Determining the number of instars in potato tuber moth Phthorimaea operculella (Zeller) using density‐based DBSCAN clustering

The potato tuber moth (PTM), Phthorimaea operculella (Zeller), is an important pest of Solanaceae crops and especially devastating to potatoes. There is no significant difference in morphological characteristics of PTM from the first to third instar larvae; therefore, it is difficult to directly determine the number of instars of this pest based on morphology. In the present study, head capsule width and length and mandible width of 340 PTM individuals were measured. Density‐based spatial clustering of applications with noise (DBSCAN) clustering was used for instar grouping. The results of DBSCAN clustering were compared with those obtained using Gaussian mixture models and k‐means clustering; the results of the three clustering methods were verified using Brooks–Dyar rule, Crosby rule and linear regression model. The clusters obtained using the three methods were the same and comprised four PTM instars with three morphological characteristics. Moreover, the results of the three methods fit the Brooks–Dyar rule, Crosby rule, frequency analysis and logarithmic regression model well. Head capsule width was the best morphological characteristic for determining the number of instars of PTM, and this characteristic may be used for determining PTM instars in the field. These results show that the DBSCAN clustering method is a promising tool for the identification of insect instars.     

西双版纳自然保护区蚁生线虫草时空分布及寄主多样性

蚁生线虫草是一种重要的蚁科专化性虫生真菌。为明确双版纳自然保护区不同生境蚁生线虫草的分布规律,以期为蚁生线虫草的开发利用提供依据,于2017年7月-2018年9月对西双版纳自然保护区石灰岩山季雨林（高、中、低海拔带）、热带季雨林、季风常绿阔叶林、热带丛生竹林、暖热性针叶林5种不同生境中蚁生线虫草的分布及其寄主进行了系统调查。结果表明,在5种不同生境中,共采集蚁生线虫草1 449株,其主要分布于石灰岩山季雨林和热带丛生竹林,相对多度分别为51.1%和24.3%;其次为暖热性针叶林生境,相对多度为15.2%;热带季雨林和季风常绿阔叶林中分布相对较少,相对多度分别为5.7%和3.7%。从同一生境的石灰岩山季雨林不同海拔带的分布来看,蚁生线虫草主要分布于高海拔地带（33.7%）,而中海拔地带（9.7%）和低海拔（7.8%）相对较少。从季节性流行规律来看,西双版纳自然保护区蚁生线虫草的流行期为湿热季的6-10月及湿热季与雾凉季交替的11月。蚁生线虫草寄主多样性丰富,包括4亚科13属16种。该研究将为西双版纳自然保护区生物多样性及蚁生线虫草保护利用提供理论依据。