Mycetocyte Inclusion in the Oocytes of Bemisia argentifolii (Homoptera: Aleyrodidae)

Abstract

This study investigates the process of transfer of endosymbiotic organisms from adult silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Bellows et al. 1994) (also known as Bemisia tabaci B biotype), into the developing ova. In dissected females, individual mycetocyte cells containing microorganisms were scattered singly among developing oocytes. Oocytes with mycetocytes included were first observed in females 16 h after emergence. The mean number of oocytes >0.1 mm in length per female increased through the 4th d after adult eclosion then leveled off. The number of oocytes containing mycetocytes followed a similar pattern. Stages of mycetocyte inclusion followed a pattern based on the size of the oocyte. Oocytes became associated with a single mycetocyte cell when they were a mean of length of 0.135 ± 0.003 mm (minimum of 0.11 mm). All mature oocytes examined contained a mycetocyte. Mycetocytes were observed inside a common membrane with oocytes, at what becomes the pedicel end of the ova, when oocytes were an average of 0.147 ± 0.004 mm long. In the final stages of ovum development, the plasma of the oocyte completely surrounded the mycetocyte and the chorion was thickened. Mycetocytes included in oocytes had a mean length of 33 ± 0.4 µm and width of 27 ± 0.5 µm. Although the females that were dissected had the opportunity to oviposit, some retained several fully developed ova. Because inclusion of mycetocytes into oocytes is a continuous process, manipulations of endosymbionts before inclusion into the oocytes should be possible at any time during adult life; however, earlier treatment of an individual would probably affect a greater proportion of their offspring.