This study investigated the influence of host plant availability and suitability to the abundance pattern ofNezara viridulaL. in soybean-growing areas of southeastern Queensland, Australia. In particular, the reasons why bug numbers are low during summer months and why the bugs concentrate and increase on fruiting soybean later in the season were investigated. Glasshouse experiments showed that the host plant species available to bugs during summer were inadequate for egg production by adult females and for nymphal survival and development. However, host plant species available to bugs in spring (the wild crucifersRapistrum rugosum(L.) All. andRaphanus raphanistrumL.) and in early autumn (fruiting soybean) were suitable. The number of nymphs produced per female was highest on these host plant species, and nymphal survival was also high. The concentration of bugs on fruiting soybean for feeding and oviposition was not caused by the attractiveness of the plant relative to other host species but may be attributed to the unavailability of other suitable hosts (species and plant growth stage) other than soybean in the area during this time of the season. The concept of host plant suitability is also reexamined specifically in relation toN. viridula-host plant interaction.