Juvenile hormone and ovarian growth in Manduca sexta

In Manduca sexta the major size increase of ovarian follicles is accomplished by two processes: (1) vitellogenesis in which follicular volume and dry weight increase simultaneously, and (2) hydration in which absorption of water by the oocyte accounts for an 80% increase in volume prior to chorion formation. Vitellogenic growth occurs in both a slow and rapid phase. Rapid vitellogenic growth is initiated only by follicles of a threshold size (1 mm) and is a juvenile hormone (JH)-dependent event. In the absence of JH follicles grow to 1 mm and then degenerate.     

Hormonal Control of Epidermal Cell Development

SYNOPSIS. During larval life the insect epidermis makes a larvalcuticle and certain pigments due to the presence of juvenilehormone (JH) at critical times during the molt cycle. The presenceof JH also permits growth of imaginal discs and maintains strictlylarval epidermis. At metamorphosis the lepidopteran epidermisresponds to a low level of 20- hydroxyecdysone (20HE) in theabsence of JH by becoming pupally committed, then later it formsa pupal cuticle when more 20HE appears, even though JH is present.During the change of commitment, DNA synthesis occurs but isnot essential, whereas both RN A and protein synthesis are.The major changes in the translatable mRNA population at thistime are threefold: a decline in most larval cuticle mRNAs,a transient increase followed by a disappearance of a few larvalcuticle mRNAs, and an appearance of at least one ‘pupalcommitment’ mRNA and two to three mRNAs for small pupalcuticular proteins. Similar changes are seen in the proteinsynthetic patterns. Thus, a pupally committed cell is one whichcan no longer make larval products but which is not yet ableto make most pupal products. Juvenile hormone prevents the changeto pupal commitment by directing some of both the primary andthe secondary actions of 20HE on the genome.     

Induction of supernumerary larval moulting in the tobacco hornworm Manduca sexta: interaction of bisacylhydrazine ecdysteroid agonists with endogenous Juvenile Hormone

Abstract When given in a critical dietary dose range, the insecticidal bisacylhydrazine ecdysteroid agonists RH‐5849 or tebufenozide (RH‐5992) cause fifth stage Manduca sexta (L.) larvae to moult to a supernumerary sixth‐stage giant larva. The effect is dependent on exposure to the chemicals immediately after the previous ecdysis. Previous removal of the corpora allata does not interfere with the induction of premature moulting by RH‐5849 but completely prevents the formation of supernumerary larvae. The juvenilizing effect is therefore due to the interaction of the moult‐promoting effect of the ecdysteroid agonists with the high titre of endogenous Juvenile Hormone that is present just after ecdysis to the fifth stage in this insect. The ecdysteroid agonists themselves appear to have no intrinsic Juvenile Hormone‐agonist properties. Sixth‐stage larvae resulting from exposure to critical dietary concentrations of RH‐5849 are morphologically completely larval in character. When transferred to diet without the ecdysteroid agonist, they feed normally and gain weight, growing much larger than control fifth stage insects. At the end of the supernumerary stage, they cease to feed, wander in the usual way, and form a normal pupal cuticle but then die as pharate pupae without shedding the sixth‐stage larval cuticle.     

Regulation of reproductive behaviour and egg maturation in the tobacco hawk moth, Manduca sexta

ABSTRACT. The virgin female tobacco hawk moth, Manduca sexta, flies during the early scotophase in an LD 16:8 cycle at 24C then begins 'calling' within 2h. Mating lasts 3–4 h. Oviposition occurs in the succeeding scotophases if a tobacco plant is present. The switch from virgin 'calling' behaviour to mated ovipositional behaviour is mediated by the presence of sperm and/or associated testicular fluids in the bursa copulatrix. The corpora allata, which are necessary for egg maturation in this species, are activated via the NCC I and II around the time of eclosion. Feeding increases the activity of the corpora allata in the virgin female (as judged by the number of eggs matured in 4 days) but mating brings about a further stimulation of the activity of the corpora allata. The stretching of the bursa copulatrix by the insertion of the spermatophore during mating is probably the trigger for this response. Continued neural input from the bursa copulatrix to the brain is necessary to maintain the increased activity of the corpora allata.     

Growth and development of the endoparasitic wasp Apanteles congregatus: dependence on host nutritional status and parasite load

ABSTRACT. Previously we have shown that the number of Apanteles congregatus Say (Hymenoptera, Braconidae) larvae developing in Manduca sexta (L.) (Lepidoptera, Sphingidae) larvae that are parasitized in the first instar determines the timing of emergence of the parasites from the host. Here we show that the first larval ecdysis of the wasps occurs after the host ecdyses to the terminal stage, regardless of whether that stage is the host's fourth, fifth or supernumerary sixth instar. Starvation of newly ecdysed terminal stage host larvae prevents emergence of the parasites. When starvation is begun at progressively later times, then an increasing proportion of the hosts have parasites that emerge, suggesting a period of indispensable host nutrition exists during which the host must feed to satisfy the developmental requirements of the parasites. In hosts fed ad libitum , the weight of the host plus its parasites at the time of emergence is positively correlated with the number of parasites developing in the host. When the weight of the parasites alone is subtracted from the weight of the host—parasite complex, the data show that heavily parasitized hosts have a larger host mass than lightly parasitized larvae. In contrast, the wasp larvae, and the adult males and females that develop from them, have lower individual weights after development in heavily parasitized hosts.