Studies On Viability Of Spodoptera Exigua Pupal Melanic Strain

Spodoptera exigua(Hubner) is a leaf-eating noctuids, which belongs to Lepidoptera, Noctuidae. It is harmful to35families and108genera and138species of plants and associated with omnivorous and polyphagous. In recent years, it has become an important insect pests of vegetables, mainly harmful to Cruciferae, Leguminosae, Convolvulaceae and Liliaceae and other vegetable crops. Melanism is one of the most marked phenotypic variations that naturally occur in a wide range of organisms. In this study, we established a homozygous melanism mutant strain (SEM) with black pupae spontaneously occurring within a wild-type (SEW) population of S.exigua. The laboratory experiments reveals that, SEM showed several advantages on both a physiological and biochemical level and stress resistance under the condition of artificial feed. Based on previous studies with the SEM and using SEW as a check clone, we have made observations in eclosion, mating rhythm and ovarian development. Then we preceded to research SEM’s growth development and reproduction on the nine species of host plants. While exploring the mating competition situation among two strains of beet armyworm and determined the flight capacity of virgin and copulated SEM adults. From there we can systematically analyse and evaluate the viability of SEM. The main conclusions are as follows:1. SEM have different eclosion, mating rhythm and ovarian development with SEW: the melanism adults can emerge throughout the day, but SEW have no eclosion occurrence in individual time, The mating behavior of SEM and SEW are observed within02:00-06:00, but the mating peak have some differences, SEW’s mating peak occurs in the middle of the night,02:00-04:00, while the SEM mating peak occurs before dawn,04:00-06:00. The ovarian development of virgin adults of SEM is almost the same as SEW. The ovarian developed significantly faster after mating. The ovarian of SEM developed slightly faster than SEW from the second day after eclosion.2. SEM can adapt itself to different host plants better. Host plants can significantly influence the survival rate, developmental durations, pupal weight and fecundity of SEM. Under the same test conditions the melanism is associated with faster development in larval life stages, increased pupa weight after eating nine different host plants. Regardless of the host plant the SEM feeds on, it’s mating frequency is less than SEW, but the total eggs of single female is significantly higher than SEW. This then makes up the deficiency of the mating times, keeping the similar population size with SEW. 3. Mating competition mechanism exists between SEM and SEW adults. Both two strains female adults of S.exigua tend to attract xenogeneic male adults for mating; the SEM and SEW male adults have a different ability to identify the conspecific and heterospecific female, which belongs to reproductive interference that may cause substitution. Meanwhile, analysis of offspring pupae and female pupa populations.the adult fecundity of SEM is significantly higher than SEW. This is also a manifestation of strong mating competitiveness about SEM.4. The flight capacity of SEM is weaker than SEW. SEM is associated with slower average flight speed, shorter mean flight duration and distance, its flight capacity of different ages is weaker than SEW. All of these may influence its migratory behavior.