The effect of floral herbivory on male and female reproductive success in Isomeris arborea

Flower-feeding herbivores can directly reduce plant reproduction by consumi ng gametes. They may have additional indirect effects if their damage disru pts pollinator service and causes uneaten gametes to go unused. In a two-ye ar study we investigated direct and indirect effects of florivory by a poll en beetle, Meligethes rufimanus, on the male and female reproductive succes s of the andromonoecious shrub, Isomeris arborea. We measured pollen export , pollen receipt, fruit set, and outcrossing rates on plants exposed to her bivores (most flowers damaged) and protected from herbivores (few flowers d amaged) by systemic insecticide. Pollen export per undamaged flower was red uced by one-half in exposed plants, as estimated by pollinator transfer of florescent dye, which demonstrated indirect negative effects on male reprod uctive success. Damaged flowers on exposed plants had a lower stigmatic pol len load than undamaged flowers on either exposed or protected plants. Furt hermore, exposed plants produced fewer fruits and seeds during the year tha n protected plants. Although damage reduces pollen receipt, hand pollinatio n experiments showed that neither exposed nor protected plants were pollen limited, which suggests that floral herbivores primarily affect female func tion through their direct destruction of gametes. Outcrossing rates did not differ between exposed plants (t(s) = 0.920) and protected plants (t(s) = 0.806), suggesting that herbivory does not indirectly reduce plant reproduc tive success by inducing autogamy and subsequent inbreeding depression. Ove rall, floral herbivory has direct consequences for both male and female rep roductive success, but indirect effects are limited to male function.