Arden O. Lea

The medial neurosecretory cells and egg maturation in mosquitoes

Abstract When the medial neurosecretory cells (mnc) were surgically removed from aedine mosquitoes immediately after emergence, egg maturation was suppressed. In older females mnc-ablation had little effect. Ablation did not interfere with ingestion or absorption of a blood meal. In blood-fed Aedes taeniorhynchus , arrest of egg development by mnc-ablation was reversed by transplantation of 1 pair of mnc from an anaesthetized donor. In sugar-fed A. taeniorhynchus , 4 pairs of mnc were required to restore autogenous egg maturation. In blood-fed hosts, male or female Aedes or female Culex were equally effective as donors. If the donor was killed, rather than anaesthetized, 4 pairs of mnc were needed to restore egg development. Both the mnc and the corpora allata are essential for egg maturation in mosquitoes. However, transplanted mnc could not restore egg development arrested by allatectomy, and transplanted corpora allata could not restore egg development arrested by mnc-ablation. Consequently, the corpora allata and the mnc regulate different processes in egg maturation.

Some relationships between environment, corpora allata, and egg maturation in aedine mosquitoes

Abstract By extirpation of the paired corpus allatum-complex, the role of the corpus allatum in both autogenous and anautogenous reproduction has been studied in four species of mosquitoes. Allatectomy performed within 1 hr of emergence: (1) stopped all autogenous yolk deposition in A. taeniorhynchus ; (2) prevented any yolk synthesis in blood-fed A. aegypti ; (3) limited yolk deposition in most blood-fed A. sollicitans to not more than that found in sugar-fed controls; (4) did not prevent egg maturation in blood-fed A. triseriatus . Follicular growth and yolk synthesis in autogenous taeniorhynchus and blood-fed aegypti , prevented by allatectomy, could be initiated by the implantation of a pair of corpora allata from any donor tested. It has been concluded, from the effect on egg development of delaying allatectomy for varying periods after emergence and of delaying blood-feeding following allatectomy, that the corpora allata of the anautogenous female was active before the first blood meal. Therefore, the difference between autogenous and anautogenous reproduction in Aedes is dependent on some other factor. Such environmental conditions as the larval diet, the adult diet (when allatectomy was delayed after emergence), and the adult holding temperature prior to allatectomy, were shown to influence the effect of the operation on egg development in blood-fed sollicitans .

Mating without insemination in virgin Aedes aegypti

Abstract Although the Aedes aegypti female will mate repeatedly soon after emergence, no sperm are transferred during copulation unless the female is 1 to 2 days old. The duration of this refractoriness to insemination varies with the strain of the female, is temperature dependent, and is influenced by a hormone from the corpora allata.

Control of the medial neurosecretory cells by the corpus allatum in Calliphora erythrocephala

Abstract The nuclei and nucleoli of the medial neurosecretory cells (MNC) undergo cyclic changes in volume: just after emergence, while feeding on a “maintenance diet” of sugar, and again, while feeding on a “reproductive diet” of meat. Changes in MNC nuclear volume are correlated with changes in the quantity of neurosecretory granules observed in the MNC perikarya. Allatectomy prevents the normal increase in MNC nuclear volume, and implanted corpora allata (CA) stimulate small nuclei to enlarge. Therefore, one function of the CA is the control of synthesis of neurosecretory material by the MNC.

Egg maturation in mosquitoes not regulated by the corpora allata

Abstract Implantation of extra corpora allata from either autogenous or anautogenous donors did not stimulate egg maturation in anautogenous Aedes aegypti or Culex pipiens pipiens fed only on sugar, contrary to the report of Larsen. Implantation of a cockroach corpus allatum did not induce egg maturation in anautogenous mosquitoes fed on sugar, although the corpora allata of larval or adult cockroaches were shown to function in A. aegypti. Therefore, the effect of Larsen and Bodensteins whole cockroach extract on mosquitoes may not have been due to corpus allatum hormone. Anautogenous Culex and Aedes, allatectomized 3 to 5 days after emergence, matured eggs following a blood meal. Therefore, the corpora allata had already secreted sufficient hormone for maturation of the anautogenous ovary before the first blood meal.

Size independent secretion by the corpus allatum of Calliphora erythrocephala

Abstract There are cyclic changes in the size of the corpus allatum (CA): (1) during sugar-feeding following emergence, and (2) following the addition of meat to the diet. The CA of flies fed on sugar were always smaller than the CA of flies fed on meat. Our test for secretory activity of the CA was the effect of an implanted CA on the volume of the nuclei of the medial neurosecretory cells of an allatectomized host. The activity of the CA was not correlated with either the size of the gland or egg maturation. Inactive CA were activated after transplantation to a host which was fed on meat.

Medial Neurosecretory Cells as Regulators of Glycogen and Triglyceride Synthesis

In the female mosquito, medial neurosecretory cells restrict synthesis of glycogen from sugar and stimulate triglyceride synthesis. Removal of these cells greatly increases the storage capacity for glycogen at the expense of triglyceride storage.

Suppression of glycogen synthesis in the mosquito by a hormone from the medial neurosecretory cells

Abstract In the female mosquito, removal of medial neurosecretory cells greatly increases the amount of glycogen and greatly diminishes the amount of fat deposited after a single meal of sugar. Implantation of medial neurosecretory cells restricts glycogen synthesis in the operated female to that in the unoperated control but does not restore the interrupted fat synthesis. These experiments indicate that glycogen synthesis is suppressed by a hormone from the medial neurosecretory cells.

Control of glycogen and fat metabolism in the mosquito

Abstract The mosquito, fed on an equicaloric amount of either sugar or blood, synthesizes a small amount of glycogen and a large amount of fat (triglycerides). The synthesis was not affected by removal of the corpora allata. When the medial neurosecretory cells were removed and the insects were fed on sugar, glycogen synthesis was greatly increased and fat synthesis greatly inhibited. This reversal of synthesis did not occur in blood-fed insects, from which the medial neurosecretory cells were removed. Utilization of glycogen and fat was not affected by removal of either the corpora allata or the medial neurosecretory cells.