Hormone Balance and the Control of Metamorphosis in Rhodnius Prolixus (Hemiptera)

A technique is described by which the intact larva of Rhodnius can be transfused with blood from another larva without interfering with ecdysis. If the 4th-stage larva receives blood from a 3rd-stage larva it develops characters little different from those of the 4th instar. This is attributed to the 3rd-stage larva producing juvenile hormone at a higher concentration. If the 4th-stage larva at 24 hr. after feeding receives blood from another 4th-stage larva at 8 days after feeding it develops characters intermediate between those of the 4th and 5th instars. This is attributed to the juvenile hormone being introduced too early in the moulting cycle. The hormone balance is upset by abnormal temperatures. The 4th-stage larva will not moult at a temperature of 36° C. although the larvae can survive up to about 40° C. At temperatures a little below 36° C. moulting is somewhat delayed and the characters developed are slightly ‘adultoid’ (prothetely). This is attributed to slightly reduced activity of the corpus allatum. At temperatures below 20° C. moulting is greatly delayed and the characters developed are slightly ‘juvenile’ (metathetely). This is attributed to relatively increased activity of the corpus allatum. Low concentrations of oxygen (less than 5 %) have an effect similar to that of high temperature. If 5th-stage larvae of Rhodnius receive implants of corpora allata from mature adults of Periplaneta they develop into 6th-stage larvae and many of these subsequently into 7th-stage larvae. The ‘juvenile hormone’ appears to be the same in the two insects. No evidence could be obtained for the persistence of juvenile hormone in the blood from one instar of Rhodnius to the next. The hypothesis of an active elimination of juvenile hormone by the corpus allatum at the time of metamorphosis remains therefore unproven.