Bird T L, Krüger K
Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
Bull Entomol Res. 2006 Feb;96(1):15-23. doi: 10.1079/ber2005398.
A fundamental question concerning crop diversification is which mechanisms determine pest population size in polycultures compared to monocultures. It has been proposed that polyphagous insects experience a difficulty in decision-making when selecting food and oviposition sites in the presence of different host plants. This hypothesis was tested in the extremely polyphagous whitefly Bemisia tabaci (Gennadius) B-biotype, where behaviour (movement) and fecundity of females were compared in choice and no-choice experiments in the laboratory. Two parallel tests, one on different crops, including cucumber, bean and tomato, and one on different tomato cultivars, were conducted using both a mixture of crops and of tomato cultivars, as opposed to the same crop or cultivar respectively. Bemisia tabaci showed a distinct behavioural preference for cucumber when exposed to different crops simultaneously suggesting that B. tabaci has no difficulty in choosing a host plant, i.e. in making a decision, when one of the plants offered in the choice test is a high-ranking host plant. Conversely, when only low-ranking hosts of similar, but not identical, signatures were present, female whiteflies appeared to have difficulty in making a decision, resulting in increased movement and reduced fecundity. This is consistent with both the hypothesis that polyphagous insects have a problem selecting a host plant when given multiple choices and with the hierarchy threshold model, under which egg loads are lessened between periods of searching for better host plants. The study illustrates how insect behaviour can be affected by inter-cropping not only with different crops, but also with different cultivars of the same crop, thus potentially providing a simple and efficient way of reducing whitefly population build-up.
一个关于作物多样化的基本问题是，与单一栽培相比，哪些机制决定了混合作物中害虫的种群规模。有人提出，多食性昆虫在有不同寄主植物存在的情况下选择食物和产卵地点时会面临决策困难。这一假设在多食性极强的烟粉虱Bemisia tabaci（Gennadius）B生物型中进行了测试，在实验室的选择和无选择实验中比较了雌虫的行为（移动）和繁殖力。进行了两项平行试验，一项针对不同作物，包括黄瓜、豆类和番茄，另一项针对不同番茄品种，试验分别使用作物混合物和番茄品种混合物，而不是相同的作物或品种。当同时接触不同作物时，烟粉虱对黄瓜表现出明显的行为偏好，这表明当选择试验中提供的植物之一是优质寄主植物时，烟粉虱在选择寄主植物即做出决策方面没有困难。相反，当只存在相似但不完全相同特征的低等级寄主时，雌性粉虱似乎难以做出决策，导致移动增加和繁殖力下降。这与多食性昆虫在面临多种选择时选择寄主植物存在问题的假设以及等级阈值模型均相符，根据该模型，在寻找更好寄主植物的间隙，卵的负载量会减少。该研究说明了间作不仅与不同作物，而且与同一作物的不同品种间作如何影响昆虫行为，从而有可能提供一种简单有效的方法来减少粉虱种群的增长。
