Successful Biological Control Agent Research Articles

Host range of a parasitoid wasp is linked to host susceptibility to its mutualistic viral symbiont.

Parasitoid wasps are one of the most species-rich groups of animals on Earth, due to their ability to successfully develop as parasites of nearly all types of insects. Unlike most known parasitoid wasps that specialize towards one or a few host species, Diachasmimorpha longicaudata is a generalist that can survive within multiple genera of tephritid fruit fly hosts, including many globally important pest species. Diachasmimorpha longicaudata has therefore been widely released to suppress pest populations as part of biological control efforts in tropical and subtropical agricultural ecosystems. In this study, we investigated the role of a mutualistic poxvirus in shaping the host range of D. longicaudata across three genera of agricultural pest species: two of which are permissive hosts for D. longicaudata parasitism and one that is a nonpermissive host. We found that permissive hosts Ceratitis capitata and Bactrocera dorsalis were highly susceptible to manual virus injection, displaying rapid virus replication and abundant fly mortality. However, the nonpermissive host Zeugodacus cucurbitae largely overcame virus infection, exhibiting substantially lower mortality and no virus replication. Investigation of transcriptional dynamics during virus infection demonstrated hindered viral gene expression and limited changes in fly gene expression within the nonpermissive host compared with the permissive species, indicating that the host range of the viral symbiont may influence the host range of D. longicaudata wasps. These findings also reveal that viral symbiont activity may be a major contributor to the success of D. longicaudata as a generalist parasitoid species and a globally successful biological control agent.

Making the best of research investment in pathogens control through biocontrol. How is research correlated with agricultural microbial biological control product availability?

While using microbial biological control products (MBCPs) to limit pathogens is one of the alternatives to the ecologically unsustainable use of synthetic pesticides that received attention, the last 2 decades have not brought the foreseen leap in developing systematic alternatives based on low-risk plant protection products (PPPs) across the globe. To explain this limited progress, we map the evolution of research on the most successful microbial biological control agents (MBCAs) worldwide. We also map the financing structure in the top funding countries and the European Union (EU) to discern the relevant trends. Available data for the European Union Member States allowed us to discover a country-level and EU-level correlation between strain-level research and biocontrol products' approval based on those strains.

Evaluation of the mechanism of action of Bacillus spp. to manage Meloidogyne incognita with split root assay, RT-qPCR and qPCR.

The goal of this research is to determine the mechanism of action of two Bacillus spp. that can manage Meloidogyne incognita population density in cotton. The overall objectives are 1) determine the efficacy and direct antagonistic capabilities of the Bacillus spp. and 2) determine the systemic capabilities of the Bacillus spp. The greenhouse in planta assay indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could manage M. incognita similarly to the chemical standard fluopyram. An in vitro assay determined that B. firmus I-1582 and its extracted metabolites were able to directly manage M. incognita second stage juveniles by increasing mortality rate above 75%. A split root assay, used to determine systemic capabilities of the bacteria, indicated B. amyloliquefaciens QST713 and B. firmus I-1582 could indirectly decrease the nematode population density. Another species, B. mojavensis strain 2, also demonstrated systemic capabilities but was not a successful biological control agent because it supported a high population density in greenhouse in planta assay and in the split root assay. A RT-qPCR assay was used to confirm any systemic activity observed in the split root assay. At 24 hours both B. amyloliquefaciens QST713 and B. firmus I-1582 upregulated one gene involved in the initial stages of JA synthesis pathway but not another gene involved in the later stages of JA synthesis. These results point to a JA intermediate molecule, most likely OPDA, stimulated by the bacteria rather than JA in a short-term systemic response. After 1 week, the Bacillus spp. stimulated a SA-responsive defense related gene. The long-term systemic response to the Bacillus spp. indicates salicylic acid also plays a role in defense conferred by these bacteria. The final assay was a qPCR to determine the concentration of the bacteria on the cotton roots after 24 days. Bacillus amyloliquefaciens QST713 and B. firmus I-43 1582 were able to colonize the root successfully, with the concentration after 24 days not significantly differing from the concentration at inoculation. This study identifies two bacteria that work via systemic resistance and will help aid in implementing these species in an integrated management system.

Foraging Behaviour and Population Dynamics of Asian Weaver Ants: Assessing Its Potential as Biological Control Agent of the Invasive Bagworms Metisa plana (Lepidoptera: Psychidae) in Oil Palm Plantations

The bagworm (Metisa plana) is a recurrent indigenous invasive defoliator in oil palm plantations. Moderate foliar injury can cost up to 40% yield loss and more for years. The main objective of this review is to disseminate published research demonstrating the versatile services that would benefit farmers by adopting the Asian weaver ant into their pest management agenda. Oecophylla smaragdina is a natural indigenous enemy applied as a successful biological control agent (BCA) and strong component of integrated pest management (IPM) against important damaging pest infestations of commercial crops in the Asia-Pacific region. Farmers facing invasion could benefit by introducing Oecophylla ants as a treatment. The foraging behavior and population dynamics of this species are poorly documented, and hence need further evaluation. Ants of the Oecophylla genus, while exhibiting an intrinsic obligate arboreal pattern, demonstrate additional lengthy diurnal ground activity. The absolute territorial characteristic via continuous surveillance is significantly valuable to maintain pest balance. The exploratory scheme of major workers over large territories is derived from their inner predation instinct. The insufficient understanding of the population dynamics of this weaver ant species diverges from the knowledge of underground species. However, population density estimations of weaver ants by direct nest visual recordings are practicable and viable. The abundance assessment of individual underground ant species colonies by excavation ends with their extinction, which is not a sustainable model for O. smaragdina. Mathematical model estimation by simulation could not resolve this issue, adding inaccuracy to the deficiency of experimental proof. Thus, long-term monitoring of the population dynamics in real time in the field is compulsory to obtain a valid dataset. Oecophylla colonies, with the criteria of population stability, individual profusion, and permanent daily patrol services, are eligible as a BCA and alternative IPM treatment. The last decades have witnessed the closing of the scientific applied research gap between Asian and African species in favor of O. longinoda with comprehensive novel findings. By introducing Oecophylla ants, two main goals are reached: easing the burden of management costs for injurious insects and ending the practice of applying highly toxic pesticides that are harmful to non-target taxa, thus promoting environmental restoration.

Dactylopius opuntiae Cockerell (Hemiptera: Dactylopiidae), an emerging global threat for Opuntia spp: a bibliometric analysis

Dactylopius opuntiae Cockerell (Hemiptera: Dactylopiidae) is a worldwide successful biological control agent for some invasive Opuntia Mill. (Caryophyllales: Cactaceae) species, and a primary pest where this species is commercially cultivated, which has renewed its scientific interest. Therefore, this research characterized regularities of the scientific production and identified emerging research trends on D. opuntiae, using one-dimensional and multidimensional bibliometric indicators. The search and retrieve of metadata from nine scientific publications databases (Biological Abstracts, Cab abstracts, Crossref, Google Academic, Dimensions, Microsoft Academic Search, Science Citation Index Expanded, Scopus, and Zoological Record) was condensed into a 193 documents collection, spanning from 1848 to 2021 using the Zotero® bibliographic reference manager. Publish or Perish® and Excel® were used to generate one-dimensional indicators and VOSviewer® for multi-dimensional indicators. Eighty percent of the publications on D. opuntiae were registered in the last 20 years, which denotes the specie´s recently acquired importance. The addressed topics in the two assessed periods showed drastic changes, since, while in the first period (1848-2000) these were directed, particularly, to its applications as a biological control agent for various Opuntia species; during the next period (2001-2021), they focused on generating strategies for its eradication and control. A high number of non-peer-reviewed publications were not included in our studies, such as serials, books, theses, and conference proceedings. Despite the recent interest in D. opuntiae and the growing number of scientific documents, no previous publications were found that address this issue. Finally, the research allowed for the identification of emerging research trends and showed their locations and who makes up the clusters or research groups, and the addressed topics, which could facilitate collaboration networks establishment and contribute to the scientific development of D. opuntiae.

Resting ecology of parasitoids in the field: safe in a bed and breakfast?

The selection of a safe place to rest at night may be an essential survival strategy for diurnal animals. Despite the importance of parasitoid wasps as consumers in terrestrial ecosystems, their selection of sites to rest and their mortality during the night have not been measured, to the best of our knowledge, reflective of a general lack of understanding of resting behaviours of insects in the field. Here, we used parasitoid wasps of the genus Aphytis (Hymenoptera: Aphelinidae), the highly successful biological control agents of the California red scale, Aonidiella aurantii (Hemiptera: Diaspididae), to study the resting ecology of parasitoids in the field over space and time, considering both external and internal correlates of parasitoid resting behaviour. At night, Aphytis wasps tended to rest on citrus tree leaves, which have a lower host density, but also fewer predators and a greater density of food sources for adult wasps, compared to fruit and branches. On this plant substrate, most of the population avoided predators and survived the night. Aphytis wasps selected leaves on which to rest at night in a nonrandom fashion. They tended to aggregate on leaves with high densities of hosts and food sources (honeydew) and with low densities of potential predators. During the day, wasps with lower egg loads tended to remain on leaves, likely resting and maturing eggs. Overall, our results demonstrate, for the first time, that parasitoids select certain sites at which to rest safely at night. These findings also suggest that the availability of safe resting places could be a valuable resource for beneficial insects in agroecosystems, especially those that have life spans extending over multiple days. • Diurnal insects search for places to rest safely at night. • We studied the resting ecology of Aphytis parasitoids in the field. • At night, they aggregated on leaves with high densities of hosts and food sources. • Parasitoids avoided resting on leaves with potential predators. • More than 90% of the parasitoids avoided predator attacks and survived the night.

Development of cost-effective media for the in vitro liquid culture of entomopathogenic nematodes

Summary Entomopathogenic nematodes (EPN) are successful biological control agents of a variety of soilborne insect pests. They have the potential to be mass-produced, using in vitro liquid culture technology, and can be formulated and sold as a biopesticide. To commercialise an EPN-based biopesticide successfully, the method of liquid mass production requires in-depth optimisation to reduce the cost of production and to increase yields, to make it affordable to the farming community. This study attempted to optimise the liquid culture protocol for the South African isolates, Steinernema jeffreyense and S. yirgalemense, by investigating the impact of cheaper medium ingredients on the recovery and yield of the liquid culture process. Studies were conducted by investigating alternative protein, lipid and nitrogen/yeast sources, compared to the more expensive laboratory-grade ingredients currently used. The results showed that egg yolk has no impact on the yield in the case of S. jeffreyense. However, for S. yirgalemense, egg yolk was shown to be a superior protein source to soy and insect-based protein in terms of nematode yield. Moreover, neither canola oil nor olive oil showed a significant difference in the yield of S. yirgalemense, with yeast extract being found to be the optimal nitrogen/yeast source. When comparing the yields with those in other liquid culture research on S. yirgalemense, yields have been successfully increased by 300%, with the cost of the nematode nutrient medium having decreased by 77%. Thus, it is imperative that, prior to a scale up to large bioreactors, the nutrient medium should be optimised to reduce the cost of production.

Effect of temperature and soil moisture on the efficacy of indigenous and imported strains of the entomopathogenic nematode, Heterorhabditis sp. against the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera/Noctuidae)

BackgroundBiotic and abiotic factors influence survival, infectivity, development, reproduction, and activity of the entomopathogenic nematodes (EPNs). EPNs have been used to suppress the soil-inhabitant insects, which applied as a successful biological control agent against the black cutworm, Agrotis ipsilon (Hufnagel) (Lepidoptera/Noctuidae) larvae, and pupae.ResultsStudying the effect of different temperatures 20, 25, and 30°C ± 2, and the soil moisture content at 10, 15, and 25% on the susceptibility of two Heterorhabditis sp. strains, Egyptian strain (TAN5) and imported strain (Hb88) against the A. ipsilon 4th and 6th larval instars and 3-day-old pupae was carried out under laboratory conditions. The tested concentrations of the two strains were 30, 60, 120, 240, and 480 IJs/cm2 of soil surface. The mortality rate of 4th instar A. ipsilon larvae was high after Heterorhabditis strain TAN5 treatments at all concentrations, which ranged between (24 and 100%) and (6–100%) at 25°C and 30°C, respectively. At 20°C, Heterorhabditis strain Hb88 recorded higher mortality percentages for A. ipsilon 4th and 6th larval instars and pupae than the indigenous strain TAN5. The soil moisture content of 25% gave the highest mortality rates for the 4th instar larvae of A. ipsilon after treatments of the two strains. The Egyptian Heterorhabditis strain TAN5 was tolerant to the increase in temperature and more tolerant to the change in the water content of the soil than the imported strain Hb88 at all concentrations tested. In a semi-field experiment, Heterorhabditis strain TAN5 at concentrations between (1000–8000 IJs/cm2 of soil surface) showed mortality rates (27–95%) for 4th instar A. ipsilon larvae and (19–81%) for the 3-day-old pupae, respectively.ConclusionsHeterorhabditis strains TAN5 can was utilized against the black cutworm of A. ipsilon at the temperatures 25 and 30°C. Heterorhabditis strains TAN5 and Hb88 can be utilized against the black cutworm of A. ipsilon at the soil moisture content from 15 to 25%. In the semi-field experiment, Heterorhabditis TAN5 and Hb88 strains were effective against larvae and pupae of A. ipsilon at high concentrations of the nematodes.

Advancements in Mass Rearing the Air Potato Beetle Lilioceris cheni.

Simple SummaryMass rearing the air potato beetle, Lilioceris cheni, is a vital contribution to the integrated pest management of the invasive air potato vine. Here, the authors report on the production, distribution, and advancements of a mass rearing method. It was determined that adults are most successful on a diet of fresh air potato leaf. Although to reduce the amount of leaf tissue needed for overwintering populations, they can survive on artificial diet for several months and can be starved for several days to two weeks depending on previous diet. Larvae cannot survive continuously on artificial diet. This information allows those mass rearing beetles to reduce the amount of tissue grown at points in the annual cycle and shows that adult beetles can survive starvation while being distributed or for short periods after release. It also indicates that fresh air potato vine must be available in at least small quantities year-round. This information will assist those attempting to mass rear and distribute the beetle.The air potato beetle, Lilioceris cheni Gressitt and Kimoto (Coleoptera:Chrysomelidae), is a successful biological control agent of the air potato vine, Dioscorea bulbifera L. (Dioscoreales: Dioscoreaceae), in the southern United States. Lilioceris cheni is currently being mass-reared by the Florida Department of Agriculture and Consumer Services Division of Plant Industry (FDACS-DPI) for biological control releases and research. The facility rears and releases over 50,000 adult beetles annually at approximately 1000 different locations. In addition to data on beetle production and distribution, studies on alternative larval and adult diets are described. Adults fed bulbils as the sole food source had reduced life spans compared with beetles given fresh air potato leaves. Adults survived without air potato leaves or bulbils for several days to two weeks depending on availability of leaves at emergence. Larvae did not survive on a modified artificial Colorado potato beetle diet containing fresh air potato vine leaves. Adults survived while consuming artificial diet but ceased oviposition. They, however, resumed egg laying less than one week after being returned to a diet of fresh air potato vine leaves.

TRICHODERMA ASPERELLUM AS A POTENTIAL BIOCONTROL AGENT AGAINST FUNGAL DISEASES OF CHILLI

: Fungal diseases are one of the major risks in chilli production. Plant diseases are being controlled commonly by the application of synthetic fungicides. Trichoderma species found to be most effective antagonism of foliar and soil borne pathogens. In the present study, dual culture assay was conducted against phytopathogenic fungi of chilli in vitro and examined percent inhibition by the potential biocontrol agent. Dual culture plate test revealed that the percentage growth inhibition of Colletotrichum gleosporoides, Fusarium oxysporum, Pythium apanidermatum, Curvularia lunata and Alternaria sp by Trichoderma asperellum were in the range of 26.4 to 83.5 %.T. asperellum, a less studied fungus, is also a successful biological control agent against a wide range of plant pathogens. Thus, the aim of this research is to assess the antagonistic ability of T. asperellum towards chilli phytopathogenic fungi under in vitro conditions. The antagonistic efficacy of T. asperellum can be exploited in the disease management of chilli in field conditions.

Biological control: a novel strategy for the control of the plant parasitic nematodes.

Plant parasitic nematodes (Root-knot nematodes, Meloidogyne spp.) are rounded worms, microscopic, and cause many agricultural economic losses. Their attacks have a direct impact on the productivity of cultivated crops by reducing their fruit quantity. Chemical control is widespread all over the world, but biological control is the most effective way to reduce the number of pests that infect crops, particularly by the use of microorganisms like fungi and bacteria. Biological control is rapidly evolving, and more products are being sold worldwide over time. They can be produced by fungi, bacteria, or actinomycetes that can destruct plant parasite nematodes and feed on them. Nematophagous microorganisms as the natural enemies of nematodes have a promising way of controlling nematodes. Some of them create net-like substances and traps to take the worms from outside and finally kill them. Other parasites serve as internal parasites in order to produce toxins and to produce virulence to kill nematodes. Comprehension of the molecular basis for microbial nematode interactions gives important insights into how successful biological nematode control agents can be created. We discuss recent advances in our understanding of nematodes and nematophagous microorganisms, with an emphasis on molecular mechanisms that infect nematodes with nematophagous microorganisms and on nematode safety from pathogenic attacks. Finally, we addressed numerous key areas for future research and development, including possible approaches to the application of our recent expertise in the development of successful biocontrol strategies.

Genomic insight into diet adaptation in the biological control agent Cryptolaemus montrouzieri

BackgroundThe ladybird beetle Cryptolaemus montrouzieri Mulsant, 1853 (Coleoptera, Coccinellidae) is used worldwide as a biological control agent. It is a predator of various mealybug pests, but it also feeds on alternative prey and can be reared on artificial diets. Relatively little is known about the underlying genetic adaptations of its feeding habits.ResultsWe report the first high-quality genome sequence for C. montrouzieri. We found that the gene families encoding chemosensors and digestive and detoxifying enzymes among others were significantly expanded or contracted in C. montrouzieri in comparison to published genomes of other beetles. Comparisons of diet-specific larval development, survival and transcriptome profiling demonstrated that differentially expressed genes on unnatural diets as compared to natural prey were enriched in pathways of nutrient metabolism, indicating that the lower performance on the tested diets was caused by nutritional deficiencies. Remarkably, the C. montrouzieri genome also showed a significant expansion in an immune effector gene family. Some of the immune effector genes were dramatically downregulated when larvae were fed unnatural diets.ConclusionWe suggest that the evolution of genes related to chemosensing, digestion, and detoxification but also immunity might be associated with diet adaptation of an insect predator. These findings help explain why this predatory ladybird has become a successful biological control agent and will enable the optimization of its mass rearing and use in biological control programs.

Can Biological Control Overcome the Threat From Newly Invasive Coconut Rhinoceros Beetle Populations (Coleoptera: Scarabaeidae)? A Review.

The coconut rhinoceros beetle (CRB: Oryctes rhinoceros Linnaeus) is one of the most damaging pests to coconut and oil palms in Asia and the Pacific Islands. Adults bore into the crown and damage developing fronds, which affects tree development and yield. The insect is native to South and Southeast Asia and was inadvertently introduced into the Pacific in 1909. It has since spread to several Pacific island nations and territories, causing significant economic impact on these important coconut and palm-growing regions. In the 1950s and 1960s, an international biological control effort was initiated to search for and release natural enemy species. Release of the Oryctes rhinoceros nudivirus Huger (OrNV) and the species complex of Metarhizium Sorokin (Hypocreales: Clavicipitaceae) was successful in controlling CRB in its invaded range. Recently a new biotype of the beetle, known as CRB-G, has spread into the Pacific Islands causing unprecedented levels of damage due to the failure of previously successful biological control agents (BCAs) to suppress this biotype. The re-emergence of CRB as a serious pest warrants a rigorous re-evaluation of potential BCAs and a new search for effective natural enemies if necessary. In this article, we review literature on CRB to 1) analyze past introductions of BCAs and their effectiveness; 2) identify potentially important natural enemies and their geographical origins; and 3) assess possible approaches for utilization of BCAs against the new wave of CRB invasion. Research gaps and directions deserving future attention are highlighted and a strategy for renovation of biological controls for CRB suggested.

Natural variation in host-finding behaviour of gastropod parasitic nematodes (Phasmarhabditisspp.) exposed to host-associated cues

The gastropod parasitic nematode Phasmarhabditis hermaphrodita has been formulated into a successful biological control agent (Nemaslug®, strain DMG0001) used to kill slugs on farms and gardens. When applied to soil, P. hermaphrodita uses slug mucus and faeces to find potential hosts. However, there is little information on what cues other species of Phasmarhabditis (P. neopapillosa and P. californica) use to find hosts and whether there is natural variation in their ability to chemotax to host cues. Therefore, using chemotaxis assays, we exposed nine wild isolates of P. hermaphrodita, five isolates of P. neopapillosa and three isolates of P. californica to mucus from the pestiferous slug host Deroceras invadens, as well as 1% and 5% hyaluronic acid - a component of slug mucus that is highly attractive to these nematodes. We found P. hermaphrodita (DMG0010) and P. californica (DMG0018) responded significantly more to D. invadens mucus and 1% hyaluronic acid than other strains. Also, P. hermaphrodita (DMG0007), P. neopapillosa (DMG0015) and P. californica (DMG0017) were superior at locating 5% hyaluronic acid compared to other isolates of the same genera. Ultimately, there is natural variation in chemoattraction in Phasmarhabditis nematodes, with some strains responding significantly better to host cues than others.

Addressing the red flags in cochineal identification: The use of molecular techniques to identify cochineal insects that are used as biological control agents for invasive alien cacti

Invasive Cactaceae cause considerable damage to ecosystem function and agricultural practices around the world. The most successful biological control agents used to combat this group of weeds belong to the genus Dactylopius (Hemiptera: Dactylopiidae), commonly known as ‘cochineal’. Effective control relies on selecting the correct species, or in some cases, the most effective intraspecific lineage, of cochineal for the target cactus species. Many of the Dactylopius species are so morphologically similar, and in the case of intraspecific lineages, identical, that numerous misidentifications have been made in the past. These errors have resulted in failed attempts at the biological control of some cactus species. This study aimed to generate a multi-locus genetic database to enable the accurate identification of dactylopiids. Genetic characterization was achieved through the nucleotide sequencing of three gene regions (12S rRNA, 18S rRNA, and COI) and two inter-simple sequence repeats (ISSR). Nucleotide sequences were very effective for species-level and D. tomentosus lineage-level identification, but could not distinguish between the two lineages within D. opuntiae commonly used for biological control of various Opuntia spp. Fragment analysis through the use of ISSRs successfully addressed this issue. This is the first time that a method has been developed that can distinguish between these two D. opuntiae lineages. Using the methods developed in this study, biological control practitioners can ensure that the most effective agent species and lineages are used for each cactus target weed, thus maximizing the level of control.

Effect of cold storage on performance of Eretmocerus mundus, larval parasitoid of Bemisia tabaci in a conventional tomato growing greenhouse

Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important pest that causes economic losses in agricultural production systems, including greenhouses. Chemical control is the main control method against B. tabaci; biological control practices, however, have also been applied against this pest, especially in greenhouse production systems. Due to its parasitism potential and adaptation to environmental conditions of the Mediterranean region, Eretmocerus mundus Mercet (Hymenoptera: Aphelinidae) is considered one of the most successful biological control agents of B. tabaci. In mass production, having adequate numbers of natural enemies is critical for the augmentative biological control programs. Therefore, this study was conducted with the aim of evaluating the efficacy of stored indigenous Er. mundus on B. tabaci under greenhouse conditions. In storage experiments, red-eyed Er. mundus pupae were stored separately for 4, 8 and 12 days at 5 and 10 °C with 45 ± 5% RH conditions. The most suitable storage duration and temperature were determined as 8 days and 10 °C for the greenhouse release experiments. In the greenhouse experiments, the treatments consisted of B. tabaci release (control), stored and unstored Er. mundus releases in the Spring of 2015 and 2016 growth seasons. For the evaluation of population development of whitefly and the parasitoid, leaf samples were taken at five-day intervals. In both years, similar parasitism fluctuations were detected in stored and unstored parasitoid-released treatments, wherein initially-lower parasitism rates showed a dramatic increase at later sampling dates. In general, statistical parasitism rates of stored and unstored Er. mundus populations were found in the same group for 2015 and 2016. The results showed that storage of the parasitoid did not have a negative effect on its parasitism ability, and eight-day-stored native strain of Er. mundus could be used successfully in the biological control of B. tabaci in greenhouse-grown tomato plants.

Genetic variability of Indonesian Oryctes rhinoceros nudivirus (OrNV) as genus of Alphanudivirus

Abstract. Rahayuwati S, Kusumah YM, Prawirosukarto S, Dadang, Santoso T. 2020. Genetic variability of Indonesian Oryctes rhinoceros nudivirus (OrNV) as genus of Alphanudivirus. Biodiversitas 21: 2047-2055. Oryctes rhinoceros nudivirus (OrNV) is known as a successful classical biological control agent. Recent reports have revealed differences in pathogenicity among OrNV isolates, with correlation suspected between virus virulence and genetic variability. The aim of the research is to study the genetic variability of OrNV isolates based on the DNA polymerase (DNA pol) gene and their phylogenetic relationship with Genus Alphanudivirus. Oryctes rhinoceros (Coleoptera: Scarabaeidae) as an OrNV host were collected from Sumatra, Belitung, Java, Kalimantan, and Sulawesi. Primers were designed to amplify complete gene of DNA pol. Sequencing, phylogenetic, and investigate genetic diversity scores were used to determine variability at nucleotide level. Five primers successfully amplified the entire DNA pol gene. Genetic variability of OrNV was high, from nine isolates found eight genetically different. Isolates could be divided into two groups of genetic diversity: high and low. High genetic diversity of OrNV supposed as an old population that occupied Sundaland and Wallacean paleogeography at first appearance in Miocene Era until early Pliocene 5 Mya. New population of OrNV had low genetic diversity were travel cross-island that supposed to correlate with oil palm plantation development and the genetic drift. The benefit information of the OrNV genetic variability is as preliminary guideline for virulence test. OrNV is a member of Nudiviridae family, Genus Alphanudivirus, and at recent moment they consist of eight species. Alphanudivirus infect Coleoptera, Diptera, Hemiptera and Orthoptera order that soil as immature niche may explain their closely related taxa.

Thermal plasticity and microevolution enhance establishment success and persistence of a water hyacinth biological control agent

AbstractAspects of the thermal physiology of the water hyacinth biological control agent Eccritotarsus catarinensis Carvalho (Hemiptera: Miridae) have been extensively investigated over the past 20 years to understand and improve post‐release establishment in the field. Thermal physiology studies predicted that the agent would not establish at a number of cold sites in South Africa, where it has nonetheless subsequently established and thrived. Recently, studies have begun to incorporate the plastic nature of insect thermal physiology into models of agent establishment. This study determined whether season and locality influenced the thermal physiology of two field populations of E. catarinensis, one collected from the hottest site where the agent has established in South Africa, and one from the coldest site. The thermal physiology of E. catarinensis was significantly influenced by season and site, demonstrating a degree of phenotypic plasticity, and that some post‐release local adaptation to climatic conditions has occurred through microevolution. We then determined whether cold acclimation under laboratory conditions was possible. Successfully cold‐acclimated E. catarinensis had a significantly lower critical thermal minimum (CTmin) compared to the field cold‐acclimated population. This suggests that cold acclimation of agents could be conducted in the laboratory before future releases to improve their cold tolerance, thereby increasing their chance of establishment at cold sites and allowing further adaptation to colder climates to occur in the field. Although the thermal tolerance of E. catarinensis is limited by local adaptations to climatic conditions in the native range, the plastic nature of the insect's thermal physiology has allowed it to survive in the very different climatic conditions of the introduced range, and there has been some adaptive change to the insect's thermal tolerance since establishment. This study highlights the importance of plasticity and microevolutionary processes in the success of biological control agents under the novel climatic conditions in the introduced range.

Direct herbivory by biological control agents, and the consequent disruption of plant-nutrient-feedback cycles, combine to reduce the invasiveness of Melaleuca quinquenervia (Myrtaceae)

Herein we present the results of a 5-year herbivore exclusion experiment in which the suppression of two successful biological control agents revealed a nutrient feedback cycle that promoted the growth and dominance of the exotic tree Melaleuca quinquenervia. When herbivory was restricted, plants produced greater quantities of aboveground biomass, which transferred a greater volume of litterfall and a larger load of nutrients to the soil surface. The resulting organic layer on the surface of the soil decomposed more quickly releasing nutrients and resulting in a larger pool of total phosphorus in the surficial soil layer. These mineralized-soil-nutrients were available for uptake by the exotic plant, which produced a greater quantity of surficial roots in the restricted-herbivory plots creating a positive nutrient-feedback cycle to biomass production. Our data suggest that, in addition to the direct suppression of exotic plants through biomass consumption, biological control agents may provide indirect suppression of weeds by preventing the establishment or altering the magnitude and/or direction of an invasion-promoting feedback cycle.

Asymmetry in reproduction strategies drives evolution of resistance in biological control systems.

The success of biological control may depend on the control agent co-evolving with its target pest species, precluding the emergence of resistance that often undermines chemical control. However, recent evidence of a decline in attack rates of a sexual pest weevil by its asexual parasitoid suggests that evolutionary arms races may not prevent the emergence of resistance if the host and parasitoid do not have reproductive strategies that generate equal amounts of genetic variation. To understand how these asymmetries in reproductive strategies may drive the emergence of resistance, we combined life history data from two pest weevils and their parasitoids (one sexual and one asexual) in the New Zealand pastoral ecosystem, with a population dynamic model that allows the coevolution of hosts and parasitoids. We found that the ratio of the genetic variance of hosts to parasitoids was a key determinant of the emergence of resistance. Host resistance eventually occurred unless the parasitoids had considerably greater additive genetic variance than their host. The higher reproductive rate of asexual parasitoids did little to offset the cost of reduced additive genetic variance. The model predictions were congruent with long-term parasitism rates observed in the field for both of the pests considered (one with a sexual and one with an asexual parasitoid). We then explored the consequences of introducing two parasitoids with different reproductive strategies that attack the same sexual host. The model showed that the sexually reproducing parasitoid always out-competed the asexually reproducing one. Our study shows that any asymmetry in reproductive strategies is extremely important for predicting the long-term success of biological control agents. Fortunately, introduction of sexually reproducing individuals after an initial introduction of asexual strains may overcome the problems of host resistance. We conclude that evolution must be considered when evaluating the long-term outcomes of importation biological control.