Reproductive efficiency of the bethylid wasp Cephalonomia tarsalis: the influences of spatial structure and host density

The parasitoid wasp Cephalonomia tarsalis (Ashmead) (Hymenoptera: Bethylidae) is commonly present in stored product facilities. While beneficial, it does not provide a high 24 degree of biological pest control against its host, the saw-toothed beetle Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae). A candidate explanation for poor host population suppression is that adult females interfere with each other’s foraging and reproductive behavior. We used simple laboratory microcosms to evaluate such mutual interference in terms of its overall effects on offspring production. We varied the density of the hosts and also the spatial structure of the environment, via the extent of population sub-division and the provision of different substrates. Production of C. tarsalis offspring was positively influenced by host density and by the isolation of females. With incomplete sub-division within microcosms offspring production was, in contrast, low and even zero. The provision of corrugated paper as a substrate enhanced offspring production and partially mitigated the effects of mutual interference. We recommend simple improvements to mass rearing practice and identify promising areas for further behavioral and chemical studies towards a better understanding of the mechanisms of mutual interference

Efficacy of entomopathogenic nematodes for control of large pine weevil, Hylobius abietis: effects of soil type, pest density and spatial distribution

The large pine weevil Hylobius abietis (L.), LPW, is a major pest of trees in replanted coniferous forests in northern Europe. The use of entomopathogenic nematodes (EPNs) applied against developing stages for population suppression is increasingly recognized as an effective alternative to plant protection using chemical pesticides. Here, we report results from a series of trials we conducted over 2 years using two species of EPN, Steinernema carpocapsae (Weiser) and Heterorhabitis downesi (Stock, Griffin, and Burnell) with different foraging strategies. Trials were conducted at lodgepole pine sites in Ireland on both mineral and peat soil type. EPN suspension was applied to the stumps of felled pine trees, and EPN efficacy was determined afterwards by directly assessing parasitism rates after debarking one quarter of the stumps and by collecting emerging adult weevils from traps erected over other treated and control stumps. Our results suggest that both species of EPN are equally effective in suppressing LPW populations to below the current, informal thresholds of economic damage. EPN were equally efficient in controlling LPW in peat and in mineral (lithosols/regosols and acid brown earth/brown podzolics) soils. Weevil density and distribution within pine stumps in peat versus mineral sites can explain patterns of LPW parasitism and suppression. Our results also suggest that infestation level (number of weevils per stump) can be an important factor in forecasting EPN application success as there is evidence of negative density-dependent parasitism when weevil densities were high. © 2016 Springer-Verlag Berlin Heidelber

Efficacy of entomopathogenic fungi against large pine weevil, Hylobius abietis, and their additive effects when combined with entomopathogenic nematodes

The large pine weevil Hylobius abietis is an important pest of reforestation in northern Europe. In field trials, we assessed the efficacy of entomopathogenic fungi (EPF) alone and in combination with entomopathogenic nematodes (EPN) against immature stages. We used commercial strains of Metarhizium brunneum and Beauveria bassiana and a strain of Beauveria caledonica isolated from the pest’s habitat. The EPN used were Steinernema carpocapsae and Heterorhabditis downesi. Efficacy was assessed by weevil infection in stumps and by numbers of adult weevils emerging in traps above the stumps. EPF infected up to 23% of pine weevils, at depths up to 25 cm below ground. Three EPF application methods were compared, but application method did not affect infection rates. When applied at half doses, EPF and EPN had additive effects: M. brunneum and S. carpocapsae caused a reduction in emergence of 58% relative to control, M. brunneum and H. downesi 93%, B. caledonica and H. downesi 86%. EPN alone offered good suppression of H. abietis populations and suppression by the mixture did not surpass suppression afforded by EPN alone. Our trials show B. caledonica is a promising species, rivalling the success of the other two species. Applied EPF, especially M. brunneum, can persist for at least 2 years in the forest setting. Additionally, different fungi can have differential action against weevils above versus below ground; therefore, EPF combinations may be beneficial. Based on our trials, further development of strains and application methods are required before EPF can be recommended for suppression of pine weevil. © 2018 Springer-Verlag GmbH Germany, part of Springer Natur

Sustenance and performance: nutritional reserves, longevity and contest outcomes of fed and starved adult parasitoid wasps

Dyadic contests for possession of resources occur across a wide range of animal taxa, with contest outcome often being heavily influenced by the energetic reserves of the competitors. The majority of studied parasitoid wasps lack de novo lipogenesis, with adult lipid reserves being limited to those acquired throughout larval development. Carbohydrate- and lipid-rich adult diets can increase adult parasitoid lifespan and fecundity by potentially acting as a maintenance energy store. However, the effects of such diets on fat reserve compositions and some aspects of parasitoid behaviour contest outcome dynamics have not been examined. This study assesses the effect of a carbohydrate rich diet (honey) on the longevity, metabolic state and contest performance of Goniozus legneri, a bethylid wasp. The longevity of honey-fed diet adults was typically more than twice that of starved wasps. Compared to similarly-aged starved wasps, honey feeding increased concentrations of common haemolymph sugars and amino acids in a 3-day old and 7-day old wasps, and higher concentrations of stored lipid in7-day old wasps. However, nutritional status did not affect the outcome of dyadic contests over host possession when both contestants were either 3 days or 7 days old. While contest dynamics outcome may be unaffected by diet, it remains possible that an enhancing effect of feeding on contest ability is matched by an effect of higher value being placed on winning by starved wasps

Mutually beneficial host exploitation and ultra-biased sex ratios in quasisocial parasitoids

Selfish interests usually preclude resource sharing, but under some conditions collective actions enhance per capita gains. Such Allee effects underlay early explanations of social evolution but current understanding focusses on kin selection (inclusive fitness). We find an Allee effect that explains unusual quasisociality (cooperative brood care) among parasitoid wasps without invoking or precluding kin selection effects. In Sclerodermus harmandi, individual females produce most offspring when exploiting small hosts alone. However, larger hosts are more successfully exploited by larger groups of females, with the per-female benefits outweighing the costs of host sharing. Further, the extremely biased sex ratios (97% female) are better explained by mutually beneficial female–female interactions that increase the reproductive value of daughters (local resource enhancement), rather than by the usually invoked local mate competition between males. Thus, atypical quasisocial behaviour in a parasitoid wasp directly enhances reproductive success and selects for very extremely female-biased sex ratios

Can the understory affect the Hymenoptera parasitoids in a Eucalyptus plantation?

The understory in forest plantations can increase richness and diversity of natural enemies due to greater plant species richness. The objective of this study was to test the hypothesis that the presence of the understory and climatic season in the region (wet or dry) can increase the richness and abundance of Hymenoptera parasitoids in Eucalyptus plantations, in the municipality of Belo Oriente, Minas Gerais State, Brazil. In each eucalyptus cultivation (five areas of cultivation) ten Malaise traps were installed, five with the understory and five without it. A total of 9,639 individuals from 30 families of the Hymenoptera parasitoids were collected, with Mymaridae, Scelionidae, Encyrtidae and Braconidae being the most collected ones with 4,934, 1,212, 619 and 612 individuals, respectively. The eucalyptus stands with and without the understory showed percentage of individuals 45.65% and 54.35% collected, respectively. The understory did not represent a positive effect on the overall abundance of the individuals Hymenoptera in the E. grandis stands, but rather exerted a positive effect on the specific families of the parasitoids of this order

Pseudococcidae and Monophlebidae

The families Pseudococcidae (mealybugs) and Monophlebidae include small scale insects (Coccoidea: Hemiptera) that suck out plant sap. The bodies of young instars and adult females are covered with a wax secretion, whereas adult males carry a pair of small wings. Feeding by these pests can cause premature leaf, flower, and fruit drop, reduce plant vigour and discolour tissues. In addition, they secrete honeydew upon which sooty-mould fungi grow, reducing photosynthesis and the market value of the product. Six species of Pseudococcidae, namely Planococcus citri (Risso), Pseudococcus cryptus Hempel, Ps. longispinus (Targioni Tozzetti), Ps. calceolariae (Maskell), Ps. viburni (Signoret) and Nipaecoccus viridis (Newstead) are economic pests of citrus in the Mediterranean area, along with Icerya purchasi Maskell, in the family Monophlebidae