Contrasting predation services of predator and omnivore diversity mediated by invasive ants in a tropical agroecosystem

Invasive natural enemies are known to either strengthen or weaken the suppression of herbivorous arthropods. However, the impact of invasive species on the predation service provided by natural enemy diversity remains largely unexplored. Here, we tease apart the roles of invasive ants as providers of a predation service and a potential disservice, i.e. reducing the diversity of natural enemies. In mango orchards on Reunion Island, we evaluated the predation service in 20 open fields by simultaneously monitoring the predation on bait eggs and arthropod communities in two strata: the ground surface and the mango tree canopy. Our results show that the predation on bait eggs was limited to the ground surface. This stratum is dominated by three invasive omnivorous ants: Pheidole megacephala and Solenopsis geminata strongly increased the predation rate of bait eggs, whereas Brachymyrmex cordemoyi was responsible for only a small decrease in predation rate. Predation rate was positively related to predator species richness, and was negatively related to omnivore species richness. The negative relationship between the predation rate and omnivore species richness is caused by the most dominant invasive ant, P. megacephala, which reduces omnivore richness and seems to strongly prey on eggs. This study demonstrates, for the first time, the distinct influence of the diversity of two trophic groups on the predation service and how these effects can be mediated by invasive ant species. (Résumé d'auteur

Inter-And Intraspecific Interactions in Two Mealybug Predators Spalgis epius and Cryptolaemus montrouzieri in the Presence and Absence of Prey

Spalgis epius and Cryptolaemus montrouzieri are the two potential predators of different species of mealybugs. However, the mode of their interactions is not known to use these predators together in the field. Hence, we investigated on the possible interactions i.e., cannibalism, intraguild predation (IGP) and competition between the predators in the presence and absence of prey Planococcus citri. In the presence of prey, no cannibalism and predation were observed in both S. epius and C. montrouzieri larvae. A pair of S. epius larvae consumed significantly more number of mealybugs than one S. epius/C. montrouzieri larva or a pair of C. montrouzieri larvae. The predation of S. epius larva by C. montrouzieri larva was significantly more than the predation of C. montrouzieri by S. epius. Conspecific and interspecific egg predation was absent both in S. epius and C. montrouzieri. Cannibalism in C. montrouzieri was more than that in S. epius. The study indicated that C. montrouzieri larvae can be used as an additive along with voracious S. epius larvae under abundant prey population. IGP was asymmetric between the two predators in the absence of prey. Both S. epius and C. montrouzieri larvae can maintain a stable coexistence when prey is abundantly available, however, in the complete absence of prey C. montrouzieri may dominate the guild. This study provides an insight into the possible complex inter- and intraspecific predatory phenomena in the field to use these two predators in the biological control of mealybug

Functionnal biodiversity in mango orchards on Reunion. Ecosystemic and landscape effects on epigeous predatory arthropods.

The knowledge of factors implicated in agroecosystem diversity is necessary to better evaluate their role. The study aims to link within-field plant diversity, cultural practices, and landscape context with terrestrial predatory arthropods in mango orchards on Reunion. Twenty-four plots distributed within the mango production area have been studied. Arthropods were sampled with pitfall traps. The land plots were grouped into three groups of agricultural practice intensity. The landscape was mapped within a circle of 400 meters around the orchards, which permitted to distinguish three different landscape contexts. Based on 83181 arthropods collected, 65124 were determined as predators, their communities were mainly composed of ants (Hymenoptera: Formicinae) and spiders (Araneae). The species richness and their equitability were influenced by factors at three different scales: (1) the within-field plant diversity improved evenness of predatory arthropods communities; (2) the moderate farming practices, as organic farming practices, had higher species richness than those obtained with “conventionnal” practices; (3) a landscape context with relevant heterogeneity and fragmentation increased the species richness of epigeal predatory arthropods in mango orchards

Natural history of four species of Platydracus Thomson (Coleoptera: Staphylinidae) in Heliconia bourgaeana Petersen (Zingiberales: Heliconiaceae) flower bracts

The insect fauna within inflorescences of Heliconia bourgaeana Petersen (Zingiberales: Heliconiaceae) was evaluated in Parque Metlac, Fortín de las Flores, Veracruz, Mexico between May and October 1995. Floral bracts were present in May and some persisted to October, despite much destruction in August by a grackle, Quiscalus mexicanus (JF Gmelin) (Icteridae). Flowers were abundant in the bracts in May-June, after which their number declined as fruits matured. Insects that fed on the flowers were most abundant in May-June; several of them could be pollinators; the immature stages of most of these insects were absent from Heliconia Linnaeus. The floral bracts contained water enriched by decomposition of the flowers, and this provided nutrition for aquatic organisms. Syrphid larvae (Diptera) contributed the largest biomass among the aquatic insects, and their distribution among bracts was more uniform in time than that of other aquatic insects. Larvae of Culicidae and Psychodidae (Diptera) were more variable in density and were more abundant after decomposition of the flowers. The most abundant aquatic predators of culicid larvae were larvae of Toxorhynchites Theobald (Culicidae). The most abundant amphibious predators of dipterous larvae were adults of four species of Platydracus Thomson (Staphylinidae), one of them yet undescribed. To capture its prey, the Platydracus adult would immerse its head and thorax, with open mandibles, to snap at passing dipterous larvae.La fauna insectil asociada con las inflorescencias de Heliconia bourgaeana Petersen (Zingiberales: Heliconiaceae) fue evaluada en el Parque Metlac, Fortín de las Flores, Ver., México entre mayo y octubre de 1995. Las brácteas florales estuvieron presentes en mayo y persistieron hasta octubre, aunque con mucha destrucción a partir de agosto debido a la acción del zanate mexicano (Quiscalus mexicanus (JF Gmelin), Icteridae). Las flores en las brácteas fueron abundantes en mayo y junio, después de lo cual su número se redujo conforme aumento el tamaño de los frutos, los cuales maduraron en octubre. Los insectos adultos que se alimentaron en las flores fueron más abundantes en mayo y julio; varios de ellos podrían actuar como polinizadores. Los estados inmaduros de la mayoría de estos insectos no fueron encontrados en Heliconia Linnaeus. Las brácteas florales contuvieron agua enriquecida por la descomposición de las flores, lo cual provey de nutrimentos para algunos de los organismos acuáticos. Las larvas de la familia Syrphidae (Diptera) constituyeron la mayor biomasa de las larvas de insectos y su distribución fue notablemente uniforme entre las brácteas en cada espiga floral y a lo largo del periodo de observación. Las larvas de las familias Culicidae y Psychodidae (Diptera) fueron más variables en su densidad, y más abundantes después de la descomposición de las flores. Los depredadores acuáticos de las larvas de Culicidae más abundantes fueron larvas de Toxorhynchites Theobald (Culicidae). Los depredadores anfibios más abundantes de las larvas de dípteros fueron cuatro especies de Platydracus Thomson (Staphylinidae), una de ellas aun no descrita. Para capturar su presa, un estafilínido sumerge su cabeza y su tórax, con mandíbulas abiertas, en el agua e intenta capturar las larvas de dípteros

Spatial relationships between dominant ants and the cocoa mirid Sahlbergella singularis in traditional cocoa-based agroforestry systems

Manipulating ant communities to control pests of cocoa has proven to be a promising strategy, especially in Asia. However, concerning African cocoa mirids, the main pests of cocoa in Africa, basic knowledge on mirid-ant relationships is still incomplete. Our study aimed to characterize the spatial relationships between dominant ant species and the mirid Sahlbergella singularis (Hemiptera: Miridae) in traditional cocoa-based agroforestry systems of Cameroon. Over two consecutive years, mirid and ant populations were assessed by a chemical knock-down sampling method in four plots of 100 cocoa trees, located in three different agroecological zones in the Centre region of Cameroon. Mapping procedures were used to display spatial distribution of mirid and ant populations. Also, we adapted spatial statistics methodologies of point pattern analysis to consider the regular tree position effects on insect positions. These techniques allow testing the statistical significance of Poisson null models, leading to the classification of the spatial patterns of insects into association vs. segregation. Our results clearly demonstrated spatial segregation between mirid and the dominant weaver ant Oecophylla longinoda, known as a key-predator in natural ecosystems. Weaver ant trumps, especially its dominant status in ant communities of cocoa ecosystems and its ecological preferences for open habitats, make it a promising candidate for conservation biocontrol against cocoa mirids in Africa. (Résumé d'auteur

Prey consumption by the mealybug predator Spalgis epius on pink hibiscus mealybug (Maconellicoccus hirsutus)

The pink hibiscus mealybug Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is a major pest of economically important crops. The apefly Spalgis epius (Westwood) (Lepidoptera: Lycaenidae) is a potential predator of various species of mealybugs. Studies of its preying potential and preference for prey stages on M. hirsutus are incomplete. An investigation was undertaken to determine the daily prey consumption and preference for prey stages by different larval instars of S. epius reared on M. hirsutus in the laboratory. During the 8-day larval development period with four larval instars of S. epius, the daily prey consumption increased from the first to the seventh day and decreased on the eighth day prior to the prepupal stage. Generally, there was a significant difference in the prey consumption on different days. The 1st to 4th instar larvae of S. epius consumed, respectively, a mean of 181.3, 679.1, 1770.4 and 4333.0 eggs or 19.1, 67.7, 153.0 and 639.0 nymphs or 2.72, 6.26, 13.8 and 32.1 adults of M. hirsutus. When an S. epius larva was fed on M. hirsutus eggs, nymphs and adults separately, it consumed a mean of 6952.6 eggs, 878.8 nymphs or 53.9 adults during its entire development. A single larva of S. epius consumed 2358.3 eggs, 151.2 nymphs and 34.3 adults of M. hirsutus during its entire development when the prey stages were offered all together. The study revealed that S. epius is a voracious predator of M. hirsutus and thus could be utilized as a potential biological control agent

Inter-And Intraspecific Interactions in Two Mealybug Predators Spalgis epius and Cryptolaemus montrouzieri in the Presence and Absence of Prey

Spalgis epius and Cryptolaemus montrouzieri are the two potential predators of different species of mealybugs. However, the mode of their interactions is not known to use these predators together in the field. Hence, we investigated on the possible interactions i.e., cannibalism, intraguild predation (IGP) and competition between the predators in the presence and absence of prey Planococcus citri. In the presence of prey, no cannibalism and predation were observed in both S. epius and C. montrouzieri larvae. A pair of S. epius larvae consumed significantly more number of mealybugs than one S. epius/C. montrouzieri larva or a pair of C. montrouzieri larvae. The predation of S. epius larva by C. montrouzieri larva was significantly more than the predation of C. montrouzieri by S. epius. Conspecific and interspecific egg predation was absent both in S. epius and C. montrouzieri. Cannibalism in C. montrouzieri was more than that in S. epius. The study indicated that C. montrouzieri larvae can be used as an additive along with voracious S. epius larvae under abundant prey population. IGP was asymmetric between the two predators intheabsence of prey. Both S. epius and C. montrouzieri larvae can maintain a stable coexistence when prey is abundantly available, however, in the complete absence of prey C. montrouzieri may dominate the guild. This study provides an insight into the possible complex inter- and intraspecific predatory phenomena in the field to use these two predators in the biological control of mealybugs

Mass rearing of Spalgis epius (Lepidoptera: Lycaenidae), a potential predator of mealybugs (Hemiptera: Pseudococcidae)

Spalgis epius (Lepidoptera: Lycaenidae) has been recorded as a potential predator of various species of mealybug crop pests worldwide. We describe the mass rearing of S. epius, as no information on this topic is available. Outdoor nylon tent cages of different dimensions were provided to achieve mating and oviposition as S. epius adults did not mate in the laboratory cages. Adults mated only in the tent cage (6 x 6 x 10 m) placed over a native tree (9 m height). The presence of a tree canopy inside the cage is essential to achieve courtship and mating. Gravid females of S. epius deposited eggs on the mealybug-infested pumpkins inside the different sized nylon cages with or without a bush/tree. Spalgis epius eggs were maintained on mealybug-infested pumpkins in the laboratory and developmental stages of the predator were reared. Adults fed on various diets laid significantly higher number of eggs than those of starved individuals. Spalgis epius with a life cycle completed in 21.2 days and 55.7 larvae, could be reared on a single mealybug-infested pumpkin

La biodiversité fonctionnelle dans les vergers de manguiers à La Réunion. Effets de facteurs écosystémiques et paysagers sur les arthropodes prédateurs terrestres épigés

Connaître les facteurs régissant la biodiversité des agroécosystèmes est nécessaire pour mieux évaluer ses services potentiels. L'étude vise à mettre en relation la diversité végétale intra-parcellaire, le mode de pratiques culturales et le contexte paysager, avec la diversité des arthropodes prédateurs terrestres en vergers de manguiers à La Réunion. Vingt-quatre parcelles ont été étudiées, réparties dans les bassins de production de mangues. Les arthropodes ont été échantillonnés au moyen de pièges à fosse. Les parcelles ont été regroupées en trois régimes d'intensité de pratiques. Le paysage a été cartographié dans un cercle de 400 m de rayon autour de chaque parcelle et trois contextes paysagers ont été distingués. À partir de 83181 individus récoltés, 65124 ont été identifiés comme prédateurs, leurs communautés sont principalement constituées d'espèces de fourmis (Hymenoptera : Formicinae) et d'araignées (Araneae). Leur diversité est influencée par des facteurs à trois échelles différentes : (1) la richesse spécifique végétale intra-parcellaire favorise l'équitabilité des communautés de prédateurs ; (2) les pratiques agricoles les plus modérées, dont celles de l'Agriculture Biologique, présentent une richesse spécifique plus élevée que les pratiques " conventionnelles " ; (3) un contexte paysager hétérogène et fragmenté assure une richesse spécifique élevée des arthropodes prédateurs épigés dans les vergers de manguiers. (Résumé d'auteur