Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2009
Publication Date: 1/1/2009
Citation: Benda, N.D., Brownie, C., Schal, C., Gould, F. 2009. Fruit abscission by Physalis species as defense against frugivory. Entomologia Experimentalis et Applicata. 130:21-27. Interpretive Summary: Many plants drop, or abscise, fruit in response to insect feeding. Because herbivore-damaged fruit may not develop properly, abscission may be an efficient way for a plant to cut its losses by not investing further in the damaged fruit. But when the offending herbivore falls off the plant along with the abscised fruit, abscission can additionally be viewed as a defensive tactic against the herbivore. Few studies have looked at fruit abscission as a strategy to rid the plant of unwanted herbivores and reduce insect feeding damage. Physalis, a relative of tomatoes, abscises fruit in response to feeding by its main frugivore, Heliothis subflexa. Heliothis subflexa (Lepidoptera: Noctuidae), is a specialist moth that feeds only on Physalis plants. In this study, we tested the ability of H. subflexa larvae placed under the plant canopy to find and climb onto the Physalis plant, ostensibly after climbing out of an abscised fruit. We used tall and short species of Physalis. Larvae located the low-growing Physalis more quickly and with a higher probability than the tall Physalis. Since larval size may also affect the ability of the larvae to reach the plant, we also tested both young (third instar) and older (fifth instar) larvae. Fifth instars outperformed third instar larvae at finding the tall Physalis, but the short Physalis was located equally as quickly by both instars. Finally, we compared the behavior of specialist H. subflexa with that of a close relative, the generalist H. virescens. Heliothis subflexa located Physalis plants more successfully and more quickly than H. virescens. Larvae dropped during Physalis fruit abscission are hindered from damaging further fruit on the plant. The higher rate of fruit drop in the low-growing Physalis may be an evolved response to its greater susceptibility to searching caterpillars.
Technical Abstract: Fruit abscission as a response to herbivory is well-documented in many plant species, but its effect on further damage by mobile herbivores that survive fruit abscission is relatively unstudied. Physalis plants abscise fruit containing feeding larvae of their main frugivore, Heliothis subflexa Guenée (Lepidoptera: Noctuidae), a specialist noctuid moth. We tested the ability of H. subflexa larvae placed under the plant canopy to find and climb onto two architecturally different Physalis species. Physalis pubescens L., a low, shrub-like, spreading plant, abscises its fruit at a higher rate than P. angulata L., a tall arborescent plant. As a result, small larvae are more often dropped from P. pubescens. Third and fifth instar larvae located P. pubescens more quickly and with a higher probability than P. angulata. Although fifth instars outperformed third instar caterpillars at finding P. angulata, P. pubescens was located equally as quickly by both instars. Heliothis subflexa located Physalis plants more successfully and more quickly than a close relative, the generalist H. virescens F. The higher fruit abscission rates in P. pubescens may be an evolved response to its greater susceptibility to searching caterpillars.