The ecology of southern African wild silk moths (Gonometa species, Lepidoptera: Lasiocampidae): consequences for their sustainable use

The pupal cocoons of two southern African wild silkmoth species, Gonometa postica and G. rufobrunnea (Lepidoptera: Lasiocampidae), are composed of high quality silk and have potential as a commercially viable resource. However, limited ecological research has been done on these species, and their population dynamics is especially poorly known. A steady and predictable supply of cocoons is paramount to the economic sustainability of a wild silk industry. There is thus an urgent need for documenting and understanding the population dynamics of southern Africa’s Gonometa species. Here, the temporal and spatial variation of pupal (and thus cocoon) abundance, as well as associated natural enemies, are described for both Gonometa species for the first time. The larval parasitoid species emerging from parasitised pupae were quantitatively associated with species-specific emergence holes, making field-identification of these species possible. Eleven sites in total were sampled, over four generations, across the region where both species have historically reached high population densities. Apparent spatial synchrony in pupal abundance found between sites suggests that climate is responsible for observed population size fluctuations. As predicted from their life history traits, temporal variability was lower than expected for classically eruptive species. Gonometa species thus have an intermediate position on the population dynamics gradient. In turn, the responses of natural enemies were not predictable from Gonometa species defensive traits, but appear to be mediated by between-species cocoon strength differences. Using data on the number of G. postica pupae per tree and associated parasitism at several sites, the importance of the degree of spatial explicitness in the quantification of aggregation and the detection of density dependence was illustrated. The spatially explicit method gave different results and more information regarding the spatial pattern of pupal abundance and parasitism than non- and semi-explicit methods. Similarly, the detection of density dependence in parasitism rates was affected by the use of spatially explicit data, with the spatial explicit approach giving different and more biologically informative results than traditional, non-spatially explicit methods. This has marked implications for previous insect-host - parasitoid studies aimed at detecting density dependence. The variability in cocoon size, a surrogate for larval performance, adult fecundity and silk yield, revealed that gender, followed by species, contributed most to observed size differences, with no clear differences between generations or localities. Finally, the between-host plant and withinhost plant distribution ofG. postica and G. rufobrunnea pupae was quantified, chiefly investigating the deterministic nature of the choice of pupation site. The distribution of both species at these scales was found to be markedly non-random, with pupae generally preferring specific tree characteristics and micro-sites. These results now provide the basis for recommending an appropriate utilisation strategy for southern Africa’s wild silk moths. Based on the spatial and temporal variability in pupal abundance observed, a constant and predictable cocoon supply for natural harvesting is unlikely. Long-term, broad-scale documentation of Gonometa species population cycles may make it possible to predict cocoon availability in the future. Until such research is done, it is recommended that the current practise of only collecting cocoons from which moths have emerged be continued. Simultaneously, artificial rearing and seeding as alternative utilisation strategies should be experimentally explored based on the information gathered and patterns identified here.Thesis (DPhil (Entomology))--University of Pretoria, 2007.Zoology and Entomologyunrestricte

Using scale–area curves to quantify the distribution, abundance and range expansion potential of an invasive species

Aim: Invasive species distribution and abundance data are essential for management decisions on mitigating impacts but is seldom available. Here, we use scale–area curves to assess the distribution, abundance and consequent management implications of an invasive plant (Acacia longifolia) within selected occupancy grid cells, spread across regional ranges and representing the full national extent. We determine whether occupancy patterns are explained by climatic suitability or range structure and identify areas where A. longifolia can still be regarded as an important invasive based on contiguous occupancy. Location: South Africa including the Fynbos, Thicket, Savanna and Grassland biomes. Methods: The quarter degree occupancy of A. longifolia was used to select core, edge, and climatically unsuitable grid cells within different regions of the national range. Cells were surveyed across a linear resolution from 25 km to 2.5 m allowing the first multi-scales description of an invasive species’ space-filling properties. Patterns from grid cells in turn were viewed regionally to describe regional variation in spatial structure. Results: In regions with contiguous areas of favourable habitat, scale–area curves indicated greater occupancy in core than edge areas, whereas patterns were reversed when suitable areas were more fragmented. Also, at times climatically suitable areas were unoccupied, while unsuitable areas were occupied. Within cells, occupancy was well explained by the presence of fynbos vegetation types, while nationally, contiguous occupancy was almost exclusive to the Fynbos Biome. Main conclusions: Scale–area curves can advance the understanding of biological invasions and invasive plant distributions. Here, we detected potential areas of invasive concern, plus differences in abundance and distribution patterns, and associated correlates, at landscape and national scales. As there was no general relationship between range position or climatic suitability and A. longifolia’s spatial structure, we propose habitat suitability as an alternative explanation which, in turn, suggests limited range expansion potential.Centre of Excellence for Invasion Biolog

Incorporating biotic interactions in the distribution models of African wild silk moths (Gonometa species, Lasiocampidae) using different representations of modelled host tree distributions

Biotic interactions influence species niches and may thus shape distributions. Nevertheless, species distribution modelling has traditionally relied exclusively on environmental factors to predict species distributions, while biotic interactions have only seldom been incorporated into models. This study tested the ability of incorporating biotic interactions, in the form of host plant distributions, to increase model performance for two host‐dependent lepidopterans of economic interest, namely the African silk moth species, Gonometa postica and Gonometa rufobrunnea (Lasiocampidae). Both species are dependent on a small number of host tree species for the completion of their life cycle. We thus expected the host plant distribution to be an important predictor of Gonometa distributions. Model performance of a species distribution model trained only on abiotic predictors was compared to four species distribution models that additionally incorporated biotic interactions in the form of four different representations of host plant distributions as predictors. We found that incorporating the moth–host plant interactions improved G. rufobrunnea model performance for all representations of host plant distribution, while for G. postica model performance only improved for one representation of host plant distribution. The best performing representation of host plant distribution differed for the two Gonometa species. While these results suggest that incorporating biotic interactions into species distribution models can improve model performance, there is inconsistency in which representation of the host tree distribution best improves predictions. Therefore, the ability of biotic interactions to improve species distribution models may be context‐specific, even for species which have obligatory interactions with other organisms.The University of Pretoria (RDP funding to Michelle Greve), the South African National Research Foundation and the South African National Biodiversity Institute.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1442-99932018-12-01hj2018Plant Production and Soil Scienc

Creating patches of native flowers facilitates crop pollination in large agricultural fields : mango as a case study

1. As cropland increases, fields become progressively isolated from pollinators, leading to declines in pollinator-dependent crop productivity. With the rise in demand for pollinatordependent foods, such productivity losses may accelerate conversion of natural areas to cropland. Pollination–compensation measures involving managed pollinators or hand pollination are not always optimal or are too costly. Introducing areas of native vegetation within cropland has been proposed as a way to supplement crop pollinators, but this measure is perceived by farmers to carry costs outweighing benefits to agricultural production. Studies quantifying benefits of small patches of native flowers to crop pollination are therefore necessary to encourage such practices. 2. To ascertain whether provision of floral resources within farmlands can facilitate pollination, and hence, crop yields, small experimental patches of perennial native plants (native flower compensation areas, NFCAs) were created in nonproductive areas of large commercial fields of several cultivars of mango Mangifera indica. 3. Pesticide use and isolation from natural habitat were associated with declines in flying visitors and in mango production (kg of marketable fresh fruit), but presence of NFCAs ameliorated these declines, and NFCAs did not harbour any mango pests. In areas far from natural vegetation, orchards near NFCAs had significantly higher diversity and abundance of mango flying visitors, as well as mango production, than orchards far from NFCAs, although these measures were still lower than in orchards close to natural areas. 4. Neither the most abundant flower visitors to mango (ants) nor initial fruit set was significantly affected by distance, pesticides or NFCAs, suggesting that although fertilization is associated with factors unaffected by isolation from natural habitat and pesticide use (i.e. selfand ant-pollination), viable fruit set (and ultimately, production) requires cross-pollination, for which flying visitors are essential. 5. Synthesis and applications. Our results show that the presence of small patches of native flowers within large farms can increase pollinator-dependent crop production if combined with preservation of remaining fragments of natural habitat and judicious use of pesticides. Native flower compensation areas represent a profitable management measure for farmers, increasing cost-effectiveness of cropland while indirectly contributing to preservation of natural habitat.South African National Biodiversity Institute,The University of Pretoria and STEP (Status and Trends of European Pollinators, grant no244090).http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-2664hb2013ab201

Valuing Insect Pollination Services with Cost of Replacement

Value estimates of ecosystem goods and services are useful to justify the allocation of resources towards conservation, but inconclusive estimates risk unsustainable resource allocations. Here we present replacement costs as a more accurate value estimate of insect pollination as an ecosystem service, although this method could also be applied to other services. The importance of insect pollination to agriculture is unequivocal. However, whether this service is largely provided by wild pollinators (genuine ecosystem service) or managed pollinators (commercial service), and which of these requires immediate action amidst reports of pollinator decline, remains contested. If crop pollination is used to argue for biodiversity conservation, clear distinction should be made between values of managed- and wild pollination services. Current methods either under-estimate or over-estimate the pollination service value, and make use of criticised general insect and managed pollinator dependence factors. We apply the theoretical concept of ascribing a value to a service by calculating the cost to replace it, as a novel way of valuing wild and managed pollination services. Adjusted insect and managed pollinator dependence factors were used to estimate the cost of replacing insect- and managed pollination services for the Western Cape deciduous fruit industry of South Africa. Using pollen dusting and hand pollination as suitable replacements, we value pollination services significantly higher than current market prices for commercial pollination, although lower than traditional proportional estimates. The complexity associated with inclusive value estimation of pollination services required several defendable assumptions, but made estimates more inclusive than previous attempts. Consequently this study provides the basis for continued improvement in context specific pollination service value estimates

CropPol: a dynamic, open and global database on crop pollination

Seventy five percent of the world's food crops benefit from insect pollination. Hence, there has been increased interest in how global change drivers impact this critical ecosystem service. Because standardized data on crop pollination are rarely available, we are limited in our capacity to understand the variation in pollination benefits to crop yield, as well as to anticipate changes in this service, develop predictions, and inform management actions. Here, we present CropPol, a dynamic, open and global database on crop pollination. It contains measurements recorded from 202 crop studies, covering 3,394 field observations, 2,552 yield measurements (i.e. berry weight, number of fruits and kg per hectare, among others), and 47,752 insect records from 48 commercial crops distributed around the globe. CropPol comprises 32 of the 87 leading global crops and commodities that are pollinator dependent. Malus domestica is the most represented crop (32 studies), followed by Brassica napus (22 studies), Vaccinium corymbosum (13 studies), and Citrullus lanatus (12 studies). The most abundant pollinator guilds recorded are honey bees (34.22% counts), bumblebees (19.19%), flies other than Syrphidae and Bombyliidae (13.18%), other wild bees (13.13%), beetles (10.97%), Syrphidae (4.87%), and Bombyliidae (0.05%). Locations comprise 34 countries distributed among Europe (76 studies), Northern America (60), Latin America and the Caribbean (29), Asia (20), Oceania (10), and Africa (7). Sampling spans three decades and is concentrated on 2001-05 (21 studies), 2006-10 (40), 2011-15 (88), and 2016-20 (50). This is the most comprehensive open global data set on measurements of crop flower visitors, crop pollinators and pollination to date, and we encourage researchers to add more datasets to this database in the future. This data set is released for non-commercial use only. Credits should be given to this paper (i.e., proper citation), and the products generated with this database should be shared under the same license terms (CC BY-NC-SA). This article is protected by copyright. All rights reserved

Delivery of crop pollination services is an insufficient argument for wild pollinator conservation

There is compelling evidence that more diverse ecosystems deliver greater benefits to people, and these ecosystem services have become a key argument for biodiversity conservation. However, it is unclear how much biodiversity is needed to deliver ecosystem services in a cost-effective way. Here we show that, while the contribution of wild bees to crop production is significant, service delivery is restricted to a limited subset of all known bee species. Across crops, years and biogeographical regions, crop-visiting wild bee communities are dominated by a small number of common species, and threatened species are rarely observed on crops. Dominant crop pollinators persist under agricultural expansion and many are easily enhanced by simple conservation measures, suggesting that cost-effective management strategies to promote crop pollination should target a different set of species than management strategies to promote threatened bees. Conserving the biological diversity of bees therefore requires more than just ecosystem-service-based arguments

Itching for an Answer: Gall-Forming Biological Control Agent Contains an Itch Mite Species Found at Localities Known for Periodic ‘Bite Outbreaks’

Biological control is an attractive option for controlling invasive plant species that are difficult to manage otherwise. However, the release of a non-native species as a biological control agent carries risks. The most obvious risk relates to impacts on plant species other than the plant species targeted for control. There are, however, also other risks. We report on a potential unintended impact of Dasineura dielsi, a gall-forming biological control agent that was released against Acacia cyclops in South Africa in 2003. We confirmed that the galls formed by D. dielsi on A. cyclops harbor mites in the genus Pyemotes (P. cf. ventricosus) within their gall structures, which are parasites of various insect species, but are also known to cause dermatitis in humans. Sporadic biting incidences have been reported in at least two locations in South Africa. The implications are that manual clearing of A. cyclops may expose humans to itch mites and to risks of bites. Gall-forming insects and fungi are known to create niches for herbivores and other gall-associated fauna. Although every possible food web interaction cannot be predicted, enough evidence exists to require that agent screening to include non-target risks other than those pertaining to non-host plants. Testing only whether agents are compromised by interactions with non-target plant species is not sufficient during agent evaluation. If such associations are known from the native range and therefore can form in the introduced range, then any known risk to health and socio-economic activities should be disclosed. We argue for the general development of objective assessment of such risks compared with the benefits potentially accruing from successful biological control of the target plant