Exploiting diapause and cold tolerance to enhance the use of the green lacewing Chrysopa formosa for biological control

Abstract

Knowledge of environmental regulation of diapause in the green lacewing Chrysopa formosa, an important polyphagous predator against various pests, is essential for understanding seasonal adaptations of insects and for increasing the shelf-life and shipment of chrysopids used in biological control programs. In the present study, we identified environmental factors responsible for induction and termination of diapause and cold tolerance in this chrysopid. C. formosa exhibits a facultative, prepupal diapause within its cocoon. The free-living third instar larva is the stage most sensitive to photoperiodic stimuli. Photoperiod is the major factor governing the induction of prepupal diapause, and temperature exerts a modulating effect. Photoperiodic response curves for C. formosa showed a typical long day response over a wide range of temperatures. Critical daylength for diapause induction was estimated to be 14.3 h at 20 °C, with a shift towards short daylengths at higher temperatures. The diapause response was maximal with a short daylength of 8L: 16D at 18 °C or 20 °C, and no diapause was induced under 16L: 8D at any temperature examined. Chilling temperature had a pronounced effect on the completion of diapause termination and post-diapause development. A chilling period of 60 days or more at 5 °C was sufficient to terminate diapause in most prepupae. An increase of chilling exposure duration synchronized post-diapause development and adult emergence. What was particularly attractive is that diapausing chrysopids could be stored at 5 °C as long as 300 days with high survival and short adult emergence time. The developmental period prior to diapause was extended significantly for diapause-destined chrysopids. Prepupal diapause in C. formosa distinctly enhanced the cold tolerance. These results suggest mechanisms that could be exploited to improve shelf-life and long distance shipment of chrysopids for release in biological control program.