Does ant predation favour leaf beetle specialization on toxic host plants?

Generalist predators are frequently seen as evolutionary forces that narrow the host range in herbivorous insects. Predators may favour specialization of herbivores on host plants containing toxic chemicals (which can be used by herbivores for their own defence) if host plant‐derived defences provide better protection from enemies than do autogenously produced defences. We compared the effectiveness of these two defensive strategies in the larvae of six species of leaf beetle (Chrysomelidae) against wood ants (Formica rufa group) in field experiments. Ants were more strongly repelled by larvae with host plant‐derived, salicylaldehyde‐containing secretions than by larvae with various autogenous secretions, but collectively foraging ants ultimately overcame any type of chemical defence by social interactions, chemical signalling, and olfactory learning. As a result, ants killed all larvae of Chrysomela lapponica defended by salicylaldehyde‐containing secretions within 2 days of their introduction to willows within 15 m of ant nests. We conclude that in the field neither type of chemical defence provides complete protection against wood ants in the vicinity of their nests, and that evolutionary shifts from autogenous production of secretion to sequestration of plant allelochemicals in leaf beetles may be favoured mostly at low ant densities on the periphery of ant foraging areas.     

Do Chrysoperla carnea and Adalia bipunctata influence the spread of Cucurbit aphid‐borne yellows virus and its vector Aphis gossypii?

The effects of two aphidophagous predators, the larvae of Chrysoperla carnea and the adults of Adalia bipunctata, on the spread of Cucurbit aphid‐borne yellows virus (CABYV) transmitted by the cotton aphid Aphis gossypii were studied under semi‐field conditions. Aphids and natural enemies were released inside insect‐proof cages with a CABYV‐infected cucumber plant placed in the centre of the cage and surrounded by 48 healthy cucumber seedlings. The spatiotemporal dynamics of the virus and vector were evaluated in the short (7 days) and long term (14 days) in the presence and absence of each predator. The spatial analysis by distance indices methodology, together with other indices measuring the dispersal around a single focus, was used to assess the spatial pattern and the degree of association between the virus and vector. The presence of C. carnea larvae and A. bipunctata adults induced A. gossypii dispersal after 14 days but not after 7 days. The reduction of the initial aphid population established in the plant located in the centre of each cage was always higher for C. carnea than for A. bipunctata. There was some evidence that the natural enemies affected the spread of CABYV, though more so for C. carnea than for A. bipunctata. This study suggests an influence of both predators on the spread of the aphid, mainly in the long term, but only weak effect of predators in the spread of the viral disease was demonstrated.     

Suppression of Bactrocera oleae (Diptera: Tephritidae) pupae by soil arthropods in the olive grove

Soil arthropods can provide ecosystem services, such as biological control of crop pests that spend part of their life cycle in the soil. This is the case of Bactrocera oleae (Rossi) (Diptera: Tephritidae), one of the most important pests of olives. The impact of edaphic arthropods on the abundance of B. oleae pupae was evaluated and their contribution for biological control of the pest was quantified. Exclusion and exposed boxes with B. oleae pupae were installed in olive groves in parallel with pitfall traps used for sampling arthropods and the percentage of pupae suppression was evaluated from January to May 2014. Forficulidae dominated the community during the winter period while Formicidae dominated in spring. Pupae suppression reached the maximum value in the beginning of spring and these results indicate that soil arthropods have strong impact in the decline of B. oleae pupae in olive groves.     

Egg mortality in the cedar processionary moth,Thaumetopoea bonjeani (Lepidoptera: Notodontidae), in an outbreak area of Algeria

The cedar processionary moth, Thaumetopoea bonjeani (Lepidoptera: Notodontidae), is one of the most serious pests of Cedrus atlantica in north-western Africa (Algeria and Morocco). We report on T. bonjeani egg mortality and the diversity and abundance of parasitoids associated with its eggs in the area of Djurdjura Mountain (Tala-Guilef, Algeria). For this goal, 223 egg batches were collected from C. atlantica over two cohorts (2012 and 2013). The average number of eggs per egg batch increased from 143 in 2012 to 171 in 2013, while the egg mortality decreased from 47.4% and 23.9%, respectively, possibly because of a dilution effect. The most important factors of egg mortality were parasitoids and predators, with hymenopteran egg parasitoids killing from 12.1% to 34.9%, and predators from 5.2% to 7.4% of the eggs. The pattern of egg parasitism was driven largely by Ooencyrtus pityocampae, accounting for about 94% of the total parasitoids, followed by Baryscapus servadeii and Trichogramma embryophagum. An hyperparasitoid Chartocerus sp. was collected for the first time from eggs of Thaumetopoea species. As the two major egg parasitoids are shared with the pine processionary moth Thaumetopoea pityocampa in the same area, it is likely that parasitoid abundance may depend on the occurrence of both hosts.     

Digestion rate in relation to alternative feeding in three species of polyphagous predators

Abstract. 1. Disappearance of different amounts of aphid ingested by three species of polyphagous predators, the carabids Bembidion lampros (Herbst) and Nebria brevicollis (F.) and the staphylinid Philonthus cognatus Stephens, was monitored by a quantitative enzyme-linked immunosorbent assay (ELISA). The effect on the rate of inactivation of prey antigens by the ingestion of subsequent, non-aphid food was also studied.
2. Antigen inactivation was significantly more rapid in the staphyilinid than in the carabids.
3. No statistically significant differences were found in the rate of antigen inactivation between beetles which consumed only aphids and those which were given a different type of food after feeding on aphids; the detection period was longer in the former groups. A higher proportion of beetles with low levels of aphid antigen were found earlier in the latter group.
4. The results did not unequivocally support the prediction derived from optimal digestion theory that beetles without continuous access to food would retain an initial meal longer than beetles with unlimited access.     

Feeding ecology of three predacious aquatic insects and two fish in a riffle of the Speed River,Ontario

The food habits of two fish (Etheostoma flabellare and Rhinichthys atratulus) and three predacious aquatic insects (Nigronia serricornis, Paragnetina media and Agnetina capitata) were examined for one year in a riffle of the Speed River, Ontario. Adult E. flabellare fed primarily on net-spinning caddisflies whereas juvenile E. flabellare relied heavily on chironomids. Rhinichthys atratulus had a more varied diet composed of chironomids, Antocha larvae (Tipulidae) and net-spinning caddisflies. Two of the aquatic insect predators consumed large numbers of net-spinning caddisflies; however, P. media contained large percentages of Hydropsyche and Cheumatopsyche whereas N. serricornis fed primarily on non-hydropsychid net-spinners. The diet of A. capitata was composed largely of chironomids and mayflies. Schoener's diet overlap index () suggested that large E. flabellare and P. media had similar diets; however, E. flabellare ingested much larger prey than P. media. Adult E. flabellare contained a significantly greater proportion of larger prey items in comparison with benthic samples whereas similar comparisons with other predators showed no selection for larger prey. These data demonstrate that E. flabellare was size selective given the range of prey sizes available whereas the other predators were not. Also, there was little dietary overlap among the fish and invertebrate predators suggesting a partitioning of resources.     

Rates of consumption of cereal aphids by some polyphagous predators in the laboratory

The consumption rates of nine species of Carabidae and five species of Staphylinidae which feed on the aphid Sitobion avenae (F.) were studied under conditions of surplus food in the laboratory. The mean daily consumption of aphids was between 2.5% and 45.6% of the predator species' mean body weight; the lowest values were for large Carabidae and the highest for small Staphylinidae. Separate significant positive relationships were found between the mean total weight of aphids consumed per day, and the mean weight of the adult of the carabid and staphylinid species at each temperature. A re-evaluation of published data also showed this. The slopes of the regression lines were steeper for the Staphylinidae than for the Carabidae and possible reasons are given. The regression equations could be used in simulation models to determine the maximum possible effects of these beetles on aphid populations.

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Résumé La consommation de Sitobion avenae F. par 9 espèces de Carabidae et de 5 de Staphylinidae a été examinée au laboratoire en condition de surapprovisionnement. Les expériences ont été répétées dans 4 conditions de températures variables caractérisées par des moyennes de 12°3, 16°6, 20°6 et 23°6. Les poids moyens de pucerons consommés variaient entre 2,5% et 45,6% du poids des prédateurs; les valeurs les plus faibles correspondant aux gros carabes et les plus élévées aux petits staphylins.Les différences entre sexes étaient vraisemblablement dues au dimorphisme pondéral. Une relation significative et positive entre le poids moyen de pucerons consommés et le poids moyen du coléoptère a été mise en évidence tant pour les carabes que les staphylins à toutes les températures (Fig. 1, Tableau 2). Cette relation ressort aussi d'une réévaluation des données publiées. L'utilisation de formules de régression dans des modèles de simulation permettra de prédire les effets des carabes et des staphylins sur les populations de pucerons dans ces conditions optimales.

     

Predators and planariid competitors of the triclad Phagocata vitta (Dugés)

When Phagocata vitta, Crenobia alpina and Polycelis felina were exposed separately to each of seventeen potential invertebrate predators in the laboratory, only two stonefly species, Dinocras cephalotes and Perlodes microcephala, fed on the three triclad species, whilst the trichopteran Rhyacophila dorsalis ate the last two triclads. On exposing pairs of triclad species to D. cephalotes, significantly more P. felina than Ph. vitta were consumed, whereas similar numbers were eaten in each of the other two triclad combinations. Cannibalism and interspecific predation by triclad species were not observed. It is concluded that predation is unlikely to have a major influence in determining the observed distribution and abundance of triclad species in a Welsh study stream which harbours low numbers of effective predators.The de Wit model of competition was used to examine the competitive relationships between Ph. vitta, and C. alpina and P. felina, using chironomids or tubificid worms as food. In mixed cultures of Ph. vitta and P. felina fed on tubificids a stable equilibrium existed within the range of relative densities used in the experiments, whereas Ph. vitta was competitively superior to C. alpina in cultures fed on each of the food types, and to P. felina fed on chironomids. However, in theory, an equilibrium could occur when 10 or 6–7 times as many Ph. vitta as P. felina and C. alpina respectively are in the culture, when intraspecific rather than interspecific competition would become more important. Where the three triclad species coexist in the Welsh study stream, they are in similar numbers. This could imply that food is not limiting, with no consequent interspecific competition, or that the laboratory experiments were too simplistic to allow any interpretation of the field situation.     

The predators' complex of pear-feeding psyllids in unsprayed wild pear trees in greece

Four insect species producing honeydew, exploited by bees, were found on wild pear trees,Pyrus amygdaliformis Vill.. Three of them were Psyllids,Cacopsylla (Hepatopsylla) notata (Flor),Cacopsylla (Thamnopsylla) pyrisuga (Förster), Cacopsylla (Hepatopsylla) pyri (L.), and one was Aphid,Dysaphis pyri D.d.F. The 1 rst one was the most abundant. Although these species are producing honeydew from spring to autumn, the bees are foraging on it only during September and October, and not every year. A total of 18 predatory species were counted. Five of them,Anthocoris nemoralis F.,Atractotomus mali Mey.,Chrysoperla carnea (Stephens),Anisochrysa flavifrons (Brauer) andAnisochrysa prasina (Burmeister) were bred in laboratory on the Psyllids. It seems that the predators of theseHomoptera may be able to cause a decrease of their population level. Three predators,Anthocoris nemoralis F.,Chrysoperla carnea (Stephens) andCoccinella septempuctata L., were very common, and the last 2 were present almost all the year round.     

Food and growth relations of the marine microzooplankter,Synchaeta cecilia (Rotifera)

The trophic interactions of the marine rotifer Synchaeta cecilia were investigated by determining its feeding and growth rates on a wide variety of marine phytoplankton and by determining its susceptibility to predation by the calanoid copepod, Acartia tonsa. Reproduction of S. cecilia was sustained in four-day feeding trails by 13 of 37 algal species tested. Growth-supporting species included species of Cryptophyceae, Dinophyceae, Chlorophyceae and Haptophyceae in sizes from 4 to 47 μm. Within these taxa, other species in the acceptable size range failed to support growth. No species of Cyanophyceae, Bacillariophyceae, or Chrysophyceae supported growth of the rotifer. S. cecilia can be maintained on unialgal cultures of Cryptophyceae but growth is enhanced by a combination of two or three species; a mixture of Chroomonas salina (Cryptophyceae), Heterocapsa pygmaea (Dinophyceae), and Isochrysis galbana (Haptophyceae) has sustained laboratory stocks of S. cecilia for over four years. The expected response of S. cecilia to food quantity was observed: as food concentration was increased from 58 to 1154 μg C 1⁻¹, the population growth constant increased from 0.17 to 0.60 d⁻¹ at 20°C. This is equivalent to population doubling times of 4.0 and 1.1 days at H. pygmaea densities of 500 and 10⁴ cells ml⁻¹, respectively. The susceptibility of S. cecilia to predation was investigated by determining its rate of capture by the omnivorous marine copepod Acartia tonsa. At prey densities of 5 to 35 μg C 1⁻¹ (0.3 to 1.9 individuals 1⁻¹), A. tonsa readily ingested S. cecilia at rates up to 3 μg C copepod⁻¹ day⁻¹.