| Water chestnut is one of the most widely planted aquatic vegetables in our country. Rampant insect pests and severe plant diseases have been amounted for decrease in yield and quality in recent years, which lead to huge economic loss. However, few studies have focused on the insect pests of the water chestnut especially Parapoynx crisonalis, leaving huge difficulties in pest control of the water chestnut. In order to effectively control the important insect pest P. crisonalis, here, the biological characteristic, phylogenetic position, dynamic regularly, age-stage two-sex life table within different temperatures were systematically investigated in the present study. The results are briefly introduced as follows:(1) The external morphology of P. crisonalis:the eggs are light yellow, circular, and covered with a layer of gel. The larvae are oval, present as five instars. The head capsule width served as an optimal index for instar division, given the least average coefficient of variation and Crosby ratio (other indexes were greater). The average head capsule width of the 1st to 5th instar larvae was 0.2493±0.0053,0.3454±0.0018,0.5079±0.0031, 0.7419±0.0190 and 1.1287±0.0369 mm, respectively. The newly formed pupae were yellowish and then turned brown; in males, the 8th abdominal segment were smooth without cracks, and the 9th presented a short lengthways crack in the middle with two distinct semi-circular strumae; while in females, the 8th abdominal segment had a central crack with flat sides and no humps, connected to the 7th and the 9th segments. The adults were characterized as follows:forewing with discoidal-stain consisting of two blackish dots, distalbinde highly streamlined; uncus relatively short, gnathos imperforated, valve exceptional form, distally wider than at the point of attachment, juxta oval and aedeagus very short, ovipositor slim and quite long, signum horseshoe-shaped.(2) Characterization of the complete mitochondrial genome of P. crisonalis and its phylogenetic position:The genome was 15,374 base pairs (bp) in length and included 13 protein-coding genes (PCGs),22 transfer RNA (tRNA) genes,2 ribosomal RNA (rRNA) genes and an AT-rich region. The A+T content was 82.00%, and the AT skew was slightly positive. All tRNA genes displayed the typical clover-leaf structure of mitochondrial tRNA.The phylogenetic relationships of 20 Pyraloidea species were determined based on 13 PCGs, 22 tRNAs and 2 rRNAs of mitochondrial genomes using Bayesian inference (BI) and maximum likelihood (ML) methods. This phylogenetic analysis provided support that aquatic nymphulin moths (P. crisonalis, E. interruptalis, P. distinctalis and P. prodigalis) form a monophyletic clade at high levels via maximum likelihood and Bayesian methods with a bootstrap value of 100% and a posterior probability of 1.00. Parapoynx-type moths occurred first and then evolved to Nymphula-type Pyralidae moths without tracheal gill to match the environment. Next, the Nymphula-type evolved to the Potamomusa-type, which possesses a single tracheal gill.(3) The population dynamics and spatial pattern of P. crisonalis:The population was relatively low in April and rapidly rises at the beginning of May. At the end of July and early August, the population drops dramatically. But there was a rebound at the end of August and early September, which referred as the second peak of population. Until the early of November, Parapoynx crisonalis diminished for overwintering. Above all, the climatic conditions, especially the temperature, and the rain were the key factors influencing the population dynamics of P. crisonalis. Between May and October, the P. crisonalis adults were distributed evenly in the pool. In May and June, the eggs of P. crisonalis present an aggregate distribution, which was because of the combined effect of environmental heterogeneity and insect aggregation behavior. And in July and August, its turned uniform distribution.(4) The age-stage two-sex life table of P. crisonalis:The temperature had a huge impact on different state development period. There was significant difference between the six temperature treatments of larvae (P<0.05). Among those six temperature gradients,21℃ gave the longest developmental stage period, which was 24.60±1.24 days, while and the shortest one is 5.00±0.57 days. The immature stage was the longest one, which is 21℃ (38.43±1.56 days), and the shortest one was 36℃ (12.00±0.54days). There was not significant differences between the treatments of 24℃ and 27℃ (P>0.05), but the others all existed distinct difference. |
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