Flight and Reproduction Variations of Rice Leaf Roller, Cnaphalocrocis medinalis in Response to Different Rearing Temperatures

Reference Genes for Expression Analysis Using RT-qPCR in Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

Cnaphalocrocis medinalis is a destructive migratory rice pest. Although many studies have investigated its behavioral and physiological responses to environmental changes and migration-inducing factors, little is known about its molecular mechanisms. This study was conducted to select suitable RT-qPCR reference genes to facilitate future gene expression studies. Here, thirteen candidate housekeeping genes (EF1α, AK, EF1β, GAPDH, PGK, RPL13, RPL18, RPS3, 18S rRNA, TBP1, TBP2, ACT, and UCCR) were selected to evaluate their stabilities under different conditions using the ∆CT method; the geNorm, NormFinder, BestKeeper algorithms; and the online tool RefFinder. The results showed that the most stable reference genes were EF1β, PGK, and RPL18, related to developmental stages; RPS3 and RPL18 in larval tissues; EF1β and PGK in larvae feeding on different rice varieties; EF1α, EF1β, and PGK in larvae temperature treatments; PGK and RPL13, related to different adult ages; PGK, EF1α, and ACT, related to adult nutritional conditions; RPL18 and PGK, related to adult mating status; and, RPS3 and PGK, related to different adult take-off characteristics. Our results reveal reference genes that apply to various experimental conditions and will greatly improve the reliability of RT-qPCR analysis for the further study of gene function in this pest.

Function of Vitellogenin receptor gene in reproductive regulation of Zeugodacus cucurbitae (Coquillett) after short-term high-temperature treatment

Climate change has increased the frequency of extreme heat events. Zeugodacus cucurbitae (Coquillett) is an important tropical pest that typically changes its reproductive strategies in response to extremely high temperatures. Newly emerged adults of three consecutive generations (F₁, F₂, and F₃) of Z. cucurbitae (Coquillett) were exposed to 25°C, 33°C, 37°C, 41°C, and 45°C treatments for 1 h to clarify the effects of short-term high temperatures on its reproduction. The influence of these temperatures on reproduction was evaluated using indicators, such as egg number. Newly emerged adults were exposed to 25°C and 45°C treatments for 1 h, and the expression of Vitellogenin receptor (VgR) gene in females was interfered with siRNA, and silencing efficiency of RNAi was evaluated. Results showed that short-term high temperatures, except for F₁ treated at 45°C for 1 h to stimulate oviposition, exert a general adverse effect on the reproduction of Z. cucurbitae (Coquillett). All F₃ died after the 45°C treatment for 1 h. Silencing of the VgR gene resulted in the significant downregulation of VgR gene expression at both 24 and 72 h. The egg number, oviposition days, and hatchability of eggs were significantly lower than those of other treatment groups after interference, and the inhibition effect of egg number was the most evident, with a decrease of 88.4% and 95.2% at 25°C and 45°C, respectively, compared with that of the Control Check (CK). Ovarian development speed and diameter were also significantly lower than those of other treatment groups after the interference. The results of this study can provide a theoretical reference for the integrated control of Z. cucurbitae (Coquillett) during high-temperature seasons.

Larval Crowding Did Not Enhance Adult Migration Propensity in Spodoptera frugiperda

Simple Summary

The fall armyworm, Spodoptera frugiperda (J. E. Smith), is a typical invasive migratory pest with a strong reproductive capacity, which has caused serious damage to crops. Larvae of S. frugiperda exhibit high levels of cannibalism associated with larval crowding. However, the response of S. frugiperda adults to such stress remains unclear. In this study, we investigated the effects of larval density on flight and reproductive parameters of S. frugiperda adults. We found that S. frugiperda reared under high-larval density conditions exhibited lower pupal and body weights, weaker flight and reproductive capacities than those reared as solitary larvae. This result was different from that of many migratory insects, where larval crowding enhanced migratory propensity of subsequent adults. In contrast, high-larval density conditions did not increase adult migration propensity in S. frugiperda. These findings enhance our understanding of migratory and reproductive behaviors of S. frugiperda in response to larval density.

Abstract

Reproduction and flight are two major adaptive strategies to cope with environmental stress in migratory insects. However, research on density-mediated flight and reproduction in the global migratory agricultural pest Spodoptera frugiperda is lacking. In this study, flight and reproductive performances in response to larval crowding were investigated in S. frugiperda. We found that larval crowding significantly reduced the pupal and body weights of S. frugiperda. Adults reared under the highest density of 30 larvae/jar had the minimum wing expansion, which was significantly smaller than that of larvae reared under solitary conditions. Larval crowding also significantly increased the pre-oviposition period (POP) and period of first oviposition (PFO) but decreased the lifetime fecundity, flight duration and flight distance. Our results showed that S. frugiperda reared under solitary conditions exhibited higher pupal and body weights and stronger reproductive and flight capacities than those reared under high-density conditions. Larval crowding did not enhance the migration propensity in S. frugiperda adults. In conclusion, larval crowding may not be a major factor affecting FAW migration due to high levels of cannibalism. These findings provide new insights into the population dynamics of S. frugiperda under larval crowding conditions.

Effects of Juvenile Hormone Analog and Days after Emergence on the Reproduction of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae) Populations

Simple Summary

Flight and reproduction are two major life history traits for coping with changing environments in migratory insects. The phenomenon of oogenesis-flight syndrome (namely, the trade-off between migration and reproduction) is regulated by juvenile hormone (JH). The oriental armyworm, Mythimna separata (Walker), is an important migratory agricultural pest with strong reproductive capacity. Previous studies have focused on discussions about the effects of JH on M. separata migrants, but little has been known about the potential influences on the residents until now. In this study, the effects of juvenile hormone treatment and age (namely, days after adult emergence) on both migrants and residents of M. separata have been studied. Our results showed that the effects of JH analog (JHA) treatment on reproduction depended on adult age of exposure to JHA and populations. The first two days and only the first day after adult emergence were the sensitive period for the exposure of residents and migrants to JHA on ovarian and reproductive development, respectively.

Abstract

Mythimna separata (Walker) is a main cereal crop pest that causes extensive damage to the world grain production. The effects of juvenile hormone on M. separata populations remain poorly understood. Here, we explored how JH analog (JHA) affected reproductive traits of both migrant and resident populations in this pest. Our results showed that the influence of JHA treatment on reproduction depended on adult age (days after emergence) of exposure to JHA and populations. Exposure of M. separata residents to JHA (methoprene) on day 1 and day 2 after adult emergence significantly shortened the pre-oviposition period, but increased the lifetime fecundity, mating frequency and grade of ovarian development compared to the controls. However, M. separata migrants exposed to JHA only on day 1 facilitated their reproduction, resulting in a reduction in the pre-oviposition period but an increase in lifetime fecundity, mating frequency and grade of ovarian development. In addition, exposure to JHA from day 2 to day 4 did not significantly affect the ovarian and reproductive development in both migrant and resident populations. These results indicated that the first two days after adult emergence were the sensitive period for residents. In contrast, only the first day after adult emergence was the sensitive stage for migrants. Our findings will contribute to a better understanding of JHA function on M. separata populations.