An adjustable action threshold using larval parasitism of Helicoverpa armigera (Lepidoptera: Noctuidae) in IPM for processing tomatoes

An adjustable action threshold that uses estimates of larval parasitism of Helicoverpa armigera (Hübner) in individual fields was assessed over three consecutive years in processing tomatoes in Hawke’s Bay, New Zealand. Tomato fields were monitored weekly for levels of infestation by H. armigera larvae. When infestation levels became of concern, either approaching or exceeding the standard action threshold of one larva per plant, collections of 30+ representative larvae were made. These larvae were measured and reared individually at 30 °C, and after 4 days rates of parasitism were estimated visually. From these data, spray recommendations were made using a formula that adjusted the action threshold to allow for mortality from parasitism. At harvest, damage assessments were made to validate these recommendations. Results showed that estimates of parasitism after 4 days were accurate predictors of final assessments of parasitism. Overall parasitism during the three seasons was 71%, confirming that the original threshold, which relies on about 50% parasitism, needed revision. The dominant parasitoid was Cotesia kazak, reared from 91% of all parasitized larvae over the 3 years. Microplitis croceipes and the self introduced polyphagous parasitoid Meteorus pulchricornis were reared from 4% and 5% of the parasitized larvae respectively. In 16 of 17 fields examined, the adjustable threshold kept fruit damage at harvest below the tolerated level of 5%. The single crop with excessive damage had only 0.5% fruit damage above this level. This adjustable threshold, which varied in this study from 1–8.3 larvae per plant, has been incorporated into an updated IPM programme and contributed to a 95% reduction in insecticide use.     

Action threshold for applying insect growth regulators to tomato for management of irregular ripening caused by Bemisia argentifolii (Homoptera: Aleyrodidae)

The whitefly Bemisia argentifolii Bellows & Perring is a major pest of tomatoes, causing an irregular ripening disorder characterized externally by incomplete or inhibited reddening of fruit, especially in longitudinal sections, and internally by an increase in the amount of white tissue. Experiments were undertaken during the spring and fall of 1997 and 1998 and the spring of 1999 to develop an action threshold for applying the insect growth regulators (IGRs) buprofezin and pyriproxyfen to manage B. argentifolii and irregular ripening. The IGRs were applied when predetermined thresholds were reached and were compared with a high rate of the systemic insecticide imidacloprid, which was applied at transplanting and provided season-long whitefly control. Only plots treated when the numbers of sessile nymphs (second through fourth instars) reached five per 10 leaflets consistently had both external and internal irregular ripening severity ratings similar to the imidacloprid standard. Results were similar for buprofezin and pyriproxyfen even though the modes of action differ. The five nymphs per 10 leaflets threshold lends itself to field scouting because nymphal counts completed in the field using the unaided eye supplemented with a 10x hand lens were linearly and significantly related to counts completed in the laboratory with a dissecting microscope.     

Comparison of economic and plant phenology-based thresholds for management of Lygus lineolaris (Hemiptera: Miridae) in Minnesota strawberries

Field studies were conducted in southeastern Minnesota, 2000-2002, to assess damage potential and management options for adult Lygus lineolaris (Palisot de Beauvois) in June-bearing strawberries (Fragaria x ananassa). The first study was designed to assess the efficacy of a published economic threshold for L. lineolaris nymphs compared with a plant phenology-based threshold management program, targeted at L. lineolaris adults. L. lineolaris nymphs were sampled using the standard white pan beat method; adults were sampled using yellow sticky traps. In the second study, during 2001-2002, caged strawberries were artificially infested with adult L. lineolaris at specific plant growth stages (i.e., vegetative, green bud, white bud, first blossom, peak blossom, first green fruit, and first ripe fruit) to determine the most susceptible growth stages of strawberry. The phenology-based thresholds proved to be more effective in managing L. lineolaris than the current economic threshold based on nymphs. Results from the infestation timing study indicate that early-growth stages (i.e., green and white bud) are most susceptible to adult L. lineolaris feeding damage. During the early-growth stages, only L. lineolaris adults were present; infestations of nymphs occurred primarily from first blossom to green berry. Results from both studies indicate that (1) management of adult L. lineolaris during the early strawberry growth stages is recommended for maximizing marketable yield and (2) the use of plant phenology-based thresholds, when adults are present, will significantly improve insecticide spray timing, and thus minimize the number of insecticide sprays.     

Adult female and neonate larval plant preferences of the generalist herbivore, Epiphyas postvittana

The polyphagous leafroller moth, Epiphyas postvittana, is a pest of many fruit crops in New Zealand. Since the larva is highly mobile, host selection in this insect may involve both the adult female and the larva. In order to test the relative importance of the adult female and the neonate larva in the selection of host plants, the ovipositional preferences of females, and the preferences or acceptances of neonate larvae towards 26 plant species, consisting of 15 plants considered hosts and 11 not considered hosts, were investigated. In the ovipositional tests, the mean preferences of females for hosts and non-hosts were very similar. In contrast, larvae showed a significantly greater mean preference or acceptance towards hosts than to non-hosts, in both choice and no-choice bioassays, respectively. There were highly significant correlations between the preferences and acceptances of larvae for plants in the choice and no-choice tests. In the no-choice tests, there was a highly significant correlation between the acceptances of neonate larvae towards plants after one and three days (i.e., acceptances changed little over time). Moreover, in these no-choice tests, there was a significant negative correlation between larval acceptance at 1 day and larval mortality after 3 days; that is, the less acceptable a given plant at 1 day, the more likely larvae would fail to establish, feed, and survive on it by three days. Female and larval preferences towards the various plants were also negatively correlated. Together, these data suggest that the selection of a plant for the neonate larva to feed on is largely governed by the preferences of the larva, rather than by the preferences of the female. However, selection of a plant for oviposition by the female, may be important in host selection for reasons unrelated to larval preferences, for example, by encouraging dispersal, perhaps to other plant species, of the neonate larvae and thereby decreasing intersibling competition.     

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.     

蚜虫对设施辣椒产量和品质的影响

[目的]探讨不同蚜害等级危害对设施辣椒产量和品质的影响,为设施蔬菜的科学防控、按质定价及制定蚜虫经济阈值提供参考.[方法]通过田间蚜虫量调查,进行蚜害分级,并测定不同蚜害等级下辣椒叶片和果实的SPAD值,采收后记录单株果数,称重,计算座果率及单株果重等产量指标;同时测定不同蚜害等级下辣椒果实可溶性蛋白、可溶性糖、维生素...     

Planting transgenic insecticidal corn based on economic thresholds: consequences for integrated pest management and insect resistance management

A simulation model of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was used to investigate whether sampling and economic thresholds can improve integrated pest management (IPM) and insect resistance management (IRM) when transgenic insecticidal crops are used for insect pest management. When transgenic corn killed at least 80% of susceptible larvae, the calculated economic threshold increased linearly as the proportion of susceptible beetles surviving the toxin increased. The use of economic thresholds slightly slowed the evolution of resistance to transgenic insecticidal crops. In areas with or without rotation-resistant western corn rootworm phenotypes, the use of sampling and economic thresholds generated similar returns compared with strategies of planting transgenic corn, Zea mays L., every season. Because transgenic crops are extremely effective, farmers may be inclined to plant transgenic crops every season rather than implementing costly and time-consuming sampling protocols.     

3 using odor-baited trap trees as sentinels to monitor plum curculio (Coleoptera: Curculionidae) in apple orchards

In commercial orchards in Massachusetts in 2003, we conducted experiments aimed at developing guidelines for use of perimeter-row trap trees baited with grandisoic acid plus benzaldehyde as sentinels in a practical approach to determining need and timing of insecticide applications against overwintered plum curculios, Conotrachelus nenuphar (Herbst). Evaluations were based on percentages of sampled fruit injured by plum curculio. Trap trees baited with grandisoic acid released at approximately 1 mg/d plus benzaldehyde released at approximately 40 mg/d performed as well as or better than trap trees baited with greater or lesser amounts of these attractants in combination. The distance over which a trap tree baited with such odor was effective in aggregating damage to fruit extended to at least 31-33 m (maximum evaluated) along a perimeter row. Trap trees at corners of orchard blocks were as effective as perimeter-row trap trees midway between corner trees. Within the canopy of a trap tree, damage did not tend significantly to be localized in the vicinity of the odor source but tended to be rather evenly distributed among various sectors of the canopy. Finally, among three candidate thresholds evaluated as a trigger for insecticide application, a threshold of one freshly injured fruit proved better than thresholds of two or four freshly injured fruit out of 50 fruit sampled on a trap tree in assuring that orchard-wide damage would remain below a preset economic injury level of 1%. Our findings lead us to suggest that after a whole-orchard application of insecticide to apple trees in Massachusetts orchards shortly after petal fall, subsequent applications of insecticide against plum curculio can be confined to peripheral-row trees and be driven by a provisional threshold of one freshly injured fruit out of 50 fruit sampled on a perimeter-row trap tree baited with the above-mentioned odor.     

Aphid resistance in Brassica crops: challenges, biotechnological progress and emerging possibilities

Aphids, (Hemiptera: Aphidoidea) a nefarious insect pest of Brassicaceae members including major vegetable and oilseed crops have coevolved with their host plant and emerged as most economically important insect pest of crop Brassicas. Their atypical feeding mechanism and unusual reproductive biology made them intractable to control below economic threshold level of damage to the crops. To a large extent aphid infestation is controlled by spraying agrochemicals of systemic mode of action and rarely by biological control. Use of systemic insecticides is highly cost intensive as well poses bigger threat of their incorporation in dietary chain. Breeding for genetic resistance against aphids has not been possible owing to the non-availability of resistance source within the crossable germplasms and lack of knowledge of the genetics of the trait. Genetic engineering with insect resistant transgenes seems to be the only potential avenue to address this difficult-to-accomplish breeding objective. Some success had been achieved in terms of developing aphid resistant cultivars through genetic engineering however, commercial utilization of such crops are still awaited. Thus protection of crops against aphids necessarily requires more research to identify either more effective insecticidal transgenes or biological phenomenon that can usher to new mechanism of resistance. The present review is an attempt to highlight the current status and possible avenues to develop aphid resistance in Brassicaceae crops.     

Realistic global scouting for pests and diseases on cut rose crops

Scouting is considered an essential component of integrated pest management strategies, but most of the techniques, which involve visual assessment, remain too time-consuming for application on a commercial scale. The global scouting method proposed here for greenhouse rose (Rosa spp.) crops combines several rapid visual methods for common pests and diseases, in a single sampling process. A 2-min observation time per sampling unit is required, with two observers. The sampling unit consists of a single stem with its flower and the corresponding basal foliage. A 90-unit regular grid (1 U/6.4 m2) was used, with weekly assessments, including a spatial distribution approach, for pest monitoring. Different grid sizes were simulated and tested with reference data, to determine whether to decrease the number of sampling units. A grid size of 1 U/21 m2 was found to be acceptable, with no significant loss of information. A more realistic and cheaper sampling strategy of this type is more likely to be accepted by growers, increasing the efficiency of crop monitoring and leading to more rational decisions.     

Decision-making tools for Frankliniella occidentalis management in strawberry: consideration of target markets

The western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), a cosmopolitan pest of many crops, is considered a major pest of low tunnel and greenhouse strawberries. The extent of damage to strawberry is unclear because different studies have produced contradictory results. Also, economic thresholds published for WFT in strawberry vary greatly, and most fail to incorporate economic factors. This study was aimed at developing a decision‐making tool for WFT management in strawberries in Israel. Toward this end, economic injury levels (EIL) and economic thresholds were calculated, based on target markets (export vs. domestic). Results indicate that serious infestation of ripe berries may cause a dull, rough appearance, and the fruit may be soft and have a reduced shelf life, rendering it unsuitable for export. Most fruit damage occurred at green and turning‐red stages of development. Two decision‐making tools were developed, one for winter, when WFT populations increase slowly but crop value is high (export market); and the second for spring, when the pest increases rapidly but crop value is low (local markets). Economic thresholds of 10 and 24 WFT/flower were calculated for winter and spring strawberries, respectively, based on direct thrips damage to fruit. This calculation does not take into account the recorded WFT damage to flowers, or its role in facilitating Botrytis cinerea fruit infection. Western flower thrips has proved only an occasional economic pest in Israeli strawberries, and no routine control measures are warranted. Furthermore, augmentative releases of Orius laevigatus or Neoseilus cucumeris against WFT are not justified in this system, because Orius colonizes strawberry fields spontaneously in high numbers when no broad spectrum insecticides are used.     

A potential threat to tomato,a congener crop to potato from invaded potato tuber moth,Phthorimaea operculella (Zeller)

Potato tuber moth (PTM) is a primary pest of potato which had invaded into Korea in 1968 and its distribution was restricted in the southern part of the peninsula. Possibly due to the climate change, its distribution expanded toward the Northern part of South Korea including Gyounggi and Gangwon province where tomato production is high. Host expansion and damage potential of PTM was evaluated on tomato, a congeneric crop of potato. Three commercial varieties of tomato (Dafnis, Bangul and Jujube) and a potato (Superior-Sumi) were subjected to PTM larvae. The results showed that host suitability of tomato to PTM was lower than potato, but PTM could completely develop and reproduce on tomato leaves or fruits. Development time was varied relative to tomato varieties and plant age. PTM showed lower performance on the leaves and fruits of cherry type tomatoes. Higher survival was observed in the large sized fruit of tomato varieties. This study showed substantial evidence that the invaded PTM could damage the tomato cultivation.     

Incidence of the introduced parasitoids Cotesia kazak and Microplitis croceipes (Hymenoptera: Braconidae) from Helicoverpa armigera (Lepidoptera: Noctuidae) in tomatoes,sweet corn,and lucerne in New Zealand

Two parasitoids,Cotesia kazak (Telenga) and Microplitis croceipes (Cresson) have been successfully introduced into New Zealand to improve control of Helicoverpa armigera (Hübner), tomato fruitworm. C. kazak has spread throughout the North Island, but M. croceipes is restricted largely to its release areas in crops in the Gisborne and Hawke’s Bay regions in the East Coast of the North Island and in pine plantations in the central North Island. Rates of mortality of H. armigera from parasitism were studied in processing tomato crops where these parasitoids are a key component of an integrated pest management programme, and in sweet corn, lucerne and soybeans. C. kazak was the dominant parasitoid in tomatoes and soybeans. It emerged from small H. armigera larvae and usually killed the host before it caused major damage to fruit. M. croceipes emerged from larger host larvae than C. kazak. Death rates from parasitism of H. armigera larvae in tomatoes increased from less than 1% caused by native parasitoids prior to parasitoid introductions, to 25–45% in 1988 and 70–80% in 1996 following the establishment of both introduced parasitoids. M. croceipes was the most common parasitoid in lucerne and total mortality from all parasitoids was similar to that in tomatoes. Low rates of parasitism by C. kazak in sweet corn were attributed to the reduced penetration of the adult parasitoid into sweet corn fields and to the protection afforded by sweet corn when H. armigera larvae burrowed into corn cobs. The implementation of an IPM programme based partly on the effectiveness of these parasitoids has contributed to a decrease in insecticide applications to processing tomatoes.     

Evaluation of Dicyphus hersperus (Heteroptera: Miridae) for biological control of Frankliniella occidentalis (Thysanoptera: Thripidae) on greenhouse tomato

The effectiveness of inoculative releases of the mirid predator Dicyphus hesperus Knight for control of Frankliniella occidentalis (Pergande) on greenhouse tomatoes was evaluated in terms of suppression of the population densities of F. occidentalis and associated fruit damage in the presence of the predator over two seasonal trials. An inoculative release of one D. hesperus per plant (approximately 0.1:10 predator:prey ratio) at a high F. occidentalis population density (140 thrips per plant) suppressed the thrips population density to a significantly lower level, compared with the nonrelease greenhouse, but not below a thrips level that caused economic fruit damage. As the predator:prey ratio increased to approximately 0.5:10 D. hesperus:F. occidentalis, the mean percentage of the thrips-damaged fruit in the D. hesperus release greenhouse decreased to 1.6%. However, the amount of fruit feeding by D. hesperus was highly correlated to the availability of prey (or predator:prey ratio) under greenhouse conditions. D. hesperus-induced fruit damage occurred when the predator:prey ratio was >1:10 D. hesperus:F. occidentalis. Considering the potential risk of fruit damage by D. hesperus and the need for effective control of F. occidentalis, a 0.5-1:10 D. hesperus:F. occidentalis ratio is recommended when the thrips population density is in the range of 60-150 thrips per plant.     

A simple action treshold for timing applications of a granulosis virus to controlPieris rapae [Lep.: Pieridae]

Pieris rapae (L.) an important pest of cole crops in the northeastern United States, is susceptible to a granulosis virus,Pieris rapae GV (PrGV), that has been shown to be an effective control measure by researchers in several countries. As an alternative to weekly applications of virus to protect cabbage, we tested the use of an action threshold of one small (first-third instar) larva per plant. Results were compared with those obtained using the same threshold with permethrin, and with weekly applications of virus. Plots treated weekly with virus received 5 applications but the action threshold was exceeded only once. In all virus-treated plots, numbers of large (fourth-fifth instar) larvae remained below 0.35 per plant, and were lower at the end of the season (0.07 in plots treated weekly and 0.1 in plots treated once) than in either the untreated or permethrin-treated plots (0.5). In late August, numbers of large larvae in the check plots reached almost 3 per plant. At harvest the number of feeding holes over 0.3 cm in diameter in the 4 innermost frame and the 4 wrapper leaves were counted. Check plots differed from treated plots by an average of 124.2±6.5 holes per plant in the frame and wrapper leave; virus-treated plots had 51.1±6.9 holes more than the permethrin plots. The difference in overall damage between plots treated 5 times with virus during the season and those treated once was not significant. Plots treated once with virus had significantly more damage (7.6±2.7) to wrapper leaves than those treated five times and marketability ratings were somewhat lower, based on fresh market standards. There were no significant differences in head weight among the treatments. At harvest, a high proportion of larvae collected from the check plots were diseased (77% versus an average of 46% in the treated plots). Because of the high numbers of large larvae in the check plots in late August and the extensive damage to plants, we assumed that virus did not affect a significant number of larvae in these plots until late in the growing season. These results indicate the usefulness of PrGV in a cabbage IPM program and that the use of action thresholds can be highly effective, particularly when insect numbers only occasionally reach damaging levels. While cabbage treated with permethrin had the least amount of injury, that treated weekly with virus was not significantly different by fresh market standards, and all cabbages treated with virus met processing standards. For the fresh market, in which cosmetic standards are more important, PrGV may have to be used weekly or with an action threshold lower than one small larva per plant.      

Tolerance responses to herbivory: implications for future management strategies in potato

Tolerance is a plant response to herbivory that allows plants to sustain defoliation without any fitness consequences. In agriculture, the maximum amount of defoliation that crops can experience without yield loss is defined as the damage threshold. Damage thresholds can be used to develop tolerance‐based management strategies, which would offer guidelines for farmers for when pest control should be enacted to minimise pesticide use while maintaining yield. Damage thresholds for many varieties of potatoes, Solanum tuberosum, have been documented, but not consolidated into a general framework. We aggregated data from published studies and quantified the effects of variety, maturity group, life stage and defoliation mechanisms on damage thresholds to inform a tolerance‐based management strategy for potato. Late maturing varieties did not have different damage thresholds than early maturing varieties. Damage thresholds were greater than 60% defoliation at emergence and post‐bloom and less than 40% defoliation pre‐bloom and during bloom. If the stems were damaged, emergence and post‐bloom damage thresholds were reduced from 60% defoliation without stem damage to 35% and 52% defoliation with stem damage. Likewise, the damage thresholds during bloom were reduced to 20% defoliation when stems were damaged. We propose using action thresholds based on defoliation as a baseline to develop a tolerance‐based management strategy for potatoes.     

Enumerative and binomial sequential sampling plans for soybean aphid (Homoptera: Aphididae) in soybean

Since the discovery of the soybean aphid, Aphis glycines Matsumura, in midwestern U.S. soybean, Glycine max L., in 2000, the aphid has become a significant economic pest. Basic information about estimating population density within fields is unknown. Therefore, we developed two sampling plans to efficiently characterize A. glycines densities. Enumerative and binomial sequential plans were developed using 89 data sets collected from 10 commercial fields sampled during 2001-2003. Re-sampling software was used to validate the enumerative plan on whole plant counts, based on Taylor's power law parameters (a = 9.157 and b = 1.543). For research applications, the enumerative plan was modified to provide an actual precision level of 0.10 (SE/mean), which resulted in an average sample number of 310 individual plants. For integrated pest management (IPM) purposes, we developed an enumerative plan with an actual precision of 0.25, which resulted in an average sample number of 38 individual plants. For IPM applications, the binomial plan will likely be more practical. Binomial plans were developed using two tally thresholds at five action thresholds. Final analysis of the operating characteristic curve for each plan indicated that the tally threshold of > or = 40 aphids per plant, and an action threshold of 0.837 (84% of the plants infested) provided the most correct treat (4%) and no-treat (95%) decisions, with very low incorrect treat (0.5%) and no-treat (0.5%) decisions. A tally threshold of > or = 40 aphids per plant and action thresholds of 84% of plants infested is equivalent to a mean density of 250 aphids per plant, a recently recommended economic threshold. Using this threshold, the minimum required sample number for the binomial plan was 11 plants.     

Relationships between the occurrence of misshapen fruit on late-season strawberry in the United Kingdom and infestation by insects, particularly the European tarnished plant bug, Lygus rugulipennis

In experiments in which the European tarnished plant bug, Lygus rugulipennis, was caged on the developing flowers or young fruits of strawberry, the insects caused malformation of the fruits. Another species of capsid, Plagiognathus chrysanthemi, caused similar damage; this species is less numerous than L. rugulipennis on late-season crops of strawberry in UK. Other insects which sometimes occur in large numbers in the flowers of late-season strawberry, i.e. various species of thrips and pollen beetles, did not cause fruit malformation in caging experiments, though thrips sometimes caused discoloration of the fruit. In field experiments where numbers of L. rugulipennis were reduced by the use of insecticides, the amount of misshapen fruit was reduced greatly compared to untreated plots. Correlations between the numbers of L. rugulipennis present at the early stages of fruit development and damage scores for fruit deformity were highly significant. This capsid is likely to be the major cause of fruit malformation in late-season crops of strawberry in the UK.     

The impact of secondary pests on Bacillus thuringiensis (Bt) crops

The intensification of agriculture and the development of synthetic insecticides enabled worldwide grain production to more than double in the last third of the 20th century. However, the heavy dependence and, in some cases, overuse of insecticides has been responsible for negative environmental and ecological impacts across the globe, such as a reduction in biodiversity, insect resistance to insecticides, negative effects on nontarget species (e.g. natural enemies) and the development of secondary pests. The use of recombinant DNA technology to develop genetically engineered insect‐resistant crops could mitigate many of the negative side effects of insecticides. One such genetic alteration enables crops to express toxic crystalline (Cry) proteins from the soil bacteria Bacillus thuringiensis (Bt). Despite the widespread adoption of Bt crops, there are still a range of unanswered questions concerning longer term agro‐ecosystem interactions. For instance, insect species that are not susceptible to the expressed toxin can develop into secondary pests and cause significant damage to the crop. Here, we review the main causes surrounding secondary pest dynamics in Bt crops and the impact of such outbreaks. Regardless of the causes, if nonsusceptible secondary pest populations exceed economic thresholds, insecticide spraying could become the immediate solution at farmers’ disposal, and the sustainable use of this genetic modification technology may be in jeopardy. Based on the literature, recommendations for future research are outlined that will help to improve the knowledge of the possible long‐term ecological trophic interactions of employing this technology.     

Electroculture of tomato plants in a commercial hydroponics greenhouse

An experiment was conducted to evaluate the effects of air ion treatment on tomato plants (Lycopersicon esculentum P. Miller) in terms of: (1) growth and health; (2) fruit yield and quality; and (3) economic factors. The plants were grown by a commercial greenhouse (G.H.) grower employing soilless culture techniques. An air ion generator and emitters were installed in such fashion that 864 plants were exposed to a high negative air ion density flux, while 576 plants grew in an area which received relatively few ions. Normal operational procedures, with certain modifications, were employed for plant culture, feed/irrigation, and environmental control. Plants responded vigouously to air ion stimulation, which equated to shortening of the seeding-to-harvest time period by two weeks as measured by vine growth, main stem height, time to blossoming, fruit set, and fruit yield. Throughout the first four-month growth period plant growth was good and no serious physiological disorders nor insect damage were observed. During the sixth harvest week a virus infection appeared in both control and ion-treated plants, but was not of sufficient severity to ruin the experimnent. Foliage and fruit samples were subjected to laboratory analyses. In general, the stimulated plants contained higher percentages of mineral elements than those of the controls. Fruit from ion-treated plants has more ascorbic and citric acid than that from control plants. Although there were no wide differences in fruit texture or flavor, a taste panel verdict indicated that fruit from the stimulated plants tasted better. An unexpected benefit was marked decrease in white fly infestation. All these factors combined with the low cost of air-ion treatment suggest that this modality offers potential for greenhouse cultivation of garden crops.