Scanning electron microscopy of Anopheles hyrcanus group (Diptera: Culicidae) eggs in Thailand and an ultrastructural key for species identification

The eggs of Anopheles argyropus, Anopheles crawfordi, Anopheles nigerrimus, Anopheles nitidus, Anopheles paraliae, Anopheles peditaeniatus, Anopheles pursati, and Anopheles sinensis are described with the aid of scanning electron micrographs. Comparisons of the egg structure among the eight species showed that the eggs differed with respect to the following characteristics: the deck—complete (An. argyropus, An. nigerrimus, An. paraliae, An. peditaeniatus, and An. sinensis); variable (complete, split and incomplete decks found together within an egg batch/An. crawfordi); and division into an area at each end (An. nitidus and An. pursati). The ratios of the entire length per maximal deck width within the area covered by floats were 3.33–6.86 (An. sinensis), 8.78–18.20 (An. peditaeniatus), 13.67–22 (An. nigerrimus), 26.33–44.25 (An. paraliae), and 26.99–75.94 (An. argyropus). The numbers of float ribs were 21–27 (An. peditaeniatus) and 28–34 (An. nigerrimus), and the total numbers of anterior and posterior tubercles were 6–8 (An. paraliae) and 9–11 (An. argyropus). Exochorionic sculpturing was of reticulum type (An. argyropus, An. crawfordi, An. nigerrimus, An. nitidus, An. paraliae, An. peditaeniatus, and An. sinensis) and pure tubercle type (An. pursati). Attempts are proposed to construct a robust key for species identification based on the morphometrics and ultrastructures of eggs under scanning electron microscopy.