Phase polymorphism in Locusta migratoria: The relative effects of geographical strains and albinism on morphometrics

An albino strain, which had originated from Okinawa, Japan, and a normally coloured strain, which had originated from West Africa, have been used to study density-dependent morphometric phase characteristics and their changes in adults of the migratory locust, Locusta migratoria (L.). By repeated crossings we also obtained congenic albinos and normal phenotypes and investigated their morphometrics with increasing West African genome, eventually reaching 99.6% West African and 0.4% Okinawa gene pool. The data were analysed by the classical morphometric ratios (F/C and E/F; F = length of the hind femur, C = maximum width of the head, E = length of the fore wings), as well as by canonical discriminant (multivariate) analysis. The latter was based on measurements of F, C and E (as above), as well as of M (minimum width of the pronotum) and H (maximum height of the pronontum). Okinawa albinos showed more solitarious morphometrics and a smaller amplitude of morphometric phase change than West African normal phenotypes. Both the morphometric ratios and the canonical discriminant analysis demonstrated clearly that these differences were caused primarily by the strain (Okinawa vs. West African). However, the pigmentation (albino vs. normal colouration) also affected morphometric phase differences; albinos showed more solitarious morphometrics and somewhat more restricted morphometric phase change than congenic normal phenotypes. The effect of the pigmentation was considerably smaller than that of the strain. The results refute Nolte's claim that albino locusts constitute an extreme solitarious phase, even under crowding. However, Nolte's less extreme claim, that albino locusts have more solitarious morphometrics than normally coloured locusts, is validated by the present results.