Mating and reproduction behaviors and strategies are fundamental aspects of an organism's evolutionary and ecological success. In locusts, intra-as well as inter-phase reproductive interactions among gregarious and solitarious locust populations have a major impact on the locust population dynamics. However, practically all previous work on locust sexual behavior has been limited to the gregarious phase. Here we provide a first detailed description of pre-copulatory behavior of solitarious desert locusts. We compare our findings with those of previous reports of pre-copulatory behavior of gregarious locusts, focusing on the behavioral elements that serve in inter-sex signaling and communication. We also studied inter-phase (mixed pairs) reproductive interactions.Solitarious males were found to invest more in pre-copulatory courtship and signaling compared to their gregarious counterparts; and the solitarious females played a comparatively more dominant role in the inter-sex communication. The solitarious females were also less prone to demonstrate the typical rejection-related behavioral patterns displayed by the gregarious females. As a consequence of the particular characteristic behavior of each phase, the most successful among intra-and inter-phase pairs were gregarious males with solitary females. Least successful were solitary males encountered with gregarious females, indicating a strong asymmetry in inter-phase reproductive interactions. We discuss these results in the context of non-random or assortative mating in locust mixed or sympatric solitarious-gregarious populations.

15Mating and reproduction behaviors and strategies are fundamental aspects of an 16 organism's evolutionary and ecological success. In locusts, intra-as well as inter-phase 17 reproductive interactions among gregarious and solitarious locust populations have a 18 major impact on the locust population dynamics. However, practically all previous work on 19 locust sexual behavior has been limited to the gregarious phase. Here we provide a first 20 detailed description of pre-copulatory behavior of solitarious desert locusts. We compare 21 our findings with those of previous reports of pre-copulatory behavior of gregarious 22 locusts, focusing on the behavioral elements that serve in inter-sex signaling and 23 communication. We also studied inter-phase (mixed pairs) reproductive interactions. 24Solitarious males were found to invest more in pre-copulatory courtship and signaling 25 compared to their gregarious counterparts; and the solitarious females played a 26 comparatively more dominant role in the inter-sex communication. The solitarious females 27 were also less prone to demonstrate the typical rejection-related behavioral patterns 28 displayed by the gregarious females. As a consequence of the particular characteristic 29 behavior of each phase, the most successful among intra-and inter-phase pairs were 30 gregarious males with solitary females. Least successful were solitary males encountered 31 with gregarious females, indicating a strong asymmetry in inter-phase reproductive 32interactions. We discuss these results in the context of non-random or assortative mating 33 in locust mixed or sympatric solitarious-gregarious populations. 34 35 36 37 Key words: Schistocerca gregaria, Locust density-dependent phase polyphenism, 38 sexual behavior, reproductive phenotype 39