Tomatoes

## TL;DR

This study shows that using yellow pan traps and considering crop growth stages helps better monitor insect diversity in Mediterranean tomato fields.

## Contribution

The study introduces a multi-trap sampling strategy for accurately capturing hymenopteran insect diversity in tomato agroecosystems.

## Key findings

- Yellow pan traps captured the highest insect diversity compared to other trap types.
- Insect diversity was highest at the start of planting and during flowering, declining sharply at harvest.
- Pollinators like Apidae and parasitoids like Braconidae were associated with specific crop stages.

## Abstract

We evaluated how different trap types and phenological stages of open-field tomato crops affect the diversity of insects belonging to the order Hymenoptera in southern Mediterranean conditions. We found that colored pan traps, especially the yellow ones, captured the highest diversity of insects, while Malaise traps captured fewer but different insect groups. Insect diversity was highest at the beginning of the crop cycle and during flowering and declined sharply at harvest. Pollinating insects belonging to the families Apidae, Halictidae, and Megachilidae were the most abundant during flowering, whereas parasitoid wasps belonging to the families Braconidae and Eulophidae were more commonly found during the fruit development stage. These results show that using a combination of trap types and considering the timing of crop development stage are essential to accurately monitor hymenopteran beneficial insect communities and to improve sustainable management of tomato agroecosystems.

The relationship between insect diversity and crop production has been of continuous scientific interest. Understanding insect community dynamics using various sampling and monitoring methods at different crop phenology stages is crucial for enhancing pest management and ecosystem service functioning. The present study assessed the influence of four trap types (Blue, Yellow, White, and Malaise) applied at four tomato developmental stages (start of planting, flowering, flowering fruit development and harvest) on insect diversity in northeastern Tunisian open-field conditions. A total of 1771 insect individuals belonging to seven orders and 31 families were trapped, with the order Hymenoptera being the most common in the sampled plots, which was represented by 25 families. Trap type exerted a strong effect on both abundance and alpha diversity parameters. Yellow pan traps showed the highest diversity, with family richness (S) ranging from 1 to 16, Shannon diversity (H) reaching 2.54, Simpson (Is) diversity ranging from 0.72 to 0.90 and Pielou’s evenness (J) ranging from 0.83 to 0.98. Blue and white traps displayed intermediate diversity (Blue: S = 6 and H = 1.7; White: S = 7 and H = 1.6), while Malaise traps captured the least diverse assemblages (S = 4, H = 1.2 and Is = 0.65). These differences were highly significant (p < 0.05). Phenological stage significantly structured Hymenoptera diversity. Richness peaked at the start of planting (S = 1–16 and H up to 2.54) and declined sharply at harvest (S = 1–6). Pollinator families (Apidae, Halictidae, Megachilidae) were the most abundant during flowering, whereas parasitoid families (Braconidae, Eulophidae) dominated during the fruit development stage. Beta diversity analyses (NMDS, stress = 0.25) and PERMANOVA showed that trap type and phenological stage jointly explained 15.5% of the variation in community composition (R2 = 0.155, p = 0.014). Although a strong taxonomic overlap among traps was observed, Indicator Value analysis revealed significant trap-specific associations, including the family Andrenidae with Blue traps and the family Scoliidae with White and Yellow traps. Overall, the results of the present study demonstrate that both trap type and crop phenology significantly influence insect population diversity. A multi-trap sampling strategy combining colored pan traps and Malaise traps could be recommended to accurately characterize insect communities and associated ecosystem services in Mediterranean open-field tomato systems.