BACKGROUND Ants are known to establish antagonistic and mutualistic interactions with honeydew‐producing hemipterans, depending on the species involved and the ecological context. The aim of this work was to infer the role that such interactions play in the population dynamics of psyllids and aphids in pear orchards. Interactions were inferred from field data and periodical sampling along a 4‐year study, and from interaction assays performed under controlled conditions. RESULTS A decline in the abundance of the pear psyllid (Cacopsylla pyri L.), parallel to an increase in the abundance of aphids, was registered over 4 years. Ants were the dominant species, representing about 90% of the predators, followed by spiders and predatory hemipterans (namely Pilophorus gallicus Remane). Ant abundance increased over the 4 years, matching the population dynamics of aphids. Evidence of mutualistic and antagonistic interactions were found for ant–aphid and ant–psyllid, respectively: (i) ant–aphid abundances on pear trees were positively correlated, and ants reduced predation on aphids by generalist predators, and (ii) ant–psyllid abundances were negatively correlated, ants have a negative effect on the psyllid population growth rates, and ants were found to prey on the psyllid. CONCLUSIONS Because of their high abundance in comparison with other predators and the mutualistic–antagonistic relationships with aphids–psyllids, ants are considered to be the principal force behind the decline of pear psyllid populations and the increase in aphid numbers. In summary, ants contribute positively to biological control by the suppresion of pests (i.e. the psyllid) which are more damaging than those they protect (i.e. aphids). © 2019 Society of Chemical Industry

Omnivorous mirids (Hemiptera: Miridae) are unusual as biocontrol agents, as they feed on both plants and pests. Therefore, extensive knowledge of their ecological behavior is required to maximize their predatory side and to minimize crop damage. Macrolophus pygmaeus is a known predator of small arthropods, used in European tomato crops for more than 20 years. This mirid is currently considered harmless to tomato, although some controversy remains in relation to the status of the species. The aim of this work was to investigate the benefits that M. pygmaeus provides as a predator and the likely damage as a plant feeder. The experiment was carried out in 6 experimental greenhouses in southern Spain. Two treatments, low and high M. pygmaeus populations, were assayed in a complete factorial randomized design with three replicates. Low and high M. pygmaeus populations were achieved by direct and pre-plant release methods, respectively. Tomato plants with a lower number of M. pygmaeus had a significantly higher number of whiteflies and Tuta absoluta galleries than those with a higher number of the mirid, and vice versa. A significantly higher proportion of aborted flowers and fruits was registered in greenhouses with higher M. pygmaeus numbers. Yield was also lower in greenhouses with higher mirid populations. The number of fruits harvested did not differ between treatments, but average fruit weight was significantly lower in the greenhouses with higher mirid numbers. The number of punctures attributed to M. pygmaeus on fruits were low in general and slightly higher in the treatment with more mirids. This work shows that M. pygmaeus provides both "services," as an efficient biocontrol agent of key pests in tomato crops, and "disservices," as it feeds on the reproductive organs of tomato plants, reducing yield. A deeper understanding of the factors that modulate the zoophytophagous response of this economically important species is needed.

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The intensification of agriculture has led to the reduction of the diversity of arthropods in agroecosystems, including that of ground-dwelling species. The aim of our work was to assess the effect of a sown cover crop on the diversity of ground-dwelling arthropods, including key predators for pest control in pear orchards. The trial was carried out in a pear orchard divided in three blocks; two treatments (cover-cropping and control) were implemented in each block. A seed mixture of 10 plant species was used in the plots with the sown cover. The densities of ground-dwelling arthropods were sampled using pitfall traps. The ground cover had a significant impact on the diversity and abundance of arthropods. The Shannon–Wiener diversity index was significantly higher for the cover than for the control plots. Several families of spiders (Linyphiidae, Lycosidae), beetles (Carabidae, Staphylinidae) and hymenopterans (Scelionidae) were significantly more abundant in the cover-sown plots. Ants and collembola had a significantly higher abundance in the control plots. Some of these groups arthropods (ants and spiders), are represented by species that may commute between ground and pear trees, having an impact on pest control. The use of cover crops is encouraged to enhance biodiversity in farmlands.

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) uses a flush‐and‐lacerate feeding strategy producing necrotic rings (NR) at feeding sites in tomato plants. The aim was to investigate the variation in the concentrations of amino acids (aa) and sugars at feeding sites, and its effect on this mirid's life‐history traits and behaviour. The concentration of nutrients was measured in different parts of stems damaged by N. tenuis and mechanically using liquid chromatography. aa concentrations increased below NR; around and above NR, the concentrations of essential and non‐essential aa declined. The concentration of glucose was lower around NR and below. The change in the distribution of aa was similar in NR and mechanically damaged stems, whereas there were no differences in sugar contents. Development time and nymphal mortality were measured on fresh leaflets, leaflets with NR and leaflets plus Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Without prey, development took longer on NR than on fresh leaflets. Development was quicker and mortality lower on leaflets plus moth eggs. Finally, behavioural events were recorded in fifth‐instar nymphs of N. tenuis in: (i) double‐choice experiments (DCE) using leaflets with and without NR; (ii) DCE using leaflets exposed and non‐previously exposed to nymphs and (iii) fresh tomato leaflets plus Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) nymphs. In (i), feeding events lasted longer at NR sites; in (ii), the behaviour of the nymphs on previously exposed leaflets was not significantly different from fresh leaflets; and in (iii), most of the time was dedicated to prey feeding. The overall results indicate that N. tenuis do not take advantage of the inhibited translocation of nutrients in the phloem. The poorer performance of nymphs on leaflets from plants previously exposed to N. tenuis might be due to a general decrease in the concentration of nutrients or to the activation of plant defences.

Pilophorus gallicus Remane is a generalist predator in southern European pear orchards. Nymphs and adults are present in orchards from March to November; their winter absence suggests either migration to other hosts or embryonic dormancy on pear trees to overcome the adverse period. In addition, it has been hypothesized that aestivation takes place to cope with extreme summer conditions. The present study aimed to investigate the reproductive strategy of P. gallicus to overcome unfavourable periods. Accordingly, (i) its population dynamics were followed during several years and (ii) females were sampled in three different seasons to study the condition (diapausing or nondiapausing) of the laying. The results obtained show that nymphs were always the first mobile instar to show up in pear orchards and the presence of adults was delayed, indicating egg overwintering. Nondiapausing eggs prevailed in spring and summer, whereas the autumn eggs were mainly diapausing. Aestivation was rejected. Worthy of note are: (i) the presence of diapausing eggs under favourable conditions and (ii) the existence of females laying both diapausing and nondiapausing eggs; thus, ‘not laying all the eggs in one basket’. The reproductive strategy of P. gallicus is considered as bet‐hedging for the short‐ and long‐term survival of the species.

BACKGROUND Psyllids are principal pests of pear orchards. Pest control based on the intensive use of chemicals is facing difficulties and strategies with a low impact on natural enemies are considered as the most suitable for psyllid control. Ants have been reported as the main predators of Cacopsylla pyri (Hemiptera: Psyllidae) in the southern Mediterranean area. The aim of this work was to determine the contribution of ants to the reduction of the fruit damage caused by psyllids at different intensities of spraying. Five levels of spraying intensity and ant exclusion were tested in a pear orchard with three blocks of five plots each. RESULTS The incidence of russet on fruits increased with the abundance of psyllids and with ant exclusion. In the absence of ants, the impact of russet increased progressively from the highest to lowest intensity of spraying. By contrast, when ants were present no significant differences were found between the lowest (two application of paraffinic oil) and the highest (six applications of abamectin plus paraffinic oil) spraying levels. In the presence of ants, the incidence of russet in the plots with three applications of paraffinic oil was similar to those with three or six applications of paraffinic oil plus abamectin). CONCLUSIONS The importance of ants for the control of psyllids and the reduction of fruit damage is shown. Reduction in the frequency of spraying and the use of low toxic insecticides for natural enemies is presented as the most sustainable strategy for psyllid control in pear orchards. © 2020 Society of Chemical Industry

Spiders are key predatory arthropods that are negatively affected by spraying pesticides in orchards. The aim of this research was to determine the structure of the community of spiders in pear orchards and the impact of the intensity of spraying. The study was carried out over three years in four pear orchards in southern Spain; two of them were conducted by ourselves with no or low-intensity spraying of insecticides, and two under the criteria of technicians (conventional). Spiders were sampled on pear trees by the beating method. The orchards hosted a rich community of spiders belonging to 13 different families and 51 genera. However, the genera Philodromus, Oxyopes, Cheiracanthium, Icius, and Neoscona accounted for 72% of the captures. Spiders were more abundant and had a higher richness of genera in the low-intensity spraying than in conventional orchards. Philodromidae, Salticidae, and Cheiracanthiidae experienced a significant population reduction in conventional orchards, while Araneidae, Linyphiidae, and Thomisidae were not significantly affected by the intensity of spraying. The wandering hunting mode could explain the negative impact on Philodromidae, Salticidae, and Cheiracanthiidae but does not explain the lack of effect on Oxyopidae and Thomisidae. No significant effect was found on any family of web builders.