Phase-related differences in egg production of the migratory locust regulated by differential oosorption through microRNA-34 targeting activinβ

Outbreaks of locust plagues result from the long-term accumulation of high-density egg production. The migratory locust, Locusta migratoria, displays dramatic differences in the egg-laid number with dependence on population density, while solitarious locusts lay more eggs compared to gregarious ones. However, the regulatory mechanism for the egg-laid number difference is unclear. Herein, we confirm that oosorption plays a crucial role in the regulation of egg number through the comparison of physiological and molecular biological profiles in gregarious and solitarious locusts. We find that gregarious oocytes display a 15% higher oosorption ratio than solitarious ones. Activinβ (Actβ) is the most highly upregulated gene in the gregarious terminal oocyte (GTO) compared to solitarious terminal oocyte (STO). Meanwhile, Actβ increases sharply from the normal oocyte (N) to resorption body 1 (RB1) stage during oosorption. The knockdown of Actβ significantly reduces the oosorption ratio by 13% in gregarious locusts, resulting in an increase in the egg-laid number. Based on bioinformatic prediction and experimental verification, microRNA-34 with three isoforms can target Actβ. The microRNAs display higher expression levels in STO than those in GTO and contrasting expression patterns of Actβ from the N to RB1 transition. Overexpression of each miR-34 isoform leads to decreased Actβ levels and significantly reduces the oosorption ratio in gregarious locusts. In contrast, inhibition of the miR-34 isoforms results in increased Actβ levels and eventually elevates the oosorption ratio of solitarious locusts. Our study reports an undescribed mechanism of oosorption through miRNA targeting of a TGFβ ligand and provides new insights into the mechanism of density-dependent reproductive adaption in insects.

The Corpus Allatum and Oogenesis in Rhodnius Prolixus (Stål.)

1. In the ovarioles of both normal and allatectomized females the spaces open between the cells of the follicle layer and vitellogenesis begins as the terminal oocyte grows through the 350-400 /µm size range. 2. In both normal and allatectomized ovarioles the growth of the larger oocytes is markedly co-ordinated so that, for example, each ovariole contains only one oocyte in active vitellogenesis. 3. A consideration of the size distribution of the terminal oocytes in normal and allatectomized ovarioles demonstrates that vitellogenesis begins later and proceeds more slowly in allatectomized animals. 4. Allatectomy markedly depresses the number of mitoses in the trophic primordium, but this is held to be a feedback phenomenon resulting from a decreased demand for the products of mature trophocytes. 5. There is a decreased level of yolk protein in the haemolymph of allatectomized animals. 6. This evidence favours the hypothesis that the primary site of action in Rhodnius of the gonadotropin from the corpus allatum is situated at the level of activation, whereby spaces open between the follicle cells and proteins from the haemolymph are allowed free access to the oocyte surface.

A neuroendocrine relationship between the nematode Hammerschmidtiella diesingi and its insect host, Blatta orientalis

Various endocrine operations were performed on the adult female cockroach Blatta orientalis and the adult populations of the nematode Hammerschmidtiella diesingi were recorded 2 or 4 weeks later. Cautery of the median neurosecretory cells (m.n.c.) caused a significant reduction in total numbers of adult nematodes after 2 or 4 weeks; after 2 weeks, removal of the retrocerebral complex (corpora cardiaca plus corpora allata) caused a significant overall reduction in the adult nematode burden and this could not be prevented by reimplanting the corpora allata immediately after the retrocerebral complex had been removed.Anomalies appeared in the data when the sex of the parasite was examined and this may be related to a possible postembryonic mode of sex determination.Both m.n.c. cautery and removal of the retrocerebral complex suppressed host terminal oocyte development and ootheca production, whilst reimplantation of corpora allata into ‘retrocerebralectomized’ cockroaches allowed reproductive processes to continue normally. Hence, the m.n.c. and corpora allata are essential for host egg development.Histological studies showed a profound reduction in fuchsinophilic material in the corpora cardiaca of m.n.c. cauterized cockroaches.Although the m.n.c. may affect the nematode directly or indirectly, a direct effect on the parasite by the corpora allata is unlikely.

Neurosecretory Control of Ovarian Development in Schistocerca Gregaria

Cautery of the neurosecretory cells of the pars intercerebralis, or removal of the corpora cardiaca, will prevent the development of the terminal oocytes in the ovaries of the desert locust. Implantation of brains into females whose neurosecretory cells have been cauterized results in some development of the terminal oocytes. Ovariectomy of immature females causes a precocious accumulation of material in the neurosecretory system. Electrical stimulation, drastic wounding, or enforced activity of 14-day-old females reared without males brings about release of material from the neurosecretory system, and also accelerates development of the terminal oocytes. Copulation by these females also results in release of material from the neurosecretory system, and is followed by rapid terminal oocyte development. It is concluded that the neurosecretory system in Schistocerca gregaria exerts a positive control over oocyte development, and that copulation may stimulate release of material from the neurosecretory system.