Mortality of second-instar larvae of Tuta absoluta produced by the hexane extract of Lycopersicon hirsutum f. glabratum (PI 134417) leaves

1 The mortality resulting from exposure of second‐instar larvae of Tuta absoluta to a hexane extract of Lycopersicon hirsutum f. glabratum (PI 134417) leaves was evaluated in the laboratory. 2 A crude hexane extract was fractionated on a silica gel column to produce 17 fractions. The toxicity of the fractions was evaluated on T. absoluta larvae at 2 and/or 6 mg/10 larvae/Petri dish along with a control. 3 Only two fractions, 4.50 and 10.18% of the total hexane extract, were found to result in very high mortality of second‐instar T. absoluta. 4 All the 17 fractions were analysed by capillary gas chromatography/mass spectrometry (GC/MS). The two most toxic fractions were virtually identical and contained mainly undeca‐2‐one (2‐UD) and trideca‐2‐one (2‐TD). 5 A third major sub‐fraction 13 (50.73% of the total hexane extract) was further fractionated on a silica gel column to obtain five additional sub‐fractions. The toxicity of all the five sub‐fractions was evaluated using second‐instar T. absoluta at 2 mg/10 larvae/Petri dish and also analysed by GC/MS. The most toxic sub‐fractions contained mostly 2‐UD and 2‐TD. 6 The results suggest that 2‐UD and 2‐TD could be related to resistance of L. hirsutum to T. absoluta.     

Biology and performance of two indigenous larval parasitoids on Tuta absoluta (Lepidoptera: Gelechiidae) in Sudan

Tuta absoluta is an alien invasive pest in Sudan. Since it was detected in the country, the pest continues to cause major tomato losses. Alarmed by its devastating nature and the speed of spread, tomato growers resorted to the indiscriminate use of broad-spectrum insecticides. Promising indigenous parasitoid(s) may contribute to suppression of this pest. The biology and performance of the native parasitoids, Bracon nigricans Szépligeti (Braconidae) and Dolichogenidea appellator (Telenga) (Braconidae), was therefore evaluated against different immature stages of T. absoluta under laboratory conditions. A significantly higher number of fourth instar larvae was accepted for oviposition by B. nigricans. Similarly, fourth instar larvae yielded a considerably higher number of parasitoid offspring compared to third instar larvae. The male ratio of B. nigricans offspring which emerged from both larval instars was high, 0.96 and 0.66 for third and fourth instar larvae of T. absoluta, respectively. There was, however, no significant difference in the number of males and females that emerged from fourth instar larvae. Conversely, the number of hosts killed by stinging behaviour or host feeding was significantly higher on third instar larvae. B. nigricans potential fecundity varied with the age of the wasp with the lowest fecundity on the day of eclosion. The performance of D. appellator in terms of the total number of offspring produced and female progeny was similar for second and third instar larvae of T. absoluta. The preimaginal developmental time for both parasitoid species did not vary with either host stage or sex of the parasitoid. B. nigricans adult longevity was similar for both sexes, while that of D. appellator significantly varied with females living longer than males. Prospects for conservative biological control of T. absoluta are discussed in the light of the results of this study.     

新疆和云南番茄潜叶蛾种群对六种杀虫剂的敏感性及其与解毒酶活性的关系

【目的】番茄潜叶蛾Tuta absoluta 是新入侵我国的对番茄具有毁灭性危害的入侵害虫,目前入侵我国的番茄潜叶蛾种群对杀虫剂的抗性尚无报道。本研究旨在明确新疆和云南番茄潜叶蛾田间种群对6种常用杀虫剂的敏感性及其与解毒酶活性的关系。【方法】采用浸叶法测定6种常用杀虫剂对番茄潜叶蛾新疆和云南种群2龄幼虫的室内毒力。通过对2龄幼虫的生物测定确定3种增效剂［CYP450抑制剂胡椒基丁醚(PBO)、酯酶抑制剂磷酸三苯酯(TPP)和GST抑制剂丁烯二酸二乙酯(DEM)］对氯虫苯甲酰胺的增效作用。采用酶活性分析测定室内敏感种群和田间抗性种群(新疆种群) 2龄幼虫体内解毒酶［细胞色素P450酶(CYP450)、谷胱甘肽S-转移酶(GST)和羧酸酯酶(CarE)］活性,以确定杀虫剂抗性与解毒酶活性的关系。【结果】番茄潜叶蛾云南种群对6种杀虫剂的敏感性由高到低依次为甲维盐、溴虫腈、多杀菌素、茚虫威、氯虫苯甲酰胺和高效氯氰菊酯。新疆种群对6种杀虫剂的敏感性由高到低依次为甲维盐、溴虫腈、氯虫苯甲酰胺、多杀菌素、茚虫威和高效氯氰菊酯。与室内敏感种群相比,云南和新疆种群对氯虫苯甲酰胺的抗性水平最高,抗性倍数分别为212.7和169.3倍。生物测定结果表明,3种增效剂PBO, TPP和DEM均对氯虫苯甲酰胺无明显增效作用。酶活性测定结果表明,番茄潜叶蛾室内敏感种群和田间抗性种群之间2龄幼虫中CYP450, GST和CarE活性无显著差异。【结论】番茄潜叶蛾新疆和云南种群对测试的6种杀虫剂产生不同程度的抗性,对氯虫苯甲酰胺的抗性最高,番茄潜叶蛾对杀虫剂的抗性与解毒酶活性无关。本研究的结果对番茄潜叶蛾的田间防治和杀虫剂抗性治理具有指导意义。     

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.     

Effects of chlorantraniliprole and chromafenozide on mortality and feeding cessation of the fall webworm,Hyphantria cunea (Lepidoptera: Arctiidae)

The fall webworm (FWW) Hyphantria cunea, native to North America, is a globally invasive pest of a wide range of forest and fruit trees. Spraying of pesticides is the primary method for the control of FWW. In this study, toxicity and feeding cessation of two potential pesticides against the FWW, chlorantraniliprole, and chromafenozide, were evaluated. Both pesticides were slow to affect FWW. For chlorantraniliprole, the highest mortality of third instar larvae occurred at 72 h with an LC₅₀ of 10.34 mg/L, while for chromafenozide, the highest mortality occurred at 72 h with an LC₅₀ value 74.0950 mg/L. Low concentrations of both pesticides led to larvae ceasing to feed after six hours (chlorantraniliprole) and 24 h (chromafenozide). Both pesticides had persistent effects; thirty days after being applied at concentrations of 16, 26.67, and 35.56 mg/L to leaves, 93.33% of newly contacted larvae died after seven days. Our study showed that chlorantraniliprole and chromafenozide could be alternatively used against FWW and form a component of integrated control programs. The results provide information to guide the usage of chlorantraniliprole and chromafenozide in FWW control.     

Suitability of the tomato borer Tuta absoluta as prey for Macrolophus pygmaeus and Nesidiocoris tenuis

The tomato borer, Tuta absoluta (Meyrick) (Lep.: Gelechiidae), is an important tomato pest native to South America, which appeared in eastern Spain at the end of 2006. Prey suitability of T. absoluta eggs and larval instars was examined under laboratory conditions to evaluate whether two indigenous predators, Macrolophus pygmaeus (Rambur) and Nesidiocoris tenuis Reuter (Hem.: Miridae), can adapt to this invasive pest. Both predators preyed actively on T. absoluta eggs and all larval stages, although they preferred first‐instar larvae. Our results demonstrate that both mirids can adapt to this invasive pest, contributing to their value as biological control agents in tomato crops.     

Host instar suitability and life-history parameters under different temperature regimes of Necremnus artynes on Tuta absoluta

Necremnus artynes is native to the Mediterranean region where it has been observed in greenhouses parasitising Tuta absoluta on tomato. In this study, we evaluated the suitability of the different instars of T. absoluta as hosts for N. artynes and the life-history traits of N. artynes at three different temperature regimes (20, 25 and 30°C) on third instar T. absoluta larvae infesting tomato. N. artynes females preferred third instar T. absoluta larvae for oviposition, whereas host-feeding was significantly higher on the second instar larvae. Duration of life stages was no different between sexes but was affected by temperature, being significantly reduced as temperature increased. Pre-imaginal survival also decreased with temperature and the percentage of females was ca. 70% under all temperature regimes. Adult longevity was 1.5-fold significantly greater at 25°C compared to 30°C with no differences between 20 and 25°C. Fecundity was estimated at 36.3±7.80, 51.8±10.65 and 52.1±10.03 eggs/female and host-feeding at 59.5±8.50, 71.6±12.07, 51.4±7.89 hosts/female at 20, 25 and 30°C, respectively, although these differences among temperatures were not significant. However, oviposition and feeding rate were significantly higher at 30 and 20°C, respectively. The estimated intrinsic rate of increase (r _m) was significantly higher as temperature increased from 20 to 30°C and it was greater than those reported for T. absoluta on tomato, indicating the potential of N. artynes to control this pest.     

Physiological susceptibility of the predator Macrolophus basicornis (Hemiptera: Miridae) to pesticides used to control of Tuta absoluta (Lepidoptera: Gelechiidae)

In order to aid the integration of biological and chemical controls for the tomato leaf miner, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), this study evaluated the relative toxicity of five insecticides to the leaf miner predator Macrolophus basicornis (Stal) (Hemiptera: Miridae). The insecticides evaluated were teflubenzuron, abamectin, chlorantraniliprole, chlorfenapyr, and cartap hydrochloride, all of which are recommended for control of T. absoluta in Brazil. Nymphs and adults of M. basicornis were exposed to tomato leaves treated with the insecticides, under laboratory and greenhouse conditions. The overall mortality caused by the products in both situations was recorded, and the survival of congeneric groups was analysed using the Weibull model. The persistence of the insecticides was also evaluated and they were categorised into toxicity classes proposed by the International Organisation for Biological Control (IOBC) based on predator mortality and persistence. Abamectin and chlorfenapyr were toxic to M. basicornis nymphs and adults in all bioassays. Cartap hydrochloride was slightly harmful to adults in laboratory assays, but harmful to nymphs, and moderately harmful under greenhouse conditions. Chlorantraniliprole and teflubenzuron were harmless in most assays, except when nymphs were exposed in the laboratory, where they were moderately and slightly harmful, respectively. Chlorantraniliprole and teflubenzuron should be preferred insecticides for use in tomato leaf miner IPM programmes that aim to conserve M. basicornis populations.     

室内测定6种化学杀虫剂对草地贪夜蛾幼虫的毒力

2019年草地贪夜蛾Spodoptera frugiperda入侵我国多个省份和地区,对我国农业生产造成重大影响。化学防治是应对入侵害虫的主要措施,因此,本研究测定了6种不同作用机制杀虫剂对草地贪夜蛾初孵和3龄幼虫的生物活性。结果表明,对初孵幼虫具有较高毒力作用的为氯虫苯甲酰胺、多杀菌素、茚虫威、阿维菌素和甲氧虫酰肼;对3龄幼虫具有较高毒力作用的为氯虫苯甲酰胺、多杀菌素和茚虫威;与初孵幼虫相比,阿维菌素、茚虫威、多杀菌素和甲氧虫酰肼的LC 50分别提高了78.06、1.70、11.73和23.09倍。本研究筛选出了对草地贪夜蛾初孵幼虫和3龄幼虫杀虫效果较好的药剂,证明了低龄幼虫对部分农药抵抗力较弱,而3龄后的幼虫抵抗力显著增加,为田间草地贪夜蛾的化学防治提供了科学的用药指导。     

Stage‐dependent synergism using Metarhizium anisopliae and Serratia entomophila against Costelytra zealandica

Larvae of the New Zealand grass grub (Costelytra zealandica) were treated with the entomopathogenic fungus, Metarhizium anisopliae, and the bacterium, Serratia entomophila, singly and in combination. The mortality of second instar larvae up to 41 days in treatments with both pathogens together was significantly greater than the additive mortalities of single pathogen treatments, and therefore synergistic. Treatment of third instar larvae with both pathogens did not increase mortality compared with the fungus alone. Second instar larvae were more resistant to M. anisopliae than third instar larvae. S. entomophila causes a chronic disease and bacterial treatments alone resulted in disease, but little mortality for either instar within 5 weeks. In both fungus alone and fungus/bacteria treatments, less than half the cadavers supported fungal sporulation. The use of a dual pathogen system for control of grass grub larvae is discussed.     

Efficacy of <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> (Berliner) in controlling the tomato borer, <Emphasis Type="Italic">Tuta absoluta</Emphasis> (Meyrick) (Lepidoptera: Gelechiidae)

The tomato borer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), is considered to be one of the most devastating pests affecting tomato crops in South America, where crop losses range from 60 to 100%. After its detection in the Spanish tomato-growing area at the end of 2006, it spread quickly to other European and northern African countries. Currently, T. absoluta management in these countries is mainly based on chemical treatments. Nonetheless, special emphasis is being placed on implementing environmentally safe strategies. Commercial formulates based on Bacillus thuringiensis may be a good alternative, as they have been used to control other insect pests successfully. The laboratory, greenhouse, and open-field experiments presented in this work are evidence that B. thuringiensis is highly efficient in controlling T. absoluta. First instar larvae were the most susceptible, while susceptibility was lower in second and third instar larvae. Our results have shown that the impact of T. absoluta can be greatly reduced by spraying only B. thuringiensis-based formulates, with no need for chemical insecticides. Furthermore, the integration of this technology with other biological control methods focused on T. absoluta eggs, such as the use of mirid predators or parasitoids, could reduce the number of B. thuringiensis treatments and the use of chemicals, with the consequent reduction of residues on fruits.     

New records of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) predation by Brazilian Hemipteran predatory bugs

The tomato borer Tuta absoluta, native to western South America, is an extremely devastating pest in tomato crops in most of South America, Europe and Africa North of the Sahel, causes yield losses up to 100% and decreases fruit quality in open field and greenhouse crops if control methods are not applied. In Brazil two other important lepidopteran pests – Neoleucinodes elegantalis and Helicoverpa zea – occur in tomato, as well as thrips, whiteflies and aphids. For control of these pests, frequent applications of pesticides of up to 5 times per week are needed, and these resulted in the appearance of resistant populations to a number of active ingredients and decimation of natural enemies. Biological control may offer a better, safer and more sustainable opportunity for pest management. Mirid predatory bugs are currently used with success in southern Europe to control T. absoluta and other pests. In Brazil, four Hemipteran predatory bugs, not yet known to attack T. absoluta, were found to successfully prey on eggs and larvae of this pest. The first results on their predation capacity, development, survival and reproduction on T. absoluta on tomato plants are presented.     

Larvicidal activities of limonoids from Turraea abyssinica (Meliaceae) on Tuta absoluta (Meyrick)

Preliminary screening of extracts of the leaves and stems of four Turraea plant species (Meliaceae) on second instar larvae of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) showed that the methanolic extract of Turraea abyssinica leaves possess good toxic potential with LD₅₀ of 270.7 ppm. Fractionation of this extract led to isolation of a new limonoid derivative, 12α‐diacetoxywalsuranolide (1) and three other known limonoids [1α,7α,12α‐triacetoxy‐4α‐carbomethoxy‐11β‐hydroxy‐14β,15β‐epoxyhavanensin (2), 11‐epi‐21‐hydroxytoonacilide (3), 11β,12α‐diacetoxycedrelone (4)]. The structures of the compounds were established by IR, UV, mass spectrometry and 1D/2D NMR analyses, and in the case of the known compounds, also by comparison with reported data. All the isolates were tested for their larvicidal activities at different dose range against second instar larvae of T. absoluta. They were found to be more active (with LD₅₀ < 7.0 ppm) compared to the reference compound azadirachtin (LD₅₀ value of 7.8 ppm).     

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.     

Spatial and temporal variation in the control failure likelihood of the tomato leaf miner,Tuta absoluta

Insecticide resistance is frequently associated with field control failure, but such an assessment of its likelihood seldom occurs. This phenomenon is a potential cause of the control failure of the tomato leaf miner Tuta absoluta (Lepidoptera: Gelechiidae); therefore we surveyed insecticide resistance as the control failure likelihood for a duration of 7 years in 20 field populations of this species. The insecticide label rate was used as the discriminating concentration, and the minimum efficacy threshold required for insecticides in Brazil (i.e. 80% efficacy) was the targeted efficacy. The spatial and temporal variations of the control failure likelihood were also assessed, as was the potential influence of land topography for the area‐wide pattern observed. Most populations of T. absoluta were susceptible to abamectin, chlorfenapyr and spinosad and not to bifenthrin, triflumuron and teflubenzuron. The indoxacarb susceptibility varied in space and time. Spatial dependence was observed for abamectin and indoxacarb. The control failure likelihood of T. absoluta was higher for bifenthrin, triflumuron and teflubenzuron. A flat topography and the wind direction may favour the spread of the control failure likelihood and should be considered in designing pest management programs for T. absoluta.     

Comparison of the growth and development of beet armyworm,Spodoptera exigua (Hübner) (Lepidoptera: Noctuidae) on two different diets

Beet armyworm (Spodoptera exigua (Hübner)) (Lepidoptera: Noctuidae) is the most economically important sugar beet (Beta vulgaris) pest worldwide. In this study, a comparison was made between two different diets: one was based on Merkx diet (Holidic diet) and the other was based on sugar beet leaf (Oligidic diet). Results showed that the whole development time from larvae to adult between two diets (Merkx and leaf) was not significantly different. For example, developmental time from first instar larvae to adult in Merkx diet was 11.33?days, whilst developmental time of larvae to adult when larvae fed with sugar beet leaf was 10.33?days. However, analysis of variance showed that in some cases like development time of the first instar, third instar and fifth instar larvae and pupae was significantly different between two treatments (p?<?0.05). Larval weight showed differences when larvae fed on Merkx diet and sugar beet leaves. For example, significant differences were shown between first, third and fourth instar larvae weight when larvae fed on Merkx diet and sugar beet leaves (p?<?0.05). However, significant differences were not observed between weight of second and fifth instar as well as pupae weight when larvae fed on Merkx diet and sugar beet leaves (p?>?0.05).     

Susceptibility of Cypriot Tuta absoluta populations to four targeted insecticides and control failure likelihood

Tuta absoluta, known as the South American tomato pinworm, is one of the most disastrous pests of tomato cultivations, presently menacing tomato cultivations worldwide. In 2006, T. absoluta invaded Spain from South America. Since then, it was rapidly spread to most European, African and Asian countries. Such alien invasive species can minimize crop production, whereas the increasing use of insecticides raises various environmental concerns as well as on control costs, control failure and the toxicity to non‐target organisms. The S. American tomato pinworm is mostly controlled by chemical insecticides, and failure to control it is not a rare phenomenon. Resistance to numerous insecticides has been reported and is mainly due to the fact that farmers do not follow a sustainable resistance management scheme. Several examples have been reported from several countries where the tomato pinworm is present. In order to develop a successful insecticide resistance management (IRM) strategy for any major pest, one needs to identify the baseline toxicity to insecticides and then monitor susceptibility levels . In Cyprus, the current status of susceptibility levels to the main insecticides that are used to control T. absoluta has never been studied before. Herein, nine Cypriot populations of the pest were subjected to laboratory bioassays between 2016 and 2018 using the main insecticides applied against it. We found that the insecticides chlorantraniliprole and indoxacarb could not control the Cypriot T. absoluta populations anymore, with a resistance ratio (RR) >28 and 3–23, respectively. Furthermore, mortality achieved by those two insecticides was 20.6%–72% for chlorantraniliprole and 27.5%–78% for indoxacarb. However, the insecticides emamectin benzoate and spinosad are very effective, since mortality to both of them ranged between 99.5% and 100%.     

Seasonal variation in natural mortality factors of Tuta absoluta (Lepidoptera: Gelechiidae) in open‐field tomato cultivation

The seasonal variation in natural mortality of phytophagous insects is determined by the relative importance of biotic and abiotic factors in agroecosystems. Knowledge regarding these factors throughout the year represents a key concern for IPM programmes. Seasonal population fluctuations of tomato pinworm, Tuta absoluta, led to an investigation of its natural mortality factors during the rainy season when the population level is low and during the dry season when population peaks occur. The aim of this study was to verify the seasonal variation in T. absoluta mortality factors in tomato crops. Immature stages of T. absoluta were obtained from laboratory‐rearing in the laboratory. These were taken to the field and monitored over two years. The mortality causes for each stage of insect development from egg to adult were assessed daily. Multiple biotic and abiotic mortality factors affected the immature T. absoluta stages such as rainfall, physiological disturbances, diseases, parasitoids and predators. The key T. absoluta mortality factor during summer–spring was predation. In addition, larvae predation correlated positively with temperature, wind velocity, photoperiod and rainfall. Nevertheless, during winter–fall, the key mortality factor was parasitism. Therefore, the critical stage for mortality was 3rd‐ and 4th‐instar larvae, being more vulnerable to natural control factors. Finally, the results showed the importance of vertical and horizontal action on natural mortality factors.     

Apple sawfly Hoplocampa testudinea (Hym., Tenthredinidae) and its parasitoid Lathrolestes ensator in Dutch apple orchards (Hym., Ichneumonidae, Ctenopelmatinae)

Abstract: Changes in population densities of the apple sawfly Hoplocampa testudinea (Klug) and its parasitoid Lathrolestes ensator (Brauns) were monitored in 15 apple orchards for a period of up to 4 years. The parasitoid species was found in all orchards except one, and was more numerous in plantings on sandier soils. Post‐bloom insecticide applications against other pests, and carbaryl for fruit thinning, often decimated both host and parasitoid in integrated pest management orchards. In organic orchards, where synthetic pesticides are banned, and Quassia is the only remedy against sawfly, the pest is more problematic. The low levels of parasitism in all organic orchards, except one, were possibly due to the application of wettable sulphur during the parasitoid flight period. The sawfly usually recovers more quickly than its parasitoid when chemical control is discontinued, because propagation of L. ensator is limited in various ways. The parasitoid is time limited, because suitable second instar host larvae are rarely available for more than a week on a single apple variety. Moreover, parasitism levels stay moderate because the parasitoid females do not avoid superparasitism. Finally, relatively more sawflies than parasitoids emerge after 10 months underground, because the incidence of prolonged diapause is more elevated in L. ensator than in the sawfly. It is suggested that both the high incidence of prolonged diapause and the inability to avoid superparasitism are useful in reducing the risk of local extinction. Elevated sawfly attack in a single early apple variety would reduce exploitation of suitable host larvae in other nearby varieties, in as far as the parasitoid is not able to distinguish fruitlets with accessible second instar host larvae from those with inaccessible older larvae. Although the former are available for a limited time, the latter may keep the parasitoids from moving to the less abundant second instar larvae in late(r) varieties. Reduction of elevated host density in such an early variety by a properly timed application of a short‐lived pesticide, such as Quassia, increases parasitism levels proportionally, and is expected to promote parasitoid movement to host larvae in other varieties nearby.     

Greenhouse Evaluation of Dose– and Time–Mortality Relationships of Two Nucleopolyhedroviruses for the Control of Beet Armyworm, Spodoptera exigua, on Chrysanthemum

Dose– and time–mortality relationships of baculoviruses in pest insects are important for the determination of effective spraying regimes. A series of experiments with Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) and Spodoptera exigua MNPV (SeMNPV) against synchronized populations of S. exigua larvae in greenhouse chrysanthemum was conducted. Dose– and time–mortality relationships of different virus concentrations and S. exigua target stages were determined and the area foliage consumption was measured. Crop injury was greatly reduced when S. exigua were controlled as second or third instar larvae, whereas virus applications against fourth instar larvae could not prevent considerable crop injury, even at high concentrations. SeMNPV was approximately 10 times as infectious as AcMNPV when applied on greenhouse chrysanthemum. The relative virulence of AcMNPV and SeMNPV corresponded reasonably well with previously published laboratory bioassay data. SeMNPV killed second and fourth instar S. exigua larvae approximately 12 h faster than did AcMNPV in chrysanthemum, but no difference in speed of action was found for third instar larvae. The relative speed of action of AcMNPV and SeMNPV determined in chrysanthemum and in laboratory bioassays did not correspond for third instar S. exigua larvae; laboratory bioassay data can therefore not simply be extrapolated to the crop level.