Introduction of a cold sensitivity‐conferring mutation into the RTA‐Bddsx hybrid system of Bactrocera dorsalis for establishment of a thermally controllable homozygous line

BACKGROUND For efficient control of the economically important fruit pest Bactrocera dorsalis , a hybrid system combining ricin toxicity and sex‐related alternative splicing of the doublesex gene has been developed. This system exhibits the expected female‐specific lethal effect; however, the transgenic females do not survive, making it difficult to raise stable homozygous lines. Since modification of ricin toxin A chain (RTA) through a single‐residue change (Gly 212 > Arg 212 ) leads to cold‐sensitive posttranslational repression of its toxicity, we utilized this unique property to obtain RTA‐Bddsx females that survive at low temperature for line maintenance. RESULTS In transient expression experiments using embryonic injection, two groups treated with RTAcs‐derived DNA (LERQcs and RTAcs) exhibited temperature‐dependent effects. The toxicity was higher at 29 °C than at 18 °C. The proportion of males was close to 50% at 18 °C in all the tested groups except LERQcs‐treated flies, which exhibited a high proportion of males (over 70%) at 29 °C. The results indicate the cold‐sensitive responses of RTA and further suggest a female‐specific lethal effect. Subsequently, 14 putative RTAcs‐Bddsx transgenic Ds‐Red + G 1 males were identified, and female‐specific lethal effects were observed in Ds‐Red + G 2 and G 3 lines under cultivation at 29 °C but not at 18 °C. The male ratio can be increased to up to 95% in G 3 line 001, indicating that RTAcs functions well in B. dorsalis . CONCLUSION The improved RTAcs‐Bddsx system with conditional toxicity represents a novel and promising step toward the practical control of B. dorsalis . © 2021 Society of Chemical Industry.