Rates of growth and increase ofMyzus persicae on virus-infected potatoes according to type of virus-vector relationship

Growth, reproduction and survival (=performance) of the aphidMyzus persicae Sulzer was measured on virus-free and virus-infected potato plants The principle objective was to evaluate if various viral infections affected aphid performance differently, and if so, whether any order in the performance response of the aphid was discernible according to the type of virus-vector relationship. Three viruses varying in their dependency onM. persicae as a vector were used. Plants infected with potato leafroll virus (PLRV), a circulative virus highly dependent uponM. persicae for dispersal and transmission, were superior hosts as determined by the significantly greater mean relative growth rate (MRGR) and intrinsic rate of increase (r_m) ofM. persicae compared with those of aphids reared on other plants. Plants infected with potato virus Y, a noncirculative virus less dependent uponM. persicae for dispersal than PLRV, were intermediate in their quality based upon intermediate MRGR and r_m values. Plants infected with potato virus X, a nonvectored virus independent ofM. persicae, were least suitable hosts along with the group of virus-free plants according to the lower MRGR and r_m values.     

Variable growth and reproduction response of the spruce shoot aphid, Cinara pilicornis, to increasing ozone concentrations

Spruce shoot aphid, Cinara pilicornis Hartig (Homoptera: Lachnidae), is an aphid species that has shown enhanced performance on trees exposed to SO₂ or mixtures of air pollutants, whereas results with ozone have been contradictory. Using a 4-week chamber fumigation experiment, we tested how different population dynamic parameters of aphids are affected by ozone (O₃). Mean relative growth rate (MRGR), development time and reproduction rate of C. pilicornis were determined using 7h day-time O₃ concentrations of 0, 40, 80 and 160 ppb. Development period from birth to reproductive stage was fastest at 80 ppb during early shoot elongation, while reproduction and intrinsic rate of population increase was not significantly affected by ozone concentration. There was a significant negative correlation between ozone concentration and the MRGR of first instar nymphs in the third fumigation week. In feeding test performed on seedlings after fumigation, the MRGR was reduced on shoots which had been exposed to 80 ppb O₃. The results suggest that elevated O₃ concentration during early shoot elongation period may stimulate population development of C. pilicornis, but on maturing shoots, high O₃ concentration has a negative effect on aphid performance. This might be due to accelerated ageing of O₃ exposed shoots.     

Effect of PGPR on population growth parameters of cotton aphid

Plant-growth-promoting rhizobacteria (PGPR) help plants by increasing plant growth and defending them against pathogens and pests. There is considerable research supporting the use of these bacteria in plant pathogens management, but the number of research papers that have focused on their effect on insect pests control is quite few. In this research, we examined the ability of four native strains of Pseudomonas fluorescens to manage the cotton aphid, Aphis gossypii, on greenhouse-grown cucumbers in Iran. The strains UTPF (University of Tehran Pseudomonas fluorescens) 68, UTPF1, UTPF6 and PF169 of P. fluorescens were used as seed treatment to evaluate their impact on both cucumber growth and cotton aphid population growth parameters. The strains UTPF68 and PF169 of this bacterium influenced phenology of cucumber by decreasing the Growing Degree Days of flowering period. Also, the plants treated with these bacterial strains had a significant increase in yield weight of approximately 58%. In the other part of the study, various effects on developmental parameters of aphid were recorded among bacterial strains, but only PF169 caused significant decreasing effect on r_m value of aphid, which is the most important factor in aphid’s life table. We conclude that the PF169 treatment had significant negative effects on population growth rate of A. gossypii. The PF169 could be reliable in a control programme for A. gossypii on cucumber plants in greenhouses.     

醉马草水浸液对豌豆蚜触杀活性及种群增长的影响

为探讨醉马草水浸液对豌豆蚜触杀活性及种群增长的影响,采用带虫浸叶法比较不同生育期醉马草带菌（E+）和不带菌（E-）水浸液对豌豆蚜触杀活性及种群生命表,测定了豌豆蚜的死亡率及触杀后对其生殖期,平均繁殖力,繁殖率及生命表参数的影响。结果表明,不同生育期醉马草带菌（E+）水浸液触杀豌豆蚜后对其各项指标均有显著影响。在苗期时,E+水浸液触杀豌豆蚜后校正死亡率最高,繁殖力最低,内禀增长率（r_m=0.145 d^-1）和净生殖率（R₀=4.802头）均为最小值。在成熟期时,E+水浸液触杀豌豆蚜24 h、48 h和72 h后校正死亡率分别为26.15%,19.01%,9.07%;繁殖期（3.87 d）,平均繁殖力（8.80头）,繁殖率（1.40%）,内禀增长率（r_m=0.208 d^-1）和净生殖率（R₀=8.820头）。在枯黄期时,E+水浸液触杀豌豆蚜后校正死亡率最低,繁殖力最强,内禀增长率（r_m=0.247 d^-1）和净生殖率（R₀=13.647头）均为最大值。不同生育期醉马草E-水浸液触杀豌豆蚜后对其种群繁殖无显著影响,与对照差异不显著（P>0.05）。综上,苗期醉马草E+水浸液对豌豆蚜有较好的触杀效果,校正死亡率高,且触杀后当代繁殖力减弱,种群扩建时间延长,不利于其种群繁殖和增长;故苗期醉马草E+水浸液具有很好的杀虫潜力,所采用水浸液方法制备简单,成本低,可为新型植物源农药研发提供重要理论依据。     

Evaluation of induced responses, insect population growth, and host-plant fitness may change the outcome of tests of the preference-performance hypothesis: a case study

The preference‐performance hypothesis predicts that insect preference should correspond to host suitability for offspring development. We studied the pattern of within‐plant preference in the aphid Sipha flava and its consequences for offspring performance on the host‐plant Sorghum halepense, regarding the role of induced responses of plants to aphid feeding. The consequences of within‐plant preference on aphid population growth and host‐plant traits were also evaluated. Our results showed that winged and wingless aphids preferred to settle on mature rather than young leaves. In contrast, aphid individual growth rate was higher on young leaves when compared with mature leaves, suggesting that the outcome of this test rejected the preference‐performance hypothesis. However, the inclusion of the factor ‘previous aphid infestation’ changed the outcome from a maladaptive choice to a neutral one. Thus, individual growth rates of S. flava increased when aphids developed on leaves that had been previously infested. Interestingly, aphid growth rate on previously infested leaves did not differ between young and mature leaves. On the other hand, aphid population reproductive rate was higher and the percentage of winged aphids lower when infestation occurred on mature rather than young leaves. Aphid infestation reduced plant and shoot biomass, and increased leaf mortality. These negative effects on plant traits related to plant fitness were greater when aphid infestation occurred on young leaves. Likewise, whereas infestation on mature leaves did not cause a significant reduction in the number of flowering plants compared with control plants, aphid infestation on young leaves did reduce the number of plants at the flowering stage. Consequently, if both the reproductive rate of aphids in the mid‐term, and host‐plant fitness are taken into account, the results indicate that aphid preference for mature leaves may be an adaptive choice, thus supporting the preference‐performance hypothesis.     

Patterns of aphid resistance in the genus Vicia

The performance of three aphid species, Aphis fubae, Acyrthosiphon pisum and Megoura viciae, was quantified on 22 taxonomically-selected host plant species from the genus Vicia (vetches), using intrinsic rate of increase (r_m) k standard errors. A. pisum proved to be the most successful aphid species, both in terms of highest potential population increase and widest host range; M. viciae was least successful, with most restricted host range and low r_m values on all but the closest relatives of Vicia faba. A wide range of antibiotic resistance was found within the genus, and host resistance to the three aphid species was found to be broadly related to classification patterns based on taxonomy and life-form. Analysis of the components of r_m revealed that nymphal survival rates were the most significant factor limiting host colonisation, not pre-reproductive period which is the most important factor in cultivars of V. faba. The consequences of aphid polyphagy on performance are discussed.     

Melon aphid performance on chrysanthemum as mediated by cultivar, and differential levels of fertilization and irrigation

Population parameters of the melon aphid, Aphis gossypii Glover, were compared for insects grown on six cultivars of chrysanthemum, Dendranthema grandiflora Tzvelev ('Fontana', 'Iridon', 'Pink Lady', 'Splendor', 'White Diamond', and 'White View Time') fertilized with 3 different levels of nitrogen (80, 160 and 240 mg N/l) and 2 levels of irrigation (high 300 ml and low 210 ml every other day). Fecundity, longevity, and survivorship of aphids were significantly affected by the cultivar treatment, but were not affected by irrigation or fertilizer treatments or by any combination of interactions among cultivar, fertilizer and irrigation. Significantly fewer aphids survived on the cultivar 'Pink Lady' (populations reduced by 20.8%) than any other cultivar examined. Intrinsic rates of increase r _m , finite rates of increase (R ₀), and population doubling times (DT) for aphids were different among fertilizer levels and cultivars, but were not different among irrigation levels. There were no significant fertilizer by irrigation interaction effects upon r _m , R ₀, or DT. The highest rate of fertilizer applied (240 mg N/liter) adversely affected the intrinsic rate of increase of melon aphids; however, aphid intrinsic rate of increase was weakly correlated with foliar soluble protein levels (r=0.989, P=0.0954). Foliar soluble protein levels were not associated with fertilization treatment. Melon aphids perform consistently better on the cultivars 'White Diamond', 'Fontana', and 'Splendor', relative to those aphids growing on 'Iridon', 'Pink Lady', or 'White View Time'. In general, melon aphids performed best on 'White Diamond' and poorest on 'Pink Lady'.     

EFFECTS OF RAPE GROWN IN SO2-ENRICHED ATMOSPHERES ON PERFORMANCE OF THE APHID,MYZUS PERSICAE (SULZER) *

Abstract Performances of the aphid, Myzus persicae, were monitored during feeding on leaves of the rape, Brassica chinensis, previously fumigated with SO₂ in a range of concentrations between 20 and 160 nl/1 at 25°C. Response of the aphids depended on dose of the air pollutant. Moderate dose of SO₂ treatment on the rape greatly enhanced the aphids' performances while high level of the pollutant heavily suppressed their growth and reproduction. They performed best at about 80 nl/l SO₂, where nymphal mean relative growth rate (MRGR), adult fecundity and intrinsic increase rate(r_m) of the population increased by 31.5%, 89.8% and 42. 7% over those of control aphids, respectively. Determination of the plant chemistry suggests that the altered relative content of methionine induced by So, exposure might be responsible for this response of dosage dependence.     

Impact of density of Aphis craccivora (Aphididae) on growth and yield of susceptible and resistant cowpea cultivars

Impact of initial density of cowpea aphid Aphis craccivora Koch (Aphididae) at infestation on the growth and yield of aphid-susceptible cowpea cultivar ICV-1 and aphid-resistant cultivar ICV-12, was investigated. Plants at the seedling, flowering and podding stages of development were infested with five aphid densities consisting of 0, 2, 5, 10 and. 20 aphids per plant and maintained for 22 days. Extended leaf heights of plants and aphid counts were recorded at 7, 12, 17 and 22 days after infestation. Two crop growth parameters (biomass duration and leaf area duration), and two plant yield parameters (number of pods per plant and number of seeds per pod) were recorded. Due to the occurrence of parthenogenesis and changes in population dynamics during infestations, aphid densities were converted into cumulative cowpea aphid-days, to facilitate data analyses and interpretation. ANOVA indicated that there was significant (P=s 0.05) difference in aphid-day accumulations between the two cultivars when infested at the seedling stage. Accumulations on cv. ICV-1 were greater than on cv. ICV-12. However, no such differences between the cultivars were detected when plants were infested at flowering and podding stages. Therefore, the seedling stage was used for comparisons of the impact of cowpea aphid-days on the growth and yield parameters of the two cultivars. At the 95% confidence intervals, ICV-12 plants were consistently taller than ICV-1 plants. Infested ICV-1 seedlings showed stunting and other growth deformities which were not observed on ICV-12 plants. Regression analyses revealed substantial reductions in the growth and yield parameters of ICV-1 relative to ICV-12. Overall, cowpea aphid-days provided a convenient and reliable method for studying the aphid population dynamics and the subsequent impact on plant growth and yield performance.     

Aphid growth and reproductive rates

Aphid size, although generally a good indicator of fecundity is not a good indicator of aphid performance over a wide range of conditions. In general, the greater the mean relative growth rate (MRGR) of apterous morphs of Rhopalosiphum padi (L.), the greater their fecundity. Intrinsic rate of increase (r_m) is even more closely correlated with mean relative growth rate than fecundity.Once these criteria are quantified for a morph of a particular species of aphid over a range of conditions the morphs intrinsic rate of increase on a particular host can be estimated by a quick measure of its mean relative growth rate.

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Résumé La taille des pucerons, bien que considérée généralement comme un bon indice de la fécondité, n'est pas un bon indice pour leurs performances dans une grande gamme de conditions. En général, plus le taux moyen de croissance relative est élevé chez les types aptères de Rhopalosiphum padi, plus leur fécondité est importante. Le taux intrinsèque de croissance (r_m) est encore plus étroitement lié au taux moyen de croissance relative que la fécondité.Une fois que ces critères ont été quantifiés pour un type d'une espèce donnée de puceron dans une gamme de conditions, les taux intrinsèques de croissance des différents types sur un hôte particulier peuvent être estimés par une mesure rapide de leur taux moyen de croissance relative.

     

The potential for population growth of Ascomorpha ecaudis

The intrinsic rate of natural increase (r_m) of the rotifer Ascomorpha ecaudis was found to be a hyperbolic function of food concentration. The threshold food concentration and r_max/2-food concentration determined for this species were significantly lower than values predicted from allometric models. These growth characteristics may be related to the mucus house in which Ascomorpha lives and/or the symbiotic algae living in its body tissues. The maximum rate of population growth recorded (0.71 d^–1) was similar to that of other soft-bodied rotifers of similar body mass. These population growth characteristics and the resistance of this species to invertebrate predation should allow it to become a dominant member of freshwater zooplankton communities. However, field observations suggest that it is not. Reasons for this are suggested.     

The effect of hydoroxamic acid concentration at late growth stages of wheat on the performance of the aphid Sitobion avenae

From a previous worldwide screen of wheat cultivars as seedings, five were selected to encompass a wide concentraiton range of the hydroxaminc acid DIMBOA (0.99-8.07 mmol Kg ^-1 fr. wt). Compared with those in seedings, the concentrations of DIMBOA in flag leaves of the same cultivars were relatively low (0.06-0.87 mmol kg^-1 fr. wt). Concentraions of hydroxamic acids in whole ears at anthesis and the early milk stage were even lower, ranging from undetectable to 0.05 mmol kg^-1 fr. wt. The three-day mean relaive growth rate (MRGR) was determined for nymphs of Sitobion avenace on the flag leaf (GS 39) and on the ear (GS 60-60) of the five cultivars. No significant differences in MRGR were found between cultivatrs at the same growth stage, although MRGR was higher on ears on than on flag leaces. The results are discussed in realtion to the potential of hydroxamic acids in programmses aimed at breeding mature-plant aphid resistance into wheat cultivars.     

Soybean plant stage and population growth of soybean aphid

The soybean aphid, Aphis glycines Matsumura, is a newly invasive species of aphid in North America. Previous studies disagree as to whether soybean, Glycine max (L.) Merr., plant stage has an impact on aphid intrinsic rate of increase. Therefore, the growth rate of soybean aphids on soybean plants of different stages was examined at two different scales in the field. A planting date experiment was used to measure the population growth of soybean aphids on plants of different stages. Clip-cages were used to measure life history characteristics of individual aphids on plants of different stages. No differences were found in the population growth or dynamics of soybean aphids in the planting date experiment. The life history characteristics of individual aphids also showed no significant difference when feeding on different growth stages of soybean plants. The impact of these findings on soybean aphid management is discussed and the possible reasons why the results differ from previous estimates of the aphid growth-plant stage relationship are considered.     

Fertility table and rate of population growth of the predator Supputius cincticeps (Heteroptera: Pentatomidae) on one plant of Eucalyptus cloeziana in the field

The reproductive potential and population growth (r_m and λ) of the predator Supputius cincticeps (Heteroptera: Pentatomidae) were evaluated using a life and fertility table. S. cincticeps was reared on one plant of Eucalyptus cloeziana in the field and fed with Tenebrio molitor (Coleoptera: Tenebrionidae) pupae. Females of this predator had a net reproductive rate (R₀) of 21.02 females/female; an intrinsic rate of population increase (r_m) of 0.041 and finite rate of increase (λ) of 1.042. This resulted in population growth of S. cincticeps in the eucalyptus plant with a doubling time of 17.01 days. This natural enemy can be reared under field conditions with alternative prey for use in biological control. Such individuals of S. cinticeps will be better adapted to field conditions when they are liberated.     

Individual growth rates do not predict aphid population densities under altered atmospheric conditions

• 1 Altered atmospheric composition, associated with climate change, can modify herbivore population dynamics through CO₂ and/or O₃‐mediated changes in plant quality.
• 2 Although pea aphid Acyrthosiphon pisum genotypes exhibit intraspecific variation in population growth in response to atmospheric composition, the proximate mechanisms underlying this variation are largely unknown.
• 3 By rearing single (green, pink) and mixed (green + pink) pea aphid genotypes on red clover Trifolium pratense at the Aspen Free Air CO₂ and O₃ Enrichment (Aspen FACE) site, we assessed whether: (i) elevated CO₂ and/or O₃ concentrations alter aphid growth and development and (ii) individual aphid growth rates predict aphid population densities.
• 4 We showed that growth and development of individual green and pink aphids were not influenced by CO₂ and/or O₃ concentrations when reared as individual or mixed genotypes. Individual growth rates, however, did not predict population densities.
• 5 Reared as a single genotype, green pea aphid populations decreased in response to elevated CO₂ concentrations, but not in response to elevated CO₂ + O₃ concentrations. Pink pea aphid populations reared as a single genotype were unaffected by augmented CO₂ or O₃. Populations of mixed genotypes, however, were reduced under elevated CO₂ concentrations, irrespective of O₃ concentrations.
• 6 Herbivore population sizes may not readily be predicted from growth rates of individual organisms under atmospheric conditions associated with global climate change.

     

Effects of potato plants expressing the nptII-gus fusion marker genes on reproduction, longevity, and host-finding of the peach-potato aphid, Myzus persicae

Transgenesis developed in the last 20 years offers new possibilities for crop protection. The transgenic process, however, requires the use of marker fusion genes to select and visualize the transformed tissues. Although the expression products of these marker genes are stably expressed in crops, little attention has been given to assess the eventual risks of these recombinant proteins on phytophage populations. Three independent transgenic potato (Solanum tuberosum) clones from the cultivar Désirée (DG5, DG18, and DG20) carrying the commonly used nptII‐gus gene construct and exhibiting different β‐glucuronidase activity (0.843 ± 0.011, 0.576 ± 0.096, and 0.002 ± 0.000 pmol min^?1.mg^?1, respectively) were evaluated to determine the impact of the encoded proteins on the behaviour, development, reproduction, and demography of the peach‐potato aphid, Myzus persicae, under laboratory‐controlled light and temperature. Our results revealed that the transgenic event can alter aphid physiology or behaviour. Experiments showed a probiotic effect of one transgenic line, the DG5, resulting in reduced prereproductive period and mortality, and enhanced daily fecundity, which was expressed in a greater population growth potential (r_m = 0.205 vs. r_m = 0.174 of the control). In contrast, aphids fed with the DG18 line exhibited reduced adult survival and reproductive period but no alteration of their demographic parameters (r_m = 0.176). Finally, no physiological alteration was induced in aphids fed on a DG20 diet (r_m = 0.170). Behavioural experiments conducted in a 4‐choice olfactometer demonstrated that insects were significantly more attracted by the odour of transgenic DG18 potato plant than that of Désirée non‐transformed plant, spending twice as much time in the DG18 plant odour. The two other transformed clones (DG5 and DG20) were as attractive as the non‐transformed cultivar. It is concluded that the β‐glucuronidase expression in potato plants might be responsible for the probiotic effect measured on the feeding aphids, whereas alteration of the foliage odour would result from a pleiotropic effect.     

Using knockout mutants to reveal the growth costs of defensive traits

We used a selection of Arabidopsis thaliana mutants with knockouts in defence genes to demonstrate growth costs of trichome development and glucosinolate production. Four of the seven defence mutants had significantly higher size-standardized growth rates (SGRs) than the wild-type in early life, although this benefit declined as plants grew larger. SGR is known to be a good predictor of success under high-density conditions, and we confirmed that mutants with higher growth rates had a large advantage when grown in competition. Despite the lack of differences in flowering-time genes, the mutants differed in flowering time, a trait that strongly correlated with early growth rate. Aphid herbivory decreased plant growth rate and increased flowering time, and aphid population growth rate was closely coupled to the growth rate of the host plant. Small differences in early SGR thus had cascading effects on both flowering time and herbivore populations.     

Estimating susceptibility of biological control agents to pesticides: influence of life history strategies and population structure

In this study we examined the influences that differing life history strategies and population structures at the time of pesticide exposure have on population susceptibility to pesticides. We used life table data and a matrix projection model to incorporate combinations of mortality (lethal effect) and reductions in fecundity (sublethal effect) into estimates of intrinsic population growth rates (r) for a predator, the seven-spot lady beetle, Coccinella septempunctata L., and its prey, the pea aphid, Acyrthosiphon pisum Harris, and an aphid parasitoid, Diaeretiella rapae (M’Intosh). All three species exhibited differences in key life history variables. The aphid had the highest r and shortest generation time, the ladybeetle had the lowest r and longest generation, while the parasitoid exhibited intermediate life history characteristics. When the model was run with populations started as neonates (aphids) or eggs (lady beetle, parasitoid) for each species, ladybeetle populations were much more susceptible than either aphid or parasitoid populations 30 days after simulated exposure to a pesticide. For example, 50% mortality and a 50% reduction in fecundity resulted in a population headed toward extinction (negative r) for the ladybeetle while the parasitoid population grew exponentially (positive r) even after sustaining 70% mortality and a 70% reduction in fecundity. The aphid species maintained exponential growth after sustaining 80% mortality and an 80% reduction in fecundity. Thus, differences in life history variables accounted for the greater susceptibility of the ladybeetle to a pesticide than its aphid prey or the parasitoid over a set time interval. These differences in susceptibility were greatly reduced when the model was run starting with a mixed age/stage population (the stable age distribution) for each species indicating that population structure at the time of pesticide exposure plays a critical role in population susceptibility. These results suggest that life history attributes as well as population structure at the time of pesticide exposure both play a major role in population susceptibility to pesticides, highlighting the need to explicitly consider differences in life history variables among species when calculating compatibility of pesticides and biological control agents as well as the population structure of beneficial species at the time of pesticide application.     

Using matrix models to explore the influence of temperature on population growth of arthropod pests

1 Population growth of four arthropod pests on agricultural crops, the pea aphid, the bird‐cherry oat aphid, the Mediterranean fruit fly, and the two‐spotted spider mite, was modelled using stage matrix models. 2 Temperature was included as a variable in the model, affecting fecundity, mortality and growth rate. Linear temperature dependence was used to describe fecundity and individual growth rate in the matrix model. Life table data collected at various constant experimental temperatures were used to parameterize the model. 3 Sensitivity analysis identified the most influential demographic parameters determining the growth rate of the population at different temperature regimes. Mortality of young adults and immature stages were found to be the most important parameters in determining population growth for all species presented. However, high temperatures increased the relative impact of individual growth rates and fecundity on the growth of the population.     

Impact of chemical elicitor applications on greenhouse tomato plants and population growth of the green peach aphid, Myzus persicae

Recent advances in the understanding of plant signaling pathways have opened the way for using elicitor‐induced plant resistance as a tactic for protecting plants against arthropod pests. Four common elicitors of induced responses in tomato, Lycopersicon esculentum Mill. (Solanaceae), were evaluated with regard to phytotoxicity, induction of plant defensive proteins, and effects on population growth and fecundity of a common pest, the green peach aphid, Myzus persicae (Sulzer) (Homoptera: Aphididae). Ethephon and methyl jasmonate (MJ) treatments caused varying degrees of phytotoxicity. Ethephon caused pronounced changes in plant growth form and severe, dose‐dependent negative impacts on plant growth and flowering. Effects with MJ were milder, but still caused temporary inhibition of development, leading to smaller plants and delayed flowering. The commercial elicitors benzothiadiazole (BTH) and harpin did not cause detectable phytotoxicity. The highest doses of ethephon and MJ significantly increased leaf peroxidase (POD) levels but only MJ treatments significantly increased polyphenol oxidase (PPO) levels. BTH and harpin had no detectable effects on POD and PPO. Populations of green peach aphids grew significantly more slowly on plants treated with BTH or MJ than on control plants or plants treated with harpin or ethephon. Slowed aphid population growth on BTH‐treated plants was due to significant reductions in aphid fecundity, although this was independent of changes in time to onset of reproduction or time to death. Aphid fecundity was also reduced on MJ‐treated plants relative to controls, but this difference was not statistically significant, suggesting that other mechanisms are involved in slowing aphid population growth on MJ‐treated plants. Growth of aphid populations on plants treated with a MJ–BTH mixture was reduced almost as much as with treatments of MJ alone, suggesting that antagonism between JA‐dependant and SA‐dependent plant signaling pathways is only mild with regard to induced defenses against aphids.