Morphometric differentiation in a field population of Dichroplus maculipennis (Orthoptera: Acrididae: Melanoplinae) under outbreak and non-outbreak situations

MARIOTTINI, Y.; SCATTOLINI, M.C.; CIGLIANO, M. M.; LANGE, C. E.

JOURNAL OF ORTHOPTERA RESEARCH

The Orthopterists Society

Año: 2015 vol. 24 p. 67 - 75

1082-6467

Dichroplus maculipennis is one of the most damaging grasshopper speciesof Argentina. Individuals of this species at high density are historically knownto show aggregation behavior and dispersal flights, attributes that mightsuggest that it does exhibit to some extent phase polyphenism in relationto population density. Phase polyphenism is a complex phenomenon andthe amplitude of phase change is usually species-dependent. Morphologicaldifferences between gregarious and solitarious locusts can be measuredand analyzed in order to characterize the phase status. The objective ofthis study was to evaluate morphometric differences between individualsof a D. maculipennis field population in the southern Pampas region ofArgentina during non-outbreak and outbreak conditions including themagnitude of sexual size dimorphism related to variation in density.Collected individuals in the outbreak condition totaled 804 (422 females,382 males) and those in non-outbreak condition were 325 (141 females,184 males). Six morphometric characters were measured and two ratios (F/Cand E/F) usually used to discriminate between solitarious and gregariousindividuals in true locust species were calculated. Results show that sizetraits of D. maculipennis change over time at the population level, and thatthese changes correlate with outbreak vs non-outbreak populations. Femalesand males of D. maculipennis in outbreak conditions are significantly largerthan in non-outbreak conditions. Furthermore, significant change over timewas recorded in values of the two ratios calculated. D. maculipennis showedfemale biased sexual size dimorphism in both outbreak and non-outbreakconditions. There is a smaller difference in body size among females andmales in outbreak conditions than in females and males in non-outbreakconditions. These results may be an indication of the presence of densitydependentphenotypic plasticity in this species, but additional experimentsare required in order to establish a causal relationship between populationdensity and changes in size traits.