Establishment Of Biological Control Agents Research Articles

Introduction and establishment of biological control agents for control of emerald ash borer (Agrilus planipennis) in Canada

Abstract The emerald ash borer, Agrilus planipennis Fairmaire (Coleoptera: Buprestidae), is a serious pest of ash (Fraxinus spp.) (Oleaceae) in North America. Control of emerald ash borer is difficult in natural forest settings; therefore, a classical biological control programme is the most feasible management option for this invasive, nonnative insect. Here, we report the first Canadian release and establishment of parasitoids Tetrastichus planipennisi Yang (Hymeoptera: Eulophinae), Oobius agrili Zhang and Huang (Hymenoptera: Encyrtidae), and Spathius galinae Belokobylskij and Strazanac (Hymenoptera: Braconidae) in natural forests in Ontario, Quebec, and New Brunswick, Canada for the control of emerald ash borer. Releases of T. planipennisi were made from 2013 to 2019, O. agrili from 2015 to 2019, and S. galinae from 2017 to 2019. Trees from release sites were destructively sampled to rear out adult emerald ash borers and parasitoids 1–3 years after parasitoid release. Recoveries of T. planipennisi were made at 81% of release sites (13 of 16) 1–2 years after release, and O. agili were recovered from 29% of release sites (4 of 14) 1–3 years after release. Spathius galinae was not recovered. These data provide important information for the development and deployment of a successful biological control programme for the management of emerald ash borer in Canada.

Modelling the dynamics of a plant pathogen and a biological control agent in relation to flowering pattern and populations present on leaves

A flexible model for biological control of a plant pathogen affecting host flowers is developed which takes into account the transfer of both the plant pathogen and the biological control agent (BCA) from the leaves to flowers. Because flowers, other than in ornamental plants, are largely ephemeral, the emphasis in analysis is on the rates of transfer and establishment on flowers. The form of the model analysed depends upon: the pattern of flowering for a particular host plant, a single instantaneous flush or continuous seasonal production; the effect of flowering phenology and morphology on transfer of both the pathogen and BCA; and the transient dynamics of such transfer. In the case of a single instantaneous flush, the relative importance of mycoparasitism and competition in protecting flowers during their short period of blooming is assessed. Where flowering is continuous but transfer lags behind because of floral phenology or morphology, a comparison is made between the initial levels of the pathogen and the BCA as they transfer to the flowers, depending again on the relative contribution of mycoparasitism and competition over the extended period of blooming. Differential rates of transfer of the pathogen and the BCA, depending on their time-dependent population densities on leaves, have a major impact on eventual biocontrol outcomes. The model results are used to analyse biocontrol strategies for contrasting host-pathogen systems which show different flowering patterns and biological control mechanisms. For Erwinia amylovora causing fireblight in pome fruit trees, an inundative biocontrol strategy targeting flowers is supported. In Botrytis cinerea, there is considerable potential for a strategy based on the establishment of BCAs on leaves for some of the plant hosts affected.

Niche-based prediction of establishment of biocontrol agents: an example with Gratiana boliviana and tropical soda apple

Successful establishment of a biological control agent is a prerequisite for effective reduction of an invasive weed. Niche-based species distribution models can generate valuable information about the potential spread of a biological control agent and help to predict its distribution. The Maximum Entropy Species Distribution Model was used in our study to predict distributions of the leaf beetle Gratiana boliviana Spaeth (Coleoptera: Chrysomelidae) and its target weed, tropical soda apple (TSA), Solanum viarum Dunal (Solanaceae). The specific objectives of this study were to (1) assess the climatic suitability for establishment of this insect across the invasive range of the weed by overlapping predicted current distributions and, (2) examine the niche-related restriction in distribution of the insect by visualising the predictive niche in multivariate space. Accuracy of predicted distributions was tested using binomial tests and area under the curve scores. The results of statistical tests confirmed that the predictions were significantly better than random. The predictions indicated that the potential distribution of G. boliviana in the USA will be more restricted than that of its host plant. Consequently, the beetle's ability to inflict damage to TSA will be geographically limited. Niche visualisation, using a PCA-based analysis, provided evidence of the niche imposed restriction on the distribution of G. boliviana. Overall, this study proposes a new approach for understanding the spatial limitations in establishment of biological control agents, allowing researchers to establish more realistic expectations of success.

Genetic and chemical variation of Tanacetum vulgare in plants of native and invasive origin

High genetic diversity of introduced plant populations may pose a key advantage under changed selection pressures but may also have important implications for biological control of such plants. However, molecular markers employed to measure genetic variation do not necessarily reflect variations in phenotypic traits such as plant chemical composition, which may be similarly important for both the invasion success of a plant and the establishment of biological control agents. The Asteraceae species Tanacetum vulgare is of Eurasian origin, but was introduced to North America, where it became invasive in some areas. This species varies greatly in terpene composition, forming different chemotypes. To assess the genetic diversity of T. vulgare in relation to its chemical diversity, we grew populations originating from different sources of the native and introduced ranges under standardized conditions. Using inter simple sequence repeat markers, we found indications for an increased genetic diversity in plants of the introduced compared to the native range. Analyses of volatile profiles of these individuals indicated similarly high chemical diversities in native and introduced populations. Clustering analyses revealed a considerable amount of unique geno- and chemo-types on both continents. No significant relation between the genetic and chemical data could be detected, demonstrating that the genetic structure of invasive populations does not necessarily offer information on its chemical diversity and vice versa. Knowledge of both the genetic structure and the actual variation in plant chemistry allows biological control research to consider factors potentially interfering with the success of biocontrol agents prior to release.

Invasion of a West Everglades wetland by Melaleuca quinquenervia countered by classical biological control

The population dynamics of Melaleuca quinquenervia were monitored over a 5-year period in a cypress-pine wetland while subjected to two levels of herbivory. The trees had been recruited during 1998–1999 after a destructive crown fire. Half of 26 experimental plots were sprayed every 4–6 weeks with an insecticide to reduce herbivory by the biological control agents Oxyops vitiosa and Boreioglycaspis melaleucae. After only 1-year melaleuca density increased by 26% in sprayed plots and by 7% in unsprayed plots. However, over the entire 5-year period melaleuca density increased in sprayed plots by 0.1% while decreasing by 47.9% in unsprayed plots when compared to initial densities. Annual mortality of melaleuca never exceeded 6% in any year in sprayed plots but ranged from 11% to 25% in unsprayed plots. There was a significant year by treatment interaction indicating the importance of the environment on tree mortality. Limited seed production occurred on sprayed trees but never on unsprayed trees. Mean tree height increased by 19.6% in sprayed plots while declining by 30.6% in unsprayed plots. Coverage by native vegetation did not increase with decreasing melaleuca density. This is the first study with controls that quantifies the population level regulation of melaleuca by introduced biological control agents and corroborates other correlative studies that documented significant changes in melaleuca communities after the introduction and establishment of biological control agents.

Integration of biological control agents with other weed management technologies: Successes from the leafy spurge (Euphorbia esula) IPM program

An invasive weed can occupy a variety of environments and ecological niches and generally no single control method can be used across all areas the weed is found. Biological control agents integrated with other methods can increase and/or improve site-specific weed control, but such combinatorial approaches have not been widely utilized. The successful leafy spurge (Euphorbia esula L.) control program provides examples for future integrated weed programs that utilize biological control agents with traditional methods. Weed control methods can be used separately, such as when the leafy spurge gall midge (Spurgia esulae Gagné) reduced seed production in wooded areas while herbicides prevented further spread outside the tree line. Traditional methods also can be used directly with biological control agents. Incorporation of Aphthona spp. with herbicides has resulted in more rapid and complete leafy spurge control than either method used alone. Also, the insect population often increased rapidly following herbicide treatment, especially in areas where Aphthona spp. were established for several years but had been ineffective. Incorporation of Aphthona spp. with sheep or goat grazing has resulted in a larger decline in leafy spurge production than insects alone and in weed density than grazing alone. Controlled burns can aid establishment of biological control agents in marginally suitable environments, but timing of the fire must be coordinated to the insect’s life-cycle to ensure survival. Integration of biological control agents with revegetation programs required the agent to be the last method introduced because the cultivation and herbicide treatments necessary to establish desirable grasses and forbs were destructive to the insect. In a practical application, herbicides were combined with Aphthona spp. to help the insect establish and control leafy spurge in the habitat of the western prairie fringed orchid (Platanthera praeclara Sheviak and Bowles), an endangered species. Several experimental designs can be used to evaluate biological control agents with cultural, mechanical, and chemical control methods or with additional biological agents.

PREDATION BY NATIVE ARTHROPODS ON THE AFRICAN PARASITOID PROROPS NASUTA (HYMENOPTERA: BETHYLIDAE) IN COFFEE PLANTATIONS OF MEXICO

The establishment or colonization of natural enemies is a critical period of adjustment for the introduced individuals in the target area. Successful colonization and its effectiveness in control, depend on the intrinsic capabilities of the species and the interaction of physical and biotic factors (Callan 1969). Although the concept of establishment is simple, in practice it is a difficult task. From 4,769 introductions of predators and parasitoids made up to 1990, only 1,445 (30.3%) were established (Greathead & Greathead 1992). Diverse reasons have been mentioned of the traits likely to reduce the establishment of biological control agents. Among the most important are: adverse climatic condition, insufficient genetic variation, poor searching capacity, interference from chemicals or cultural practices, inadequate numbers of individuals introduced, lack of synchrony with the host and interference by native organisms (Hopper et al. 1993, Hopper 1996). Prorops nasuta Waterston is an African parasitoid of the coffee berry borer (CBB) Hypothenemus hampei (Ferrari) (Coleoptera: Scolytidae), which is considered as the main pest of coffee worldwide (Le Pelley 1968, Baker 1999). R nasuta females usually spend most of its life inside of a coffee fruit infested by the CBB. The wasp feeds on all juvenile stages, but only paralyses and oviposits on the full-grown larvae and pupae. The larva starts to feed externally after hatching and one host is sufficient for the development of each wasp. When the parasite larva is fully developed, it spins a cocoon and enters to the pupal stage (Hargreaves 1935; Infante 1998). The life cycle of P nasuta form egg to adult lasts 28 days at 220C (Infante 2000), but adults remain in the coffee fruit for a few days more in order to copulate. As with other bethylids, this species has males emerging before their sisters with which they mate. The new generation of wasps leave the berry during the day, searching for infested coffee fruits (Hargreaves 1935, Murphy & Moore 1990). In the last few years this parasitoid has been introduced to Mexico, Guatemala, El Salvador, Honduras, Ecuador, Colombia, Jamaica, Indonesia and India. In all these countries P nasuta has been released and is presently under evaluation as a biological control agent (Klein-Koch et al. 1988, Barrera et al. 1990, Baker 1999). In the case of Mexico, repeatedly releases of parasitoids have been carried out in Chiapas since 1992. Recovery surveys indicated that up to now, there is no evidence of the establishment of P nasuta in the country (Infante et al. 2001). Identifying the factors that interfere in the establishment of P nasuta is essential to the success of biological control programmes for the CBB. For that reason, the present paper reports on some native arthropods that were found predating on this species in coffee plantations of Chiapas. The wasps used in releases were reared in the laboratory on borer infested coffee fruits. Parasitoids were taken to the field as adults and released from one liter plastic jars directly onto the branches of coffee trees. From 1992 to 1996, ca. 156,000 individuals were released in the field usually in the morning (before 12:00 hr). Colonization sites for releases consisted of 22 locations, each approximately one-fourth of a hectare. Because few people observe insects under field conditions (P. S. Baker, personal communication), we stayed in the field for about 1-2 hours following parasitoid liberations, to observe the wasps and any possible interaction with other organisms. The organisms detected as interacting with P nasuta were collected and taken to the laboratory for identification. A list of arthropods preying on adults of P nasuta is presented in Table 1. Meantime females were searching for infested fruits, they were easy prey for ants, which normally were present on coffee trees. It was possible to detect at least five species of ants preying on adults of P nasuta. Also six species of spiders caught parasitoids on their webs. As spiders were collected in alcohol, it was not possible to verify their predation on P nasuta. However, we would assume they do, considering they are generalist predators. Recent studies have reported that spiders, such as, Cyclosa caroli, Leucauge mariana and L. vetusta capture and consume individuals of the CBB and its bethylid parasitoid Cephalonomia stephanoderis (Henaut et al. 2001). Because of the small size of P nasuta (2mm), observations were especially difficult to carry out. We could not measure the intensity in which predators were acting, but presumably they are only imnnrt.nnt diiring releases. or mavbe when the

FACTORS INFLUENCING THE CHANCE OF POPULATION ESTABLISHMENT: IMPLICATIONS FOR RELEASE STRATEGIES IN BIOCONTROL

Successful establishment of biological control agents is hampered by factors that put small populations at risk of extinction; among these are demographic stochasticity, environmental variability, and Allee effects. I used a stochastic simulation model to tease apart the influences of these three factors on the relationship between release size and the probability of population establishment. The fates of simulated colonies indicated that demographic stochasticity alone is not likely to be important in the establishment of biological control agents, but both environmental variability and Allee effects are crucial. These two factors are distinct in the way they interact with the initial colony size. The presence of an Allee effect results in a threshold response; below a critical colony size a population is doomed, and above that size establishment is likely. In contrast, environmental variability reduces the likelihood of establishment over the entire range of colony sizes. In combination, these factors have an intermediate effect, that is, a gradual increase in establishment rate with initial colony size. These results can be used to design release strategies that will maximize the probability of successful establishment given the inherent trade-off between the size of each release and the number of releases. In a variable environment, a large number of very small-sized releases will maximize the chance of overall establishment. When an Allee effect is present (in a constant environment), a single large release is optimal. For some combinations of both factors, there will be an intermediate optimum release size (and corresponding number of releases). This study provides an avenue for improving the rate of successful biological control through wisely designed releases. The results of this study have important implications for the conservation and reintroduction of threatened populations as well.

The EVect of Release Size on the Probability of Establishment of Biological Control Agents: Gorse Thrips ( Sericothrips staphylinus ) Released Against Gorse ( Ulex europaeus ) in New Zealand

Many biocontrol agents released against alien weeds and pests fail to establish in the field. Here, we ask whether better release strategies could improve the likelihood of successful establishment. A manipulative field experiment was used to investigate the relationship between the probability of establishment and the number of individuals released for a weed biocontrol agent. In this experiment, replicated releases of 10, 30, 90, 270 and 810 gorse thrips, Sericothrips staphylinus Haliday, were made on to isolated gorse bushes in New Zealand. The sampling eY ciency was determined using a further experiment in which known numbers of thrips were released on to bushes. The data obtained showed that in approximately nine out of 10 releases of 10 thrips, at least one thrips would be found. The thrips in the size of release experiment were sampled 1 year after their release. A higher proportion of the small releases became extinct during this time period: thrips were recovered from 100% of the releases of 270 and 810 thrips, but only from 33% of releases of 10, 30 and 90 thrips. Using gorse thrips as an example, a protocol was developed to determine the optimal release size for biocontrol agents. It is suggested that for a fixed number of insects available for release, smaller releases may increase the overall establishment rate. W hile a single large release can easily become extinct by chance, it is extremely unlikely that a large number of small releases will do so over the same time period. The optimal release size (i.e. that which maximizes the average number of successful establishments) for gorse thrips in New Zealand might be fewer than 100 thrips/ release site. This contrasts with the current strategy in New Zealand of 1000 thrips/release and the suggestion in the biocontrol literature that large releases optimize establishment. Over 1 year of observation the thrips had no eVect on gorse growth rate. The EVect of Release Size on the Probability of Establishment of Biological Control Agents: Gorse Thrips ( Sericothrips staphylinus ) Released Against Gorse ( Ulex europaeus ) in New Zealand

Nitrogen, phosphorus and potassium in Salvinia molesta Mitchell in the field: effects of weather, insect damage, fertilizers and age

More than 1700 samples of Salvinia molesta Mitchell were collected from sites distributed from close to the equator in Papua New Guinea to 33°S in Australia. Nitrogen content ranged from 0.62 to 4.0% dry weight, phosphorus from 0.03 to 1.07% and potassium from 0.31 to 5.32%. Tops contained more concentrated N and P than roots, while K was more concentrated in roots. Concentrations of N and P were significantly correlated. Rainfall, followed by runoff, resulted in peaks of N, P and K in plants in one lake, but the sequence could not be demonstrated at other sites. At sites experiencing marked seasonal changes in temperature, N and P contents were inversely correlated with temperature, probably due to greater growth and utilisation of nutrients in summer. Damage caused by the biological control agent Cyrtobagous salviniae Calder and Sands decreased K content, while N and P contents were increased in some cases, but not in others. Thick mats of S. molesta in Papua New Guinea contained less concentrated N and P than thin mats, but this was not necessarily the case in the Australian sites. The reasons for these differences, and the likely effects on biological control agents, are discussed. Urea and superphosphate were found to increase N and P concentrations in the plant by amounts useful for experimental purposes and for aiding establishment of biological control agents. An equation related N concentration to the amount of urea applied and background N content of the plant. Concentrations of N, P and K decreased with age. Levels of N and P dropped most quickly as buds opened, then dropped slowly until the onset of senescence caused another rapid decline. The implications of these changes for insects feeding on S. molesta are discussed.