title: An adaptive kernel smoothing method for classifying Austrosimulium tillyardianum (Diptera: Simuliidae) larval instars.
abstract: In insects, the frequency distribution of the measurements of sclerotized body parts is generally used to classify larval instars and is characterized by a multimodal overlap between instar stages. Nonparametric methods with fixed bandwidths, such as histograms, have significant limitations when used to fit this type of distribution, making it difficult to identify divisions between instars. Fixed bandwidths have also been chosen somewhat subjectively in the past, which is another problem. In this study, we describe an adaptive kernel smoothing method to differentiate instars based on discontinuities in the growth rates of sclerotized insect body parts. From Brooks' rule, we derived a new standard for assessing the quality of instar classification and a bandwidth selector that more accurately reflects the distributed character of specific variables. We used this method to classify the larvae of Austrosimulium tillyardianum (Diptera: Simuliidae) based on five different measurements. Based on head capsule width and head capsule length, the larvae were separated into nine instars. Based on head capsule postoccipital width and mandible length, the larvae were separated into 8 instars and 10 instars, respectively. No reasonable solution was found for antennal segment 3 length. Separation of the larvae into nine instars using head capsule width or head capsule length was most robust and agreed with Crosby's growth rule. By strengthening the distributed character of the separation variable through the use of variable bandwidths, the adaptive kernel smoothing method could identify divisions between instars more effectively and accurately than previous methods.
authors.affiliation: Department of Applied Mathematics, College of Mathematics and Informatics, South China Agricultural University, Guangzhou 510642, China.
authors.forename: Guanjun
authors.initials: G
authors.lastname: Cen
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China Corresponding author, e-mail: yonghaoyucn@yeah.net.
authors.forename: Yonghao
authors.initials: Y
authors.lastname: Yu
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
authors.forename: Xianru
authors.initials: X
authors.lastname: Zeng
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
authors.forename: Xiuzhen
authors.initials: X
authors.lastname: Long
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
authors.forename: Dewei
authors.initials: D
authors.lastname: Wei
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
authors.forename: Xuyuan
authors.initials: X
authors.lastname: Gao
authors.affiliation: Guangxi Key Laboratory of Biology for Crop Diseases and Insect Pests/Institute of Plant Protection, Guangxi Academy of Agricultural Sciences, Nanning 530007, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Zeng
mesh_terms: D000818:Animals; D006257:Head / Q000033:anatomy & histology / Q000254:growth & development; D007814:Larva / Q000033:anatomy & histology / Q000254:growth & development; D012843:Simuliidae / Q000033:anatomy & histology / Q000254:growth & development*
keywords: Austrosimulium tillyardianum; adaptive kernel smoothing estimation; bandwidth selection; instar determination method