Reducing predation of orb-web spiders by controlling common wasps (Vespula vulgaris) in a New Zealand beech forest

1. Introduced common wasps ( Vespula vulgaris ) reach high densities in the beech forests ( Nothofagus spp.) of the northern South Island, New Zealand, and may be having a severe impact on populations of native invertebrates. An experimental approach was used to test whether reducing the abundance of common wasps increases the probability of native invertebrates surviving. Garden orb-web spiders ( Eriophora pustulosa ) were used because they were easy to collect and could be trained to build webs on a standard frame. Thirty orb-web spiders were placed out on web-frames in each of four study sites in beech forest during periods of low, medium and high wasp abundance, and their rate of removal was measured over a 4-h period. Wasp numbers were reduced by poisoning in two study sites. Using wasp-abundance data from weekly Malaise trap samples in the poisoned and non-poisoned sites, the probability of spider survival over the entire wasp season was modelled and the level of wasp control necessary to protect natural populations of orb-web spiders was estimated.
2. Wasp abundance and the probability of spider survival were negatively correlated, and smaller spiders were likely to survive longer than larger spiders. At the peak of the wasp season, significantly more spiders survived in the poisoned areas than in the non-poisoned areas.
3. The probability of a spider surviving to the end of the wasp season was virtually nil in the non-poisoned sites (5.08 × 10^–18), but was also very unlikely in the poisoned areas (3.47 × 10^–5).
4. The survival model predicts that wasp abundance would need to be reduced by 80–89.5% over the entire wasp season to protect populations of orb-web spiders.
5. Extrapolation from the model predicts that the invertebrate taxa most vulnerable to wasp predation may have already been removed from the beech forest ecosystem during the 40 years of wasp occupation.     

Successful removal of German yellowjackets (Hymenoptera: Vespidae) by toxic baiting

Vespula germanica (F.) is a social vespid that has invaded many parts of the world, including Argentina. This wasp usually becomes a pest, affecting several economic activities. It also may impact the host community through predation or competition. The purpose of our study was to field test toxic baiting for reduction of wasp abundance. Wasps were poisoned with 0.1% fipronil mixed with raw minced beef in two beech forest sites on 20 February 2000 in northwestern Patagonia. All nests (46) within the two 6-ha sites with poisoned bait stations were killed, whereas Malaise traps in those sites captured 81.1% fewer wasps at the end of the season than traps in the two control sites. The average reduction of forager wasps on nontoxic baits was 87%. Fipronil was very effective in controlling wasp numbers, although there are limitations to the method, especially concerning conservation purposes. Toxic baiting can be useful in controlling wasp numbers in honey bee hive yards, farms, and parks.     

Abundance of wasps and prey consumption of paper wasps (Hymenoptera, Vespidae : Polistinae) in Northland, New Zealand

Polistine and vespine wasps were captured in Malaise traps in two fire-modified shrubland habitats of varying canopy height and composition at Lake Ohia, Northland, New Zealand. Prey consumption rates were calculated for the Asian paper wasp (Polistes chinensis antennalis) occupying these two areas of shrubland and a home garden in Whangarei, Northland. The sites were systematically searched for nests and wasp prey determined by intercepting foragers returning to nests. The Asian paper wasp predominated in the Malaise trap samples from the low- growing habitat while the German wasp (Vespula germanica) was more common in the taller vegetation type. The Asian paper wasp was more abundant than the German wasp in the samples in February and early March. Only four Australian paper wasps (Polistes humilis) and no common wasps (Vespula vulgaris) were caught. Asian paper wasps collected an estimated 15 000 prey loads per ha per season from one of the shrubland areas, and 478 000 prey loads per ha per season from the second area. These convert to estimates of 31 and 957 g per ha per season of invertebrate biomass removed by paper wasps from each habitat, respectively. The estimate for the garden site was 79 g per ha per season. Wasp nest densities varied between 20 and 210 nests per hectare. The biomass estimates are similar to average figures calculated for vespine wasps in scrubland and pasture. Both Asian paper wasps and Australian paper wasps preyed mainly on lepidopteran larvae. The cabbage white butterfly (Pieris rapae) was the most commonly collected species. Noctuid species were also well represented. Both male and female Asian paper wasps collected nectar in late March and early April.     

The impact of an exotic social wasp (Vespula germanica) on the native arthropod community of north-west Patagonia, Argentina: an experimental study

Abstract 1. Biological invasions are usually thought to have a negative impact on native communities. However, data supporting this idea are often based on comparative studies between invaded and non‐invaded areas, and are spatially and temporally limited. 2. The present study experimentally assessed the impact of an exotic wasp, Vespula germanica, on the native arthropod community of north‐west Patagonia during 3 years in an area of 80 ha. Vespula germanica is an exotic social vespid that invaded north‐west Patagonia 20 years ago. It has been suggested that its populations affect native arthropods because of its broad diet and also because Patagonia lacks natural enemies and potential competitors for these wasps. 3. Using wasp‐specific toxic baits, V. germanica abundance was reduced in five sites of native woodlands during 3 consecutive years. The abundance, species richness, and composition of arthropods between non‐poisoned (control) and poisoned sites was then compared, both before and after the wasps were poisoned. 4. Wasp abundance represented 6% of the total arthropod catches in non‐poisoned sites and was reduced, on average, by 50% in the treated areas. The abundance, species richness, and composition of the arthropod community (305 species, 24 600 individuals) did not differ between control areas and areas where the abundance of V. germanica was reduced. Significant differences in response variables were found only before wasp poisoning had begun and were related to variations among sites. 5. These results suggest that V. germanica is not affecting the local arthropod assemblages, contradicting past work in other regions. The low relative abundance of wasps in Patagonia, when compared with other invaded regions, might explain the findings. 6. The present study provides further evidence for the importance of large‐scale experimental work with before/after comparisons to fully understand the impact of invaders on natural communities.     

Impacts of introduced common wasps (Vespula vulgaris) on experimentally placed mealworms in a New Zealand beech forest

An introduced social wasp Vespula vulgaris may compete with native birds for honeydew and invertebrates in New Zealand forests. Experimentally hidden mealworms (Tenebrio molitor) persisted longer at two sites following wasp poisoning that at two sites where wasps were not poisoned. Mealworms persisted longer in the morning than in the afternoon within all study sites. An unusually low mealworm removal rate during a morning trial before wasp poisoning heavily influences the results of this experiment but we have no ecological reason to ignore it. Wasps may therefore be having a heavy impact on invertebrate abundance on very short time scales (within a day following dawn emergence). They may also remove cached food items that would otherwise be retrieved by the South Island robin (Petroica australis australis) during cold or dark feeding conditions.     

Impact of the arundo wasp,Tetramesa romana (Hymenoptera: Eurytomidae), on biomass of the invasive weed,Arundo donax (Poaceae: Arundinoideae), and on revegetation of riparian habitat along the Rio Grande in Texas

An invasive grass, Arundo donax, occupies thousands of hectares of arid riparian habitat along the Rio Grande in Texas and Mexico, and has negative impacts on national security, water resources, and riparian ecosystems. The shoot-tip-galling wasp Tetramesa romana was released in 2009 between Brownsville and Del Rio, Texas, and has dispersed over 800?km along the river channel. Plots along the river were surveyed for shoot counts of arundo and all other plant species in 2016 at seven sites in regions in which prior studies had documented a 22% decline in arundo biomass (estimated from live shoot length) from 2007 to 2014. Estimated live biomass declined a further 32% between 2014 and 2016. Native plants accounted for 86% of the 44 species encountered in plots. Individual plots averaged five plant species, and arundo was most abundant in only 9 of 21 plots. Arundo live biomass and shoot density were negatively associated with plant diversity, indicating that live arundo interferes with germination and/or survival of other plant species. The proportion of dead shoots in plots, proportion of wasp-galled shoots, and density of exit holes made by emerging adult wasps per metre live main shoot length were positively associated with plant diversity in a combined model. Regressions indicated that the effects of wasp damage measures on diversity were mediated through their effects on main shoot mortality. By reducing live arundo biomass, the arundo wasp is fostering recovery of native plant communities at riparian sites along the Rio Grande.     

Preference by Vespula germanica (Hymenoptera: Vespidae) for processed meats: implications for toxic baiting

The German yellowjacket, Vespula germanica (F.) (Hymenoptera: Vespidae), was introduced into Australia in 1959 and has established throughout southern Australia. In urban environments, V. germanica is frequently a nuisance pest at public gatherings and to homeowners. In native environments, it has the potential to pose a threat to native invertebrates. The current practice for controlling the wasps is nest destruction with pesticide. However, locating the nest(s) is not always practical or possible. Meat baits impregnated with an insecticide that foraging wasps cut and carry back to the nest offer a means of suppressing wasps where the nest sites are unknown. The success of meat baits depends on the attractiveness and acceptance of the meat to the wasp and the mode of action of the insecticide. Our objective was to determine wasp preference and acceptance of five processed meats: canned chicken or fish and freeze-dried chicken, fish, or kangaroo. We found that more wasps visited and took freeze-dried kangaroo and canned chicken than the other baits. Canned and freeze-dried fish were similarly preferred, and freeze-dried chicken was the least attractive and accepted by foraging wasps. Our findings demonstrate that wasps prefer some processed meats and hence take more loads back to the nest. By combining a suitable insecticide with a meat bait preferred by wasps, the likelihood of effective suppression of nuisance wasp populations should be increased.     

聚果榕榕果小蜂种群分布格局及其生境和季节差异比较

采用多个指数对西双版纳地区聚果榕榕果小蜂的种群分布格局进行了检测,并重点运用基于方差／均值比率法的t值测度比较了其生境和季节差异．结果表明,6种聚果榕榕果小蜂的种群分布格局皆呈聚集分布;传粉小蜂聚集强度在生境序列上,原始雨林≈严重干扰地段>>中度干扰地段。在季节序列上,雨季>干热季>雾凉季;非传粉小蜂不同种类不同性别随着生境和季节变化皆表现出明显的聚集强度差异。对各种聚集强度变化的发生机理与其对聚果榕-传粉者互惠共生体进化稳定性进行了讨论,认为保护榕树、保护榕树和传粉昆虫互惠共生体的重点应放在保护其原始森林生境方面。     

聚果榕榕果小蜂种群分布格局及其生境和季节差异比较

采用多个指数对西双版纳地区聚果榕榕果小蜂的种群分布格局进行了检测,并重点运用基于方差/均值比率法的t值测度比较了其生境和季节差异.结果表明,6种聚果榕榕果小蜂的种群分布格局皆呈聚集分布;传粉小蜂聚集强度在生境序列上,原始雨林≈严重干扰地段中度干扰地段,在季节序列上,雨季>干热季>雾凉季;非传粉小蜂不同种类不同性别随着生境和季节变化皆表现出明显的聚集强度差异.对各种聚集强度变化的发生机理与其对聚果榕传粉者互惠共生体进化稳定性进行了讨论,认为保护榕树、保护榕树和传粉昆虫互惠共生体的重点应放在保护其原始森林生境方面.     

N:P stoichiometry in Ficus racemosa and its mutualistic pollinator

Aims Nitrogen (N) and phosphorus (P) are limiting nutrients to life across a variety of ecosystems. N:P stoichiometry, concerning the balance of these two elements, has recently received great attention. However, little is known about the nature of N:P stoichiometry in obligate mutualism.Methods N:P stoichiometry of Ficus racemosa and its pollinating wasp Ceratosolen fusciceps, an example of coevolving obligate mutualism, was investigated, and the N:P stoichiometric traits of male versus female wasps were compared.Important findings Nutrient concentrations in C. fusciceps were much higher than in its host. N enrichment in fig wasp was evidently stronger than phosphorus. N concentrations of male fig wasps were significantly higher than those of females, while P concentrations of female fig wasps were remarkably higher than those of male ones. Therefore, N:P ratios in male fig wasps were significantly greater than in female fig wasps. N:P ratio in fig-pollinating wasp displayed linear functions to fig N contents, suggesting that N limitation in fig wasps may dominate the nutritional relationship between fig pollinator and its host. Fig wasp population size had significant influences on N concentrations in host fig and female wasp per se. Driven by the nutritional stress of pollinating and parasite insects, fig fruit preferred increasing its diameter first but not nutrient richness. Values for N and P contents of fig pollinators showed seasonal differences with greater N:P ratios in dry season than in rainy season. The observations suggest that tropical climate change would result in more severe N limitation to fig-pollinating wasp and may further influence the stability of fig–fig wasp mutualism.     

Overwintering colonies of German (Vespula germanica) and common wasps (Vespula vulgaris) (Hymenoptera: Vespidae) in New Zealand

Abstract

Nests of both common (Vespula vulgaris) and German wasps (V. germanica) sometimes overwinter in New Zealand. Three overwintering common wasp colonies were found in low-altitude honeydew beech forest; about 2% of the colonies initiated there in 1988 survived the winter. Wasp traffic rates from nests in Nelson city and a nation wide survey of wasp abundance, showed that more German wasp than common wasp workers were on the wing in winter and spring. German wasp colonies in Nelson city were more likely to overwinter than were common wasp colonies. Of the active German wasp colonies recorded in Nelson in January and February 1989, only two (4%) had previously overwintered, but these two nests accounted for 38% of all German wasp workers estimated to leave nests in the area. Had other overwintering colonies not been poisoned, overwintering colonies might have accounted for up to 11 % of nests and produced up to 64% of German wasp workers on the wing in January and February 1989.

Overwintering common wasp colonies did not produce queens or drones in their first year or second spring, but all 10 overwintering German wasp colonies examined produced sexuals at both times. German wasp queens produced in winter and spring may influence the number of colonies successfully initiated and affect the population dynamics of German wasps in New Zealand.     

Competition for food between the exotic wasp <Emphasis Type="Italic">Vespula germanica</Emphasis> and the native ant assemblage of NW Patagonia: evidence of biotic resistance?

The success of a biological invasion may depend on the interactions between the invader and the native biota. However, little experimental evidence demonstrates whether local species can successfully compete with exotics. We experimentally determined the existence of competition for food between the exotic wasp Vespula germanica, one of the most recent Patagonian invaders, and the native ant assemblage. Both wasps and ants are generalist predators and scavengers, sharing habitat and food resources. We selected 30 sites within scrubland habitats where both ants and wasps were present. At each site, we placed containers with protein baits under three treatments: wasp exclusion, ant exclusion, and control (i.e., free access for wasps and ants). Ant exclusion increased the number of wasps (with regard to a control), but wasp exclusion did not affect ant abundance. This result suggests that native ants affect the foraging activity of exotic wasps but not vice versa. Aggressive behaviors and worker aggregation may explain the competitive advantage of ants. Ants bite wasp legs and massively aggregate on food sources, physically limiting the landing of wasps on baits. If the outcome of interactions at baits reported here influence wasp population-level parameters, this competitive interaction could be one of the factors explaining the low abundance of this exotic wasp in NW Patagonia in comparison with other invaded regions.     

垂叶榕榕小蜂群落及种间互作网络季节动态

群落中的物种相互作用构成了复杂的生态网络。有关物种的数量和组成的季节性动态变化已有较多的研究, 但是对于生态网络的动态变化知之甚少。揭示生态网络的动态变化对于理解群落的稳定性以及群落的动态变化过程和机理具有重要意义。本研究以垂叶榕(Ficus benjamina)榕小蜂群落为研究对象, 分别在西双版纳的干季和雨季采集了榕小蜂的种类和数量信息。比较了两个季节榕小蜂群落的动态变化以及共存网络的参数(例如网路直径、连接数、嵌套性和群落矩阵温度)变化。结果显示: 雨季榕果内传粉榕小蜂Eupristina koningsbergeri所占比例高于干季, 传粉榕小蜂的种群数量也高于干季, 而在干季非传粉榕小蜂的种类增加(干季15种小蜂, 雨季14种)。从榕树-传粉榕小蜂互利共生系统的适合度来看, 干季非传粉小蜂的增加对传粉榕小蜂和榕树的适合度是不利的。在干季, 共存网络物种间的连接数(干季0.95, 雨季0.47)多于雨季, 群落矩阵温度(干季23.24, 雨季2.64)也显著高于雨季。表明干季榕小蜂群落组成及种间关系较雨季更为复杂而多样, 高的矩阵温度暗示群落受到的干扰更大。     

Restructuring of Lepidoptera communities by introduced Vespula wasps in a New Zealand beech forest

Introduced social wasps (Vespula vulgaris) reach high densities in some New Zealand beech forests, because honeydew provides an abundant high-energy food source. We manipulated wasp density to estimate an “ecological damage threshold” for large, free-living Lepidoptera larvae. There will be a continuum of ecological damage thresholds for wasp density depending on the prey species or habitat. Experimentally placed small caterpillars had a significantly higher survival rate than large caterpillars, and the survival rate of both groups decreased with increasing wasp density. Spring-occurring caterpillars have a probability of surviving of 0.90–0.95, assuming wasps are the only source of mortality. However, at the peak of the wasp season we predict caterpillars would have virtually no chance (probability of 10⁻⁷⁸ to 10⁻⁴⁰) of surviving to adults. Wasp abundance must be reduced by at least 88% to conserve the more vulnerable species of free-living caterpillars at wasp densities similar to those observed in our study sites. This equates to a damage threshold of 2.7 wasps per Malaise trap per day. It was exceeded for about 5 months of the year in non-poisoned sites. There are currently no biological or chemical control techniques available in New Zealand that will reduce wasp abundance below this damage threshold throughout the year. Our models show that most Lepidoptera with spring caterpillars will be able to persist, but species with caterpillars occurring in the peak wasp season will be eliminated. Received: 5 January 1998 / Accepted: 10 February 1999     

Climate change impact on neotropical social wasps

Establishing a direct link between climate change and fluctuations in animal populations through long-term monitoring is difficult given the paucity of baseline data. We hypothesized that social wasps are sensitive to climatic variations, and thus studied the impact of ENSO events on social wasp populations in French Guiana. We noted that during the 2000 La Niña year there was a 77.1% decrease in their nest abundance along ca. 5 km of forest edges, and that 70.5% of the species were no longer present. Two simultaneous 13-year surveys (1997–2009) confirmed the decrease in social wasps during La Niña years (2000 and 2006), while an increase occurred during the 2009 El Niño year. A 30-year weather survey showed that these phenomena corresponded to particularly high levels of rainfall, and that temperature, humidity and global solar radiation were correlated with rainfall. Using the Self-Organizing Map algorithm, we show that heavy rainfall during an entire rainy season has a negative impact on social wasps. Strong contrasts in rainfall between the dry season and the short rainy season exacerbate this effect. Social wasp populations never recovered to their pre-2000 levels. This is probably because these conditions occurred over four years; heavy rainfall during the major rainy seasons during four other years also had a detrimental effect. On the contrary, low levels of rainfall during the major rainy season in 2009 spurred an increase in social wasp populations. We conclude that recent climatic changes have likely resulted in fewer social wasp colonies because they have lowered the wasps'' resistance to parasitoids and pathogens. These results imply that Neotropical social wasps can be regarded as bio-indicators because they highlight the impact of climatic changes not yet perceptible in plants and other animals.     

茉莉酸甲酯诱导大戟三萜类代谢的研究

京大戟是多年生草本药用植物,入药部分是其干燥根,但可入药的京大戟资源由于生长缓慢以及环境污染的加剧而越发匮乏,因此解决大戟资源日益紧张的问题是当今药用植物资源开发与利用方向的重要课题。京大戟含有三萜类、二萜类、黄酮类等丰富的活性成分,一些常见药用植物的有效成分是三萜类化合物,其在抗病毒、抗肿瘤、免疫调节等方面具有很好的活性。对植物萜类物质代谢起重要作用的关键酶,如3-羟基,3-甲基戊二酰辅酶A还原酶(hmgr)、鲨烯合酶(sqs)、法尼基焦磷酸合酶(fps)的基因克隆及活性研究取得了进展和突破,但通过调控萜类物质代谢途径中关键酶基因的表达来诱导终产物合成的研究鲜有报道。通过研究大戟萜类物质代谢途径进而利用基因工程手段提升目的物质的产量来解决京大戟药源短缺问题具有重要意义。该研究以大戟愈伤组织为材料,使用茉莉酸甲酯分别按时间梯度和浓度梯度进行诱导,将诱导后的愈伤组织分为两部分:一部分提取其总RNA,以actin为内参基因进行反转录,实时定量RT-PCR分析大戟三萜类代谢途径中hmgr、sqs与fps基因的相对表达差异;另一部分用于提取其总三萜并使用分光光度法进行含量测定。实时定量RT-PCR分析结果表明,茉莉酸甲酯可诱导3个基因的表达,但其表达模式不一样。相应的京大戟愈伤组织中总三萜的含量明显提高,最高可较未处理样品增加27%。研究结果可为茉莉酸甲酯促进药用植物大戟三萜类物质积累的分子机制研究提供参考。     

榕小蜂温度耐受性及其对种间共存关系的影响

全球已知有约800种榕属(Ficus)植物, 主要分布在热带, 部分种类延伸至亚热带地区。温度是限制榕‒蜂共生系统分布北界的主要因素, 也显著影响榕树及其榕小蜂的繁殖成功, 其中榕小蜂对温度的响应更加敏感。榕小蜂只有在一定的温度范围内才能保持正常的生理机能, 其对温度耐受能力直接影响榕果内小蜂种群数量和群落内种间关系。然而目前对榕小蜂温度耐受性的研究尚少, 榕小蜂的温度耐受能力如何影响榕果内小蜂的共存关系还未见报道。本文研究了分布于西双版纳的2种雌雄同株和1种雌雄异株榕树果内传粉榕小蜂和非传粉小蜂的温度耐受能力。结果表明: 3种传粉榕小蜂对高温的耐受性极差, 相对于雌雄同株的高榕(F. altissima)和聚果榕(F. racemosa)传粉榕小蜂, 雌雄异株的鸡嗉子榕(F. semicordata)传粉榕小蜂对低温有增强的耐受趋势。聚果榕小蜂群落结构显示: 在适宜其生长的西双版纳地区, 传粉榕小蜂的数量占绝对优势, 在温度较低的季节其数量显著减少; 而非传粉榕小蜂呈相反模式, 较强的温度耐受能力使其在低温的雾凉季维持了较高的种群数量。鸡嗉子榕果内非传粉小蜂Sycoscapter trifemmensis相对于Philotrypesis dunia有更强的温度耐受能力, 在种群数量和种间关系上有更多的竞争优势及数量。榕小蜂的温度耐受性差异在物种分布、种间关系的维持和共存上起了重要作用, 本研究结果为阐明榕小蜂种间共存的维持机制提供了科学依据。     

Prey Diets and Population-Densities of the Wasps

Prey collected by Vespula vulgaris and V. germanica were sampled by intercepting foragers returning to nests at two sites in scrubland-pasture near Hamilton. About 12% of returning foragers carried animal prey and 5% carried wood pulp. The remaining 83% carried no external load. The most common prey item for both species was Diptera, followed by Lepidoptera and Araneae (spiders). Even in similar habitats the two species collected different prey, with V. germanica collecting more Diptera and V. vulgaris more Lepidoptera. The prey changed slightly over time at both sites, V. germanica and V. vulgaris collected an estimated 1800 g and 600 g of prey nest-1 season-1 respectively. The wasps collected an estimated 75 000 prey loads ha-1 season-1 at Mystery Creek and 12 000 at Ruakura. This represents biomasses of 50 and 470 g ha-1, respectively, which are at least an order of magnitude lower than estimates of prey biomass for honeydew beech forest in parts of the South Island. The distribution of wasp nests was patchy however, and the biomass of prey collected exceeded 10 kg ha-1 in some places.     

Carbohydrate bait preferences of wasps (Vespula vulgaris and V. germanica) (Hymenoptera: Vespidae) in New Zealand

Abstract

Carbohydrates are both a source of food and a potential bait for control of common and German wasps. Carbohydrate preferences of wasps were determined in a series of paired trials by counting the number of wasps caught in traps baited with carbohydrate‐based baits versus a standard protein‐based bait. Factors influencing wasp attraction to carbohydrate‐based baits included bait type, season, weather, and location. A 30% sucrose solution was more attractive than honey, jams, gels, or dry (solid) sugars. The sucrose solution was more attractive in spring and autumn than in summer, probably because rainfall washed away natural carbohydrate supplies. There was a significant relationship between rainfall in the previous week and the proportion of wasps caught in traps baited with sucrose solution versus sardine cat‐food. A higher proportion of German wasps than common wasps was caught in sucrose‐baited traps. This may have been related to seasonal differences in abundance and/or behavioural differences between the two species. In some locations, more wasps were caught in traps baited with sucrose solution than in those baited with sardine cat‐food. The proportion of wasps caught in sucrose‐baited traps was higher in locations without beech scale honeydew than with beech scale honey‐dew. Proportionally more non‐target species (mainly honey bees) and fewer wasps were caught in traps baited with sucrose solution than in those baited with sardine cat‐food. All five bee repellents tested also repelled wasps. These results indicate the importance of determining the bait preferences of wasps (carbohydrate or protein) and the presence of non‐target species before attempting a poison‐baiting operation. They also emphasise the need for a wasp‐specific carbohydrate‐based bait.     

Seasonal change in the structure of fig-wasp community and its implication for conservation

Figs (Moraceae) and their pollinating wasps (Agaonidae) constitute a famous reciprocal mutualism in which figs provide some female flowers for the development of fig wasp offspring while the fig wasps pollinate fig flowers. However, figs also host many non-pollinating wasps which are either parasitoids or resource competitors of pollinators, and bring no benefit for figs and are detrimental to fig’ fitness. Our data onFicus racemosa in Xishuangbanna showed that the numbers of non-pollinators and the mature syconia without pollinator wasps increase in rainy season, especially in the highly fragmented forest. This might be because of the longer developing time of the syconia and thereby longer oviposition time to non-pollinators in the dry season. The galled flower and the viable seed percentages in dry seasons are also larger than in rainy seasons in both primary forest and fragmented forest, and the development of non-pollinators is mainly at the expense of pollinator wasps. Our results showed that there exists a discriminative seasonal impact of non-pollinators and fragmentation effects on population size of fig’s pollinators. This implies that fig/fig wasp mutualism is more fragile in dry season, and that the critical population size and breeding units of figs in seasonal area might be larger than previously estimated without considering the seasonal change of pollinator population.