Soldiers of a European gall aphid,Pemphigus spyrotecae (Homoptera: Aphidoidea): Why do they molt?

A non-migratory aphid,Pemphigus spyrothecae, produces 1 st-instar larvae of 2 types in the gall: thick-legged ones and normal-legged ones. It was found that the thick-legged larvae play a defensive role, hence they may be called soldiers. Unlike the soldiers of other species hitherto reported, at least some soldiers of this species molt and become adults. Their incomplete sterility is explained historically: 1) The migratory ancestor ofP. spyrothecae once produced monomorphic 1st-instar larvae attacking predators in the gall. 2) It acquired a non-migratory life cycle by the larviposition of emigrants in the gall. 3) As a result, 1 st-instar larvae of another morph, which had lived on the secondary host without attacking predators, joined the gall inhabitants. This hypothesis is supported strongly by the fact that the normal-legged 1 st-instar larvae very much resemble the 1 st-instar larvae of migratoryPemphigus species produced on the secondary hosts.     

The effect of the rate of successful dispersal of a Phytoseiid mite,Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) on the persistence in the interactive system between the predator and its prey

Dispersal behaviour was studied on a predacious phytoseiid mite, Phytoseiulus persimilisAthias-Henriot in response to the density of its prey, Tetranychus kanzawaiKishida . And the effect of the change in the rate of successful dispersal of the predators among patches was tested on the persistence of the predator-prey system. The results of the study are summarized as follows:

1. With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
2. When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
3. In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
4. In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
5. It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.

     

The effect of the rate of successful dispersal of a phytoseiid mite,Phytoseiulus persimilis Athias-Henriot (Acarina: Phytoseiidae) on the persistence in the interactive system between the predator and its prey

Dispersal behaviour was studied on a predacious phytoseiid mite, Phytoseiulus persimilisAthias-Henriot in response to the density of its prey, Tetranychus kanzawaiKishida . And the effect of the change in the rate of successful dispersal of the predators among patches was tested on the persistence of the predator-prey system. The results of the study are summarized as follows:

1. With a severe decline in prey density available per individual predator, the predators exhibited a marked behavioural change and dispersed to other areas.
2. When two neighboring host plants did not touch with each other and the dispersal of the predators was possible only through a 20cm plywood “bridge” which connected the two plants, the rate of successful dispersal of the predators was only 20 to 25%, whereas it was 95% when the plants touched with each other.
3. In the system where 32 host plants touched with each other, the predators succeeded in immigrating into all the plants by the 16th day, and they completely eliminated all the prey by the 33rd day.
4. In another system, the 32 plants were equally divided into eight “patches” which were connected with each other with two of the bridges and the predators could move between them only through the bridges as mentioned above. In such a system the predators and their prey coexisted about three times longer than in the other one.
5. It is suggested that for a longer continued coexistence of the predators and prey, it would be necessary to introduce more physical barrier against the dispersal of the predators and to provide more chances for the prey to disperse.

     

Predation and avoidance of tough leaves by aquatic larvae of the moth Parapoynx rugosalis (Lepidoptera: Pyralidae)

Abstract.

• 1 Aquatic larvae of the pyralid moth Parapoynx rugosalis Möschler repeatedly construct protective cases by cutting portions (discs) from leaves of the waterlily Nymphaea ampla and sandwich themselves between the disc and the underside of the host leaf. Construction of a new case requires leaving the old case, thus increasing exposure to predators and parasites.
• 2 In an experiment, larvae with protective cases experienced no mortality due to predation by fish, whereas larvae without cases experienced substantial predation.
• 3 In a series of choice tests, larvae preferentially selected young, tender leaves over old, tough leaves for construction of cases, and larvae spent significantly less time completing their shelters when cutting discs from young, tender leaves.
• 4 A partial explanation of why larvae select young, tender leaves for construction of their protective shelters may be that exposure time to predators during construction is minimized.
• 5 The same mechanism linking preferences for tender leaves to reduced exposure to predators during construction may also apply to other insect herbivores exhibiting leaf-rolling or case-building behaviour.

     

The costs of reduced feeding due to predator avoidance: potential effects on growth and fitness in Ischnura elegans larvae (Odonata: Zygoptera)

ABSTRACT.

• 1 This paper investigates the behaviour, in the laboratory, of a forager simultaneously confronted with the conflicting needs to feed and to avoid predators. The foragers were larvae of the damselfly Ischnura elegans Van der Linden, feeding on Daphnia magna Strauss. The predators were adult females of Notonecta glauca L.
• 2 Patch choice by Ischnura larvae was significantly modified by the presence of predators. Larvae moved to feed in patches of high prey density when predators were absent but preferred dense cover, even though virtually no prey were available, when predators were present. This behaviour was not altered by hunger, up to 12 days without food. In other words, Ischnura larvae were risk averse in their foraging behaviour.
• 3 In experiments with abundant prey available, the feeding rates of Ischnura larvae confined to a single patch were also significantly reduced by the presence of hydrodynamically and chemically detectable predators. Predators detectable only by vision had little effect.
• 4 Calculations made from published data show that reduced larval feeding rates can lead to slower growth and development and prolonged instar durations in Ischnura elegans larvae. This may have important consequences for larval survival and adult reproductive fitness.

     

Alarm pheromone eliciting attack and escape responses in the sugar cane woolly aphid,Ceratovacuna lanigera (Homoptera,Pemphigidae)

All nymphal stages and apterous adults ofCeratovacuna lanigera secreted droplets containing an alarm pheromone from their abdominal cornicles when stimulated with a pin. When fresh droplets on piece of filter paper were put near the aphids, 1st-instar nymphs originating from apterous adults attacked it, but the advanced instar nymphs and adults escaped from the spot. Nymphs and adults originating from alate adults showed escaping behavior only. These different responses strongly correlated with morphological differences, such as relative lengths of the frontal horns and legs. When a syrphid larva,Allograpta javana, was placed on a colony of aphids, many 1st-instar nymphs attacked it using their frontal horns. During the attack, these nymphs spontaneously secreted droplets and adhered them to the syrphid body. When these droplets were placed on the body, the syrphid larva was agressively attacked by additional 1st-instar nymphs.     

The effect of invertebrate and vertebrate predators on the foraging movements of Ischnura elegans larvae (Odonata: Zygoptera)

SUMMARY.

• 1 The foraging movements of late instar Ischnura elegans larvae were monitored in laboratory experiments to study the effects of predators on larval feeding behaviour.
• 2 Ischnura larvae are sit-atid-wait, or ambush, foragers, moving occasionally between perches in search of profitable feeding sites. Larval foraging movements, monitored at different densities of Daphnia prey, increased significantly when prey were absent.
• 3 In experiments without prey, larval movement was inhibited by the presence of fish predators, as well as by invertebrate predators (Notonecta glauca), but not by closely related, non-predatory invertebrates (Corixa punctata) or physical disturbance of the water (intermittent air bubbles).
• 4 Further experiments varied Ischnura hunger levels (0–8 days without food) and illumination (light or dark) with and without notonectid predators. Hunger had no consistent effect on penultimate instar behaviour but final instar foraging activity was significantly modified: movements increased after 4 days starvation and decreased again after 8 days. This response was suppressed by the presence of predators. Both larval instars moved significantly less often in the light, even when predators were absent.
• 5 These phenotypically flexible predator-avoidance responses are likely to decrease the risk of predation by both visual and tactile predators. However, predators clearly have an important influence on the feeding niche of Ischnura larvae, and may decrease the overall feeding efficiency, growth rate, and survival of larvae by constraining their movement in search of profitable feeding sites.

     

Increasing conspecific density weakens the ability of intermediate predators to develop induced morphological defences to top predators

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The biology of Chrysopidae and Hemerobiidae (Neuroptera), with reference to their usage as biocontrol agents: a review

• 1 Many regions have well-developed faunas of Chrysopidae and Hemerobiidae, many of which are potential control agents, but only a few widely distributed species have been seriously considered as such.
• 2 Most of the biological information available concerns Chrysopa species in north temperate areas. C.carnea Stephens, in particular, has been utilised in many pest control programmes. Prepupal or adult diapause constitutes a well-defined stage in the life cycles of many temperate species.
• 3 Larval searching behaviour is efficient, and larvae of most species studied can utilise a wide range of prey organisms or sugar-based foods. The quality of the larval food can affect reproduction of the ensuing adults. Cannibalism is frequent, and may serve as the main food supply when other sources are scarce. Artificial diets for mass rearing are outlined.
• 4 Adult Hemerobiidae are predators. Adult Chrysopidae are either predators or honey-dew feeders, the latter possessing symbiotic yeasts which aid amino acid synthesis. Sprays based on sugar and yeast hydrolysates can be applied in the field as (i) attractants and (ii) alternative or additional food.
• 5 A wide range of predators and hymenopterous parasites attack all stages. Many widespread and non-specific parasites may attack lacewings introduced from other areas.
• 6 Potential use of Chrysopidae and Hemerobiidae in integrated control is enhanced by their tolerance to some insecticides.
• 7 Lacewings are potential control agents of pests in greenhouse, field crops, and orchards. Native species should be augmented rather than others introduced. It would probably be wise to encourage only one or few lacewing species against any given pest.

     

Reproductive and subsocial behaviour in the ovoviviparous leaf beetle Gonioctena sibirica (Coleoptera: Chrysomelidae)

Abstract.

• 1 In the spring, females of the leaf beetle Gonioctena sibirica deposited larvae on the ventral surface of growing young leaves situated on the apical position of shoots of the willow Salix bakko.
• 2 The parent females remained with the larvae usually on the underside of the basal part of leaves, facing toward the base of shoots. When other arthropods approached, the females temporarily moved towards these intruders, showing aggressive behaviour such as swinging the body or stamping the legs. Many females remained with their larvae until the larvae grew into the final (fourth) instar. No female produced an additional brood in the field.
• 3 Broods from which parent females were experimentally removed suffered higher mortality than those in which females were left intact. Arthropods such as spiders and ants were observed preying on the larvae. In contrast, the survivorship of broods from which females were removed and intruders were excluded with a sticky substance applied to the base of twigs was not different from that of control broods. These results demonstrate that the main mortality factor of offspring is pedestrian arthropod predators and females physically repel the predators.
• 4 Potentially alternative reproductive strategies, such as producing a large number of offspring by iteroparity and/or larger brood(s) with less or no care, seem to be inhibited in G.sibirica by larval dependence on growing young leaves which are temporally limited and by ovoviviparity which may have limited brood size.

     

The influence of larval case design on vulnerability of Limnephilus frijole (Trichoptera) to predation

• 1 We examined the potential selective pressures exerted by different types of predators on morphological prey defences using the case-building larvae of the limnephilid caddisfly, Limnephilus frijole. The predators were a predaceous minnow, Gila pandora, and an aeschnid dragonfly naiad, Oplonaeschna armata.
• 2 The influence of larval case design on vulnerability to predators was evaluated in a series of laboratory experiments. Larval L. frijole were collected from a stream without fish or dragonflies. In the laboratory, larvae still occupying their field-built cases were exposed to the two predators, with which L. frijole co-occurs in other streams. Following 24 h exposure of caddisfly larvae to a specific predator, the pre-trial case length, case strength, case width, and case composition of victims and survivors were compared.
• 3 Principal components analysis (PCA) indicated substantial independent variation for all four case parameters in the study population. The cases of larvae surviving exposure to either dragonfly naiads or fish were significantly stronger and wider than cases of victims of predation. Cases of survivors were also longer and had a greater mineral fraction than those of victims, but differences were either marginally significant or not significant.
• 4 These results demonstrate that specific aspects of case design affect the vulnerability of caddisfly larvae. In addition, predaceous fish and predaceous invertebrates, using different predation techniques, may exert similar selective pressures on these defenses. Case aspects influencing vulnerability in these experiments are broadly consistent with natural variation in case design associated with predator-rich and predator-free habitats for related caddisfly species.

     

Cost of shield defence for tortoise beetles (Coleoptera: Chrysomelidae)

Abstract.

• 1 Tortoise beetle larvae possess a shield composed of exuviae and faeces which functions as an effective defence against some invertebrate predators.
• 2 In the laboratory, Charidotella bicolor, Deloyala guttata and Chelymorpha cassidea larvae with their shields experimentally removed did not exhibit enhanced performance (i.e. decreased development time, increased body mass, or higher survival) compared to control larvae with shields intact.
• 3 Disturbance caused during shield removal did not adversely affect larvae because performance did not differ among controls (undisturbed larvae with intact shields), disturbance controls (shield removal simulated, but shield left in place), and larvae with shields removed.
• 4 Larvae without shields did not exhibit compensatory feeding to reconstruct the shield following its removal.
• 5 In a field experiment in which predators were excluded, larvae with shields removed did not develop faster than controls; in fact, survival was slightly reduced (10%) for larvae without shields and may have resulted from desiccation.
• 6 For slow-moving tortoise beetle larvae, the cost of bearing the shield is minimal. Thus, larval shields, composed of recycled waste products, provide an inexpensive mode of protection from some natural enemies.

     

Responses of pre‐dispersal seed predators to sequential flowering of Dipterocarps in Malaysia

Many species of Dipterocarpaceae and other plant families reproduce synchronously at irregular, multi‐year intervals in Southeast Asian forests. These community‐wide general flowering events are thought to facilitate seed survival through satiation of generalist seed predators. During a general flowering event, closely related Shorea species (Dipterocarpaceae) stagger their flowering times by several weeks, which may minimize cross pollination and interspecific competition for pollinators. Generalist, pre‐dispersal seed predators might also track flowering hosts and influence predator satiation. We addressed the question of whether pre‐dispersal seed predation differed between early and late flowering Shorea species by monitoring flowering, fruiting and seed predation intensity over two general flowering events at the Pasoh Research Forest, Malaysia. Pre‐dispersal insect seed predators killed up to 63 percent of developing seeds, with Nanophyes shoreae, a weevil that feeds on immature seeds being the most important predator for all Shorea species. This weevil caused significantly greater pre‐dispersal seed predation in earlier flowering species. Long larval development time precluded oviposition by adults that emerged from the earliest flowering Shorea on the final flowering Shorea. In contrast, larvae of weevils that feed on mature seeds before seed dispersal (Alcidodes spp.), appeared in seeds of all Shorea species almost simultaneously. We conclude that general flowering events have the potential to satiate post‐dispersal seed predators and pre‐dispersal seed predators of mature fruit, but are less effective at satiating pre‐dispersal predators of immature fruit attacking early flowering species.     

Ecological consequences of amphibian larvae and their native and alien predators on the community structure of temporary ponds

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Hierarchical structure in kairomone preference of the predatory mite Amblyseius potentillae: dietary component indispensable for diapause induction affects prey location behaviour

ABSTRACT.

• 1 The phytoseiid predator Amblyseius potentillae (Garman) responded to volatile kairomones emitted from leaves infested by the two-spotted spider mite (Tetranychus urticae Koch), the apple rust mite (Aculus schlechtendali (Nalepa)) or the thrips Frankliniella pallida (Uzel), only when the predators had been reared on a carotenoid-free diet. In contrast A.potentillae responded to the European red spider mite (Panonychus ulmi (Koch)) both when the predators had been reared on a carotenoid-containing and a carotenoid-free diet.
• 2 Carotenoid-deficient predators did not respond to odour emitted from a host plant that was infested by larvae of the fruit-tree leaf roller (Adoxophyes orana (F.v.R)), a carotenoid-containing phytophage, that cannot be preyed upon by A.potentillae.
• 3 Carotenoids are indispensable for diapause induction in A.potentillae. Hence, carotenoid-deficient predators can increase their fitness by feeding from a carotenoid source. This may explain the response of carotenoid-deficient predators to the kairomones of the two-spotted spider mite, F.pallida and the apple rust mite (all containing ingestible carotenoids). As the fruit-tree leaf roller cannot serve as prey and thus as a carotenoid source, it makes sense that the predators lacking carotenoids do not respond to the kairomone of this phytophagous insect.
• 4 Two-choice experiments in a Y-tube olfactometer showed that the kairomone preference of A.potentillae has a hierarchical structure: the kairomone of the European red spider mite is the most preferred one, followed by that of apple rust mite, whereas the kairomone of the two-spotted spider mite is the least preferred of these three.

     

Dispersal of the emerald ash borer, Agrilus planipennis, in newly-colonized sites

• 1 Emerald ash borer Agrilus planipennis Fairmaire (Coleoptera: Buprestidae) is an invasive forest insect pest threatening more than 8 billion ash (Fraxinus spp.) trees in North America. Development of effective survey methods and strategies to slow the spread of A. planipennis requires an understanding of dispersal, particularly in recently established satellite populations.
• 2 We assessed the dispersal of A. planipennis beetles over a single generation at two sites by intensively sampling ash trees at known distances from infested ash logs, the point source of the infestations. Larval density was recorded from more than 100 trees at each site.
• 3 Density of A. planipennis larvae by distance for one site was fit to the Ricker function, inverse power function, and the negative exponential function using a maximum likelihood approach. The prediction of the best model, a negative exponential function, was compared with the results from both sites.
• 4 The present study demonstrates that larval densities rapidly declined with distance, and that most larvae (88.9 and 90.3%) were on trees within 100 m of the emergence point of the adults at each site. The larval distribution pattern observed at both sites was adequately described by the negative exponential function.

     

Predation and disease: understanding the effects of predators at several trophic levels on pathogen transmission

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When to cut your losses: Dispersal allocation in an asexual filamentous fungus in response to competition

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Dispersal and edge behaviour of bark beetles and predators inhabiting red pine plantations

• 1 Quantifying dispersal in predator–prey systems can improve our understanding of how these species interact in space and time, as well as their relative distributions across complex landscapes.
• 2 We measured the dispersal abilities of three forest insects associated with red pine decline: the eastern five spined pine engraver Ips grandicollis (Coleoptera: Curculionidae), its main predator Thanasimus dubius (Coleoptera: Cleridae) and the basal stem and root colonizer Dendroctonus valens (Coleoptera: Curculionidae). We also examined the edge behaviours of these species and the predator Platysoma spp (Coleoptera: Histeridae) between red pine stands (habitat) and clearings (nonhabitat).
• 3 Thanasimus dubius dispersed 12 times farther than its prey I. grandicollis, with 50% of predators dispersing farther than 1.54 km. This profound difference in dispersal behaviour between prey and predator may contribute to the clumped distribution of I. grandicollis.
• 4 Most T. dubius and D. valens were confined in the pine forest, thus showing strong edge behaviour. This differed from I. grandicollis and Platysoma spp., which were commonly found in open areas adjacent to red pine plantations.
• 5 The bark beetle I. grandicollis and one of its main predators, T. dubius, exhibited different patterns of movement within a fragmented landscape. Despite a greater dispersal ability of T. dubius within forests, the spatial distribution of this predator may be restricted by fragmentation of its habitat, and provide an opportunity for partial escape of its prey.
• 6 The present study contributes to our knowledge of top‐down forces within red pine stands undergoing decline. Differences of dispersal patterns and edge behaviour could contribute to the initiation of new pockets of decline, as well as the connectedness among existing ones.

     

Wetland isolation facilitates larval mosquito density through the reduction of predators

• 1 Wetlands harbour high biodiversity and offer important ecosystem services, but they are also a habitat for mosquito larvae (Diptera: Culicidae), which are important disease vectors.
• 2 Isolation among remnant, or newly created wetlands and ponds, and their consequent density in the landscape, is a key factor that can influence a variety of food web processes, including effects on mosquitoes which are important prey to many predators.
• 3 We assess the impact of habitat isolation on the density of pond‐breeding mosquitoes (several Anopheles and Culex species) both directly and indirectly through the food web.
• 4 Results from structural equation modelling of survey data shows that larval mosquitoes are denser in ponds that are more isolated from one another, and that this result was primarily driven indirectly by a reduction of larval mosquito predators (e.g. predaceous insects and amphibians). Furthermore, results from a long‐term mesocosm experiment factorially manipulating isolation and predator reduction show that the effect of isolation on mosquito density was eliminated when predators were experimentally reduced.
• 5 It is concluded that metacommunity processes, both directly and indirectly mediated through predators, can play an important role in the local abundance of wetland breeding mosquitoes and possibly the diseases they spread.