Salinity and shade preferences result in ovipositional differences between sympatric tiger beetle species

1. Adult tiger beetles of the genus Cicindela often co‐occur within a habitat but larvae do not. Larvae are sedentary and form usually permanent burrows at the site of oviposition where they require 1–3 years for development. 2. To test niche partitioning based on ovipositional preference, the behaviour of two sympatric salt marsh tiger beetles, Cicindela circumpicta and C. togata (Coleoptera: Cicindelidae), were examined. 3. In laboratory studies, female C. circumpicta and C. togata distinguished between experimental salinities, with the former preferring 4 parts per thousand (ppt) and the latter preferring 12 ppt. In the field, C. circumpicta larvae were associated with lower salinities (1–3 ppt) and vegetation along the edges of salt flats while C. togata larvae were found on open salt flats often near halophytes (average salinity = 7.8 ppt). 4. In the field, females chose sites for oviposition in response to shade but not vertical landmarks. In a direct test, 53 of 56 new larval burrows occurred in shaded treatments, three in nonshaded controls. 5. Compared with nonshaded controls, shade increased survival of eggs that were collected in the laboratory and placed in the field. For C. circumpicta eggs, 78% placed in shaded treatments hatched, while significantly fewer (22%) hatched in exposed treatments. For C. togata, 43% of eggs placed in the shade hatched, while no eggs placed in exposed treatments hatched. 6. These results support the hypothesis of niche partitioning between C. circumpicta and C. togata based on ovipositional choice and resulting larval habitat.     

Role of intraguild predation in aphidophagous guilds

The concept of intraguild predation (IGP) appeared in 1987–1989 to describe trophic interactions within a guild of arthropods inhabiting a sand dune desert: consumers B prey on consumers A and both of them prey on a common resource. Theory predicts that the two types of consumers should only coexist if consumer A is more efficient in the conversion of the common resource than B. As a consequence, this resource is more abundant in the presence than in the absence of intraguild predators. Such a theoretical prediction probably explains the vivid interest shown by ecologists involved in biological control for IGP. It is therefore not surprising that many papers report on IGP among natural enemies of aphids. A close examination of these reported cases indicates that they rarely fulfil the theoretical requirements for IGP. That is, guilds of aphidophagous insects are rarely the theatre of IGP but frequently of interspecific predation. This is confirmed by experimental assessment of the cost of attacking and eating intraguild prey instead of extraguild in ladybird beetles.     

Spatial interactions between sympatric carnivores: asymmetric avoidance of an intraguild predator

Interactions between intraguild species that act as both competitors and predator–prey can be especially complex. We studied patterns of space use by the black-footed ferret (Mustela nigripes), a prairie dog (Cynomys spp.) specialist, and the American badger (Taxidea taxus), a larger generalist carnivore that competes for prairie dogs and is known to kill ferrets. We expected that ferrets would spatially avoid badgers because of the risk of predation, that these patterns of avoidance might differ between sexes and age classes, and that the availability of food and space might influence these relationships. We used location data from 60 ferrets and 15 badgers to model the influence of extrinsic factors (prairie dog density and colony size) and intrinsic factors (sex, age) on patterns of space use by ferrets in relation to space use by different sex and age categories of badgers. We documented asymmetric patterns of avoidance of badgers by ferrets based on the sex of both species. Female ferrets avoided adult female badgers, but not male badgers, and male ferrets exhibited less avoidance than female ferrets. Additionally, avoidance decreased with increasing densities of prairie dogs. We suggest that intersexual differences in space use by badgers create varying distributions of predation risk that are perceived by the smaller carnivore (ferrets) and that females respond more sensitively than males to that risk. This work advances understanding about how competing species coexist and suggests that including information on both intrinsic and extrinsic factors might improve our understanding of behavioral interactions between sympatric species.     

Effect of emigration on cannibalism and intraguild predation in aphidophagous ladybirds

Abstract.  1. The incidence and timing of emigration, cannibalism, and intraguild predation of larvae of three aphidophagous ladybirds (Coleoptera: Coccinellidae), Harmonia axyridis Pallas, Coccinella septempunctata brucki Mulsant, and Propylea japonica Mulsant, relative to the presence of prey was determined in the laboratory in single- and mixed-species populations.
2. In single-species populations, 80% of the larvae of C. s. brucki emigrated prior to the extinction of the aphid population and no larvae were lost due to cannibalism; however > 80% of the larvae of the other two species were still present when the aphid became extinct and the losses due to cannibalism for H. axyridis and P. japonica were 25% and 14% respectively. Finally, 28% of the P. japonica larvae completed their development, whereas no larvae of the other two species became adult.
3. In mixed-species populations, mortality of P. japonica attributable to cannibalism or intraguild predation increased greatly to 60%, whereas that of the other two species remained about the same. Consequently, survival of H. axyridis larvae improved and survival of P. japonica worsened; however the survival of C. s. brucki larvae was not affected by the other two species. Early emigration by C. s. brucki larvae may have enabled them to escape intraguild predation by H. axyridis in this system.     

Effects of intraguild predation on aphid parasitoid survival

To assess the potential selection pressure caused by intraguild predation between predators and parasitoids of aphids an estimate was made of the predation risk to Aphis fabaeScop. mummified by Lysiphlebus fabarum(Marshall, 1896) on sugar beet. Mummified aphids were exposed to a natural community of predators. Their survival time was estimated during a 10-day field survey. Additionallythe role of alternative prey on parasitoid survival was investigated by adding unparasitised aphids to half of the mummy aggregations.The field data were evaluated by survival analysis. Two covariates were tested within a Cox proportional hazard model: (i) the presence of the alternative prey and (ii) the patch structure (number of proximal mummies attacked). Within 4–5 days after exposure predators destroyed approx. 50% of the mummies. The model with both covariates revealed a significant difference concerning survival of the mummies in the two treatments (Likelihood ratio test, ²=78.03, P=0.0001). Alternative prey reduced the predation risk on mummies by 29%, while a high level of predation on proximal mummies increased the individual predation risk by 4%. The results are discussed in the context of prey location by predators and the evolution of anti-predator mechanisms.     

寄生对集团内捕食系统中物种入侵的影响

寄生已被证明是影响生物入侵动态的关键因素,可通过直接或间接作用影响物种间相互作用。基于元胞自动机模型,探讨了寄生感染对宿主种群的间接作用(寄生对宿主的密度调节和特征调节效应)在外来种入侵动态中的作用。结果显示,寄生对宿主的3种调节效应均对外来种的入侵起到了抑制作用;同时,相对于密度调节效应,寄生的特征调节对捕食者种群入侵的抑制作用更明显,而两者的耦合调节效应对入侵的抑制能力明显高于单种效应的作用。综上,该研究在一定意义上丰富和发展了生物入侵的理论,为生物入侵的有效控制提供了理论参考。     

The enemy of my enemy is my friend: intraguild predation between invaders and natives facilitates coexistence with shared invasive prey

Understanding and predicting the outcomes of biological invasions is challenging where multiple invader and native species interact. We hypothesize that antagonistic interactions between invaders and natives could divert their impact on subsequent invasive species, thus facilitating coexistence. From field data, we found that, when existing together in freshwater sites, the native amphipod Gammarus duebeni celticus and a previous invader G. pulex appear to facilitate the establishment of a second invader, their shared prey Crangonyx pseudogracilis. Indeed, the latter species was rarely found at sites where each Gammarus species was present on its own. Experiments indicated that this may be the result of G. d. celticus and G. pulex engaging in more intraguild predation (IGP) than cannibalism; when the ‘enemy’ of either Gammarus species was present, that is, the other Gammarus species, C. pseudogracilis significantly more often escaped predation. Thus, the presence of mutual enemies and the stronger inter- than intraspecific interactions they engage in can facilitate other invaders. With some invasive species such as C. pseudogracilis having no known detrimental effects on native species, and indeed having some positive ecological effects, we also conclude that some invasions could promote biodiversity and ecosystem functioning.     

两种植绥螨的同类相残和集团内捕食作用

巴氏新小绥螨(Neoseiulus barkeri)和黄瓜新小绥螨(N.cucumeris)是两种多食性植绥螨,主要捕食叶螨和蓟马等,目前在我国广泛应用于农业生物防治中.本文研究了这两种植绥螨种内的同类相残(cannibalism)和种间的集团内捕食作用(intraguild predation)以及相互之间的攻击强度,以明确两者之间的相互关系,为合理构建天敌组合及评估生物防治的作用提供依据.结果显示:两种植绥螨对同种或异种幼螨的捕食量最大,其次是若螨,而对卵的捕食量极低.两种植绥螨对异种幼螨或若螨的捕食量均极显著高于对同种幼螨或若螨的捕食量.可见,无其他猎物存在情况下,两种植绥螨同时发生时更倾向于发生种间的集团内捕食.而巴氏新小绥螨对异种幼螨或若螨的捕食量均高于黄瓜新小绥螨对异种幼螨或若螨的捕食量,并且巴氏新小绥螨和黄瓜新小绥螨相比,巴氏新小绥螨对异种幼螨的攻击性更强,因此当这两种植绥螨发生集团内捕食时,巴氏新小绥螨是潜在的集团内捕食者,而黄瓜新小绥螨是潜在的集团内猎物.     

Long handling times of Praon unicum by Harmonia axyridis result in protection from predation

The intraguild predator Harmonia axyridis has a longer handling time of Praon unicum mummies in contrast to Aphidius matricariae mummies and the pest aphid Myzus persicae. In addition, the rejection rate of P. unicum is higher as compared to the A. matricariae and M. persicae. Harmonia Axyridis also has a shorter residence times when foraging in P. unicum patches. The longer handling time may provide P. unicum with a refuge from intraguild predation by H. axyridis. Thus, Praon unicum could be a better biocontrol agent than A. matricariae in the presence of intraguild predation, as it will face lower predation rates.     

三种捕食性瓢虫成虫对卵的种内自残及其集团内捕食作用

捕食性瓢虫是农田生态系中一类重要的天敌昆虫,种内自残和集团内捕食现象在捕食性瓢虫中普遍存在。本研究在室内通过选择性和非选择性试验比较分析了异色瓢虫、七星瓢虫及龟纹瓢虫成虫对卵的种内自残和集团内捕食作用以及卵表面的化学物质对集团内捕食作用的影响。结果表明:在非选择性试验中,3种捕食性瓢虫成虫对卵表现出相似的取食现象,即对龟纹瓢虫卵取食最多,其次为七星瓢虫卵,对异色瓢虫卵取食相对较少;在选择性试验中,七星瓢虫和龟纹瓢虫较偏好取食同种卵,对异色瓢虫卵取食均较少;而异色瓢虫喜欢取食异种卵,对同种卵取食相对较少。3种瓢虫卵经正己烷漂洗后,异色瓢虫、七星瓢虫和龟纹瓢虫成虫却未对卵表现出取食偏好性。本研究可为捕食性瓢虫组合释放与协调利用、田间集团内捕食作用评定及其在生物防治中的应用提供理论依据。     

Diet of intraguild predators affects antipredator behavior in intraguild prey

In two-predator, one-prey systems with intraguild predationand patchily distributed prey, the intraguild prey may facea choice between prey patches with and without intraguild predators.To minimize falling victim to intraguild predation, intraguildprey are expected to perceive cues specifically associated withthe presence of intraguild predators. We investigate whetherintraguild prey avoided intraguild predators and which cuestriggered this behavior in a system composed of plant-inhabitingarthropods. We found that intraguild prey recognized intraguildpredators from a distance, based on their diet: they avoidedodors of intraguild predators that had consumed shared preybut did not avoid odors of intraguild predators that had fedon other diets, including a diet of conspecifics. When intraguildprey were foraging on a patch, detection of intraguild predatorsled to longer periods of immobility and to fewer captures ofthe shared prey. However, intraguild predators that were eitherstarved or had previously consumed intraguild prey posed a higherrisk to intraguild prey than did intraguild predators that hadconsumed the shared prey. We conclude that the cues used byintraguild prey to avoid intraguild predators are associatedwith the circumstances under which they encounter intraguildpredators in the field and not to different degrees of danger.     

Mating behavior and genitalic counterparts in tiger beetles (Carabidae: Cicindelinae)

Comparative studies on the structure of genitalia in Pseudoxychila tarsalis Bates and the copulating behavior in 5 species of Cicindela respectively complement similar findings by Freitag [1] on Cicindela spp. and Palmer [4] on P. tarsalis. These strengthen the hypothesis that in tiger beetles the flagellum fits into the spermatheca duct during copulation; that the main function of the flagellum, which is closed at the apex and not connected to the ejaculatory duct, is to open and prepare the lumen of the spermatheca duct for sperm movement from the bursa copulatrix to the spermatheca; and that copulation proceeds in 3 phases: phase 1 in which the lumen of the spermatheca duct is cleared by the flagellum, phase 2 in which the flagellum is withdrawn from the spermatheca duct, and phase 3 in which semen is transferred from the gonopore of the ejaculatory duct to the bursa copulatrix, usually with a spermatophore.     

Food and specific macronutrient limitation in an assemblage of predatory beetles

Habitats vary in food resources with carnivores often being prey limited, but it is unclear whether habitats facilitate a nutritionally balanced diet. Two paradigms in nutritional ecology, ecological stoichiometry and nutritional geometry, predict that carnivores are limited mainly by protein or lipid, respectively. Using the carabid beetle Anchomenus dorsalis and 10 other predatory beetles from agricultural fields, we developed and tested two simple procedures for quantifying macronutrient‐specific habitat conditions without requiring information about the natural prey. Both procedures assume that predators forage for nutrients rather than specific prey. Our results show that 10 of 11 species were food limited. Five species were lipid limited and one species was protein limited in the field. Co‐existing predator species showed considerable segregation of fundamental macronutritional niches. A linear relationship between specific nutrient limitation and the target lipid:protein (L:P) intake ratio indicates that species with high L:P target are more protein limited while species with low L:P target are more lipid limited. The study illustrates how species within a natural assemblage vary in nutritional niche and in specific nutrient limitation.     

三种瓢虫集团内捕食卵对初龄幼虫生长发育的影响

种内和种间捕食卵现象常见于对食蚜瓢虫的研究报道中。源自亚洲、入侵北美和欧洲的异色瓢虫(Harmonia axyridis)由于卵含有生物碱而被认为可能是威胁本土瓢虫生存的原因,但该推测只有在明确异色瓢虫在原产地是否对本土瓢虫具有类似负面影响后,才能确证。通过饲喂实验,旨在明确异色瓢虫在原产地是否对本土七星瓢虫(Coccinella septempunctata)和龟纹瓢虫(Propylea japonica)具有食卵负面作用,为揭示异色瓢虫入侵机理提供依据。实验中用蚜虫(对照)和3种瓢虫卵对瓢虫初孵1龄幼虫进行饲喂处理,观察幼虫生长发育指标。对瓢虫初龄幼虫存活表现的分析结果表明:(1)龟纹瓢虫初孵幼虫取食同种卵和七星瓢虫卵后存活至2龄的比率均高于取食异色瓢虫卵的近7倍;(2)七星瓢虫幼虫取食异色瓢虫卵未存活到2龄,但取食其他瓢虫卵和蚜虫后85%以上个体存活至2龄;(3)异色瓢虫初孵幼虫取食同种和其他2种瓢虫卵后有90%以上存活至2龄。龟纹瓢虫和七星瓢虫1龄幼虫取食异种卵比同种卵后的发育历期显著延长,但异色瓢虫并未表现出差异。龟纹瓢虫和异色瓢虫1龄幼虫取食同种和异种卵后的体增重相同,但七星瓢虫取食龟纹瓢虫卵后体增重比取食同种卵减小。研究结果说明,异色瓢虫卵对七星瓢虫和龟纹瓢虫初孵幼虫的生存具有负面影响,反之不然。所以,取食异色瓢虫卵本身并非是导致北美和欧洲本土瓢虫数量减少的原因。     

Cannibalism prevents evolutionary suicide of ontogenetic omnivores in life‐history intraguild predation systems

The majority of animal species are ontogenetic omnivores, that is, individuals of these species change or expand their diet during life. If small ontogenetic omnivores compete for a shared resource with their future prey, ecological persistence of ontogenetic omnivores can be hindered, although predation by large omnivores facilitates persistence. The coupling of developmental processes between different life stages might lead to a trade‐off between competition early in life and predation later in life, especially for ontogenetic omnivores that lack metamorphosis. By using bioenergetic modeling, we study how such an ontogenetic trade‐off affects ecological and evolutionary dynamics of ontogenetic omnivores. We find that selection toward increasing specialization of one life stage leads to evolutionary suicide of noncannibalistic ontogenetic omnivores, because it leads to a shift toward an alternative community state. Ontogenetic omnivores fail to re‐invade this new state due to the maladaptiveness of the other life stage. Cannibalism stabilizes selection on the ontogenetic trade‐off, prevents evolutionary suicide of ontogenetic omnivores, and promotes coexistence of omnivores with their prey. We outline how ecological and evolutionary persistence of ontogenetic omnivores depends on the type of diet change, cannibalism, and competitive hierarchy between omnivores and their prey.     

Effect of intraguild predation on the survival and development of three species of aphidophagous ladybirds: consequences for invasive species

Abstract 1 Survival and development of hatchling larvae of three aphidophagous ladybirds (Coleoptera: Coccinellidae), Harmonia axyridis Pallas, Coccinella septempunctata brucki Mulsant and Adalia bipunctata Linnaeus, when fed their own and the other species eggs were recorded. 2 In all three species, the larvae survived when fed conspecific eggs. 3 The percentage of larvae of H. axyridis that survived decreased to 35% and 85% when fed eggs of A. bipunctata and C. s. brucki, respectively. All the larvae of A. bipunctata and C. s. brucki died after eating eggs of H. axyridis. None of the larvae of C. s. brucki died after eating eggs of A. bipunctata, whereas 46% of those of A. bipunctata died after eating eggs of C. s. brucki. 4 In general, larvae were reluctant to eat the eggs of other species. However, larvae of C. s. brucki showed less reluctance than H. axyridis to eat the eggs of A. bipunctata. 5 The consequence of this for invasive species of ladybird is discussed.     

Role of surface chemicals in egg cannibalism and intraguild predation by neonates of two aphidophagous ladybirds, Propylea dissecta and Coccinella transversalis

Abstract:  The role of surface chemicals in egg cannibalism and intraguild predation by neonates of two aphidophagous ladybirds, Propylea dissecta and Coccinella transversalis were examined. Neonates of both species prefer to eat non-sibling conspecific eggs than heterospecific eggs, with higher preference in P. dissecta . Surface chemicals appear to play a major role for the preference of conspecific eggs, as the ladybird behaviour was reversed when these chemicals were interchanged. The surface chemicals present on the eggs possibly act as feeding stimulants to conspecific neonates but not for heterospecific neonates. Egg clustering enhances the effect of surface chemical and stimulate non-sibling egg cannibalism and appears to reduce intraguild predation. Egg clustering is advantageous to ladybirds, as it can stimulate non-sibling cannibalism by neonates. It appears that aggregation of chemicals present on the conspecific egg surface possibly attracts the hungry conspecific neonate, providing the first meal for its survival, while protecting against heterospecific predators. Neonates of both ladybirds were reluctant to eat heterospecific eggs.     

A test of the hypothesis that a pathway of intraguild predation limits densities of a wolf spider

Abstract.  1. The high number of potential predatory interactions among the many arthropod generalist predators in terrestrial food webs makes exhaustive testing of interaction strengths by field experiments unfeasible. Thus, correlative patterns and laboratory observations of behaviour often form the basis of inferences about the strength of interaction pathways involving generalist predators (intraguild predation).
2. Previous research has revealed a negative correlation between survival of juvenile wolf spiders of the genus Schizocosa (Lycosidae) and densities of another abundant spider family, the Gnaphosidae.
3. Feeding trials in laboratory microcosms with a leaf-litter substrate revealed that gnaphosids prey on juvenile Schizocosa in a structurally complex habitat.
4. Gnaphosid densities were manipulated in two different field experiments, each conducted in a different year, in order to test directly the hypothesis that intraguild predation by gnaphosids limits densities of juvenile Schizocosa .
5. Reducing numbers of gnaphosids, and doubling their numbers to two times the mean natural density, had no impact on the survival of juvenile Schizocosa in either field experiment. This finding suggests that correlative patterns in nature and feeding trials in the laboratory may at times provide deceptively simple and potentially misleading generalisations about the strengths of interaction pathways in complex networks of generalist predators.