Sexes in gynodioecious Geranium sylvaticum do not differ in their isotopic signature or photosynthetic capacity

• In gynodioecious plants, females are expected to produce more or better seeds than hermaphrodites in order to be maintained within the same population. Even though rarely measured, higher seed production can be achieved through differences in physiology.
• In this work, we measured sexual dimorphism in several physiological traits in the gynodioecious plant Geranium sylvaticum. Photosynthetic rate, stomatal conductance, transpiration rate, WUE and isotopic signatures were measured in plants growing in two habitats differing in light availability.
• Females have been reported to produce more seeds than hermaphrodites. However, we did not observe any significant difference in seed output between the sexes in these experimental populations. Similarly, the sexes did not differ in any physiological trait measured. Seed production was strongly limited by light availability. Likewise, differences between plants growing in full light versus low light were detected in most physiological parameters measured.
• Our results show that the sexes in G. sylvaticum do not show any evidence of sexual dimorphism in physiology, which concurred with a lack of sexual differences in seed output.

     

Nerium oleander as an alternative host plant for south Florida milkweed bugs, Oncopeltus fasciatus

Abstract.

• 1 Life history data were gathered for south Florida Oncopeltus fasciatus reared from eggs on Nerium oleander seeds and milkweed seeds in the laboratory.
• 2 Milkweed seeds were found to be a superior food source since O.fasciatus grew faster, laid more clutches, and has a higher total fecundity on milkweed seeds.
• 3 Fruiting N.oleander was found to be a better food source than nonfruiting milkweeds in a summer field study in south Florida since no nymphs survived to the adult stage on nonfruiting milkweeds but some did on N.oleander.
• 4 O.fasciatus adults and nymphs are abundant on N.oleander in the summer in south Florida when N.oleander is fruiting; no O.fasciatus nymphs are found in the summer on the milkweeds which are not fruiting.
• 5 O.fasciatus leave N.oleander in the autumn when milkweeds start to fruit and can then be found on fruiting milkweeds.

     

Nitrogen and water supplies affect peach tree–green peach aphid interactions: the key role played by vegetative growth

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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.

     

Ricochet pollination in Senna (Fabaceae) – petals deflect pollen jets and promote division of labour among flower structures

• Naturalists Fritz and Hermann Müller hypothesised that heteranthery often leads to a division of labour into ‘feeding’ and ‘pollinating’ stamens; the latter often being as long as the pistil so as to promote successful pollination on the bees’ back. In many buzz‐pollinated species of Senna, however, the so‐called pollinating stamens are short and not level with the stigma, raising the question of how pollen is shed on the bees’ back. Here we explore a mechanism called ‘ricochet pollination’. We test whether division of labour is achieved through the interaction between short lower stamens and strongly concave ‘deflector petals’.
• We studied the arrangement and morphology of the floral organs involved in the ricochet pollination, functioning of the flowers through artificial sonication and observed the interactions between bees and flowers in the field.
• The middle stamens are adapted to eject pollen downwards, which can be readily collected on the bee mid legs. Most of the pollen is ejected towards the deflector petal(s). Pollen from this set of stamens is more likely to contribute to pollination. The pollen grains seem to ricochet multiple times against the deflector petals to eventually reach the bee's back.
• The pollen ricochet mechanism promotes a division of labour by involving additional floral organs, such as petals, reinforcing the Müllers’ division‐of‐labour hypothesis. However, alternative, non‐multiexclusive hypotheses could be explored in genus Senna and other angiosperm species.

     

Searching strategies and attack rates of parasitoids of the ash bark beetle (Leperisinus varius) and its relevance to biological control

Abstract.

• 1 Point estimates of parasitoid behaviour indicated that braconid parasitoids of the bark beetle, Leperisinus varius, spend 70% of their host searching time stationary on the bark surface, in sharp contrast to the chalcidoid parasitoids which spend 60–70% of their host searching time moving across the bark surface.
• 2 Aggressive encounters between searching parasitoids are common and the data suggest that they do not occur at random.
• 3 The chalcidoid parasitoids, Cheiropachus quadrum and Eurytoma morio, are more frequently involved in aggressive encounters than expected and can displace ovipositing individuals of other species.
• 4 Attack rates for the parasitoids were estimated to vary from two hosts per day for the braconid Coeloides filiformis to four hosts per day for E.morio, and net reproductive rates vaned from 6.3 for C.filiformis to 0.8 for Coeloides melanotus.
• 5 These data suggest that while all parasitoids of the scolytid can act as primary parasitoids, at least some of the chalcidoid parasitoids are facultative cleptoparasitoids and should be avoided in classical biological control introductions.

     

Attachment may be a basis for specialization in oak aphids

ABSTRACT.

• 1 The potential role of tarsal attachment in host selection was studied in the specialist aphids Tuberculoides annulatus Hartig and Myzocallis schreiberi Hille Ris Lambers and Stroyan.
• 2 M.schreiberi could walk freely on its host, Quercus ilex and on Q.robur, whereas T.annulatus could walk freely on its host, Q.robur but had difficulty on Q. ilex.
• 3 Attachment to the rough-textured leaves of Q.robur was achieved by means of the pretarsal claws, and to the smooth upper surface of individual trichomes on the lower surface of Q.ilex using flexible pretarsal empodia.
• 4 Both behavioural and allometric differences can account for the inability of T.annulatus to grip onto Q.ilex.
• 5 The role of attachment by phytophagous insects in host plant resistance and selection is discussed.

     

Mutualism or parasitism: Partner abundance affects host fitness in a fish reproductive interaction

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Weed seed granivory by carabid beetles and crickets for biological control of weeds in commercial lowbush blueberry fields

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A review on temperature and humidity effects on Drosophila suzukii population dynamics

1. Drosophila suzukii is an invasive polyphagous pest of wild and cultivated soft‐skinned fruits, which can cause widespread economic damage in orchards and vineyards.
2. The simulation and prediction of D. suzukii's population dynamics would be helpful for guiding pest management. Therefore, we reviewed and summarized the current knowledge on effects of air temperature and relative humidity on different life cycle parameters of D. suzukii.
3. The literature summary presented shows that high oviposition rates can occur between 18 and 30 °C. Temperatures between 16 and 25 °C resulted in fast and high egg‐to‐adult development success of more than 80%. Oviposition and adult life span were positively affected by high relative humidity; however, the factor humidity is so far rarely investigated.
4. We assume that this is one reason why relative humidity usually is not considered in modelling approaches, which are summarized herein. The high number of recently published research articles on D. suzukii's life cycle suggests that there is already a lot of knowledge available on its biology. However, there are still considerable research gaps mentioned in the literature, which are also summarized herein.
5. Nevertheless, we conclude that sufficient temperature data in the literature are suitable to understand and predict population dynamics of D. suzukii, in order to assist pest management in the field.

     

Changes in the feeding behaviour of a malaria vector,Anopheles farauti Lav., following use of DDT as a residual spray in houses in the British Solomon Islands Protectorate

• 1 To investigate the failure of DDT to interrupt malaria transmission in parts of the British Solomon Islands Protectorate, regular all-night man-biting catches of malaria vectors were made before and after DDT house spraying on San Cristobal Island.
• 2 Changes were observed in the man-biting behaviour of Anopheles farauti. There was a reduction in the degree of entry into houses and a shifting of the times of peak biting. Whereas before spraying the indoor and outdoor biting cycles differed, after spraying there was no difference although both the indoor and outdoor cycles had altered.
• 3 DDT was found to have a deterrent effect on An.farauti but this effect decreased with time.
• 4 DDT also appears to eliminate a dominant indoor feeding fraction of the farauti population. Following this there can be an increase in an outdoor feeding fraction which can be responsible for a resumption of malaria transmission.
• 5 Biting cycles obtained before spraying are also shown for An.koliensis and An.punctulatus.

     

REGULARLY ARRANGED PROTEIN ON THE SURFACES OF GRAM-NEGATIVE BACTERIA

• 1 Many species of Gram-negative bacteria carry a layer of regularly arranged sub-units on the outer surface of their outer membrane. The subunits are arranged tetra-gonally or hexagonally and have centre-to-centre spacings ranging from 4 to 35 nm, depending on the bacterial species.
• 2 The regularly arranged layer has been detected by electron microscopy in whole cells, cell walls, outer membranes and assemblies of isolated subunits. The regular arrays can be seen in intact cells by shadowing or freeze-etching and, occasionally, in thin sections or after negative-staining. Freeze-etching and negative-staining have been used to show the regular arrays in isolated cell walls and outer membranes. Negative-staining is used in the examination of assembled isolated subunits.
• 3 Optical diffraction of electron micrographs provides more detailed information of the fine structure of the subunits in the regular array.
• 4 The regularly arranged surface layer can be removed by protein perturbants, by chelation of divalent cations with EDTA and EGTA, by cation substitution or by acidification.
• 5 The two surface subunits which have so far been purified have been found to be acidic proteins with molecular weights of 67000 (Acimtobacter 199A) and 140000 (Spirillum serpens).
• 6 In Acinetobacter 199A the surface protein is attached to the protein of the outer membrane through a salt bridge involving Ca²⁺ or Mg²⁺. Evidence exists that there may be a similar mode of attachment in other species.
• 7 Isolated surface proteins from Acinetobacter 199A and from Spirillum spp. have the ability to reassemble into the same pattern as that seen on the bacterial surface, either in isolation or in the presence of cell-wall fragments to act as nucleating agents. Self-assembly of Acinetobacter 199A a-protein requires chloride ions.
• 8 Acinetobacter 199A a-protein can only be incorporated onto the bacterial surface if an intact lipopolysaccharide membrane is formed first to receive the intrinsic membrane proteins to which the a-protein attaches. Impairment of lipopolysaccharide synthesis by bacitracin prevents incorporation of a-protein and other membrane proteins into the outer membrane.
• 9 Continuing incorporation of pre-formed radioactive a-protein into the outer membrane in Acimtobacter 199A can be detected for 10 min after transference from radioactive to non-radioactive growth medium.
• 10 Spirillum metamorphum, Flexibacter sp. and Acinetobacter 199A synthesize more surface protein than is required to cover the cell surface. The excess is secreted into the growth medium.
• 11 The regularly arranged surface protein of Acinetobacter 199A provides partial protection against isolated lysosomal proteinases from polymorphonuclear leucocytes. Spirillum spp. is protected from Bdellovibrio invasion by the surface protein.
• 12 Secreted a-protein from Acimtobacter 199A has phospholipase A, activity. No phospholipase activity can be detected when the a-protein is bound to the bacterial surface.

     

Life history traits related to resource partitioning between synhospitalic species of Colocasiomyia (Diptera, Drosophilidae) breeding in inflorescences of Alocasia odora (Araceae)

Abstract.

• 1 Two closely related species of Colocasiomyia alocasiae (Okada) and C.xenalocasiae (Okada) (Diptera, Drosophilidae) breed in inflorescences of Alocasia odora C. Koch (Araceae), a hermaphroditic understorey clonal herb.
• 2 The two drosophilid species form a synhospitalic pair in Okinawa with alocasiae breeding in the upper half of the inflorescence and xenalocasiae breeding in the lower half.
• 3 C.alocasiae also has the following combination of life history traits: small body size, many eggs, and early reproductive maturity. In contrast, xenalocasiae can be described as having larger body size, fewer eggs, and delayed reproductive maturity.
• 4 Resource partitioning between the two species on the same host may be affected by these life history traits which are associated with their larval habitats.

     

Seasonal biological variation in some leaf-miner parasites in the genus Achrysocharoides (Hymenoptera, Eulophidae)

ABSTRACT.

• 1 Most Achrysocharoides species and their Phyllonorycter hosts (Lepidoptera, Gracillariidae) have two generations per year in Britain.
• 2 In those species with separate sex broods, peak male emergence tends to be earlier than peak female emergence. This female emergence lag is shorter in the second generation.
• 3 The mean brood size in the second generation is significantly smaller than in the first in A.cilla males and females, A.latreilli females, mixed sex broods of A.atys, and A.carpini females. A.cilla, A.latreilli and A.niveipes generally have a significantly greater proportion of males in the second generation, but A.atys does not.
• 4 There is a shift to killing later instar Phyllonorycter larvae in the second generation, when a much higher percentage parasitism is generally achieved.
• 5 The intergeneration differences in sex ratio and brood size may be explained by a change in oviposition behaviour of females of the first and second generations.

     

Marginal attack rate,k-values and density dependence in the analysis of contemporaneous mortality factors

1. Procedures for calculating the marginal attack rates and associated k-values from observed death rates are presented for contemporaneous predators or parasitoids that either do or do not discriminate against previously parasitized hosts.
2. The relationships among previous methods for quantifying contemporaneous mortalities are discussed.
3. Solutions to the problem of calculating marginal rates taken from human survival analysis are given under the assumption of proportional hazards. These calculations are easily extended to three or more contemporaneous sources of mortality.
4. The conditions under which proportional hazards can be expected are discussed.
5. These methods are compared to that of Varley et al., 1973 for assessment of density dependence among contemporaneous predators.

     

Development and application of environmental DNA surveillance for the threatened crucian carp (Carassius carassius)

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Patch-leaving rules for parasitoids with imperfect host discrimination

Abstract.

• 1 The solitary parasitoid Anagrus delicatus attacks hosts (plant-hopper eggs) that exist in distinct batches and that are readily detectable to the foraging parasitoid. However, Anagrus delicatus attacks only a small fraction of the available hosts within a batch of eggs and then disperses (Cronin & Strong, 1993a). Here we address the question: Why is A.delicatus abandoning seemingly high quality patches?
• 2 A parasitoid with an imperfect ability to discriminate between unparasitized hosts and hosts that it has attacked earlier within the same patch experiences a risk of self-superparasitism when attacking multiple hosts within a single patch. Self-superparasitism can incur costs in the form of lost time and eggs. Early patch leaving can be favoured as a means of avoiding the costs of self-superparasitism.
• 3 A simple static model demonstrates that patch leaving is favoured by low costs of travelling to a new patch, high error rates in discriminating previously self-parasitized hosts, and high levels of parasitism in the currently occupied patch.
• 4 A more detailed dynamic state variable model, parameterized for A.delicatus, demonstrates that this parasitoid's seemingly enigmatic behaviour can be explained under our hypothesis. In order for this to be the case, we predicted that A.delicatus cannot recognize previously parasitized hosts. Subsequent to our prediction, Cronin & Strong (1993b) demonstrated that experienced A.delicatus do not avoid ovipositing in previously self-parasitized hosts.
• 5 Optimal patch leaving rules can be highly sensitive to even very low host discrimination error rates, which may be widespread among parasitoids.

     

Adaptive dispersal and appetitive flight in the green lacewing, Chrysopa cornea

Abstract.

• 1 The flight behaviour of Chrysopa cornea Steph. (Neuroptera: Chrysopidae) with regard to dispersal activity has been investigated in field experiments. There are three main types of flight activities.
• 2 Shortly after emergence (in the first two nights) the adults perform adaptive dispersal flights which are straight downwind flights mostly at elevations higher than 3 m above ground. The lacewings do not react to the presence of honey dew in the crop.
• 3 After 2—3 days the scent of honeydew becomes a strong landing stimulus. The flight is now an appetitive downwind flight which usually is lower than 3 m above ground.
• 4 Once landed, the lacewings' subsequent flights are toward the source of the kairomone which signals honeydew. This can be termed appetitive upwind flight. It is a low stepwise flight within the ‘boundary layer’ which rarely exceeds 1 m above crop level.
• 5 Dispersal takes place in a continuous ‘rolling’ downwind movement of the whole lacewing population. The immigration rate into a field is thus not a function of the quality of that field but rather of upwind fields. Emigration, however, strongly depends on the presence of honeydew (retaining of ovipositing immigrants) and the density of aphids or other food for the larvae (production of new adults).

     

The life history and population biology of an intertidal aphid,Pemphigus trehernei Foster

• 1 The fluctuations in the density and composition of populations of Pemphigus trehernei, an aphid that lives on the roots of the halophyte Aster tripolium, were followed on an area of saltmarsh on the north Norfolk coast between 1971 and 1973.
• 2 The aphid has a typical Pemphigus life-cycle, but the emphasis is on the non-sexual anholocycle. Many diapausing aphids overwinter on the marsh and relatively few alates fly to or from it.
• 3 The aphids are confined to the top 11 cm of soil and are highly aggregated: the dispersion of the population can be fitted to the negative binomial. The absolute density of the populations is relatively low, with a mean value of about 2000 aphids/m² of available marsh area.
• 4 Temperature, host-plant growth and fungal attack are probably the most important factors affecting seasonal population fluctuations. Up to 50% of the populations may be infected with the fungus Metarrhizium anisopliae, which is widespread in the soil.

     

Monogamy to communal breeding: exploitation of a broad resource base by burying beetles (Nicrophorus)

Abstract.

• 1 To investigate the range of resource size that burying beetles (Nicrophorus) exploit, small (21–33 g), medium (50–90 g) and large (120–210g) carcasses, were placed in the field and then exhumed after 1, 4, 8, 12 or 18 days.
• 2 Nicrophorus attempts to utilize carcasses over this entire size range but has greater success on smaller carcasses.
• 3 Larger carcasses were more difficult to exploit because: (a) they took longer to conceal beneath the leaf litter; (b) they were less likely to be rounded into brood balls; (c) they were more likely to be utilized by dipterans; and (d) they were occupied by greater numbers of congeners.
• 4 Larger carcasses, however, did support greater numbers of larvae and contained broods of greater total mass than smaller carcasses.
• 5 Beetles sometimes bred communally on larger carcasses in the field and same-sex adults were observed to feed young.
• 6 Two follow-up experiments were conducted in the laboratory. On a large carcass N.defodiens, N.tomentosus or N.orbicollis can raise a maximum of 35–50 young. Nicrophorus pustulatus, in contrast, appears to be unique among Nicrophorus in that it can raise nearly 200 young on larger carcasses.
• 7 Nicrophorus orbicollis and Nicrophorus sayi are extremely dependent on parental regurgitations and young fail to survive to the second instar if parents are removed. Young of Nicrophorus defodiens, N.tomentosus and N.pustulatus can develop normally without parental regurgitations.
• 8 I discuss these results in the context of reproduction on carcasses of different size and hypothesize that this breeding system is facultatively quasisocial.