In the current paper, we used a method based on stink bug egg-protein immobilization on filter paper by drying, followed by post-(storage and shipping) extraction in acidified acetonitrile containing matrix, to discriminate between nine different species using MALDI-TOF MS. We obtained 87 correct species-identifications in 87 blind tests using this method. With further processing of the unblinded data, the highest average Bruker score for each tested species was that of the cognate reference species, and the observed differences in average Bruker scores were generally large and the errors small except for Capocoris fuscispinus, Dolycoris baccarum, and Graphosoma italicum, where the average scores were lower and the errors higher relative to the remaining comparisons. While we observed clear discrimination between the nine species using this method, Halyomorpha halys and Piezodorus lituratus were more spectrally related than the other pairwise comparisons.
Abstract Nearly 65 years ago, D.G. Harcourt developed the first of 74 life tables of the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae), on the Central Experimental Farm in Ottawa, Ontario, Canada and at nearby sites. This work is cited whenever authors discuss the life history of the diamondback moth and its parasitoids in Canada. Since Harcourt’s study, climate change, urbanisation, and crop diversity may have altered the population dynamics of both the diamondback moth and its natural enemy community in the original study area. To follow up on Harcourt’s work, we used two approaches to build life tables to describe mortality factors in the field and the natural enemies attacking diamondback moth in Ottawa: destructive sampling of mature cabbage, Brassica oleracea Linnaeus (Brassicaceae), plants similar to Harcourt’s approach and a modern sentinel-based approach with an enemy exclusion cage treatment. After 65 years, the primary parasitoids attacking diamondback moth remained the same, although more parasitoid diversity was revealed by the destructive sampling technique. Total mortality and parasitism levels also remained similar. In one notable difference, we attributed more diamondback mortality to predation. Overall, however, diamondback moth population dynamics have changed little in Ottawa in the decades since Harcourt’s studies.
Predicting how much of a host or prey population may be attacked by their natural enemies is fundamental to several subfields of applied ecology, particularly biological control of pest organisms. Hosts or prey can occupy refuges that prevent them from being killed by natural enemies, but habitat or ecological refuges are challenging or impossible to predict in a laboratory setting-which is often where efficacy and specificity testing of candidate biological control agents is done. Here we explore how intraspecific variation in continuous traits of individuals or groups that confer some protection from natural enemy attack-even after the natural enemy has encountered the prey-could provide partial refuges. The size of these trait-based refuges (i.e., the proportion of prey that survive natural enemy encounters due to protective traits) should depend on the relationship between trait values and host/prey susceptibility to natural enemy attack and on how common different trait values are within a host/prey population. These can be readily estimated in laboratory testing of natural enemy impact on target or nontarget prey or hosts as long as sufficient host material is available. We provide a general framework for how intraspecific variation in protective host traits could be integrated into biological control research, specifically with reference to nontarget testing as part of classical biological control programs. As a case study, we exposed different host clutch sizes of target (pest) and nontarget (native species) stink bug (Hemiptera: Pentatomidae) species to a well-studied exotic biocontrol agent, the egg parasitoid Trissolcus japonicus (Hymenoptera: Scelionidae). We predicted that the smallest and largest clutches would occupy trait-based refuges from parasitism. Although we observed several behavioral and reproductive responses to variation in host egg mass size by T. japonicus, they did not translate to increases in host survival large enough to change the conclusions of nontarget testing. We encourage researchers to investigate intraspecific variation in a wider variety of protective host and prey traits and their consequences for refuge size.
Abstract Unintentional introduction of natural enemies has increased in recent years due to a massive rise in global trade and tourism. One such natural enemy is the Asian egg parasitoid Trissolcus japonicus , a promising agent for classical biological control of Halyomorpha halys. In Europe, adventive T. japonicus populations have been detected in Switzerland, Italy and Germany. Host specificity testing demonstrated that its fundamental host range is fairly broad; however, it is unclear whether spatial or temporal refuges reduce parasitism of non-target species in the field. To address this, the realized host range of T. japonicus was assessed over three years by exposing sentinel egg masses of H. halys and 18 non-target species and collecting naturally laid egg masses in Switzerland and Italy. In total, 15 of 18 non-target species were successfully parasitized by T. japonicus in the field, confirming its broad fundamental host range. However, most non-target species were less parasitized by T. japonicus than H. halys , profiting from either partial temporal or spatial refuges from parasitism. Species with an unusual life cycle and the same ecological niche as H. halys , such as Pentatoma rufipes , which was the most parasitized non-target species in both countries, potentially face an increased risk of parasitism. In contrast, beneficial non-target effects may occur for the invasive pest, Nezara viridula , which suffered high non-reproductive mortality induced by T. japonicus . In both cases, life table studies will be needed to determine the impact of non-target parasitism and the potential consequences at the population level.
When searching for promising biological control agents, generations of researchers have tried to find a sure way of predicting beforehand which biological control agents will lead to economic pest suppression and which will fail. Although many approaches have been proposed for characterizinggoodbiological control agents, most of these have only resulted in general guidelines with limited predictive value. To facilitate the evaluation of the potential of biological control agents prior to release, a variety of desirable attributes have been suggested. Among others these include, a high level of host specificity, a good searching capacity, a shorter generation time, a positive response to increasing host densities, a good temporal synchronisation of host and agent, and a good dispersal ability. However, the variable outcome of past biological control projects urges the need for reviewing the predictive value of these attributes. Particularly reviewing biological control agents that have been proven to be successful in the past can help to identify those general characteristics that lead to economic pest suppression. An example for a successful new association biological control agent is the European Peristenus digoneutis, which has significantly reduced native Lygus lineolaris populations after its establishment in the eastern United States in the 1980s. In the present study we review current knowledge on P. digoneutis and try to relate certain biological attributes accountable for the success or failure of release programmes in the past. Peristenus digoneutis as a case study in the review of desirable attributes of biological control agents suggests that a broad understanding of the ecology and interactions of a biological control agent and its target pests in the area of origin is the key factor for a reliable evaluation of the potential success of a biological control project.
Trissolcus japonicus (Ashmead) (Hymenoptera: Scelionidae) and Anastatus japonicus Ashmead (Hymenoptera: Eupelmidae) are the most important egg parasitoids of Halyomorpha halys Stål (Hemiptera: Pentatomidae) in northern China. In this study, we assessed the fitness of these two parasitoid species at different temperatures. We examined the intrinsic competition of these parasitoids inside host eggs by providing each parasitoid species with H. halys egg masses previously parasitized by the other species, at different time intervals between attacks. We also investigated their intraguild competition for H. halys eggs by releasing a single species (one female T. japonicus or five female A. japonicus per cage) or both parasitoid species (one female T. japonicus and five female A. japonicus per cage) simultaneously in exclusion cages stocked with three host egg masses per cage in a kiwifruit orchard. Our results showed that the developmental time from eggs to adults of both parasitoids decreased with increased temperatures, between 15 °C and 30 °C, and T. japonicus developed much faster than A. japonicus during the immature stages in host eggs. Both T. japonicus and A. japonicus were able to parasitize a host already parasitized by the other parasitoid, and sex ratios of their offspring from multi-parasitized hosts were male-biased for both parasitoids. Inside host eggs, T. japonicus outcompeted A. japonicus when the time lags between the first and second attacks were less than or equal to 1 day, regardless of the order of attack by the two parasitoids, whereas A. japonicus began to dominate when the time lag was 2 to 5 d. The host location, exploitation and impact indexes of the two parasitoids were influenced by their exploitation modes and/or releases in the exclusion cage tests in the field. However, regardless of single or simultaneous release, the parasitism rates of the two parasitoids were not so much affected. We concluded that the combined release of T. japonicus and A. japonicus at the given parasitoid densities did not show any advantage compared to the single release of either species. The two parasitoids employed different reproductive strategies contributing to the outcome of their interspecific competition, which should be considered in any future biological control program for the sustainable management of H. halys.
ABSTRACT Biological control is widely successful at controlling pests, but effective biocontrol agents are now more difficult to import from countries of origin due to more restrictive international trade laws (the Nagoya Protocol). Coupled with increasing demand, the efficacy of existing and new biocontrol agents needs to be improved with genetic and genomic approaches. Although they have been underutilised in the past, application of genetic and genomic techniques is becoming more feasible from both technological and economic perspectives. We review current methods and provide a framework for using them. First, it is necessary to identify which biocontrol trait to select and in what direction. Next, the genes or markers linked to these traits need be determined, including how to implement this information into a selective breeding program. Choosing a trait can be assisted by modelling to account for the proper agro‐ecological context, and by knowing which traits have sufficiently high heritability values. We provide guidelines for designing genomic strategies in biocontrol programs, which depend on the organism, budget, and desired objective. Genomic approaches start with genome sequencing and assembly. We provide a guide for deciding the most successful sequencing strategy for biocontrol agents. Gene discovery involves quantitative trait loci analyses, transcriptomic and proteomic studies, and gene editing. Improving biocontrol practices includes marker‐assisted selection, genomic selection and microbiome manipulation of biocontrol agents, and monitoring for genetic variation during rearing and post‐release. We conclude by identifying the most promising applications of genetic and genomic methods to improve biological control efficacy.
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