Diapause Induced by Temperature and Photoperiod Affects Fatty Acid Compositions and Cold Tolerance of Phthorimaea Operculella (Lepidoptera: Gelechiidae)

Photoperiodism of Diapause Induction in the Silkworm, Bombyx mori

The silkworm Bombyx mori exhibits a photoperiodic response (PR) for embryonic diapause induction. This article provides a comprehensive review of literature on the silkworm PR, starting from early works on population to recent studies uncovering the molecular mechanism. Makita Kogure (1933) conducted extensive research on the PR, presenting a pioneering paper on insect photoperiodism. In the 1970s and 80s, artificial diets were developed, and the influence of nutrition on PR was well documented. The photoperiodic photoreceptor has been investigated from organ to molecular level in the silkworm. Culture experiments demonstrated that the photoperiodic induction can be programmed in an isolated brain (Br)-subesophageal ganglion (SG) complex with corpora cardiaca (CC)-corpora allata (CA). The requirement of dietary vitamin A for PR suggests the involvement of opsin pigment in the photoperiodic reception, and a cDNA encoding an opsin (Boceropsin) was cloned from the brain. The effector system concerning the production and secretion of diapause hormone (DH) has also been extensively investigated in the silkworm. DH is produced in a pair of posterior cells of SG, transported to CC by nervi corporis cardiaci, and ultimately released into the hemolymph. Possible involvement of GABAergic and corazonin (Crz) signal pathways was suggested in the control of DH secretion. Knockout (KO) experiments of GABA transporter (GAT) and circadian clock genes demonstrated that GAT plays a crucial role in PR through circadian control. A model outlining the PR mechanism, from maternal photoperiodic light reception to DH secretion, has been proposed.

The evolutionary ecology of fatty-acid variation: Implications for consumer adaptation and diversification

The nutritional diversity of resources can affect the adaptive evolution of consumer metabolism and consumer diversification. The omega-3 long-chain polyunsaturated fatty acids eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3) have a high potential to affect consumer fitness, through their widespread effects on reproduction, growth and survival. However, few studies consider the evolution of fatty acid metabolism within an ecological context. In this review, we first document the extensive diversity in both primary producer and consumer fatty acid distributions amongst major ecosystems, between habitats and amongst species within habitats. We highlight some of the key nutritional contrasts that can shape behavioural and/or metabolic adaptation in consumers, discussing how consumers can evolve in response to the spatial, seasonal and community-level variation of resource quality. We propose a hierarchical trait-based approach for studying the evolution of consumers' metabolic networks and review the evolutionary genetic mechanisms underpinning consumer adaptation to EPA and DHA distributions. In doing so, we consider how the metabolic traits of consumers are hierarchically structured, from cell membrane function to maternal investment, and have strongly environment-dependent expression. Finally, we conclude with an outlook on how studying the metabolic adaptation of consumers within the context of nutritional landscapes can open up new opportunities for understanding evolutionary diversification.

The Effect of Temperature and Photoperiod on Diapause Induction in Pupae of Scrobipalpa ocellatella (Lepidoptera: Gelechiidae)

Scrobipalpa ocellatella (Boyd) (Lepidoptera: Gelechiidae) is one of the most important pests of sugar beet that causes quantitative and qualitative yield loss in the late summer. To locate the position for diapause induction, combinations of constant temperatures at 15, 18, 20, and 25°C and day lengths of 8, 10, 12, 14, 16, and 24 h were studied from egg to adult emergence. The incidence of diapause peaked at 15 and 18°C, with the day lengths of 12 and 11 h, whereas low temperatures did not improve the effects of short photoperiods (day lengths of 8 and 10 h) in diapause induction. The results showed that the critical day length for diapause induction was 12.8 h at overall 15 and 18°C. It was observed that the third instar larvae were the most sensitive stage to the inductive photoperiod (12:12 [L:D] h). The non-24-h light-dark experiment showed that the nigh length is more important than the day lengths measurement. In a set of 24-h light-dark cycles at 2:12 (L:D) h, a 1-h light pulse declined diapause induction markedly 1 h after scotophase. Field monitoring of the S. ocellatella for 2 yr (2015 and 2016) showed that the 50% of larvae enter winter pupal diapause in early September and this proportion increases in response to a decrease in the day lengths and temperature. From this study, it was concluded that low temperature acts in conjunction with short-day photoperiod in diapause induction of S. ocellatella.