In addition, larger late instars and adult specimens are much easier to exude feces from for analysis; smaller instars are often ignored because of handling difficulties.
Field studies of overwintering mountain pine beetles have found that cold exposure disproportionately killed early (smaller) instars relative to later (larger) instars (Amman, 1973; Safranyik et al., 1974; Langor, 1989; Safranyik & Linton, 1998).
We tested small (second and third instars; length<1.5 cm) and large (fourth and fifth instars; length≥1.5 cm) Z. annulosus nymphs reared in plastic boxes in the laboratory.
For colonization, we counted larvae of several species by instar or size class and we used those data to record colonization events (or hatchings after water refilled treeholes) based on appearance of first instar or small larvae.
The extent to which the small tents of the early instars of Malacosoma americanum warmed when irradiated by sunlight was investigated by continuous electronic monitoring of field colonies for 137 colony-days.
Wing disks are very small until the last larval instar, when they increase dramatically in size, are invaded by branching tracheae from the wing base that precede the formation of the wing veins, and begin to develop patterns associated with several landmarks of the wing.
The resulting scatterplot suggests a number of groupings that may represent instars, although the smallest individuals fall very close together and are difficult to separate.
Early in the third (final) larval instar (L3), a small peak of the steroid hormone ecdysone has been proposed to induce a developmental transition known as critical weight (Mirth and Riddiford, 2007; Mirth and Shingleton, 2012).
The hanging spider Anelosimus aulicus showed a strong positive ontogenetic allometry of leg length with body size (MAslope = 4.2; 95% CIs: [2.9 7.4]), suggesting that even within the same species, longer legs can also benefit the larger instars relative to the small ones.
It is interesting to note that despite the variation included within each life stage (e.g., multiple embryonic stages, different larval instars) and the very small sample sizes, life stages were still strongly differentiated in terms of gene expression.
