Complete Biological Control Research Articles

Economic evaluation of chemical and biological control of four aquatic weeds in South Africa

ABSTRACT Invasive alien plants (IAPs) pose a threat to biodiversity and the economy of the countries they invade. In South Africa, the Department of Environment, Forestry and Fisheries, Natural Resources Management Programmes, previously The Working for Water Programme (WfW) is tasked with controlling IAPs in a way that protects the environment, as well as producing maximum return to society through poverty alleviation. Biological control is one of the management tools used to control IAPs in South Africa. Four aquatic weeds, Pista stratiotes, Salvinia molesta, Azolla filiculoides and Myriophyllum aquaticum, are under complete biological control in South Africa. However, in the absence of biological agents, the WfW programme would have used herbicides to control these weeds. This paper presents a retrospective analysis of the relative herbicide cost-saving associated with the use of biological control instead of chemical control. The study used cost benefit analysis (CBA) framework with an 8% discount rate. The estimated cost of the biological control on all four aquatic weeds was about R7.8 million, while the estimated cost of chemical control to achieve the same level of control varied between R150 million and R1 billion, depending on the method of application and number of follow up operations. Benefit to cost ratios varied between 90:1 and 631:1, again depending on method of application and number of follow up sprays. The results remained robust under a 5% and 10% sensitivity test and show that biological control is the most cost-effective management option for aquatic weeds in South Africa.

Evaluating the efficacy of Hypogeococcus sp. as a biological control agent of the cactaceous weed Cereus jamacaru in South Africa

We evaluated the efficacy of Hypogeococcus sp. (Hemiptera: Pseudococcidae) as a biological control agent of the cactaceous weed Cereus jamacaru De Candolle (Queen of the Night cactus) in South Africa. This weed has been described as being under complete biological control due to the action of Hypogeococcus sp., although no formal post-release evaluation had been conducted prior to this study. Biological control was associated with significant reductions in fruiting, plant survival and plant densities, while plant population age structures were negatively affected. Weed populations infected by Hypogeococcus sp. were typified by low or non-existent recruitment and are expected to diminish with time. Populations where Hypogeococcus sp. was absent displayed extensive recruitment, and are predicted to expand or self-replace, if left unchecked. These data indicate that Hypogeococcus sp. has a significant negative effect on C. jamacaru at the individual plant and population level, and given sufficient time provides complete biological control over this weed in South Africa.

A proposed national strategic framework for the management of Cactaceae in South Africa

Background: South Africa has a long history of managing biological invasions. The rapid increase in the scale and complexity of problems associated with invasions calls for new, more strategic management approaches. This paper explores strategic management approaches for cactus invasions in South Africa. Cacti (Cactaceae) have had a long history of socio-economic benefits, considerable negative environmental and socio-economic impacts, and a wide range of management interventions in South Africa. Objectives: To guide the future management of cactus invasions, a national strategic framework was developed by the South African Cactus Working Group. The overarching aim of this framework is to reduce the negative impacts of cacti to a point where their benefits significantly outweigh the losses. Method: Four strategic objectives were proposed: (1) all invasive and potentially invasive cactus species should be prevented from entering the country, (2) new incursions of cactus species must be rapidly detected and eradicated, (3) the impacts of invasive cacti must be reduced and contained and (4) socio-economically useful cacti (both invasive and non-invasive species) must be utilised sustainably to minimise the risk of further negative impacts. Results: There are currently 35 listed invasive cactus species in the country; 10 species are targeted for eradication and 12 are under partial or complete biological control. We discuss approaches for the management of cactus species, their introduction and spread pathways and spatial prioritisation of control efforts. Conclusion: A thorough understanding of context-specific invasion processes and stakeholder support is needed when implementing strategies for a group of invasive species.

Parasitoid Discrimination between Suitable and Unsuitable Congener Hosts

The eucalyptus longhorned borer, Phoracantha semipunctata (F.) (Coleoptera: Cerambycidae), is under complete biological control in California following introduction of the encyrtid egg parasitoid, Avetianella longoi Siscaro. The cerambycid congener, Phoracantha recurva Newman¸ subsequently established in the state and has been subject to limited parasitization by the wasp. Behavioral analysis demonstrated that female parasitoids follow the same sequence of ovipositional behaviors when encountering eggs of both beetle species, but discriminate between the species and make a decision to lay an egg only after inserting the ovipositor into an egg. Previous research has demonstrated that the eggs of P. recurva are capable of encapsulating and killing eggs of A. longoi. Eggs of P. semipunctata do not produce a host defense to parasitization. Consequently, the ability of a female to distinguish between the congeneric species has critical fitness consequences.

Potential risks of systemic imidacloprid to parasitoid natural enemies of a cerambycid attacking Eucalyptus

A community of insect herbivores has established on eucalyptus species in California following their introduction from Australia. A number of the species are under complete or partial biological control. A response to introduction of additional pest species into the complex has been the application of systemic insecticides to infested trees. Natural enemies that have been introduced to control the various pest species feed on the nectar of treated trees, and thus may be affected by these pesticides. In this study, Eucalyptus rudis trees were treated at label rates with the neonicotinoid systemic insecticide imidacloprid and nectar sampled at 5 months post-treatment during the spring bloom. The concentration of imidacloprid and its toxic metabolites in nectar was measured by ELISA at 660 ppb. Adults of the encyrtid egg parasitoid Avetianella longoi that were fed floral nectar collected from treated trees had significantly lower survival and reproductive fitness than adults fed nectar from untreated trees. In feeding bioassays, in which the adults were fed a range of concentrations of imidacloprid in sugar water, the LC 50 for A. longoi was 212 ppb imidacloprid. Bioassays were also conducted with the braconid larval parasitoid, Syngaster lepidus. The LC 50 for S. lepidus was 288 ppb imidacloprid. The insecticide appears to be concentrating in the nectar at higher levels than reported from other plant species and at concentrations exceeding the LC 50 for two important parasitoids. If tree treatments become widespread as a result of continual introductions of new eucalypt herbivores, established biological control programs could be at significant risk.

Relation between Soil Health, Wave-like Fluctuations in Microbial Populations, and Soil-borne Plant Disease Management

A healthy soil is often defined as a stable soil system with high levels of biological diversity and activity, internal nutrient cycling, and resilience to disturbance. This implies that microbial fluctuations after a disturbance would dampen more quickly in a healthy than in a chronically damaged and biologically impoverished soil. Soil could be disturbed by various processes, for example addition of a nutrient source, tillage, or drying-rewetting. As a result of any disturbance, the numbers of heterotrophic bacteria and of individual species start to oscillate, both in time and space. The oscillations appear as moving waves along the path of a moving nutrient source such as a root tip. The phase and period for different trophic groups and species of bacteria may be shifted indicating that succession occurs. DGGE, Biolog and FAME analysis of subsequent populations in oscillation have confirmed that there is a cyclic succession in microbial communities. Microbial diversity oscillates in opposite direction from oscillations in microbial populations. In a healthy soil, the amplitudes of these oscillations will be small, but the background levels of microbial diversity and activity are high, so that soil-borne diseases will face more competitors and antagonists. However, soil-borne pathogens and antagonists alike will fluctuate in time and space as a result of growing plant roots and other disturbances, and the periods and phases of the oscillations may vary. As a consequence, biological control by members of a single trophic group or species may never be complete, as pathogens will encounter varying populations of the biocontrol agent on the root surface. A mixture of different trophic groups may provide more complete biological control because peaks of different trophic groups occur at subsequent locations along a root. Alternatively, regular addition of soil organic matter may increase background levels of microbial activity, increase nutrient cycling, lower the concentrations of easily available nutrient sources, increase microbial diversity, and enhance natural disease suppression.

Biological Control of Melanaspis Obscura on Oaks in Northern California

In 1988, Encarsia aurantii (Howard) (Hymenoptera: Aphelinidae) was introduced into northern California to control an isolated infestation of obscure scale, Melanaspis obscura (Comstock) (Coccoidea: Diaspididae), on native and exotic oaks (Quercus spp.) in Sacramento’s Capitol Park. By 2002, there was no longer any need for chemical control of the scale (i.e., complete biological control). Both parasite and host are univoltine; peak emergence of adult parasites coincides with the peak of newly settled, first-instar scales. Increase of the parasite and concomitant decline of the scale from 1992 to 2004 are documented for one native and one exotic oak tree. During spring of 2004, mean density of female scales (based on 100 twigs per tree) on 12 previously infested oak trees was generally low, ranging from <1 (eight trees) to ∼15 (single tree) scales/twig. Mean percentage parasitization (per twig) ranged from ∼30 to ∼85%, and was density independent (spatial context) for each of five trees. Two refuges for the scale population were noted: some scale crawlers settled and developed under the parental scale cover (spatial refuge) and some female scales continued to produce crawlers into late summer and early fall, when adult parasites were no longer available (temporal refuge). This case illustrates how an introduction strategy (i.e., single-species release of E. aurantii), which was derived from an analysis of the parasite guild of the pest, was executed in the field and ultimately led to successful biological control.

Alfalfa Weevil (Coleoptera: Curculionidae) Population Dynamics and Mortality Factors in Virginia

The alfalfa weevil, Hypera postica (Gyllenhal), is a major pest of alfalfa in Virginia despite being under complete biological control in the northeastern states. In 1997 we initiated a 2-yr study of alfalfa weevil populations at three different geographic regions of Virginia to better understand the ecological mechanisms underlying the differences in pest pressure among the major alfalfa-growing regions of the state. Alfalfa weevil populations from the low-lying Piedmont plateau, Shenandoah Valley, and southwestern mountain-valley regions were sampled regularly from No- vember until first harvest in each season. Fields located in the Piedmont had significantly higher alfalfa weevil numbers than those in the Shenandoah Valley and southwestern region. Warmer winter temperatures in the Piedmont contributed to a much higher rate of alfalfa weevil oviposition and concomitant higher infestations of larvae in the spring compared with the higher elevations. Parasitization of adult weevils by Microctonus aethiopoides (Loan), which plays a key role in reducing alfalfa weevil reproduction in the northeastern states, was low in all regions of Virginia, particularly the Piedmont. Mortality of alfalfa weevil larvae was comparable to that reported in more northerly states. The dominant natural enemy of weevil larvae was the parasitoid, Bathyplectes anurus (Thom- son), which parasitized 36—92% of larvae. Analysis of alfalfa weevil life tables showed that different mortality factors were important in explaining variations in total alfalfa weevil mortality.

Obscure scale declines after parasitic wasp introduced

Obscure scale, a pest of oak and pecan trees, was found in Sacramento's Capitol Park in 1962. By 1980 the scale was threatening the park's oaks. Red oaks seemed especially susceptible. In 1987–88 the imported parasite Encarsia aurantii was released to control the scale; the parasite's establishment was confirmed in 1990. By the end of 1996, scale infestations on both native and introduced oaks in the park were reduced to levels approaching complete biological control.

Biological Control of Obscure Scale (Homoptera: Diaspididae) in California: An Experimental Approach

Obscure scale, Melanaspis obscura (Comstock), is native to the eastern half of the United States where it is associated with hosts in the genera Quercus, Carya, and Castanea. In its native home, the scale is exploited by a complex of natural enemies, including predators, parasites, and pathogens. Although obscure scale is generally maintained at low levels in natural habitats (presumably by natural enemies), it is a major pest of pin oak in urban areas and a minor pest of pecan. In 1962, an infestation of obscure scale was detected on oaks in Capitol Park in Sacramento, CA; efforts to eradicate the infestation were not successful, and this population became a target for classical biological control in 1981. Because the infestation was restricted and spread slowly, there was sufficient time for preintroductory investigations. Exploration for candidate natural enemies for importation into California was directed at parasites associated with obscure scale on pecan in southern Texas. Eleven species in 8 genera were recovered; the major species were Ablerus clisiocampae (Ashmead), Coccophagoides fuscipennis (Girault), Encarsia aurantii (Howard), and Physcus varicornis (Howard). Instead of releasing all of the major primary parasites (empirical approach), a more experimental approach was employed--that is, single-species release of E. aurantii. This species was chosen because of its thelyotokous reproduction, high egg load at emergence (highest among major primary parasites), and abundance in the native home of obscure scale. Over 11,000 females were released in 1988 and establishment was confirmed in 1990. From 1992-1994, the parasite population increased steadily while the abundance of scale crawlers declined by 3-fold; the crawler-to-parasite ratio declined from approximately 25 to approximately 7. Through selective pruning, parasitization by E. aurantii, and timing of insecticide treatments, obscure scale is now under integrated pest management (IPM) in Capitol Park, and it may eventually come under complete biological control. This project illustrates how preintroductory investigations both in the native home of the target pest and under quarantine conditions can be used to derive an introduction strategy in classical biological control. Some additional aspects of introduction strategy are discussed.

Effects of air pollution on the searching behaviour of an insect parasitoid

To assess the impact of air pollutants on the population dynamics of herbivores, the effects of pollutants on their natural enemies including predators, parasites, and pathogens must be evaluated in addition to direct effects and indirect effects mediated via the host plant. Insect parasitoids are an important group of such natural enemies providing many examples of partial or complete biological control of pest species. This study examined the effects of air pollutants (ozone (O3), sulphur dioxide (SO2), and nitrogen dioxide (NO2)) on the searching behaviour of insect parasitoids. A series of experiments comprising short-term, closed chamber fumigations of O3, SO2, and NO2 (100 nl l−1) of the braconid parasitoid (Asobara tabida) and aggregated distributions of its host larvae (Drosophila subobscura) was set up. Analysis of chamber results showed that the proportion of hosts parasitised and the searching efficiency of the parasitoids were both significantly reduced with O3 fumigation, but not with NO2 or SO2 fumigations. O3 fumigation reduced percentage parasitism by approximately 10%. Parasitoids were able to avoid patches with no hosts, both in filtered air controls and when exposed to pollutants. However in the O3 and NO2 treatments they appeared less able to discriminate between different host densities, suggesting that pollutants may interfere with the olfactory responses of the parasitoids. These results indicate the potential for air pollutants, particularly O3, to negatively influence the searching behaviour of parasitoids, and hence reduce the efficiency of natural enemy control of many pest species.

Evaluation of genetically improved strains ofMetaseiulus occidentalis(Nesbitt) (Acarina: Phytoseiidae) for integrated control of spider mites on roses in greenhouses

Biological control of spider mites is difficult in California greenhouses. Reliable supplies of high quality predators are lacking, available natural enemies are susceptible to pesticides, and predators are thought to be unable to regulate spider mites in sufficiently low densities to prevent economic loss, especially on ornamental plants. This paper evaluates the performance of genetically improved strains of a phytoseiid, Metaseiulus occidentalis (Nesbitt), that possess traits that could provide effective, permanent control of Tetranychus urticae Koch on roses. Laboratory tests determined the relative toxicity of 11 rose house pesticides to a non-diapausing, carbaryl- and organophosphorus-resist-ant strain of M. occidentalis and T. urticae. At normal label rates, acephate was the only one rated highly toxic to this predator strain. Carbaryl, pirimicarb, endosulfan, hexakis, dienochlor, benomyl, triforine, parinol, piperalin, and oxycarboxin were rated as having low toxicity to M. occidentalis. Hexakis and benomyl were toxic to T. urticae, endosulfan was moderately toxic, and all others exhibited low toxicity. The non-diapausing strain of M. occidentalis remained reproductive all year under simulated rose house conditions, whereas the diapausing strain did not. Biological attributes of the non-diapausing strain were sufficiently good to conclude this strain could be effective all year. Metaseiulus occidentalis was evaluated for its ability to regulate T. urticae on small noncommercial rose house plots during 2 years. Carbaryl, pirimicarb, triforine, oxycarboxin, hexakis, and dienochlor were successfully used for pest and disease control without disrupting the predators, confirming the laboratory data. Metaseiulus occidentalis is unlikely to provide complete biological control of T. urticae on greenhouse roses, however. Acaricidal control may be needed (using reduced rates) while M. occidentalis establishes, and following annual pruning. Large-scale commercial trials should be considered with the non-diapausing pesticide-resistant strain.

Cost of Biological Control of Weeds by Insects in Canada

The purpose of the paper is to permit the calculation of prospective costs before starting the biological control of a weed. The cost of the Canadian program from its start in 1950 to the end of 1976 was tabulated in scientist-years by target weed, agent, and the type of study done. This information and international data on the number of agents required to control a weed were used to calculate expected costs. A complete biological control program is likely to cost 18.8–23.7 scientist-years or currently $1.2 to 1.5 million and thus is only economic for use against major weeds. However, it is often possible to capitalize on studies done elsewhere, and under these circumstances biological control may be economic for solving more minor weed problems.

The establishment of two parasites of the diamond-back mothPlutella xylostella [Lep.: Plutellidae] in Trinidad, W.I.

The diamond-back moth,Plutella xylostella (L.) is a major pest of cruciferous crops in Trinidad, West Indies. Pesticides are applied as a control measure but it is now resistant to several of them. Indigenous parasitesApanteles aciculatus (Ashm.),Apanteles sp. (glomeratus group),Spilochalcis hirtifemora (Ashm.) andTrichogramma brasiliensis (Ashm.) are unable to exert economic control.Apanteles plutellae (Kurdj.) andTetrastichus sokolowskiiKurdj. were introduced and are now well established. It is recommended to introduce additional parasitesMacromalon sp. andThyraeella collaris (Grav.) in order to obtain complete biological control.

Complete Biological Control of Lepidosaphes beckii1 on Texas Citrus with Aphytis lepidosaphes23

The purple scale, Lepidosaphes beckii (Newman), has been reduced from the 4th most important pest of Texas citrus to an incidental pest by the introduced parasite, Aphytis lepidosaphes Compere. The evidence of complete biological control is the scarcity of the purple scale during 1971–73 and the ability of the parasite to suppress the relatively small numbers of scales that increase following applications of carbaryl, sulfur, and azinphosmethyl.

The Comstock Mealybug in California and Observations on Some of Its Natural Enemies1

Following discovery 1967 of Pseudococcus comstocki (Kuwana) infesting 10 square miles in the city of Porterville, Calif., efforts were undertaken (1) to assess the potential destructiveness of the pest; (2) to test the possibilities for its complete biological control; (3) to explore the feasibility of temporary biological, and mechanical containment practices: and (4) to collect facts pertinent to a decision by the California State Department of Agriculture as to whether eradicative measures should be undertaken. The probability of severe damage by this pest, should it spread to other California areas, appeared likely. Poor prospects for completely successful biological control were indicated from trials with 3 imported Japanese parasites: pseudaphycus malinus Cahan, Allotropa burrelli Muesebeck, and Clausenia purpurea Ishii. The results of these investigations of natural enemies and of the plant host relationships of the mealybug peculiar to the infested area suggest the desirability of certain chemical, biological, and mechanical containment practices until eradicative measures can be inaugurated.

Biological Control of Crown Gall: Field Measurements and Glasshouse Experiments

Summary: An ecological study showed that the pathogeniec form of Agrobacterium radiobacter (A.r. var. tumefaciens), biotype 2 was present in soil near galled almond seedlings, where it formed a significant proportion of the total biotype 2 population; the pathogen was not detected near healthy plants. One nonpathogenic biotype 2 isolate was able, when present in numbers approximately equal to the pathogen, to prevent crown gall induction in tomato and peach seedlings. This isolate gave complete biological control of crown gall in a glasshouse test. Six other nonpathogenic isolates did not significantly inhibit gall induction by equal numbers of the pathogen. In the field, gall induction probably depends on the size of the population of the pathogen (both absolutely and relative to that of the nonpathogen) at a wound site and on the inhibitory efficiency of the nonpathogen.

SOME ASPECTS OF ASSESSING EFFICIENCY OF NATURAL ENEMIES

AbstractDrawing retrospectively and collectively on results of a single individual and his associates covering some 22 years of field and laboratory studies, the authors present three documented case histories of technically complete biological control. They use these examples to illustrate the potential for greater use of this method of pest control, and they discuss the theory of biological control as related to whether or not introductions of a complex of enemy species will inherently lead to competitive interference and a lesser degree of control than if only the "best" species were introduced. They conclude that the three case histories are a refutation of this thesis, as are certain theoretical considerations, and the net results from all biological control programs on a worldwide basis.The authors also point to weaknesses in the use of currently available methods for quantitatively rating or appraising the control and regulating power of density-dependent factors that act with a lag (entomophagous parasites and predators), and emphasize chat regression and modelling methods should be used in conjunction with "check-methods" or other experimental means.

Root infection by ascospores of Ophiobolus graminis as a factor in epidemiology of the take-all disease

No infection of wheal seedling toots by ascospores of Ophiobolus graminis (Sacc.) Sacc. could be obtained when the roots were growing through unsterilized soil or sand, though infection of roots in completely sterilized soil or sand was readily obtained, thus confirming an earlier report by Garrett (1939) . But ascospores were regularly able to infect the exposed proximal pari of the seminal roots of wheat seedlings sown on the surface of natural, unsterilized soil. Further experiments have led to the conclusion that the normal soil microflora exerts a virtually complete biological control of ascospore infection of roots growing within the soil, usually by inhibiting ascospore germination. The occurrence of ascospore infection, in the manner described above, is thought to explain the origin of past outbreaks of take-all in wheat crops grown on the newly drained polders of the former Zuider Zee in the Netherlands.