Effects Of Photoperiod On The Biology Of The Adult Of Helicoverpa Armigera(Lepidoptera:Noctuidae)

The cotton bollworm,Helicoverpa armigera(Hubner)(Lepidoptera:Noctuidae),is an important agricultural pest in the world.It is an omnivorous insect with more than 200 species of host plants.The biology of insects is regulated by both endogenous(biological clock genes)and exogenous factors(photoperiod,etc.).Photoperiod is one of the important environmental factors affecting the biology of the cotton bollworm.Photoperiod,as a classical timing factor,not only affects the expression of clock genes and regulates the biological rhythm of insects,but also plays a role in cell,tissue,organ and behavior,which has been proved in many researches.In the intelligent artificial climate box with temperature of(22±)℃ and relative humidity of(75±5)%,this paper systematically studied the effects of different photoperiods(L:D=24:0,L:D=16:8,L:D=12:12,D:L=12:12,L:D=8:16 and L:D=0:24)on the emergence rhythm of cotton bollworm pupae and on the growth and development,fecundity,flight ability and wingbeat frequency.In addition,the expression of three important clock genes in different tissues(head,antennae,chest,abdomen,foot)and developmental stages(eggs,5th instar larvae,old cockroaches,adults)of cotton bollworm adults was investigated by real-time fluorescence quantitative PCR(qRT-PCR).The main results are as follows:(1)The results of the emergence of the cotton bollworm under different photoperiod indicate that all the eclosion peaks appear in the scotophase.Except for full-light and full-dark conditions,the eclosion activity of the cotton bollworm in the other photoperiods showes a certain rhythm with the alternation of light and darkness.The eclosion behavior of adults under full-light conditions belongs to a completely discrete eclosion pattern,but it shows eclosion rhythm under full-dark conditions.For pupae,the eclosion peak appeared earlier in a shorter scotophase.(2)The growth and development of cotton bollworm adult under different photoperiod conditions shows that different photoperiod changes have significant effects on the life span of female moths,but have no significant effect on the life span of male moths.The average life span of adult was 11.84±0.51 d-18.56 ± 1.04 d.(3)The results of different reproductive activities of the cotton bollworm under different photoperiods shows that the changes of photoperiod also have significant effects on the pre-oviposition duration,mating occurrences of female moth and the hatchability of eggs,but have no significant effects on the fecundity,oviposition period and mating rate of female moths.Under the full illumination condition of L24:D0,the pre-ovulation period is 4.47 ± 0.18 d,which is significantly longer than other photoperiod treatments.(4)Studies on the flight ability of the cotton bollworm under different photoperiods showed that different photoperiods also had significant effects on the flight distance and flight time of adult bollworm,but had no significant effects on the average flight rate.The flight parameters between the female moth and the male moth of the cotton bollworm have significant differences in flight distance and flight time under the photoperiod L16:D8 condition,and there was no difference in flight rate.There was no difference in the flight ability of male and female moths of the cotton bollworm under other photoperiod conditions.(5)Using the stroboscope,the flapping frequency of the cotton bollworm was measured at 1,3,5,7 and 9 days old under different photoperiod conditions.The results showed that the photoperiod had a significant difference in the flapping frequency of the cotton bollworm at 1 and 3 days of age,but there was no significant difference in the flapping frequency between the different photoperiods at 5,7 and 9 days of age.The initial eclosion of the cotton bollworm moths has a lower frequency of wing vibration,and the 1-3 days of age is the period in which the frequency of the wing vibrations changes the most,and the frequency of the flaps increases rapidly.After 3 days of age,the cotton bollworm began to mate and lay eggs,and the frequency of flapping gradually decreased.(6)qRT-PCR results showed that these three circadian clock genes showed significant spatial and temporal expression specificity.The expression levels of mRNA of three clock genes in different tissues and organs of the cotton bollworm were significantly different,mainly in the antennae and head,but the expression patterns of genes were slightly different.At the same time,the expression levels in different developmental stages were also significantly different.Both were significantly higher in the adult stage than in other stages of development.The above results indicate that photoperiod is an important environmental factor affecting the emergence,growth,reproduction,and flight of the cotton bollworm,and the clock gene plays an important role in endogenous regulation.Studying the emergence rhythm reveals the relationship between the photoperiod and the dynamic changes of the population of the cotton bollworm,and improves the forecasting level.Fertility is the main life parameter of insect population proliferation.The determination of flight ability and flap frequency is an important basis for studying the law of migration.Mastering the information on the dynamic changes of the cotton bollworm population can improve the forecasting level of the cotton bollworm,and provide an important basis for exploring the appropriate period of prevention and control and taking effective prevention and control measures.