A comparison of phase-related shifts in behavior and morphometrics of an albino strain, deficient in [His7]-corazonin, and a normally colored Locusta migratoria strain

The albino Okinawa strain of Locusta migratoria is deficient in the neurohormone [His7]-corazonin. This peptide induces darkening of the cuticle, one of the typical features of gregarious locusts. As part of a broader study on the possible role of [His7]-corazonin in phase transition, we explored whether corazonin-deficiency might be associated with differences in behavior and morphometrics between albino and normal phenotypes of L. migratoria. Using a modification of the logistic-regression assay of behavioral phase state previously derived for Schistocerca gregaria, we found that there were strain dependent behavioral differences between crowd-reared nymphs of the albino Okinawa and the normally colored African strain, with no evidence of the albino strain being obligatorily solitarious. However, upon isolation, a shift towards more solitarious behavior occurs in both strains, even more profoundly in the Okinawa albinos. A shift could also be recorded in morphometrics. The conclusion is that the albino strain, although showing some solitarious features even when crowd-reared, is not, as has been suggested, obligatory solitarious and, as a consequence, the complete absence of corazonin is not sufficient to bring about the solitarious state.