Biological control of arthropod pests using banker plant systems: Past progress and future directions

The goal of banker plant systems is to sustain a reproducing population of natural enemies within a crop that will provide long-term pest suppression. The most common banker plant system consists of cereal plants infested with Rhopalosiphum padi L. as a host for the parasitoid Aphidius colemani L. Aphidius colemani continually reproduce and emerge from the banker plants to suppress aphid pests such as Aphis gossypii Glover and Myzus persicae Sulzer. Banker plant systems have been investigated to support 19 natural enemy species targeting 11 pest species. Research has been conducted in the greenhouse and field on ornamental and food crops. Despite this there is little consensus of an optimal banker plant system for even the most frequently targeted pests. Optimizing banker plant systems requires future research on how banker plants, crop species, and alternative hosts interact to affect natural enemy preference, dispersal, and abundance. In addition, research on the logistics of creating, maintaining, and implementing banker plant systems is essential. An advantage of banker plant systems over augmentative biological control is preventative control without repeated, expensive releases of natural enemies. Further, banker plants conserve a particular natural enemy or potentially the ‘right diversity’ of natural enemies with specific alternative resources. This may be an advantage compared to conserving natural enemy diversity per se with other conservation biological control tactics. Demonstrated grower interest in banker plant systems provides an opportunity for researchers to improve biological control efficacy, economics, and implementation to reduce pesticide use and its associated risks.     

In search of artificial domatia for predatory mites

Banker plants can enhance biological pest control by providing both floral resources and appropriate oviposition sites, e.g. through acarodomatia, to predator species. The use of materials mimicking domatia i.e. artificial domatia may be an economically favourable alternative to the use of banker plants bearing domatia. The aim of the present study was to identify materials that are able to host eggs of the Neoseiulus californicus predatory mite but not those of the Tetranychus urticae pest mite. In a laboratory experiment, the oviposition of predatory and phytophagous mites were compared in Petri dishes containing leaves. The different modalities compared were (i) natural domatia of Viburnum tinus or (ii) one of twelve potential artificial domatia materials. The overall oviposition response of predatory mites to all artificial domatia was similar to that of the natural domatia. The oviposition of the Tetranychus urticae pest mite did not increase in response to the artificial domatia. Five artificial domatia hosted as many eggs of the predatory mite as observed in the natural domatia. The effect of the physical properties of artificial domatia was also tested and N. californicus was found to favour the artificial domatia that had high heat retention capacities for oviposition. Three of these artificial domatia were tested on rose plants in a greenhouse experiment; none of which enhanced the biological control on the plants under these conditions. The present study highlights the difficulty in identifying and using suitable artificial domatia as substitutes to banker plants in biological pest control efforts.     

Establishment of papaya banker plant system for parasitoid, Encarsia sophia (Hymenoptera: Aphilidae) against Bemisia tabaci (Hemiptera: Aleyrodidae) in greenhouse tomato production

The silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), is a key pest of tomato (Solanum lycopersicum L.) and other vegetable crops worldwide. To combat this pest, a non-crop banker plant system was evaluated that employs a parasitoid, Encarsia sophia (Girault & Dodd) (Hymenoptera: Aphelinidae) with whitefly, Trialeurodes variabilis (Quaintance) (Hemiptera: Aleyrodidae), as an alternative host for rearing and dispersal of the parasitoid to the target pest. (a) Multi-choice and no-choice greenhouse experiments were conducted to determine host specificity of T. variabilis to papaya (Carica papaya L.) and three vegetable crops including tomato, green bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L.). The result showed that papaya was an excellent non-crop banker plant for supporting the non-pest alternative host, T. variabilis, whose adults had a strong specificity to papaya plants for feeding and oviposition in both multi-choice and no-choice tests. (b) The dispersal ability of E. sophia was investigated from papaya banker plants to tomato and green bean plants infested with B. tabaci, as well as to papaya control plants infested with T. variabilis; and (c) the percent parasitism by E. sophia on T. variabilis reared on papaya plants and on B. tabaci infested on tomato plants was also evaluated. These data proved that E. sophia was able to disperse at least 14.5 m away from papaya plants to target tomato, bean or papaya control plants within 48–96 h. Furthermore, E. sophia was a strong parasitoid of both T. variabilis and B. tabaci. There was no significant difference in percent parasitism by E. sophia on T. variabilis (36.2–47.4%) infested on papaya plants or B. tabaci (29–45.9%) on tomato plants. Thus, a novel banker plant system for the potential management of B. tabaci was established using papaya as a non-crop banker plant to support a non-pest alternative host, T. variabilis for maintaining the parasitoid to control B. tabaci. The established banker plant system should provide growers with a new option for long-term control of B. tabaci in greenhouse vegetable production. Ongoing studies on the papaya banker plant system are being performed in commercial greenhouses.     

Biological control of Myzus persicae (Hemiptera: Aphididae) through banker plant system in protected crops

Banker plants with Aphidius colemani were tested in greenhouse for control of Myzus persicae on arugula and sweet pepper crops and compared to inoculative releases of parasitoids. Banker plants system consisted of pots of oat (non-crop plant) infested with Rhopalosiphum padi (non-pest herbivore). The non-pest herbivore serves as an alternative host for A. colemani (parasitoid of the target crop pest). In the arugula crop significant differences in the pest population between the two strategies of biological control showed the lowest densities of the pest when introducing the banker plant system. In the sweet pepper crop, there was no difference in the pest population between the two strategies of biological control.     

Ornamental pepper as banker plants for establishment of Amblyseius swirskii (Acari: Phytoseiidae) for biological control of multiple pests in greenhouse vegetable production

Silverleaf whitefly, Bemisia tabaci biotype B (Gennadius) (Hemiptera: Aleyrodidae), western flower thrips, Frankliniella occidentalis (Pergande), and chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), are key pests of vegetable crops in the US. The present study established ornamental peppers as banker plants supporting Amblyseius swirskii (Acari: Phytoseiidae) against the three pests. Specifically, this study (a) evaluated survival and population buildup of A. swirskii on three ornamental pepper varieties, Masquerade (MA), Red Missile (RM), and Explosive Ember (EE) in both laboratory and greenhouses and (b) determined the predation of A. swirskii reared on ornamental pepper plants to the targeted pests under greenhouse conditions. The results showed that the three pepper varieties were excellent banker plants and able to support at least ∼1000 of all stages of A. swirskii per plant in greenhouse conditions and allow them to complete their life cycle. A. swirskii dispersed or released from the banker plants to target plants, resulting in significant suppression of the three pests, i.e., after 14 d post-release, a significantly lower average of 2.75 B. tabaci and 13.4 all stages of thrips (chilli thrips and western flower thrips) were found per bean plant, respectively, compared to 379.5 B. tabaci and 235.4 all stages of thrips per plant in the control. Furthermore, our experiment observed that the sweet pepper seedlings closed to banker plants were healthy, whereas those without banker plants were heavily infested by chilli thrips; their growth seriously stunted or died. This is the first report of ornamental pepper as banker plants supporting A. swirskii against three notorious pests. This established banker plant system could be a new addition to the integrated pest management programs for sustainable control of these three pests in greenhouse vegetables.     

Pollen increases fitness and abundance of Orius insidiosus Say (Heteroptera: Anthocoridae) on banker plants

Banker plants are intended to enhance biological control by sustaining populations of natural enemies. Banker plants do this by providing alternative sources of food for natural enemies, such as pollen for omnivorous predators, thus decreasing the likelihood of their starvation and emigration from a cropping system when pest populations are low or absent. A banker plant system consisting of the Black Pearl pepper, Capsicum annuum ‘Black Pearl’, and the omnivorous minute pirate bug, Orius insidiosus Say (Hemiptera: Anthocoridae) has recently been proposed to improve biological control of thrips. Therefore, we studied how pollen from the Black Pearl pepper plant affects O. insidiosus fitness and abundance through a series of laboratory and greenhouse experiments. We found that a mixed diet of pollen and thrips increased O. insidiosus female longevity, decreased nymphal development time, and yielded larger females compared to a diet of thrips alone. Furthermore, O. insidiosus abundance was greater on flowering pepper plants than non-flowering pepper plants. From these results, we suggest that pollen from Black Pearl pepper banker plants could increase adult O. insidiosus abundance for the purpose of biological control in two ways: (1) reduce starvation and increase longevity of O. insidiosus when prey is absent; (2) enhance O. insidiosus fitness and fecundity when prey is present by mixing plant and prey diets. These results encourage future studies with the Black Pearl pepper as a banker plant for improving biological control of thrips in commercial greenhouses.     

Evaluation of the indigenous parasitoid Encarsia transvena (Hymenoptera: Aphelinidae) for biological control of the whitefly Bemisia tabaci (Hemiptera: Aleyrodidae) in greenhouses in India

The efficiency of the native parasitoid, Encarsia transvena Timberlake for the management of greenhouse whitefly, Bemisia tabaci (Gennadius) was studied in cages and a greenhouse in India. Parasitism by Enc. transvena of B. tabaci on Lycopersicon esculentum L. (tomato), Solanum melongena L. (eggplant) and Nicotiana tabacum L. (tobacco) was evaluated in cages to compare the utility of each species as potential banker plants. B. tabaci populations were consistently present on all three host plant species for almost two months providing sufficient hosts for parasitoid multiplication. Significantly more B. tabaci nymphs/unit leaf area were found on N. tabacum (77.7) and on S. melongena (76.5) than L. esculentum (45.9) in the initial growing period of the plants, that increased more on L. esculentum as the crops grew older. A greater proportion of B. tabaci were parasitised by Enc. transvena on L. esculentum than on N. tabacum and S. melongena. Rate of parasitism on L. esculentum was 25.19 and on N. tabacum was 24.70 in greenhouse. Parasitism, although occurring throughout greenhouses, was greatest on plants within 3 metres of introduced banker plants. The results suggest the utility of the three plant species as potential banker plants for the management of whiteflies in greenhouses.     

Functional response of Nesidiocoris tenuis (Hemiptera: Miridae) to Trialeurodes vaporariorum (Hemiptera: Aleyrodidae): effect of different host plants

The influence of three host plants, namely cucumber, tomato and eggplant, on functional response of male, virgin and mated female predatory bug Nesidiocoris tenuis was investigated on different densities of Trialeurodes vaporariorum nymphs. The 24-h experiment conducted at laboratory conditions revealed that N. tenuis exhibited a type II functional response to T. vaporariorum on host plants. There were no significant differences between attack rates, as well as handling times estimated for each adult stage of the predator between host plants. However, on each host plant, the handling time estimated for the mated female in comparison with two other adult stages had lower values (0.7952, 0.6827 and 0.8884?h^?1 on cucumber, tomato and eggplant, respectively). Handling time estimated for the mated female on cucumber was significantly lower than that estimated for the male predator. The highest maximum handling rate (T/T_h) was estimated for the mated female followed by the virgin female and male on all host plants. For three adult stages of the predator, the highest value of this parameter was determined on tomato followed by cucumber and eggplant. Unlike virgin and mated females, the host plant significantly affected prey consumption by the male. Prey consumed by mated females was higher than those obtained for two other adult stages of the predator on each host plant. The difference in trichome density between three host plants may be responsible for the obtained results. These results revealed that N. tenuis is more effective in the biological control of T. vaporariorum on tomato in comparison with cucumber and eggplant.     

Nesidiocoris tenuis as a pest in Northwest Europe: Intervention threshold and influence of Pepino mosaic virus

The use of Nesidiocoris tenuis (Hemiptera: Miridae) as a biocontrol agent is controversial as it is considered a pest in Northwest European tomato greenhouses, due to its tendency to damage the plant and fruit. Necessary chemical plant protection products to control N. tenuis have toxic side effects on important beneficials like Macrolophus pygmaeus (Hemiptera: Miridae), which jeopardizes the whole IPM programme. In this study, several commercial tomato greenhouses were monitored for mirid populations. The relationship between the number of N. tenuis individuals and plant damage was assessed in function of availability of prey and interaction with M. pygmaeus. These greenhouse data were used to determine a practical density intervention threshold. Next, the hypothesis that a Pepino mosaic virus (PepMV) infection increases plant and fruit damage by N. tenuis (as has been shown for M. pygmaeus) was tested. Plant damage occurred when the average number of predatory bugs in the head of the plant exceeded 16 per ten plants. Plant damage increased in severity at increasing predatory bug densities, independent of the availability of prey and M. pygmaeus presence. Plant and fruit damage were not affected by the presence of PepMV, as was shown for fruit damage in previous studies for M. pygmaeus. Our study provides a practical density intervention threshold for growers in greenhouse crops. Simple monitoring of the number of predatory bugs in the head of the plant can be used to take specific biocontrol actions. It was also shown that only the predatory bug N. tenuis itself causes damage, and there is no interaction with PepMV.     

Release rate for a pre-plant application of Nesidiocoris tenuis for Bemisia tabaci control in tomato

Nesidiocoris tenuis Reuter (Het.: Miridae) is widely used as a biological control agent of whiteflies and other pests in greenhouse-grown tomatoes. It is typically released augmentatively some weeks after transplanting and needs several weeks to establish. Releasing N. tenuis prior to transplanting could accelerate its establishment. However, timing for releases could affect biological control and require changes in release rates of the predator. Because N. tenuis is also phytophagous it must be released at a rate which provides the best equilibrium between adequate biological control of Bemisia tabaci Genn. and acceptable injury to the crop. The objective of this study was therefore to evaluate different release rates for releasing N. tenuis prior to transplanting for maximizing control capacity and minimizing injury to crop. The study was carried out in two subsequent trials in which different release rates were evaluated under a worst case scenario of rapid immigration of the pest into a tomato greenhouse. In the first experiment (winter experiment), four treatments were compared: (1) B. tabaci (0 N. tenuis/plant), (2) B. tabaci?+?0.5?N. tenuis/plant, (3) B. tabaci?+?1?N. tenuis/plant and (4) B. tabaci?+?2?N. tenuis/plant. In the second experiment (summer experiment), the treatments were: (1) B. tabaci (0 N. tenuis/plant), (2) B. tabaci?+?0.5?N. tenuis/plant and (3) B. tabaci?+?1?N. tenuis/plant. All the evaluated rates significantly reduced the population of whitefly and gave adequate control of the pest. However, only 0.5?N. tenuis/plant did not increase crop damage compared to the treatment with no N. tenuis.     

Effects of an alternative diet of Artemia cysts on the development and reproduction of Nesidiocoris tenuis (Hemiptera: Miridae)

The small green mirid Nesidiocoris tenuis Reuter (Hemiptera: Miridae) preys on pest insects such as whiteflies and serves as a biological control agent in many greenhouses. However, this mirid is limited in its application, because individuals tend to escape from agricultural fields and soon die due to a lack of available food sources. In addition, the food traditionally used to culture N. tenuis is expensive. Thus, identifying low-cost foods for N. tenuis would help to increase the species’ further utilization. Brine shrimp (Artemia spp., Anostraca: Artemiidae) cysts are potentially useful as a low-cost alternative diet to sustain populations of predatory natural enemies. We evaluated the developmental and reproductive performance of N. tenuis when reared on Artemia salina L. cysts supplied in dry or wet form. The dry cysts showed a similar performance to that of Mediterranean flour moth (Ephestia kuehniella Zeller, Lepidoptera: Pyralidae) eggs, which are often used as a nutritional diet for mass rearing of N. tenuis. Although the wet cysts contributed to growth, compared to other diets, they were inferior in nymphal development time and longevity. These results suggest that relatively inexpensive Artemia dry cysts can be used to successfully breed N. tenuis and sustain populations in crop fields.

     

Response of mirid predators to synthetic herbivore‐induced plant volatiles

Zoophytophagous plant bugs feed on plant tissue as a source of water and nutrients, besides feeding on prey. By phytophagy, mirid predators activate plant defense responses through different pathways, resulting, among others, in the release of herbivore‐induced plant volatiles (HIPVs). These compounds could repel herbivores and attract parasitoids and predators, and synthetic versions could potentially be used in biological control. Nevertheless, little is known about the influence of synthetic volatiles on mirid attraction. Using Y‐tube olfactometer trials, we evaluated the responses of Nesidiocoris tenuis (Reuter), Macrolophus pygmaeus (Rambur), and Dicyphus bolivari Lindberg (Hemiptera: Miridae), important natural enemies used to control various greenhouse pests, to 10 synthetic versions of HIPVs released from tomato (Solanum lycopersicum L., Solanaceae) plants induced by N. tenuis and M. pygmaeus. Nesidiocoris tenuis responded to five of the 10 HIPVs, whereas M. pygmaeus and D. bolivari responded to four of the 10 HIPVs. Two green leaf volatiles, (Z)‐3‐hexenyl propanoate and (Z)‐3‐hexenyl acetate, and the ester methyl salicylate (MeSA) were attractive to all three mirid predator species. Our results demonstrate that the volatiles released by tomato plants activated by N. tenuis and M. pygmaeus phytophagy are attractive to their conspecifics and also to D. bolivari. Further studies should evaluate the potential of these compounds to attract predatory mirids in the field.     

Survey of flowering plants in Hawaii as potential banker plants of anthocorid predators for thrips control

Flowering plants in gardens and along roadsides on the Big Island of Hawaii were sampled for thrips and anthocorid predators of thrips. A total of 171 plant samples, comprising 859 plant sample units (e.g. flowers or flower clusters) were collected from 56 species of plants in 25 families. Adult thrips were found on 43 plant species, and 32 of these also had larval thrips of the same species, indicating the plant species was a breeding host for thrips. Five different species of anthocorids – Orius persequens, Orius tristicolor, Paratriphleps laeviusculus, Montandoniola confusa, and Blaptostethus pallescens – were collected on 22 different plant species in 10 plant families. The plants with the highest numbers of anthocorid adults and nymphs present were Macaranga tanarius (Blush Macaraga), Verbesina encelioides (Golden Crownbeard), Tithonia diversifolia (Tree Marigold), Acalypha hispida (Chenille bush), and Coreopsis lanceolata (Lance-leaf Coreopsis). Macaranga tanarius was found to be the best host plant for anthocorids, with an average of 25.5 adult and 21.1 larval anthocorids per plant sample. Orius persequens was the most abundant anthocorid on M. tanarius with average adult and larval densities of 24.1 and 17.3 per plant sample, respectively. None of the insects found in association with M. tanarius are known pests. Macaranga tanarius has great potential as a banker plant to help suppress thrips populations in greenhouse crops with anthocorid predators.     

Evaluation of pest control efficiencies for different banker plant systems with a simple predator–prey model

The banker plant system has been introduced for the biological control of various pest species in Japanese greenhouses. With the banker plant system, non-crop plants infested with a host insect (a non-commercial crop pest) are placed in the greenhouse to provide alternative resources for the parasitoids or predators. We want to evaluate the effectiveness for controlling pests on the crop in a quantitative way by immigrating predators from the banker plant. Therefore, we developed a simple model for the interaction of the pest and predator in the crop and included the banker plant only as a source for predators. For three different pest-predator systems we parameterised the model and used these models to predict under what conditions biological control in a banker plant system is successful. We defined successful as keeping the pest below the economic injury level of the crop estimated from damage analysis. Because the crop is mostly grown during a period that lasts less than a year our analysis should not only focus on the equilibrium dynamics. In contrast, it should also focus on the transient dynamics. Our main analytical result, from the equilibrium analysis, is that for successful control the maximum lifetime consumption of immigrating predators should exceed the daily prey growth at half the value of the maximum consumption rate. For practical purpose this translates into the fact that the immigration of predators at a low initial pest density is crucial for successful control.     

Visualizing eggs of Nesidiocoris tenuis (Heteroptera: Miridae) embedded in tomato plant tissues

Nesidiocoris tenuis (Heteroptera: Miridae) is a predator of some major pests of Solanaceae crops, yet it is scarcely used in biological control because it also feeds on plants and may damage crops. The study of N. tenuis biology may promote the ability to use it as a biological control agent. Because N. tenuis, like some other insect taxa, oviposits into plant tissues, its eggs are hard to detect. This limits our ability to study N. tenuis – plant interactions. We therefore looked for a staining method for plant‐embedded eggs, which will allow their detection within tomato plants, a common host of N. tenuis. We first used lactophenol solution with acid fuchsin to stain eggs inside tomato foliage. Because of the high toxicity of lactophenol, we later substituted lactophenol with a lactoglycerol solution, which was found to be similarly efficient. Five minutes immersion in the staining solution at 80°C followed by a two‐minute soak in hot water made the eggs stain deep red, while the foliage became transparent and was stained weak red. Eggs within leaves were easily visible under 10–30× magnification with sub‐stage lighting; top‐lighting was needed for the detection of eggs embedded in less‐transparent tissues such as stems. This rapid staining method improves the ability to study some important biological aspects of N. tenuis, such as its fecundity. Also, the elimination of phenol made the method cheaper and safer to use. Finally, this method may be adapted for other arthropod–plant systems.     

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.     

Host-range study about four aphid parasitoid species among 16 aphid species for constructing banker–plant systems

To provide fundamental information for the biological control of aphids in vegetable greenhouses, we compared the host ranges of four aphid parasitoid species, Aphidius colemani Viereck, Aphidius gifuensis Ashmead, Diaeretiella rapae (M’Intosh), and Ephedrus nacheri Quilis (Hymenoptera: Braconidae: Aphidiinae). The acceptability as host of 11 vegetable-pest aphids, Acyrthosiphon pisum (Harris), Aphis craccivora Koch, Aphis gossypii Glover, Aulacorthum solani (Kaltenbach), Brevicoryne brassicae (Linnaeus), Chaetosiphon fragaefolii (Cockerell), Lipaphis erysimi (Kaltenbach), Macrosiphoniella sanborni (Gillette), Macrosiphum euphorbiae (Thomas), Myzus persicae (Sulzer), and Uroleucon formosanum (Takahashi), in addition to five aphid species, Melanaphis sacchari (Zehntner), Rhopalosiphum maidis (Fitch), Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), and Sitobion akebiae (Shinji) (Hemiptera: Aphididae) that serve as alternative hosts in banker–plant systems for the four aphid parasitoid species, were investigated. A newly emerged pair of parasitoid adults were provided to 100 aphids of each species on caged host plants in a 25 °C chamber for 24 h. The numbers of mummified aphids and emerged adults were counted in 10 trials for each aphid species. Aphidius colemani, A. gifuensis, D. rapae and E. nacheri parasitized four, two, three, and eight pest species, respectively, and four, three, three, and five alternative host species, respectively. Ephedrus nacheri had the broadest host range among the four species, and all the four species parasitized M. persicae, R. maidis, and S. graminum. This information will be useful for selecting candidate of biological control agents for aphids and for constructing banker–plant systems.

     

Development of a PCR‐based method to monitor arthropod dispersal in agroecosystems: Macrolophus pygmaeus (Hemiptera: Miridae) from banker plants to tomato crops

Development of conservation biological control programs requires the identification of sources that contribute to predator colonization of crops. Macrolophus pygmaeus (Rambur) (Hemiptera: Miridae) is an efficient polyphagous predator used in biological control programs in vegetable crops in Europe. We have developed a marking method based on spraying with a solution of the brine shrimp Artemia spp. (Anostraca: Artemiidae) cysts, followed by a PCR detection of Artemia DNA to monitor M. pygmaeus dispersal from banker plants to tomato crops. Experiments conducted in climatic chambers show that the topical application of this marking solution on M. pygmaeus does not significantly reduce adult longevity and that it is detected up to 6 d after the application. When this Artemia solution was applied on Calendula officinalis L. banker plants harboring M. pygmaeus and maintained outdoors, Artemia DNA was still detected on 62% of the insects after 6 d. The conducted field applications in commercial greenhouses have confirmed the usefulness of this method to monitor M. pygmaeus dispersal from banker plants to a newly planted tomato crop. This method can be used to assess arthropod movement, being an interesting molecular approach for further improving future pest management strategies.     

The combined use of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> and <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> against the tomato borer <Emphasis Type="Italic">Tuta absoluta</Emphasis>

Since Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) was first detected at the end of 2006 in the Mediterranean Basin, several endemic natural enemies have been reported to prey on this exotic pest. The predator Nesidiocoris tenuis Reuter (Hemiptera: Miridae) can regulate T. absoluta populations, because it is able to prey efficiently on T. absoluta eggs. Furthermore, previous studies have demonstrated that first-instar larvae of T. absoluta are highly susceptible to Bacillus thuringiensis (Bt) treatments. In this work, we tested the combination of both approaches under greenhouse conditions. B. thuringiensis formulations were sprayed weekly for two months, three months or throughout the growing cycle, and in all cases, one N. tenuis per plant was also released. Control plants were completely destroyed by the infestation levels reached by T. absoluta. In contrast, all treatments based on B. thuringiensis treatments and releases of N. tenuis reduced leaf damage by more than 97% when compared to the untreated control, with no significant differences among them. Furthermore, yield in the control plants was significantly reduced when compared with all Bt–N. tenuis treatments. Our results demonstrate that when B. thuringiensis treatments are applied immediately after the initial detection of T. absoluta on plants, they do not interfere with N. tenuis establishment in the crop because T. absoluta eggs are available. According to our data, treatments with B. thuringiensis later in the growing season would no longer be necessary because mirids alone would control the pest.     

The effect of banker plant species on the fitness of Aphidius colemani Viereck and its aphid host (Rhopalosiphum padi L.)

Banker plants, a type of open-rearing unit, are increasingly used in greenhouse crops to sustain natural enemy populations at times of low pest abundance. The most common banker plant system is a non-crop, cereal plant which supports Rhopalosiphum padi L. as an alternative host for Aphidius colemani Viereck. Although bottom-up effects of plants are known to affect natural enemies, this aspect has generally been ignored in previous investigations of banker plant efficacy. Here, we tested four cereal plant species with three varieties each to investigate host plant effects on R. padi and A. colemani. Though limited differences were observed in laboratory experiments spanning one aphid or parasitoid generation, longer greenhouse experiments spanning several generations revealed significant plant effects on both insects. R. padi performed poorly on oats (Avena sativa L.), resulting in wasps with the longest female development time, lowest emergence rates, and the lowest number of wasps produced per unit. Rye (Secale cereal L.) – intermediate in terms of aphid performance – produced a significantly male-biased wasp population with the smallest males. Conversely, R. padi placed onto either wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) performed consistently well in terms of aphid and parasitoid fitness and abundance, though neither species was obviously superior over the other. Overall, cultivars within each plant species did not significantly affect outcomes. As each plant species tested had different positive effects on aphid and parasitoid phenotypes, the potential benefits of mixing of cereal species is an area for future investigation.