Risk assessment to interpret the physiological host range of Hydrellia egeriae, a biocontrol agent for Egeria densa

Egeria densa Planchon (Hydrocharitaceae) is a submerged macrophyte native to South America. It forms part of a new suite of invasive aquatic plants that has benefited from open nutrient-rich freshwater systems following the successful biological control of floating aquatic plants in South Africa. The specificity of the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was tested, using traditional laboratory host-specificity testing (i.e., no-choice and paired choice). Only one non-target species, Lagarosiphon major Deeming (Hydrocharitaceae) supported larval development during pair-choice tests. In order to avoid the rejection of a safe and potentially effective agent, continuation (i.e., multiple generations) tests were conducted to measure the ability of the non-target species to nutritionally support a population indefinitely. None of these species could sustain a viable agent population for more than three generations. Laboratory host-specificity tests are limited as they exempt certain insect-host behaviours. To enhance the interpretation of host-specificity results, a risk assessment was conducted using agent preference (i.e., choice tests) and performance (i.e., choice and continuation tests) results. The feeding and reproductive risk that H. egeriae poses to non-target species is below 2%. Based on these findings, permission for its release in South Africa has been obtained

Risk assessment to interpret the physiological host range of Hydrellia egeriae, a biocontrol agent for Egeria densa

Egeria densa Planchon (Hydrocharitaceae) is a submerged macrophyte native to South America. It forms part of a new suite of invasive aquatic plants that has benefited from open nutrient-rich freshwater systems following the successful biological control of floating aquatic plants in South Africa. The specificity of the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was tested, using traditional laboratory host-specificity testing (i.e., no-choice and paired choice). Only one non-target species, Lagarosiphon major Deeming (Hydrocharitaceae) supported larval development during pair-choice tests. In order to avoid the rejection of a safe and potentially effective agent, continuation (i.e., multiple generations) tests were conducted to measure the ability of the non-target species to nutritionally support a population indefinitely. None of these species could sustain a viable agent population for more than three generations. Laboratory host-specificity tests are limited as they exempt certain insect-host behaviours. To enhance the interpretation of host-specificity results, a risk assessment was conducted using agent preference (i.e., choice tests) and performance (i.e., choice and continuation tests) results. The feeding and reproductive risk that H. egeriae poses to non-target species is below 2%. Based on these findings, permission for its release in South Africa has been obtained

Population genetics of invasive and native Nymphaea mexicana Zuccarini: Taking the first steps to initiate a biological control programme in South Africa

Nymphaea mexicana Zuccarini (Nympheaceae) (Mexican waterlily) is a rooted floating-leaved aquatic plant native to southern USA and Mexico that has become a problematic invasive alien plant in South Africa. Biological control is considered a desirable management strategy for the plant in South Africa. A good understanding of the genetic structure of invasive populations has been useful in other biological control programmes because taxonomic uncertainty about the target plant can result in natural enemies that are not adapted to the invasive populations being considered as potential agents. For N. mexicana, hybrids exist in the wild and horticultural trade, but identification is difficult, so understanding the genetic structure of populations is required to ensure that potential agents are collected off plants similar to invasive populations in South Africa. ISSR (inter-simple sequence repeats) analysis was used to determine whether invasive N. mexicana populations from South Africa were genetically similar to native range populations from USA or whether they were hybrids. Results from these analyses were matched with the morphotypes of each population based on petal colour, shape, and size. The genotypes suggested by the ISSR analyses corroborated the presence of both hybrid and pure forms of N. mexicana in South Africa. Populations of N. mexicana in the invaded range that are genetically similar to native range populations are more likely to be suitable for biological control, while other populations are likely to be hybrids formed by crossing of parents from the native range or within the horticultural trade, which may present difficulties for management using biocontrol

Objective and subjective components of resource value in lethal fights between male entomopathogenic nematodes

Males sometimes engage in fights over contested resources such as access to mates; in this case, fighting behaviour may be adjusted based on the value they place on the females. Resource value (RV) can have two components. First, males can assess the quality of females, which constitutes an objective assessment of RV. Second, internal state such as previous mating experience can also influence motivation to fight thus constituting a subjective assessment of RV. If mating opportunities are scarce and available females have a major impact on the lifetime reproductive success of males, then fighting can be fatal; in this situation it is uncertain whether males would adjust fighting behaviour based on RV. We found that both female quality, that is, virginity (objective component of RV) and male mating status (subjective component of RV) influenced fighting intensity between males of the entomopathogenic nematode Steinernema longicaudum which engage in lethal fights. Male nematodes were more likely to engage in fighting and fought longer and more frequently in the presence of virgin (high-quality) females than in the presence of mated (lower-quality) females. Male mating status was also found to influence fighting behaviour: mated males were the winners in staged fights between mated and virgin males. Mated males may have superior fighting ability (greater resource-holding potential), but RV asymmetries between mated and virgin males cannot be excluded. Males were more likely to win when they were resident, but we did not find a significant interaction effect between male mating and residency status

Risk assessment of the host range of Hydrellia lagarosiphon for the biological control of Lagarosiphon major in Ireland

Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae) is a submerged freshwater plant native to South Africa, and a destructive invader of waterways across Europe, Australasia and the USA. Native range exploration identified a leaf mining ephydrid fly, Hydrellia lagarosiphon, as a promising biological control candidate agent. Host specificity was conducted on H. lagarosiphon, using laboratory no-choice and paired choice tests. A number of non-target native Potamogeton species sustained feeding damage under no-choice and paired choice testing. To prevent rejection of a potentially safe agent, multi-generational population persistence trials were conducted on select native Potamogetonaceae. The non-target species could not sustain a viable H. lagarosiphon population beyond two generations. A risk assessment, incorporating the preference and relative survival, indicated that three non-target species presented extremely low (< 1.3 %) risk of sustaining damage relative to that of L. major. Potamogeton polygonifolius and P. x lanceolatus present a reproductive risk of 5.61% and 11.5% respectively but could not support a viable population beyond the 2nd generation. These results, coupled with damage efficacy and predicted colonisation, demonstrate the potential H. lagarosiphon has as a biological control agent for L. major in Ireland.Irish Research CouncilThe Central Fisheries Board (CFB) CAISIE Project EU Life+ ProgrammeTo check citing and date details in 6 m, amend embargo accordingly (12 m) and also to change publishers set text date accordingly, pleas

Improving culturing techniques with revised diets

Preservation of an insect culture under laboratory conditions is essential for its study. Numerous diets have been developed for entomophagous insects undergoing screening as biological control agents in attempts to improve the nutritional quality of food provided in laboratory settings. However, less emphasis has been given to developing a more effective laboratory diet for phytophagous insects with life stages not dependant on the target species. The larvae of Hydrellia lagarosiphon Deeming (Diptera: Ephydridae) mine the leaves of Lagarosiphon major (Ridl.) Moss ex Wager (Hydrocharitaceae). This species is currently under consideration as a biological control agent of this aquatic invasive. Rearing techniques for the adult stage of other Hydrellia species have been developed but current diets are not ideal as they result in relatively low reproduction rates. We compared alternative nutritional regimes and quantified their impact on life history attributes of H. lagarosiphon. The diets included the previously-developed yeast-sugar diet, a newly-developed insect-derived diet and a diet that combined the two. Total fecundity was significantly higher for females on an insect-derived diet compared with the traditional carbohydrate diet and the net reproductive rate (Ro) was also higher. Population doubling time (Td) was lower, decreasing by 30% compared to the traditional laboratory diet developed for Hydrellia species. Adult females fed the combination diet, including both insect and non-insect foods, laid 30% fewer eggs than those reared on an insect diet alone. Consequently, insect derived nutritional regimes could improve culturing techniques significantly and if permission to release the agent is granted, this diet may benefit mass rearing efforts potentially saving time and reducing associated costs.Irish Research CouncilCAISIE Project EU Life+ Programm

Molecular characterization of Hydrellia lagarosiphon, a leaf mining biological control agent for Lagarosiphon major, reveals weak variance across large geographic areas in South Africa

First paragraph: Native range exploration to identify new biological control agents is technically difficult and time-consuming, yet it is the foundation on which all other elements of a successful biological research programme ultimately depend (Goolsby et al., 2006). During field surveys agents demonstrating a high degree of host specificity and damage efficacy are prioritized. However, due to logistical and technical constraints potentially favourable natural enemies are usually only collected from one or a small number of source populations. Selecting the natural enemy population for host range testing and eventual release is important, as it has become increasingly evident that insect species occurring across a wide geographical range are generally structured into genetically differentiated populations (Madeira et al., 2001, Rauth et al., 2011). Highlighting these biogeographical population level differences can help anticipate potential variation in an agent’s climatic adaptations or host-related traits (Paterson et al., 2016), and this information can in turn guide the selection of a more effective and safe agent

Increasing ecological heterogeneity can constrain biopesticide resistance evolution

Microbial biopesticides containing living parasites are valuable emerging crop protection technologies against insect pests, but they are vulnerable to resistance evolution. Fortunately, the fitness of alleles that provide resistance, including to parasites used in biopesticides, frequently depends on parasite identity and environmental conditions. This context-specificity suggests a sustainable approach to biopesticide resistance management through landscape diversification. To mitigate resistance risks, we advocate increasing the range of biopesticides available to farmers, whilst simultaneously encouraging other aspects of landscape-wide crop heterogeneity that can generate variable selection on resistance alleles. This approach requires agricultural stakeholders to prioritize diversity as well as efficiency, both within agricultural landscapes and the biocontrol marketplace.Output Type: Opinion Output Status: Forthcoming/Available Onlin

Increasing ecological heterogeneity can constrain biopesticide resistance evolution

Microbial biopesticides containing living parasites are valuable emerging crop protection technologies against insect pests, but they are vulnerable to resistance evolution. Fortunately, the fitness of alleles that provide resistance, including to parasites used in biopesticides, frequently depends on parasite identity and environmental conditions. This context-specificity suggests a sustainable approach to biopesticide resistance management through landscape diversification. To mitigate resistance risks, we advocate increasing the range of biopesticides available to farmers, whilst simultaneously encouraging other aspects of landscape-wide crop heterogeneity that can generate variable selection on resistance alleles. This approach requires agricultural stakeholders to prioritize diversity as well as efficiency, both within agricultural landscapes and the biocontrol marketplace

Population genetics of invasive and native Nymphaea mexicana Zuccarini: Taking the first steps to initiate a biological control programme in South Africa

Nymphaea mexicana Zuccarini (Nympheaceae) (Mexican waterlily) is a rooted floating-leaved aquatic plant native to southern USA and Mexico that has become a problematic invasive alien plant in South Africa. Biological control is considered a desirable management strategy for the plant in South Africa. A good understanding of the genetic structure of invasive populations has been useful in other biological control programmes because taxonomic uncertainty about the target plant can result in natural enemies that are not adapted to the invasive populations being considered as potential agents. For N. mexicana, hybrids exist in the wild and horticultural trade, but identification is difficult, so understanding the genetic structure of populations is required to ensure that potential agents are collected off plants similar to invasive populations in South Africa. ISSR (inter-simple sequence repeats) analysis was used to determine whether invasive N. mexicana populations from South Africa were genetically similar to native range populations from USA or whether they were hybrids. Results from these analyses were matched with the morphotypes of each population based on petal colour, shape, and size. The genotypes suggested by the ISSR analyses corroborated the presence of both hybrid and pure forms of N. mexicana in South Africa. Populations of N. mexicana in the invaded range that are genetically similar to native range populations are more likely to be suitable for biological control, while other populations are likely to be hybrids formed by crossing of parents from the native range or within the horticultural trade, which may present difficulties for management using biocontrol