关键词: 骆驼斯氏副柔线虫病, 西方角蝇, 截脉角蝇, 幼虫龄期, 咽骨体

Abstract: 【Aim】 This study aims to investigate the criteria for dividing the larval instars of horn flies Haematobia irritans and H. titillans, which will be fundamental for the determination of larval instars of the two horn flies, the development of nematode Parabronema skrjabini in its vectors, and the development of efficient control measures of camel parabronemosis. 【Methods】 The larvae of the two horn flies at different developmental stages were obtained by laboratory artificial rearing. Three morphological variables, i.e., the body length, and the length and width of pharyngeal sclerite of the larvae, were measured, and the data were analyzed by SPSS Statistics19.0. Combined with the Crosby growth rule, the difference in the three morphological variables between the larvae of the two horn flies was compared, and the best criteria of instar division were determined. 【Results】 The results indicate that the larvae of the two horn flies can be divided into three instars. Pharyngeal sclerite is the characteristic structure of the larvae of the two horn flies, and the variables of the larvae of the two species in different ages show the same growth pattern with the increase of larval instars. The length of pharyngeal sclerite is the best morphological variable for separating the larvae of the two horn flies, while the width of pharyngeal sclerite can be used as an assistant variable for the division of the larval instars. However, there is an overlap in the variation range of body length between the adjacent larval instars of the two horn flies, so body length can not be used to separate the instars accurately. 【Conclusion】 Our study indicates that the morphological characteristics of larval pharyngeal sclerite can be used to identify the larval instars of  H. irritans  and H. titillans  conveniently, rapidly and correctly.

Key words:  Camel parabronemosis; , Haematobia irritans, H. titillans, larval instars, pharyngeal sclerite