Ethyl formate as a postharvest fumigant for selected pests of table grapes

Ethyl formate (EF) in combination with CO2 was tested for control of arthropods commonly infesting California table grapes. In addition, table grape tolerance to EF exposure was evaluated. LC99 estimates were developed for target pests by using a range of EF concentrations (0.04-4.7% EF). Response to treatments varied greatly between species, as well as life stages within species. Western flower thrips, Frankliniella occidentalis (Pergande), and adult and crawler stages of grape mealybug, Pseudococcus maritimus (Ehrhorn), were most susceptible to EF treatments. Least susceptible were grape mealybug eggs; Pacific spider mite, Tetranychus pacificus McGregor; and omnivorous leafroller, Platynota stultana Walsingham. The LC99 for target pests fell within the range of EF concentrations tolerated by table grapes with the exception of 1-, 3-, and 5-d-old omnivorous leafroller pupae.     

Efficacy of Silwet L-77 against several arthropod pests of table grape

Silwet L-77, an organosilicone surfactant, was applied to several arthropod pests of California table grapes. Eggs of grape mealybug, Pseudococcus maritimus (Ehrhorn), and omnivorous leafroller, Platynota stultana Walsingham, were tolerant to 0.1, 0.25, and 0.5% treatment solutions; however, eggs of Pacific spider mite, Tetranychus pacificus McGregor, were highly susceptible with mortality >99.4% (0.1% Silwet L-77). Mortality of immature and adult stages of cotton aphid (Aphis gossypii Glover), Western flower thrips (Frankliniella occidentalis Pergande), and Pacific spider mite (Tetranychus pacificus McGregor) was > or = 93.8, > or = 98.5, and > or = 99.4% for 0.1, 0.25, and 0.5% Silwet L-77, respectively. Grape mealybug crawlers had 100% mortality when treated with 0.5 and 1.0% Silwet L-77 solutions; however, mortality was only 6.7% when 0.1% Silwet L-77 was applied. 'Thompson Seedless' table grapes were not damaged when treated with up to 1% Silwet L-77; however, grapes treated with the 0.5 and 1.0% solutions appeared wet after removal from cold storage because of the effect of the surfactant spreading the water condensation. Grapes dried with the normal bloom on the berries when they reached room temperature.     

Mode of action of a novel nonchemical method of insect control: atmospheric pressure plasma discharge

Atmospheric pressure plasma discharge (APPD) has been applied to a number of industrial applications, including the bacterial sterilization of medical equipment of bacteria. APPD may also have applications in insect control. A positive correlation was found between exposure time to APPD and mortality of western flower thrips, Frankliniella occidentalis (Pergande); tobacco thrips, Frankliniella fusca (Hinds); Asian tiger mosquito, Aedes albopictus (Skuse); twospotted spider mite, Tetranychus urticae Koch; and German cockroach, Blattella germanica (L.), with the level of mortality also increasing with time after treatment. Cockroaches exposed to APPD for 60, 90, 120, and 180 s lost on average 7.5 +/- 0.8, 8.1 +/- 0.6, 8.7 +/- 0.4, and 10.1 +/- 1.1 (+/-1 SEM) mg of water weight, respectively, which was an increase over that of the controls. The metabolic rate of cockroaches exposed to plasma for 180 s increased from 0.79 +/- 0.03 to 1.07 +/- 0.04 ml of oxygen consumed mg-cockroach(-1) h(-1) at standard temperature and pressure. The level of cuticular hydrocarbons identified by electron impact gas chromatography-mass spectrometry were not significantly affected by plasma exposure in the green peach aphid, Myzus persicae (Sulzer), German cockroach, and citrus mealybug, Planococcus citri (Risso), except for a reduction in n-tritriacontane in the latter. However, changes in the behavior of cockroaches after plasma exposure, including the loss of photo-, vibro-, and thigmotropic responses, inability to right themselves, and hyperexcitatory symptoms, suggest that the site of action of APPD in insects is the nervous and/or neuromuscular system.     

Response of omnivorous leafroller (Lepidoptera: Tortricidae) and onion thrips (Thysanoptera: Thripidae) to low-temperature storage

Eggs and first-fifth instars of omnivorous leafroller, Platynota stultana Walshingham, had a mean percentage survival to the adult stage of 60.7-95.2% for nonexposed immatures and 14.5-54.3% for immatures exposed to 1 wk at 0-1 degree C. Exposures of 2-5 wk resulted in 0-6.7% survival, and a 6-wk exposure resulted in < 1% survival of all stages tested. A significant reduction in survival of all larval stages occurred between exposures of 0 and 1 wk and between 1 wk and 2-6 wk. Survival of eggs after exposures of 0 and 1 wk was significantly different than survival after exposures of 2-6 wk. The second instar was the stage least susceptible to low-temperature storage. Adults that were exposed to low temperature for 1 wk in the third through fifth instars laid a mean of 120-289 eggs per female, and the mean percentage viability of the eggs ranged from 56.2 to 71.4%. Mean percentage survival of adults and nymphs of onion thrips, Thrips tabaci Lindeman, was inversely related to the duration of exposure from 1 through 3-6 wk at 0-1 and 5 degrees C and was lower at 0-1 (0.2-52.5%) than at 5 degrees C (17.6-66.6%). Exposure to 0-1 degree C for 4 wk attained 91.2% control, which increased to 99.8% after 6 wk. Low-temperature storage has potential to control omnivorous leafroller in table grapes, Vitis vinifera L., and onion thrips in onions, Allium cepa L.     

Temperature-dependent fumigant activity of essential oils against twospotted spider mite (Acari: Tetranychidae)

Fumigant activity of 34 commercial essential oils was assessed on female adults and eggs of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) at three temperatures (5, 15, and 25 degrees C). Common thyme, cinnamon, and lemongrass oils were equally effective on twospotted spider mite adults showing 85.8-100% mortality at 5 and 10 microl/liter air at 25 degrees C. At a lower temperature of 15 degrees C, lemongrass and peppermint resulted in > or =90% mortality of adults at 10 microl/liter air. Only lemongrass was relatively active at 5 microl/liter air, at 15 degrees C. At 5 degrees C, lemongrass and peppermint caused significantly higher adult mortality than controls but only at 10 microl/liter air. Common thyme oil showed the highest ovicidal activity at 5 microl/liter air at 25 degrees C. Among the main components of common thyme and lemongrass oils, citral was lethal to twospotted spider mite adults at all tested temperatures. Carvacrol, thymol, and citral caused the same inhibitory effects on the hatch of twospotted spider mite eggs at 25 degrees C. However, citral was more active than other compounds to twospotted spider mite eggs at 15 degrees C. Therefore, we conclude that citral has the best potential for development as a fumigant against twospotted spider mite on agricultural products harvested late in the growing season.     

Host-plant-mediated interaction between populations of a true omnivore and its herbivorous prey

Western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), are competitors with twospotted spider mites, Tetranychus urticae Koch (Acari: Tetranychidae), for plant resources and potential predators on spider mites when the opportunity arises. Which interaction predominates may depend on relative population densities and individual species’ responses to the plants on which they co‐occur. We examined interactions between populations of thrips and spider mites on several cultivars of two bedding plants: impatiens (Impatiens wallerana Hook.f) cultivars ‘Impulse Orange’ and ‘Cajun Carmine’, and ivy geranium [Pelargonium peltatum (L.) L’Her ex Aiton] cultivars ‘Sybil Holmes’ and ‘Amethyst 96’. Four combinations of thrips and mite numbers were studied: thrips alone, mites alone, and two densities of thrips and mites together. We compared population numbers after 4 weeks. Overall, mite numbers increased more rapidly than thrips did, but both species increased more rapidly on impatiens than on ivy geraniums. Between impatiens cultivars, thrips and mites increased more slowly on ‘Cajun Carmine’ (i.e., it was more resistant) than on ‘Impulse Orange’. On ivy geraniums, spider mites increased more slowly on ‘Sybil Holmes’ than on ‘Amethyst 96’ but the reverse was the case for thrips. Regardless of plant species or cultivar, thrips had a strong negative effect on spider mites whenever they co‐occurred, suppressing mite population growth by around 50% compared to when mites were alone. However, the effect of spider mites on western flower thrips depended on the quality of the plant species. On impatiens, thrips co‐occurring with spider mites increased slightly more than thrips alone did, while on ivy geranium mites had a small negative effect on thrips. Contrary to expectations, thrips had a larger negative impact on spider mites on plants that were more susceptible to thrips than they did on plants more resistant to thrips. We suggest that host plants mediate the interaction between an omnivore and its herbivorous prey not only by altering individual diet choice but by changing the relative population dynamics of each species.     

Effects of soil moisture and temperature on reproduction and development of twospotted spider mite (Acari: Tetranychidae) in strawberries

The effects of soil moisture and temperature on the reproduction of twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), were examined in laboratory and field tests in strawberries, Fragaria x ananassa Duchesne, in Florida. Different soil moisture levels (low, moderate, and high) were compared to determine how soil moisture affects the reproduction and development of twospotted spider mite. In addition to soil moisture, different irrigation techniques (drip versus drip/overhead) were compared to determine their effects on twospotted spider mite reproduction as well as the incidence of angular leaf spot, Xanthomonas fragaria Kennedy & King disease. Similar studies were conducted to determine how different temperatures (18, 27, and 35 degrees C) affect the reproduction and development of twospotted spider mites. In the laboratory, low soil moisture as well as temperatures >27 degrees C promoted twospotted spider mite development. A similar trend was observed in a field study with low soil moisture promoting twospotted spider mite reproduction during the early season (11 November--8 December). Irrespective of moisture levels, a significantly higher incidence of X. fragaria was recorded in treatments with drip/overhead irrigation systems compared with drip irrigation. Implications for management of soil moisture levels are discussed with respect to the abundance of twospotted spider mite and X. fragaria in strawberries.     

Evaluation of predatory mites and Acramite for control of twospotted spider mites in strawberries in north central Florida

Greenhouse and field experiments were conducted from 2003 to 2005 to determine the effectiveness of two predatory mite species, Phytoseiulus persimilis Athias-Henriot and Neoseiulus californicus (McGregor), and a reduced-risk miticide, Acramite 50 WP (bifenazate), for control of twospotted spider mite, Tetranychus urticae Koch, in strawberries (Fragaria x ananassa Duchesne). In greenhouse tests, three treatments consisting of releases of P. persimilis, N. californicus, and an untreated control were evaluated. Both species of predatory mites significantly reduced twospotted spider mite numbers below those found in the control during the first 3 wk of evaluation. However, during week 4, twospotted spider mite numbers on the plants treated with P. persimilis increased and did not differ significantly from the control. Field studies used releases of P. persimilis and N. californicus, applications of Acramite, and untreated control plots. Both N. californicus and P. persimilis significantly reduced populations of twospotted spider mite below numbers recorded in the control plots. During the 2003-2004 field season P. persimilis took longer than N. californicus to bring the twospotted spider mite population under control (< 10 mites per leaflet). Acramite was effective in reducing twospotted spider mite populations below 10 mites per leaflet during the 2003-2004 field season but not during the 2004-2005 field season, possibly because of a late application. These findings indicate that N. californicus releases and properly timed Acramite applications are promising options for twospotted spider mite control in strawberries for growers in north Florida and other areas of the southeast.     

Efficacy and persistence of rosemary oil as an acaricide against twospotted spider mite (Acari: Tetranychidae) on greenhouse tomato

Efficacy of rosemary, Rosmarinus officinalis L., essential oil was assessed against twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae), as well as effects on the tomato, Lycopersicum esculatum Mill., host plant and biocontrol agents. Laboratory bioassay results indicated that pure rosemary oil and EcoTrol (a rosemary oil-based pesticide) caused complete mortality of spider mites at concentrations that are not phytotoxic to the host plant. The predatory mite Phytoseiulus persimilis Athias-Henriot is less susceptible to rosemary oil and EcoTrol than twospotted spider mite both in the laboratory and the greenhouse. Rosemary oil repels spider mites and can affect oviposition behavior. Moreover, rosemary oil and rosemary oil-based pesticides are nonpersistent in the environment, and their lethal and sublethal effects fade within 1 or 2 d. EcoTrol is safe to tomato foliage, flowers, and fruit even at double the recommended label rate. A greenhouse trial indicated that a single application of EcoTrol at its recommended label rate could reduce a twospotted spider mite population by 52%. At that rate, EcoTrol did not cause any mortality in P. persimilis nor did it affect their eggs. In general, EcoTrol was found to be a suitable option for small-scale integrated pest management programs for controlling twospotted spider mites on greenhouse tomato plants.     

Friend or foe?: a plant's induced response to an omnivore

Omnivorous natural enemies of herbivores consume plant-based resources and may elicit induced resistance in their host plant. A greater induction threshold for damage produced by omnivorous predators than for strict herbivores might be expected if omnivore performance is enhanced on noninduced plants, allowing them to reduce future levels of herbivory. Currently, it is not known if a plant responds to feeding by omnivorous predators and by herbivores similarly. To examine this question, we chose herbivore and omnivore species that produce the same kind of quantifiable damage to cotton leaves, enabling us to control statistically for the intensity of plant damage, and ask whether plant responses differed depending on the identity of the damaging species. We first compared changes in plant peroxidase activity, gossypol gland number and density, and leaf area in response to feeding by the spider mite Tetranychus turkestani (Ugarov and Nikolski) (an herbivore) and by one of the mite's principal natural enemies, the western flower thrips Frankliniella occidentalis (Pergande) (an omnivore). Both species increased the activity of peroxidase, but when we controlled for the amount of damage, the peroxidase activity of mite-damaged plants was higher than that of thrips-damaged plants. We also found that thrips, but not spider mites, increased the density of gossypol glands in the second true leaf. In a second experiment we included an additional herbivore, the bean thrips Caliothrips fasciatus (Pergande), to see if the different responses of cotton to thrips and mite herbivory we first observed were attributable to differences in trophic function (herbivore versus omnivore) or to other differences in feeding generated by thrips versus mites. Cotton plants exhibited the same pattern of induced responses (elevated peroxidase, increased number of glands, reduced leaf area) to herbivory generated by the bean thrips (an herbivore) and western flower thrips (an omnivore), suggesting that trophic function was not a key determinant of plant response. Thrips-damaged plants again showed a significantly higher density of gossypol glands than did mite-damaged plants. Overall, our results suggest that (1) an omnivorous predator systemically induces resistance traits in cotton and (2) whereas there is evidence of taxonomic specificity (thrips versus mites), there is little support for trophic specificity (herbivorous thrips versus omnivorous thrips) in the elicitation of induced responses.     

Modified atmosphere treatments as a potential disinfestation technique for arthropod pests in greenhouses

Incidental transport of arthropods on plant material can be a significant mode of pest entry into greenhouses. We evaluated the use of controlled atmosphere treatments as a potential way to eliminate arthropod pests on plant propagules (i.e., cuttings or small rooted plants). Lethal exposures to CO2 or N2 were determined for common greenhouse pests including fungus gnat larvae, Bradysia sp.; green peach aphid, Myzus persicae (Sulzer); sweetpotato whitefly, Bemisia sp.; twospotted spider mite, Tetranychus urticae Koch; and western flower thrips, Frankliniella occidentalis (Pergande). We also studied the effect of pest species, life stage, and presence or absence of plants on efficacy of modified atmosphere treatments. Finally, effects of modified atmospheres on plant quality were evaluated for several bedding plant species including begonia, Begonia semperflorens-cultorum Hort. 'Cocktail Series', chrysanthemum, Dendranthema grandiflora Tzvelev., geranium, Pelargonium X hortorum L.H. Bailey, and impatiens, Impatiens wallerana Hook f., and among cultivars of geranium and chrysanthemum. Exposure for 12-18 h to >99% N2 or CO2 caused complete mortality of aphids, mites, thrips, and whiteflies. Fungus gnat larvae were more tolerant of hypoxic conditions. Adult mites and eggs were equally susceptible. For most pests, there was no difference in response to atmospheres modified by CO2 or N2. However, there was variation in response among plant species and cultivars, with effects ranging from delayed flowering to mortality. Despite the possibility of adverse effects on some plants, this work indicates that use of modified atmospheres has potential to eliminate arthropod pests on plant propagules before they are introduced into greenhouses.     

Resistance status of the carmine spider mite,Tetranychus cinnabarinus and the twospotted spider mite,Tetranychus urticae to selected acaricides on strawberries

The carmine spider mite, Tetranychus cinnabarinus (Boisduval) and the twospotted spider mite, Tetranychus urticae Koch, are serious pests of strawberries and many other horticultural crops. Control of these pests has been heavily dependent upon chemical acaricides. Objectives of this study were to determine the resistance status of these two pest species to commonly used acaricides on strawberries in a year‐round intensive horticultural production region. LC₉₀ of abamectin for adult carmine spider mites was 4% whereas that for adult twospotted spider mites was 24% of the top label rate. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 0.5%, 0.5%, 1.4% and 83% of their respective highest label rates for carmine spider mite eggs, 0.7%, 2.7%, 12.1% and 347% of their respective highest label rates for the nymphs. LC_90s of spiromesifen, etoxazole, hexythiazox and bifenazate were 4.6%, 11.1%, 310% and 62% of their respective highest label rates for twospotted spider mite eggs, 3%, 13%, 432,214% and 15% of their respective highest label rates for the nymphs. Our results suggest that T. cinnabarinus have developed resistance to bifenazate and that the T. urticae have developed resistance to hexythiazox. These results strongly emphasize the need to develop resistance management strategies in the region.     

东亚小花蝽对西方花蓟马和二斑叶螨的捕食选择性

多食性天敌对猎物的捕食选择性及猎物密度对天敌捕食的干扰作用直接影响到天敌对不同猎物的控制作用.在实验室条件下研究了东亚小花蝽对西方花蓟马和/或二斑叶螨不同虫态的捕食选择性,以及两猎物中一种猎物的密度变化对小花蝽取食另一种猎物的影响.结果如下:东亚小花蝽5龄若虫和成虫对西方花蓟马2龄若虫的捕食选择性均强于对其成虫,对二斑叶螨的选择性为雌成螨>若螨>幼螨.实验中西方花蓟马2龄若虫是东亚小花蝽最喜好的虫态.二斑叶螨雌成螨密度固定为60头/19.63cm2,西方花蓟马若虫密度从10增加到60时显著地减少了东亚小花蝽对二斑叶螨的取食.反之,固定西方花蓟马同样密度,增加二斑叶螨密度却没有显著改变小花蝽对西方花蓟马的取食.此结果进一步表明,西方花蓟马是东亚小花蝽更喜好的猎物.     

Leaf damage and prey type determine search effort in Orius tristicolor

Components of search effort were determined for adult females of Orius tristicolor (White) (Hemiptera: Anthocoridae) on bean, Phaseolus vulgaris L., leaves with either western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) or twospotted spider mites, Tetranychus urticae (Koch) (Acari: Tetranychidae) as prey. In the absence of prey, females of O. tristicolor allocated significantly more search time to leaves damaged by western flower thrips than to leaves damaged by twospotted spider mites, artificially damaged leaves or undamaged leaves. In the presence of prey, search time increased with increasing amounts of leaf damage for both prey species, but was not affected by prey species. Amounts of leaf damage or type of prey did not affect giving-up-time. The proportion of predators that successfully located thrips increased with increasing amounts of thrips damage on leaves. Females of O. tristicolor appeared to follow some simple, behavioural rules-of-thumb for allocation of search effort. The presence and type of damage determined the initial effort allocated to searching a leaf. Subsequent effort was determined by successful capture of prey, regardless of species. The implications of these results for application of Orius spp. for biological control are discussed.     

Introduction ofPhytoseiulus persimilis for twospotted spider mite control in greenhouses in Egypt [Acari: Phytoseiidae,tetranychidae]

The exotic predaceous mite,Phytoseiulus persimilis Athias-Henriot and the 2 native onesPhytoseius finitimus Ribaga andAmblyseius gossipi Elbadry were released on greenhouse cucumber plants in Egypt to examine their efficiency to control the twospotted spider miteTetranychus urticae Koch.P. persimilis proved to be sufficiently effective for the twospotted spider mite control under greenhouse conditions in Egypt. The 2 before-mentioned native predators were lost soon after release in the greenhouse although they are key mite predators on outdoor crops in this area.      

Acaricidal properties of a Chenopodium-based botanical

The emulsifiable concentrate UDA-245 [25% EC (vol:vol)], based on an essential oil extract from Chenopodium ambrosioides variety ambrosioides, a North American herbaceous plant, was compared with commercially available pesticides for their effectiveness to control the adult stage and egg hatch of the twospotted spider mite, Tetranychus urticae Koch (Acari: Tetranychidae) and the European red mite, Panonychus ulmi (Koch) (Acari: Tetranychidae). After a laboratory bioassay with adult twospotted spider mites, a 0.5% concentration of UDA-245 was more effective than 0.7% (AI) of neem oil (Neem Rose Defense). After a similar bioassay with the European red mite, a 0.5% concentration UDA-245 was as effective as 0.006% (AI) of abamectin (Avid). UDA-245 at 0.5% significantly reduced egg hatch of the twospotted spider mite, 5 and 9 d after treatment and of the European red mite 6 d after treatment. Egg hatch was significantly lower using 0.006% (AI) of abamectin, 0.7% of neem oil, and 1.0% insecticidal soap than UDA-245. Residual tests indicated that UDA-245 may be persistent in the environment only for a few hours. Only 23% mortality was noted when mites were introduced on bean leaves 1 h after treatment with a 2% concentration of UDA-245. At the recommended dose of 0.5%, UDA-245 was not considered phytotoxic for most plants tested, i.e., lettuce, roses, and tomatoes. Results suggest that a greenhouse integrated pest management program using UDA-245 could effectively and selectively control mite infestations by treating "hot spots" with negligible effect on biological control agents when treating before introduction or when natural enemies are absent.     

Pest species diversity enhances control of spider mites and whiteflies by a generalist phytoseiid predator

To test the hypothesis that pest species diversity enhances biological pest control with generalist predators, we studied the dynamics of three major pest species on greenhouse cucumber: Western flower thrips, Frankliniella occidentalis (Pergande), greenhouse whitefly, Trialeurodes vaporariorum (Westwood), and two-spotted spider mites, Tetranychus urticae Koch in combination with the predator species Amblyseius swirskii Athias-Henriot. When spider mites infested plants prior to predator release, predatory mites were not capable of controlling spider mite populations in the absence of other pest species. A laboratory experiment showed that predators were hindered by the webbing of spider mites. In a greenhouse experiment, spider mite leaf damage was lower in the presence of thrips and predators than in the presence of whiteflies and predators, but damage was lowest in the presence of thrips, whiteflies and predators. Whitefly control was also improved in the presence of thrips. The lower levels of spider mite leaf damage probably resulted from (1) a strong numerical response of the predator (up to 50 times higher densities) when a second and third pest species were present in addition to spider mites, and (2) from A. swirskii attacking mobile spider mite stages outside or near the edges of the spider mite webbing. Interactions of spider mites with thrips and whiteflies might also result in suppression of spider mites. However, when predators were released prior to spider mite infestations in the absence of other pest species, but with pollen as food for the predators, we found increased suppression of spider mites with increased numbers of predators released, confirming the role of predators in spider mite control. Thus, our study provides evidence that diversity of pest species can enhance biological control through increased predator densities.     

Host plant-induced changes in detoxification enzymes and susceptibility to pesticides in the twospotted spider mite (Acari: Tetranychidae)

Adult female twospotted spider mites, Tetranychus urticae Koch, reared on lima bean plants were moved to cucumber, maize, or new lima bean plants (the latter being a control) and evaluated after 24 h or 7 d for changes in susceptibility to three pesticides and in levels of related detoxification enzymes. The largest and most consistent changes were observed in mites feeding on cucumber. Susceptibility of mites on cucumber to the synthetic pyrethroids bifenthrin and lambda-cyhalothrin was greater than that of mites reared on lima bean and maize after only 24 h on the plants, and remained higher after 7 d. Mites on cucumber also were more susceptible to the organophosphate dimethoate than were mites on lima bean, but only after 7 d on the host. Susceptibility was inversely related to activities of both general esterase and glutathione S-transferase (GST) in mites on cucumber; general esterase and GST activities were 60 and 25% lower, respectively, than activities of twospotted spider mite on lima bean after 7 d of feeding. Mites on maize were slightly but significantly more susceptible than those on lima bean to bifenthrin, but not to lambda-cyhalothrin, after 7 d and to dimethoate after 24 h but not after 7 d. General esterase and GST activities in twospotted spider mite fed on maize for 24 h were 20 and 16% higher, respectively, than activities in twospotted spider mite on lima bean, but general esterase activity was 30% lower than lima bean-fed mites and GST was not different after 7 d. Thus, plant-induced changes in general esterase activity, perhaps in combination with GST activity, in twospotted spider mite appear to be inversely related to, and possibly responsible for, changes in susceptibility of twospotted spider mite to several pesticides, particularly the synthetic pyrethroids. General esterases appear to play less of a role in the detoxification of the organophosphate insecticide dimethoate.     

Jasmonic acid induced resistance in grapevines to a root and leaf feeder

We investigated the effects of induced resistance to the folivore Pacific spider mite, Tetranychus pacificus McGregor (Acari: Tetranychidae), as well as the root-feeding grape phylloxera Daktulosphaira vitifoliae (Fitch) (Homoptera: Phylloxeridae) in grapevines using exogenous applications of the natural plant inducer, jasmonic acid. Foliar jasmonic acid application at concentrations that caused no phytotoxicity significantly reduced the performance of both herbivores. There were less than half as many eggs produced by spider mites feeding on the induced leaves compared with control grapevine leaves. Induction reduced the numbers of phylloxera eggs and nymphal instars by approximately threefold and twofold, respectively, on induced compared with control grapevine roots. The negative demographic effects of jasmonic acid application appeared to be caused by changes in fecundity for the Pacific spider mite, and possibly changes in development rate and fecundity for grape phylloxera.     

西花蓟马、二斑叶螨与黄瓜新小绥螨的相互关系研究

西花蓟马Frankliniella occidentalis（Pergande）和二斑叶螨Tetranychus urticae Koch是温室花卉与蔬菜上的重要害虫（螨）。植物常被两者同时危害。黄瓜新小绥螨Amblyseius cucumeris（Oudemans）是世界上广泛应用的温室蓟马的生物防治物,有时也被用来防治二斑叶螨。本研究中,在人工气候室盆栽条件下利用黄瓜新小绥螨防治西花蓟马和/或二斑叶螨。结果显示,当每豆株上接入10或20头二斑叶螨时,按照1∶4的益害比释放黄瓜新小绥螨可有效控制二斑叶螨。同样密度比的情况下,5和10头黄瓜新小绥螨的释放量可显著控制西花蓟马的接入量。二斑叶螨密度的增加没有显著影响到黄瓜新小绥螨对西花蓟马的控制作用。西花蓟马可捕食黄瓜新小绥螨的卵,日捕食量达1.2粒。本文对利用黄瓜新小绥螨防治温室中西花蓟马进行了讨论。