Evaluation of the heat tolerance and synergistic mechanism of phosphine fumigation combined with heat treatment on fruit fly

Yisha Ma

Fruit flies (Tephritidae) are highly destructive agricultural pests in fruits, vegetables and flowers with heat treatment being common for its control in internationally traded produce. However, the potential adverse effects of heat on produce quality limit its broader application. In this study, phosphine fumigation combined with heat treatment (P+H), as well as phosphine with controlled atmosphere temperature treatment (P+CATT), demonstrated significant synergistic effects in controlling fruit flies. First, the heat tolerance of three fruit flies (Bactrocera correcta, B. dorsalis, and B. cucurbitae) was systematically evaluated, the results indicated that B. correcta showed the highest thermal tolerance, followed by B. dorsalis, while B. cucurbitae was the most sensitive, with eggs being more tolerant than third-instar larvae. According to these findings, four heat treatment methods—heat treatment (H), controlled atmosphere temperature treatment (CATT), phosphine fumigation followed by heat treatment (P+H), and phosphine fumigation followed by controlled atmosphere temperature treatment (P+CATT)—were compared. Treatment efficacy was highest with P+CATT, followed by P+H, CATT, and lowest with heat alone, demonstrating the synergistic effect of combined treatments. Further molecular investigations revealed that P+H treatment modulated HSP gene expression through the MAPK/ERK signaling pathway and HSF-1 dephosphorylation, suppressing heat-induced HSP responses. Energy allocation constraints may further restrict HSP synthesis, leading to increased HSP expression under P+H treatment, albeit at lower levels than in heat treatment alone, reducing insect heat tolerance. Finally, application studies on the mortality of B. dorsalis carried by dragon fruits and the fruits postharvest quality demonstrated that P+H treatment significantly reduced the required heat exposure time while enhancing B. dorsalis mortality. Probit analysis showed that the time needed to reach 50 % mortality was reduced to 72.5 % for eggs and 66.5 % for third-instar larvae compared to heat treatment alone. Additionally, Fruit soluble solids content and titratable acidity have no adverse affected by the P+H treatment, although respiration was slightly inhibited. Our study reveals a synergistic effect of phosphine when combined with heat treatment, including heat treatment (H) and Controlled Atmosphere Temperature Treatment (CATT). This synergism not only improves treatment efficacy but also sheds light on the underlying molecular mechanisms, providing a novel strategy to improve quarantine treatments, especially for heat-sensitive fruits.

Evaluation of the heat tolerance and synergistic mechanism of phosphine fumigation combined with heat treatment on fruit fly

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