Behavioural responses of the Colorado potato beetle to trichomes and leaf surface chemicals of Solanum tarijense

Wild Solanum species constitute a source of resistance to several pests and diseases of potato. Several species of wild tuber‐bearing potato have been identified as resistant to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), including Solanum tarijense Hawkes (Solanaceae). Our objective was to determine the mechanism of resistance of S. tarijense to the Colorado potato beetle and, because the resistance is limited to the adult stage of the insect, to study the host selection behaviour on resistant plants. In the field, Colorado potato beetles demonstrated a unique behaviour when in contact with S. tarijense, abandoning the plant by falling to the ground after a few minutes. The abundant trichomes on the leaves of S. tarijense induced the falling behaviour. However, on S. tarijense feeding remained low even after the trichomes were mechanically removed. Observations demonstrated that the normal sequence of behaviour leading to feeding was interrupted before adult beetles fed on S. tarijense leaves. Feeding experiments using volatile and non‐volatile fractions of leaf surface extracts identified a phagodeterrent effect of the volatile fraction. Our results contrast with a similar evaluation of the mode of resistance of Solanum berthaultii Hawkes, a close relative of S. tarijense, on which some feeding occurred and adults did not show falling behaviour. This study presents information on S. tarijense as a new source of resistance to the Colorado potato beetle that can be used for potato breeding.     

Glandular trichomes of Solanum berthaultii and resistance to the Colorado potato beetle

The defensive mechanisms of the wild potato, solanum berthaultii Hawkes, to larvae of the Colorado potato beetle, Leptinotarsa decemlineata (Say), were studied by selective removal of glandular trichomes and trichome exudates from leaflets, and by comparing performance on S. berthaultii and on the cultivated potato, S. tuberosum L., which lacks defensively active type A and B glandular trichomes. Removal of type A trichomes increased the proportion of larvae that fed on S. berthaultii. Removal of the exudate from type B trichomes increased the proportion of larvae that fed and led to a decrease in mortality. The predominant active compounds in type B exudate, i.e. fatty acid esters of sucrose, were only effective in the presence of type A trichomes. Sucrose esters did not affect larval feeding on S. tuberosum leaflets or on S. berthaultii leaf discs from which the type A trichomes had been removed. Growth of surviving larvae was not significantly affected by removing type A trichomes or type B exudate. Growth of larvae was significantly increased when S. berthaultii leaflets were presented in artificial diet which eliminated the physical barrier of the type B stalks. Growth was no different on artificial diet containing either S. berthaultii or S. tuberosum leaf material (fresh or lyophilized powder) but was poorer on these diets than on S. tuberosum leaflets. The presence of type A trichomes is a fundamental requirement for expression of S. berthaultii resistance to L1 L. decemlineata. Type B droplets containing sucrose esters increase the expression of resistance in the presence of defensively-active type A trichomes.

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Résumé Les mécanismes de défense de la pomme de terre sauvage, S. berthaultii Hawkes, aux larves de Leptinotarsa decemlineata Say, ont été étudiés par ablation sélective des trichomes glandulaires et par l'élimination de leur exsudat des folioles, et par comparaison avec S. tuberosum L. qui a perdu les trichomes glandulaires défensifs A et B. L'ablation des trichomes A a augmenté la proportion de larves ayant consommé S. berthaultii. L'élimination de l'exsudat des trichomes B a augmenté la proportion de consommatrices et réduit la mortalité. Les principaux composés actifs de l'exsudat B, c'est-à-dire des esters d'acides gras de sucrose, n'étaient actifs qu'en présence de trichomes A. Les esters de sucrose n'ont pas modifié la consommation larvaire sur folioles de S. tuberosum, ou sur disques de feuilles de S. berthaultii dont les trichomes A avaient été enlevés. La croissance des larves survivantes n'a pas été modifiée significativement par l'ablation des trichomes A ou l'élimination de l'exsudat de B. La croissance des larves a été significativement augmentée quand les folioles de S. berthaultii ont été incorporés dans l'aliment artificiel après élimination de la barrière physique due aux pédoncules B. La croissance a été de même importance sur aliments artificiels contenant des feuilles (fraiches ou en poudre lyophylisée) de S. berthaultii ou de S. tuberosum, mais plus faible que sur folioles de S. tuberosum. La présence de trichomes A est indispensable à la résistance de S. berthaultii aux L, de L. decemlineata. Les gouttelettes de type B contenant des esters de sucrose augmentent l'expression de la résistance en présence d'une défense active par trichomes A.

     

Contact and residual toxicities of 30 plant extracts to Colorado potato beetle larvae

Abstract

Contact and residual toxicities of 30 plant extracts were investigated on third instar larvae of Colorado potato beetle, Leptinotarsa decemlineata. The plant samples were collected during the spring and summer of 2002 and were dried and ground. The plant samples were treated with methanol and the residue was eluted with distilled water containing 10% acetone, resulting in plant extracts. In contact bioassays, the beetle larvae were treated with 40% (w/w) plant extract using a Potter Spray Tower. The insects were incubated at 28±2°C under a 16 h: 8 h photo regime and the mortality was recorded at 24 h intervals for 7 days. The plant extracts exhibited varying toxicity to the larvae ranging from 0 – 91% after 24 h incubation and Artemisia vulgaris, Hedera helix, Humulus lupulus, Lolium temulentum, Rubia tinctoria, Salvia officinalis, Sambucus nigra, Urtica dioica, Verbascum songaricum, and Xanthium strumarium extracts resulted in significantly higher mortality than the control. Generally, prolonged incubation time did not result in an increase in mortality. After 48 h of incubation, 10 plant extracts yielded a significant mortality and H. lupulus extract, the most toxic extract among those tested, caused 99% mortality which is similar the mortality caused by the chemical standard, imidacloprid. In residual assays, potato leaflets were treated with 20% (w/w) plant-extract concentrations using a Potter Spray Tower. Third instar larvae were added to a glass jar to which treated leaflets were transferred before incubation at the temperature and photo regime described above. Mortality was recorded at 24 h intervals for 7 days. Five plant extracts, H. lupulus, L. temulentum, Reseda lutea and Solanum nigrum, induced significantly higher mortalities compared with controls. Chenopodium album extract was the most toxic, killing 34.9% of exposed larvae, followed by L. temulentum, H. lupulus and S. nigrum after 72 h incubation. The results exhibited that certain plant extracts were toxic to the beetle larvae and may have potential for controlling this destructive pest under field conditions.     

Role of galeal sensilla in host recognition and feeding behaviour of the Colorado potato beetle

Abstract. Close-range interactions with plants and the early stages of feeding behaviour of adult Colorado potato beetles, Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), were studied using beetles with and without various mouthpart sensilla. Representative host, potato (Solarium tuberosum) , and non-host, tomato (Lycopersicon esculentum) , leaves were treated very differently by beetles with and without their galeal or palpal sensilla. Galeal sensilla were particularly important for beetles interacting with these two plants. Compared with normal beetles, fewer beetles without galeae fed on potato leaves, and those that did feed spent more time assessing the plant and took more bites before feeding. On tomtato, more beetles without galeae fed, spent less time assessing the plant and took fewer bites before feeding. Beetles without galeae also had lower consumption rates on potato and higher consumption rates on tomato. Beetles were very reluctant to feed on tomato if the galeae were present so removal of maxillary sensilla was studied only on potato. Without the sensilla on the maxillary palpi only the time between first touch and first bite was affected (lengthened). The importance of galeal sensilla in host recognition by this species and the implications for chemosensory studies are discussed here and in a companion paper.     

Orientation of Colorado potato beetle to natural and synthetic blends of volatiles emitted by potato plants

1 Behavioural responses of the Colorado potato beetle (CPB), Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae), to volatiles emitted from solanaceous host plants (potato and tomato), a non‐host legume (soybean), and 13 synthetic blends or three individual chemicals emitted by potato plants were investigated in laboratory bioassays. 2 Both male and female CPB were attracted to volatiles emitted by mechanically damaged potato foliage, but not to mechanically damaged tomato foliage; CPB offered a choice between the two damaged solanaceous plants did not show a preference. 3 Among 16 odourous blends or individual chemical components of potato plant emissions tested, six blends were attractive, two were repellent, and eight elicited no preference in laboratory bioassays. Volatile blends containing relatively high amounts of the green leaf volatiles (E)‐2‐hexen‐1‐ol and (Z)‐3‐hexen‐1‐ol, or the sesquiterpene β‐ caryophyllene, were unattractive or repellent. Minimal blends attractive to CPB were comprised of (Z)‐3‐hexenyl acetate (±)‐linalool and methyl salicylate: the combination of all three chemicals elicited sexually dimorphic attraction of males; two component blends comprised of (Z)‐3‐hexenyl acetate and either (±)‐linalool and methyl salicylate attracted both sexes. Individual compounds were inactive. No significant difference was noted between two attractive blends, or an attractive synthetic blend vs. mechanically damaged potato foliage. 4 These results show that CPB are attracted to blends of specific chemicals emitted by their host plants and provide a basis for the use of plant attractants as a component of integrated management of pestiferous populations.     

Resistance of three wild tuber-bearing potatoes to the Colorado potato beetle

The resistance of Solanum okadae Hawkes & Hjert. (PI 458367), Solanum oplocense Hawkes (PI 473368), and Solanum tarijense Hawkes (PI 414150) to the Colorado potato beetle, Leptinotarsa decemlineata (Say) (Chrysomelidae: Chrysomelini), was studied. In replicated field trials all three accessions showed a high level of resistance to the beetle. No significant genetic variability between genotypes of the same species was found. Results from host acceptance behavior experiments, suitability for larval development tests, foliage consumption tests, and adult survival and oviposition tests supported the hypothesis that the mode of resistance differs between the three wild Solanum species. Solanum okadae and S. oplocense affected host acceptance and consumption. Because the beetle reacted differently to these two species it was hypothesized that the antifeedant chemical(s) differed in nature or quantity. S. tarijense contrasted with the other two species by affecting mostly adult colonization and oviposition.     

Antifeedant and toxic effects of drimanes on Colorado potato beetle larvae

Among the drimane compounds tested, the dialdehydes polygodial and warburganal were the most active as antifeedants against Colorado potato beetle larvae, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), in a dual-choice assay with potato, Solanum tuberosum L., leaf discs. Lactones were less effective. Direct observations showed that decreased feeding on leaf discs treated with polygodial and warburganal was accompanied by increased locomotry activity. Topical application of these two compounds on the insect's cuticle decreased food intake of untreated leaf discs, indicating that besides deterrent effects, toxic properties of these molecules influence feeding behaviour.     

Combining genetic engineering and traditional breeding to provide elevated resistance in potatoes to Colorado potato beetle

The sustainable deployment of resistant crop varieties is a critical issue for the implementation of biotechnology in crop pest management. Feeding, biomass accumulation, and mortality were evaluated for susceptible, insecticide‐resistant, and Bacillus thuringiensis (Bt) Cry 3A‐selected Colorado potato beetle (Leptinotarsa decemlineata Say) (Coleoptera, Chrysomelidae) larvae fed on: cultivated potato, a Solanum chacoense line expressing leptine glycoalkaloids, a transformed line expressing Bt toxin, or the leptine line transformed to express Bt toxin. Larvae selected for resistance to Bt‐Cry3A performed better on Bt foliage, but not as well on the leptine foliage, compared to susceptible or insecticide‐resistant larvae. Neither leptine nor Bt toxin completely inhibited the feeding and growth of 3rd and 4th instars of all three strains of Colorado potato beetle. However, for all three strains of Colorado potato beetle on leptine + Bt foliage, feeding was almost zero, growth was zero or negative, and mortality was near 100%.     

Glandular trichomes ofSolanum berthaultii alter host preference of the Colorado potato Beetle,Leptinotarsa decemlineata

Choice and no-choice studies were conducted to determine how the glandular trichomes of the wild potato,Solanum berthaultii Hawkes, affect host preference of the Colorado potato beetle,Leptinotarsa decemlineata (Say). Given a feeding choice betweenS. tuberosum andS. berthaultii, larvae and adults preferred the foliage ofS. tuberosum, but adults were more discriminating. When foliage ofS. berthaultii was appressed toS. tuberosum leaflets, fewer adults fed on the appressed leaflets. When given a choice between ‘trichome-intact’ and ‘trichome-removed’S. berthaultii foliage, adults preferred to feed on the latter. The preference for ‘trichome-removed’ foliage and the percent of adults initiating feeding, increased with the degree of trichome removal. These studies provide evidence that the resistance ofS. berthaultii is associated with feeding deterrents localized in the glandular trichomes, thatS. berthaultii possesses more than one mechanism of resistance to the Colorado potato beetle, and that the expression of resistance is dependent on the developmental stage of the insect.     

Feeding behavior of potato aphid affected by glandular trichomes of wild tomato

Mortality of the potato aphid, Macrosiphum euphorbiae (Thomas), on Lycopersicon pennellii (Corr.) D'Arcy and its F₁ hybrid with Lycopersicon esculentum Mill. was significantly greater than that on L. esculentum. Physical entrapment was not the sole mechanism of resistance in L. pennellii since few late instar aphids were found trapped in the sticky glandular exudate of the type IV trichomes; entrapment could, however, affect survival of early instars. Aphid settling on L. pennellii was dramatically less than that on L. esculentum, suggesting that starvation may have contributed to high mortality. Compared to L. esculentum, aphid feeding behavior on L. pennellii and the F₁ was characterized by a delay in the time to first probe, a reduction in the number of probes, and a decrease in the total proportion of time spent feeding. Removal of the glandular exudate of the type IV trichomes from L. pennellii resulted in a decrease in preprobe time and an increase in both the number of probes and the percent of time spent probing. Transfer of glandular trichome exudate of L. pennellii to leaflets of L. esculentum resulted in an increase in resistance as measured by these three parameters.

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Zusammenfassung Die Absterberate der Kartoffellaus, Macrosiphum euphorbiae Thomas, auf Lycopersicon pennellii (Corr.) D'Arcy, sowie auf der Kreuzung L. esculentum Mill. und L. pennellii, war deutlich grösser als auf L. esculentum. Das mechanische Verfangen der Läuse war nicht der Hauptgrund der Resistenz von L. pennellii. Wenige tote Läuse wurden in dem klebrigen Sekret der Typus IV Trichome gefunden. Auf L. pennellii siedelten sich die Läuse in viel geringerer Zahl an als auf L. esculentum. Dies führte zum Schluss, dass Verhungern eine der Ursachen der hohen Mortalität der Läuse war. Im Vergleich zum Saugverhalten auf L. esculentum war das Saugverhalten auf L. pennellii, wie auch auf F₁, durch Folgendes gekennzeichnet 1) Verspätung des ersten Stichversuchs, 2) Verminderung der Stichversuche pro Zeiteinheit und 3) Verminderung des Zeitanteils, der zum Saugen verwendet wurde. Die Entfernung des Sekrets der Typus IV Trichomen auf L. pennellii verursachte 1) eine kürzere Zeitspanne vor dem ersten Stichversuch, 2) eine Vergrösserung der Anzahl Stichversuche pro Zeiteinheit, 3) eine Verlängerung der Saugzeit. Die Uebertragung des Sekretes von L. pennellii auf Blätter von L. esculentum verbesserte deren Resistenz gegen Blattläuse gemessen mit den genannten drei Kriterien.

     

Growth compensation and faster development of Colorado potato beetle (Coleoptera: Chrysomelidae) feeding on potato foliage expressing oryzacystatin I

Feeding, growth, development, and food conversion efficiency of Colorado potato beetle larvae reared on foliage from a “Kennebec” potato line expressing oryzacystatin I (OCI) at about 1% of its total soluble proteins were compared to those of larvae feeding on untransformed foliage from the same line. During stages L1 to L3, larvae feeding on OCI consumed leaf material 14% faster, gained weight 28% faster, and weighed 20% more at the end of the L3 stage, compared to controls. Continued exceptional performance on OCI during the final L4 stage was expressed as faster development than controls, an effect that persisted during pupal development and resulted in emergence of similar weight adults 1 day earlier than controls. Larvae initially maintained on control foliage and switched to OCI foliage during L4 did not overcompensate as those on OCI foliage throughout development, but performed similarly to larvae on control foliage throughout. Total azocaseinase activity in midgut extracts from these 4th instars 1 d after switching to OCI foliage was sensitive to inhibition by a recombinant form of OCI expressed in Escherichia coli, but was no longer sensitive 4 d after switching, indicating a gradual adaptation of the insect digestive protease system, based on the production of OCI insensitive proteases. Despite OCI potato foliage being consumed faster by small larvae using it for food, there was no indication that it was less efficient than untransformed foliage as food protein. Arch. Insect Biochem. Physiol. 40:69–79, 1999. © 1999 Wiley‐Liss, Inc.     

Molecular markers locate genes for resistance to the Colorado potato beetle,Leptinotarsa decemlineata,in hybrid Solanum tuberosum x S. berthaultii potato progenies

The wild Bolivian potato, Solanum berthaultii Hawkes, has been used as a source of resistance to the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say, one of the most significant pests of potato. In this study, two reciprocal backcross S. tuberosum x S. berthaultii potato progenies, BCB and BCT, were mapped with RFLP markers and screened for resistance to CPB consumption, oviposition and defoliation. The genotypic and phenotypic data were combined and analysed to locate quantitative trait loci (QTLs) for resistance to CPB. Three QTLs on three chromosomes in BCB, and two QTLs on two chromosomes in BCT influenced resistance. The QTLs were generally additive but one instance of epistasis was noted. Each QTL accounted for 4–12% of the phenotypic variation observed in resistance. In the more resistant BCB population, a three QTL model explained ca. 20% of the variation in CPB oviposition. When alleles at the three QTLs were homozygous S. berthaultii, oviposition was reduced ca. 60% compared to the heterozygotes. The QTLs for resistance to CPB were compared to those previously identified for the type A and B glandular trichomes, which have been implicated in resistance in the same progenies. Generally, the QTLs for resistance to CPB coincided with loci associated with the glandular trichomes confirming the importance of the glandular trichomes in mediating resistance. However, a relatively strong and consistent QTL for insect resistance in both BCB and BCT on chromosome 1 was observed that was not associated with any trichome traits, suggesting the trichomes may not account for all of the resistance observed in these progenies.     

Inhibition of Colorado potato beetle larvae by a locust proteinase inhibitor peptide expressed in potato

The cDNA for a 73-mer peptide containing two locust serine proteinase inhibitors was cloned, fused to the constitutive CaMV35S promoter and introduced into potato by Agrobacterium-mediated transformation. From 23 independent transgenic lines, three with high mRNA level and proteinase inhibitory activity were propagated in vitro and transferred to pots. The peptide from the leaves was identified by its N-terminal sequence and by K_i values against chymotrypsin and trypsin. Colorado potato beetle larvae reared on transgenic plants grew slightly but significantly more slowly than those on control plants. This supports the notion that expression of multifunctional proteinase inhibitors of insect origin might be a good strategy to improve insect resistance in plants.     

The genetic architecture of a niche: variation and covariation in host use traits in the Colorado potato beetle

The genetic basis of host plant use by phytophagous insects can provide insight into the evolution of ecological niches, especially phenomena such as specialization and phylogenetic conservatism. We carried out a quantitative genetic analysis of multiple host use traits, estimated on five species of host plants, in the Colorado potato beetle, Leptinotarsa decemlineata (Coleoptera: Chrysomelidae). Mean values of all characters varied among host plants, providing evidence that adaptation to plants may require evolution of both behavioral (preference) and post-ingestive physiological (performance) characteristics. Significant additive genetic variation was detected for several characters on several hosts, but not in the capacity to use the two major hosts, a pattern that might be caused by directional selection. No negative genetic correlations across hosts were detected for any 'performance' traits, i.e. we found no evidence of trade-offs in fitness on different plants. Larval consumption was positively genetically correlated across host plants, suggesting that diet generalization might evolve as a distinct trait, rather than by independent evolution of feeding responses to each plant species, but several other traits did not show this pattern. We explored genetic correlations among traits expressed on a given plant species, in a first effort to shed light on the number of independent traits that may evolve in response to selection for host-plant utilization. Most traits were not correlated with each other, implying that adaptation to a novel potential host could be a complex, multidimensional 'character' that might constrain adaptation and contribute to the pronounced ecological specialization and the phylogenetic niche conservatism that characterize many clades of phytophagous insects.     

Response to host plant odors and aggregation pheromone by larvae of the Colorado potato beetle on a servosphere

Using a servosphere (locomotion compensator), locomotory behavior of Colorado potato beetle Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) larvae was measured in detail in response to pulsed and non-pulsed odors of hostplant and conspecific pheromone. Second instars showed decreased straightness of movement, and all larvae showed decreased speed, in response to potato odor. Change in straightness by 2nd instars was also significantly affected by the interaction of pheromone and pulsing treatments. Fourth instars showed increased positive anemotaxis in response to the combined hostplant and pheromone odors. To our knowledge, this is the first demonstration of larval behavioral responses to adult pheromone in a holometabolous insect.     

Effects of selected physical and chemical treatments of Colorado potato beetle eggs on host acceptance and development of the parasitic wasp, Edovum puttleri

Effects of various physical and chemical treatments of Colorado potato beetle [Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)] eggs on parasitization and development of the egg parasitoid Edovum puttleri (Hymenoptera: Eulophidae) were investigated. UV irradiation did not affect host acceptance but reduced host suitability for UV exposure times 90 min. Susceptibility of host eggs to UV irradiation varied with host age; eggs were most vulnerable to damage from irradiation at 12, 18, and 24 h post-oviposition. The rate of parasitization also was influenced by host age. Percent parasitization was greatest in freshly laid eggs and 24–30 h old eggs. Seventy-seven percent of host eggs frozen at –20 °C (5 min) were parasitized by E. puttleri, but extended exposure of eggs to –20 °C reduced both acceptance and suitability. Host eggs that had been washed with hexane (removal of kairomone and sticky layer) also were parasitized. After 5 min of washing, application of kairomone significantly increased the rate of parasitism (from 74.7% to 88.2%), but with longer periods of washing, kairomone application had no significant effect on percent parasitism. Thus, the sticky material(s) coating the egg did not appear to be essential for parasitization to occur. Our results provide effective methods and times for treating Colorado potato beetle eggs to maximize parasitization and development of E. puttleri.     

Host plant finding in phytophagous insects: the case of the Colorado potato beetle

A short critical review is given on the literature of host plant finding in phytophagous insects with main emphasis on the Colorado potato beetle (Leptinotarsa decemlineata Say, col.: Chrysomelidae). The literature data are compared with the results of field experiments: (1) the foraging behaviour of adults was observed in a field arena on bare ground, and (2) adults were released in closed plant stands and recaptured by potted potato plants. It is concluded that host plant finding is a chance event in this species. The observed high directionality of move must be an adaptation increasing probability of host finding. Implications on population dynamics and agricultural practice are discussed.     

Predation of Colorado potato beetle eggs by a polyphagous ladybeetle in the presence of alternate prey: potential impact on resistance evolution

The influence of prey choice on the predation of a target prey item by a polyphagous insect predator was investigated in field plot studies. The target prey consisted of eggs of the Colorado potato beetle (CPB), Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), and the predator was the 12‐spotted ladybeetle, Coleomegilla maculata Lengi (Coleoptera: Coccinellidae). Eggs of the European corn borer (ECB), Ostrinia nubilalis Hübner (Lepidoptera: Pyralidae), and nymphs and adults of the green peach aphid, Myzus persicae Sulzer (Homoptera: Aphididae), comprised the alternative prey choices. The objectives of these studies were to: (1) examine predation in a multiprey scenario likely to occur in an agroecosystem, and (2) use the data to simulate the impact of predator‐induced mortality on the evolution of resistance to Bt‐transgenic plants in the target herbivore. Simulations of the rate of resistance evolution were carried out using a deterministic genetic model. Experiments were performed using potato field plots planted in a manner reflecting a 25% or 50% non‐transgenic refuge. CPB eggs were infested so as to mimic the densities of resistant and susceptible populations that might occur in commercial Bt‐transgenic plantings. Densities of predators and alternate prey species were chosen to represent those that might typically occur in potato crops in the eastern USA. Simulation results indicated that when ECB eggs were present, predation on CPB eggs either became inversely spatially density‐dependent, or increased significantly in a density‐dependent manner. When aphids were present, predation became positively density‐dependent. Model simulations predicted that ECB egg presence is beneficial, in that resistance was delayed by up to 40 pest generations (as compared to the scenario with CPB as the only prey), while aphid presence accelerated resistance evolution by 18 generations. Results suggest that resistance management strategies should take into account the composition of prey species available to generalist predators typically present, so as to best delay pest adaptation to Bt‐toxins.     

A comparison of food-related behaviour between geographic populations of the Colorado potato beetle (Coleoptera, Chrysomelidae), on six solanaceous plant species

Some components of the food-related behaviour (biting, feeding, walking on the plant or walking elsewhere, and resting) of two North American and three European Colorado potato beetle (CPB) populations, on six solanaceous plant species were monitored with the help of a microcomputer-based program, testing the hypothesis whether populations showed differences at the behavioural level to alternative host plants (S. melongena, S. dulcamara, andLycopersicon esculentum), as well as to non-host plants occasionally encountered (S. luteum, S. nigrum.). The few significant differences found were among populations of the same continent in 1) the number of activities monitored, 2) the duration of feeding periods, 3) the number of bites taken to the onset of feeding, 4) the ‘amount of behavioural plasticity’, and 5) the ‘behavioural diversity’. On the basis of two-way ANOVA analyses, no plant-by-population interactions were detected indicating that the CPB populations studied did not have specific relationships with any of the plant species tested. The lack of substantial differences in food-related behaviour was unexpected since considerable isolation in space and time exists between the populations occurring on the two continents.