周期性羽化昆虫形成机制

Evolutionary mechanisms of periodical emergence insects

当昆虫类群表现为长生命周期k(k>1)年时,成虫的羽化表现为非周期性、周期性和过渡周期性3种形式。非周期性即为成虫每年均羽化,周期性即为成虫每k年才羽化1次,过渡周期性为非周期昆虫逐渐进化为羽化周期性的必经阶段,不同年份羽化的同生群在密度上产生了显著差异,形成了小同生群和优势同生群。自然界中表现出完全羽化周期性的昆虫种类是较少的,但由于其高种群密度的成虫同步性羽化现象,对比非周期性昆虫更易暴发成灾。为明确周期性昆虫演化进程并为林区虫害防控提供理论指导,总结了周期性昆虫的种类和生活特性,不同年间的气候异质性、自然灾害、扩散到未分布区域、天敌、种间和种内竞争等因素均有可能成为过渡周期现象形成的最初驱动力,生活史延长、寄主-天敌互作、低温驱动效应、天敌不敏感-捕食者饱足效应、种间和种内竞争等是促使昆虫羽化周期性形成的可能机制。在林区管理实践中,应提前评估害虫羽化周期性产生的趋势和程度。当成虫表现出完全羽化周期性,应在集中羽化年份内采取见效快的综合防控策略,降低唯一同生群密度至经济阈值以下。当成虫表现出过渡周期性,应加大优势同生群防治力度、降低小同生群防治频率,以及采取天敌林间释放和保育技术以平衡天敌对目标害虫的不同发育阶段种群的控制作用大小,遏制或减缓天敌-寄主互作驱动下的周期性演化进程,逐渐实现由过渡周期阶段向非周期性的逆转。当成虫表现出非周期性,应减少专化性天敌的释放和针对害虫特定阶段的防治措施使用频率,优先选择作用于所有发育阶段且致死率不存在显著差异的防治手段,避免因人为干扰产生的周期性演化和进一步的成灾。

When an insect population has a long life cycle of k years(k>1),the adult emergence will show three forms:non-periodicity,periodicity,proto-periodicity.The non-periodicity indicates that adults would emerge every year.The periodicity indicates that adults only emerge once in every k years.The proto-periodicity is a necessary period during which the non-periodical insects gradually evolve into periodical species,emergence broods of different years would show the significant differences in abundance,producing minor cohorts and dominant cohorts.In nature,it is rare that insect species display perfectly periodical emergence,whereas due to adult emergence synchronization with a relatively higher population density,the periodical insects will be more prone to cause outbreaks than related non-periodical species.In order to analyze the evolutionary process of periodic insects and provide theoretical guidance for forest pest control practice,we introduced the types and life characteristics of periodical insects in this article.Initial development of proto-periodical condition could be facilitated through climate variability of different years,natural catastrophes,dispersal into an unoccupied region,natural enemies,interspecific and intraspecific competitions.Possible mechanisms that allow periodicity evolution include life cycle prolongation,host-natural enemy interaction,low temperature driving effects,natural enemy foolhardiness-predator satiation effects,interspecific and intraspecific competitions.In forestry management practices,the tendency and extent of insect pest emergence periodicity should be evaluated in advance.When adults exhibit perfectly periodical emergence,the high efficient integrated control strategies should be adopted during the concentrated emergence year to reduce the density of only one brood below the economic threshold.When adults exhibit proto-periodical emergence,the control efforts on dominant cohorts should be strengthened,while the control frequency on small cohorts should be reduced.Field release and conservation of natural enemies should be carried out to balance the impacts of natural enemies on different developmental stages of target insect pests.As a result,the evolutionary process of periodicity through the natural enemy-host interaction would be ceased or slowed.Meanwhile,the reversion of population emergence status from proto-periodicity to non-periodicity could be gradually achieved.When adults exhibit non-periodical emergence,we should reduce the frequency of field release of specialized natural enemy species and application of control measures on specific developmental stages,and the priority should be given to select control measures that act on all developmental stages of insect pests and show no obvious differences in mortality rates,in order to avoid periodicity evolution and further outbreaks that are induced by artificial interference.