The effect of background plant odours on the behavioural responses of Frankliniella occidentalis to attractive or repellent compounds in a Y‐tube olfactometer

The western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), causes major losses in agricultural and horticultural crops worldwide. The volatile compounds methyl isonicotinate, p‐anisaldehyde, eugenol, and linalool are known as olfactory attractants, and salicylaldehyde is known as a repellent for F. occidentalis under clean‐air conditions in laboratory experiments. In the present study we assessed the responses of F. occidentalis to these compounds when presented alone, in combination, and in the presence of background odours emanating from cucumber (Cucumis sativus L., Cucurbitaceae), capsicum (Capiscum anuum L., Solanaceae), chrysanthemum (Chrysanthemum morifolium Ramat., Asteraceae), clove basil (Ocimum gratissimum L.), and lavender (Lavandula angustifolia L., both Lamiaceae) plants in a Y‐tube olfactometer. In the presence of any background plant odour, the attractiveness of pure methyl isonicotinate to F. occidentalis proved to be consistently significant. Compared to clean‐air conditions, a slightly lower percentage of thrips chose the Y‐tube arm loaded with 10% p‐anisaldehyde in the presence of cucumber leaf odour. With non‐flowering clove basil plants in the background, F. occidentalis responses to 1% eugenol, a constituent of clove basil essential oil, were neutral, and the same applied to responses to pure linalool, a constituent of lavender essential oil, in the presence of flowering lavender plants. Also, thrips responses to pure or diluted salicylaldehyde were clearly influenced by plant background odours. We simulated a push‐pull situation and found a trend indicating that the percentage of F. occidentalis choosing the airflow loaded with the attractant methyl isonicotinate was higher when the airflow in the other arm of the Y‐tube was loaded with the repellent salicylaldehyde compared to clean air, and vice versa. We showed interactions between attractive or repellent volatile compounds and the environmental odours in the chemical ecology of F. occidentalis and the potential of a combined use of these compounds in thrips pest management.     

Continuous exposure to the deterrents cis‐jasmone and methyl jasmonate does not alter the behavioural responses of Frankliniella occidentalis

Behavioural responses of Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), a generalist, cell sap‐feeding insect species with piercing‐sucking mouthparts, after continuous exposure to two deterrent secondary plant compounds are investigated. We compared in choice assays on bean leaf discs, the settling, feeding, and oviposition preferences of F. occidentalis females that had no experience with the two fatty acid derivatives methyl jasmonate and cis‐jasmone before testing (naïve thrips) vs. females that had been exposed to the deterrent compounds before testing (experienced thrips). The thrips were exposed to the deterrents at low or high concentrations for varied time periods and subsequently tested on bean leaf discs treated with the respective deterrent at either a low or a high concentration. Frankliniella occidentalis females avoided settling on the deterrent‐treated bean leaf discs for an observation period of 6 h, independent of their previous experience. Our results demonstrate that feeding and oviposition deterrence of the jasmonates to the thrips were not altered by continuous exposure of the thrips to the jasmonates. Habituation was not induced, neither by exposure to the low concentration of the deterrents nor by exposure to the high concentration. These results indicate that the risk of habituation to two volatile deterrent compounds after repeated exposure is not evident in F. occidentalis. This makes the two compounds potential candidates to be integrated in pest management strategies.     

嗜食植物与非嗜食植物对西花蓟马成虫寄主选择性的影响

【目的】西花蓟马是世界性害虫,利用西花蓟马对寄主植物嗜食性的差异,通过驱避作用防控西花蓟马,能够为绿色治理提供依据。【方法】在西花蓟马嗜食的甘蓝和非嗜食的大蒜上互喷汁液,采用黄瓜+甘蓝、黄瓜+大蒜2种相间种植方式,研究它们对西花蓟马寄主选择性的影响。【结果】在甘蓝上喷洒大蒜汁液后,甘蓝叶片上西花蓟马的虫量和产卵量均明显减少。大蒜汁液浓度越高,减少得越多;在大蒜上喷洒甘蓝汁液后,大蒜植株上西花蓟马的虫量和产卵量明显增加,且增加程度与甘蓝汁液的浓度呈正相关。黄瓜和甘蓝相间排列时,西花蓟马在黄瓜叶片上的数量与单作黄瓜叶片上无明显差异;但黄瓜和大蒜相间排列时,西花蓟马在黄瓜上的数量明显高于单作黄瓜上的虫数,多52.4%。【结论】在嗜食寄主植物上喷洒非嗜食植物汁液或间作非嗜食的寄主可以明显减少西花蓟马的选择性。研究结果为利用非嗜食植物挥发物防控西花蓟马提供了理论依据和新的方法。     

Apple pollen as a supplemental food for the western flower thrips, Frankliniella occidentalis: response of individuals and populations

Experiments were performed to investigate the influence of apple pollen, plant diet, and relative humidity on the individual life‐history traits and on the population growth of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). In experiments with individual thrips, availability of bean pods plus a mixture of apple pollen and lycopodium shortened larval development time, and hence time from egg to adult, compared to bean pods alone. Similarly, the total number of eggs laid and the mean number of eggs laid per female per day were greater in the presence of pollen plus bean pods than on bean pods alone. Diet did not affect survival or length of the pre‐oviposition and oviposition periods. A diet including bean pods plus pollen shortened the generation time and population‐doubling time, and increased the net reproductive rate and the intrinsic rate of increase, compared to bean pods alone. In experiments on populations, growth was measured with different amounts of pollen on bean pods under two relative humidities, ca. 38% and 66%, and separately on two bean substrates, pods or leaves, at ca. 45% r.h. The presence or amount of pollen had no effect on population growth regardless of the other variables. Greater population growth occurred under the higher relative humidity regardless of substrate. Population growth was greater on bean pods than on bean leaves. Despite reports on the nutritional benefit of pollen for F. occidentalis, this benefit may be affected by pollen type, host plant, and other factors. In situations in which pollen has little influence on the growth of F. occidentalis populations, pollen that benefits a thrips predator could be used in an integrated management plan for controlling thrips.     

Oviposition preference of western flower thrips for cucumber leaves from different positions along the plant stem

While the distribution of herbivorous insects over leaves along the stem often shows a peak at some distance from the apex this does not necessarily reflect an innate preference as alternative explanations can be provided such as impact of predators and inter- or intraspecific competitors. It is of interest to determine which factors shape the distribution of insects over the leaves of a plant. Do leaves from different positions differ in suitability for insects and is that reflected in the insect's preference, or are other factors involved? In this paper we assess how the herbivorous insect western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), chooses among leaves from different positions relative to the apex of cucumber, Cucumis sativus (L.) plants. On leaf discs of a susceptible and three partially resistant cucumber accessions, thrips reproduction was highest on apical leaves and lowest on basal leaves. In dual-choice essays thrips females preferred younger leaves over older leaves for oviposition in all cucumber accessions tested, as was predicted from the no-choice assay. This indicates that differences in leaf suitability are an important factor in determining thrips distribution on cucumber plants.     

Life history of western flower thrips, Frankliniella occidentalis (Thysan., Thripae), on five different vegetable leaves

Biological characteristics of western flower thrips, Frankliniella occidentalis (Pergande) (Thysan., Thripae), were investigated on excised leaves of five vegetables: cabbage (Brassica oleracea L. var. Jingfeng 1), cucumber (Cucumis sativus L. var. Zhongnong 8), capsicum (Capsicum annuum L. var. Zhongjiao 5), kidney bean (Phaseolus vulgaris L. var. Gonggeizhe) and tomato (Lycopersicon esculentum M. var. zhongza 9). The developmental time from egg to adult on the cucumber, cabbage, bean, capsicum and tomato leaf was 9.22 ± 0.13, 10.19 ± 0.08, 10.42 ± 0.06, 12.15 ± 0.07 and 12.91 ± 0.04 days, respectively. Survivorship of immatures on cucumber, cabbage and tomato was high (75–80%) but low on capsicum (50%). The total number of first instars produced was highest on cabbage (76.62 ± 11.79), while the daily first instar production was highest on cucumber (6.12 ± 1.81), whereas the total and daily first instar production rates were lowest on capsicum (7.67 ± 3.35 and 1.89 ± 0.91). F. occidentalis had the highest intrinsic rate of increase (r_m) on cucumber (0.208), followed by cabbage (0.184), bean (0.164), tomato (0.100) and capsicum (0.017). The results indicate that cucumber was the most suitable host plant for F. occidentalis, whereas capsicum was the least suitable.     

西花蓟马在黄瓜和架豆上的空间分布型及理论抽样数

西花蓟马Frankliniella occidentalis（Pergande）已在北京部分蔬菜园区成功定居,对蔬菜生产造成危害。为了解该虫在蔬菜田的种群空间分布型,指导田间取样,本文应用几种聚集度指标的计算公式以及Taylor、Iwao的回归方程式,分析和测定了西花蓟马的种群空间分布格局。结果表明：在黄瓜和架豆上西花蓟马的空间分布型一致,均为聚集分布型;该虫的空间分布型不受种群密度的影响,并且也不随取样时间的变化而变化。种群数量动态研究显示西花蓟马成虫和若虫在黄瓜植株的中部叶片分布较多（从顶部向下数第4叶至第17叶片上成、若虫的分布数量多于其他叶片上的数量）,未展开的叶片、嫩叶和下部老叶危害较轻。用Iwao回归法中α、β参数计算出在允许误差范围内的理论抽样数。     

Food supplementation affects interactions between a phytoseiid predator and its omnivorous prey

The beneficial effect of food supplements in supporting populations of generalist arthropod predators in agricultural systems has been shown to enhance pest control. When providing additional foods in a crop that is attacked by an omnivorous pest, food supplements may be available to both pest and predator populations resulting in more complex interactions. We assessed the consequences of adding extra food sources to a tritrophic system in the laboratory, consisting of leaf discs of kidney bean plants (Phaseolus vulgaris), western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) and the predatory mite Amblydromalus limonicus (Acari: Phytoseiidae). The supplemental food sources tested were cattail pollen, Typha latifolia, dry decapsulated cysts of the brine shrimp, Artemia franciscana (Branchiopoda: Artemiidae) and eggs of the Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae). Larvae of F. occidentalis were observed to feed on all three food sources when applied to bean leaves. The immature development time of F. occidentalis was significantly shorter when T. latifolia pollen was provided compared to bean leaves only and bean leaves supplemented with A. franciscana or E. kuehniella. The predation rate of A. limonicus females on first instars of F. occidentalis decreased with about 30% irrespective of food type supplemented to the leaf discs. The presence of additional foods reduced antipredator behavior of F. occidentalis larvae killing predator eggs. Thrips larvae did not attack eggs of A. limonicus when cattail pollen was added to the leaf discs, whereas 2.5 predator eggs per day were consumed without food supplementation. Leaf damage decreased substantially when Typha pollen was present on the leaf discs. The findings of this study indicate that food supplementation shifts tritrophic interactions both top-down and bottom-up and may affect the outcome of an augmentative biological control program.     

Life history characteristics of Frankliniella occidentalis on cucumber leaves with and without supplemental food

The development time, fecundity, longevity, and resultant intrinsic growth rate of the western flower thrips Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae] encaged on a cucumber leaf were compared among seven types of food supplied: six pollen species and a mixture of milk powder and yeast. The rationale was to find a food source that offers the least benefit for thrips and could therefore be considered as a food source for the preventative introduction of thrips predators. With the exception of the mixture of milk powder and yeast, all the food sources tested offered a nutritional benefit for the thrips. The addition of pollen increased fecundity and reduced development time, mainly during the larval stage. Betula pubescens and Corylus avellana pollen also increased adult longevity. The nutritional benefit of Pinus sylvestris pollen was greater than that of the other five pollen species, as manifested by its significantly greater positive effect on fecundity. The other pollen species could not be ranked in terms of nutritional benefit to F. occidentalis. The negative effect of the milk powder plus yeast mix on the life‐table parameters of F. occidentalis probably only occurs in an encaged situation where thrips cannot escape from the unfavorable environment. The crude estimate of the intrinsic growth rate of F. occidentalis increased from 0.163 on the plain cucumber leaf to 0.240 when P. sylvestris pollen was added to the leaf. The differences in intrinsic growth rate mainly reflect the differences in fecundity among the food sources. Thus, the peak oviposition rate may be used as a measure of the nutritional benefit F. occidentalis can obtain by feeding on supplemental food sources. The positive effect of a supplemental food source on thrips does not necessarily mean it is unsuitable for the preventative introduction of thrips predators, because the supplemental food can also affect the population dynamics of the predator and the predator–prey interaction and, hence, the outcome of biological control.     

Does natural deposition of pine pollen affect the ovipositional behavior of Frankliniella occidentalis and Frankliniella fusca?

Tree pollen, especially Pinus spp. (Pinaceae), is shed in large quantities every spring in North America. Pine pollen deposition onto leaves was found to significantly influence the ovipositional behaviors of certain thrips species (Thysanoptera: Thripidae) in peanut and tomato leaf choice and no‐choice tests. Pine pollen (Pinus elliottii Engelm.) increased the oviposition rate 2.9‐fold for Frankliniella occidentalis (Pergande) (western flower thrips) and 1.6‐fold for Frankliniella fusca (Hinds) (tobacco thrips) in choice tests averaged over both plant species. These results support the idea that pollen has a greater impact on F. occidentalis behavior than on F. fusca behavior. The most dramatic increase was in peanut, where F. occidentalis only oviposited on leaves dusted with pollen, suggesting that the addition of pollen stimulated this flower thrips to lay eggs on a poor host‐plant part. The impact of pollen on the rate of oviposition by thrips is important because it is the early‐instar nymphs that acquire tomato spotted wilt virus (TSWV), which these two thrips species vector. In a laboratory bioassay, the addition of pine pollen to TSWV‐infected peanut foliage increased the percentage of infected F. fusca after one generation.     

Life-history parameters of western flower thrips on susceptible and resistant cucumber genotypes

The life-history parameters reproduction rate, developmental time and age specific survival of the western flower thrips,Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], were determined on susceptible and resistant cucumber (Cucumis sativus L.) genotypes. Both newly emerged andF. occidentalis females of mixed ages showed a substantial reduction (36 to 50%) of the reproduction rate on all resistant genotypes, in particular after the second day. On the resistant genotypes 9127 and 9140,F. occidentalis had a prolonged developmental period. This was primarily due to a prolongation of the second larval stage. On all resistant genotypes,F. occidentalis suffered from high (82 to 97%) preadult mortality, predominantly at the second larval stage. It is conclude that the resistant genotypes do not cause an immediate intoxication of adult nor preadult thrips stages.     

Influence of plant species and plant growth stage on Frankliniella occidentalis pupation behaviour in greenhouse ornamentals

The influence of plant stage and plant species on the pupation behaviour of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), was investigated in flowering and non‐flowering potted chrysanthemums and mini roses. On non‐flowering chrysanthemums and roses, 92–93% of the F. occidentalis pupated in the soil. On flowering roses, 87% pupated in the soil, and on flowering chrysanthemums only 60% chose the soil as a pupation site and 40% stayed on the plant. This means that, in the presence of flowers, especially complex inflorescences like chrysanthemums, a large proportion of F. occidentalis chooses stay on the plant to pupate.     

Habituation in Frankliniella occidentalis to deterrent plant compounds and their blends

Feeding and oviposition deterrence of three secondary plant compounds and their 1:1 blends to adult female Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) and the potential for habituation of the thrips to the pure compounds and the 1:1 blends at various concentrations were investigated. In choice assays, we tested dose‐dependent feeding and oviposition deterrence of the two fatty acid derivatives methyl jasmonate and cis‐jasmone, the phenylpropanoid allylanisole, and their blends when directly applied to bean leaf discs. The concentration required to reduce the feeding damage by 50% relative to the control treatment (FDC₅₀) was lowest for cis‐jasmone and highest for allylanisole. The feeding deterrent effect of both jasmonates was increased when blended with allylanisole. Feeding deterrence and oviposition deterrence were strongly correlated. In no‐choice assays conducted over four consecutive days, we discovered that dilutions at low concentrations (FDC₁₅) applied to bean leaves resulted in habituation to the deterrents, whereas no habituation occurred at higher concentrations (FDC₅₀). We observed a tendency that the 1:1 blends reduce the probability that thrips habituate to the deterrent compounds. Our results may be useful in the development of integrated crop protection strategies with the implementation of allelochemicals as pest behaviour‐modifying agents.     

Olfactory response towards its prey Frankliniella occidentalis of wild and laboratory‐reared Orius insidiosus and Orius laevigatus

Orius species are important biological control agents of thrips in protected crops. Rearing conditions in mass production facilities may affect their performance in the crop when searching for the target prey. The aim of this study was to evaluate and compare the search behaviour and orientation towards prey of two Orius species, O. laevigatus (Fieber) and O. insidiosus (Say) that have been reared in the laboratory under different conditions, with wild (field‐collected) individuals. Adult predator females were placed in a Y‐tube olfactometer and offered a choice between the odours released by plants of different species (cotton, common bean, sweet pepper and cucumber), which were either non‐infested or infested with Frankliniella occidentalis (Pergande) adults.O. laevigatus and O. insidiosus responded to odours from thrips‐infested plants and these responses were influenced by the origin of the colonies. A larger percentage of laboratory‐reared O. laevigatus females (42%) did not made a choice between thrips‐infested or clean plants, compared with wild individuals (17%). Of those females that did respond to plant odours, a smaller percentage of laboratory‐reared O. laevigatus females (34%) responded to the odours from thrips‐infested plants compared with wild insects (76%). No significant differences were found inO. insidiosus females that did not make a choice between thrips‐infested or clean plants (14% for wild vs. 17% for lab individuals). Also, no significant differences were found between O. insidiosus females that selected thrips‐infested plants at the corresponding proportion of wild (75%) and laboratory‐reared (70%) individuals. We propose that the olfactometer test could be a complementary evaluation aspect to the already developed quality criteria for performance of mass‐reared Orius predators.     

Intraspecific larval competition in two solitary parasitoids, Apoanagyrus (Epidinocarsis) lopezi and Leptomastix dactylopii

Analysis of total aromatic amino acid (free and bound) in some cucumber accessions selected previously for resistance to western flower thrips, Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], indicated that low concentrations of these essential nutrients, relative to total leaf protein, were correlated with a reduction in damage by the insect. Further analysis of samples of four important horticultural crops (lettuce, tomato, pepper and cucumber) with unknown levels of resistance to thrips showed a significant genotypic variation in the concentrations of total aromatic amino acids relative to the total leaf protein. Accessions from each crop with low or high concentrations of aromatic amino acids in proteins were exposed to thrips larvae. Regression analysis showed a highly significant positive correlation between aromatic amino acid concentration in leaf protein and thrips damage, regardless of crop species. It is concluded that higher concentrations of aromatic amino acids in plant proteins are important for successful thrips development. These results provide plant breeders with a promising tool for indirect selection without using undesirable insect bioassays.     

Root colonization by the arbuscular mycorrhizal fungus Glomus mosseae and enhanced phosphorous levels in cucumber do not affect host acceptance and development of Frankliniella occidentalis

Abstract

We tested the effect of root colonization of cucumber (Cucumis sativus L.) by the arbuscular mycorrhizal fungus (AMF) Glomus mosseae on different parameters of a plant-thrips (Frankliniella occidentalis Pergande) interaction. In leaf disc bioassays, the feeding activity, the oviposition rate, the settling preference of adult females and the developmental time (first instar larva to adult) on leaves of mycorrhizal and non-mycorrhizal plants were studied. To distinguish between a nutritional effect through an improved phosphorous (P) status of the mycorrhizal plant and other effects caused by mycorrhization, non-mycorrhizal plants watered with a nutrient solution with (+P) or without P (?P) were included in the study. Mycorrhization did not affect any of the parameters on host acceptance tested, whereas on plants with a higher P-level the duration of the non-feeding stages (pronymphae, nymphae) of F. occidentalis was shortened, but all other developmental parameters were similar as in the control and the mycorrhizal plants. Our data indicate that the polyphagous thrips F. occidentalis is neither affected by mycorrhization of cucumber plants nor by enhanced P-levels.     

Resistance to three thrips species in Capsicum spp. depends on site conditions and geographic regions

Capsicum species are commercially grown for pepper production. This crop suffers severely from thrips damage and the identification of natural sources of thrips resistance is essential for the development of resistant cultivars. It is unclear whether resistance to Frankliniella occidentalis as assessed in a specific environment holds under different conditions. Additionally, other thrips species may respond differently to the plant genotypes. Screening for robust and general resistance to thrips encompasses testing different Capsicum accessions under various conditions and with different thrips species. We screened 11 Capsicum accessions (C. annuum and C. chinense) for resistance to F. occidentalis at three different locations in the Netherlands. Next, the same 11 accessions were screened for resistance to Thrips palmi and Scirtothrips dorsalis at two locations in Asia. This resulted in a unique analysis of thrips resistance in Capsicum at five different locations around the world. Finally, all accessions were also screened for resistance to F. occidentalis in the Netherlands using a leaf disc choice assay, allowing direct comparison of whole plant and leaf disc assays. Resistance to F. occidentalis was only partially consistent among the three sites in the Netherlands. The most susceptible accessions were consistently susceptible, but which accession was the most resistant differed among sites. In Asia, one C. chinense accession was particularly resistant to S. dorsalis and T. palmi, but this was not the most resistant accession to F. occidentalis. Overall, resistance to F. occidentalis correlated with S. dorsalis but not with T. palmi resistance in the C. annuum accessions. Damage inflicted on leaf discs reflected damage on the whole plant level. Our study showed that identifying broad spectrum resistance to thrips in Capsicum may prove to be challenging. Breeding programmes should focus on developing cultivars suitable for growing in defined geographic regions with specific thrips species and abiotic conditions.     

Prey suitability of western flower thrips,Frankliniella occidentalis,and onion thrips,Thrips tabaci,for the predatory mite Amblyseius swirskii

Western flower thrips, Frankliniella occidentalis, and onion thrips, Thrips tabaci, are both important polyphagous pests of vegetables and ornamentals in greenhouses. Difficulties in biological control of these pests have prompted a search for new natural enemies. Most recently, the predatory mite Amblyseius swirskii has been commercialised as biological control agent of whiteflies and thrips. However, little is known about the suitability of thrips as prey for A. swirskii. We therefore assessed prey acceptance and life history of A. swirskii when feeding on F. occidentalis and T. tabaci at 25±1°C. Amblyseius swirskii juveniles preyed upon first larval instars of both F. occidentalis and T. tabaci but suffered from high mortality (67 and 78%). Developmental time (egg to adult) of A. swirskii was 7.8 days with either prey species. Adult A. swirskii females readily accepted first larval instars of both thrips species, which were attacked in <20 min on a leaf and <10 min in an artificial cage. Oviposition rates (0.92 and 0.99 eggs/female/day) and offspring sex ratios (63 and 70% females) were similar with F. occidentalis and T. tabaci as prey. Less than one-third of juveniles reaching adulthood and oviposition rates below one egg/female per day resulted in relatively low intrinsic rates of increase (r _m) (0.056 and 0.024 per day with F. occidentalis and T. tabaci, respectively). Altogether, our study suggests that the recently reported superiority of A. swirskii to the widely used Neoseiulus cucumeris in suppression of thrips is due to other traits than its population growth capacity with thrips as prey.     

Suppression of the Defence-Related Oxidative Burst in Bean Leaf Tissue and Bean Suspension Cells by the Necrotrophic Pathogen Botrytis cinerea

The interaction of two selected isolates of Botrytis cinerea with bean suspension cells and bean leaf discs was compared in relation to levels of reactive oxygen intermediates (ROI). Isolate B 1.7 was arrested by a hypersensitive‐like necrosis of bean leaf tissue. According to its inability to spread and produce conidia on the bean leaf tissue it was classified as non‐aggressive. The second isolate induced a fast expanding light brownish necrosis of the leaf tissue. It was able to produce conidia on bean leaf discs and was classified as aggressive. The generation of superoxide was followed biochemically in inoculated bean cell suspensions. Both isolates induced a similar early superoxide peak approximately 18‐h post inoculation (hpi). While the non‐aggressive isolate induced a much stronger secondary superoxide burst at 33 hpi, the level of superoxide of suspension cells inoculated with the aggressive isolate was below the control level. This is the first report on the occurrence of a biphasic oxidative burst in plant cells induced by a fungal pathogen. Such a suppression of superoxide generation was also observed in bean leaf discs inoculated with the aggressive isolate. An oxidative burst‐suppressing agent was extracted from inoculated cell culture medium and determined as 2‐methyl‐succinate (2‐MS) by GC/MS analysis. The compound was detected approximately 20 hpi in the aggressive fungus–plant interaction. 2‐MS was able to suppress the hypersensitive response‐like necrosis on leaf discs as well as the second superoxide burst in suspension cells when inoculated with the non‐aggressive isolate. The early superoxide burst at 18 hpi was not affected. The results confirm the important role of enhanced production of ROI in plant resistance reactions, also for a necrotrophlike B. cinerea.     

Effect of Test Leaf and Temperature on Mortality of Frankliniella occidentalis in Leaf Dip Bioassay of Insecticides

Effects of the kind of test leaf and temperature on leaf dip bioassay to the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), were examined with nine different insecticides. For the test of different leaves, cucumber, pepper and potato leaves were evaluated. The test leaves significantly influenced thrips mortalities on leaf dip bioassay. Generally the mortalities on pepper leaf were higher than on cucumber leaf or filter paper. Temperature effects were determined at 15, 20, 25 and 30°C. Regardless of the test leaf, the mortality was increased with increasing temperature except for the case of imidacloprid. Local variations in mortality of F. occidentalis populations were not observed in this study.