Ecdysis, insects treated with

Earlier work investigated growth effects from monoterpenoids dosed topically on last-instar larvae of the house fly (19). Development and metamorphosis failures occurred with several compounds. Cineole was the most active inhibitor of pupal eclosion (40% inhibition at a dose of 10 /lig/insect) and of imaginal differentiation, within those uneclosed pupae. Camphene, eugenol, and a-pinene were also active. Inhibition of pupal ecdysis was highest in insects treated with camphene, although carvone and several others were also effective. 

If the compound is causing the insect to be stressed or intoxicated, the insect larva (in this case a prepupa) may have trouble casting the old cuticle, yet be capable of tanning. Thus, the insect becomes a tanned larva or what appears to be a half pupa/half larva (due, in part, to incomplete ecdysis). For example, larvae treated with paraoxon (200 nmol./larva data not included in Table I due to high mortality) caused the formation of tanned larvae in all larvae treated. However, all of these larvae had obviously been adversely affected (intoxicated) by the paraoxon... 

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