Biological Control Of Insect Pests Research Articles

Biological control of insect pests on oilseed rape in Europe

Biological control of insect pests on oilseed rape in Europe

Response of an aphid parasitoid, Aphelinus asychis to its host, plant, host‐plant complex, and to malathion

Abstract Aphelinus asychis (Walker) can be valuable as a biocontrol agent of the aphid, Schizaphis graminum (Rondani), a major pest on grain crops in the United States. This study reports the wind tunnel, and olfactometric responses of this parasitoid to the host (aphid), plant (sorghum), and host‐plant complex (aphid‐infested sorghum). In addition, the parasitoids' response to malathion‐treated plants is also presented. The goal of the present study was to test the hypothesis that volatiles associated with the host attract natural enemies, as reported in cases of many hymenopterous parasitoids, and also to learn about the effects of insecticides on these parasitoids. In wind tunnel studies, these parasitoids moved upwind in the direction of the host‐infested plant. There was no direct flight observed, however, these parasitoids were observed to hop and jump, and sometimes walk to their host. In the olfactometer experiments, we found that A. asychis is attracted to host‐plant complex. The parasitoids' response to malathion in the olfactometer suggested that a malathion formulation when applied to plants can lure these beneficials, thus providing new insight into the ongoing task of integrating chemical and biological control of insect pests.

Gut Colonization by an Ice Nucleation Active Bacterium,Erwinia(Pantoea)ananasReduces the Cold Hardiness of Mulberry Pyralid Larvae

To evaluate the suitability of using ice nucleation active (INA) bacteria for the biological control of insect pests, the supercooling point (SCP) of larvae of mulberry pyralid,Glyphodes duplicalis,and silkworm,Bombyx mori,ingesting INA strains ofErwinia(Pantoea)ananasandPseudomonas syringaewas determined. Mean SCP of the guts of silkworm larvae ingesting INA strains ofE. ananasranged from −2.5 to −2.8°C, being 5°C higher than that in control treatments. Similarly, mean SCP of mulberry pyralid larvae ingesting INA strain ofE. ananas,which can grow well in the gut, was −4.7°C at 3 days after treatment, being 6.5°C higher than that in control treatments. On the other hand, mean SCP of the larvae-ingesting INA strain ofP. syringae,which cannot grow in the gut, was −9.0°C at 3 days after treatment, rising by only 2.5°C higher than that in the control treatments. In addition, more than 80% of the larvae of mulberry pyralid ingesting the INA strain ofE. ananasfroze and eventually died when exposed to −6°C for 18 h, while only 36% of the larvae ingesting the INA strain ofP. syringae,or approximately 20% of the control larvae, froze and died. Thus, the gut colonization by INA strains ofE. ananasreduced remarkably the cold hardiness of the insects. These findings suggest that INA strains ofE. ananascould be effective as a potential biological control agent of insect pests.

The effects of parasitoid fecundity and host taxon on the biological control of insect pests: the relationship between theory and data

Summary1. A simple, intuitive argument and the tenets of the biological control literature both suggest that, in general, parasitoids with a greater fecundity will provide better control of their hosts, and will thus be better biological control agents.2. A model of host‐parasitoid dynamics, based on the standard Thompson–Nicholson–Bailey approach and incorporating the effects of parasitoid fecundity‐limitation and host density‐dependence, also indicates that as parasitoid fecundity decreases so does local stability and the degree of host suppression.3. A taxonomically diverse data set obtained from the biological control record failed to support this theoretical prediction, but at the same time indicated a strong effect of host taxon on the outcome of biological control.4. The hypothesis that the fecundity of parasitoids is correlated positively with their ability to suppress host populations is supported by data exclusively from the host order Lepidoptera.5. Possible explanations for the divergence between the fecundity‐limitation hypothesis and the complete data set include: the ability of parasitoids to provide long‐term control of pests without the presence of a stable host–parasitoid equilibrium; differences between the concepts of successful control in theory and practice; evolutionary trade‐offs between fecundity and other parasitoid life‐history features, such as search efficiency, leading to better pest control by parasitoids with low fecundity; and differing windows of vulnerability to parasitoid attack between host taxa.

Chitinases in biological control.

The public concern over the harmful effects of chemical pesticides on the environment and human health has enhanced the search for safer, environmentally friendly control alternatives. Control of plant pests by the application of biological agents holds great promise as an alternative to the use of chemicals. It is generally recognized that biological control agents are safer and more environmentally sound than is reliance on the use of high volumes of pesticides. Due to the importance of chitinolytic enzymes in insect, nematode, and fungal growth and development, they are receiving attention in regard to their development as biopesticides or chemical defense proteins in transgenic plants and microbial biocontrol agents. In this sense, biological control of some soil-borne fungal diseases has been correlated with chitinase production. Fungi- and bacteria-producing chitinases exhibit antagonism against fungi, and inhibition of fungal growth by plant chitinases has been demonstrated. Insect pathogenic fungi have considerable potential for the biological control of insect pests. Entomopathogenic fungi apparently overcome physical barriers of the host by producing multiple extracellular enzymes including chitinolytic enzymes, which help to penetrate the cuticle and facilitate infection. In this chapter, the role of chitinases in biological control and their potential use in the improvement of biocontrol agents and crop plants by genetic engineering is analyzed in view of recent findings.

Ecological Characterization ofSteinernema rarum

Entomopathogenic nematodes are used for inundative biological control of insect pests but also have potential for use in augmentative and/or inoculative biological control. Numerous new species are being described but generally, little information is provided on their ecology. Moreover, many species have been described previously without subsequent ecological information. This paper presents a number of simple experiments examining a nematode's physiological host range, host-foraging behavior, thermal activity range, and soil moisture activity range that provides the basic information necessary for further studies of a new species as a biological control agent. We suggest that any taxonomic description of new species should be combined with such an ecological study. This kind of information should also be generated for species in which no ecological studies have been done. In our study, we found that the entomopathogenic nematodeSteinernema rarumwhich was described in 1986 infected a wide range of arthropod species under laboratory conditions but appeared to be best adapted to lepidopteran larvae as hosts. It used an intermediate foraging strategy infecting both mobile hosts on the soil surface and sedentary hosts below the soil surface efficiently. The range of soil moisture at whichS. rarumwas effective suggested an adaptation to the fluctuating soil moisture in the upper soil layers. Its temperature optimum of 25°C corresponded well to the warm temperate climate of its area of origin in Argentina. The optimal storage temperature was around 15°C. Our study suggests thatS. rarumis well adapted to lepidopteran hosts with larvae spending part of their live on the soil surface and/or that pupate in the soil.

Effects of Iberis umbellata (Brassicaceae) on Insect Pests of Cabbage and on Potential Biological Control Agents

Noncrop borders surrounding field crops may enhance biological control of insect pests by drawing pests away from the crop and by providing a suitable habitat for natural enemies. We quantified the effects of borders of flowering Iberis umbellata L. (candytuft) on cabbage pest and predator abundance by repeatedly sampling arthropod abundance in plots of Brassica oleracea L. I. umbellata provides potential food for crucifer herbivores as well as nectar and pollen resources for predators. Although I. umbellata harbored large populations of hemipteran predators, few of these predators were found on the adjacent crop plants. Iberis borders did not change the abundance of crop pests within the crop but had mixed effects on natural enemies. Interestingly, the spatial distribution of Pieris rapae L. and Trichoplusia ni (Hübner) eggs on B. oleracea differed significantly between treatments, indicating that the presence of flowering I. umbellata may have altered the movement and oviposition behavior of these lepidopteran pests. Our results point to the importance of considering predator and pest movement when investigating how alternative habitats, such as flowering borders, affect arthropod population dynamics.

Ecology in the service of biological control: the case of entomopathogenic nematodes.

Biological control manipulations of natural enemies to reduce pest populations represent large-scale ecological experiments that have both benefited from and contributed to various areas of modern ecology. Unfortunately, economic expediency and the need for rapid implementation often require that biological control programs be based more on trial and error than on sound ecological theory and testing. This approach has led to some remarkable successes but it has also produced dismal failures. This point is particularly well illustrated in the historical development and use of entomopathogenic nematodes for the biological control of insect pests. Intense effort has focused on developing these natural enemies as alternatives to chemical insecticides, in part because laboratory assays indicated that these nematodes possess a broad host range. This illusory attribute launched hundreds of field releases, many of which failed due to ecological barriers to infection that are not apparent from laboratory exposures, where conditions are optimal and host-parasite contact assured. For example, the entomopathogenic nematode Steinernema carpocapsae is a poor choice to control scarab larvae because this nematode uses an ambusher foraging strategy near the soil surface whereas the equally sedentary scarab remains within the soil profile, shows a weak host recognition response to scarabs, has difficulty overcoming the scarab immune response, and has low reproduction in this host. Conversely, two other nematodes, Heterorhabditis bacteriophora and S. glaseri, are highly adapted to parasitize scarabs: they use a cruising foraging strategy, respond strongly to scarabs, easily overcome the immune response, and reproduce well in these hosts. Increased understanding of the ecology of entomopathogenic nematodes has enabled better matches between parasites and hosts, and more accurate predictions of field performance. These results underline the importance of a strong partnership between basic and applied ecology in the area of biological control.

On the ethics of biological control of insect pests

Of the four types of biological control, (1) natural, (2) conservation, (3) augmentation, and (4) importation), ethical concerns have been raised almost exclusively about only one type: importation. These concerns rest largely on fears of extinction of animal species. Importation biological control is a cost-effective alternative to chemical control for basic food crops of resource-poor farmers. Regarding the other types of biological control, natural biological control is not consciously manipulated by humans. Augmentation has some technical concerns, but is generally an environmentally-sound, viable alternative to chemicals and offers local employment. Conservation can help empower farmers to preserve native species, while saving labor and money and reducing chemical insecticides.

Culture of 1–2 cell bovine embryos in oviducts of heifers

Several entomopathogenic nematode species are currently under evaluation for mass production and field efficacy for biological control of insect pests. However, quality and quantity of in vitro-produced entomopathogenic nematodes vary considerably, depending on media, temperature, and production method. In addition, nematode production should be cost effective. We investigated nematode yield, production time, total lipid content, and fatty acid composition of Heterorhabditis bacteriophora produced in artificial media supplemented with different lipid sources. Lipid source significantly affected lipid quantity and quality in H. bacteriophora. Media supplemented with extractable insect lipids produced yields 1.9 times higher than did beef fat- or lard-supplemented media. Moreover, the developmental rate in media supplemented with host lipids was 1.7 times faster than that in media supplemented with beef fat or lard. Nematodes grown in media supplemented with insect lipids accumulated significantly higher lipid proportion per dry biomass than those grown in media supplemented with other lipid sources. H. bacteriophora produced in media supplemented with insect lipids, olive oil, or canola oil had similar fatty acid patterns, with oleic (18:1) acid as the major lipid fatty acid. Media supplemented with other lipid sources produced nematodes with fatty acid patterns different from those of media supplemented with insect lipids. We recommend addition of fatty acid mixtures that resemble natural host lipids for mass-producing entomopathogenic nematodes. This could provide nematode quality similar to in vivo-produced nematodes and could improve yield.

Theory for Biological Control: Recent Developments

It has been argued that ecological theory has not been useful to the practice of biological control. The purpose of this article is to show how recent theoretical advances may reverse this situation. We first discuss four issues that have arisen in the development of theory for biological control. (1) Recent work has clarified and resolved earlier disagreements concerning the effect of aggregation of the parasitoid to local host density on the stability of parasitoid—host models; this work emphasizes that such aggregation increases the ability of the parasitoid to reduce pest density. (2) There has been disagreement over the conditions under which stability, in the mathematical sense and on a local spatial scale, is an appropriate goal for classical biological control of insect pests, and whether a metapopulation may sometimes provide a more appropriate framework. We also comment on (3) relative size of refuges, which has been proposed as a unifying concept, and (4) density dependence and ratio dependence. We then discuss recent models using a stage—structured approach, particularly those that compare potential biological control agents or agents that have been differentially successful in practice. We argue that this approach has already produced valuable insights into the factors operating in several field situations. It demonstrates the importance of identifying which pest stages are most injurious to the crop, since the natural enemy that wins in competition may not be the most effective at suppressing the crucial pest stage(s): in general, the winning parasitoid reduces the density of the host stage attacked by its competitor below the level at which the latter can maintain a positive growth rate when at low density. A useful criterion is that pest equilibrium density is suppressed most by the parasitoid species that needs the fewest host individuals to allow a female parasitoid to replace herself in the next generation. Caveats are that this may apply only under equilibrium conditions and that the pest stage most suppressed is the one we wish to control. We discuss the connection between successful biological control and evolutionary considerations.

Rearing beneficial insects for biological control purposes in resource poor areas of africa

Biological control of insect pest and weeds using beneficial insects in resource poor areas is not very well supported. Poor funding has affected in particular the importation of classical biological control agents, quarantine, rearing, research facilities, and the research programmes.

Traditional knowledge and rationale for weaver ant husbandry in the Mekong delta of Vietnam

The weaver ant, Oecophylla smaragdina Fabricius (Hymenoptera: Formicidae), has long been known as perhaps the first example of human manipulation of a natural predator population to enhance the natural biological control of insect pests. The practice of ant husbandry in Vietnamese citrus orchards and the knowledge associated with the use of weaver ants in the Mekong delta are described. In contrast to other regions of Asia, where weaver ants are noted for their role in the protection of citrus from insect damage, citrus farmers in the Mekong delta explain the benefits of ant husbandry in terms of an improvement in fruit quality, likened to the influence of fertilizers, that occurs in direct response to excretory products deposited by the weaver ants as they patrol the fruit. A series of tests, carried out in 1993–94, rated the external shine, sweetness, juiciness, and overall appeal, as characteristics of fruit quality, for paired comparisons of sweet orange, mandarin, and pummelo fruit that had been grown in the presence of weaver ants or from which ants had been excluded. The tests indicate a strong influence of the presence of the weaver ant on external shine, juiciness, and overall appeal for each of the citrus fruits, but particularly for mandarin. The significance of these results and ant husbandry practices in the Mekong delta are discussed in relation to the development of citrus production in Vietnam.

Biological Control of Insect Pests in Turfgrass

Biological Control of Insect Pests in Turfgrass

"Strains" and the classical biological control of insect pests

The classical biological control technique of introducing two or more populations of the same species of beneficial agent to increase the genetic diversity of that species (and so increase the chances of achieving a successful project) is reviewed. From standard literature sources, all cases of multiple introductions of conspecific populations against insect targets were listed and the effect of subsequent introductions on the outcome of the project was recorded. Of 178 projects identified, involving 417 separate importations, only 11 (6.2%) were successful through a second or later importation of the same morphologically defined species of beneficial agent. Of these, five involved host-related "strains" that are likely to be cryptic species, so the success rate for the introduction of conspecific populations falls to 3.4%. The possibility that some (or even all) of the other six cases also involved cryptic species awaits investigation. Our analysis demonstrates that introducing two or more populations of the same species is less likely to result in enhanced success than if other species of natural enemies are sought for "normal" classical biological control (historical success rate 12–16%). In our discussion we focus on the genetic theory of species which underpins this area of applied biology and find that there is also no theoretical support for the continued introduction of strains.

Potential of Plant Cystatins for the Production of Transgenic Strawberry Plants Resistant to the Black Vine Weevil

Transformation of plant genomes with cysteine proteinase inhibitor (cystatin) genes represents an attractive option for the biological control of insect pests. However, this strategy must be carefully considered, because the transgenic plant endogenous proteinases may represent potential target enzymes for the exogenous inhibitors produced. For example, we are considering the transformation of strawberry (Fragaria ×ananassa) with cystatin cDNA clones, to control the Coleoptera pest black vine weevil (BVW; Otiorynchus sulcatus). Electrophoretic analyses of adult BVW proteinases have revealed the involvement of at least five proteinase forms for protein digestion, and the major form was strongly inhibited by oryzacystatins (OCI and OCII), two cystatins isolated from rice seeds. A similar analysis of proteinases showed the existence of OC-sensitive proteinase activity in the leaves of strawberry, suggesting a possible risk of interference of the inhibitors in the transformed plants. In addition, the two rice inhibitors were rapidly hydrolyzed at 25C when incubated with proteinase extracts from either young, mature or senescent leaves. An efficient control of BVW by plant cystatin-expressing transgenic strawberry plants is therefore potentially possible, but the correct targeting of the inhibitors in the plant cells using appropriate signal peptides could be necessary.

Chaos: A potential problem in the biological control of insect pests

Erratic variations are normally observed in the populations of insect pests that destroy crop plants. To establish a scientific basis for developing effective control procedures, we have developed a model system for the European Corn Borer (ECB) ( Ostrinia nubilalis) for which extensive field data, as well as laboratory results, have been accumulated during the past four decades. The model includes both a natural ECB pathogen and a genetically engineered toxin-producing agent as possible means of biological control. Our aim was to determine the conditions that could cause the population to vary erratically, as observed in the field. The erratic behavior in our simulations was analyzed to determine whether it is chaotic; chaos is a distinct type of erratic behavior which shows extreme sensitivity to initial conditions, i.e., the starting size of the population. Our simulations show that an increase in the death rate of the infected ECB, or a decrease in the birth rate of uninfected ECBs from infected ones, variables that are known to be affected by weather conditions, can induce a chaotic regime in which ECB population peaks reach values far higher than before chaos set in. Population peaks are even greater in the presence of both biological control agents. The results show that a biological control regime cannot be effective under conditions that induce chaotic population dynamics. Microcosm studies could be used to determine whether this situation would occur in the field.

Transmission Dynamics of a Virus in a Stage‐Structured Insect Population

Despite the blossoming interest in host—microparasite epidemiology, and in use of viruses in the biological control of insect pests, few empirical studies have attempted to quantify transmission and mortality rates under field conditions. We report a laboratory and field study in which the transmission parameter (u) and mortality rate (a) due to nuclear polyhedrosis virus (NPV) are measured in different larval instars of the cabbage moth, Mamestra brassicae (Lepidoptera: Noctuidae). Laboratory studies of food consumption and virus susceptibility were used to produce crude estimates of relative transmission rates in successive instars. Increased in the rate of feeding outstrip increases in virus resistance with instar, so we predict that transmission rates should increase in older larvae (assuming rate of intake of virus to be proportional to rate of feeding). This prediction was tested in a field experiment in which a constant initial density of susceptible and infected (moribund) larvae were reared together on cabbage plants for 2—8 d. Estimates of the linear transmission parameter (u) did not differ between instars and gave a mean value of 2.16 x 10—12 for all instars and time points. Causes for the discrepancy between predictions based on laboratory data and field measurements are discussed. Differences were found between instars in the time from infection to death (?) (equivalent to 1/a, where @a is the rate of mortality due to viral infection). Second—instar larvae died more rapidly once infected than third instars, which, in turn, died more rapidly than fourth instars. The effect of host population stage structure on patterns of viral infection can be pronounced and if recognized, may significantly increase the accuracy and predictive value of models of host pathogen systems.

The chemistry of eavesdropping, alarm, and deceit.

Arthropods that prey on or parasitize other arthropods frequently employ those chemical cues that reliably indicate the presence of their prey or hosts. Eavesdropping on the sex pheromone signals emitted to attract mates allows many predators and parasitoids to find and attack adult insects. The sex pheromones are also useful signals for egg parasitoids since eggs are frequently deposited on nearby plants soon after mating. When the larval stages of insects or other arthropods are the targets, a different foraging strategy is employed. The larvae are often chemically inconspicuous, but when they feed on plants the injured plants respond by producing and releasing defensive chemicals. These plant chemicals may also serve as "alarm signals" that are exploited by predators and parasitoids to locate their victims. There is considerable evidence that the volatile "alarm signals" are induced by interactions of substances from the herbivore with the damaged plant tissue. A very different strategy is employed by several groups of spiders that remain stationary and send out chemical signals that attract prey. Some of these spiders prey exclusively on male moths. They attract the males by emitting chemicals identical to the sex pheromones emitted by female moths. These few examples indicate the diversity of foraging strategies of arthropod predators and parasitoids. It is likely that many other interesting chemically mediated interactions between arthropod hunters and their victims remain to be discovered. Increased understanding of these systems will enable us to capitalize on natural interactions to develop more ecologically sound, environmentally safe methods for biological control of insect pests of agriculture.

Effects of Mechanical Handling on Green Lacewing Larvae (Chrysoperla Rufilabris)

Lacewing larvae (Chrysoperla rufilabris), used for biological control of insect pests, are typically released by hand for treatment of small-scale ornamental and fruit crops. This study investigated the potential for mechanical release of larvae. Second instar larvae were mixed into vermiculite and rice hull carriers and subjected to vibrational and rotational motion. The number of live, mobile larvae reclaimed from the treated material was determined. While the mechanical treatments did not significantly reduce the number of mobile larvae recovered, rotation resulted in slightly greater larval damage than vibration.