Biological control of Lygus lineolaris by Peristenus spp. in strawberry

Peristenus digoneutis Loan (Hymenoptera: Braconidae) was introduced to the US for biological control of the tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hemiptera: Miridae), and has since spread through much of the northeast. The purpose of this study was to determine if P. digoneutis and a native congener, Peristenus pallipes (Curtis), parasitize L. lineolaris in strawberry (where it is a key pest), and what factors relate to parasitism levels. During 1997–1999 we monitored parasitism on 17 strawberry farms in 14 counties in eastern and western New York State. We found that in eastern NY (where P. digoneutis has been established since the early 1990s), overall mean parasitism was 19.7% (ranging from 0 to 70%), mostly by P. digoneutis. Mean parasitism was significantly lower (12.3%, ranging from 0 to 58%) in western NY (where P. digoneutis was first recorded in 1999), and was mostly by P. pallipes. P. pallipes parasitism was significantly lower in eastern than western NY, suggesting the potential for competitive interaction with P. digoneutis. The insecticide regime of a farm was an important factor influencing parasitism rate, which was 5- to 6.5-fold higher on organic or casually sprayed farms than on intensely treated farms, though pest density under these three regimes was not significantly different. L. lineolaris density, and parasitism rate in nearby alfalfa and abandoned fields were also significant factors for parasitism in strawberry.     

植物替代控制3种入侵杂草技术的研究与应用进展

植物替代控制是利用一种或多种植物的生长优势控制入侵杂草的方法,它是控制外来杂草危害的有效途径之一;因其既可控制入侵杂草危害又能取得一定的经济效益及生态效益而被人们广泛接受。本文简要介绍了我国3种入侵杂草植物替代控制技术研究与应用现状,系统总结了植物替代控制技术阻截和修复豚草、紫茎泽兰及黄顶菊扩散危害的技术模式和效果,提出了植物替代控制技术未来研究的方向和重点。     

Pseudocercospora cryptostegiae-madagascariensis sp. nov. on Cryptostegia madagascariensis, an Exotic Vine Involved in Major Biological Invasions in Northeast Brazil

Cryptostegia madagascariensis is a plant native from Madagascar, belonging to the Apocynaceae that is invading the native vegetation in Northeast Brazil and threatening the unique riverine formations dominated by the carnauba palm. Individuals of C. madagascariensis cultivated in the campus of the Universidade Federal de Viçosa, state of Minas Gerais, Brazil, showing leaf spot symptoms of unknown etiology were observed. Two fungal species were found associated to such leaf spots: Colletotrichum gloeosporioides and a new species of Pseudocercospora. The latter was named Pseudocercospora cryptostegiae-madagascariensis and described herein. The discovery of those two fungal pathogens on C. madagascariensis coincide with the recognition that the weedy vine that is involved in the infestations in the Northeast of Brazil is not Cryptostegia grandiflora as formerly reported. These mycological findings are of greater importance now since C. madagascariensis is likely to become a target for biological control together with its former status in Brazil of an ornamental plant of limited relevance.     

Understanding the recent colonization history of a plant pathogenic fungus using population genetic tools and Approximate Bayesian Computation

Understanding the processes by which new diseases are introduced in previously healthy areas is of major interest in elaborating prevention and management policies, as well as in understanding the dynamics of pathogen diversity at large spatial scale. In this study, we aimed to decipher the dispersal processes that have led to the emergence of the plant pathogenic fungus Microcyclus ulei, which is responsible for the South American Leaf Blight (SALB). This fungus has devastated rubber tree plantations across Latin America since the beginning of the twentieth century. As only imprecise historical information is available, the study of population evolutionary history based on population genetics appeared most appropriate. The distribution of genetic diversity in a continental sampling of four countries (Brazil, Ecuador, Guatemala and French Guiana) was studied using a set of 16 microsatellite markers developed specifically for this purpose. A very strong genetic structure was found (F_st=0.70), demonstrating that there has been no regular gene flow between Latin American M. ulei populations. Strong bottlenecks probably occurred at the foundation of each population. The most likely scenario of colonization identified by the Approximate Bayesian Computation (ABC) method implemented in 𝒟ℐ𝒴𝒜ℬ𝒞 suggested two independent sources from the Amazonian endemic area. The Brazilian, Ecuadorian and Guatemalan populations might stem from serial introductions through human-mediated movement of infected plant material from an unsampled source population, whereas the French Guiana population seems to have arisen from an independent colonization event through spore dispersal.     

Biological control of thrips and whiteflies by a shared predator: Two pests are better than one

We studied the capacity of one species of predator to control two major pests of greenhouse crops, Western flower thrips (Frankliniella occidentalis (Pergande)) and the greenhouse whitefly (Trialeurodes vaporariorum (Westwood)). In such a one-predator–two-prey system, indirect interactions can occur between the two pest species, such as apparent competition and apparent mutualism. Whereas apparent competition is desired because it brings pest levels down, apparent mutualism is not, because it does the opposite. Because apparent competition and apparent mutualism occurs at different time scales, it is important to investigate the effects of a shared natural enemy on biological control on a time scale relevant for crop growth. We evaluated the control efficacy of the predatory mites Amblyseius swirskii (Athias-Henriot) and Euseius ovalis (Evans) in cucumber crops in greenhouse compartments with only thrips, only whiteflies or both herbivorous insects together. Each of the two predators controlled thrips, but A. swirskii reduced thrips densities the most. There was no effect of the presence of whiteflies on thrips densities. Whitefly control by each of the two predators in absence of thrips was not sufficient, yet better with E. ovalis. However, whitefly densities in presence of thrips were reduced dramatically, especially by A. swirskii. The densities of predators were up to 15 times higher in presence of both pests than in the single-pest treatments. Laboratory experiments with A. swirskii suggest that this is due to a higher juvenile survival and developmental rate on a mixed diet. Hence, better control may be achieved not only because of apparent competition, but also through a positive effect of mixed diets on predator population growth. This latter phenomenon deserves more attention in experimental and theoretical work on biological control and apparent competition.     

Biological control of the water fernSalvinia molesta infesting a lily pond in Bangalore (India) byCyrtobagous salviniae

The aquatic fernSalvinia molesta D.S. Mitchell is a serious weed in India, espacially in the state of Kerala. The weevilCyrtobagous salviniae Calder and Sands (Col.: Curculionidae) was introduced from Austrialia and successfully controlled the weed infesting a lily pond at Bangalore. Contribution No. 174/85 of the Indian Institute of Horticultural Research, Bangalore, India.     

Biological control ofAphis pomi [Hom.: Aphididae] ofAphidoletes aphidimyza [Dip.: Cecidomyiidae]; a predator-prey model

Predation ofAphis pomi DeGeer [Hom.: Aphididae] byAphidoletes aphidimyza (Rondani) [Dipt.: Cecidomyiidae] was simulated in Michigan apple orchards using a computer and output validated against field data collected from sleeve cages enclosing aphid infested apple terminals. Lower and upper temperature thresholds for development were 2.9 and 35°C for nymphs ofA. pomi with a mean immature developmental period of 162.3 heat units. Median survivorship of adultA. pomi was 364.3 heat units with an average fecundity of 60.7 offspring per female.A. aphidimyza egg and larval lower threshold and developmental periods were 10.5 and 25.5, 8.1°C and 65.5 heat units, respectively. Larval functional response showed Type II behavior with a y-asymptote of 45 aphids killed per predator. Multiple generation model runs performed under different initial predator: prey densities indicated that current critical predator: prey ratios used in the field for control decisions may underestimate predator efficacy.      

Biological control of Phytophthora blight in red pepper (Capsicum annuum L.) using Bacillus subtilis

Phytophthora blight is one of the most important devastating diseases of red pepper plants. Forty-one bacterial isolates were obtained from rhizosphere soil and subsequently tested for antagonistic activity under in vitro and in vivo conditions. Among the 41 isolates tested, 12 exhibited a maximum antagonistic activity in dual culture assay. These 12 isolates were further screened for disease suppression on red pepper plants in both natural and greenhouse conditions. All the antagonists showed varying levels of antagonism, whereas the isolates R33 and R13 exhibited the maximum (86.8 and 71%) ability to reduce the disease severity in in vivo conditions. Based on the 16S rDNA sequencing, the most effective isolates were identified as Bacillus subtilis. In addition, the isolates were also screened for siderophores, hydrogen cyanide and hydrolytic enzymes. Further, the isolates increased the root and shoot length of the red pepper, which is an added advantage of the isolates while performing the desired function.     

Role of plant phenology in mediating interactions between two biological control agents for spotted knapweed

The role of spotted knapweed phenology on the attack rate of two seed-head insects Urophora affinis and Larinus minutus was assessed in a series of field studies at four study sites in south-eastern British Columbia, Canada. Slow or later developing knapweed plants had more seed heads that contained only single or multiple U. affinis whereas early or faster developing plants had more seed heads containing L. minutus alone or in combination with U. affinis. L. minutus did not distinguish between seed heads with or without U. affinis larvae when laying eggs. However, seed heads with multiple U. affinis present, produced fewer L. minutus adults than expected. The probability of single or multiple U. affinis galls being present increased with seed-head diameter but was not affected by seed-head height. Attack by L. minutus increased with seed-head diameters >5 mm and was lower at plant heights above 50 cm. These results demonstrate two mechanisms that enable U. affinis to successfully coexist with L. minutus: differences between the species in their response to the developmental phenology of knapweed heads, and increased survivorship of U. affinis in heads with multiple U. affinis galls through niche interference competition. These mechanisms provide a possible explanation for the persistence of U. affinis populations on spotted knapweed, in spite of high levels of within seed-head mortality that have been observed with increasing L. minutus populations.     

Biological control ofSenecio jacobaea in Northern California,an enduring success

Senecio jacobaea, a poisonous weed from Eurasia, was brought under successful biological control in the Ft. Bragg, California area by 1976, through the combined action of the defoliating cinnabar moth (Tyria jacobaeae) and a root feeding flea beetle (Longitarsus jacobaeae). In 1987, 4 previously infested Ft. Bragg sites (3 sites where control had been documented and another unstudied site) were examined.Senecio jacobaea densities at these sites were 0.0, 0.0, 0.01 and 0.18 plants/m², indicating both continued and improved control of the weed. The flea beetle and the cinnabar moth both persist at the sites, despite very low numbers ofS. jacobaea plants. The control ofS. jacobaea has resulted in the return of near natural vegetation at the 2 coastal prairie sites and regained productivity at the 2 pasture sites. c/o American Embassy APO San Francisco 96301     

Biological control by Clonostachys rosea as a key component in the integrated management of strawberry gray mold

Gray mold, caused by Botrytis cinerea, is an important strawberry disease. As gray mold control is difficult, there is a need to evaluate integrated methods to successfully manage the disease. The efficiency of integrating Clonostachys rosea sprays, fungicide sprays, and crop debris removal to manage gray mold was evaluated in field experiments conducted in 2006 and 2007. Leaf colonization by C. rosea (LAC), average number of B. cinerea conidiophores (ANC), gray mold incidence in both flowers (Iflower) and fruits (Ifruit), and yield were evaluated weekly. In both years, LAC was higher in the treatments with no fungicide. When compared to the check, ANC, Iflower and Ifruit were most reduced in treatments that included C. rosea sprays. Maximal reductions were achieved with the combination of C. rosea sprays, fungicide sprays and debris removal (96.62%, 86.54% and 65.33% reductions of ANC, Iflower and Ifruit, respectively). Otherwise, maximal yield (103.14% increase as compared to the check) was achieved with the combination of the three treatments. With just C. rosea sprays, ANC, Iflower and Ifruit were reduced by 92.01%, 68.48% and 65.33%, respectively, whereas yield was increased by 75.15%. Considering the individual effects, application of C. rosea was the most efficient treatment. Chemical control was effective only in plots without debris removal. Elimination of crop debris was the least effective method in reducing gray mold incidence in both flowers and fruits. The integrated control approach enhanced the efficacy of the individual methods of gray mold control and provided high strawberry yield. An important component of this integrated approach it the biological control with C. rosea.     

Biological control of Pythium aphanidermatum in cucumber with a combined application of Lysobacter enzymogenes strain 3.1T8 and chitosan

Pythium aphanidermatum (Edson) Fitzp., causing root and crown rot in cucumber, was successfully managed by Lysobacter enzymogenes strain 3.1T8. Greenhouse experiments were performed with cucumber plants grown in rockwool blocks up to 5 weeks with a recirculated nutrient solution. Application of L. enzymogenes 3.1T8 in combination with chitosan (the deacetylated derivative of chitin) reduced the number of diseased plants by 50–100% in four independent experiments relative to the Pythium control. Application of chitosan or the bacterial inoculant alone was not effective. Washed bacterial cells plus chitosan inhibited Pythium-induced disease, but the supernatant without bacterial cells combined with chitosan was not effective. The most effective and convenient type of commercially available chitosan was selected. Chitosan disappeared from the hydroponic system within 24 h after application, which we attribute to enzyme expression of L. enzymogenes 3.1T8 induced by the exposure to chitosan. Plate counts of the nutrient solution on a general bacterial medium showed the dominance of the inoculated strain, and an increased bacterial population growing on chitin and chitosan as single carbon source. The population density of L. enzymogenes 3.1T8 on the cucumber roots was investigated with a strain specific real-time TaqMan PCR. Highest chitosan concentrations applied (0.1 and 0.03 g/plant) resulted in the highest numbers of L. enzymogenes 3.1T8 present on roots; i.e. 10⁸–10⁹ cells/g root. Substantially higher numbers of bacterial cells were observed by scanning electron microscopy after application of chitosan; no morphological or other qualitative differences were found. The results indicate that addition of chitosan enhanced the biocontrol efficacy of L. enzymogenes 3.1T8; either chitosan serves as C- and N-source for the antagonist, induces antagonistic gene expression, or both.     

Mycoflora of tuber surface of white yam (Dioscorea rotundata poir) and postharvest control of pathogens with Bacillus subtilis

Bacillus subtilis (Enrenberg) Cohn was investigated for its antagonistic properties against surface mycoflora of yam (Dioscorea rotundata Poir) tubers in storage. Yam tubers inoculated with a spore suspension of B. subtilis in potato dextrose broth using a knapsack sprayer showed a drastic reduction in the range and number of mycoflora, including pathogens of the tuber surface in contrast to the control tubers, during the five-month storage period in a traditional yam barn. However, B. subtilis maintained a high frequency of occurrence during the same period. Botryodiploidia theobromae Pat, Fusarium moniliforme Wollen and Reink., Penicillium sclerotigenum Yamamoto, and Rhizoctonia sp. were displaced completely on the treated tubers. The antagonism of B. subtilis was so effective that the normal tuber surface mycoflora was greatly reduced throughout the storage period of five months by a simple initial application of the antagonist.This revised version was published online in October 2005 with corrections to the Cover Date.     

Biological control of the oil palm pestLatoia viridissima [Lepidoptera,limacodidae], in Cote d'Ivoire,by a new picornavirus

Among the major oil palm pest insects in the Côte d'Ivoire,Latoia viridissima Holland [Lepidoptera, Limacodidae] is the most frequently observed defoliator. During a pullulation of this species, a natural epizootic permitted us to demonstrate the occurrence of a small isometric RNA virus of 30nm in diameter. The buoyant density of the virus particles was 1.34. The virus capsid contained 2 major proteins with molecular weights of 30,000 (55%) and 31,000 (20%) and 3 minor proteins. One genome component was detected with molecular weight 2,9×10⁶. Agarose gel diffusion tests showed this virus was distinct from any other described insect Picornavirus. Trials with different doses of viral suspensions were tested on industrial oil palm plantation, allocated byL. viridissima, from ground level, using an automatic air carried sprayer. One week after the treatment, a mortality gradient, increasing from 11 to 61% according to the dose applied, was obtained. Two weeks after the treatment the mortality reached 92% of the larvae in the treated parcels. During the next generation, the number of caterpillars on the same parcel was very low.     

A new Monstera (Araceae: Monsteroideae) from Brazil

A new species ofMonstera (Araceae),M. praetermissa, is described, illustrated, and compared to its most similar relatives,M. xanthospatha andM. obliqua. The new species is so far only known from Brazil, but has a broad distribution there, ranging from the south to the northeast of the country.     

Search for effective natural enemies of Tetranychus evansi in south and southeast Brazil

Tetranychus evansi Baker & Pritchard is an important pest of Solanaceae in several countries. Introduced accidentally to Africa, it presently occurs in many countries of that continent. In some of them, it is considered a key pest. The suspected area of origin of this mite is South America. The objective of the present study was to identify phytoseiid mites on solanaceous plants in association with T. evansi in south and southeast Brazil for introduction in the African continent for use in a classic biological control program. Almost 1,400 predatory mites of the family Phytoseiidae were collected, on 22 solanaceous species. The Amblyseiinae were the most diverse group in this study. Twenty-three of the species found belong to this subfamily, while only three belong to the Typhlodrominae and two to the Phytoseiinae. The most abundant and most frequent phytoseiid species were Phytoseius guianensis De Leon and Galendromus annectens (De Leon) of the Phytoseiinae and Typhlodrominae, respectively. The most frequent and abundant species of Amblyseiinae was Neoseiulus tunus (De Leon). Phytoseius guianensis and N. tunus were never found in association with T. evansi and G. annectens was found only once in association with it. Two factors suggested Phytoseiulus longipes Evans as the most promising predator found in this study. It could walk very well on tomato leaves infested by T. evansi, without being hampered by the profuse webbing produced by the prey and by the trichomes. In addition, several specimens of both sexes including eggs and nymphs of the predator were found associated with T. evansi on three different plant species and in two different periods of the year, when T. evansi was the only arthropod present on the leaves.     

Biological control of thrips [Thysanoptera: Thripidae] on greenhouse cucumber byAmblyseius cucumeris

The predatory miteAmblyseius cucumeris (Oudemans) [Acarina: Phytoseiidae] was evaluated as a biological control forThrips tabaci Lindeman andFrankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] on greenhouse grown seedless cucumber.A. cucumeris spread throughout the greenhouses and provided control of both species of thrips.A. cucumeris adults persisted on plants for 7 weeks in the virtual absence of prey, and increased numerically in response to increases in prey population. On the basis of these resultsA. cucumeris is recommended as a useful biological control forT. tabaci andF. occidentalis on greenhouse cucumber. Publication No. 361, Agassiz Research Station, Agriculture Canada, Agassiz, B.C. Canada VOM 1AO.     

Biological control of Botrytis cinerea on stem wounds with moderately halophilic bacteria

Infection of tomato stem wounds by Botrytis cinerea is an important problem which can cause severe economic losses in greenhouse tomato crops. Three moderately halophilic bacteria were tested for their ability to protect pruning wounds from attacks by B. cinerea under growth chamber conditions. The severity of the disease estimated by the length of the rotted stem was used to calculate the area under the disease progress curves (AUDPC). Bacterial antagonists (B1, B2 and B3) were very effective in controlling Botrytis-infection on the tomato stems during the first 6 days and later by the end of the experiment. Plants treated with Bacillus subtilis (B1) had the lowest AUDPC (0). It was followed by B. subtilis (B3) and Halomonas sp. (B2) with AUDPC of 9.8 and 17.02, respectively. While the B1 strain best inhibited grey mold development when applied as young culture (24 h), the B3 strain performed better as an older culture (48 h). In contrast to the results obtained with Bacillus species, the efficacy of the bacterial treatment B2 seems to be independent of the growth phase. The co-cultures with fungal spores and either B. subtilis (B1) or Halomonas sp. (B2) applied as a 24 h bacterial culture completely inhibited the germination of B. cinerea after 24 h at 21°C.     

Changes in abundance of native and introduced parasites (Hymenoptera: Braconidae), and of the target and non-target plant bug species (Hemiptera: Miridae), during two classical biological control programs in alfalfa.

High numbers of tarnished plant bugs [Lygus lineolaris (Palisot)], were once common in alfalfa, as was a low level of parasitism (9%) by the native Peristenus pallipes (Curtis). After the bivoltine European parasite Peristenus digoneutis Loan became well established, average parasitism of the first and second generations increased to 64%, and tarnished plant bug numbers dropped by 65%. This reduced host density eventually caused a decline in total parasitism by both parasite species to 22%. A few P. digoneutis also attacked the alfalfa plant bug, Adelphocoris lineolatus (Goeze), but did not reduce this pest or increase its parasitism rate. At another location, where P. digoneutis is not established, parasitism of first generation alfalfa plant bugs, an adventive (accidently introduced) pest, was increased to 21% by the introduced univoltine parasite, Peristenus conradi Marsh, and a slight reduction in the pest may have resulted. P. digoneutis did not parasitize the meadow plant bug, Leptopterna dolabrata (L.), an adventive pest of forage grasses, so did not affect this mirid or its parasite. Neither introduced parasite eliminated the native parasites of the tarnished or alfalfa plant bugs. The narrow host ranges of the braconid parasites of mirid nymphs are contrasted with the broad host range of the native tachinid parasite [Phasia robertsoni (Towns.)] of adult mirids. The major changes in mirid abundance and their mortality by parasites that slowly occurred during this 19-year study demonstrate the need for long-term field research, to adequately document and understand these complex interactions.