A possibility of using synthetic analogues of juvenile hormone (juvenoids) to disrupt imaginal diapause of the apple blossom weevil, Anthonomus pomorum females was demonstrated. Out of three preparations tested (methoprene, fenoxycarb and W-328) methoprene and fenoxycarb appeared to be effective. Sensitivity to juvenile hormone analogues develops early after imaginal emergence (even before the female starts to feed) and lasts throughout the whole aestivo-hibernation dormancy. Although the juvenoids could stimulate the onset of oogenesis at any time during diapause, the propensity of the ovaries to form normal eggs developed only during hibernation part of the dormancy; in earlier stages of diapause accumulation of yolk was observed but matured eggs were not produced. Methoprene treatment caused marked increase of locomotory activity accompanied with decrease of dry weight, increase of water content, depletion of trehalose resources, decrease of cold hardiness and, finally, 100% mortality within four weeks in the weevils treated during their feeding or aestivation stages. Although similar changes were observed in the treated pre-feeding weevils, they later recovered and survived until next spring without apparent loss of cold hardiness. A possibility of designing a control method based on this principle is discussed and the results of small-scale field trials that support its plausibility are reported.
Screening for puparium formation accelerating activity of neuropeptides and/or analogues belonging to 14 different peptide families revealed the strong activity of members and analogues of the pyrokinin/PBAN (pheromone biosynthesis activating neurohormone) family that all share the common C-terminal sequence, FXPRLamide (X = V, T, S, or G). Both pupariation behaviour and cuticular tanning can be accelerated by a C-terminal pentapeptide fragment composed of only the FTPRLamide sequence. Truncation of the C-terminal sequence to the tetrapeptide TPRLa did not diminish either aspect of the activity. Markedly reduced, but still significant, activity was observed after further truncation to the pyrokinin C-terminal tripeptide. The RLa terminal fragment showed no activity. Thus the C-terminal tripeptide appears to be the active core for pupariation acceleration. The core sequence for a maximum response is the C-terminal tetrapeptide TPRLa. This represents a major difference from the activity profile observed in other pyrokinin assays, in which the C-terminal pentapeptide is required. The C-terminal amide group is also of great importance to pupariation acceleration activity, as LPK acid induces a large drop in threshold activity. Periviscerokinin-2 contains a C-terminal tripeptide sequence (PRVamide) that is quite similar to the pyrokinin C-terminal tripeptide PRLamide and, accordingly, elicits a lower level pupariation acceleration activity. The locust pyrokinin Lom-MT-TV preferentially promotes acceleration of the behavioural over the tanning aspects of pupariation and can therefore, in large measure, provide a means of separating the two aspects. Ligation experiments demonstrated that the effect of the LPK analogues on pupariation behaviour is likely mediated through the CNS, while the action on cuticular tanning is of a peripheral nature.
The role of 20-hydroxyecdysone (20E) in the metamorphosis of the central nervous system was investigated by recording feeding, wandering and pupariation behaviour as the measures of hormonal effects on the neural tissues in the flesh fly Neobellieria (Sarcophaga) bullata. The minimum amount of food essential for the commitment to metamorphosis is rather small and constant and the larvae ingest it during the first 4 to12 h of the last instar. Underfed larvae maintain food appetency for a certain time and this period of hunger can be considerably shortened by the application of 20E. Application of 20E also significantly shortens or abolishes the intake of additional food offered to starving larvae. Thus 20E has an effect on neural mechanisms controlling both termination of the period of hunger and suppression of feeding behaviour. Application of 20E at any time during the wandering stage stimulates the precocious onset of pupariation. The central neurons controlling motor patterns of pupariation behaviour are committed to perform properly their programme some 15 h earlier than the larval integument is ready to transform into normal puparium. As a result of this temporal shift of tissue determination, some precociously formed puparia are not properly shaped despite the fact that the larva is exhibiting normal patterns of pupariation behaviour.