The impact of ant mutualistic and antagonistic interactions on the population dynamics of sap-sucking hemipterans in pear orchards

Behavioural changes in the city: The common black garden ant defends aphids more aggressively in urban environments

Urbanisation alters biodiversity patterns and threatens to disrupt mutualistic interactions. Aside from pollination, however, little is known about how mutualisms change in cities. Our study aimed to assess how urbanisation affects the protective mutualism between ants and aphids, investigating potential behavioural changes in mutualistic ants and their implications for aphids in urban environments. To do so, we studied the protective mutualism between the pink tansy aphid (Metopeurum fuscoviride) and the black garden ant (Lasius niger) along an urbanisation gradient in Berlin, Germany. In nine locations along this gradient, we measured aphid colony dynamics and proxies for parasitism, quantified the investment of ants in tending aphids and conducted behavioural assays to test the aggressiveness of ant responses to a simulated attack on the aphids. We found that aphid colonies flourished and were equally tended by ants across the urbanisation gradient, with a consistent positive density dependence between aphid and ant numbers. However, ants from more urbanised sites responded more aggressively to the simulated attack. Our findings suggest that this protective mutualism is not only maintained in the city, but that ants might even rely more on it and defend it more aggressively, as other food resources may become scarce and more unpredictable with urbanisation. We thereby provide unique insights into this type of mutualism in the city, further diversifying the growing body of work on mutualisms across urbanisation gradients.

Arthropods as possible losses and solutions on Terminalia argentea (Combretaceae) saplings

Terminalia argentea native tree to Brazil and used in landscaping, wood and coal production, and civil construction, is adapted to poor and dry soils and cultivated in severely disturbed ecosystems. This plant has insecticidal activity, but arthropods can cause damage to its saplings. This study evaluates the herbivorous insects and of their natural enemies on 48 T. argentea saplings which were divided according to the damage they cause or reduce it on these saplings using the percentage of the Importance Index-Production Unknown (% I.I.-P.U.). The Lamprosoma sp., Epitragus sp., Tropidacris collaris, Cerambycidae, Cratosomus sp., Psiloptera sp., Parasyphraea sp., Trigona spinipes, and Aphis spiraecola showed the highest % I.I.-P.U. on leaves of T. argentea. The Aphirape uncifera, Mantis religiosa, Uspachus sp., Podisus sp., and Araneidae, with the highest % I.I.-P.U. on leaves of T. argentea saplings are possible solutions to reduce damage by these pests. These natural enemies can reduce herbivorous insects on T. argentea saplings. However, their populations should be increased, especially spiders. Nevertheless, the Brachymyrmex sp. associated to A. spiraecola, in future T. argentea commercial plantations, can increase populations of sap-sucking insect and, consequently, their damage.

Density thresholds and the incorporation of biocontrol into decision-making to enhance the control of Cacopsylla pyri in pear (cv. Ercolini) orchards

BACKGROUND

Economic injury level (EIL) and economic threshold (ET) are customary tools for integrated pest management. Cacopsylla pyri L. is a major pest in pear orchards. The aim of this work was to establish EIL and ET for the optimization of the use of insecticides to control this psyllid, considering biocontrol and two spraying strategies (low-toxicity versus broad spectrum chemicals). This research was conducted over 4 years in five commercial pear, cv. Ercolini, orchards in south-eastern Spain.

RESULTS

Psyllids and ant populations were followed using periodic sampling, and the russet on fruits was quantified. The effect of spray intensity and ant exclusion on psyllid abundance and yield were also tested: both had a significant effect on the cumulative number of C. pyri (CNP), yield and fruit weight. Yield was found to be negatively correlated with CNP. The russet index (RI) increased in a sigmoidal fashion as a function of CNP, being significantly higher with than without ant exclusion. The commercial categorization of fruits was explained satisfactorily as a function of CNP and the cumulative number of ants (CNA). The quantitative EIL was established at a CNP of 427.2 for spraying with paraffinic oil and 425.7 for abamectin. As for the cosmetic EIL, when CNA was zero, this EIL was 24.2, at a CNP of 16.6 for spraying with paraffinic oil or abamectin.

CONCLUSIONS

The use of products of low toxicity, for the conservation of ants, is expected to increase ET and, thus, reduce the intensity of spraying. © 2021 Society of Chemical Industry.

Percentage of importance indice-production unknown: loss and solution sources identification on system

Abstract Indices are used to help on decision-making. This study aims to develop and test an index, which can determine the loss (e.g., herbivorous insects) and solution (e.g., natural enemies) sources. They will be classified according to their importance regarding the ability to damage or to reduce the source of damage to the system when the final production is unknown. Acacia auriculiformis (Fabales: Fabaceae), a non-native pioneer species in Brazil with fast growth and rusticity, is used in restoration programs, and it is adequate to evaluate a new index. The formula was: Percentage of the Importance Indice-Production Unknown (% I.I.-PU) = [(ks1 x c1 x ds1)/Σ (ks1 x c1 x ds1) + (ks2 x c2 x ds2) + (ksn x cn x dsn)] x 100. The loss sources Aethalion reticulatum L., 1767 (Hemiptera: Aethalionidae), Aleyrodidae (Hemiptera), Stereoma anchoralis Lacordaire, 1848 (Coleoptera: Chrysomelidae), and Tettigoniidae, and solution sources Uspachus sp. (Araneae: Salticidae), Salticidae (Araneae), and Pseudomyrmex termitarius (Smith, 1877) (Hymenoptera: Formicidae) showed the highest % I.I.-PU on leaves of A. auriculiformis saplings. The number of Diabrotica speciosa Germar, 1824 (Coleoptera: Chrysomelidae) was reduced per number of Salticidae; that of A. reticulatum that of Uspachus sp.; and that of Cephalocoema sp. (Orthoptera: Proscopiidae) that of P. termitarius on A. auriculiformis saplings. However, the number of Aleyrodidae was increased per number of Cephalotes sp. (Hymenoptera: Formicidae) and that of A. reticulatum that of Brachymyrmex sp. (Hymenoptera: Formicidae) on A. auriculiformis saplings. The A. reticulatum damage was reduced per number of Uspachus sp., but the Aleyrodidae damage was increased per number of Cephalotes sp., totaling 23.81% of increase by insect damages on A. auriculiformis saplings. Here I show and test the % I.I.-PU. It is an new index that can detect the loss or solution sources on a system when production is unknown. It can be applied in some knowledge areas.

Insects and spiders on Acacia mangium (Fabaceae) saplings as bioindicators for the recovery of tropical degraded areas

Acacia mangium is a pioneer species with fast growth and frequently used in the recovery of degraded areas. The objectives were to evaluate insects and spiders, their ecological indices and interactions on A. mangium saplings in a tropical degraded area in recovering process. The experimental design was completely randomized with 24 replications, with treatments represented by the first and second years after A. mangium seedling planted. Numbers of leaves/branch, branches/sapling, and ground cover by A. mangium saplings, Hemiptera: Phenacoccus sp. and Pachycoris torridus; Hymenoptera: Tetragonisca angustula and Trigona spinipes, Brachymyrmex sp., Camponotus sp. and Cephalotes sp.; Blattodea: Nasutitermes sp. and Neuroptera: Chrysoperla sp.; abundance, species richness of pollinating insects, tending ants, and the abundance of Sternorrhyncha predators were greatest in the second year after planting. Numbers of Hemiptera: Aethalium reticulatum, Hymenoptera: Camponotus sp., Cephalotes sp., Polybia sp., T. angustula, T. spinipes, tending ants, pollinating insects, Sternorrhyncha predators and species richness of tending ants were highest on A. mangium saplings with greatest numbers of leaves or branches. The increase in the population of arthropods with ground cover by A. mangium saplings age increase indicates the positive impact by this plant on the recovery process of degraded areas.

Ecology and biology of the parasitoid Trechnites insidiosus and its potential for biological control of pear psyllids

Pear cultivation accounts for a large proportion of worldwide orchards, but its sustainability is controversial because it relies on intensive use of pesticides. It is therefore crucial and timely to find alternative methods to chemical control in pear orchards. The psyllids Cacopsylla pyri and Cacopsylla pyricola are the most important pests of pear trees in Europe and North America, respectively, because they infest all commercial varieties, causing damage directly through sap consumption or indirectly through the spread of diseases. A set of natural enemies exists, ranging from generalist predators to specialist parasitoids. Trechnites insidiosus (Crawford) is undoubtedly the most abundant specialist parasitoid of psyllids. In our literature review, we highlight the potential of this encyrtid species as a biological control agent of psyllid pests by first reviewing its biology and ecology, and then considering its potential at regulating psyllids. We show that the parasitoid can express fairly high parasitism rates in orchards, and almost perfectly matches the phenology of its host and is present early in the host infestation season, which is an advantage for controlling immature stages of psyllids. We propose new research directions and innovative approaches that would improve the use of T. insidiosus in integrated pest management strategies in the future, regarding both augmentative and conservation biocontrol. We conclude that T. insidiosus has many advantages and should be included as part of integrated biological control strategies of pear psyllids, along with predators, in-field habitat conservation, and the rational use of compatible chemicals. © 2021 Society of Chemical Industry.

Arthropod fauna on the abaxial and adaxial surfaces of Acacia mangium (Fabaceae) leaves

Acacia mangium (Willd., 1806) (Fabales: Fabaceae) is a fast growing, rustic, pioneer species, with potential to fix nitrogen, and for programs to recover degraded areas. The objective was to evaluate the distribution and the functional diversity of interactions and the K-dominance of arthropod groups on A. mangium saplings. The number of individuals of eleven species of phytophagous insects, three bee species, and fourteen natural enemy species were highest on the adaxial leaf surface of this plant. Abundance, diversity and species richness of phytophagous insects and natural enemies, and abundance and species richness of pollinators were highest on the adaxial A. mangium leaf surface. The distribution of five species of sap-sucking hemipterans and six of protocooperating ants (Hymenoptera), with positive interaction between these groups, and three bee species (Hymenoptera) were aggregated on leaves of A. mangium saplings. Aethalion reticulatum (L.) (Hemiptera: Aethalionidae) and Bemisia sp. (Hemiptera: Aleyrodidae); Brachymyrmex sp. and Camponotus sp. (Hymenoptera: Formicidae); and Trigona spinipes Fabricius (Hymenoptera: Apidae) were the most dominant phytophagous insects, natural enemies, and pollinators, respectively, on A. mangium leaves. Knowledge of preferred leaf surfaces could help integrated pest management programs.

Distribution pattern of arthropods on the leaf surfaces of Acacia auriculiformis saplings

Acacia auriculiformis A. Cunn. Ex Benth. (Fabaceae), a non-native pioneer species in Brazil with fast growth and rusticity, is used in restoration programs. Our goal was to assess during a 24-month survey the pattern of arthropods (phytophagous insects, bees, spiders, and predator insects) on the leaf surfaces of A. auriculiformis saplings. Fourteen species of phytophagous, two of bees and eleven of predators were most abundant on the adaxial surface. The values of the ecological indexes (abundance, diversity, and species richness) and the rarefaction, and k-dominance curves of phytophagous, bees and arthropod predators were highest on the adaxial leaf surface of A. auriculiformis. The k-dominance and abundance of Aleyrodidae (Hemiptera) (both leaf surfaces), the native stingless bee Tetragonisca angustula Latreille (Hymenoptera: Apidae) (both leaf surfaces) and the ant Brachymyrmex sp. (adaxial surface) and Pheidole sp. (Hymenoptera: Formicidae) (abaxial surface) were the highest between the taxonomic groups of phytophagous, bees, and predators, respectively on A. auriculiformis saplings. The ecological indexes and rarefaction, abundance, and k-dominance curves of phytophagous insects, bees, and predators were highest on the adaxial leaf surface. The preference of phytophagous insects for the adaxial leaf surface is probably due to the lower effort required to move on this surface. Understanding the arthropod preferences between leaf surfaces may help to develop sampling and pest management plans for the most abundant phytophagous insects on A. auriculiformis saplings. Also, knowledge on the preference pattern of bees and predators may be used to favour their conservation.

Assessment of the biocontrol potential of natural enemies against psyllid populations in a pear tree orchard during spring

BACKGROUND

Modern pest control management systems are based on the support of naturally occurring arthropod predators, as it has been shown that such predators offer an important ecosystem service. However, most naturally occurring arthropod predators are generalists (euryphagous). Their role in the biological control of specific pests has been recognized but remains poorly studied. Here, we focused on the naturally occurring arthropod predators of psyllids - the main insect pest of pear trees. We investigated the abundance of psyllids and all of their potential enemies in an abandoned pear orchard on a weekly basis from early spring to early summer. In addition, employing polymerase chain reaction diagnostics and specific primers, we investigated the predation rate on psyllids in all predators collected.

RESULTS

We found four predatory groups: spiders were the most abundant (60%, N = 756), followed by coccinellid beetles, anthocorid bugs and cantharid beetles. Anthocorids and spiders had the highest predation rates among the predatory groups. Among spiders, >50% of foliage-dwelling spiders (belonging to the genera Philodromus and Clubiona; N = 206) were positive for psyllids and showed a numerical response to the abundance of psyllids.

CONCLUSION

We conclude that foliage-dwelling spiders are, of the four groups, the most important natural enemies of psyllids on pear trees during spring in Central Europe, as they outnumber specialized Anthocoris bugs. © 2021 Society of Chemical Industry.

Structure of the Assemblages of Spiders in Mediterranean Pear Orchards and the Effect of Intensity of Spraying

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.