Immune defense often differs between the sexes, with males often having a weaker response, at least among many vertebrates. We examined encapsulation ability, a cell-mediated immune response, in laboratory and field populations of two species of field crickets, Teleogryllus oceanicus (Le Guillou, 1841) and Teleogryllus commodus (Walker, 1869), which have different life histories. In the seasonally breeding T. commodus, males show a stronger encapsulation response than females in both the laboratory and the field, although the difference is more marked under field conditions. The aseasonal T. oceanicus showed no sex difference in encapsulation in either field or laboratory samples fed ad libitum, but when food was experimentally reduced, the same pattern of stronger male response emerged. It is possible that this pattern may result from selection on females to increase investment in reproduction when time and energy for breeding are limited, as is more likely for seasonal breeders or animals under food restriction.