AN “INTERVAL TIMER” FOR THE PRODUCTION OF OVIPARAE IN APHIS RUBICOLA (HOMOPTERA: APHIDIDAE)

Abstract

Post‐fundatrix lineages of Aphis rubicola Oestlund exposed to continual short‐day photoregimes of 8 or 10 h resisted sexual‐promoting influences for varying lengths of time. Lineages originating from fundatrices and continually exposed to short days lasted 18.5–31.5 days before consisting of 50% ovipara producers. When 13–67 16‐h days preceded continual short‐day exposure, lineages lasted 11.5–19 days before consisting of 50% ovipara producers. A short‐lived interval timer for the production of oviparae was thus demonstrated. The timer expired gradually, not abruptly, so that the greater the distance was in days from the newly hatched fundatrix, the less was the time required for 50% of the adults to be ovipara producers (r = −0.892). Weakening in a curvilinear fashion, the timer lost its greatest amount of resistance between the 5th and 13th days of deposition by fundatrices. ZUSAMMENFASSUNG EIN “INTERVALL‐ZEITMESSER” FÜR DIE BILDUNG VON OVIPAREN BEI APHIS RUBICOLA (HOMOPTERA: APHIDIDAE) Linien von Fundatrigenien von Aphis rubicola Oestlund, welche kontinuierlichem Kurztag von 8 rsp. 10 Stunden ausgesetzt wurden, widerstanden den die Bildung von Geschlechtstieren fördernden Einflüssen für verschiedenlange Zeit. Linien, welche ständig Kurztag ausgesetzt wurden, brauchten 18,5 bis 31,5 Tage, bis sie zu 50% aus Sexuparen bestanden. Wenn die Linien vorgängig für 26,5 bis 80,5 Tage Langtag (16 Stunden) ausgesetzt wurden, bevor sie zu Kurztag kamen, brauchte es 11,5 bis 19 Tage, bis 50% Sexupare waren. Damit wurde ein kurzlebiger Intervall‐Zeitmesser für die Bildung von Geschlechtstieren nachgewiesen. Dieser Zeitmesser erlöscht allmählich in krummliniger Form und nicht plötzlich. Je grösser der zeitliche Abstand von der Junglarve der Fundatrix, um so kleiner war die erforderliche Zeit, bis 50% der Adulten Sexupare waren (n = −0,892).

Transgenerational seasonal timer for suppression of sexual morph production in the pea aphid, Acyrthosiphon pisum

“…A seasonal timer that expires by autumn would be adaptive for responding appropriately to shortened days. The present findings were similar to those of previous studies in M. viciae and A. rubicola: Mothers that had been reared successively under long days and transferred to short days produced many oviparous females (Brodel and Schaefers, 1979;Lees, 1960). These results altogether showed that the sexual polyphenism in aphids is regulated by two mechanisms, and one of them depends on photoperiod whereas the other does not.…”

“…The present results show that in A. pisum, the seasonal timer measured the number of days from hatching, not the number of generations, in accord with the reported findings in M. viciae and A. rubicola (Brodel and Schaefers, 1979;Lees, 1960).…”

“…In many previous studies, however, it was unclear whether the number of days or the number of generations from hatching is important (Campbell and Tregidga, 2006;Dixon, 1972Dixon, , 1971Dixon and Glen, 1971;Lushai et al, 1996;Margaritopoulos et al, 2002;Wilson, 1938). Temperature affects the duration for which the seasonal timer can function in M. viciae, whereas photoperiod has no effect on the duration in Aphis rubicola (Brodel & Schaefers 1979;Lees 1960). Although the physiological and molecular mechanisms suppressing sexual morph production remain unknown (Tagu et al, 2005), determining the physiological characteristics of the seasonal timer might provide insights into these mechanisms.…”

Multigenerational maternal inhibition of prepupal diapause in two Trichogramma species (Hymenoptera: Trichogrammatidae)

“…The similar results were obtained in experiments with Aphis chloris Koch. Aphis rubicola Oestlund, Drepanosiphum platanoides (Schrank), Eucallipterus tiliae L., Myzus persicae (Sulzer), and Phorodon humuli (Schrank) although in these aphids, the ability to produce sexuales gradually increased over several generations (Brodel and Schaefers, 1979;Campbell and Tregidga, 2006;Dixon, 1971Dixon, , 1972Margaritopoulos et al, 2002;Wilson, 1938). It is interesting that we have found both gradual (in T. principium) and relatively rapid (in T. telengai) waning of the maternal restraining effect.…”

“…Of course, metabolic and signal mechanisms are not mutually exclusive, but long-term effects are most probably based on transfer of signals rather than nutrients. In the regulation of insect diapause, these effects are often manifested as 'interval timers' which measure time intervals independently of the number of elapsed generations, although 'generation counters' reducing the effect in accordance with the number of generations passed can be also conceived (Brodel and Schaefers, 1979;Campbell and Tregidga, 2006;Denlinger, 1998Denlinger, , 2002Dixon, 1971Dixon, , 1972Lees, 1960Lees, , 1966Lushai et al, 1996;Margaritopoulos et al, 2002;Ogawa and Miura, 2014;Saunders et al, 2002). At present, biochemical and molecular mechanisms of diapause induction are intensively investigated (Denlinger, 2002;Denlinger et al, 2012) but 'classic physiological experiment' still remains an important tool for future studies (Goto and Numata, 2014).…”