Density thresholds for Nesidiocoris tenuis (Heteroptera: Miridae) in tomato crops

Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae) is common in vegetable crops of the Mediterranean area, with an increasing worldwide range of geographical distribution. This omnivore is a reputed predator of small arthropod pests, but also produces injuries on vegetative and reproductive plant parts. The aim was to estimate density thresholds based on N. tenuis and whitefly abundance for the management of N. tenuis in tomato crops. The assay was carried out in mesh-walled and plastic greenhouses in southern Spain during 2004 and 2007. The natural population dynamics of N. tenuis and whitefly were monitored, and impact on yield quantified. The economic injury level and intervention threshold were predicted based on the zoophytophagous response of N. tenuis and the yield compensation of tomato plants. The proportion of aborted flowers on the tomato plants was related directly to the abundance of N. tenuis and inversely to the interaction between the number of N. tenuis and the number of whitefly immatures. Over-compensation of fruit weight was predicted for flower abortion rates due to N. tenuis lower than 0.171. No yield reduction is expected for values <0.65 N. tenuis per leaf, independent of the whitefly abundance, nor for up to 5 N. tenuis and >26 whitefly immatures per leaf. For intermediate N. tenuis levels, the outcome depends on the prey density. The probability of N. tenuis producing yield loss in tomato crops increases at N. tenuis:whitefly ratios >0.168. Yield reduction is expected after N. tenuis population peaks, when whitefly numbers have been reduced.     

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.     

Predation by <Emphasis Type="Italic">Nesidiocoris tenuis</Emphasis> on <Emphasis Type="Italic">Bemisia tabaci</Emphasis> and injury to tomato

Tomato is the most important vegetable crop in Spain. The mirid bug Nesidiocoris tenuis (Reuter) commonly appears in large numbers in protected and open-air tomato crops where little or no broad-spectrum insecticides are used. Nesidiocoris tenuis is known to be a predator of whiteflies, thrips and several other pest species. However, it is also considered a pest because it can feed on tomato plants, causing necrotic rings on stems and flowers and punctures in fruits. Our objectives were to evaluate predation by N. tenuis on sweetpotato whitefly Bemisia tabaci Gennadius under greenhouse conditions and establish its relationship to N. tenuis feeding on tomato. Two different release rates of N. tenuis were compared with an untreated control (0, 1 and 4 N. tenuis plant⁻¹) in cages of 8 m². Significant reductions of greater than 90% of the whitefly population and correspondingly high numbers of N. tenuis were observed with both release rates. Regression analysis showed that necrotic rings on foliage caused by N. tenuis were best explained by the ratio of B. tabaci nymphs:N. tenuis as predicted by the equation y = 15.086x − 0.6359.

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.     

Response of the zoophytophagous predators Macrolophus pygmaeus and Nesidiocoris tenuis to volatiles of uninfested plants and to plants infested by prey or conspecifics

Knowledge about the orientation mechanisms used by two important predaceous mirids (Macrolophus pygmaeus Rambour and Nesidiocoris tenuis (Reuter)) in finding their prey (whitefly Bemisia tabaci (Gennadius) and the tomato borer Tuta absoluta (Meyrick)) is limited. In a Y-tube olfactometer, we tested the behavioral responses of naïve and experienced predators to uninfested plants, herbivore-induced plant volatiles (HIPVs) from plants infested with T. absoluta and/or B. tabaci, the sex pheromone of T. absoluta, and volatiles produced by plants injured by the predators. Nesidiocoris tenuis responds to volatiles produced by uninfested plants only after experience with the plant, whereas naïve and experienced M. pygmaeus show positive chemotaxis. Both predators are attracted to volatiles from prey-infested plants, and we provide the first evidence that experience affects this response in M. pygmaeus. Infestation of the same plant by both prey species elicited similar responses by the two predators as plants infested by either herbivore singly. Neither predator responded to sex pheromones of T. absoluta. Macrolophus pygmaeus avoided plants injured by conspecifics, while N. tenuis females were attracted by such plants. The implications of these results for augmentative biological control are discussed.     

Sugar as nutritional supplement for the zoophytophagous predator Nesidiocoris tenuis

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is a zoophytophagous predator widely used in integrated pest management programs in both greenhouse and open-field tomato crops. Mass rearing of N. tenuis is greatly dependent on Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) eggs as food source. Moreover, the addition of this factitious prey after the inoculative releases of N. tenuis under field conditions is recommended to facilitate establishment of this mirid. However, E. kuehniella eggs are expensive and availability is limited. One possible strategy to reduce the amount of E. kuehniella eggs needed is the provision of sugar. In this work, the effect of sucrose as nutritional supplement on selected life-history traits of N. tenuis was studied. The addition of sucrose (0.5 M) ad libitum to a diet of E. kuehniella eggs significantly increased the progeny of N. tenuis and did not affect survival of nymphs nor developmental time. Moreover, addition of sucrose significantly reduced the number of E. kuehniella eggs consumed. These results may have practical implications of interest in mass rearing systems of N. tenuis and its management in fields and greenhouses as a part of biological control programs.     

Nutritional variations at Nesidiocoris tenuis feeding sites and reciprocal interactions between the mirid and tomato plants

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) uses a flush‐and‐lacerate feeding strategy producing necrotic rings (NR) at feeding sites in tomato plants. The aim was to investigate the variation in the concentrations of amino acids (aa) and sugars at feeding sites, and its effect on this mirid's life‐history traits and behaviour. The concentration of nutrients was measured in different parts of stems damaged by N. tenuis and mechanically using liquid chromatography. aa concentrations increased below NR; around and above NR, the concentrations of essential and non‐essential aa declined. The concentration of glucose was lower around NR and below. The change in the distribution of aa was similar in NR and mechanically damaged stems, whereas there were no differences in sugar contents. Development time and nymphal mortality were measured on fresh leaflets, leaflets with NR and leaflets plus Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Without prey, development took longer on NR than on fresh leaflets. Development was quicker and mortality lower on leaflets plus moth eggs. Finally, behavioural events were recorded in fifth‐instar nymphs of N. tenuis in: (i) double‐choice experiments (DCE) using leaflets with and without NR; (ii) DCE using leaflets exposed and non‐previously exposed to nymphs and (iii) fresh tomato leaflets plus Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) nymphs. In (i), feeding events lasted longer at NR sites; in (ii), the behaviour of the nymphs on previously exposed leaflets was not significantly different from fresh leaflets; and in (iii), most of the time was dedicated to prey feeding. The overall results indicate that N. tenuis do not take advantage of the inhibited translocation of nutrients in the phloem. The poorer performance of nymphs on leaflets from plants previously exposed to N. tenuis might be due to a general decrease in the concentration of nutrients or to the activation of plant defences.     

How does a predator find its prey? Nesidiocoris tenuis is able to detect Tuta absoluta by HIPVs

The Zoophytophagous predator, Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is one of the most important candidates for controlling Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato crops. This predator uses different signals including morphological plant traits, prey insects, and volatile substances produced by the infested plants and prey signals to find its suitable prey. These signals are different in each cultivar of a plant. We aimed to understand how N. tenuis finds its prey using volatiles from tomato plants damaged or infested with T. absoluta. The predator’s responses to various plant treatments on two cultivars of tomato plants were tested in a flight tunnel and a four-choice olfactometer. The volatile compounds released from the treatments were also collected and identified. The results of the olfactory experiments showed that the predators even in the absence of light chose the plants bearing their insect prey. This behavior was not the same in both cultivars, and N. tenuis had a tendency toward mechanically damaged of Early Urbana Y cultivar more than Cal JN3 cultivar. The differences in the amount of monoterpenes, sesquiterpenes, and eugenol between cultivars may play a role in the differential attraction of N. tenuis towards infested plants. The difference in the volatile compounds was evident in two cultivars, and this was consistent with our bioassay results. Therefore, the choice of appropriate cultivar and use of herbivore-infested plant volatiles are important for developing a control strategy against T. absoluta and attract its predators.     

Preplant release of Nesidiocoris tenuis and supplementary tactics for control of Tuta absoluta and Bemisa tabaci in greenhouse tomato

An early release system developed for Nesidiocoris tenuis Reuter (Heteroptera: Miridae) could provide a good control of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato. Tuta absoluta and the whitefly Bemisia tabaci Gennadius (Hemiptera: Aleyrodidae) often appear simultaneously in tomato crops and this might affect control capacity. Therefore, the new approach needs to be tested in a situation with both pests present. In addition, Bacillus thuringiensis Berliner and Trichogramma achaeae Nagaraja & Nagarkatti (Hymenoptera: Trichogrammatidae) have been shown to be effective against T. absoluta and could be a supplement to N. tenuis. Two experiments were carried out to evaluate the potential of this approach and its combination with supplementary control agents against T. absoluta. In the first experiment four treatments were compared (T. absoluta, B. tabaci, T. absoluta + N. tenuis, and T. absoluta + B. tabaci + N. tenuis) and N. tenuis was able to control T. absoluta and B. tabaci either alone or together. In the second experiment, five treatments were compared: T. absoluta, T. absoluta + N. tenuis, T. absoluta + N. tenuis + T. achaeae, T. absoluta + N. tenuis + B. thuringiensis, and T. absoluta + N. tenuis + T. achaeae + B. thuringiensis. Nesidiocoris tenuis again proved capable of significantly reducing T. absoluta populations, and the implementation of additional agents did not increase its effectiveness.     

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.     

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.     

Population suppression of Bemisia tabaci (Hemiptera: Aleyrodidae) using yellow sticky traps and Eretmocerus nr. rajasthanicus (Hymenoptera: Aphelinidae) on tomato plants in greenhouses

We conducted three experiments for management of Bemisia tabaci (Gennadius) biotype ‘B’ on tomatoes under greenhouse conditions: (i) vertically placing yellow sticky cards either parallel or perpendicular to tomato rows at a rate of 1 per 3‐m row; (ii) releasing Eretmocerus sp. nr. rajasthanicus once at 30 adults/m² in the high whitefly density greenhouses (> 10 adults/plant), or twice at 15 adults/m² at a 5‐day interval in the low whitefly density greenhouses (< 10 adults/plant); and (iii) using combinations of yellow sticky cards that were placed vertically parallel to tomato rows and parasitoids released once at 30/m² in high whitefly density greenhouses or twice at 15/m² at a 5‐day interval in low whitefly density greenhouses. Our data show that yellow sticky cards trapped B. tabaci adults and significantly reduced whitefly populations on tomato. The yellow sticky cards that were placed parallel to tomato rows caught significantly more whitefly adults than those placed perpendicular to tomato rows on every sampling date. In the treatment where parasitoids were released once at 30/m² in high whitefly density greenhouses, the number of live whitefly nymphs were reduced from 4.6/leaf to 2.9/leaf in 40 days as compared with those on untreated plants on which live whitefly nymphs increased from 4.4/leaf to 8.9/leaf. In the treatment where parasitoids were released twice at 15/m² in low whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.1/leaf to 1.7/leaf in 20 days as compared with those on untreated plants on which numbers of live nymphs of B. tabaci increased from 2.2/leaf to 4.5/leaf. In the treatment of yellow sticky cards and parasitoid release once at 30/m² in high whitefly density greenhouses, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 7.2/leaf to 1.9/leaf, and in the treatment of yellow sticky cards and parasitoid release twice at 15/m² at a 5‐day interval at low whitefly density, the numbers of live nymphs of B. tabaci on tomato leaves were reduced from 2.5/leaf to 0.8/leaf; whereas the numbers of live nymphs of B. tabaci on untreated plants increased from 4.4/leaf to 8.9/leaf. An integrated program for management of B. tabaci on greenhouse vegetables by using yellow sticky cards, parasitoids and biorational insecticides is discussed.     

Intraguild predation and competitive displacement between Nesidiocoris tenuis and Dicyphus maroccanus,two biological control agents in tomato pests

Dicyphus maroccanus Wagner and Nesidiocoris tenuis Reuter (Hemiptera: Miridae) are 2 biological control agents in tomatoes. Through the crop seasons, a natural shift in the occurrence of both mirids in favor of N. tenuis has been observed at the end of the cropping cycle in eastern Spain. To better optimize their conservation, the reasons for the observed change, such as intraguild interactions (IGP) or the influence of environmental conditions, are worth elucidating. To do this, we first studied the IGP of adult females on heterospecific nymphs in the laboratory. We next studied exploitative competition between adults and nymphs of each species when feeding on Ephestia kueniella Zeller (Lepidoptera: Pyralidae) eggs in the laboratory. Finally, to analyze the competitive displacement between both mirids, we conducted a semifield experiment in which both predators were released together. All experiments were conducted at 2 temperature regimes (20 and 25°C). Adult‐to‐nymph intraguild interactions occurred only at 25 ºC at very low levels, showing that N. tenuis attacked and consumed a greater proportion of heterospecific nymphs. Nesidiocoris tenuis was a better competitor than D. maroccanus when feeding on the shared prey in the presence of its heterospecific nymph at 25 ºC. In semifield conditions, N. tenuis showed a competitive advantage over D. maroccanus at both temperatures. We conclude that there is not direct interference between both species, however, N. tenuis has a greater ability to outcompete, since it is best adapted to higher temperatures and it is able to remove food sources for D. maroccanus.     

Sugars as complementary alternative food for the establishment of Nesidiocoris tenuis in greenhouse tomato

Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae) is an omnivorous generalist predator which is augmentatively released and conserved for control of whiteflies (Hemiptera: Aleyrodidae) and Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) in tomato crops. Eggs of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae) are often provided as factitious prey to improve the establishment of N. tenuis after its release. We first tested different amounts of E. kuehniella eggs per plant to optimize N. tenuis establishment and then investigated whether the amount of eggs that optimized N. tenuis establishment might be reduced by adding sugars (hydrocapsules filled with 0.5 m sucrose) under walk‐in cage and commercial greenhouse conditions. These experiments demonstrated that the addition of sugar to the diet of N. tenuis could half the amount of E. kuehniella eggs required to establish N. tenuis. Under greenhouse conditions, the progeny of N. tenuis per plant did not differ significantly between E. kuehniella alone or the half amount of E. kuehniella plus hydrocapsules. These results demonstrated that the sugar could partially substitute for E. kuehniella eggs improve establishment of N. tenuis and suggest that natural sugars such as nectar and honeydew might also beneficial.     

The effects of mullein plants (Verbascum thapsus) on the population dynamics of Dicyphus hesperus (Heteroptera: Miridae) in tomato greenhouses

The response of Dicyphus hesperus Knight (Heteroptera: Miridae) to whitefly populations in tomato greenhouses was measured in the presence and absence of mullein (Verbascum thapsus L.) as an alternative host plant. The dynamics of the D. hesperus population on tomato (Lycopersicon esculentum Mill.) and on mullein plants were followed through an entire growing season. In houses with mullein plants, more predators occurred on mullein when whitefly density was low on tomato. A mark-release-recapture experiment where rabbit IgG was used as an external marker showed that D. hesperus adults moved from mullein plants to tomato plants. D. hesperus was always more abundant in houses with mullein than in the houses with tomato plants alone. Movements between tomato and mullein plants are discussed as a strategy to optimize predator foraging. The use of mullein as an alternative host plant may contribute to the establishment of D. hesperus and help to preserve the predator population when prey on tomato crops is scarce.     

Intraguild predation and sublethal interactions between two zoophytophagous mirids,Macrolophus pygmaeus and Nesidiocoris tenuis

The omnivorous predators Macrolophus pygmaeus and Nesidiocoris tenuis (Hemiptera: Miridae) are important biological control agents of pests on tomato crops. In this study, potential intraguild predation (IGP) interactions between the two species were investigated on tomato. We examined: (a) the within plant distribution of both species in the field, (b) the within plant distribution of each predatory species when co-occurred at high densities on tomato caged plants, (c) their behavioral interactions when enclosed in experimental arenas and (d) the development young and old nymphs of M. pygmaeus when enclosed together with N. tenuis adults. Results revealed that the two predators showed a different distribution pattern on the plants, with N. tenuis exploiting mostly the upper part, whereas M. pygmaeus were mostly observed on the 5th to the 7th leaf from the top. However, when the predators co-occurred, N. tenuis or M. pygmaeus individuals were recorded with increased numbers on the lower or the higher part of the plant, respectively. In the presence of N. tenuis adult young nymphs of M. pygmaeus completed their development to the adult stage, when alternative prey (lepidopteran eggs) was present on the plant, however failed to reach adulthood in the absence of alternative prey. A high percentage of the dead nymphs found with their body fluids totally sucked indicating predation by N. tenuis. However, large 4th instar nymphs of M. pygmaeus were much less vulnerable to N. tenuis than younger. The behavior of N. tenuis was affected by the presence of M. pygmaeus, but at a rate similar to that when two individuals of N. tenuis were enclosed together. Contacts between the predators were recorded in a similar frequency in mono- and heterospecific treatments, whereas aggressive behavior was not observed. This study shows that intraguild interactions between M. pygmaeus and N. tenuis occur but are not intensive. The potential implications of the outcomes for biological control are discussed.     

Tracking the movement of Nesidiocoris tenuis among banker plants and crops in a tomato greenhouse by DNA markers of host plants

The zoophytophagous predator, Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae), is an important biological control agent. To maintain this insect, several non-crop host plants are used as banker plants in greenhouse crop systems. To optimize the efficiency of the predator-banker plant interaction, it is necessary to investigate how individual predators move between banker plants and crops. However, the movement is difficult to quantify under field conditions. Therefore, we investigated the movement of N. tenuis between tomato plants (Solanum lycopersicum L., Solanales: Solanaceae) and three banker plants (Cleome hassleriana Chod., Brassicales: Cleomaceae; Sesamum indicum L., Lamiales: Pedaliaceae; and Verbena × hybrida Voss, Lamiales: Verbenaceae) in a greenhouse by conducting PCR using plant-species-specific primers. Laboratory analysis results showed that our molecular method could detect N. tenuis activity within a relatively short time (≤ 24 h). In addition, N. tenuis predation on a pest species was unlikely to result in false detection of plant DNA in the pest (suggesting that N. tenuis had been on the plants). Multiple plant species were detected in adult insects collected from the greenhouse plants, indicating that N. tenuis frequently moved across the mentioned plant species. The movement patterns of N. tenuis between plant species varied substantially based on the plant species from which they were collected, which suggested each of the plant species had different functions for N. tenuis. Our findings revealed that planting multiple host plants would stabilize the N. tenuis population in biological control programs.

     

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.     

Compatibility of early natural enemy introductions in commercial pepper and tomato greenhouses with repeated pesticide applications

Successful integrated pest management in protected crops implies an evaluation of the compatibility of pesticides and natural enemies (NE), as control strategies that only rely on one tactic can fail when pest populations exceed NE activity or pests become resistant to pesticides. Nowadays in Almería (Spain), growers release NE prior to transplanting or early in the crop cycle to favor their settlement before pest arrival because this improves biocontrol efficacy, although it extends pesticide exposure periods. The purpose of this research was to evaluate the compatibility of two applications of pesticides with key NE in 2‐year trials inside tomato and sweet pepper commercial greenhouses: Nesidiocoris tenuis (Reuter) (Hemiptera: Miridae), Orius laevigatus (Say) (Hemiptera: Anthocoridae) and Amblyseius swirskii (Athias‐Henriot) (Acari: Phytoseiidae). In tomato, flubendiamide and chlorantraniliprole (IOBC category 1) were compatible with N. tenuis, but chlorpyrifos‐methyl and spinosad (IOBC categories 2–3), which effectively reduced Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) density, compromised its predatory activity. In sweet pepper, chlorantraniliprole (IOBC category 1) was the only pesticide compatible with O. laevigatus while chlorantraniliprole, emamectin benzoate, spirotetramat and pymetrozine were harmless (IOBC category 1) to Amblyseius swirskii, and sulfoxaflor slightly harmful (IOBC category 2) to this phytoseiid predator.     

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.