Chlorophyll loss caused by soybean aphid (Hemiptera: Aphididae) feeding on soybean

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a worldwide pest of soybean, Glycine max (L.) Merr. Studies to find control methods were initiated in 2000 when it was first detected in North America. A. glycines can reduce yields by as much as 50%, and it is the vector of several viral diseases. A. glycines removes phloem sap, which can result in a reduction of chlorophyll content. Quantification of chlorophyll loss caused by A. glycines feeding on soybean is of vital importance. The SPAD-502 chlorophyll meter is a device that has been used to measure chlorophyll loss caused by nonchewing insects. Chlorophyll loss was studied in no-choice tests on the infested and uninfested leaves of a susceptible check (KS4202). The minimum combined number of days and aphids needed to detect significant chlorophyll loss was 30 aphids confined for 10 d. In a similar experiment, seven resistant entries and two susceptible checks were evaluated. There was no significant chlorophyll reduction between infested and uninfested leaves of five of the resistant entries (K1621, K1639, Pioneer 95B97, Dowling, and Jackson). Percentage of loss of chlorophyll in the susceptible checks was approximately 40%; Jackson and Dowling had a significantly lower percentage loss (13 and 16%, respectively) compared with the susceptible checks. The percentages of chlorophyll loss of K1621, K1639, and Pioneer 95B97 were not statistically different from the percentage of loss of Jackson.     

Field and laboratory evaluations of soybean lines against soybean aphid (Hemiptera: Aphididae)

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a major pest of soybean, Glycine max (L.). Merr., that significantly reduces yield in northern production areas of North America. Insecticides are widely used to control soybean aphid outbreaks, but efforts are underway to develop host plant resistance as an effective alternative management strategy. Here, previously identified resistant lines were evaluated in laboratory tests against field-collected populations of soybean aphid and in field-plot tests over 2 yr in South Dakota. Six lines previously identified with resistance to soybean aphid--Jackson, Dowling, K1639, Cobb, Palmetto and Sennari--were resistant in this study, but relatively high aphid counts on Tie-feng 8 in field plots contrasted with its previously reported resistance. Bhart-PI 165989 showed resistance in one of two laboratory tests, but it had relatively large aphid infestations in both years of field tests. Intermediate levels of soybean aphid occurred in field plots on lines previously shown to have strong (Sugao Zairai, PI 230977, and D75-10169) or moderate resistance to soybean aphid (G93-9223, Bragg, Braxton, and Tracy-M). Sugao Zairai also failed to have a significant proportion of resistant plants in two laboratory tests against aphids field-collected in 2008, but it was resistant in laboratory tests with aphids collected in 2002, 2005, and 2006. Overall, results showed that lines with Rag (i.e., Jackson) or Rag1 gene (i.e., Dowling) had low aphid numbers, whereas lines with Rag2 (i.e., Sugao Zairai, Sennari) had mixed results. Collectively, responses of soybean aphid populations in laboratory and field tests in 2008 resembled a virulence pattern reported previously for biotype 3 soybean aphids, but virulence in soybean aphid populations was variable and dynamic over years of the study. These results, coupled with previous reports of biotypes virulent to Rag1, suggest that deployment of lines with a single aphid-resistance gene is limited for soybean aphid management, and that deployment strategies relying on multiple resistance genes may be needed to effectively use plant resistance against soybean aphid.     

Feeding behavior by the soybean aphid (Hemiptera: Aphididae) on resistant and susceptible soybean genotypes

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is a major pest of soybean, Glycine max (L.) Merr. Since 2000, when A. glycines was detected in the United States, several studies on this insect have been done in different areas, but there is no report of any studies of stylet penetration behavior by A. glycines on resistant and susceptible soybean. Assessment of feeding behavior of this aphid species was compared on four resistant entries (K1639, Pioneer 95B97, Dowling, and Jackson) and a susceptible check (KS4202) by using the electrical penetration graph (EPG) technique. Feeding behavior of A. glycines adults was recorded during a 9-h period. The average time needed to reach the first sieve element phase by A. glycines was 3.5 h in KS4202, whereas it was 7.5 h in the resistant entries. The total duration in the sieve element phase was longer than an hour in KS4202, and only 2 to 7 min in the resistant entries. These results suggest that morphological or chemical factors in the phloem tissue of resistant plants affect stylet penetration activities of A. glycines. In the majority of the recordings, however, the aphid stylet reached the xylem phase before penetrating the sieve element, and the time that aphids spent ingesting xylem sap was not different among all entries. Therefore, it is possible that xylem sap in the resistant entries may contain toxic substances that change aphid behavior and that affect further activities in the sieve element phase.     

Characterization of antibiosis and antixenosis to the soybean aphid (Hemiptera: Aphididae) in several soybean genotypes

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is an introduced pest of soybean, Glycine max (L.) Merr., in North America, and it can reduce yields by 50%. Since 2000, when A. glycines was first detected in the United States, studies of this insect and possible control methods have been initiated. Plant resistance to this aphid species is one important component of integrated control. Reproduction of A. glycines was compared on 240 soybean entries in a pesticide-free greenhouse. Eleven entries had fewer nymphs produced, compared with the susceptible checks, and these entries were used in follow-up experiments to assess antibiosis and antixenosis. Antibiosis was estimated in true no-choice tests, in which adults were confined individually in double-sided sticky cages stuck to the upper side of leaves. Antixenosis was assessed in choice tests, in which all entries were planted in a single pot. Adult aphids were placed in the center of the pot, and 24 h later the number of adults on each plant was counted. Of the 11 entries evaluated, nine showed a moderate antibiotic effect to A. glycines, and the other two entries (K1639 and Pioneer 95B97) showed not only a strong antibiotic effect but also exhibited antixenosis as a category of resistance to A. glycines. The resistant soybean entries found in this work are potential sources for A. glycines control.     

Effect of soil potassium availability on soybean aphid (Hemiptera: Aphididae) population dynamics and soybean yield

Studies were conducted to examine the effect of potassium (K) on soybean aphid, Aphis glycines Matsumura, population growth. A laboratory feeding assay examined the effect of K-deficient foliage on life table parameters of soybean aphids, and field experiments were designed to determine the effect of three soil K treatment levels on aphid populations and their impact on soybean yields. The feeding assay found that life table parameters differed between aphids feeding on the K-deficient and nondeficient soybean leaves. Soybean aphids in the K-deficient treatment exhibited significantly greater intrinsic rate of increase (r(m)), finite rate of increase (lambda), and net reproductive rate (Ro) relative to aphids feeding on nondeficient leaves. No significant difference was observed in mean generation time (T) between the two treatments. However, the field experiment repeated over 2 yr showed no effect of K on soybean aphid populations. Soybean aphid populations were high in unsprayed plots and feeding resulted in significant yield losses in 2002 at all three K treatment levels: when averaged across 2001 and 2002, unsprayed treatments yielded 22, 18, and 19.5% less than the sprayed plots in the low, medium, and high K treatments, respectively. No significant interaction was observed between aphid abundance and K level on soybean yields in either year. This study therefore suggests that although aphids can perform better on K-deficient plants, aphid abundance in the field may be dependent on additional factors, such as dispersal, that may affect final densities within plots.     

Determining the optimal timing of foliar insecticide applications for control of soybean aphid (Hemiptera: Aphididae) on soybean

Field experiments were performed over 3 yr to examine the impact of insecticide application timing to control soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), populations and to prevent soybean yield losses. Experiments were conducted in early and late-planted soybean, Glycine max (L.) Merr. Insecticide applications were made based on soybean growth stages. In 2001, applications were made at V1, V3, R2, and R3 growth stages; in 2002 and 2003, applications were made at R2, R3, and R4 stages. Additional treatments consisted of an unsprayed control and a multiple spray treatment that received insecticide applications at 7-10-d intervals. Soybean aphid densities were recorded throughout the growing season, and yields were measured. Soybean aphid populations varied considerably across years and planting dates. In general, late-planted soybean exhibited higher aphid pressure than early planted soybean, and experiments in 2002 had lower aphid numbers than those in 2001 and 2003. The multiple spray treatment significantly increased yield over the control in four of the six experiments, the exceptions being 2002 late planted and 2003 early planted. This suggests that soybean aphid populations were not large enough to cause yield losses in these two experiments. The R3 spray treatment increased yield in three of the six experiments (2001 late planting, 2002 early planting, and 2003 late planting), the R2 spray treatment increased yield in two of six experiments (2001 and 2003 late plantings), and the V1 application increased yield over the control in the 2001 late-planted experiment. Results suggest that when aphid populations are high insecticide applications made at R2 and R3 plant stages are most effective in preventing yield loss.     

Within-plant distribution of soybean aphid (Hemiptera: Aphididae) and development of node-based sample units for estimating whole-plant densities in soybean

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), is capable of reducing soybean, Glycine max (L.) Merr., yield up to 40% during severe outbreaks. Frequent sampling, which can be costly and time-consuming, is essential to making informed management decisions. However, one way to decrease sampling effort is to use a reduced sample unit when possible. The objectives of this study were to describe the vertical distribution of soybean aphid within soybean over time and to define node-based sample units of varying sizes by testing the ability of selected units to accurately estimate whole-plant aphid density. Within-plant distribution of soybean aphid changed significantly with time. However, the average nodal position where soybean aphids were found on soybean remained within the top half of the plant at all three locations studied across all sample dates. Consequently, selecting the node with the highest aphid density multiplied by the total number of infested nodes (N(MAX)') was the best predictor of aphids on remaining soybean components in both the original (r2 = 0.855) and validation (r2 = 0.824) data sets. For sample units that included more than a single node to estimate densities, a weighted formula, which incorporated changes observed in the within-plant aphid distribution, improved model performance (higher r2 values) and reduced variability around parameter estimates compared with a node-averaged formula. Our results suggest that smaller sample units provide reliable estimations of whole-plant aphid density throughout the growing season for differently maturing soybean, which is essential to their use in pest management decisions and development of future sampling plans.     

Photosynthetic responses of soybean to soybean aphid (Homoptera: Aphididae) injury

The soybean aphid, Aphis glycines Matsumara, was discovered in the United States in the summer of 2000. Since that initial discovery, the aphid has spread across northern soybean production regions. In 2001, we examined the physiological responses of soybeans to low aphids densities (fewer than 50 aphids/leaf). In this study, we determined photosynthetic rates, leaf fluorescence responses, and photosynthetic responses to variable carbon dioxide and light levels. In addition, analyses for chlorophyll content and stable carbon isotope ratios were used to differentiate potential differences in stomatal versus mesophyll limitations to photosynthesis. We observed rate reductions of up to 50% on infested leaflets, including lealets with no apparent symptoms of aphid injury (such as chlorosis). Differences in fluorescence data indicated that photoelectron transport was not impaired. These results indicate that substantial physiological impact on soybean is possible even at low aphid densities. Also, the conventional view of aphid injury acting through reductions in chlorophyll content and light-harvesting reactions of photosynthesis is not supported by our findings in this system.     

Testing soybean antibiosis to three clones of soybean aphid, Aphis glycines (Hemiptera: Aphididae) using sprouts and leaflets

Antibiosis of eight soybean cultivars to three clones of soybean aphids (Aphis glycines Matsumura) was evaluated using both soybean sprouts and leaflets. Overall, the performance of soybean aphid was better on sprouts than on leaflets. We confirmed previous reports that Dowling and Jackson cultivars exhibited strong resistance to a clone of soybean aphids from the US, but not to either Japanese or Indonesian clones. The USA clone had delayed development, fewer offspring, and low emergence rates on these two cultivars. However, abnormal offspring were only investigated on the Tachinagaha cultivar. We confirmed that Bay and Himeshirazu cultivars were strongly resistant to the Japanese aphid clone; aphids produced fewer offspring and deformed offspring on Bay and had delayed development and a low rate of emergence on Himeshirazu. None of the eight soybean cultivars were resistant to the Indonesian clone, although abnormal offspring were produced on Jackson, Adams, and Tachinagaha cultivars. These data suggest that there are genetic differences among the three tested clones of soybean aphid and that the characteristics of local soybean aphid clones must be considered when developing resistant soybean cultivars for a given geographic area.     

Pan trapping soybean aphids (Hemiptera: Aphididae) using attractants

Since its introduction into the United States in the past 10 yr, soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), has been a damaging pest to soybean, Glycine max (L.) Merrill. During 2008 and 2009, fields in central and north central Iowa experienced pockets of high soybean aphid populations. Electroantennograms have shown that soybean aphid alatae are capable of detecting host plant volatiles and sex pheromones. Here, we evaluated baited pan traps as a potential soybean aphid attractant. Yellow pan traps were placed in soybean fields after planting along with lures that contained plant volatiles and sex pheromones in 2008 or sex pheromones only in 2009. Pan trap contents were collected weekly, and plant counts also were conducted. Aphids were identified, and soybean aphids were counted to determine whether one chemical lure was more attractive to spring migrants than other lures. In both years, soybean aphids collected in pan traps with lures were not significantly different from the other products tested.     

Impact of Rag1 aphid resistant soybeans on Binodoxys communis (Hymenoptera: Braconidae), a parasitoid of soybean aphid (Hemiptera: Aphididae)

Multiple strategies are being developed for pest management of the soybean aphid, Aphis glycines Matsumura; however, there has been little published research thus far to determine how such strategies may influence each other, thereby complicating their potential effectiveness. A susceptible soybean (Glycine max L.) variety without the Rag1 gene and a near isogenic resistant soybean variety with the Rag1 gene were evaluated in the laboratory for their effects on the fitness of the soybean aphid parasitoid, Binodoxys communis (Gahan). The presence or absence of the Rag1 gene was verified by quantifying soybean aphid growth. To test for fitness effects, parasitoids were allowed to attack soybean aphids on either a susceptible or resistant plant for 24 h and then aphids were kept on the same plant throughout parasitoid development. Parasitoid fitness was measured by mummy and adult parasitoid production, adult parasitoid emergence, development time, and adult size. Parasitoids that attacked soybean aphids on susceptible plants produced more mummies, more adult parasitoids, and had a higher emergence rate compared with those on resistant plants. Adult parasitoids that emerged from resistant plants took 1 d longer and were smaller compared with those from susceptible plants. This study suggests that biological control by B. communis may be compromised when host plant resistance is widely used for pest management of soybean aphids.     

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.     

Discovery of English grain aphid (Hemiptera: Aphididae) biotypes in China

The English grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae), is an important pest insect of wheat, Triticum aestivum (L.), in China. Grain aphid biotypes are necessary to breed aphid-resistant wheat varieties; however, none have currently been identified. Here, we describe a method to identify grain aphid biotypes and survey the aphid biotype variation in the wheat growth area of China. Clones of S. avenae were collected from 11 locations in China and used to establish culture populations. These populations were then used to assess the resistance of 12 wheat varieties. Based on resistance responses, seven differential hosts were selected to identify the biotype of S. avenae: Amigo, 'Fengchan No. 3', Zhong 4 wumang, JP1, L1, 885479-2, and 'Xiaobaidongmai'. S. avenae was ultimately classified into five biotypes: EGA I, EGA II, EGA III, EGA IV, and EGA V. These methods provide a mechanism to detect the variation and evolution of grain aphids in different wheat-growing locations and also allow for selection of appropriate aphid-resistant germplasm for wheat breeding of commercial wheat cultivars.     

Biotypic diversity in Colorado Russian wheat aphid (Hemiptera: Aphididae) populations

The biotypic diversity of the Russian wheat aphid, Diuraphis noxia (Kurdjumov) (Hemiptera: Aphididae), was assessed in five isolates collected in Colorado. Three isolates, RWA 1, RWA 2, and an isolate from Montezuma County, CO, designated RWA 6, were originally collected from cultivated wheat, Triticum aestivum L., and obtained from established colonies at Colorado State University. The fourth isolate, designated RWA 7, was collected from Canada wildrye, Elymus canadensis L., in Baca County, CO. The fifth isolate, designated RWA 8, was collected from crested wheatgrass, Agropyron cristatum (L.) Gaertn., in Montezuma County, CO. The four isolates were characterized in a standard seedling assay, by using 24 plant differentials, 22 wheat lines and two barley, Hordeum vulgare L., lines. RWA 1 was the least virulent of the isolates, killing only the four susceptible entries. RWA 8 also killed only the four susceptible entries, but it expressed intermediate virulence on seven wheat lines. RWA 6, killing nine entries, and RWA 7, killing 11 entries, both expressed an intermediate level of virulence overall, but differed in their level of virulence to 'CO03797' (Dn1), 'Yumar' (Dn4), and 'CO960293-2'. RWA 2 was the most virulent isolate, killing 14 entries, including Dn4- and Dny-containing wheat. Four wheat lines, '94M370' (Dn7), 'STARS 02RWA2414-11', CO03797, and 'CI2401', were resistant to the five isolates. The results of this screening confirm the presence of five unique Russian wheat aphid biotypes in Colorado.     

Clonal mixing in the soldier-producing aphid Pemphigus spyrothecae (Hemiptera: Aphididae)

Illuminating the genetic relationships within soldier-producing aphid colonies is an essential element of any attempt to explain the evolution of the altruistic soldier caste. Pemphigus spyrothecae is a soldier-producing aphid that induces galls on the leaf petioles of its host (trees of the genus Populus). At least a quarter of the aphids within the clonally produced gall population are morphologically and behaviourally distinct first-instar soldiers that defend the gall population from predation. Using field trapping and microsatellites, we investigated the degree of clonal mixing within natural gall populations. Field trapping in the UK showed that all the migrants of P. spyrothecae and of two other Pemphigus species were wingless first-instar soldiers. The average degree of mixing estimated from trapping P. spyrothecae migrants was 0.68% (range = 0-15%). Microsatellite genotyping of 277 aphids from 13 galls collected in Italy revealed an average mixing level of 10.4% (range = 0-59%). Six galls contained more than one clone (range = 2-5 clones). Non-kin aphids were not restricted to the soldier caste but were evenly distributed across instars. An additional gall, from which 527 occupants were genotyped, contained 12 non-kin aphids distributed among nine clones, showing that clonal diversity can be high even when mixing is very low. These observations suggest that although soldiers migrate regularly and can moult and reproduce within foreign galls, clonal mixing in this species is generally low and is unlikely to provide a barrier to the evolution of investment by the aphid clones in an altruistic soldier caste.     

Comparisons of salivary proteins from five aphid (Hemiptera: Aphididae) species

Aphid (Hemiptera: Aphididae) saliva, when injected into host plants during feeding, causes physiological changes in hosts that facilitate aphid feeding and cause injury to plants. Comparing salivary constituents among aphid species could help identify which salivary products are universally important for general aphid feeding processes, which products are involved with specific host associations, or which products elicit visible injury to hosts. We compared the salivary proteins from five aphid species, namely, Diuraphis noxia (Kurdjumov), D. tritici (Gillette), D. mexicana (Baker), Schizaphis graminum (Rondani), and Acyrthosiphon pisum (Harris). A 132-kDa protein band was detected from the saliva of all five species using sodium dodecyl sulfate polyacrylamide gel electrophoresis. Alkaline phosphatase activity was detected from the saliva of all five species and may have a universal role in the feeding process of aphids. The Diuraphis species cause similar visible injury to grass hosts, and nine electrophoretic bands were unique to the saliva of these three species. S. graminum shares mutual hosts with the Diuraphis species, but visible injury to hosts caused by S. graminum feeding differs from that of Diuraphis feeding. Only two mutual electrophoretic bands were visualized in the saliva of Diuraphis and S. graminum. Ten unique products were detected from the saliva of A. pisum, which feeds on dicotyledonous hosts. Our comparisons of aphid salivary proteins revealed similarities among species which cause similar injury on mutual hosts, fewer similarities among species that cause different injury on mutual hosts, and little similarity among species which feed on unrelated hosts.     

Demography of soybean aphid (Homoptera: Aphididae) at summer temperatures

Soybean aphid, Aphis glycines Matsumura, is now widely established in soybean, Glycine max L., production areas of the northern United States and southern Canada and is becoming an important economic pest. Temperature effect on soybean aphid fecundity and survivorship is not well understood. We determined the optimal temperature for soybean aphid growth and reproduction on soybean under controlled conditions. We constructed life tables for soybean aphid at 20, 25, 30, and 35 degrees C with a photoperiod of 16:8 (L:D) h. Population growth rates were greatest at 25 degrees C. As temperature increased, net fecundity, gross fecundity, generation time, and life expectancy decreased. The prereproductive period did not differ between 20 and 30 degrees C; however, at 30 degrees C aphids required more degree-days (base 8.6 degrees C) to develop. Nymphs exposed to 35 degrees C did not complete development, and all individuals died within 11 d. Reproductive periods were significantly different at all temperatures, with aphids reproducing longer and producing more progeny at 20 and 25 degrees C than at 30 or 35 degrees C. Using a modification of the nonlinear Logan model, we estimated upper and optimal developmental thresholds to be 34.9 and 27.8 degrees C, respectively. At 25 degrees C, aphid populations doubled in 1.5 d; at 20 and 30 degrees C, populations doubled in 1.9 d.     

Flight performance of the soybean aphid, Aphis glycines (Hemiptera: Aphididae) under different temperature and humidity regimens

The soybean aphid, Aphis glycines (Matsumura), is native to eastern Asia and has recently invaded North America, where it is currently the most important insect pest of soybeans. The soybean aphid has spread rapidly within North America, presumably through a combination of active and passive (wind-aided) flight. Here, we studied the active flight potential of A. glycines under a range of environmental conditions using an aphid flight mill. Winged (alate) A. glycines were tested on a specially designed 32-channel, computer-monitored flight mill system. Aphids that were 12-24 h old exhibited the strongest flight behavior, with average flight durations of 3.3-4.1 h, which represented flight distances of 4.6-5.1 km. After the age of 72 h, A. glycines flight performance rapidly declined. The optimum temperature range for flight was 16-28 degrees C, whereas optimum relative humidity was 75%. Our findings show that A. glycines posseses a fairly strong active flight aptitude (ability and inclination) and point to the possibility of flight initiation under a broad range of environmental conditions. These results have the potential to aid forecasting and management protocols for A. glycines at the landscape level.     

Density and distribution of soybean aphid,Aphis glycines Matsumura (Hemiptera: Aphididae) in response to UV radiation

Increasing ultraviolet radiation (UV) has led to greater interest in its current and potential effects on organisms, including herbivorous insects. Here we report the short-term effects of UV on soybean aphids (Aphis glycines Matsumura), a common phytophagous pest of soybeans. We used two complementary approaches to examine how modifying UV radiation affects this phloem-feeding herbivore via changes to soybean aphid densities and their within plant distribution. We found that artificially adding UV in a lab setting decreased soybean aphid population size compared to a low UV control; however, blocking UV radiation in the field had minimal effects on aphid density. Further observations suggest that soybean aphid location could mediate UV effects; feeding on the underside of leaves may shield aphids from some harmful effects of UV. Our results demonstrate the potential importance of UV to insect herbivores and how behavior may influence such effects.