Phase Characteristics of the Israeli Population of the Migratory Locust, Locusta migratoria (L.) (Orthoptera: Acrididae)

An Israeli population of Locusta migratoria (L.) is described. It does not exhibit density related changes in morphometrics and in the abundance of small basiconica, antennal sensilla presumably involved in contact chemoreception. In these respects it differs from L. m. migratorioides (Reiche & Fairmaire) and could be described as persistently solitarifornm'. Solitariform characteristics are retained in the F, and F2 progeny reared in the laboratory under crowded conditions, sufficient to induce the appearance of the gregarious phase in L. m. migratorioides. However, the abundance and distribution of coeloconica (antennal sensilla presumably involved in olfactory chemoreception), are significantly affected by population density and the two behavioural parameters examined-activity level and associative indexin nymphs of the Israeli population reared under crowded conditions, are also typical of the gregarious phase. The Israeli population and L. m. migratorioides cultures cross-breed in the laboratory. Hybrids are viable and fertile. The hybrid behaviour is similar to that of L. m. migratorioides. We conclude that while the behavioural response of the Israeli population to density is similar to L. m. migratorioides and is accompanied by changes in the abundance and distribution of coeloconic antennal sensilla, its morphometrics remain unaffected, at least in the short term. The implications of these peculiarities are discussed.