Nitrogen homeostasis in a willow leaf beetle, Plagiodera versicolora, is independent of host plant quality

While foliar nitrogen (N) content of host plants depends on environmental conditions, N content of herbivorous insects may remain relatively constant due to homeostasis. However, it is unknown to what extent insects can maintain their body elemental composition against natural variation in host plant quality. The present study examined the performance and N content of a willow leaf beetle, Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae), when fed leaves of host willow, Salix eriocarpa Franchet et Savatier (Salicaceae), with varying nutritional status. Water content, toughness, and N content of willow leaves varied seasonally, and they affected performance of the leaf beetle. The leaf beetle achieved high performance when fed young leaves. On the other hand, the N content of the leaf beetle changed little, and it was independent of that of willow leaves, indicating strong N homeostasis of the leaf beetle. We discussed the function of N homeostasis in herbivorous insects in tritrophic level interactions.     

The suitability of damaged willow leaves as food for the leaf beetle, Phgiodera versicolora

Abstract. 1. The effect of previous damage on the suitability of willow ( Mix bubylonicu and S.ulbu 'Tristis') leaves as food for the imported willow leaf beetle, Plugiodera versicoloru Laich. (Coleoptera: Chrysomelidae), was evaluated by feeding adults and larvae leaves from damaged and undamaged branchlets.
2. Females had lower fecundity when fed leaves from artificially damaged branchlets of S.ufba 'Tristis'. A similar result was obtained when beetles ate leaves from naturally damaged branchlets of S.babylonica .
3. Feeding preference tests suggest that the reductions in leaf suitability were not due to adults avoiding damaged leaves as a food source.
4. PZugiodera versicolora larvae required longer to develop and attained a lower adult weight when fed leaves from damaged branchlets.
5. Changes in leaf suitability brought about by herbivore feeding may affect the seasonal abundance of P.versicoloru on its willow hosts.     

Interactions among leaf toughness, chemistry, and harvesting by attine ants

Abstract. 1. Young and mature leaves of a tropical legume, Inga edulis var. minutula Schery, are strikingly different in secondary chemistry, especially condensed tannins, and leaf toughness.
2. Bioassays with the two different leaf types indicate that leaf cutter ants, Atta cephalotes (L.), always find mature leaves relatively more acceptable than young leaves when selection was based on chemical cues.
3. Since extracts of young leaves show greziter inhibition of fungal pectinases we suggest that leaf-cutter ants are capable of distinguishing which leaf types are most suitable for the growth of their symbiotic fungus.
4. However, mature leaves are 3 times tougher than young leaves and this prevents leaf-cutter ants from harvesting the more suitable mature leaves.
5. Consequently, bioassays which require cutting before leaf removal indicate that some colonies actually harvest more from the less suitable young leaves.
6. We suggest that the quality of a colony's habitat may indicate whether a colony will harvest more of the less suitable young leaves. Colonies which are harvesting from highly suitable host plants avoid the tropical legume I.edulis while those in poorer habitats accept I.edulis but, because of leaf toughness, mostly harvest the less suitable young leaves.     

Spatio-temporal abundance of flushing leaves shapes host selection in the willow leaf beetle, Plagiodera versicolora

In the willow leaf beetle, Plagiodera versicolora (Laicharting) (Coleoptera: Chrysomelidae), food resources available for adults are severely restricted by leaf toughness, which increases with age. Nevertheless, females require their own food almost all their life in order to produce eggs. In this paper, we have focused our attention on the spatio-temporal abundance of flushing leaves and have examined its effect on host-plant selection by adults among four co-occurring willow species ( Salix chaenomeloides , Salix eriocarpa , Salix integra , and Salix serissaefolia ) (Salicaceae) by field observations and experiments at two spatial scales. Among the various factors associated with this, the amount of new leaf production contributed maximally to variation in adult abundance. By conducting two experiments, we confirmed that the adults preferentially flew towards willow trees with abundant flushing leaves. Furthermore, we detected substantial seasonal changes in new leaf abundance and realized fecundity in the field, and a strong positive correlation was observed between them. Availability of adult food resources limited the reproductive performance of adults, particularly in mid-summer when only S. serissaefolia produced a few new leaves. These results supported the substantial effect of new leaf abundance on adult abundance in the field. Thus, we concluded that adult feeding is a critical factor that shapes the host-plant selection of P. versicolora and determines its seasonal occurrence through the dispersal and settlement of adults.     

Bottom-up cascade in a tri-trophic system: different impacts of host-plant regeneration on performance of a willow leaf beetle and its natural enemy

Abstract.  1. Plant quality can directly and indirectly affect the third trophic level. However, little attention has been paid to how changes in plant quality affect the performance of predators through trophic levels, and which herbivores or predators are affected more strongly by host-plant quality. The present study examined the effects of artificial cutting of willows on the performance of a willow leaf beetle ( Plagiodera versicolora Laicharting) and its predatory ladybird beetle ( Aiolocaria hexaspilota Hope).
2. Laboratory experiments showed that performance (survival rate, developmental time, and adult mass) of the willow leaf beetle was higher when fed with leaves of cut willows than when fed with leaves of uncut willows. Performance (developmental time and adult mass) of the predatory ladybird was also improved when it was fed on the leaf beetle larvae that had been fed on leaves of cut willows, compared with those that had been fed on leaves of uncut willows. This indicates that a bottom-up cascade occurs in the tri-trophic system.
3. In a comparison of improved performance parameters between the leaf beetle and the ladybird, regenerated willows shortened the developmental time of the willow leaf beetle more than that of the ladybird. This indicates that the impacts of willow cutting on insect performance differ between the second and third trophic levels.     

The effect of nitrogen fertilization and rust fungus infection, singly and combined, on the leaf chemical composition of Rumex obtusifolius

1. The chrysomelid beetle Gastrophysa viridula occurs on Rumex obtusifolius growing in a range of nutrient conditions and also on plants infected with the foliar fungus Uromyces rumicis . In a controlled environment, we investigated the effect of fertilizing plants with eight nitrate and four ammonium concentrations, with or without infection, on leaf nutritional quality.
2. Increasing nitrate fertilization increased leaf oxalate, total nitrogen and nitrate concentrations and water content, and decreased total non-structural carbohydrate (NSC) concentrations. Increasing ammonium fertilization increased leaf nitrogen concentration and water content, decreased nitrate and NSC concentrations, and had no effect on oxalate concentrations.
3. Infection produced a mainly additive effect to fertilization, increasing NSC and oxalate, and decreasing nitrate and nitrogen concentration in whole plants fed nitrate, and increasing nitrate and NSC in whole plants fed ammonium.
4. Young leaves on infected plants remained uninfected and had greater nitrogen and NSC concentrations, and lower oxalate and nitrate concentrations, than infected leaves on the same plant.
5. These results are discussed in relation to changes in C:N and NSC:organic nitrogen ratios, the effect of nitrate and oxalate, and the known feeding and oviposition preferences of the beetle. The results suggest that there is an optimum nitrogen fertilization level for G. viridula development.     

Preference for protected feeding sites by larvae of the willow-feeding leaf beetle Galerucella lineola

1. Free-living insects are often thought of as more vulnerable to environmental hazards than concealed insects, such as galling or mining insects. The possibility that larvae of the free-living leaf beetle Galerucella lineola seek out existing plant structures and thereby become partly concealed was explored.
2. Neonate larvae of G. lineola frequently feed in rolled-in margins of young leaves of their host plant, Salix viminalis . In addition to nutritional benefits from feeding on young leaves, larvae may also gain protection against adverse weather conditions and general predators by feeding in the leaf rolls. Field and laboratory experiments were conducted to test these hypotheses.
3. Artificial shelters were constructed and cohorts of neonate larvae were placed on experimental plants. In all experiments, larvae preferred to feed in shelters, even when shelters were constructed on mature leaves.
4. In one of the experiments, fewer larvae disappeared when shelters were provided. In a predator exclusion experiment, however, no differences in predator-inflicted mortality on G. lineola were found between shelter-containing shoots and control shoots.
5. A laboratory experiment showed increased protection from desiccation when shelters were present; growth rate was higher for larvae feeding on plants with shelters.
6. Thus, free-living insects may not always be as exposed to environmental hazards as is often assumed. In particular, young larvae may take advantage of preformed structures on their host plant and feed in a concealed microhabitat. Because mortality, in general, is high during early instars, shelter-seeking behaviour may increase survival significantly. The existence of preformed shelters may therefore be a plant characteristic that should be considered when exploring the environmental risks associated with the free-living habit.     

The influence of Salix leaf abscission on leaf-miner survival and life history

Abstract. 1. Early abscission of mined leaves was an important mortality factor of a Phyllonorycter species (Lepidoptera: Gracillariidae) on Salix lasiolepis Benth. (Salicaceae). A larger percentage of mined leaves abscised early (34.4% in 1990; 24.5% in 1991), and Phyllonorycter survival was greatly reduced in these abscised leaves.
2. Leaf-mining by Phyllonorycter was associated with increased early leaf abscission. An egg removal experiment demonstrated that leaf mining induced this increase in leaf abscission.
3. The induction of early leaf abscission was dependent upon the timing of herbivory and simulated herbivory (mechanical damage). Early mechanical damage induced leaf abscission, late mechanical damage did not. Mines which expanded early were more likely to induce leaf abscission than mines which expanded more slowly.     

Host plant variation in plant-mediated indirect effects: moth boring-induced susceptibility of willows to a specialist leaf beetle

Abstract.  1. We examined the plant-mediated indirect effects of the stem-boring moth Endoclita excrescens (Lepidoptera: Hepialidae) on the leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) in three willow species, Salix gilgiana , S. eriocarpa , and S. serissaefolia.
2. When the stem-boring moth larvae damaged stems in the previous year, willows were stimulated to produce vigorously growing lateral shoots on these stems. These new lateral shoots were significantly longer and the upper leaves had significantly higher nitrogen and water content than current-year shoots on unbored stems, although the carbon content and leaf dry mass were not different between lateral and current-year shoots.
3. In the field, leaf beetle larvae and adults had significantly greater densities on lateral shoots of bored stems than on current-year shoots of unbored stems. A laboratory experiment showed that female beetles had significantly greater mass and fecundity when fed on leaves of newly-emerged lateral shoots. Thus, the stem-boring moth had a positive effect on the temporally and spatially separated leaf beetle by increasing resource availability by inducing compensatory regrowth.
4. The strength of the indirect effects on the density and performance of the leaf beetle differed among willow species, because there was interspecific variation in host quality and herbivore-induced changes in plant traits. In particular, we suggest that the differences in magnitude of the changes among willow species in shoot length and leaf nitrogen content greatly affected the strength of the plant-regrowth mediated indirect effect, coupled with host-plant preference of the leaf beetle.     

Effects of leaf and sap feeding insects on photosynthetic rates of goldenrod

Summary Herbivory can alter the balance between sources and sinks within a plant, and changes in the source-sink ratio often lead to changes in plant photosynthetic rates. We investigated how feeding by three insect herbivores affected photosynthetic rates and growth of goldenrod (Solidago altissima). One, a phloem-sap feeding aphid (Uroleucon caligatum), creates an additional sink, and the other two, a leaf-chewing beetle (Trirhabda sp.) and a xylem-sap feeding spittlebug (Philaenus spumarius) both reduce source supply by decreasing leaf area. Plants were grown outside in large pots and insects were placed on them at predetermined densities, with undamaged plants included as controls. All insects were removed after a 12-day feeding period. We measured photosynthetic rates both of damaged leaves and of undamaged leaves that were produced after insect removal. Photosynthetic rates per unit area of damaged leaves were reduced by spittlebug feeding, but not by beetle or aphid feeding. Conductance of spittlebugdamaged leaves did not differ from controls, but internal carbon dioxide concentrations were increased. These results indicate that spittlebug feeding does not cause stomatal closure, but impairs fixation within the leaf. Effects of spittlebug feeding on photosynthetic rates persisted after the insects were removed from the plants. Photosynthetic rates per unit area of leaves produced after insect removal on spittlegug-damaged plants were lower than control levels, even though the measurements were taken 12 days after insect removal. The measurement leaf on spittlebugdamaged plants was reduced in area by 27% relative to the controls, but specific leaf area (leaf area/leaf weight) was increased by 18%. Because of the shift in specific leaf area, photosynthetic rates were also examined per unit leaf weight, and when this was done there were no significant differences between control and spittlebug-damaged plants. Beetle and aphid feeding had no effects on the photosynthetic rate of the leaves produced after insect removal. Plant relative growth rates (in terms of height) were reduced by spittlebugs during the period that the insects were feeding on the plants. Relative growth rates of spittlebug-damaged plants were increased above control levels after insect removal, but these plants were still shorter than controls 17 days after insect removal. Beetles and aphids did not affect plant relative growth rates or plant height. Feeding by both spittlebugs and beetles reduced leaf area, and the effect of the spittlebug was more severe than that of the beetle. These results show that effects of herbivory on photosynthetic rates cannot be predicted simply by considering changes in the source-sink ratio, and that spittlebug feeding is more damaging to the host plant than beetle or aphid feeding.     

Responses of leaf miners to atypical leaf production patterns

Abstract. 1. Larvae of two bivoltine species of leaf-mining Lepidop-tera, Acrocercops sp. and Neurobathra strigifinitella (Clem.), restrict feeding to young, second-flush leaves of their host trees in north Florida.
2. During 1980 and 1981, densities of both species varied greatly among thirty small water oaks ( Quercus nigra ), as did timing and extent of secondary leaf production.
3. In both years leaf-miner density at the end of the first generation (mid-August) was positively correlated with secondary leaf production.
4. Five trees abscised their leaves and reflushed new ones at atypical times of the growing season. When refoliation coincided with emergence of ovipositing adults, Acrocercops sp. and N.strigifinitella densities increased dramatically, indicating that both species are at times limited by availability of young leaves.
5. By staggering termination of diapause these leaf miners can exploit a temporally variable resource.     

Evolution of feeding preference in a leaf beetle: the importance of phenotypic plasticity of a host plant

Much attention has been paid to ecology and evolution of damage-induced plant responses. Recently, it has been emphasized that phenotypic plasticity, such as induced plant responses, has the potential to lead to evolutionary changes of interacting partners. Here, we report that induced plant regrowth promotes a locally adaptive feeding preference of a leaf beetle, Plagiodera versicolora . We found that there was among-population variation in the strength of the feeding preference of the leaf beetle for leaf-age types of conspecific host plants. The strength of the preference was positively correlated to leaf production of host plants across populations, and the intensity of induced regrowth was likely to have been responsible for geographic variation in new leaf production. Within one population, we detected a significant additive genetic variance and heritability in the preference for consuming new vs. old leaves. Moreover, the strength of preference was significantly related to egg production depending on the leaf-age types. Thus, allopatric populations can evolutionarily develop different adaptive preference, according to locally distinct patterns of induced host regrowth.     

Plant phenology-mediated indirect effects: The gall midge opens the phenological window wider for a leaf beetle

We examined whether larvae of the gall midge Rabdophaga rigidae (Diptera: Cecidomyiidae) can modify the seasonal dynamics of the density of a leaf beetle, Plagiodera versicolora (Coleoptera: Chrysomelidae), by modifying the leaf flushing phenology of its host willow species, Salix serissaefolia and Salix eriocarpa (Salicaceae). To test this, we conducted field observations and a laboratory experiment. The field observations demonstrated that the leaf flushing phenology of the willows and the seasonal dynamics of the beetle density differed between shoots with stem galls and shoots without them. On galled shoots of both willow species, secondary shoot growth and secondary leaf production were promoted; consequently, leaf production showed a bimodal pattern and leaf production periods were 1 to 2 months longer than on non‐galled shoots. The adult beetle density on galled shoots was thus enhanced late in the season, and was found to change seasonally, synchronizing with the production of new leaves on the host willow species. From the results of our laboratory experiment, we attributed this synchrony between adult beetle density and willow leaf flush to beetles’ preference to eat new leaves rather than old. Indeed, beetles consumed five times more of the young leaves when they were fed both young and old leaves. These results indicate that stem galls indirectly enhance the adult beetle density by enhancing food quality and quantity late in the beetle‐feeding season. We therefore conclude that midge galls widen the phenological window for leaf beetles by extending the willows’ leaf flush periods.     

Defensive larval secretions of leaf beetles attract a specialist predator Parasyrphus nigritarsis

1. Noxious larval secretions of leaf beetles, which repel generalist predators, do not deter specialist syrphid fly predators (genus Parasyrphus ). These flies cause considerable mortality to the beetles, but little is known about their foraging behaviour.
2. Larvae of Parasyrphus nigritarsis were attracted to the volatile larval secretions produced by two prey species Phratora vitellinae and Linaeidea aenea. Parasyrphus nigritarsis feeds on both beetles in nature. Phratora vitellinae feeds on willows and utilizes host plant compounds for secretion production, while the alder-feeding L. aenea produces an autogenous secretion.
3. Fly larvae were strongly attracted to pieces of filter paper treated with larval secretion of the beetles. They attempted to feed on them for up to 7 min, and were equally attracted to the secretions of Ph. vitellinae and L. aenea . Fly larvae were also attracted to pure salicyl aldehyde, the main component of the secretion of Ph. vitellinae .
4. Fly larvae searched extensively for prey on leaves that had been damaged by beetle larvae. They also followed trails made with solutions containing faecal matter of prey larvae. They showed no differential preference for Ph. vitellinae or L. aenea , but always rejected larvae of the non-prey leaf beetle Agelastica alni .
5. Beetle secretions thus play an important, but unexpected, role in the feeding behaviour of P. nigritarsis . This predator uses the beetle secretion to locate its prey. The implications of these results for three trophic level interactions are discussed.     

Oviposition site selection on oats: the effect of plant architecture,plant and leaf age,tissue toughness,and hardness on cereal leaf beetle,Oulema melanopus

In sequentially planted oat stands, the cereal leaf beetle (CLB), Oulema melanopus (L.) (Coleoptera: Chrysomelidae: Lemini), is found in greater numbers, and lays more eggs, on later planted (younger) oats (Avena sativa L.) (Poaceae). Plant characteristics that could explain this ovipositional preference were examined in a series of experiments. Cage and open field whole plant preference tests confirmed the attraction of ovipositing females to younger oats. A cage effect illustrated the role of plant architecture (plant height) in CLB host selection. Two multiple‐choice and one no‐choice excised leaf experiments determined that characteristics of individual leaves associated with leaf insertion level (leaf number from base to apex) and age influence ovipositional site selection. Leaves of higher insertion level have higher nitrogen content, but fewer eggs are laid on those leaves. Two experiments examining the interaction between total leaf nitrogen and leaf insertion level showed that only leaf insertion level affected oviposition choice. Published literature suggests variation in secondary plant compounds cannot explain O. melanopus ovipositional preference among leaves. Grass leaves of higher insertion level have more extensively developed cells associated with tissue toughness and hardness. The data and supporting literature suggest tissue toughness and hardness are deterring oviposition on oat leaves of higher insertion level. However, newly eclosed larvae are able to feed on leaves usually avoided as oviposition sites. The explanation for this result may be a lack of correlation between host suitability and ovipositional preference.     

Influence of plant silicon and sugarcane cultivar on mandibular wear in the stalk borer Eldana saccharina

1 Silicon can increase the resistance of plants to attack by herbivorous insects. The present study aimed to determine the effect of silicon and cultivar on mandibular wear in larvae of the sugarcane stalk borer Eldana saccharina Walker (Lepidoptera: Pyralidae).
2 Four sugarcane cultivars, resistant (N21, N33) and susceptible (N11, N26) to E. saccharina were grown in a pot trial in silicon deficient river sand, with (Si+) and without (Si−) calcium silicate. Individual third-instar larvae were confined on the sugarcane stalk at three known feeding sites (leaf bud, root band and internode) and left to feed for 21 days.
3  Eldana saccharina larval heads were mounted on stubs, with the mandibles oriented horizontally and photographed under a scanning electron microscope. Mandibular wear was measured from the digital images using a quantitative method.
4 Although there was a trend for increased wear in larvae that developed on Si+ cane, no significant effect of silicon, cultivar or site on mandibular wear of E. saccharina was shown.
5 This is the first study to accurately and quantitatively measure the mandibular wear of an insect fed on Si+ plants.     

Response of the elm leaf beetle to host plants induced by oviposition and feeding: the infestation rate matters

We investigated by olfactometry and feeding‐ and oviposition‐choice‐tests how the highly specialised elm leaf beetle, Xanthogaleruca luteola Müller (Coleoptera: Chrysomelidae), responds to conspecifically induced defences in the field elm Ulmus minor Miller (Ulmaceae). While egg deposition of the beetle induced elms to release volatiles attractive to the egg parasitoid Oomyzus gallerucae Fonscolombe (Hymenoptera: Eulophidae), feeding alone did not. In the present study, females of the elm leaf beetle showed preferences for the odours of twigs induced by low egg deposition and feeding over odours from uninfested twigs. In contrast, heavy infestation rendered elm odours less attractive to the beetles. Feeding and oviposition bioassays revealed an oviposition preference for leaves from uninfested twigs when compared to locally infested leaves. However, beetles preferred to feed upon systemically induced leaves compared to uninfested ones. The different preferences of the elm leaf beetle during host plant approach might be explained by a strategy that accounts for both gaining access to high quality nutrition and avoiding competition or parasitism.     

Leaf beetle grazing does not induce willow trichome defence in the coppicing willow Salix viminalis

Abstract 1 Willows are frequently attacked and defoliated by adult leaf beetles (Phratora vulgatissima L.) early in the season and the plants are then attacked again when new larvae emerge. The native willow Salix cinerea has previously been shown to respond to adult grazing by producing new leaves with an increased trichome density. Subsequent larval feeding was reduced on new leaves. This type of induced plant response may reduce insect damage and could potentially be utilized for plant protection in agricultural systems. 2 Here, we investigated if the willow species most commonly used for biomass production in short rotation coppice, Salix viminalis, also responds to adult beetle grazing by increasing trichome density. Larval performance and feeding behaviour on plants previously exposed to adult beetles was compared with that on undefoliated control plants in a greenhouse. 3 We found an overall decrease in trichome density within all the plants (i.e. trichome density was lower on new leaves compared to that for older basal leaves on S. viminalis). However, leaves of beetle defoliated plants had a higher trichome density compared to control plants. Larval growth and feeding was not affected by this difference between treatments. Larvae appeared to remove trichomes when feeding on S. viminalis, a behaviour that might explain the lack of difference between treatments.     

Preferential Feeding and Occupation of Sunlit Leaves Favors Defense Response and Development in the Flea Beetle,Altica brevicollis coryletorum – A Pest of Corylus avellana

The monophagous beetle, Altica brevicollis coryletorum, is a major leaf pest of Corylus avellana (common hazel). In contrast to majority of the other studied species of shrubs, sunlit leaves are grazed to a much greater extent than shaded leaves. Since the observation of a link between leaf irradiance level and A. brevicollis feeding is unique, we hypothesized that feeding preference of this beetle species is related to the speed needed to escape threats i.e. faster jumping. We also hypothesized that sunlit leaves are more nutritious and easier to consume than the leaves of shaded shrubs. Results indicated that beetle mass was greater in beetles occupying sunlit leaves, which is consistent with our second hypothesis. The study also confirmed under laboratory conditions, that larvae, pupae and beetles that were fed full-light (100% of full light) leaves were significantly heavier than those fed with shaded leaves (15% of full light). In the high irradiance conditions (higher temperature) duration of larval development is also reduced. Further results indicated that neither the concentration of soluble phenols, leaf toughness, or the number of trichomes could explain the insect’s preference for sunlit leaves. Notably, measurements of jump length of beetles of this species, both in the field and under laboratory conditions, indicated that the defense pattern related to jumping was associated with light conditions. The jump length of beetles in the sun was significantly higher than in the shade. Additionally, in laboratory tests, beetle defense (jumping) was more strongly affected by temperature (15, 25, or 35°C for 24h) than by leaf type. The effect of sunlit, higher nutrient leaves (greater level of non-structural carbohydrates) on defense (jumping) appears to be indirect, having a positive effect on insect mass in all developmental stages.     

Effect of leaf surface extraction on palatability of romaine lettuce to Diabrotica balteata

Abstract The leaf surface of a plant, especially its chemical components, constitutes the first line of resistance to herbivores and other pests. Our previous research indicated that ‘Valmaine’ (Val) romaine lettuce, Lactuca sativa L., was highly resistant to feeding by adult banded cucumber beetle, Diabrotica balteata LeConte, while ‘Tall Guzmaine’ (TG) was highly susceptible. We investigated the leaf surface chemistry of these two cultivars for its possible role in their resistance to D. balteata. Three solvents with different polarity (hexane, methylene chloride, and methanol) were tested to remove leaf surface chemicals, but only methylene chloride and methanol extracts were used in feeding bioassays. Adult D. balteata consumed much more of the leaf tissue of Val and TG when their surface chemicals were removed with methylene chloride, but not methanol, compared to nonextracted leaf tissue, leading us to hypothesize that methylene‐chloride extractable leaf surface chemicals may have a role in the expression of lettuce resistance. However, leaf surface chemicals extracted from Val with methylene chloride were not a deterrent to adult D. balteata when applied to palatable lima bean leaf surfaces at various concentrations in dual‐choice tests. Furthermore, the application of surface extracts from TG did not stimulate beetle feeding in similar choice tests. In a no‐choice feeding test, there was no significant difference in leaf area consumption on lima bean leaves sprayed with extracts of Val or TG. These results suggest that leaf surface chemicals in romaine lettuce do not explain the resistance of Val to adult D. balteata, and that factors inside the leaf may play a role in resistance. We discuss the possibility that the solvent may have increased the palatability of lettuce leaves to D. balteata by causing enzymatic browning and cellular damage, which is likely to have degraded internal feeding deterrents and impaired the plant's ability to emit latex.