Buteler Micaela, Weaver David K, Peterson Robert K D
Department of Land Resources and Environmental Sciences, Montana State University, 334 Leon Johnson Hall, Bozeman, MT 59717-3120, USA.
Environ Entomol. 2009 Dec;38(6):1707-15. doi: 10.1603/022.038.0624.
Insect herbivores typically oviposit on the most suitable hosts, but choices can be modulated by detection of potential competition among conspecifics, especially when eggs are deposited cryptically. Larvae of the wheat stem sawfly, Cephus cinctus Norton, developing within an already infested stem, experience elevated risk when only one will survive because of cannibalism. To increase our understanding of host selection when the choices made by females can lead to severe intraspecific competition, females were presented with either uninfested wheat plants or with plants previously exposed to other females in laboratory choice tests. The oviposition behavior of this insect was described by recording the behavioral sequences that lead to and follow the insertion of the ovipositor in both previously infested and uninfested stems. No significant differences were found in frequencies of specific behaviors or behavioral transitions associated with oviposition. In choice tests, there was no difference in the numbers of eggs laid in infested and uninfested plants. Taller plants received more eggs, irrespective of infestation. Females neither preferred nor avoided previously infested hosts. Other characteristics of the host, such as stem height, may be more important in determining suitability for oviposition. These findings support the use of management tactics relying on the manipulation of oviposition behavior, such as trap cropping. Given that there is no evidence for response to previously infested hosts, the infested plants in a trap crop would remain as suitable as they were when uninfested, which could also lead to an increase in mortality caused by intraspecific competition.
植食性昆虫通常会在最合适的寄主上产卵，但这种选择可能会受到对同种个体间潜在竞争的感知的调节，尤其是当卵被隐蔽地产下时。小麦茎蜂（Cephus cinctus Norton）的幼虫在已经被侵染的茎内发育，当由于同类相食只有一只幼虫能够存活时，其面临的风险会增加。为了增进我们对雌性昆虫做出的选择可能导致严重种内竞争时寄主选择的理解，在实验室选择试验中，给雌性小麦茎蜂提供未被侵染的小麦植株或之前已被其他雌性昆虫接触过的植株。通过记录在之前被侵染和未被侵染的茎中导致产卵器插入以及紧随其后的行为序列，描述了这种昆虫的产卵行为。在与产卵相关的特定行为或行为转变的频率上未发现显著差异。在选择试验中，在被侵染和未被侵染的植株上产下的卵的数量没有差异。无论是否被侵染，较高的植株会接收到更多的卵。雌性昆虫既不偏好也不避开之前被侵染的寄主。寄主的其他特征，如茎的高度，在决定是否适合产卵方面可能更重要。这些发现支持采用依赖于操控产卵行为的管理策略，如诱集作物种植。鉴于没有证据表明对之前被侵染的寄主有反应，诱集作物中的被侵染植株将保持与未被侵染时一样适合产卵，这也可能导致种内竞争引起的死亡率增加。
