温度对食蚜瘿蚊生长发育的影响

在19,22,25,28,31℃和RH为80%的组合下,测定食蚜瘿蚊Aphidoletes aphidimyza Rondani的发育历期,分析发育速率与温度的关系,并且测定各温度下食蚜瘿蚊的化蛹率和羽化率等生物学参数。实验结果表明:温度对食蚜瘿蚊的生长发育有较大影响。在19~28℃范围内,食蚜瘿蚊各虫态的发育历期随温度的升高而缩短,而在28~31℃范围内,食蚜瘿蚊各虫态的发育历期随着温度的升高而略为延长。采用线性日度模型和Logistic模型对卵期、幼虫期、蛹期和全世代的发育速率进行模拟分析,2种模型均能较好地反映各虫态的发育速率。不同温度下食蚜瘿蚊的5天化蛹率和总羽化率差别较大,但以25℃下为最高,分别为88.00%和94.70%;而22℃下的化蛹率和羽化率与25℃下较为接近,分别为84.00%和90.66%,经分析差异不显著。食蚜瘿蚊最适生长发育温度为22~25℃。     

应用生命表评价食蚜瘿蚊扩繁系统

应用生命表技术,考察我国食蚜瘿蚊Aphidoletes aphidimyza大量扩繁系统主要环节的效率。结果表明,卵期、1龄幼虫期、蛹期的死亡率较大,分别为13.5%、18.2%和19.0%,是影响种群数量增长的主要因子。通过对各发育阶段的观察,初步明确了造成死亡的主要因素,连续多代饲养中的性比失调问题对卵的饱满率及产卵量有很大影响,化蛹的场所条件、发育及贮藏条件、1龄幼虫的食物供给状况也是造成实验种群大量死亡的主要因子。本实验结果为进一步改进该天敌的扩繁体系,提高扩繁效率,具有指导作用。     

食蚜瘿蚊触角的扫描电镜观察

用扫描电子显微镜对食蚜瘿蚊角角进行了观察.结果显示,雌雄触角都为14节,其中雄性约为2000μm,雌性约为1 050μm.电镜下可观察到食蚜瘿蚊触角有6种类型的感受器,即：刺形感受器、毛形感受器、锥形感受器、腔形感受器、柱形感受器和环丝.刺形感受器较长,约67.5μm,基部有膜状的窝.毛形感受器长约61μm,末端弯曲.锥形感受器呈钉状着生在表皮上,长约4.7μm.腔形感受器呈凹陷状,腔的直径约为1.2μm.柱形感受器着生在雄虫鞭节的第二亚节,长约21μm,直径约为1.5μm.环丝,是瘿蚊类昆虫触角中特殊的结构,它通过着生在一系列腔中的的短梗,连结成环状附着在触角各亚节的表面.刺形和锥形感受器在数量上,雌雄之间差别不大;柱形感受器只在雄虫中发现;雄虫触角上的腔形感受器在数量上要比雌虫多.     

When to estimate sex ratio in natural populations of insects? A study on sex ratio variations of gall midges within a generation

Precise estimation of arthropods' sex ratio is an important issue in a wide range of ecological studies and biological control programs. Although, in many cases changes in arthropods' sex ratio may be under the control of parents or some symbiotic microorganisms, biased sex ratios in some other species are caused by some extrinsic factors, neglect of which may lead to under/overestimation of true sex ratio. In this paper, we pursued those factors that cause false estimation of sex ratio in insects' species. We studied the predatory gall midge, Aphidoletes aphidimyza Rondani (Diptera: Cecidomyiidae), an important biological control agent of aphids, that shows protandry (i.e. early male emergence), differential lifespan of sexes, and differential distribution of sexes across habitat. Ten populations of A. aphidimyza were released separately in transparent cages and their sex ratio variations were recorded every 12 hours. The primary sex ratio in this species seems to be slightly male‐biased (52.41% males), however early emergence of males biases the sex ratio up to 72% males in a few hours after emergence. Shortly after the emergence of females, the sex ratio reaches its primary situation, but as a result of male‐biased mortality after mating, the proportion of females increases gradually to 97% by the fourth and fifth days after emergence. These results explicitly suggest that direct estimation of sex ratio in natural populations may be affected by some secondary factors such as differential mortality of sexes, protandry, and differential distribution of males and females over time and/or across habitat.     

Does insect mother know under what conditions it will make their offspring live?

According to the optimal oviposition theory, the larval success of insects depends on the oviposition site selection by females. Females are expected to choose a site with many resources and few competitors or predators to allow the best performance for their progeny, assuming that “mother knows best.” However, this is not systematically observed. The Aphidoletes aphidimyza larvae are generalist aphid predators and females consequently lay their eggs near or inside aphid colonies. The goal of this study was to investigate the impact of intraspecific competition on oviposition behavior of A. aphidimyza females. First, we counted the number of eggs laid by a female on a leaf with 20 aphids, in the presence of 0, 2, 4, or 6 conspecific eggs or in the absence of eggs but in presence of 3 virgin females. The same experiment was also performed under choice condition with 2 oviposition sites. Our results show that the presence of low densities of conspecific eggs, or the presence of conspecific females, have no significant impact on the number of eggs laid by A. aphidimyza females. One of the hypotheses advanced to explain these results is the advantages of conspecifics presence. At low densities, the presence of eggs on an oviposition site can indicate the suitability of the site for the females. The conspecific presence can also insure a dilution effect against predator and increase the presence of potential mating partners for this monogenic species.     

Within-colony feeding selectivity by a corallivorous reef fish: foraging to maximize reward?

Foraging theory predicts that individuals should choose a prey that maximizes energy rewards relative to the energy expended to access, capture, and consume the prey. However, the relative roles of differences in the nutritive value of foods and costs associated with differences in prey accessibility are not always clear. Coral‐feeding fishes are known to be highly selective feeders on particular coral genera or species and even different parts of individual coral colonies. The absence of strong correlations between the nutritional value of corals and prey preferences suggests other factors such as polyp accessibility may be important. Here, we investigated within‐colony feeding selectivity by the corallivorous filefish, Oxymonacanthus longirostris, and if prey accessibility determines foraging patterns. After confirming that this fish primarily feeds on coral polyps, we examined whether fish show a preference for different parts of a common branching coral, Acropora nobilis, both in the field and in the laboratory experiments with simulated corals. We then experimentally tested whether nonuniform patterns of feeding on preferred coral species reflect structural differences between polyps. We found that O. longirostris exhibits nonuniform patterns of foraging in the field, selectively feeding midway along branches. On simulated corals, fish replicated this pattern when food accessibility was equal along the branch. However, when food access varied, fish consistently modified their foraging behavior, preferring to feed where food was most accessible. When foraging patterns were compared with coral morphology, fish preferred larger polyps and less skeletal protection. Our results highlight that patterns of interspecific and intraspecific selectivity can reflect coral morphology, with fish preferring corals or parts of coral colonies with structural characteristics that increase prey accessibility.     

Ants and Habitat Specificity in Aphids

A number of rare butterflies are known to only utilise their host plant species when they grow in particular situations. Field data are presented showing that two rare species of aphid also only utilised their host plants when they grew in particular situations, namely near ant nests. The oak-feeding aphid Stomaphis quercus only occupied trees within 17 m of a Lasius fulignosus nest. The thyme-feeding aphid Aphis serpylli only occurred in a region of a Breckland grass heath where the sward contained a high density of Lasius niger nests, and then most commonly only in quadrats containing ant nests. The sward that was suitable for A. serpylli was generated by the action of farm traffic. It is concluded that ants indirectly impose habitat specificity on these aphids.