Objective To clarify the differences in feeding selectivity of Tuta absoluta between processing tomatoes and fresh tomatoes and its correlation with leaf nutrient contents, and to explore the variation of detoxification enzyme activities in larvae after feeding on different tomato types, so as to provide a theoretical basis for revealing the host adaptability of T. absoluta to different tomato varieties.
Method The leaf disc method was adopted to test the feeding preference of the 2nd-instar larvae of T. absoluta on two processing tomato varieties (H9888, XF36) and one fresh tomato variety (TF2H). We measured the water content, amino acid content and protein content of tomato leaves, and analyzed the correlation between larval feeding selectivity and leaf nutrients via Pearson correlation analysis. The activities of glutathione S-transferase (GST), carboxylesterase (CarE), mixed-function oxidase (MFO) and acetylcholinesterase (AChE) in larvae were determined at 12, 24 h and 48 h after feeding.
Result There were significant differences in feeding selectivity of T. absoluta among the three tomato varieties, and the preference order was fresh tomato TF2H > processing tomato H9888 > processing tomato XF36, which remained stable over time. Pearson correlation analysis showed that larval feeding selectivity was significantly negatively correlated with leaf protein content (P<0.01), and also significantly negatively correlated with amino acid content at 24 h and 48 h (P<0.05), with protein content showing the strongest negative correlation. After feeding on fresh tomato TF2H, the activities of the four detoxification enzymes in larvae generally decreased; after feeding on processing tomatoes H9888 and XF36, the activities of the four detoxification enzymes increased as a whole, and the enzyme activity increase amplitude of larvae fed on XF36 was higher than that on H9888.
Conclusion T. absoluta exhibits stronger feeding preference for fresh tomatoes than processing tomatoes. Its feeding selectivity is significantly negatively correlated with leaf protein and amino acid contents, and larvae tend to select tomato varieties with lower leaf protein content. After feeding on fresh tomato TF2H, larval detoxification enzyme activities change slightly and stay at a low level; after feeding on processing tomatoes, detoxification enzyme activities rise rapidly and reach higher levels, indicating that fresh tomatoes are more suitable for the feeding and metabolic demands of this pest. This study proves that T. absoluta has stronger adaptability to fresh tomatoes, but there still exists a potential risk of its shifting to damage processing tomatoes.
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