Effects of larval food shortage on diapause induction and adult traits in Taiwanese Monochamus alternatus alternatus

To confirm the facultative diapause of Monochamus alternatus alternatus Hope (Coleoptera: Cerambycidae) and to determine the relationships between available larval food resources, diapause, and adult traits, newly hatched larvae were inoculated singly on 98 Pinus densiflora Siebold & Zuccarini (Pinaceae) bolts and reared at 25 °C, 100% r.h., and L16:D8. Fifty adults emerged from them, between 70 and 126 days after larval inoculation. The remaining 48 bolts that did not produce adults were divided into two groups. One group was transferred to 10 °C, 100% r.h., and L8:D16, and returned 140–154 days later to the original conditions, resulting in adult emergence. The other group was maintained under the original conditions for a mean of 358 days. These bolts did not produce adults. Dissection revealed that development was arrested at final instar in pine bolts. The larvae developed into adults after being exposed to 10 °C, 100% r.h., and L8:D16 for 146 days. Consequently, this species has facultative diapause. Diapause incidence was estimated to be 0.42. Non‐linear model and one‐way ANOVA showed a positive correlation between adult body size and available food resources under conditions of food shortage, and no effects of diapause or available food resources on the ovariole number, respectively. When larvae were inoculated on 28 pine branch sections, the results were similar to those obtained from pine bolts and led to estimation of a low diapause incidence of 0.045. The combined data showed the inhibitory effect of food shortage on diapause induction. Diapause of M. a. alternatus, especially reduced diapause induction in response to environmental deterioration (food shortage), is discussed in relation to risk‐spreading.