| Since its invasion of Yunnan Province,China in December 2018,Spodoptera frugiperda(Smith),the armyworm,has spread rapidly in China,posing a substantial threat to agricultural production.Meanwhile,employing parasitoids is an environmentally friendly control method and an important means to achieve green and sustainable control of the armyworm,which has garnered considerable attention from researchers.Trichogramma chilonis Ishii and Telenomus remus(Nixon)are the dominant egg parasitoids of armyworm.However,the competitive relationship between the two parasitoids remains unclear.Consequently,this study aims to investigate the competitive relationship between Trichogramma chilonis and Telenomus remus concerning armyworm eggs.The ensuing results are as follows:1.The parasitism behavior exhibited by T.chilonis and T.remus on armyworm eggsThe parasitism behaviors of T.chilonis and T.remus encompass searching,detecting,oviposition,and cleaning.However,following oviposition,T.chilonis will use its antennae to probe the host egg in a circular motion.,while the T.remus use its ovipositor to gently rub the villi surrounding the host egg.The average search time for T.chilonis and T.remus was 3.57 minutes and 6.62 minutes,respectively,while the initial oviposition time at 165.14 seconds and 78.63 seconds.Notably,the subsequent oviposition time for both parasitoids proved significantly shorter compared to their initial oviposition time.2.The parasitism potential exhibited by T.chilonis and T.remus on armyworm eggsThe parasitism potential of T.remus surpasses that of T.chilonis on armyworm eggs.The parasitism rates of T.chilonis and T.remus stand at 33.78% and 84.65%,respectively,yielding offspring quantities of 35.80 and 65.80 individuals,with an egg count of 100.3.Effects of different proportion on the competitive relationship between the two parasitoidsWhen parasitized individually,T.remus exhibited a higher parasitism rate on armyworms than that of T.chilonis.The number of parasitoids in the offspring of both species directly correlated with the initial number of parasitoids,while the quantity of parasitoids did not significantly impact the parasitism rate of a monofemale parasitoid.In cases of combined parasitism,the highest number of offspring wasps(70.04)was observed when the proportion of T.chilonis to T.remus was 3:1.Conversely,when the proportion was 2:1 and 1:1,the number of offspring wasps decreased to 45.16 and 47.29,respectively.Increasing the proportion of T.chilonis to T.remus resulted in an increase in the number of monofemale parasitism events by T.remus.The highest number of monofemale parasitism occurrences for T.remus(28.53)was observed when the proportion of T.chilonis to T.remus was 1:3.Additionally,the number of monofemale parasitism events for T.remus was significantly influenced by the parasitism proportion,with the highest number(30.02)occurring when the proportion of T.chilonis to T.remus was 1:1.Combined parasitism led to a prolonged developmental period for T.chilonis offspring,while the developmental period of T.remus offspring was less affected.4.Effects of different parasitism order and temporal gap on the competitive relationship between the two parasitoidsThe offspring number of parasitoids was highest at 54.13 and 55.80 when the two parasitoid were parasitized at the same time and T.chilonis parasitized 24 h in advance,respectively.As the interval of parasitism time extended,the count of T.chilonis decreased,the female ratio of T.chilonis increased,and the developmental period of T.chilonis was prolonged.When T.chilonis was parasitized in advance within the same time interval,the count,female ratio,and development duration of T.chilonis diminished.The count of offspring for T.remus remained unaffected by the time interval of parasitism;however,T.remus could only hatch from eggs parasitized 24 hours earlier by T.chilonis,while eggs parasitized 48 and 72 hours earlier by T.chilonis did not result in eclosion for T.remus..5.The inter-specific competition and interference behavior exhibited by T.chilonis and T.remus during their parasitism of armyworm eggsT.chilonis emerges as the prevailing competitor in the inter-specific interaction with T.remus.Only when the T.remus parasitized 48 hours in advance,can the T.remus win the competition from the host eggs.In the inter-specific competition between these two parasitoids,when they engage in simultaneous oviposition,T.remus exhibits a subtle predominance in direct competition,characterized by its interference behavior.Typically,encounters between these parasitic wasps do not incite aggressive behaviors;however,the presence of T.remus can influence the egg-laying behavior of T.chilonis to some extent.In conclusion,T.chilonis and T.remus exhibit considerable potential in regulating armyworm egg populations.The varying proportions,parasitic order,and temporal gap of these parasitoids have notable impacts on the quantity,female ratio,and developmental duration of their offspring.Furthermore,the efficacy of monofemale parasitism is also subject to diverse influences.The direct interactions and competitive encounters between the parasitoids further influence their emergence rates.Thus,it is imperative to thoroughly contemplate the effects of T.chilonis and T.remus proportions,sequencing,and intervals on armyworm control.This study also establishes a scientific foundation for the practical implementation of T.chilonis and T.remus in field applications. |
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