Intervention thresholds for Aphis spiraecola (Hemiptera: Aphididae) on Citrus clementina

The production of clementine fruit was affected by varying densities of Aphis spiraecola Patch (Hemiptera: Aphididae) maintained on four groups of clementine, Citrus clementina Hort. ex Tan., trees individually isolated in mesh cages. A formula relating the number of aphids per square meter of canopy per group of trees to yield loss in that group of trees was obtained, permitting us to calculate the economic injury levels (EILs) and economic thresholds (ETs) for treatment against A. spiraecola, i.e., EIL, ET, environmental economic injury level (EEIL), and environmental economic threshold (EET). In an example case with current values, EIL = 370, ET = 322, EEIL = 614, and EET = 533 aphids per m2 of canopy. Formulae designed for easier use in the field were obtained to express each of these thresholds. The formulae are compared with those obtained for Aphis gossypii Glover in a previous study; the intervention thresholds for A. spiraecola are slightly higher than those found for A. gossypii.     

Economic damage by Limothrips denticornis in rye, triticale and winter barley

Abstract:  Limothrips denticornis is a common thrips infesting rye, triticale and winter barley in Sweden. Field experiments with insecticides were carried out 1983–1996 in farmers' fields to investigate the damage to the plant and to evaluate the relationship between thrips density and crop yield losses. The total number of experiments was 99 in rye, 41 in triticale and nine in winter barley. The mean number of thrips per leaf sheath was around 8 in all three crops. The highest number found was 27 thrips per leaf sheath. The population density in the leaf sheath was correlated with the damage observed on the leaf sheath as percentage damaged surface. The effect on the leaf sheath alone contributed to a significant proportion of the yield loss. Thrips in the ear and aphids also contributed to the damage but with multiple regression methods it was possible to estimate the damage done solely by L. denticornis . The yield loss caused by L. denticornis was about the same in all three crops, with a variation between 21 and 26 kg per thrips per leaf sheath and hectare. Compared with the yield loss for aphids, which is about 40 kg per aphid per tiller and hectare, this is considerably lower. The economic injury level was found to be about 14 thrips per straw. The economic threshold for L. denticornis has to be decided when the females are flying into the crop and it was found to be 0.5 females per straw at earing. Economic damage by L. denticornis alone was estimated to be 20% of the total number of experiments for all three crops but economic damage for the three pests together was estimated at 40% of the total number of experiments.     

Effect of tobacco budworm (Lepidoptera: Noctuidae) infestation level on budworm-resistant and -susceptible varieties of flue-cured tobacco in North Carolina

Field experiments were conducted from 1972 to 1978 and from 1998 to 1999 to evaluate tobacco budworm, Heliothis virescens (F.) (Lepidoptera: Noctuidae), larval feeding on flue-cured tobacco, Nicotiana tabacum (L.), yield in eastern North Carolina. In the earlier studies, using variety Coker 319, treatment plots were evaluated when either 0 or 100% of plants in a plot were infested with H. virescens larvae. Treatment differences based on actual yield loss (kilograms per hectare) were compared with estimations of yield loss based on leaf consumption and leaf loss. Results indicate actual yield loss when 100% of plants were infested was less than the corresponding estimates of yield loss. In the later experiments, two tobacco budworm-resistant lines, 'CU 263' and 'CU 370', were compared with a commercial susceptible variety, K 326, when 0, 10, 20, or 40% of plants were infested (1998) and 0, 10, 40, 75, or 100% of plants were infested (1999). Although significant increases in leaf equivalents consumed were associated with infestations exceeding the recommended threshold, differences were not detected for yield (kilograms per hectare), quality (dollars per kilogram), and value (dollars per hectare) within each tobacco line. Additionally, there was not a significant correlation between value and infestations level for any of the tobacco lines. These results provide economic support for tolerance of a higher treatment threshold. Although K 326 sustained more leaf equivalent loss than CU 263 and CU 370, the value of K 326 harvested was higher than that of CU 263 and CU 370. To justify use of resistant varieties, the combination of pest pressure and the benefit of host plant resistance must be greater than the capacity of a susceptible variety to produce competitive yields, despite sustaining significantly higher loss.     

典型草原啮齿动物密度与牧草损失量的关系

研究啮齿动物密度对牧草损失量的关系,对于计算草地经济损害水平至关重要,可以为草地畜牧业管理决策提供指导。本研究于2012 - 2016 年,在锡林郭勒典型草原(东乌珠穆沁旗),应用标志重捕法和样方法对啮齿动物密度以及9 月份植物地上生物量进行调查,用啮齿动物密度及其日食量来估算鼠类对牧草的损害程度,确定牧草损失量。研究结果表明:(1)啮齿动物密度与牧草损失量的最佳拟合曲线是三参数S 型曲线,为:Loss = k/(1+e ^{a - rdensity});(2)当啮齿动物密度>906 个标准鼠单位/hm² 时,牧草产量发生最大损失(牧草产量损失比=23.30% );(3)根据所拟合的曲线,得出该类型草地啮齿动物对牧草损害的危害阈值为174 个标准鼠单位/hm² 。     

Using banded sunflower moth (Lepidoptera: Tortricidae) egg density to estimate damage and economic distance in oilseed sunflower

The banded sunflower moth, Cochylis hospes Walsingham (Lepidoptera: Tortricidae), is an important economic pest of sunflower in the Upper Great Plains of North America. Economic losses due to reductions in seed number, weight, and quality can be significant. Previously, the potential for economic losses were estimated by sampling for adult moths. However, sampling for moths can be difficult and inaccurate. An alternative is to sample for banded sunflower moth eggs, which can be accurately counted in the field by using a binocular 3.5 headband magnifier. The egg counts are used to calculate the economic injury level (EIL) (EIL = C/VWPK), where C is the cost of treatment per unit area, V is the crop market value per unit of weight, W is the slope of the regression between banded sunflower moth egg densities and weight loss per plant, P is a term for plant population per unit area, and K is the control treatment efficacy. Estimates of populations of banded sunflower moth eggs are taken from the center of 400-m spans along all field sides. From these samples and the calculated EIL, a map of the extent of the economically damaging banded sunflower moth population throughout the field is made using economic distance; ED = e ( ( (EIL/E)-1.458)/-0.262). Economic distance estimates the distance an economic population extends into the field interior along a transect from the sampling site. By using egg samples to calculate the EIL and mapping the distribution of economic populations throughout a field, producers can then make more effective pest management decisions.     

Insect economic levels in relation to crop production

Levels of economic insect damage and their effects on crop production are the most often-discussed issue in insect management today. The economic injury level (EIL) concept is the base for decision-making in most integrated pest management (IPM) programs. IPM programs are fundamentally different from control approaches that handle insect problems by focusing on tolerating insect effects. EIL is essential for IPM programs as it indicates which levels of insect populations can be tolerated and which cannot. By increasing our ability to tolerate insects, it is possible to eliminate or reduce the need for management tactics. Scientists can maintain environmental quality through better decisions on the use of those tactics. EILs help maintain environmental quality by reducing unnecessary use of management tactics, especially insecticides. However, including environmental considerations explicitly in the decision-making process could greatly improve the ability of IPM to sustain environmental quality. The EIL components include economic damage, economic thresholds, and the EIL itself. Increased availability of calculated EILs and their related economic thresholds would reduce unnecessary use of management tactics. An environmental EIL evaluates a management tactic based not only on its direct costs and benefits to the user but also on its effects on the environment. There are many factors that can reduce crop yield. One important cause is insects. Insects that cause loss to the fruits are frequently more destructive than those that damage leaves, stems and roots. For example, cotton is infested by Spodoptera littoralis (Boisd.), Pectinophora gossypiella (Saund.), Helicoverpa armigera (Hün.) and Earias insulana (Boisd.) cause the greatest yield losses. The amount of yield loss is dependent upon a number of factors, i.e., plant variety, soil fertility, insect population and skill in handling crop production, etc. Comparatively tolerant varieties, even at the cost of slightly less yield potential, will be more suitable under such conditions.     

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.     

What is the economic threshold of soybean aphids (Hemiptera: Aphididae) in enemy-free space?

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a serious pest of soybean, Glycine max (L.) Merr., in the North Central United States. Current management recommendations rely on the application of insecticides based on an economic threshold (ET) of 250 aphids per plant. Natural enemies are important in slowing the increase of aphid populations and can prevent them from reaching levels that can cause economic losses. However, biological control of A. glycines is inconsistent and can be affected negatively by the intensity of agricultural activity. We measured the impact of a natural-enemy-free environment on the capacity of the current ET to limit yield loss. In 2008 and 2009, caged microplots were assigned to one of three treatments: plants kept aphid-free (referred to as the control), plants that experienced a population of 250 aphids per plant (integrated pest management [IPM]), and plants that experienced unlimited aphid population growth (unlimited). The population growth rate of aphids in the unlimited treatment for the 10 d after the application of insecticides to the IPM treatment was calculated using linear regression. The linear equation was solved to determine the mean number of days between the ET and the EIL for an aphid population in absence of predators. The number of days was determined to be 6.97 +/- 1.11 d. The 2-yr average yield for the IPM treatment was 99.93% of the control treatment. Our study suggests the current soybean aphid ET of 250 aphids per plant can effectively protect yield even if the impact of natural enemies is reduced.     

Economic injury level and crop loss assessment for Tuta absoluta (Lepidoptera: Gelechiidae) on different tomato cultivars

Specifying the relationship between pests and their host plants in terms of damage is one of the basic concepts of integrated pest management (IPM) programmes. The crop loss and economic injury level (EIL) of Tuta absoluta (Lepidoptera: Gelechiidae) were determined on different tomato cultivars using gain threshold (field experiment) and regression (semi‐field experiment) methods. By assessing the crop loss in 2015 and 2016, four out of seven infested tomato cultivars had a significant yield loss in terms of weight of total fruits versus the control under the open‐field conditions. However, the total number of tomato cultivars had no significant difference to control treatment. The semi‐field experiment included six treatments (0, 2, 4, 6, 8 and 10 gravid females/plant) and examined two tomato cultivars. The tomato cages with between 6 and 10 gravid females/plant showed the highest number and weight of damaged fruits. Based on pesticide control costs, the market value of tomato and the control efficacy, we determined the EIL for T. absoluta. In the field experiment, the EIL value for T. absoluta on “Petomech,” “Cal JN3,” “Rio Grande” and “Early Urbana Y” cultivars was 4.15, 4.47, 4.70 and 5.04 larvae per plant, respectively. Based on regression equations, we calculated the EIL values for T. absoluta on “Cal JN3” and “Early Urbana Y” to be 4.75 and 5.44 larvae/plant, respectively. Crop loss assessment and EIL are necessary components of cost‐effective IPM programs and can be effective tools for making decisions about the application of pesticides against T. absoluta.     

Seasonal dynamics of economic injury levels for Tetranychus urticae Koch (Acari, Tetranychidae) on Cucumis sativus L.

Abstract:  Economic injury level (EIL) for Tetranychus urticae Koch on glasshouse cucumbers was established in two ways: EILs based on the number of T. urticae introduced to cucumber early in the growing season and EILs based on mite density and feeding durations (i.e. cumulative mite-days) in each of four growing seasons. The relationship between yield loss and T. urticae infestation level varied among four growing seasons. One mite introduced to cucumber early in the growing season could reduce the cucumber yield by 5.03, 3.20, 1.12 and 2.86 g per plant in spring, summer, autumn and winter, respectively. One mite-day (i.e. one mite feeding in a day) reduced cucumber yield by 0.0123, 0.0074, 0.0035 and 0.0073 g per plant in spring, summer, autumn and winter, respectively. When the seasonal dynamics of market values of cucumber was considered, EILs were the lowest in spring and the highest in autumn. When four seasonal data were combined, EILs can be calculated as EIL = C /(0.00276 ×  K ) for the number of T. urticae introduced early in the growing season and EIL = C /(6.8342 × 10⁻⁶ ×  K ) for cumulative mite-days, where K is efficacy of control measure and C the management cost. This study demonstrated the seasonal dynamics of EILs for T. urticae on glasshouse cucumbers, suggesting that decision making for T. urticae management on cucumber needs to be seasonally different under the glasshouse condition.     

小麦叶蜂危害的产量损失与防治指标研究

当小麦叶蜂幼虫数量相等时,在较干旱的年份（1988）危害较重;而在气候较湿润的年份（1989）危害较轻。虫量与产量损失成正相关（r=0．9821**）,其中以25头／m2幼虫危害的产量损失突增,达显著水平,可以认定为防治指标。     

Thresholds and management strategies for Aulacorthum solani (Hemiptera: Aphididae) in greenhouse pepper

Economic injury level (EIL) and economic threshold (ET) were established for Aulacorthum solani (Kaltenbach) (Hemiptera: Aphididae) in greenhouse pepper, Capsicum annuum L. The high toxicity of the salivary secretion of A. solani produces deformation and decoloration of leaves, complete plant defoliation, and unmarketable deformed fruits at high densities. Low, high and null infestation rate treatments provided a broad range of population densities to determine the relationship between yield and the cumulative A. solani-days (CAD). In all infested compartments, A. solani reached a very high population density that eventually produced the complete defoliation of the plants and losses in total and marketable yield. At low A. solani density, pepper plants showed a tolerance response. Generalized Additive Models (GAM) and Gompertz equation were used to determine the relationship between yield and CAD. Both models explained a high proportion of the variance and described well the relationship between the two variables. However, GAM predicted the tolerance phase of the yield-CAD relationship more satisfactorily. The theoretical damage curve predicted by GAM describes a tolerance, compensation and a linearity part. EIL was estimated at 57 CAD. ET was established at 20 CAD to prevent aphid density from reaching EIL within the gap between sampling periods.     

Economic threshold for soybean aphid (Hemiptera: Aphididae)

Soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), reached damaging levels in 2003 and 2005 in soybean, Glycine max (L.) Merrill, in most northern U.S. states and Canadian provinces, and it has become one of the most important pests of soybean throughout the North Central region. A common experimental protocol was adopted by participants in six states who provided data from 19 yield-loss experiments conducted over a 3-yr period. Population doubling times for field populations of soybean aphid averaged 6.8 d +/- 0.8 d (mean +/- SEM). The average economic threshold (ET) over all control costs, market values, and yield was 273 +/- 38 (mean +/- 95% confidence interval [CI], range 111-567) aphids per plant. This ET provides a 7-d lead time before aphid populations are expected to exceed the economic injury level (EIL) of 674 +/- 95 (mean +/- 95% CI, range 275-1,399) aphids per plant. Peak aphid density in 18 of the 19 location-years occurred during soybean growth stages R3 (beginning pod formation) to R5 (full size pod) with a single data set having aphid populations peaking at R6 (full size green seed). The ET developed here is strongly supported through soybean growth stage R5. Setting an ET at lower aphid densities increases the risk to producers by treating an aphid population that is growing too slowly to exceed the EIL in 7 d, eliminates generalist predators, and exposes a larger portion of the soybean aphid population to selection by insecticides, which could lead to development of insecticide resistance.     

Estimation of economic injury level of Aphis craccivora Koch. (Homoptera: Aphididae) infesting faba bean in new reclaimed area

This work was based on field screening procedure to detect the population density of Aphis craccivora for two successive seasons (2004–2005) and (2005–2006) to emphasis the relation between the economic injury level (EIL) and yield loss.

Results obtained showed that the equilibrium position (steady point) during the first and second season was 9.06 and 3.32 individuals/five leaflets, respectively, while the injury level was 3.4 and 1.16 individuals/leaflets. When the bean plant was subjected to three successive insecticidal applications during the early growing, season is sufficient to decrease the yield loss significantly (yield capacity 21.43 Ard./fed.) with comparing to untreated plant (14.98 Ard./fed.), while the plants exposure for one treatment was 17.36 Ard./fed. The EIL was 8.6 individual of aphids/plant depending on the market price of bean and control cost during the season.     

水稻食叶类害虫等量损害系统与复合防治指标

稻纵卷叶螟Cnaphalocrocis.medinalis Guenèe中华稻蝗Oxya chinensis(Thunberg)稻苞虫Parnara guttatus (Bremer et Grey)是江苏地区水稻的主要食叶类害虫,取食水稻叶片,导致光合叶面积减少.剪叶模拟试验表明,水稻不同生育阶段叶面积损失率与产量损失率呈线性相关.其回归方程分蘖期、孕穗期、腊熟期分别为 D(I_t)=72.50759I_t^1.15906、D(I_t)=141.61737I_t^1.08002、D(I_t)=25.12434I_t^1.00569.在叶面积损失率相同的情况下,产量损失率孕穗期>分蘖期>腊熟期.试验通过三种害虫的各龄取食量,不同生育阶段水稻叶面积及为害与损失率之间的关系,建立了不同生育阶段的经济允许损害水平(EIL_t).并根据各种害虫的相对潜在取食量,计算了校正等量损害系数,为制订复合防治指标提供了依据.实践证明:以等量损害为单位的复合防治指标有较大的实用价值,生态效益、经济效益、社会效益明显.     

Determining an economic injury level for the persea mite,Oligonychus perseae,a new pest of avocado in Israel

The persea mite, Oligonychus perseae Tuttle, Baker & Abbatiello (Acari: Tetranychidae), a pest of avocado, was first discovered in Israel in the autumn of 2001. It has since spread to most avocado growing areas in Israel. To establish an economic injury level (EIL), based on the percentage of leaf area damaged (PLAD), we conducted an extensive field study. For three consecutive seasons we created distinct pest infestation levels on the Hass avocado cv., by applying acaricides (spirodiclofen and abamectin) at 50, 100, and 250 mites per leaf levels, along with non‐sprayed controls in a replicated block design. At harvest time we evaluated the level of leaf damage and fruit yields across treatments. In two out of the 3 years, trees sprayed at 50 and 100 mites per leaf levels had similar PLAD values, differing from trees treated at the 250 mites per leaf level and the non‐treated control, the latter pair also being similar. Over the 3 years, mean yield attained at the two higher infestation levels was reduced by 20% in comparison to the mean yields recorded for plots sprayed at the lower thresholds. Accordingly, we suggest that scouts adopt an action threshold (AT) of 50–100 mites per leaf. Future research is needed to refine this AT. Mean annual cumulative mite days (CMDs) of the two higher levels was ca. 13500 ± 700 per leaf. Using the linear regression equation PLAD = 0.0009CMDs + 2.42, describing leaf damage as a function of CMDs, we estimated an EIL of ca. 15 PLAD.     

Competition between grass‐cutting Atta vollenweideri ants (Hymenoptera: Formicidae) and domestic cattle (Artiodactyla: Bovidae) in Argentine rangelands

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Water Relations, Diurnal Acidity Changes, and Productivity of a Cultivated Cactus, Opuntia ficus-indica

Physiological responses of the Crassulacean acid metabolism (CAM) plant Opuntia ficus-indica (Cactaceae) were studied on a commercial plantation in central Chile. Young cladodes (flattened stems) and flower buds exhibited daytime stomatal opening, whereas mature cladodes and fruit exhibited the nocturnal stomatal opening characteristic of CAM plants. Severe water stress suppressed the nocturnal stomatal opening by mature cladodes, but their high water vapor conductance occurring near dawn was not affected. Nocturnal acidity increases were not as sensitive to water stress as was the nocturnal stomatal opening. The magnitude of the nocturnal acidity increases depended on the total daily photosynthetically active radiation (PAR), being 90% PAR-saturated at 27 moles per square meter per day for a mean nighttime air temperature of 5°C and at 20 moles per square meter per day for 18°C. Inasmuch as the PAR received on unshaded vertical surfaces averaged about 21 moles per square meter per day, nocturnal acidity increases by the cladodes were on the verge of being PAR-limited in the field. The net assimilation rate, which was positive throughout the year, annually averaged 3.4 grams per square meter per day for 1.0- and 2.0-year-old plants. Plants that were 5.4 years old had 7.2 square meters of cladode surface area (both sides) and an annual dry weight productivity of 13 megagrams (metric tons) per hectare per year when their ground cover was 32%. This substantial productivity for a CAM plant was accompanied by the highest nocturnal acidity increase so far observed in the field, 0.78 mole H⁺ per square meter.     

Effects of altitude on aphid-mediated processes in the canopy of Norway spruce

Abstract 1 The abundance of aphids and their honeydew are important in shaping the ecology of food web interactions and nutrient cycling in forests of Norway spruce. Here, the effects of the different environmental conditions at two study sites located at different altitudes (500 m, 765 m a.s.l.), in the Fichtelgebirge, north‐eastern Bavaria, Germany, on the abundance of Cinara pilicornis and their influence on epiphytic microorganisms on shoots of Picea abies were compared. Subsequent changes in throughfall fluxes were measured over a period of 12 weeks beneath infested and reference trees. In a laboratory experiment, the effects of ultraviolet (UV) radiation on microbial mortality and C and N concentrations in leachates were determined. 2 The warmer and drier conditions at the low altitude site favoured an early onset to aphid multiplication in spring compared with the high altitude site, where aphid numbers peaked 3 weeks later. 3 The presence of honeydew was associated with a significant increase in the total number of cultured epiphytic filamentous fungi, yeasts and bacteria in 12 of the 18 sample units, indicating better culturability or growth, whereas altitude had no significant effect on cultured cell numbers. By contrast to the reference trees, the high dissolved organic carbon (DOC) and hexose‐C fluxes beneath infested trees at the peak in aphid abundance, in June and July, resulted in a concomitant decrease in the fluxes of total inorganic nitrogen beneath infested trees (low altitude: ?19.7%; high altitude: ?52.3%). Fluxes of organic nitrogen were significantly higher beneath infested trees at the time of infestation. Similarly, potassium fluxes in throughfall increased 1.6–2.0‐fold in response to aphid infestation. 4 The exposure of infested and uninfested shoots of Norway spruce to UV‐A and UV‐B radiation only weakly affected epiphytic microbial mortality and did not affect the concentrations of the different nitrogen compound in leachates. However, bacteria, tended to be more active in the leachates collected from infested shoots, which resulted in the higher concentrations of aminosugar‐N. The aphids had a more pronounced effect on the concentrations of DOC in leachates, with average DOC concentrations being 4.2‐fold higher than in leachates from uninfested shoots. 5 It is suggested that, even at very low densities, aphids exert a strong influence via honeydew on the performance of microorganisms, and nutrient and energy flow, in spruce forests.     

Characteristics of the population build-up of the Russian wheat aphid Diuraphis noxia and the effect on wheat yield in the eastern Orange Free State

Diuraphis noxia infestations were monitored in early winter and winter wheat during 1983–1985. The aphid population increase was logarithmic in all three years and on both cultivars 100 % infestation levels were recorded. The period of exponential increase in both percentage infestation and in the number of D. noxia per stem took place when the plants had reached the stem elongation stage. The mean number recorded at peak population levels was 150–160 aphids per stem. During the period of plant senescence numbers dropped rapidly. Large reductions in yield were recorded on all infested plants. Single-plant data showed that yield reductions in the early winter cv. Betta were related to the duration of infestation. Relative to sprayed controls, reduction in kernel mass ranged from 25–80% and in 1000-kernel mass from 15–45%. However, the yield reductions of the faster-growing cv. Flamink, appeared to be dependent on the number of aphids per plant during the later growth stages and not the duration of infestation.