Comparison of aerial conidia and blastospores from two entomopathogenic fungi against Diaphorina citri (Hemiptera: Liviidae) under laboratory and greenhouse conditions

This study compared the insecticidal activity of liquid culture-produced blastospores and solid substrate-produced aerial conidia of Beauveria bassiana GHA and Isaria fumosorosea ARSEF3581 strains against Diaphorina citri adults. Insects exposed to 10⁷ propagules/ml in a spray residue contact leaf bioassay died within 6 days at 25°C, with no significant differences between fungal treatments. At higher concentrations (10⁸ propagules/ml), I. fumosorosea conidia killed psyllids faster compared to its blastospore formulation, i.e. 4 versus 5 days, respectively. In greenhouse tests, the same treatments applied to infested citrus plants (2?×?10⁶ spores/ml) all significantly reduced the number of nymphs compared with the untreated controls over 3 weeks; however, only I. fumosorosea blastospores significantly reduced the number of F1 adult psyllids when compared with controls. Similar results were observed in the follow-up greenhouse test, where I. fumosorosea blastospores were the most effective treatment overall, reducing D. citri populations by about 60% after 21 days; by contrast, imidacloprid killed almost 100% of psyllids within a week in both tests. Fewer psyllids exhibited mycosis in the greenhouse (i.e. ≈20 versus?≥?87% in the laboratory). This is the first report comparing both conidial and blastospore formulations of B. bassiana and I. fumosorosea for the control of a psyllid pest. Field testing is required to determine how successful different spore formulations might be under various environmental conditions.     

Effect of photoperiod and host distribution on the horizontal transmission of Isaria fumosorosea (Hypocreales: Cordycipitaceae) in greenhouse whitefly assessed using a novel model bioassay

A model bioassay was used to evaluate the epizootic potential and determine the horizontal transmission efficiency of Isaria fumosorosea Trinidadian strains against Trialeurodes vaporariorum pharate adults under optimum conditions (25±0.5°C, ~100% RH) at two different photoperiods. Untreated pharate adults were arranged on laminated graph paper at different distributions to simulate varying infestation levels on a leaf surface. Four potential hosts were located 7, 14 and 21 mm away from a central sporulating cadaver simulating high, medium and low infestation levels, respectively. Percent hosts colonized were recorded 7, 12, 14 and 21 days post-treatment during a 16- and 24-h photophase. After 21 days, mean percent hosts colonized at the highest, middle and lowest infestation levels were 93 and 100%, 22 and 58%, 25 and 39% under a 16- and 24-h photophase, respectively. From the results, it was concluded that the longer the photophase, the greater the percentage of hosts colonized, and as host distance increased from the central sporulating cadaver, colonization decreased. The use of this novel model bioassay technique is the first attempt to evaluate the epizootic potential and determine the horizontal transmission efficiency of I. fumosorosea Trinidadian strains under optimal environmental conditions at different photoperiods. This bioassay can be used to assess horizontal transmission efficiency for the selection of fungi being considered for commercial biopesticide development.     

Evaluating the potential of the extract of Perilla sp. as a natural insecticide for Bemisia tabaci (Hemiptera: Aleyrodidae) on sweet peppers

The sweetpotato whitefly, Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae), is a major pest on greenhouse crops including sweet pepper (Capsicum annuum L.), which is one of the leading greenhouse crops in South Korea. Synthetic insecticides, especially the neonicotinoids, have been used to conventionally control this pest. There have been continuous efforts to develop plant‐derived compounds as insecticides, deterrents, and repellents to reduce spraying synthetic insecticides. To develop new plant‐extract insecticides, we investigated the insecticidal effects of Perilla sp. (Perilla frutescens var. crispa) extract on B. tabaci in laboratory conditions. The Perilla sp. extract induced 90 % mortality within one hour, but phytotoxicity symptoms on sweet pepper leaves were also observed. We monitored the population change and spatial distribution of adult B. tabaci in an experimental sweet pepper greenhouse using yellow sticky traps, and analyzed distribution patterns by spatial analysis with distance indices (SADIE). Based on monitoring data and SADIE analysis, we concluded that B. tabaci aggregated near the greenhouse entrances, and it showed aggregation and association pattern as time passed. Therefore, we recommend spraying Perilla sp. extract near the entrances or wild host before the pest population penetrates. It will be one of the alternative pest management strategies to reduce B. tabaci population with fewer negative effects from chemical insecticide. Further study is required to reduce the phytotoxicity symptoms from Perilla sp. extract spray and insecticidal effect should be evaluated under field conditions.     

Laboratory and greenhouse evaluation of a new entomopathogenic strain of Beauveria bassiana for control of the onion thrips Thrips tabaci

Abstract

The onion thrips Thrips tabaci is one of the most important pests of greenhouse and open-field broccoli, onion and other crops. However, the current strategy of using synthetic pesticides for its control is inadequate and unsustainable, leading to a growing interest in novel and effective biological control alternatives such as entomopathogenic fungi. Among 20 isolates of Beauveria bassiana tested for virulence against T. tabaci in laboratory bioassays, we found strain SZ-26 as the most potent, causing 83–100% mortality in adults at 1×10⁷ mL^?1conidia after 4–7 days. Further experiments in greenhouses showed the strain SZ-26 significantly lowered the numbers of adult and larval stages.     

Visually and olfactorily enhanced attractive devices for thrips management

‘Lure-and-infect’ is an insect pest management strategy with high potential but so far there are few examples of its application. Using traps as surrogates for auto-dissemination devices, we tested the attractiveness to naturally occurring thrips (Thysanoptera: Thripidae) of three trap types differing in colour and structure, with and without the thrips lure methyl isonicotinate (MI), and sticky plate traps as a control. The aim was to find more effective traps that could be further developed into devices for auto-dissemination and lure-and-infect of thrips. The number of thrips captured varied substantially with trap type and the presence of the MI lure. We found a high visual response to a sticky ‘white ruffle’ trap (i.e., a 30-cm-long cylindrical outline of folded fabric), compared to a commonly used blue sticky plate trap (Bug-scan) as the control. This effect was seen both in a greenhouse with roses (Rosa spp.), where we encountered western flower thrips, Frankliniella occidentalis (Pergande), and in a grass field, where we encountered onion thrips, Thrips tabaci Lindeman, and New Zealand flower thrips, Thrips obscuratus (Crawford). In the absence of MI, the white ruffle trap caught 7–22× more thrips than the control Bug-scan trap. A similarly designed blue ruffle trap and a modified Lynfield trap caught lower thrips numbers than the white ruffle and the control Bug-scan traps. Presence of MI substantially increased the captures of T. tabaci in all three trap types in the field (2.5–18×). In the greenhouse, without MI the white ruffle trap caught 3.5–14× more thrips than the Bug-scan, blue ruffle, or modified Lynfield traps. Presence of MI increased the captures of F. occidentalis males and females in the Lynfield and blue ruffle traps (1.4–2.8×), but not in the white ruffle trap in the greenhouse (ca. 1.1×). The importance of visual and olfactory factors for the design of effective auto-dissemination and lure-and-infect strategies for thrips management is discussed.     

Effects of undersown clover on host-plant selection by Thrips tabaci adults in leek

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters – number of leaves and stem diameter – were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.     

Effect of Ifchit1 gene of Isaria fumosorosea on mortality,oviposition and oxidase activities of Bemisia tabaci

Isaria fumosorosea is one of important entomopathogenic fungi showed a good potential in controlling Bemisia tabaci. The effects of I. fumosorosea ⊿Ifchit1 mutant (Ifchit1 gene deletion mutant) on the mortality, oviposition, and host immunological response of B. tabaci, on Brassica campestris L. plant, were evaluated under laboratory conditions. The wild-type fungal strain infection significantly increased insect mortality and reduced the oviposition effeciency of B. tabaci, whereas the ⊿Ifchit1 mutant was much less effective, resulting in higher survival and ovipositing of B. tabaci. The activities of four insect enzymes were examined during a time course of fungal infection. Insect phenoloxidase, perioxidase, and catalase activities were decreased in whiteflies treated with the wild type and mutant I. fumosorosea strain at 12–36?h post treatment. However, these enzyme activities increased in fungal-treated whiteflies as compared to controls between 36 and 60?h post-infection, reaching peak values. Superoxide dismutase activity in fungal-treated whiteflies was higher than that in controls during the entire experimental time course examined. The overall enzyme activity profiles in ⊿Ifchit1 mutant-treated whiteflies were significantly different from wild-type strain treatments. Our results showed that loss of the Ifchit1 gene in I. fumosorosea affects whitefly mortality, ovipositioning and various antioxidant enzyme activities, providing new insights into the role of chitinases in I. fumosorosea-insect host–pathogen interactions.     

Evaluation of the lady beetle,Serangium parcesetosum for control of Bemisia tabaci on greenhouse eggplant in the Mediterranean region

Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) is one of the most serious pests of greenhouse crops. It is mainly controlled by chemical means, requiring some 10–12 sprays during the average growing season in Turkey. There is growing interest in finding alternatives to pesticides for control of B. tabaci in greenhouse crops because this heavy pesticide usage disrupts biocontrol and leads to rapid build-up of insecticide resistance in the pest. In our study, the control of B. tabaci on greenhouse eggplants was evaluated following releases of the lady beetle Serangium parcesetosum Sicard (Coleoptera: Coccinellidae). In cage experiments, four adults per plant were introduced and, within 3–4 weeks, resulted in 97 and 98% reductions in whitefly populations in 2004 and 2005, respectively. In a large plot experiment, two adults per plant were released only one time. Beetle larvae were observed through 2–9 weeks after release. The density of whitefly in large plot receiving beetle adults showed fluctuations to a level lower than in control plot receiving no beetle in 2004 and 2006. Further study is needed to develop new managing strategies in biological control of B. tabaci with S. parcesetosum in protected culture.     

Within-Crop Air Temperature and Humidity Outcomes on Spatio-Temporal Distribution of the Key Rose Pest Frankliniella occidentalis

Frankliniella occidentalis (Pergande) is a key pest of various crops worldwide. In this study, we analyse the dependence of the infestation of this pest on spatially distributed micro climatic factors in a rose greenhouse. Despite the importance of this subject, the few existing studies have been realized in laboratory rather than in greenhouse conditions. However, recent progress on greenhouse microclimate characterisation has highlighted the strong indoor climate heterogeneity that may influence the within-crop pest distribution. In this study, both microclimate (air temperature and humidity) and thrips distribution were simultaneously mapped in a rose greenhouse. The measurements were sensed in a horizontal plane situated at mid-height of the rose crop inside the greenhouse. Simultaneously, thrips population dynamics were assessed after an artificial and homogeneous infestation of the rose crop. The spatio-temporal distribution of climate and thrips within the greenhouse were compared, and links between thrips infestation and climatic conditions were investigated. A statistical model was used to define the favourable climate conditions for thrips adults and larvae. Our results showed that (i) the air temperature and air humidity were very heterogeneously distributed within the crop, (ii) pest populations aggregated in the most favourable climatic areas and (iii) the highest population density of thrips adults and larvae were recorded at 27°C and 22°C for temperature and 63% and 86% for humidity, respectively. These findings confirm, in real rose cropping conditions, previous laboratory studies on the F. occidentalis climatic optimum and provide a solid scientific support for climatic-based control methods against this pest.     

Identification of plant chemicals attracting and repelling whiteflies

The harmful side effects of chemical pest control have focused increasing attention on the potential for environmentally friendly, sustainable and efficient methods to control the sweet potato whitefly, Bemisia tabaci (Gennadius). One control method employs a volatile repellent (push), and an alluring volatile trap (pull) to manipulate the distribution and control the whitefly. Here, a Y-tube olfactometer was used to investigate the orientation responses of the whitefly toward the volatile components of six plants: tomato, tobacco, cabbage, cotton, cucumber and celery. Gas chromatography coupled with mass spectrometry was used to identify and quantify extracts from the six plants. Six treatments were conducted to demonstrate the “push–pull” method’s effects on the host selection behaviors of B. tabaci in a greenhouse. Four of the plant extracts tested had exceedingly attractive effects on the adult insects, but not those from celery. B. tabaci exhibited a prominent attraction response to (E)-2-hexenal, 3-hexen-1-ol and mixtures of these compounds, with the response rates exceeding 80 % for all tested proportions. Limonene diluted 500 times had a 62 % greater deterrent effect on adults than was observed in its absence, and it repelled egg-laying by more than 80 % in the greenhouse experiment. These data show that (E)-2-hexenal, 3-hexen-1-ol and limonene can be expected to be used for the “push–pull” method to control B. tabaci.     

Evaluation of the predatory mite <Emphasis Type="Italic">Phytoseiulus macropilis</Emphasis> (Acari: Phytoseiidae) as a biological control agent of the two-spotted spider mite on strawberry plants under greenhouse conditions

The predatory mite Phytoseiulus macropilis is a potential biological control agent of the two-spotted spider mite (TSSM) Tetranychus urticae on strawberry plants. Its ability to control TSSM was recently assessed under laboratory conditions, but its ability to locate and control TSSM under greenhouse conditions has not been tested so far. We evaluated whether P. macropilis is able to control TSSM on strawberry plants and to locate strawberry plants infested with TSSM under greenhouse conditions. Additionally, we tested, in an olfactometer, whether odours play a role in prey-finding by P. macropilis. The predatory mite P. macropilis required about 20 days to achive reduction of the TSSM population on strawberry plants initially infested with 100 TSSM females per plant. TSSM-infested plants attract an average of 27.5 ± 1.0% of the predators recaptured per plant and uninfested plants attracted only 5.8 ± 1.0% per plant. The predatory mites were able to suppress TSSM populations on a single strawberry plant and were able to use odours from TSSM-infested strawberry plants to locate prey in both olfactometer and arena experiments. Hence, it is concluded that P. macropilis can locate and reduce TSSM population on strawberry plants under greenhouse conditions.     

Evaluation of Isaria fumosorosea (Hypocreales: Cordycipitaceae) for control of the Asian citrus psyllid,Diaphorina citri (Hemiptera: Psyllidae)

A laboratory bioassay was developed to evaluate strains of Isaria fumosorosea Wize, against Diaphorina citri. Up to 100% of adult psyllids were killed at concentrations between 10⁶ and 10⁷ blastospores/ml after 12 days, with derived LC₅₀ values (at 7 days post treatment) between 1.4 × 10⁵ and 2.0 × 10⁶ blastospores/ml for strains ARSEF 3581, FE 9901 and Apopka-97. A significantly higher value (1.5 × 10⁷) was obtained with a conidial formulation of Apopka-97. Average survival times were dosage dependent, i.e. between 10.2 days at 10³ blastospores/ml and 3.5 days at 10⁸ blastospores/ml. Rates of mycosis were also dosage dependent, with up to 100% sporulation on cadavers at 10⁸ blastospores/ml but declining at lower concentrations. The Apopka-97 strain (commercially available as PFR-97) was tested against established D. citri infestations in potted citrus in greenhouse cages. Treatments at label rates reduced psyllid populations by approximately 50% over 3 weeks. The combination of PFR-97 with emulsifiable oils (0.25% v/v) did not increase psyllid mortality compared with either agent alone. Imidacloprid applied as a drench killed 100% of psyllids within 3 weeks. Subsequent greenhouse tests during humid conditions were hampered by natural dissemination of I. fumosorosea to untreated psyllids, suggesting that this fungus is spread by air movement and may be highly effective under very humid conditions. In later tests, a Cladosporium sp. rapidly colonised psyllid cadavers and leaf surfaces, but was not pathogenic in laboratory tests. Our studies confirm the potential of I. fumosorosea to be used in IPM strategies for D. citri that rely on other tactics, such as insecticidal oils and native or introduced biological control agents.     

New records of entomopathogenic fungi infecting Bemisia tabaci and Trialeurodes vaporariorum, pests of horticultural crops, in Argentina

The whiteflies Bemisia tabaci (Gennadius) and Trialeurodes vaporariorum (Westwood) (Hemiptera: Aleyrodidae) are major crop pests throughout the world. Although extensive research about biological control of whitefly by parasitoids and predators has been conducted, also entomopathogenic fungi can be considered as potential biological control agents. Surveys for entomopathogenic fungi were carried out in organic and conventional horticultural crops in greenhouses and open fields in Buenos Aires and Corrientes provinces, Argentina. These surveys resulted in the recovery and isolation of the following fungi from whiteflies: Lecanicillium lecanii (Zimmerm.) Zare & W. Gams, L. muscarium (Petch) Zare & W. Gams, L. longisporum (Petch) Zare & W. Gams, Isaria fumosorosea Wize and I. javanica (Frieder. & Bally) Samson & Hywel-Jones. Pathogenicity tests were conducted against T. vaporariorum nymphs using a conidial suspension (1 × 10⁷ conidia/ml) of the fungi. A mortality rate between 26.6% and 76.6% was obtained at 7 days post-infection. These are the first records of natural infections in the southernmost region of the South American continent of L. lecanii, L. muscarium, L. longisporum and Isaria javanica (Ascomycota: Hypocreales) on T. vaporariorum and also the first report of I. fumosorosea on B. tabaci.     

Compatibility and efficacy of the lady beetle <Emphasis Type="Italic">Thalassa montezumae</Emphasis> and the entomopathogenic fungus <Emphasis Type="Italic">Isaria fumosorosea</Emphasis> for biological control of the green croton scale: laboratory and greenhouse investigations

The lady beetle Thalassa montezumae and the entomopathogenic fungus Isaria fumosorosea (Ifr) were assessed alone and in combination to suppress green croton scale, Phalacrococcus howertoni, populations on croton plants using laboratory bioassays and greenhouse cage studies. The acquisition of Ifr blastospores by beetle larvae (3rd instar) and adults during contamination in well plates was used to simulate exposure to direct spraying and subsequent possible fungal infection was assessed. Spore dispersal by the insects was determined after the blastospore-contaminated T. montezumae life stages roamed on agar plates for 24 h by counting the number of colony-forming units (CFUs) produced in the plates. There were no significant differences in survival times at 14 days post-treatment between beetle larvae and adults exposed to Ifr and those exposed to water only. Mean survival time of larvae exposed to Ifr was 14 days and water 12 days, whereas for adults it was 13 days compared to 13 days, respectively. Plates with Ifr blastospore-contaminated T. montezumae adults roaming on the agar surface displayed significantly more fungal trails as CFUs compared to plates with larvae. In greenhouse cage studies, the mean mortality rates of the scale exposed to beetle larvae, either alone (80.8%) or in combination with Ifr (89.1%), were not significantly different. Scale mortality rates in the fungus-only (60.5%) and beetle larvae-only treatments were statistically similar. The treatment with both biocontrol agents had a significantly higher scale mortality rate compared to the treatment with Ifr only. Therefore, spraying Ifr prior to releasing T. montezumae is an effective and compatible biological control strategy for management of the green croton scale on croton plants.     

Machine vision algorithm for whiteflies (Bemisia tabaci Genn.) scouting under greenhouse environment

One of the main problems in greenhouse crop production is the presence of pests. Detection and classification of insects are priorities in integrated pest management (IPM). This document describes a machine vision system able to detect whiteflies (Bemisia tabaci Genn.) in a greenhouse by sensing their presence using hunting traps. The extracted features corresponding to the eccentricity and area of the whiteflies projections allow to establish differences among pests and other insects on both the trap surfaces and dust generated artefacts. Because of whiteflies geometrical characteristics, it was possible to design an efficient (related to manual counting) machine vision algorithm to scout and count units of this pest within a greenhouse environment. These algorithm results show high correlation indexes for both, sticky screens (R² = 0.97) and plant leaf situations (R² = 1.0). The machine vision algorithm reduces the scouting time and the associated human error for IPM‐related activities.     

Odour masking of tomato volatiles by coriander volatiles in host plant selection of Bemisia tabaci biotype B

The silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most important pest insects in tomato crop systems worldwide. It has been previously demonstrated that intercropping tomato [Solanum lycopersicum L. Mill. (Solanaceae)] with coriander [Coriandrum sativum L. (Apiaceae)] reduces the incidence and severity of damage caused by B. tabaci. However, it is not yet known how coriander affects the insect′s behaviour. We evaluated the attractiveness of tomato constitutive volatiles to B. tabaci and what effect coriander constitutive volatiles have on the insect′s behaviour. To this end, we conducted three bioassays in a multiple‐choice four‐arm olfactometer (‘×’ type), measuring B. tabaci behaviour when offered tomato and coriander constitutive volatiles presented alone as well as together. We also evaluated the colonisation and establishment of B. tabaci in experimental plots with only single tomato plants and tomatoes intercropped with coriander in a greenhouse. Bemisia tabaci males and females recognised tomato constitutive volatiles as a positive stimulus (kairomonal effect), indicating that semiochemicals from this plant can play an important role in the insect’s host plant selection. Coriander constitutive volatiles reduced the attractiveness of tomato volatiles but no repellency to these volatiles was observed. Greater numbers of adults and nymphs of B. tabaci per plant were observed in tomato monoculture plots than in tomato intercropped with coriander. We suggest that coriander constitutive volatiles have an odour masking effect on tomato volatiles, thus interfering in the host plant selection of B. tabaci.     

Predation of a biological control agent,Nesidiocoris tenuis (Hemiptera: Miridae), by the spider Leucauge blanda in greenhouse eggplant crops

Nesidiocoris tenuis (Hemiptera: Miridae) is used widely around the world as a biological control agent. In Kochi Prefecture, Japan, at the end of each greenhouse eggplant crop production period, the N. tenuis populations that have developed are collected and transferred to ‘natural-enemy-rearing greenhouses’ so that farmers can use the bug in the next production period. However, spider numbers have been increasing at the end of the production periods and it is becoming difficult to collect N. tenuis in some greenhouses. Therefore, we constructed specific primers for N. tenuis mtDNA to test whether the species was being preyed upon by the predominant spider species, Leucauge blanda. In polymerase chain reactions, these primers amplified a 148-bp fragment of the mitochondrial cytochrome oxidase subunit I gene of N. tenuis but not of any of the 13 other arthropod species tested that occurred in eggplant greenhouses. In a laboratory experiment, the rates of detection of N. tenuis DNA in the spiders after the end of a period of feeding on the bug were 90% at 0?h, 60% at 24?h, and 0% at 72?h. In a greenhouse field experiment, the rate of detection of N. tenuis DNA in the spider was 95%. These results suggest that L. blanda is responsible for the observed suppression of N. tenuis populations in greenhouse eggplant crops.     

Management of <Emphasis Type="Italic">Tetranychus urticae</Emphasis> (Acari: Tetranychidae) in strawberry fields with <Emphasis Type="Italic">Neoseiulus californicus</Emphasis> (Acari: Phytoseiidae) and acaricides

The purpose of this study was to evaluate the performance of Neoseiulus californicus (McGregor) for the control of Tetranychus urticae Koch in commercial strawberry fields, under greenhouse conditions, in association or not with the use of acaricides. The N. californicus strain used in this study was tolerant or resistant to several pesticides. Three experiments were carried out in the State of São Paulo, Brazil. For the first experiment, the initial infestation of T. urticae was 87.1 active stages per leaflet. Two applications of propargite were made on the first and the 14th day of the experiment. Approximately 2 h after each propargite application, N. californicus was released at a rate of 3.0 and 1.9 adult mites per plant, respectively, for each application. The population of T. urticae decreased from 87.1 to 2.8 mites per leaflet in the first three weeks. After this period, the population of T. urticae was maintained at low levels (≤1.5 mites/leaflet) until the end of the experiment (10th week). Propargite and dimethoate sprayed on the strawberry field did not affect significantly the population of this predaceous mite. For the second experiment, the infestation of T. urticae was 29.1 mites per leaflet, when the acaricide chorfenapyr was applied on the strawberry field. The release of N. californicus (2 mites per plant) was made 2 weeks after spraying the acaricide. The population of T. urticae was maintained at low levels (≤2.8 mites/leaflet) for 8 weeks (evaluation period). The T. urticae infestations in plots with N. californicus were significantly lower than in non-release plots, for the experiments 1 and 2. In the third experiment, the initial infestation of T. urticae was 40.5 mites per leaflet (55.5 active stages/leaflet on release plants; 25.5 active stages/leaflet on non-release plants). Three releases of N. californicus (average rate of 3.0 adult mites/plant), without any acaricide application, were not sufficient to reduce significantly the T. urticae population in release plots (release plants + non-release plants) in 6 weeks from the first release, however, the spider mite population decreased from 55.5 to 7.8 active stages per leaflet on release plants, during this period. Interplant dispersal of N. californicus was low in this strawberry field with high infestation of T. urticae. The studies indicate the viability of the use of this strain of N. californicus for the control of T. urticae in strawberry fields under greenhouse conditions, especially in association with selective acaricides.     

Evaluation of the local population of Eretmocerus mundus (Hymenoptera: Aphelinidae) for biological control of Bemisia tabaci biotype B (Hemiptera: Aleyrodidae) in greenhouse peppers in Argentina

Bemisia tabaci biotype B is a key pest in pepper crops in Argentina. The parasitoid Eretmocerus mundus is frequently found parasitizing this whitefly in greenhouses without pesticide applications. The present studies were carried out with the objective of evaluating control obtained with different rate and number of parasitoid releases under experimental conditions. Release rate: cages with pepper pots were positioned in an experimental greenhouse and randomly assigned to the release rate treatments (0, 1 and 3 pairs of E. mundus/plant/week with a total of three introductions). Number of releases: similar cages were assigned to the number of parasitoid introduction treatments (0, 1, 2 and 3) with the best release rate obtained in the previous trial. In both assays whitefly (adults and nymphs) and parasitoid (parasitized nymphs) population sizes in each cage were monitored weekly for a period of 10 weeks. Results suggested that the introduction of 2 E. mundus/plant/week was enough to suppress host population compared to control treatment (peaks of 7.75 adults and 58.75 nymphs/cage and 643.75 adults and 1598 nymphs/cage, respectively) (p < 0.05), with 85% of parasitism. E. mundus had to be introduced three times to achieve the best pest control (peaks of 1.17 adults and 20.33 nymphs/cage vs. 55.67 adults and 75 nymphs/cage in control treatment) with 84% of parasitism (p < 0.05). These results were then validated in a pepper crop under experimental greenhouse conditions. Whitefly population was lower in those greenhouses where E. mundus was released compared to control greenhouses (0.15 adults and 0.71 nymphs/4 leaves and 0.73 adults and 1.64 nymphs/4 leaves, respectively), with a peak of 54% of parasitism (p < 0.05). We concluded that good suppression of B. tabaci could be achieved using E. mundus under spring conditions in Argentina.     

The use of egg counts and suction trap samples to forecast the infestation of spring-sown field beans, Vicia faba, by the black bean aphid, Aphis fabae

Daily suction trap samples at a height of 12·2 m collected throughout the year, winter egg and ‘spring’ population counts on the spindle tree, Euonymus europaeus, and initial infestations of the black bean aphid, Aphis fabae, on field bean, Vicia faba, crops are available from Southern England since 1970. In different areas, estimates of the sizes of the autumn migrations, the over-wintering egg populations, the spring fundatrigeniae and the spring migrations, have been used to forecast field bean crop infestation levels which, in turn, project subsequent trap catches of alatae. The forecasts of crop infestation become progressively more accurate from the autumn migration to the following spring migration, accounting for 28%, 54%, 54% and 64% of the variance respectively. In areas where traps are sited, the spring migration trap samples give the most accurate estimate of the size and timing of crop infestation. Autumn trap catches are particularly useful as very early forecasts of likely very large or very small populations on field beans about 8 months later, but otherwise they lack precision. Egg sampling in winter provides a considerably more accurate forecast approximately 5 months before crop infestations. In spring (May), fundatrigeniae sampled on spindle are most useful for predicting time of migration, and provide approximately 2 weeks' warning for insecticide application, if needed. Finally, trap sampling of the spring migration provides the latest estimate of both the sizes of crop infestations and the timing of insecticide treatment. The E. europaeus and aerial sampling systems are complementary, the traps providing systematic, continuous information and the E. europaeus samples greater detail. Combined, they can provide excellent long-term fore-warning of the need for chemical control and short-term warning of control timing. Forecasts have been 90% correct in eight years out of nine. The error in the ninth year may be due to immigration from the European mainland.