Effects of larval density and food stress on life‐history traits of Cnaphalocrocis medinalis (Lepidoptera: Pyralidae)

Abstract

High population density and nutrition restriction can lead to phase variation in morphology and development, and subsequently induce changes in the reaction norms of adult flight in migrant insects. However, response of migratory propensity to such stress in Endopterygote insects, especially in several species of Lepidoptera, remains unclear. In this study, larval and adult developmental responses to crowding and food stress were investigated in the migratory moth, Cnaphalocrocis medinalis (Guenée). A high larval rearing density significantly reduced pupal mass, survival rate and female fecundity. Larvae developed rapidly under crowding conditions, and time to pupation was 2 days earlier than individuals reared alone. By contrast, short‐term starvation and associated compensatory growth prolonged larval duration by 3–4 days and pupal duration by 1–2 days. It also reduced the pupal mass, but showed no detectable effects on female reproductive performance. Both sexes had similar development strategies; however, females seemed to be more sensitive to crowding and food shortage than males. A positive effect was expected if such stress factors acted as cues that triggering a behavioural or physiological shift to a distinct migratory phase. To the contrary, we found no proof that crowding and starvation caused maturation delay in female reproductive development. All treatments did not significantly increase female pre‐oviposition period. Therefore, we concluded that life developmental responses to crowding and food shortage in this species were different. Adult migration propensity was not enhanced under such stress conditions during the larval phase.

Female bias in an immigratory population of Cnaphalocrocis medinalis moths based on field surveys and laboratory tests

“…Since C. medinalis does not overwinter in Jiangyan, the moths captured by the searchlight trap in the early stage were mainly from the immigrant population. Moreover, it takes approximately one month for C. medinalis to emerge from the egg and reach the adult stage 55,56 . According to the field survey data of the moth, there were almost no C. medinalis moths in early July or before (Supplementary Fig.…”

“…Larvae of C. medinalis had previously been collected from rice fields in Nanjing, China, and reared using wheat seedlings 56 . Pupae were reared using the methods detailed above.…”

The effects of food level and social density on reproduction in the Least Killifish, Heterandria formosa

“…To be sure, there have been extensive studies of each effect in small mammals (Batzli, 1977;Boonstra & Boag, 1992;Gauthier, Berteaux, Krebs, & Reid, 2009;Krebs, Lambin, & Wolff, 2007;Oksanen, Oksanen, Dahlgren, & Olofsson, 2008;Wolff, 1997) and aquatic invertebrates (Beserra, Freitas, Souza, Fernandes, & Santos, 2009;Brent, 2010;Burns, 1995;Carvalho & Hughes, 1983;Guisande, 1993;Hooper, Sibly, Hutchinson, & Maund, 2003;Rose, Rees, & Grubb, 2002;Yang, Hu, Shi, & Zhai, 2015). In particular, the relative contributions of food limitation and the inhibition of reproduction through the social stress of crowding remain unexplored.…”

The Effects of Population Density on the Incidence of Developmental Deformities in Chemosensory Organs of Tobacco Hornworm Larvae (Lepidoptera: Sphingidae)

“…These effects are similar to those of certain other lepidopterans, such as the speckled wood butterfly Parage aegeria ( Gibbs et al 2004 ) and the silkworm Philo samia ( Dutta et al 2013 ). Interestingly, the opposite effects were seen in larvae of the Glanville fritillary butterfly Melitaea cinxia which grew faster and larger when reared in high-density conditions ( Rosa et al 2017 ), as did larvae of the gypsy moth Lymantria dispar ( Pavlushin et al 2019 ) and the moth rice leaf roller Cnaphalocrocis medinalis ( Yang et al 2015 ). Thus, crowding effects on life history traits appear to be common phenomena, but we are unaware of any density-related occurrences of missing or deformed chemosensilla in other species.…”