Stable isotopes as markers to investigate host use by Rhyzopertha dominica

Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) is a serious worldwide pest of stored cereal grains that also has the ability to breed in non‐agricultural host plant material. Stable isotope signatures (concentrations of isotopes) were used as internal tissue markers to determine dietary differences among adult R. dominica and to make inferences about source habitats of field‐trapped insects. Adult R. dominica collected near granaries or from non‐agricultural forested sites near Stillwater, OK, USA, and insects reared on selected hosts under laboratory conditions were studied to determine the carbon and nitrogen isotope signatures. Laboratory‐reared R. dominica showed δ¹³C (stable isotope ratio of carbon) values similar to the host on which they developed with an enrichment of about 1 in the insect body. Insects reared on seeds of wheat and oak, which have C₃ photosynthetic pathways, showed much depleted δ¹³C values (–23.7 and –26.2, respectively) in comparison to insects reared on seeds of corn, a C₄ photosynthetic plant (–11.3). A majority of the field‐collected R. dominica showed δ¹³C values similar to expectations for a C₃ host. However, a few field‐collected insects had δ¹³C signatures similar to the C₄ plant‐reared insects in the laboratory experiment. Stored grain of C₄ crops were lacking at many of the sample field sites. These results suggest that R. dominica occurs on either C₃‐ or C₄‐based hosts in the field, and point to utilization of non‐grain C₄ plants as hosts. Our studies indicated that ¹³C isotope is a reliable marker to infer types of hosts used in the feeding history of R. dominica.     

Role of the plant–conspecific complex in host location and intra-specific communication of Lygus rugulipennis

Abstract.  Wind tunnel and vertical open Y-shaped olfactometer studies are used to test whether volatile cues from the host plant ( Vicia faba ), from conspecific bugs, and from a plant–conspecifics combination, would elicit behavioural responses in mated males and females of Lygus rugulipennis . In the olfactometer, females move towards volatiles from healthy plants but they do not respond to volatiles released by oviposition- and/or feeding-damaged plants without conspecifics, nor to conspecifics alone. Both in the wind tunnel and olfactometer, females respond to volatiles emitted by the plant–insect complex. By contrast, in the wind tunnel, both sexes move significantly towards damaged host plants, even if the presence of conspecifics on these plants enhances only the female response. However, the presence of eggs from conspecifics on host plants reduces the responses of both sexes in the wind tunnel. Finally, males, as well as females, are less responsive to conspecifics alone compared with damaged plants, especially when conspecifics are present on the host plants (host plant– Lygus complex). The results suggest that volatiles emitted by plants and conspecifics influence L.   rugulipennis behaviour, giving information to both sexes on the presence of suitable host plants that have been colonized by other conspecifics acting as pioneers, or providing information on the presence of an already exploited host plant (presence of eggs), thus preventing competition. Males also can use this information to increase the probability of encountering mature females.     

Attraction of pepper weevil to volatiles from damaged pepper plants

Pioneer herbivorous insects may find their host plants through a combination of visual and constitutive host‐plant volatile cues, but once a site has been colonized, feeding damage changes the quantity and quality of plant volatiles released, potentially altering the behavior of conspecifics who detect them. Previous work on the pepper weevil, Anthonomus eugenii Cano (Coleoptera: Curculionidae), demonstrated that this insect can detect and orient to constitutive host plant volatiles released from pepper [Capsicum annuum L. (Solanaceae)]. Here we investigated the response of the weevil to whole plants and headspace collections of plants damaged by conspecifics. Mated weevils preferred damaged flowering as well as damaged fruiting plants over undamaged plants in a Y‐tube olfactometer. They also preferred volatiles from flowering and fruiting plants with actively feeding weevils over plants with old feeding damage. Both sexes preferred volatiles from fruiting plants with actively feeding weevils over flowering plants with actively feeding weevils. Females preferred plants with 48 h of prior feeding damage over plants subjected to weevil feeding for only 1 h, whereas males showed no preference. When attraction to male‐ and female‐inflicted feeding damage was compared in the Y‐tube, males and females showed no significant preference. Wind tunnel plant assays and four‐choice olfactometer assays using headspace volatiles confirmed the attraction of weevils to active feeding damage on fruiting plants. In a final four‐choice olfactometer assay using headspace collections, we tested the attraction of mated males and virgin and mated females to male and female feeding damage. In these headspace volatile assays, mated females again showed no preference for male feeding; however, virgin females and males preferred the headspace volatiles of plants fed on by males, which contained the male aggregation pheromone in addition to plant volatiles. The potential for using plant volatile lures to improve pepper weevil monitoring and management is discussed.     

Population development of Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae) on different stored products

The lesser grain borer, Rhyzopertha dominica, is an important pest of various stored products around the world. In this study, the development, survival, reproduction, and life table parameters of R. dominica were investigated on six stored products (angelica, jujube, maize, rice, soybean, and wheat). The developmental time of the immature stage of R. dominica was shortest on wheat (40.20 days) and longest on angelica (67.04 days). The survival rate of the immature stage was highest on wheat (76.33%) and lowest on angelica (41.00%). The fecundity level of R. dominica was highest on wheat (246.05 eggs/female) and lowest on angelica (69.38 eggs/female). The net reproductive rate (R₀) and intrinsic rate of increase (r_m) of R. dominica differed significantly among the six stored products. The highest R₀ of R. dominica was on wheat (68.50), followed by rice (41.28), maize (32.32), soybean (27.17), jujube (23.16), and angelica (20.18); the r_m values showed a similar trend, with values of 0.059, 0.046, 0.042, 0.039, 0.036, and 0.033, respectively. Our results indicate that wheat was the most suitable stored product, whereas angelica was the least suitable, for the feeding, development, and population increase of R. dominica. These findings provide basic information about the occurrence trends and characteristics of R. dominica that will be useful for the control of this pest on different stored products. The physicochemical properties of angelica should be further explored for potential application in the control or integrated management of R. dominica.     

Mate finding in the forest cockchafer, Melolontha hippocastani, mediated by volatiles from plants and females

The response of the forest cockchafer, Melolontha hippocastani F. (Coleoptera, Scarabaeidae), towards volatiles emitted by different host plants and conspecifics was tested in field experiments during the flight period at dusk. Funnel traps containing artificially damaged leaves from the host plants Carpinus betulus L. and Quercus rubra L., as well as from the non‐host plant Prunus serotina Ehrh. caught significantly more beetles than empty control traps. On the other hand, traps baited with undamaged leaves from Q. rubra did not catch significantly more beetles than empty controls. Leaves from C. betulus damaged by beetle feeding did not attract more beetles than artificially damaged leaves. By use of gas chromatography coupled with electroantennographic detection (GC‐EAD) electrophysiological responses of males and females were shown for 18 typical plant volatiles. A synthetic mixture of selected typical green plant volatiles was also highly attractive in the field. A total of 9982 beetles was caught during the field experiments, among them only 33 females. This suggests that attraction to damaged foliage during flight period at dusk is male‐specific. Field experiments testing the attractiveness of female M. hippocastani towards conspecific males by employing caged beetles and beetle extracts indicated that males of M. hippocastani use a female‐derived sex pheromone for mate location. On wired cages containing either unmated feeding females, or unmated females without access to foliage, or feeding males in combination with extracts from unmated females, significantly more males landed during the flight period than on comparable control cages containing feeding males or male extracts. A possible scenario of mate location in M. hippocastani involving feeding‐induced plant volatiles and a female‐derived sex pheromone is discussed.     

Males of the predatory mirid bug Macrolophus caliginosus exploit plant volatiles induced by conspecifics as a sexual synomone

The olfactory responses of male and female Macrolophus caliginosus Wagner (Heteroptera: Miridae) adults towards volatiles from green bean plants previously exposed to feeding by conspecifics and to direct odours from conspecifics were tested in a Y-tube olfactometer. Female M. caliginosus did not respond to volatiles from plants exposed to mirid feeding or to odours emitted directly by adult mirids. In contrast, male mirid bugs were attracted both to volatiles from plants previously exposed to feeding by conspecific females and to odours emitted by conspecifics only with a marginally significant preference for the former. The gas chromatography-mass spectrometry analysis showed that mirid feeding induced the release of 11 additional compounds as compared to the volatiles emitted from clean plants. Three of these substances (5-ethyl-2(5H)-furanone, Z-3-hexenyl tiglate, and E,E-α-farnesene) were released only after feeding by females. Furthermore, 21 compounds were identified in volatiles emitted directly by mirids, 12 of which were unique to the mirids (i.e., not present in clean plants or plants previously exposed to mirid feeding). The results suggest that female-specific herbivore-induced plant volatiles play a role as mate-finding cues by the male mirids. The ecological implications of the findings are discussed, and the term ‘sexual synomone’ is introduced.     

Host feeding experience affects host plant odour preference of the polyphagous leafminer Liriomyza bryoniae

Herbivorous insects use highly specific volatiles or blends of volatiles characteristic to particular plant species to locate their host plants. Thus, data on olfactory preferences can be valuable in developing integrated pest management tools that deal with manipulation of pest insect behaviour. We examined host plant odour preferences of the tomato leafminer, Liriomyza bryoniae (Kaltenbach) (Diptera: Agromyzidae), which is an economically important agricultural pest widespread throughout Europe. The odour preferences of leafminers were tested in dependence of feeding experiences. We ranked host plant odours by their appeal to L. bryoniae based on two‐choice tests using a Y‐tube olfactometer with five host plants: tomato, Solanum lycopersicum Mill.; bittersweet, Solanum dulcamara L.; downy ground‐cherry, Physalis pubescens L. (all Solanaceae); white goosefoot, Chenopodium album L. (Chenopodiaceae); and dead nettle, Lamium album L. (Lamiaceae). The results imply that ranking of host plant odours by their attractiveness to L. bryoniae is complicated due to the influence of larval and adult feeding experiences. Without any feeding experience as an adult, L. bryoniae males showed a preference for the airflow with host plant odour vs. pure air, whereas females did not display a preference. Further tests revealed that adult feeding experience can alter the odour choice of L. bryoniae females. After feeding experience, females showed a preference for host plant odour vs. pure air. Feeding experience in the larval stage influenced the choice by adults of both sexes: for males as well as females reared on bittersweet the odour of that plant was the most attractive. Thus, host feeding experience both in larval and/or adult stage of polyphagous tomato leafminer L. bryoniae influences host plant odour preference by adults.     

Immediate alteration of Macrosiphum euphorbiae host plant-selection behaviour after biotic and abiotic damage inflicted to potato plants

The effects of potato [Solanum tuberosum L. (Solanaceae)] plant damage on the host plant-selection behaviour of the potato aphid, Macrosiphum euphorbiae Thomas (Homoptera: Aphididae), were studied. The damage inflicted to the plant was only of short duration and observations on aphid behaviour were made immediately following plant damage. The underlying questions of the study were to know how much time it takes for plant defence mechanisms to be activated and if this activation had noticeable repercussions on aphid behaviour. We considered stresses of various natures: biotic (pre-infestation by conspecifics or by Colorado potato beetles) and abiotic (scissor cuts). Aphid responses to host plant semiochemicals were investigated using a darkened arena bioassay and the probing behaviour was assessed using the electrical penetration graph technique. Aphids were attracted to their host plant (undamaged or damaged). In a preference test (undamaged plant vs. damaged plant), plants previously infested by conspecifics were preferred to undamaged plants, but this preference was not observed for heterospecific and abiotic damage. However, aphid probing behaviour was not modified on plants previously infested by conspecifics, whereas some changes were observed subsequently to heterospecific and abiotic damages. Our data present evidence that plants can respond to biotic and abiotic stresses soon after the damage is inflicted and when the damage is of short duration. The diverse consequences of these various local plant responses on M. euphorbiae behaviour are discussed in the context of plant defence strategies against aphid colonization.     

Oviposition preference of Lygocoris pabulinus (Het., Miridae) in relation to plants and conspecifics

Abstract: To predict possible locations of Lygocoris pabulinus (L) in the field during the summer, we determined their oviposition preference under summer conditions. With L. pabulinus reared on potato, oviposition preference was determined for potato, tomato or green bean. As preference may depend on larval or early adult experience, the oviposition preference of bugs reared on green bean for three generations, and of bugs captured from the field 12 h prior to the experiment was also determined. All females showed a strong preference for potato plants, on which fecundity was higher. Hence, although L. pabulinus is a generalist in its feeding habits, the summer generation seems to be an oviposition specialist. Aggregation of ovipositing females does not seem to occur; similar amounts of eggs were oviposited in plants with clip cages containing conspecifics as in plants without conspecifics. More eggs were oviposited in damaged plants than in undamaged plants. Plant volatiles released upon damage may aid L. pabulinus females in finding suitable oviposition sites.     

Cross habituation to feeding deterrents and acceptance of a marginal host plant byPieris rapae larvae

Sensitivity of the cabbage butterfly,Pieris rapae L. to feeding deterrents was compared for larvae reared on different food sources under laboratory conditions. Since cabbage-reared larvae normally reject nasturtium,Tropaeolum majus L., the effects of previous exposure to allelochemicals on larval acceptance or rejection of this plant were also examined. When compared with cabbage-reared larvae, nasturtium-reared larvae were less sensitive to feeding deterrents including cymarin, erysimoside and 2-O-β-d-glucosyl cucurbitacin E. Nasturtium-reared larvae were insensitive to chlorogenic acid, which was deterrent to cabbage-reared larvae. Feeding by larvae reared on a wheat germ diet was not deterred by these compounds. The results indicate that dietary experience can extensively affect larval sensitivity to feeding deterrents and that cross habituation of larvae to deterrents occurs in response to certain chemical constituents of nasturtium and wheat germ diet. Digitoxin, however, proved to be an exception. Larvae reared on either nasturtium or wheat germ diet were as sensitive to digitoxin as those reared on cabbage. Previous results have shown that rejectionof nasturtium by cabbage-reared larvae is due to the presence of strong feeding deterrents in this plant. However, more than 50% of 2nd instar larvae reared from neonate on cabbage leaves treated with strophanthidin, cymarin, erysimoside, digitoxigenin and digitoxin accepted nasturtium as a food source. 2-O-β-d-glucosyl cucurbitacin E, 2-O-β-d-glucosyl cucurbitacin I and rutin were also active in causing larvae to feed on nasturtium. Thus dietary exposure to unrelated plant chemicals can profoundly affect insect acceptance of a plant that contains feeding deterrents.     

Apparent transgenerational effects of host plant in the leaf beetle Ophraella notulata (Coleoptera: Chrysomelidae)

The natural host of Ophraella notulata is Iva frutescens (Asteraceae); its close relative feeds on a related plant, Ambrosia artemisiifolia. We reared beetles on both plants, obtained progeny from the four possible crosses (two sexes X two parental hosts), and reared the progeny on both plant species. Survival to the imaginal stage of progeny reared on Iva varied with both maternal and paternal host. Hatchling feeding response to both plants showed a maternal host X paternal host interaction. Consumption of Ambrosia by adult beetles was, counter to expectation, higher for progeny of Iva-reared males than Ambrosia-reared males. Oviposition response, although based on too few data to be definitive, was peculiar: parental host did not affect oviposition on Ambrosia; on Iva daughters of Iva-reared males laid significantly more eggs than did daughters of Ambrosia-reared males, but only if they had been reared on Iva; those reared on Ambrosia displayed the reverse pattern. We discuss the possibility that nongenetic paternal transmission of host plant effects may explain these results, but offer a somewhat uncomfortable hypothesis of selection as a preferable explanation. An important outcome of the experiment is that it provided no evidence of maternal effects of host plant on offspring feeding or oviposition.     

Electrophysiological response to herbivore-induced host plant volatiles in the moth Spodoptera littoralis

In cotton, Gossypium hirsutum (Malvacae), the volatiles emitted from the plant change in response to herbivory. Ovipositing females of the Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) can discriminate between cotton plants subjected to larval feeding and undamaged plants during oviposition. In this study we investigate whether females of this moth can detect the herbivore-induced cotton volatiles. The response of female S. littoralis antennae to volatiles collected from cotton plants subjected to larval feeding was studied using GC-EAD (coupled gas chromatography electroantennographic-detection). By GC-EAD, responses to over 10 different cotton volatiles were observed. Using single sensillum technique the responses of short sensilla trichodea on the antennae of S. littoralis females to 19 cotton volatiles and 12 general plant volatiles were investigated. Responses to these volatiles were recorded from 108 receptor neurones. Several neurones activated by herbivore-induced cotton volatiles were recorded. For example, a neurone type responding to two homoterpenes [(E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene and (E)-4,8-dimethyl-1,3,7-nonatriene] and (E,E)-α-farnesene was frequently found. We also observed sensitive neurones responding specifically to the herbivore-induced volatiles (+/–)-linalool and indole. In general, a stimulus load of less than 1 ng was needed to activate these neurones. In addition, specific neurones were found for constitutive cotton volatiles released in connection with damage to the plant. An abundant neurone type responded to β-caryophyllene and α-humulene. Another neurone type responded specifically to the non-induced cotton volatile (Z)-jasmone. These results show that females of S. littoralis have receptor neurones that would make it possible to discriminate between damaged and undamaged plants using volatile signals.     

麦长管蚜和禾谷缢管蚜对小麦植株挥发物及蚜害诱导挥发物的行为反应

用四臂嗅觉计测定了麦长管蚜Macrosiphum avenae和禾谷缢管蚜Rhopalosiphum padi对小麦植株挥发物及麦蚜取食诱导挥发物的行为反应,揭示了2种麦蚜的嗅觉及小麦植株的诱导防御反应特点.在所选的13种小麦植株挥发物及蚜害诱导挥发物组分中,6-甲基-5-庚烯-2-酮、6-甲基-5-庚烯-2-醇和水杨酸甲酯对这2种蚜虫表现出强的驱拒作用;反-2-己烯醛对麦长管蚜的有翅和无翅蚜的吸引作用最强;反-2-己烯醇对禾谷缢管蚜的无翅蚜吸引作用最强,反-3-己酰醋酸酯对禾谷缢管蚜有翅蚜的吸引作用最强.说明麦蚜取食能诱导小麦植株的防御反应,麦长管蚜和禾谷缢管蚜及其不同蚜型间嗅觉反应的特点不同.     

Resistance of potatoes transgenic for a cry1Ac9 gene, to Phthorimaea operculella (Lepidoptera: Gelechiidae) over field seasons and between plant organs

Stable performance of insect‐resistant transgenic plants across field seasons and between plant organs damaged by the insect pest is critical for management of this resistance in the field. To evaluate this, potato (Solanum tuberosum) lines transgenic for a cry1Ac9 gene with resistance to potato tuber moth (Phthorimaea operculella) were established in the field during the southern hemisphere summers of 1997/98, 1998/99 and 1999/00 as small field plots, each of 10 plants. Replicate plots of the non‐transgenic parent cultivars (at least one for every three independently derived transgenic lines) were planted randomly throughout the trials. Field‐grown foliage was challenged with larvae in the laboratory and a growth index (GI) was calculated for recovered larvae from each transgenic and non‐transgenic potato line. Larval growth on young and mature leaves, and on newly harvested or stored tubers was also measured in the laboratory. Foliage from the transgenic lines inhibited larval growth in all seasons tested. For both control and transgenic lines, larvae had slightly lower GIs when reared on mature leaves compared with young leaves, although the correlation between mean GI for young and mature transgenic leaves was high (r = 0.97). The correlation between the mean GIs of larvae on newly harvested tubers and on those stored for 5 months was also high (r = 1.0). However, the GIs of larvae on newly harvested transgenic tubers were larger than on transgenic tubers stored for 5 months. The relative growth indices (RGI = mean GI/number days before final weighing) of larvae reared on newly harvested tubers from transgenic lines were generally higher than those from young transgenic foliage, while the RGIs of larvae reared on non‐transgenic tubers were slightly lower than those fed non‐transgenic foliage. The correlation between mean RGIs of larvae fed tubers or foliage was 0.62. The transgenic potato lines exhibited stable resistance to larvae across field seasons, between affected plant organs, and between plant organs of different ages.     

Larval diet influence on oviposition behaviour inSpodoptera littoralis

Females ofSpodoptera littoralis Boisd. (Lepidoptera: Noctuidae) with different feeding experiences during their larval development were tested for their ovipositional response to methanol extracts of larval frass and semisynthetic diets. The effect of the following frass, diet and diet component extracts was tested: (a) frass fromS. littoralis orAgrotis segetum larvae fed on a potato-based diet; (b) frass fromS. littoralis larvae fed on a wheat germ-based diet; (c) potato and wheat germ-based diets; and (d) potatoes and wheat germ. Ovipositing females without prior experience of the potato diet were deterred by extracts of: (1) larval frass from either species fed on potato diet; (2) the potato-based diet; (3) potato. Also females with experience of the potato diet during only a part of their larval development were deterred from oviposition by frass of larvae reared on the potato diet and by the diet itself. However, for females reared on the potato diet for their entire larval development, oviposition was no longer deterred by either of the three extracts listed above. Extracts of: (1) frass from larvae of either species reared on wheat germ diet: (2) the wheat germ diet; or (3) wheat germ did not significantly affect oviposition. Females with ablated antennae were still deterred by frass extracts from larvae fed on potato diet, when they had been reared on the wheat germ diet. In feeding experiments, larvae of larval stage one and of larval stage three-four reared on either of the two diets preferred to feed on the wheat germ diet. However, the preference was significantly stronger for larvae with no prior contact with the potato diet. The effect of larval experience on the loss of oviposition-deterring activity by extracts of larval frass, diets and diet components is discussed in view of induction and selection.     

The effect of rearing history and aphid density on volatile‐mediated foraging behaviour of Diaeretiella rapae

1. Parasitoid females foraging for hosts rely on cues derived from the insect host, the host plant and/or their interaction, and all of these can be learned during the immature and adult stages. 2. The present study investigated the importance of rearing history on foraging behaviour of Diaeretiella rapae, an endoparasitoid often associated with aphids feeding on brassicaceous plant species. 3. Parasitoids were reared on one of the four possible combinations, comprising two brassicaceous host plant species, Brassica nigra or Raphanus sativus, and two aphid species Brevicoryne brassicae or Myzus persicae. These parasitoids were tested in a Y‐tube olfactometer and given the choice between volatiles emitted by an aphid‐infested plant (25 or 100 aphids per plant) and an uninfested control plant. The parasitoid's responses were compared when offered: (i) the same plant–aphid combination as the one on which it had been reared; (ii) the same host plant infested with the alternative aphid species; or (iii) an alternative plant with the alternative aphid species. 4. Aphid density did affect the behavioural responses to the various odour sources, but rearing history did not. Diaeretiella rapae only preferred aphid‐induced to non‐induced plant volatiles at low aphid infestation level, whereas they did not discriminate between volatiles at high aphid infestation level. 5. It is concluded that aphid‐induced volatiles of brassicaceous plants play an important role during host habitat location, but seem less important for parasitoids to locate the aphid host itself. The data are discussed in the light of manipulation of host plant defences by aphids.     

A Male-Produced Aggregation Pheromone Facilitating Acalymma vittatum [F.] (Coleoptera: Chrysomelidae) Early-Season Host Plant Colonization

We conducted field studies to investigate the involvement of volatile cues in early-season host plant colonization by striped cucumber beetle, Acalymma vittatum (F.) (Coleoptera: Chrysomelidae). Wind-directed traps were baited with male or female A. vittatum, potted cucumber (Cucumis sativus) seedlings that were of near-isogenic lines which either contained or lacked cucurbitacin, or combinations of male or female A. vittatum feeding on one or the other cucumber variety. We found no response to undamaged plants of either cucumber variety or plants that were actively being fed upon by A. vittatum females, whereas the response to volatiles associated with male A. vittatum was strong. Both male and female conspecifics and totals of up to sevenfold the number of males in the trap lures were caught overnight. Feeding males attracted more than double the number of conspecifics that responded to nonfeeding males. Active consumption of cucurbitacin in the plant on which the males were feeding, however, had no effect on attraction. A shift in sex ratio from a male to a female bias during field colonization season also supports the hypothesis that host finding is initiated by pioneer males. The importance of this aggregation pheromone in early-season host plant colonization and the evolutionary and adaptive significance of this pheromone are discussed.     

Predicting the risk of non-target damage to a close relative of a target weed using sequential no-choice tests,paired-choice tests and olfactory discrimination experiments

We investigated host-plant utilisation by the candidate biocontrol agent Paradibolia coerulea (Coleoptera: Chrysomelidae) on the target plant Spathodea campanulata Beauv. (Bignoniaceae) and a closely related non-target plant, Kigelia africana (Lam.) Benth. (Bignoniaceae). Paired-choice and sequential no-choice experiments were performed and coupled with olfactory discrimination experiments to test the insects’ responses to volatiles from both plant species as well as to cues from conspecific beetles. Although K. africana was utilised by P. coerulea, S. campanulata was preferred for both adult feeding and oviposition. Interestingly, whereas females were attracted to olfactory cues emitted by S. campanulata, males demonstrated no such olfactory discrimination. Females were also attracted to cues deposited by males, and males were deterred by cues from other males, but neither sex responded to female olfactory cues. Very few eggs were recorded on K. africana and none of the larvae that hatched on K. africana survived the first instar. Both S. campanulata and K. africana are suitable for adult feeding, but persistent utilisation of K. africana in the field is unlikely because larval development is only possible on S. campanulata and because the adult females are strongly attracted to volatiles emitted by the target plant. Nevertheless, if P. coerulea is released as a biocontrol agent, spill-over adult feeding could potentially occur on K. africana growing sympatrically with S. campanulata. Because P. coerulea cannot complete its development on K. africana, non-target damage will only occur where the target plant is present, with an intensity dependent on densities of adult beetles locally.     

Role of larval host plant experience and solanaceous plant volatile emissions in Tuta absoluta (Lepidoptera: Gelechiidae) host finding behavior

The tomato leafminer, Tuta absoluta (Lepidoptera: Gelechiidae), is considered to be a major pest that damages tomato (Solanum lycopersicum L; Solanaceae) crops in South American, European, and Mediterranean countries. This insect species is polyphagous (i.e., feeds on many types of food); hence, it could also develop on other cultivated host plants, principally solanaceous plants, such as potato (S. tuberosum L.; Solanaceae) and eggplant (S. melongena L.; Solanaceae). Therefore, we tested the hypothesis that host plant choice by adult T. absoluta is influenced by plant volatile organic compounds and larval host plant experience. One tomato cultivar (cv.) ‘Moneymaker’ and three potato cv. ‘Charlotte’ ‘Bintje,’ and ‘Nicola’ were tested. Using a flying tunnel, we observed that females reared on tomato preferred flying toward tomato and, to a lesser extent, potato cv. ‘Charlotte.’ These preferences might be explained by the high release of terpenes by these two plants. When conducting oviposition choice assays, we found no preference between tomato and potato in the number of eggs laid by females that had been previously reared on either host plant. This study indicates that the host finding behavior of T. absoluta is mediated by solanaceous volatiles, while oviposition behavior appears to depend on additional stimuli. These results provide baseline information for use in the development of new control strategies against T. absoluta using semiochemicals and plant breeding.     

Behavioural responses of the vine weevil, Otiorhynchus sulcatus, to semiochemicals from conspecifics, Otiorhynchus salicicola, and host plants

The vine weevil Otiorhynchus sulcatus is a parthenogenetic reproducing species which forages for suitable host plants at night, but is found congregated in dark places during the day. Frass of this weevil species is suspected to contain attractive compounds that are host‐plant related. Using a still‐air olfactometer, we tested adult vine weevils at night for their behavioural response to odours from conspecifics, feeding on a mixture of spindle tree (Euonymus fortunei) and yew (Taxus baccata), and to a sexually reproducing related species (Otiorhynchus salicicola), feeding on a mixture of ivy (Hedera helix) and cherry laurel (Prunus laurocerasus). Their attraction to conspecifics and O. salicicola appeared to be related to frass production. Freshly collected frass from O. sulcatus and from O. salicicola males and females was attractive. Prunus laurocerasus and H. helix have not been observed to be hosts of the vine weevil in the field. However, our tests showed that the vine weevil was attracted to mechanically damaged leaves of both plant species, whereas undamaged leaves were not attractive. Only undamaged young unfolding leaves of H. helix were also attractive. The attraction to odours from mechanically damaged host and non‐host plants suggested the involvement of compounds that are commonly found in many plant species. The involvement of plant compounds and/or aggregation pheromones in attraction to frass of the vine weevil and frass of the related weevil species O. salicicola is discussed.