Laboratory study of cannibalism and interspecific predation in ladybirds

Abstract.

• 1 In the absence of aphids, adult females of Adalia bipunctata (L.) showed a greater reluctance to eat eggs than males.
• 2 Eggs and young larvae were more vulnerable to cannibalism than older larvae and starved larvae were more vulnerable than well-fed larvae.
• 3 Both egg and larval cannibalism is inversely related to the abundance of aphids.
• 4 Eggs are a better food, in terms of larval growth and survival, than aphids.
• 5 In the absence of aphids interspecific predation occurred, but not equally, between the coccinellids A.bipunctata, A.decempunctata (L.), Coccinella septempunctata L. and C.undecempunctata L.
• 6 Larvae and adults of A. bipunctata and C.septempunctata were reluctant to eat conspecific eggs painted with a water extract of the other species' eggs and larvae of C. septempunctata were more likely to die after eating a few eggs of A.bipunctata than vice versa.
• 7 These results indicate that cannibalism occurs mainly when aphid prey is scarce and is adaptive in that it improves the chances of survival, and coccinellids, to varying degrees, are defended against interspecific predation.

     

Intra‐ and interspecific interactions between aphidophagous ladybirds: the role of prey in predator coexistence

Cannibalism (CANN) and intraguild predation (IGP) may provide energy and nutrients to individuals and eliminate potential competitors. These negative competitive interactions could also affect the coexistence of predatory species. The co‐occurrence of aphidophagous ladybird species in crops creates opportunities for CANN and IGP, especially when aphids become scarce. The Lotka–Volterra model predicts the coexistence of two species if intraspecific competition is stronger than interspecific interference interactions. Cycloneda sanguinea L. and Eriopis connexa (Germar) (both Coleoptera: Coccinellidae) coexist in sweet pepper crops in La Plata (Argentina) consuming mainly Myzus persicae (Sulzer) (Hemiptera: Aphididae). The present study used laboratory experiments to estimate levels of CANN and IGP by adults and larvae on eggs, and by adults on larvae, in both the presence and absence of prey (i.e., M. persicae), to explain the effect of prey on coexistence of these two predators. Levels of CANN by C. sanguinea and E. connexa were high in the absence of aphids, and decreased when prey was present. Intraguild predation was bidirectional and asymmetric. Adults and larvae of E. connexa were more voracious IG predators of C. sanguinea than vice versa, the former being the stronger IG predator and interference competitor. Eriopis connexa always won when larvae of the same instar were compared, whereas the larger larva always won when larvae were of different instars, regardless of species. In the presence of prey, CANN by both species decreased, but IGP by E. connexa on C. sanguinea remained high, suggesting that E. connexa could displace C. sanguinea via interspecific interference competition. Other factors potentially affecting the coexistence of C. sanguinea and E. connexa in sweet pepper crops are discussed.     

Behavioural and developmental responses of predatory coral reef fish to variation in the abundance of prey

Ecological theory suggests that the behaviour, growth and abundance of predators will be strongly influenced by the abundance of prey. Predators may in turn play an important role in structuring prey populations and communities. Responses of predators to variation in prey abundance have most commonly been demonstrated in low-diversity communities where food webs are relatively simple. How predators respond in highly diverse assemblages such as in coral reef habitats is largely unknown. This study describes an experiment that examined how the movement, diet and growth of the coral reef piscivore, Cephalopholis boenak (Serranidae) responded to variation in the abundance of its prey. Predator densities were standardised on small patch reefs made from the lagoonal reef-building coral, Porites cylindrica. These patch reefs exhibited natural variation in the abundance and community structure of multiple species of prey. However, our experiment generated a relatively simple predator–prey relationship, with C. boenak primarily responding to the most abundant species of prey. Three responses of predators were observed: aggregative, functional and developmental. Thirty-one per cent of individuals moved between patch reefs during the experiment, all from areas of relatively low to high prey density. Feeding rates were higher on patch reefs of high prey density, while growth rates of fish that remained on low prey density reefs throughout the experiment were lower. Growth rates of C. boenak on the experimental reefs were also much higher than for those living on natural patch reefs over the same time period, corresponding with overall differences in prey abundance. These results suggest that local abundance, feeding rate and growth of C. boenak were closely linked to the abundance of their main prey. This combination of predatory responses is a potential mechanism behind recent observations of density-dependent mortality and population regulation of prey in coral reef fish communities.     

Cannibalism and interspecific predation in the phytoseiid mites Phytoseiulus persimilis and Neoseiulus californicus: predation rates and effects on reproduction and juvenile development

We examined intra- and interspecific predation of adult females and immature stages of the generalist Neoseiulus californicus and the specialist Phytoseiulus persimilis. Adult females and immatures of both predators exhibited higher predation rates on larvae than on eggs and protonymphs. N. californicus fed more inter- than intraspecifically. Predation on P. persimilis by N. californicus was more severe than vice versa. P. persimilis had higher predation rates on conspecifics than heterospecifics and was more prone to cannibalism than N. californicus. When provided with phytoseiid prey, P. persimilis suffered higher mortality than N. californicus. When held without food, adult females and protonymphs of N. californicus survived longer than the corresponding stages of P. persimilis. N. californicus females were able to sustain oviposition when preying upon P. persimilis, whereas cannibalizing females did not lay eggs. Females of P. persimilis were not able to sustain oviposition, irrespective of con- or heterospecific prey. Immatures of both predators were able to reach adulthood when provided with either con- or heterospecifics. Juvenile development of N. californicus was shorter with heterospecific vs. conspecific larvae; mortality of P. persimilis immatures was less when feeding on conspecific vs. heterospecific larvae. Different behavioral pattern in intra- and interspecific predation are discussed in regard to their feeding types (generalist vs. specialist).     

Development and reproduction of a predatory stinkbug, Podisus nigrispinus in relation to two different prey types and environmental conditions

Abiotic factors, prey availability, prey type, and plant host actsimultaneously under field conditions. Their combined effects werepartially investigated for the predatory stinkbugPodisus nigrispinus(Dallas) (Heteroptera: Pentatomidae) preying on tomato leafminer (TLM)caterpillars Tuta absoluta (Meyrick)(Lepidoptera: Gelechiidae) (a preyfeeding on a plant host), and compared to yellow mealworm (YMW)Tenebrio molitor (Coleoptera: Tenebrionidae)pupae (a prey not feeding ona plant host). These experiments were carried out in the laboratory and inan open-sided greenhouse. In general, the environmental variationsbetween laboratory and open-sided greenhouse did not induce differencesin life history characteristics forP. nigrispinus feeding on the sameprey type. However, development and reproductionof P. nigrispinuswas greatly affected by prey type. Nymphal developmental times weresimilar between prey types under laboratory conditions; but were longer(and produced adults of lower body weight) when predators in theopen-sided greenhouse were fed on TLM compared with YMW. Mean mortalityduring the second instar was higher on both prey types in the open-sidedgreenhouse than in the laboratory. Adult emergencewas 38.5 and 50% inthe laboratory, and 32.5 and 48.6%in the open-sided greenhouse for bugsfed on TLM and YMW, respectively. Reproductive characteristics weresimilar for the different environmental conditions when the predator fed onthe same prey, but offspring production was greater for females fed on YMWcompared to females fed on TLM. These results suggest thatP. nigrispinus can adjust its performance accordingto the type of prey available, independently from environmentalvariations. It has the ability to survive on alternative prey,enabling it to maintain a presence in thetomato ecosystem until a primary pest species arrives.     

Oviposition patterns in a predatory mite reduce the risk of egg predation caused by prey

Abstract 1. Predatory arthropods lay their eggs such that their offspring have sufficient prey at their disposal and run a low risk of being eaten by conspecific and heterospecific predators, but what happens if the prey attacks eggs of the predator? 2. The egg distribution and time allocation of adult female predatory mites Iphiseius degenerans as affected by predation of their eggs by prey, the western flower thrips Frankliniella occidentalis, were studied on sweet pepper plants. The predatory mites attack the first instar of thrips but all active stages of thrips are capable of killing the eggs of the predator; however the predatory mite is used for biological control of thrips. 3. The majority of predatory mite eggs was laid on the underside of leaves in hair tufts (domatia). During the experiment, females spent increasing amounts of time in flowers where they fed on pollen and thrips larvae. The risk of predation on predator eggs by thrips was lower on leaves than in flowers where the majority of thrips resides. Moreover, predation risk was higher outside leaf domatia than inside. 4. This suggests that predators avoid ovipositing in places with abundant prey to prevent their eggs from being eaten by thrips.     

Evolution of slow and fast development in predatory ladybirds

The frequency distribution of the durations of development of 516 larvae of Adalia bipunctata is unimodal, and the fast‐ and slow‐developing larvae can be identified at the beginning of the fourth (=last) instar. To determine the advantages of fast and slow development, the survival, duration of development, growth and number of aphids consumed by fast‐ and slow‐developing fourth instar larvae fed different numbers aphids were recorded. The percentages of fast‐ and slow‐developing fourth instar larvae that survived when fed 0.5, 1 or an excess of aphids per day, surprisingly, did not differ. The slow‐developing larvae of both sexes took longer to complete their development than the fast‐developing larvae when fed 1 or an excess of aphids per day, and although the weights of the fast‐ and slow‐developing fourth instar larvae differed at the beginning of the instar, they did not differ at the end of this instar when fed 1 aphid per day. However, when reared on an excess of aphids per day, the adult weights of the fast‐developing individuals was greater than that of slow‐developing individuals. The average durations for which the larvae in the two groups survived when fed 0.5 aphids/day differed with the larvae of the fast‐developing individuals surviving for 9.8 ± 0.5 days and slow‐developing individuals 17 ± 1.3 days. Assuming that it is the rate of predator biomass increase, which is maximized by evolution, a model of the relationship between the rate of development/growth of a predator and that of its prey indicates that the optimum growth rate of a predator is positively associated with that of its prey. The evolutionary implications of these results are discussed.     

Nonlinear and population-specific offspring sex ratios in relation to high variation in prey abundance

Montagu's harrier ( Circus pygargus ), a specialist raptor in western France, faces huge variations in the abundance of its main prey, the common vole ( Microtus arvalis ). This simple predator–prey system provides fine-tuned data for investigating patterns of sex allocation under environmental variability. We analysed variations in brood sex ratio at fledging (1364 chicks from 451 broods) in two adjacent harrier populations for respectively 16- and 8-year surveys of both the predator and its prey. Overall sex ratio (number of males/total number of offspring) was close to parity (0.513) but this apparent equilibrium resulted in fact from opposite skews in the two populations which differed by almost 10% (0.561 vs 0.464). Brood reduction only is unlikely to produce such a difference in average brood sex ratios. Brood sex ratio of the predator was affected by prey abundance. Contrary to expectations and whatever the population, relatively more offspring of the smaller sex were produced during peak years of the vole cycle but also during poor years, thus providing the first evidence for a nonlinear influence of environmental quality (prey abundance) on sex ratio. Assuming that observed sex ratios in both populations are the result of an adaptive strategy that maximizes harrier reproductive output, we discuss possible origins of the bias and why nonlinearity may be involved in sex ratio adjustment. These results further point out that sex ratio analyses should take into account population characteristics, and more generally, environmental variations both in space and time.     

The distribution and abundance of predatory Coleoptera overwintering in field boundaries

Soil samples were taken over the period December - February in 1981-82 and in 1982-83 from four types of field boundaries on farmland in Hampshire to estimate the distribution and abundance of overwintering polyphagous predatory Coleoptera. Supplementary data were obtained from surface searches in four types of field boundaries on farmland in Essex. Different species of predators occurred in significantly higher numbers in specific types of field boundaries but in Hampshire, hedge banks and shelterbelts were more attractive as overwintering sites than grass banks or grass strips for most species and in Essex a combined grass bank, ditch and hedge boundary was more suitable than other boundary types for three of the four species studied.     

The effect of prey composition and abundance on the predation rate and selectivity ofMysis relicta

The predation rate and selection of specific prey byMysis relicta in Lake Tahoe depends on both the total and the relative densities of prey classes. Functional responses of mysids to changes in the density of two species of calanoid copepod prey were curvilinear in laboratory experiments. In the field and in 2-prey treatments, preference was usually positive forEpischura and negative forDiaptomus. However, the preference forEpischura was greatest at the lowest combined densities of prey in the laboratory and decreased at densities >100Epischura / m3 in the field. Several hypotheses to explain the inverse relationship between selectivity and prey density are discussed. Field assemblages of prey vary vertically, horizontally and seasonally. Potential effects of this hetrogeneity on both predator and prey populations are examined.     

Variation in the diet of red foxes on Scottish moorland in relation to prey abundance

The diet of red fox Vulpes vulpes was investigated through analysis of 340 scats collected during 1992-1996 from moorland in south-west Scotland. Rodents, game-birds, lagomorphs, carrion and insectivores were the most frequently occurring food types. Fox diet and prey abundance were compared between heather dominant and grass dominant habitat types within the study area. Rodents were the most frequently occurring food type in each habitat and occurred in 63% of seats overall. Rodents occurred more often in scats from grass dominant sites while gamebirds and lagomorphs were more frequent in scats from heather dominant sites. The occurrence of rodents in winter fox scats increased with rodent abundance. In contrast, the occurrence of gamebirds in winter fox scats was unrelated to gamebird abundance but negatively related to rodent abundance. It appeared that foxes switched to gamebirds in years, or habitats, where rodents were uncommon.     

Spatial consistency in susceptibility of prey species to predation by two Accipiter hawks

Predators impose strong selection on their prey, regulate prey populations and engage in coevolutionary interactions with their prey. The intensity of selection and the strength of coevolutionary interactions will depend on how stringent predators are in their choice of prey. We estimated susceptibility of different species of birds to predation by two common raptors, the northern goshawk Accipiter gentilis and the Eurasian sparrowhawk A. nisus, in an agricultural landscape in Denmark and boreal forests in Finland. We estimated susceptibility to predation as the deviation of the log₁₀‐transformed observed frequency of prey of different species from the log₁₀‐transformed expectation based on population density during the breeding season. We found a high degree of consistency in susceptibility to predation by the goshawk in two areas in Finland. More importantly, there was significant consistency in susceptibility to predation between Denmark and Finland, albeit the degree of consistency in the goshawk was higher than in the sparrowhawk. There was considerable overlap in susceptibility to predation between goshawk and sparrowhawk in Denmark, but not in Finland, implying differences in intensity of interspecific competition as reflected by a much higher extent of goshawk predation on sparrowhawks in Denmark than in Finland. Our findings suggest that hawks impose similar selection pressures on their prey populations, and that the degree of consistency has implications for intensity of interspecific killing.     

Diel variation in predator abundance, predation risk and prey distribution in shallow-water estuarine habitats

Predation by visual predators is often affected by light conditions and may therefore exhibit strong diel variation. The dominant predators on grass shrimp, Palaemonetes pugio, are finfish predators that are thought to locate their prey by visual cues. We examined the response of grass shrimp to diel variation in predation risk in the nearshore shallow waters of the Chesapeake Bay. We used diel shoreline seines to assess the relative abundance of predators. We assessed the relative risk of predation with shrimp tethered at refuge (30 cm) and nonrefuge (60 cm) depths. To measure grass shrimp response to predation risk, we used dipnets to monitor habitat use. Four predominantly visual predators dominated the shoreline seine catches, Fundulus heteroclitus, Micropogonias undulatus, Morone americana and Morone saxatilis. Total predator abundance had a diel component, with dramatic nighttime decreases in total abundance, whereas guild composition and relative abundance remained unchanged. Relative predation risk for tethered shrimp exhibited significant time by habitat interaction. During the day, depth negatively affected survivorship of tethered shrimp while at night overall survivorship increased and there was no effect of depth. Shrimp habitats use reflected diel predation risks. Abundances in the near shore were highest during the day with decreased abundances at night. Together, the seine and tethering data highlight the importance for a refuge (e.g., shallow water) from predation during the daytime and a relaxation of predation pressure at night.     

Foraging activity of two species of predatory leeches exposed to active and sedentary prey

Summary The foraging activity of the freshwater leeches Nephelopsis obscura and Erpobdella punctata during acclimation to active or sedentary prey, starvation and refeeding was examined by filming over a 24 h cycle. For both species, the time of activity of individual leeches and the total number of leeches active were significantly correlated. Activity in the dark was significantly higher than in the light with the activity of N. obscura in the dark 16.2 times higher in terms of time and 6.7 times higher in terms of numbers of individuals moving than E. punctata. Large N. obscura were significantly more active than medium or small individuals and encountered more sedentary prey. With lower levels of activity E. punctata encounters and feeds on more active prey, and in lotic ecosystems its lower exposure to fish predation and drift is, at least partially, responsible for its numerical abundance over N. obscura. There were no significant differences in the activity of N. obscura or E. punctata fed on active or sedentary prey during either subsequent starvation of 1 to 10 d, or after refeeding, suggesting that unchanged foraging activity provides the optimun net energy gain during periods of change in prey type and availability.     

天敌瓢虫种群遗传学及其在生物防治中的应用

天敌瓢虫常在农业生产的生物防治中被广泛引进和使用。这种使用过程往往会导致天敌瓢虫在遗传水平的改变,并最终影响到其生物防治的使用效果和本地生态多样性。对天敌瓢虫种群遗传学的研究,有助于我们认识甚至预测这种遗传改变的规律和生态机制,从而为生物防治计划的优化提供理论基础。本文介绍了种群遗传学的研究方法,分析在生物防治中促进天敌瓢虫遗传改变的因素,以及几种常见的天敌瓢虫种群演变情况,并讨论种群遗传学在天敌瓢虫研究的未来方向。     

Physiological mechanism governing slow and fast development in predatory ladybirds

Aphidophagous and coccidophagous ladybirds, similar to their prey, show marked differences in their pace of life (Dixon, 2000), in particular in their rate of development, with all stages of aphidophagous species developing much faster than those of coccidophagous species. Two hypotheses are proposed to account for the large difference in the pace of life of these two groups. These are that differences in the rate of development are a result of differences in lower temperature thresholds for development or the quality of their respective prey as food (Dixon et al., 2011). Analysis of published results on the rates of development of the eggs of ladybirds indicates that the inverse relationships between the number of day‐degrees required for development (K) and the lower temperature threshold for development (td_min) of these two groups are significantly different. In particular, the respective td_min overlap and K of the aphidophagous and coccidophagous species with a similar td_min are, on average, 38 and 117 day‐degrees (D^o). The relationship between the rate of development (R) and temperature (T) for aphids reared on poor‐ or high‐quality foods indicates that, although the value of td_min of a species depends on food quality, K does not, showing that it is unlikely that K is governed by food quality. Thus, there is little support for differences in either the td_min or food quality governing the difference in the pace of life of these two groups of ladybirds. The results indicate that the physiological mechanism that may govern the difference in the pace of life between these two groups is the number of day‐degrees (K) needed to complete their development. The possible evolutionary reason for this is discussed.     

Responses of the predatory rotifer Asplanchna intermedia to prey species differing in vulnerability: laboratory and field studies

1. We have studied the numerical and functional responses of campanulate morphs of Asplanchna intermedia fed five species of rotifer ( Brachionus rubens , B. patulus , B. calyciflorus , Hexarthra mira and Filinia longiseta ). The vulnerability of the prey varied with their morphology and mode of swimming.
2. To test the numerical and functional responses, prey species differing in their morphology and mode of swimming were provided. Responses were also tested with mixtures of evasive and non-evasive prey provided in three different ratios.
3. A. intermedia showed a type II functional response to all the prey species provided.
4. The population growth rate of A. intermedia on the various prey species provided ranged from a minimum of –0.24 to a maximum of 0.68. There was a significant correlation between the capturability of a prey species and the population growth rate of the predator feeding on it. The capturability of a prey species also has a significant influence on the maximal predator density but not on the time taken to reach it.
5. Observations from a field study undertaken over a 10-month period to study the prey preferences of A. intermedia in nature were corroborated by the laboratory findings.     

Responses of the predatory rotifer Asplanchna intermedia to prey species differing in vulnerability: laboratory and field studies

1. We have studied the numerical and functional responses of campanulate morphs of Asplanchna intermedia fed five species of rotifer ( Brachionus rubens , B. patulus , B. calyciflorus , Hexarthra mira and Filinia longiseta ). The vulnerability of the prey varied with their morphology and mode of swimming.
2. To test the numerical and functional responses, prey species differing in their morphology and mode of swimming were provided. Responses were also tested with mixtures of evasive and non-evasive prey provided in three different ratios.
3. A. intermedia showed a type II functional response to all the prey species provided.
4. The population growth rate of A. intermedia on the various prey species provided ranged from a minimum of –0.24 to a maximum of 0.68. There was a significant correlation between the capturability of a prey species and the population growth rate of the predator feeding on it. The capturability of a prey species also has a significant influence on the maximal predator density but not on the time taken to reach it.
5. Observations from a field study undertaken over a 10-month period to study the prey preferences of A. intermedia in nature were corroborated by the laboratory findings.     

Frugivory and seed dispersal by foxes in relation to mammalian prey abundance in a semiarid thornscrub

Abstract We examine the role of the native fox, Pseudalopex culpaeus, as a frugivore and seed disperser in a semiarid thornscrub of Chile. We quantified the fruit and animal components in its diet versus the availability of fruits and small mammals in the field over a 2‐year period (January 1998 through February 2000). We tested the legitimacy and effectiveness of foxes as dispersers by quantifying the percentages of seed viability and of germination of seeds that passed through fox gut versus those picked from plants. We also studied their efficiency as dispersers, monitoring the fate of seeds in faeces placed in the field. The highest frequencies of fruit consumption by foxes were observed when abundances of small mammal prey were <6 individuals per hectare, regardless of fruit abundance in the field. Thus, foxes consumed fruits as a supplementary food resource. Based on 326 faeces, the total number of fruits consumed was about 34 000 over the 2‐year study period, and fruits from the alien shrub Schinus molle represented 98% of that total, with the native Porlieria chilensis a distant second. Germination and viability of defecated seeds of P. chilensis were reduced by 66% and 48%, respectively, in comparison to controls. In contrast, germination of seeds of S. molle increased by 50% and no effect on viability was observed. With regard to P. chilensis, foxes were legitimate (they defecated viable seeds), but ineffective (seeds in faeces had lower germination than those taken directly from parental plants and there was no seedling establishment in the field) and inefficient dispersers (seeds in faeces were deposited on microhabitats hostile to seed germination and seedling establishment). However, with regard to S. molle, foxes were legitimate, effective (seeds in faeces had higher germination than those taken directly from parental plants; there was germination but no establishment in the field), and efficient dispersers (over 41% of seeds were deposited on safe microsites). Thus, a native fox may be contributing to the spread of an alien shrub, co‐opting existing community processes.