Use Of Biological Control Agents Research Articles

Susceptibility of Duponchelia fovealis Zeller (Lepidoptera: Crambidae) to Soil-Borne Entomopathogenic Fungi.

Duponchelia fovealis (Lepidoptera: Crambidae) is an invasive species that has had a large impact on strawberry crops in Brazil. Pesticides have had limited effectiveness and the use of biological control agents to improve its management is the most appropriate approach. The aim of this study was to evaluate the pathogenicity and virulence of entomopathogenic fungi—isolated from soil—against Duponchelia fovealis larvae under laboratory and greenhouse conditions. Pathogenicity screenings were performed for twenty isolates from Beauveria bassiana, Beauveria caledonica, Isaria javanica, Metarhizium anisopliae, and Lecanicillium sp. against third instar larvae of D. fovealis at the concentration of 109 conidia·mL−1. Lethal concentration (LC50) and lethal time (LT50) were determined for the most pathogenic isolates and for one commercial mycoinsecticide. Mortality rates varied from 10 to 89%. The isolates B. bassiana Bea1, Bea110, Bea111 and I. javanica Isa340 were the most pathogenic. The most virulent isolates were B. bassiana Bea111 and I. javanica Isa340 with LC50 values of 2.33 × 106 and 9.69 × 105 conidia·mL−1, respectively. Under greenhouse conditions, the efficacy of LC50 of the isolates I. javanica Isa340 and B. bassiana Bea111 were 45% and 52%, respectively. Our results indicate that these isolates are strong candidates for application in the control of D. fovealis. This study is the first evaluation of soil-borne entomopathogenic fungi against D. fovealis.

Transcriptional Changes in Mycorrhizal and Nonmycorrhizal Soybean Plants upon Infection with the Fungal Pathogen Macrophomina phaseolina.

Macrophomina phaseolina is a soil-borne fungal pathogen with a wide host range that causes charcoal rot in soybean [Glycine max (L.) Merr.]. Control of the disease is a challenge, due to the absence of genetic resistance and effective chemical control. Alternative or complementary measures are needed, such as the use of biological control agents, in an integrated approach. Several studies have demonstrated the role of arbuscular mycorrhizal fungi (AMF) in enhancing plant resistance or tolerance to biotic stresses, decreasing the symptoms and pressure caused by various pests and diseases, including M. phaseolina in soybean. However, the specific contribution of AMF in the regulation of the plant response to M. phaseolina remains unclear. Therefore, the objective of the present study was to investigate, under strict in-vitro culture conditions, the global transcriptional changes in roots of premycorrhized soybean plantlets challenged by M. phaseolina (+AMF+Mp) as compared with nonmycorrhizal soybean plantlets (-AMF+Mp). MapMan software was used to distinguish transcriptional changes, with special emphasis on those related to plant defense responses. Soybean genes identified as strongly upregulated during infection by the pathogen included pathogenesis-related proteins, disease-resistance proteins, transcription factors, and secondary metabolism-related genes, as well as those encoding for signaling hormones. Remarkably, the +AMF+Mp treatment displayed a lower number of upregulated genes as compared with the -AMF+Mp treatment. AMF seemed to counteract or balance costs upon M. phaseolina infection, which could be associated to a negative impact on biomass and seed production. These detailed insights in soybean-AMF interaction help us to understand the complex underlying mechanisms involved in AMF-mediated biocontrol and support the importance of preserving and stimulating the existing plant-AMF associates, via adequate agricultural practices, to optimize their agro-ecological potential.

Trichoderma asperellum isolated from African maize seed directly inhibits Fusarium verticillioides growth in vitro

Maize is a globally important crop that is affected by fungal diseases causing yield losses annually. One fungus, Fusarium verticillioides, causes the disease Fusarium Ear Rot (FER), which reduces grain quality and produces mycotoxins called fumonisins that are harmful to animals and humans. As chemical fungicides are expensive and have negative environmental effects, the use of biological control agents (BCAs) has become favourable in recent years. A commonly used fungal BCA is Trichoderma spp., which has been effective in reducing disease incidence as well as enhancing crop growth. In this study, T. asperellum was isolated from an African maize line and was shown to significantly inhibit growth of F. verticillioides in an in vitro competition assay.

Daun Mimba, Sirih, dan Pahitan sebagai Fungisida Nabati: Efektifitas dan Kompatibelitasnya dengan Trichoderma untuk Pengendalian Penyakit Akar Gada (Plasmodiophora brassicae)

<p>The research aims to evaluate effectiveness of leaf extract oh neem, piper, and eupathorium as botanical pesticide and its compatibility which use of biological control agents <em>Trichoderma </em>for control of club root disease. The test conducted in greenhouse belong to Faculty of Agriculture, University of Sebelas Maret at Surakarta., on June till September 2004. The research used completely randomized design with 3 replications consisted 10 soil treatments before planting using leaf extract of neem (<em>Azadirachta indica</em>), Piper betle, and <em>Eupathorium inulifolium </em>and <em>Trichoderma </em>or its combinations. As dependent variables are disease severity, weight of health root, weight of fresh biomass and dryy biomass.</p><p>The result of the research showed that soil treatment using leaf extract of neem, piper, and euphatorium could reduce effectively disease severity of club root. Treatment combinations of leaf extract of neem, piper, and euphatorium could increase effectiveness of control of club root and compatible with soil treatment using <em>Trichoderma </em>so it could increase effectiveness of the disease control.</p>

Tapping the marvelous power of microorganisms for sustainable disease management

In recent years there are increasing concerns regarding insufficient disease control with fungicides due to development of fungicide resistant pathogen population and presence of fungicide residues above the specified maximum residue levels at harvest in many agricultural commodities. This has once again emphasized on the need for increased use of biological control agents for safe and sustainable crop protection. Microorganisms like Trichoderma, Bacillus and Pseudomonas have a multi-pronged bio-control mechanism hence there is no known instance of development of resistance in pathogens against them. On the other hand they are effective against fungicide resistant pathogen population and can be useful in resistant management programs. In the last half a century, a vast number of native bio-control strains have been isolated, evaluated and found useful for control of a number of plant diseases. These studies focused on control of a particular disease on a particular commodity in a particular region and thus a large number of effective native strains were identified for each pathogen-commodity-location. A very large numbers of local firms entered into the business of production and supply of these strains to nearby farmers, but in many instances the biocontrol products did not meet the minimum quality requirements and resulted in lower than expected disease control in field. This hurdle in the successful exploitation of these microorganisms can be overcome, if the production is on a larger commercial scale which may be possible only if the number of bio-control strains are few. Hence, it is essential to identify one or two super-efficient strains, from the available isolates, for multiple disease control under a wide geographical area. The larger market demand for such a superior strains would encourage the necessary investment in development of effective formulations and delivery systems. However, concerted efforts by all stakeholders will be essential to make bio-control a reality in today’s agricultural scenario.

Indigenous Pseudomonas spp. Strains from the Olive (Olea europaea L.) Rhizosphere as Effective Biocontrol Agents against Verticillium dahliae: From the Host Roots to the Bacterial Genomes.

The use of biological control agents (BCA), alone or in combination with other management measures, has gained attention over the past decades, driven by the need to seek for sustainable and eco-friendly alternatives to confront plant pathogens. The rhizosphere of olive (Olea europaea L.) plants is a source of bacteria with potential as biocontrol tools against Verticillium wilt of olive (VWO) caused by Verticillium dahliae Kleb. A collection of bacterial isolates from healthy nursery-produced olive (cultivar Picual, susceptible to VWO) plants was generated based on morphological, biochemical and metabolic characteristics, chemical sensitivities, and on their in vitro antagonistic activity against several olive pathogens. Three strains (PIC25, PIC105, and PICF141) showing high in vitro inhibition ability of pathogens' growth, particularly against V. dahliae, were eventually selected. Their effectiveness against VWO caused by the defoliating pathotype of V. dahliae was also demonstrated, strain PICF141 being the rhizobacteria showing the best performance as BCA. Genotypic and phenotypic traits traditionally associated with plant growth promotion and/or biocontrol abilities were evaluated as well (e.g., phytase, xylanase, catalase, cellulase, chitinase, glucanase activities, and siderophore and HCN production). Multi-locus sequence analyses of conserved genes enabled the identification of these strains as Pseudomonas spp. Strain PICF141 was affiliated to the “Pseudomonas mandelii subgroup,” within the “Pseudomonas fluorescens group,” Pseudomonas lini being the closest species. Strains PIC25 and PIC105 were affiliated to the “Pseudomonas aeruginosa group,” Pseudomonas indica being the closest relative. Moreover, we identified P. indica (PIC105) for the first time as a BCA. Genome sequencing and in silico analyses allowed the identification of traits commonly associated with plant-bacteria interactions. Finally, the root colonization ability of these olive rhizobacteria was assessed, providing valuable information for the future development of formulations based on these strains. A set of actions, from rhizosphere isolation to genome analysis, is proposed and discussed for selecting indigenous rhizobacteria as effective BCAs.

Effects of Metarhizium anisopliae on host choice of the bee-parasitic mite Varroa destructor

The ectoparasitic mite Varroa destructor poses one of the biggest threats to the western honeybee Apis mellifera. Possibilities to control the mites are limited; therefore, it is important to assess the performance of novel alternatives like the use of biological control agents. The goal of our work was to evaluate the effects of the entomopathogenic fungus Metarhizium anisopliae var. anisopliae BIPESCO 5, which is a potential biological control agent against the bee parasitic mite V. destructor, on the behavior of the parasite. In detail, we investigated whether the presence of fungal spores on the surface of host nurse bees, A. mellifera, affects the host choice behavior of adult female mites. We conducted two behavioral assays to monitor the behavior of the mites towards adult bees inoculated with a solution of fungal spores. Both choice and no-choice experiment revealed that M. anisopliae has a significant repellent influence on V. destructor‘s host selection behavior. The mites preferred, and stayed longer on, nurse bees free from fungal spores over bees carrying fungal spores. Our study provides the first evidence of sub-lethal behavioral effects of a fungal biocontrol agent against Varroa mites.

Use of biocontrol agents and botanicals in integrated management of Botrytis cinerea in table grape vineyards.

There is increasing interest in the use of biological control agents (BCAs) and botanicals (BOTs) due to increasing awareness of the environmental and human health risks associated with synthetic plant protection products. The BCAs Bacillus subtilis strain QST713, Bacillus amyloliquefaciens strain D747 and Aureobasidium pullulans strains DSM14940 and DSM14941, and the BOTs Melaleuca alternifolia and terpenic extracts are proposed for the control of grey mould in vineyards. This study was aimed at evaluating their effectiveness in integrated crop management strategies and their outcomes in terms of the management of fungicide resistance and residues. In field trials carried out on table grapes in southern Italy, use of BCAs or BOTs alternately or mixtures of BCAs or BOTs with the succinate dehydrogenase inhibitor fungicide fluopyram showed efficacy of up to 96% against grey mould on bunches, comparable with the chemical reference strategy (up to 87%). By contrast, use of BCAs or BOTs (up to 11 sprays) alone was not effective (< 30%) under high disease pressure. The integrated use of BCAs or BOTs reduced the spread of succinate dehydrogenase inhibitor-resistant conidia, as well as fungicide residues in grapes. Spray schedules based on integration of BCAs or BOTs with fungicides are effective against grey mould and reduce the risk of fungicide resistance in B. cinerea and fungicide residues in grapes. © 2017 Society of Chemical Industry.

English

In Mexico, fruit flies (Anastrepha Schiner) are one of the main pests that affect production and limit the commercialization of fresh fruits. In regions producing municipalities such as Ruiz (Nayarit), the insect is actively multiplying in marginal areas, in fruits such as Mangifera indica L. (mango), Psidium guajava L. (guava), Spondias sp. (jobo) and Psidium sartorianum (Berg), from where they move to commercial orchards. An alternative solution is the use of biological control agents, which is why, in 2012, the population fluctuation of Anastrepha species and the effectiveness of augmentative releases of the parasite, Diachasmimorpha longicaudata Ashmead (Hymenoptera: Braconidae) on the pest were determined. Of 2,853 fruits and 1,690 larvae, 740 adults of Anastrepha emerged (395 females, 345 males: sexual ratio of 1: 0.87): Anastrepha obliqua (422), Anastrepha striata (208) and Anastrepha ludens (110), with 545 parasitoids recovered (265 females, 280 males: sexual ratio 1: 1.06), and annual mean parasitism of 42.41%, where the highest value corresponded to December (69.57%) and the greatest impacts of parasitism was on P. sartorianum (62.50%). &nbsp; Key words: Fruit flies, Diptera-Tephritidae, Anastrepha species, Hymenoptera-Braconidae, parasitoid releases, parasitism.

Entomopathogenic fungi and nematodes against larvae of the chestnut weevil, Curculio elephas (Coleoptera: Curculionidae): a laboratory evaluation

ABSTRACTPest control in chestnut orchards is mainly achieved by chemicals, but there is growing focus on the potential use of biological control agents. The larval susceptibility of the chestnut weevil Curculio elephas L. (Coleoptera: Curculionidae) to different strains/species of entomopathogenic fungi and nematodes was evaluated in laboratory by soil cup bioassays. In the experiments with fungi, a wild strain of Metarhizium anisopliae caused the highest larval mortality (about 90%) compared with a commercial and a wild strain of Beauveria bassiana (80% and 77% respectively). Regarding nematodes, the commercial strain of Heterorhabditis bacteriophora was more effective in the control of chestnut larvae (77% insect mortality) than Steinernema carpocapsae (43%).

Chitosan Increases Tomato Root Colonization by Pochonia chlamydosporia and Their Combination Reduces Root-Knot Nematode Damage.

The use of biological control agents could be a non-chemical alternative for management of Meloidogyne spp. [root-knot nematodes (RKN)], the most damaging plant-parasitic nematodes for horticultural crops worldwide. Pochonia chlamydosporia is a fungal parasite of RKN eggs that can colonize endophytically roots of several cultivated plant species, but in field applications the fungus shows a low persistence and efficiency in RKN management. The combined use of P. chlamydosporia with an enhancer could help its ability to develop in soil and colonize roots, thereby increasing its efficiency against nematodes. Previous work has shown that chitosan enhances P. chlamydosporia sporulation and production of extracellular enzymes, as well as nematode egg parasitism in laboratory bioassays. This work shows that chitosan at low concentrations (up to 0.1 mg ml-1) do not affect the viability and germination of P. chlamydosporia chlamydospores and improves mycelial growth respect to treatments without chitosan. Tomato plants irrigated with chitosan (same dose limit) increased root weight and length after 30 days. Chitosan irrigation increased dry shoot and fresh root weight of tomato plants inoculated with Meloidogyne javanica, root length when they were inoculated with P. chlamydosporia, and dry shoot weight of plants inoculated with both P. chlamydosporia and M. javanica. Chitosan irrigation significantly enhanced root colonization by P. chlamydosporia, but neither nematode infection per plant nor fungal egg parasitism was affected. Tomato plants cultivated in a mid-suppressive (29.3 ± 4.7% RKN egg infection) non-sterilized clay loam soil and irrigated with chitosan had enhanced shoot growth, reduced RKN multiplication, and disease severity. Chitosan irrigation in a highly suppressive (73.7 ± 2.6% RKN egg infection) sterilized-sandy loam soil reduced RKN multiplication in tomato. However, chitosan did not affect disease severity or plant growth irrespective of soil sterilization. Chitosan, at an adequate dose, can be a potential tool for sustainable management of RKN.

First Global Record ofPodisus nigrispinus(Hemiptera: Pentatomidae) as Predator ofGonipterus platensis(Coleoptera: Curculionidae) Larvae and Adults

Summary Native to Australia Gonipterus platensis Marelli (Coleoptera: Curculionidae) is the main beetle defoliator of eucalyptus worldwide, causing damage in various regions in which it was introduced, where its management relies mostly on biological control with the parasitoid Anaphes nitens (Girault) (Hymenoptera: Mymaridae). In this report, we present the first laboratory evidence of efficient predation by Podisus nigrispinus Dallas (Hemiptera: Pentatomidae) on G. platensis larvae. This predatory species is native to Brazil and a promising biological control agent for use in the integrated pest management of G. platensis.

Interactions between soil‐dwelling arthropod predators and Ixodes scapularis under laboratory and field conditions

AbstractThe primary vector for Lyme disease and several other medically significant tick‐borne diseases, Ixodes scapularis (blacklegged tick), spends over 95% of its two‐year life cycle exposed to the soil environment. However, the effect of soil‐dwelling arthropod predator populations on I. scapularis survival either in the laboratory or under field conditions is unclear. We collected soil‐dwelling obligate arthropod predators from the field, representing 13 taxonomic families, and investigated whether they would target two I. scapularis life stages (nymph/engorged larva) under laboratory conditions. After 48 h, 30.6% of the predator species targeted I. scapularis nymphs, while 41.3% targeted engorged larvae. One spider species, Schizocosa ocreata, targeted both I. scapularis life stages reliably under laboratory conditions. We used this species to test whether an arthropod predator would affect I. scapularis survival in field microcosms which contained alternative prey items and a complex soil environment. We also investigated the direct and indirect effects of surface litter on I. scapularis survival by removing the leaf litter layer from half of the microcosms. Predator addition reduced the number of nymphs recovered from the microcosms after 21 d by 32.9%. Litter removal also had a negative effect on tick survival, and interacted weakly with the addition of a predator further decreasing tick survival. Additionally, we found that when leaf litter was removed, I. scapularis survival was positively correlated with the organic matter content of the soil within the microcosms. Naturally occurring arthropod predators may play an important role in regulating population dynamics of I. scapularis and show potential as biological control agents for use in integrated pest management protocols.

Humic Fertilizer and Vermicompost Applied to the Soil Can Positively Affect Population Growth Parameters of Trichogramma brassicae (Hymenoptera: Trichogrammatidae) on Eggs of Tuta absoluta (Lepidoptera: Gelechiidae).

The tomato leaf miner, Tuta absoluta (Meyrick), is a devastating pest of tomato worldwide. One of the control measures of T. absoluta is the use of biological control agents, such as Trichogramma wasps. Interactions between natural enemies and insect pests may be affected by application of fertilizers, because changes in plant quality through the fertilizer application may therefore affect herbivore characteristics and suitability of them to parasitism. Laboratory tests were carried out to evaluate the life table parameters of Trichogramma brassicae Bezdenko on T. absoluta eggs reared on tomato plants treated either with vermicompost (40%), humic fertilizer (2g/kg soil), or control (suitable mixture of field soil and sand). Population growth parameters of T. brassicae were affected by fertilizer treatments. Significant differences were found for immature life period and total fecundity of T. brassicae on the treatments. Differences of intrinsic rate of natural increase (r m), finite rate of increase (λ), net reproductive rate (R 0), mean generation time (T), and doubling time (DT) of T. brassicae among treatments were also significant. The lowest values of r m, λ, and R 0 were recorded for T. brassicae developed on T. absoluta eggs on control treatment, whereas the highest values of these parameters were observed on 2g/kg humic fertilizer. Furthermore, T. brassicae had the shortest T and DT values on 2g/kg humic fertilizer and 40% vermicompost treatments. Our results showed that application of humic fertilizer and vermicompost could positively affect population growth parameters of T. brassicae on eggs of T. absoluta fed on tomato plants.

A baseline study using Plantwise information to assess the contribution of extension services to the uptake of augmentative biological control in selected low- to lower- middle- income countries

The uptake of augmentative biological control agents (BCAs) is still limited, particularly in many low- to lower- middle- income countries. This study focuses on factors that affect the uptake of BCAs for arthropod pests by national extension partners (NEPs) in Plantwise—an agricultural development programme facilitating the establishment of plant clinics where farmers can obtain diagnosis and plant health advice. Using data generated by NEPs, BCA recommendations in extension material and given by extension workers in Ghana, Kenya, Zambia, India, Nepal and Pakistan were analysed. The rate of BCA recommendation ranged from 13.0 (Zambia) to 61.1% (India) in extension materials and from 0.0 (Zambia) to 18.2% (India) in recommendations given by extension workers. Knowledge, availability and price were identified as the main factors affecting the uptake of BCAs by NEPs. This baseline study gives novel insight into the potential of NEPs to facilitate the use of BCAs.

English

Management of tomato early blight pathogen (Alternaria solani) has relied principally on application of synthetic fungicides. The use of biological control agents has been recognized as a viable option to synthetic chemicals in plant disease control. The present study evaluated the effects of Pseudomonas fluorescens, P. aeruginosa, P. putida, and P. cepacia on tomato early blight pathogen and investigated their efficacy on the yield components and yield of tomato plants infected with A. solani. Tomato seeds raised in the nursery beds were transplanted to the main field after three weeks. The experiment was laid in a randomized complete block. Treatment application was done by immersion of roots of three-week-old seedlings of tomato in Pseudomonas solution prior to transplanting. The treatments consisted of plots treated with P. fluorescens, P. aeruginosa, P. putida, P. cepacia and the control. Data were collected on disease severity, plant height, stem girth, number of fruits per plant, fruit length and fruit weight. Tomato plants in the control plot had significantly (p<0.05) higher disease severity (52.0) There was no significant difference in the severities of early blight on tomato plants treated with P. fluorescens, P. putida and P. cepacia. Tomato plants treated with P. aeruginosa had significantly (p<0.05) higher height (39.0 cm) than all other treatments. There was no significance difference in the fruit weights of tomato plants treated with P. fluorescens, P. aeruginosa, P. putida, and P. cepacia. Tomato plants in the control plots had a significantly lower fruit weight (69.5 g). Findings of the present study demonstrated a promising approach of biological control of early blight pathogen with Pseudomonas species. Results of this work could be used as bedrock for formulation of an effective and eco-friendly strategy for the management of early blight disease. Key words: Tomato, Alternaria solani, Pseudomonas, biological control, early blight.

From effective biocontrol agent to successful invader: the harlequin ladybird (Harmonia axyridis) as an example of good ideas that could go wrong.

The use of biological control agents to control pests is an alternative to pesticides and a tool to manage invasive alien species. However, biocontrol agents can themselves become invasive species under certain conditions. The harlequin ladybird (Harmonia axyridis) is a native Asian biocontrol agent that has become a successful invader. We reviewed articles containing “Harmonia axyridis” to gather information on its presence and surveyed entomologists researching Coccinellidae around the world to investigate further insights about the current distribution, vectors of introduction, habitat use and threats this species pose. The harlequin ladybird has established populations in at least 59 countries outside its native range. Twenty six percent of the surveyed scientists considered it a potential threat to native Coccinellidae. Published studies and scientists suggest Adalia bipunctata, native to Europe, is under the highest risk of population declines. Strict policies should be incorporated to prevent its arrival to non-invaded areas and to prevent further expansion range. Managing invasive species is a key priority to prevent biodiversity loss and promote ecosystem services.

Low labor “in vivo” mass rearing method for entomopathogenic nematodes

The wide spread use of biological control agents in commercial agriculture is frequently limited by the high cost of the biological control agents. We describe in this paper an entomopathogenic nematode (EPN) “in vivo” mass rearing method, not based on the White trap concept, which is both “low technology” and “low labor”, reducing the cost of producing large quantities of EPN IJ to the level conducive for use in an area-wide biocontrol program. Rearing temperature has a significant impact on the number of EPN IJ produced per host larvae and the IJ viability at any point in time. Emerged IJs remain within a non-aqueous, high humidity environment with improved oxygen access without extra steps or equipment. Depending on storage conditions, IJs remain viable for 7–14d without extra labor. Our laboratory has used this rearing method to rear more than 100 billion IJ in the past 8years to support an area wide biological control program.

Isolation, Identification and Characterization of Trichoderma Species as a Potential Biocontrol Agent against Ceratocystis paradoxa

Ceratocystis paradoxa is a plant pathogen causing diseases in several plants including coconut (Cocos nusifera). Infected coconut plants manifest “Stem bleeding” which is very common in Hambantota district in Sri Lanka. Coir and coir pith obtained from coconut husk provide substrates for the growth of the pathogen. The use of biological control agents (BCAs) has gained more attention in controlling plant pathogens because it minimizes the application of synthetic pesticides. In many researches, various strains of Trichoderma species have been studied to be used as BCAs against many plant pathogens. The present investigation was carried out in an attempt to isolate various strains of Trichoderma spp. from soil, litter and coir samples collected from different locations in Lunuwila area in the North Western Province of Sri Lanka, and to evaluate their potential as BCAs in controlling C. paradoxa. Several Trichoderma spp. were isolated into PDA plates. Colony morphology and morphological features of sporulating structures and spores were compared among the Trichoderma isolates. Genomic variability of isolates was determined by RFLP analysis of the PCR amplified DNA for the ITS region of the isolates using AluI enzyme. Potential ability of Trichoderma isolates in controlling the pathogen was observed using dual culture technique. Accordingly, ten different Trichoderma isolates were identified from soil but none from coir. The isolates were identified as T. viridae, T. polysporum, and T. harzianum. As BCAs, almost all Trichoderma isolates exhibited more than 60% growth inhibition of C. paradoxa on the seventh day of incubation in a dual culture.

Competition between biological control fungi and fungal symbionts of ambrosia beetles Xylosandrus crassiusculus and X. germanus (Coleoptera: Curculionidae): Mycelial interactions and impact on beetle brood production

Ambrosia beetles Xylosandrus crassiusculus and X. germanus are among the most important exotic pests of orchards and nurseries in the US and are difficult to control using conventional insecticides because of their cryptic habits. The use of biological control agents may prove effective by targeting both beetles and fungal symbionts inside tree galleries: entomopathogenic fungi could be used to target beetle foundresses and their brood, or mycoparasitic fungi, e.g., Trichoderma harzianum, could be used to target their associated fungal symbionts. We used a combination of in vitro assays and beetle bioassays to examine competition between symbionts and biological control fungi and the impact of biological control fungi on beetle brood production. The in vitro assays showed T. harzianum outcompeted different strains of Ambrosiella roeperi and A. grosmanniae associated with X. crassiusculus and X. germanus, respectively, whether in primary or secondary resource capture assays. In contrast, entomopathogenic fungi Beauveria bassiana and Metarhizium brunneum blocked the spread of symbionts only in primary competition assays. Complementary beetle bioassays showed that beetle galleries in T. harzianum-treated beech stems had sparse symbiont growth, many with no or only a small number of eggs present. Brood numbers produced by foundresses in T. harzianum-treated stems were comparable to those in stems treated with either entomopathogen at the higher dosages, in which brood reduction was likely due to foundress mortality prior to laying eggs or after laying only a small number of eggs. These results show the potential of using biological control fungi in targeting ambrosia beetle populations either directly by killing foundresses and reducing brood production or indirectly by suppressing symbiont growth in their galleries.