Leaf damage by herbivores affects attractiveness to pollinators in wild radish, Raphanus raphanistrum

Abstract

We carried out two experiments to determine the effect of leaf damage on plant attractiveness to pollinators using wild radish, Raphanus raphanistrum (Brassicaceae), a self-incompatible annual herb. Pairs of plants from 36 full-sib families were grown in pots in the greenhouse. One member of each pair was damaged by Pieris rapae larvae that were allowed to remove half of the leaf area of each of the first four rosette leaves. The plants were subsequently taken out for pollinator observations once a week from the beginning of flowering in late June until the end of August. We conducted two experiments to examine how foliar damage affected visitation by pollinators. In the first experiment, numbers of pollinators visiting plants were compared between damaged and control sibling plants. In the second experiment, the number of open flowers during observations was controlled to be the same for both damaged and undamaged sibs. Damage significantly decreased the number and size of flowers during the first observations in late June. Damaged plants received fewer visits by native bees during the first week of observations. Since damage did not affect native bee visits when the number of open flowers was equalized between treatments, flower number was probably the main cue attracting native bees to plants. In the experiment without flower number control, syrphid flies, the other abundant pollinator taxon, spent more time per flower on the undamaged than on the damaged plants. When flower number was controlled, flies probed significantly more flowers during each visit on the undamaged than on the damaged plants and had higher visitation rates to undamaged plants early in the season. Since syrphid flies preferred undamaged plants both with and without flower number control, they apparently used cues apart from flower number for visitation. The difference between undamaged and damaged plants in floral characteristics and pollinator visitation vanished within a few weeks after the start of flowering. This result suggests that early damage may not have a strong fitness effect through reduction in mating success. However, poor weather conditions can cause early mortality of plants in the field, and nutrient depletion and competition decrease fruit set of later flowers. Therefore, conditions exist under which visitation to early flowers may affect plant fitness.

Herbivory by sucking mirid bugs can reduce nectar production in Asphodelus aestivus Brot.

“…Similar results were noted in desert populations of A. aestivus, where the mirid bug's feeding included flower buds and flowers (Ayal and Izhaki 1993): damage to the buds would most likely cause a reduction in the total number of flowers. Production of fewer flowers because of herbivory is not rare and has been observed on other plants also (Karban and Strauss 1993;Quesada et al 1995;Strauss et al 1996;Juenger and Berelson 1997;Lehtilä and Strauss 1997;Mothershead and Marquis 2000). This activity may exert an important influence on reproductive success, as it can reduce the plant's attractiveness to pollinators and thereby reduce its fitness (Willson and Price 1976;Strauss et al 1996;Lehtilä and Strauss 1997;Keasar et al 2008).…”

“…Production of fewer flowers because of herbivory is not rare and has been observed on other plants also (Karban and Strauss 1993;Quesada et al 1995;Strauss et al 1996;Juenger and Berelson 1997;Lehtilä and Strauss 1997;Mothershead and Marquis 2000). This activity may exert an important influence on reproductive success, as it can reduce the plant's attractiveness to pollinators and thereby reduce its fitness (Willson and Price 1976;Strauss et al 1996;Lehtilä and Strauss 1997;Keasar et al 2008). Environmental conditions such as temperature and humidity have been regarded in the past as major factors in determining nectar yield (Corbet 1978;Bertsch 1983;Pleasants 1983).…”

The biology of Canadian weeds. 132. Raphanus raphanistrum L.

“…The principal pollinators, i.e the native bees and syrphid flies, showed a preference for undamaged plants, visiting them more frequently and spending more time on them compared with those damaged by Pieris rapae larvae (Strauss et al 1996). However, bees, unlike the flies, did not distinguish between damaged and undamaged plants when flower numbers were controlled (Lehtilä and Strauss 1997). Under herbivory, male fitness traits, such as pollen size and number, were reduced, whereas female fitness traits, such as ovule size and number, were not affected (Lehtilä and Strauss 1999).…”

Herbivory reduces plant interactions with above‐ and belowground antagonists and mutualists

“…Numerous studies have shown that leaf damage can alter floral attractive traits that influence pollinator attraction (Adler 2007) such as flower number Strauss 1997, Hamback 2001), flower size (Aizen and Raffaele 1996, Strauss et al 1996, Lehtila¨and Strauss 1997, Mothershead and Marquis 2000, nectar production or quality (Adler et al 2006, Samocha andSternberg 2010), and floral volatiles Halitschke 2009, Theis et al 2009). These changes can reduce pollinator attraction (Strauss et al 1996, Lehtila¨and Strauss 1997, Mothershead and Marquis 2000 Halitschke 2009), with negative consequences for plant reproduction (Strauss and Murch 2004). For example, leaf herbivory in Oenothera macrocarpa (Onagraceae) resulted in smaller flowers that attracted fewer pollinators, reducing both fruit set and seed production as a result of pollen limitation (Mothershead and Marquis 2000).…”