Low temperature triggers physiological and behavioral shifts in adult oriental armyworm, Mythimna separata

Migratory insects display diverse behavioral strategies in response to external environmental shifts, via energy allocation of migration-reproduction trade-offs. However, how migratory insects distribute energy between migration and reproduction as an adaptive strategy to confront temporary low temperatures remains unclear. Here, we used Mythimna separata, a migratory cereal crop pest, to explore the effects of low temperature on reproductive performance, behavior, and energy allocation. We found that the influence of low temperatures on reproduction was not absolutely negative, but instead depended on the intensity, duration, and age of exposure to low temperature. Exposure to 6°C for 24 h significantly accelerated the onset of oviposition and ovarian development, and increased the synchrony of egg-laying and lifetime fecundity in 1-day-old adults compared to the control, while female's flight capacity decreased significantly on the first and second day after moths were exposed to 6°C. Furthermore, the abdominal and total triglycerides levels of females decreased significantly from exposure to low temperature, but their thoracic triglyceride content was significantly higher than the control on the third and fourth day. These results indicated that low temperatures induced M. separata to reduce energy investment for the development of flight system. This resulted in the shifting of moths from being migrants to residents during the environmental sensitive period (first day post-emergence). This expands our understanding of the adaptive strategy employed by migratory insects to deal with low temperatures and aids in the management of this pest species in China.

Design, Synthesis and Biological Evaluation of Novel Thienylpyridyl- and Thioether-Containing Acetamides and Their Derivatives as Pesticidal Agents

Referring to the structural information of the “hit” compound A from the reported pharmacophore-based virtual screening, a series of novel thienylpyridyl- and thioether/sulfoxide/sulfone-containing acetamide derivatives have been designed and synthesized. The structures of new compounds were confirmed by 1H NMR, 13C NMR and HRMS. The single-crystal structure of A was firstly reported. All the new synthesized compounds were evaluated for insecticidal activities on Mythimna separata Walker and Plutella xylostella L. Through a step-by-step structural optimization, the high insecticidal agents, especially towards Plutella xylostella L., have been found, and thienylpyridyl- and sulfone/thioether-containing acetamides Iq, Io, Ib and A, which are comparable with the control insecticides cartap, triflumuron and chlorantraniliprole in the present study, can be used as novel lead structures for new insecticides innovation research. In addition, some of the compounds, e.g., A, Ih, Id, Io and Iq, also exhibited favourable fungicidal activities against Physalospora piricola, Rhizoctonia cerealis and Sclerotinia sclerotiorum and would provide useful guidance for the design and development of new fungicides.

Synthesis and Antifungal and Insecticidal Activities of Novel N-Phenylbenzamide Derivatives Bearing a Trifluoromethylpyrimidine Moiety

Seventeen novel N-phenylbenzamide derivatives bearing a trifluoromethylpyrimidine moiety were synthesized via four-step reactions. Their antifungal and insecticidal properties were evaluated. Antifungal test results demonstrated that some of the synthesized compounds showed better in vitro bioactivities against Phomopsis sp., Botryosphaeria dothidea (B. dothidea), and Botrytis cinerea (B. cinerea) at 50 μg/mL than pyrimethanil. Unfortunately, the synthesized compounds revealed lower insecticidal activities against Spodoptera frugiperda (S. frugiperda) and Mythimna separata (M. separata) at 500 μg/mL than chlorantraniliprole.

Flying males mediate oviposition and migration in female Mythimna separata (Lepidoptera: Noctuidae)

In recent decades, the oriental armyworm, Mythimna separata (Walker), has caused severe damage to staple grains in China. However, little is known about when M. separata begin their first migration and the role of males in reproduction and migration. Here, the migratory benefits and reproductive costs of flight frequency were examined in adults under laboratory conditions. We found that flying males had a positive effect on ovarian and reproductive development in females who flew for 1–2 nights by comparing two treatment groups (flying and nonflying male groups). Moreover, flying males decreased the flight capacity and flight propensity of females. In contrast, flight for more than two nights by males significantly inhibited ovarian and reproductive development in adult females. Compared with the controls (0 night), male flight for 1–2 nights significantly shortened the preoviposition period but significantly increased ovarian and reproductive development in females. However, male flight for more than three nights significantly inhibited female reproduction and flight capacity. These results indicate that M. separata begin their first migration within 2 days after emergence and fly for two nights. Prolonged flight times can result in significant reproductive costs. Females initiated their first migration earlier than males due to a stronger flight capacity. These observed findings will be useful for forecasting and monitoring population dynamics to prevent outbreaks of M. separata and reduce crop losses.