Development of the wing discs of Zophobas atratus under natural and experimental conditions: occurrence of a gradual larval-pupal commitment in the epidermis of tenebrionid beetles

Abstract

Using light and electron microscopy, we studied the development of the wing discs in the large beetle Zophobas atratus, under natural and experimental conditions. A reversible differentiation of the wing discs is usually observed during supernumerary instars of crowded larvae. Juvenile hormone analog (JHA) application during the wandering period or compelled experimental crowding during the larval-pupal switchover - or commitment - inhibits the onset of metamorphosis. Isolation, followed by recrowding, also induces the disc cells to secrete unusual cuticular material. Recrowding is able to trigger the reversal of metamorphosis during the 4-day period when larval-pupal commitment is taking place. Likewise, feeding behaviour which normally stops at commitment often recovers. Ecdysis of intermediate instar animals (prothetelic larvae) corroborates the occurrence of a temporal and spatial variation to commitment, unique to each organ. All these data lead us to consider this 4-day period, which we have called the C period or commitment period, extending from the wandering stage (the previous T period) to the crooked posture stage (i.e. from eyestage 4 to 7) as the physiological time during which the larval organs are gradually committed to differentiate into pupal organs.

The role of Broad in the development ofTribolium castaneum:implications for the evolution of the holometabolous insect pupa

“…The expression of these isoforms during the prepupal period appears to correspond to the time when the ecdysteroid titer rises prior to pupation in Tribolium and Tenebrio molitor (Hirashima et al, 1995;Quennedey and Quennedey, 1999). As in Bombyx penultimate stage larvae (Ijiro et al, 2004;Nishita and Takiya, 2004), low levels of br are present earlier in Tribolium larvae, and even the embryos (Konopova and Jindra, 2008), but no disruption of larval development has been noted after br dsRNA treatment in the penultimate (our study) or earlier (Konopova and Jindra, 2008) stages.…”

“…3A), and the expression remained high for the remainder of the instar. This rise in expression occurs around 1 to 2 days before the larvae enter the stationary crooked posture stage that signals the onset of visible metamorphosis (Quennedey and Quennedey, 1999). It should be noted that different numbers of cycles were used for each isoform, and, based on the number of cycles alone, br-Z4 mRNA appears to be most abundantly expressed, whereas br-Z2 mRNA is expressed least abundantly.…”

Caste morphology and development intermitogetonnr.planus(insecta, isoptera, rhinotermitidae)

“…So-called "regressive molts," at which wing buds are reduced or lost, are a common occurrence in Kalotermitidae (Grassé and Noirot, 1947;Roisin, 1990) and some Rhinotermitidae (Miller, 1942;Buchli, 1958), but up to now such molts were never shown to constitute an obligatory event in any individual's ontogeny. An analogous phenomenon, involving a reversion of the differentiation of wing disc cells, has also been observed in tenebrionid beetles under particular conditions of crowding or experimental treatment by JH analogs (Quennedey and Quennedey, 1999).…”

bHLH-PAS family transcription factor methoprene-tolerant plays a key role in JH action in preventing the premature development of adult structures during larval–pupal metamorphosis

“…Both studies have shown that loss of sensitivity of wing discs and epidermal cells to JH completes the commitment process. Application of JHA during the final instar of tenebrionid beetles revealed the commitment period for wings, antennae, eyes, prothorax and tarsi (Connat et al, 1984;Quennedey and Quennedey, 1999). Though we could not directly relate because of the difference in developmental period of T. castaneum, the commitment period is likely to occur through the end of the feeding stage (Parthasarathy and Palli, unpublished).…”