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Journal Article

Visual orientation of overwintered Anthonomus pomorum (Coleoptera : )

Author(s): Hausmann, Claudia; Samietz, Jörg; Dorn, Silvia

Publication Date: 2004-10

Permanent Link: https://doi.org/10.3929/ethz-b-000160281

Originally published in: Environmental entomology 33(5), http://doi.org/10.1603/0046-225X-33.5.1410

Rights / License: In Copyright - Non-Commercial Use Permitted

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ETH Library BEHAVIOR Visual Orientation of Overwintered Anthonomus pomorum (Coleoptera: Curculionidae)

1 CLAUDIA HAUSMANN, JO¨ RG SAMIETZ, AND SILVIA DORN

Institute of Plant Sciences, Applied Entomology, Swiss Federal Institute of Technology, Clausiusstrasse 25, CH-8092 Zurich, Switzerland

Environ. Entomol. 33(5): 1410Ð1415 (2004) ABSTRACT Vision is considered to be an important component of the sensory system used by herbivorous to locate host plants. We investigated preferences for transmissive colors and contrasts in the blossom weevil, Anthonomus pomorum L., which colonizes apple trees, Malus domestica Borkh., in early spring. The main components of the supposed visual system, green, blue, and UV light, were offered to the weevils versus black or versus each other in a dual choice arena. Furthermore, silhouettes of two different achromatic contrasts were offered in front of the colors blue and green. We also tested whether visual preferences change with time, i.e., 2, 4, and 6 d after termination of diapause in early spring. Female weevils chose UV, green, and blue over black, whereas males only chose UV over black in a series of dual choice experiments. Both sexes preferred blue to green. Weevil response to silhouettes of different contrasts was inßuenced by the background color, i.e., the silhouette with the higher contrast was preferred in front of green, whereas the silhouette with the lower contrast was preferred in front of blue. The preferences during visual orientation did not change with time after diapause. The more discriminating response of females may reßect a greater visual acuity or a greater visual responsiveness in females than in males because of a higher afÞnity for the host plant. Our Þndings indicate that weevils might have a trichromatic visual system and that they are able to include visual cues for the location of host plants in the Þeld.

KEY WORDS Anthonomus pomorum, colors, vision, host Þnding, host plant

ALL HERBIVORE INSECTS SHOW some degree of selectivity Most insects studied for their visual systems possess in terms of host plants, and vision represents an im- green receptors maximally sensitive at Ϸ530 nm, UV ␭ Ϸ ␭ portant component of the sensory system involved receptors ( max 350 nm), and blue receptors ( max during this process, often combined with olfaction Ϸ 440 nm) (Briscoe and Chittka 2001). Chittka (1996) (Prokopy and Owens 1983, Judd and Borden 1991, suggested that this set of UV, blue, and green photo- Kogan 1994). Accumulated evidence suggests that a receptors is ancestral to Insecta and that some lineages distant plant at the horizon is detected by an have since lost or added receptors, presumably as a herbivore primarily on the basis of a gross silhouette result of different selection pressures. against a brighter, more uniformly lit, sky, with little if True color vision has only been shown for a limited any perception of the dominant reßected wavelength number of insect species and has not yet been shown or details of form (Prokopy and Owens 1983, Jermy et in coleopterans (Menzel and Backhaus 1991, Briscoe al. 1988). When an herbivore is in close proximity of and Chittka 2001). By far the most studied insect in a plant, it seems that the spectral quality of the light this regard is the honey bee, Apis mellifera L., because emitted by the plant becomes the predominant cue of its importance in agriculture and because it is ame- eliciting detection and alightment (Prokopy and nable to training. Proof of color vision requires, for Owens 1983). The visual response of an insect may be example, differentiated behavioral response of a spe- investigated by its behavior and by electroretinogram cies to wavelengthcues in combination withresults studies, but spectral sensitivity does not imply dis- from physiological studies or that the species can be crimination of dominant wavelengths, and thus, be- trained for color cues (Menzel and Backhaus 1991). It havioral evidence is necessary to prove true color is therefore difÞcult to show color vision in many vision. insect species. Therefore, lack of proof of true color vision in coleopterans does not mean that they cannot distinguishcolors. On thecontrary, electroretino- 1 Corresponding author: Agroscope FAW Waedenswil, Swiss Fed- grams have shown differential wavelength sensitivity eral ResearchStation for Horticulture, Postfach185, CH-8820 Wa ¨- in the eyes of at least eight coleopteran species: A denswil, Switzerland (e-mail: [email protected]). trichromatic visual system with UV, blue, and green

0046-225X/04/1410Ð1415$04.00/0 ᭧ 2004 Entomological Society of America October 2004 HAUSMANN ET AL.: VISUAL ORIENTATION OF A. pomorum 1411 receptors was found in Photuris lucicrescens Barber (Lall et al. 1982) and in Coccinella septempunctata L. (Lin and Wu 1992). Two peaks of spectral sensitivity, in the UV and green region, were found in six other species, i.e., Liocola brevitarsis (Lewis), Cicin- dela japonica (Tunberg), Cicindela specularis (Chau- doir) (Lin and Wu 1992), Photuris versicolor F. (Lall 1981), Photuris pyralis L. (Lall et al. 1980), and Leptinotarsa decemlineata (Say) (Mischke 1981). Studies on the visual ecology of two weevil species report that Anthonomus grandis Boheman showed color preference for blue-green in a Y-shaped test chamber in the laboratory (Hollingsworth et al. 1964), and the plum curculio, Conotrachelus nenuphar (Herbst), oriented preferentially to tall sticky green rectangles (Butkewichand Prokopy 1997). Taken to- gether, these studies suggest that have the physiological capability for, at least, dichromatic vi- sion and that colors may affect behavior. The apple blossom weevil, Anthonomus pomorum L., is a univoltine herbivore of apple trees, Malus domes- tica Borkh. Most adults overwinter in leaf litter of Fig. 1. Visual test arena: two perpendicular chambers forests or hedgerows. Early in the season, weevils bisected each other in the center forming a cross. Each of the immigrate into orchards and colonize apple trees four arms (15 by 15 by 30 cm) led to one of two visual cues, (Toepfer et al. 1999, 2002). Orientation of the weevils 1or2. toward the host tree may include plant-derived chem- ical cues (Kalinova et al. 2000), although experimental withfreshpieces of and sprayed withwater at evidence on the behavioral effect of single or com- weekly intervals. Weevils were kept in diapause for a bined compounds is lacking. Thus far, nothing is minimum of 20 wk, because Ctvrtecka and Zdarek known about the weevilÕs perception of visual cues. (1992) showed that 65% of A. pomorum females The aim of this study was to investigate the behav- showed initiation of ovarian development after a 5-mo ioral response of overwintered apple blossom weevils cold treatment (3Ð4ЊC). to visual cues. Weevil orientation toward transmissive Depending on the time treatment after diapause, 2, colors and UV light was tested in a dual choice arena. 4, or 6 d before the experiments, weevils were kept for The main components of the hypothesized visual sys- 24 hin a climate chamber(BK 6160; Heraeus, Balin- tem, green, blue, and UV light, were offered to the gen, Germany) witha constant temperature of 10 ЊC weevils versus black and versus each other. Further- (L:D ϭ 12:12, Ϸ80% RH, 3,000 Lux), and then they more, the response of the weevils toward silhouettes were placed in a climate chamber with a constant of different achromatic contrasts in front of the colors temperature of 15ЊC (L:D ϭ 12:12, Ϸ80% RH, 3,000 blue and green was investigated. In addition, we stud- Lux). Suchacclimatization treatment reduced their ied the inßuence of the physiological state of over- initial mortality of 80Ð90% to Ͻ10% (Ctvrtecka and wintered weevils on color preference by testing their Zdarek 1992). The adults were fed with pieces of apple response at different days after termination of dia- fruit and provided withwater. pause. Suchan endogenous effect would modify the Visual Test Arena. The visual test arena (Fig. 1) weevilÕs success in locating host plants during orchard consisted of a cross made of Plexiglas (5 mm thick; colonization. Plexiglas XT, Ro¨hm, Darmstadt, Germany). The cen- ter of the arena consisted of a rectangular chamber (15 by 15 by 30 cm). Four arms (15 by 15 by 30 cm) Materials and Methods produced channels in each direction. At the end of Insects. Capped brown blossoms bearing A. pomo- each channel, the arena had an opening (15 by 30 cm) rum pupae were collected in May 2002 in northern for a frame to hold color Þlters. The inner walls of the Switzerland. On emergence, weevils were kept in arena were covered withmirrors to avoid biases plastic boxes (28 by 20 by 24 cm) and were fed with caused by diffuse reßection of the light falling into the freshapple leaves and pieces of apple fruit until the arena. The ßoor of the arena was coated with black onset of aestivation (3Ð4 mo after emergence). The paper (Mi-Teintes, Pastel; Canson, Annonay, France). adults were sexed by the characteristic differences in The Plexiglas top of the arena was covered with gray the dorsal part of the last abdominal plates (Duan et transparency (acetate sheet, Tektronix Phaser 850, al. 1999). The weevils were overwintered in a cooling 50% gray) and was provided witha 20-cm-diameter lid chamber (SR Ka¨ltetechnik, Winterthur, Switzerland) to insert the weevils. The color Þlter at the end of each at 4 Ϯ 1ЊC in plastic boxes (19 by 9 by 8 cm). Strips of channel was lit from the outside with a lamp. The corrugated cardboard were offered as shelter. Even intensity of eachlamp was regulated witha dimmer to during aestivo-hibernation, the weevils were provided achieve radiation energy of 150 W/m2 in the center of 1412 ENVIRONMENTAL ENTOMOLOGY Vol. 33, no. 5 the test arena. Filters were made of high-quality color crawling occurred during this time (Hausmann et al. transparencies (Go¨ttinger FarbÞlter, Go¨ttingen, Ger- 2004). many) withnarrow wavelengthbands and maximum The weevils were given the choice between the wavelengths of 350 (UV), 455 (green), and 550 nm following pairs of visual stimuli: UV versus green, UV (blue). Black paper (Mi-Teintes, Pastel; Canson) was versus blue, UV versus black, green versus blue, green used instead of the Þlters to provide the black cue. versus black, and blue versus black. Also compared The green and blue color Þlters were illuminated were silhouettes of low and high achromatic contrast witha Tungsten-halogenlamp (78 mm-R7s-150 W, in association withgreen and withblue Þlters. Forty- Halotone; Royal Philips Electronics, Roosendaal, Hol- Þve male and 45 female weevils (15 individuals each land); the UV Þlter was illuminated with a UV lamp 2, 4, and 6 d after termination of diapause) were tested (HPW-125TS-125W/E27; Royal Philips Electronics). per treatment combination. All choice experiments 2 The black paper was also illuminated with a Tungsten- were analyzed by ␹ tests, with the zero hypothesis of halogen lamp to provide the same temperature in each homogeneity in the distribution of individuals re- channel of the arena. Spectral analyses of the color sponding to the choices offered in the bioassays (Zar Þlters and measurements of radiation energy to set the 1998). intensity of lamps were made by placing a Þber optics reßective spectrometer (SD 2000 UV-VIS; Ocean Op- Results tics, Dunedin, Florida, USA) at the point where the weevils were released i.e., 22.5 cm from the cues. The Female weevils show a preference for UV, green, ␹2 ϭ ϭ white reference for the spectral analyses was mea- and blue over black (UV versus black: 15.21, df Ͻ ␹2 ϭ ϭ ϭ sured on a commercial reference standard (WS 1; 1, P 0.001, green versus black: 8.02, df 1, P ␹2 ϭ ϭ ϭ Ocean Optics). 0.005; blue versus black: 8.02, df 1, P 0.005; Fig. 2). Male weevils show a preference for UV over To test the effect of silhouettes of different achro- ␹2 ϭ ϭ ϭ matic contrasts, a light or a dark gray transparency black (UV versus black: 10.79, df 1, P 0.001), (Tektronix Phaser 850, 6% gray, 30% gray, 4.5 cm wide but they show no preference when the colors green versus black or blue versus black were offered (green by 30 cm tall) was placed vertically in front of the ␹2 ϭ ϭ ϭ green or blue Þlter. The coefÞcient of transmission of versus black: 0.20, df 1, P 0.655; blue versus black: ␹2 ϭ 3.76, df ϭ 1, P ϭ 0.053; Fig. 2). The time the light gray silhouette was 0.75, i.e., 75% of the after diapause did not inßuence the color choice of the radiation penetrated the transparency (low achro- males and females (UV versus black: females: ␹2 ϭ matic contrast). For the dark gray silhouette, the co- 1.68, df ϭ 2, P ϭ 0.431, males: ␹2 ϭ 2.81, df ϭ 2, P ϭ efÞcient of transmission was 0.33, i.e., 33% of the ra- 0.245; green versus black: females: ␹2 ϭ 0.22, df ϭ 2, diation penetrated the transparency (high achromatic P ϭ 0.898, males: ␹2 ϭ 3.75, df ϭ 2, P ϭ 0.153; blue contrast). 2 versus black: females: ␹ ϭ 1.51, df ϭ 2, P ϭ 0.469, Bioassay. All bioassays were carried out in a climate males: ␹2 ϭ 3.10, df ϭ 2, P ϭ 0.212). chamber (Conviron PVG 36; Controlled Environ- When green or blue was offered versus UV light, ment, Winnipeg, Canada). To have a temperature of females and males show no preference (green versus Ϸ18Ð20ЊC in the center of the visual test arena, the temperature in the climate chamber during the ex- periments was adjusted between 10 and 15ЊC (70% RH). Within the test arena, a choice of two different visual stimuli was presented at the same time. Oppo- site channels were equipped with the same color Þlter to avoid an inßuence of radiation reßecting from the channels. One weevil at a time was introduced through the lid on the top and placed in a small white plastic dish (1.7 cm diameter) in the middle of the arena. As soon as the weevil crawled into one of the channels, it was scored as choosing a particular visual stimulus, and the weevil was removed. Each weevil was only tested once, and the black paper on the ßoor was exchanged for a new unused one after each trial. To exclude possible unexpected inßuences from the arena or the climate chamber, the colors were changed between the channels after every tested wee- vil. Eachweevil was observed for a maximum time of 30 min. If the weevil did not enter a channel within this time, it was removed and not scored. All experiments were carried out in the afternoon between 1200 and Ϸ Fig. 2. Color choice of overwintered female and male 1500 hours, i.e., 5Ð8 h after the beginning of the apple blossom weevils in the visual test arena when green, photophase, because in the Þeld, it was found that the blue, and UV are offered versus black (n ϭ 45). * SigniÞcant maximum colonization of apple trees by ßight and by difference (␹2 test, P Ͻ 0.05). October 2004 HAUSMANN ET AL.: VISUAL ORIENTATION OF A. pomorum 1413

Fig. 4. Choice of overwintered female and male apple blossom weevils in the visual test arena when blue and green are offered with a vertical silhouette, resulting in a high versus low achromatic contrast (n ϭ 45). Females and males separately: No signiÞcant differences. Pooled females and males: SigniÞcant difference of choice in the green versus the Fig. 3. Color choice of overwintered female and male blue range (␹2 test, P Ͻ 0.05). apple blossom weevils in the visual test arena when blue, green, and UV are tested against eachother( n ϭ 45). * Sig- ␹2 Ͻ niÞcant difference ( test, P 0.05). ors. Furthermore, weevil response to silhouettes of different achromatic contrasts is inßuenced by the UV: female: ␹2 ϭ 0.56, df ϭ 1, P ϭ 0.456, male: ␹2 ϭ 0.56, background color. These results indicate that weevils df ϭ 1, P ϭ 0.456; blue versus UV: female: ␹2 ϭ 1.09, might include visual cues in their host plant location df ϭ 1, P ϭ 0.206, male: ␹2 ϭ 0.56, df ϭ 1, P ϭ 0.456; in the Þeld. Physiological changes within the Þrst 6 d Fig. 3). Females and males showed a preference for after diapause did not inßuence the behavioral re- blue when the green and blue were offered (females: sponses to the visual stimuli offered in our experi- ␹2 ϭ 5.00, df ϭ 1, P ϭ 0.025; males: ␹2 ϭ 6.42, df ϭ 1, ments. P ϭ 0.011; Fig. 3). The time after diapause did not Visual cues are considered to be important for host inßuence the color choice of the males and females plant location in insects (Prokopy and Owens 1983), (green versus UV: females: ␹2 ϭ 0.72, df ϭ 2, P ϭ 0.698, and a variety of solutions have evolved to locate plant males: ␹2 ϭ 1.26, df ϭ 2, P ϭ 0.533; blue versus UV: resources. For example, host plant location in Eriois- females: ␹2 ϭ 5.10, df ϭ 2, P ϭ 0.078, males: ␹2 ϭ 0.72, chia brassicae (Bouche´) cabbage root ßies involves df ϭ 2, P ϭ 0.698; green versus blue: females: ␹2 ϭ 0.60, response over a distance of several meters to host df ϭ 2, P ϭ 0.741, males: ␹2 ϭ 0.31, df ϭ 2, P ϭ 0.902). volatile compounds, presumably coupled withclose When analyzed separately, females and males range response to plant visual stimuli (Hawkes 1974). showed no preference between silhouettes of a low or The opposite seems to occur in Trialeurodes vaporari- a high contrast in blue or green (green low versus orum (Westw.) whiteßies, where initial detection of high contrast: female: ␹2 ϭ 1.09, df ϭ 1, P ϭ 0.297, male: host and nonhost plants from a distance is visual, and ␹2 ϭ 1.8, df ϭ 1, P ϭ 0.180; blue low versus high host olfactory stimuli are involved only at very close contrast: female: ␹2 ϭ 2.69, df ϭ 1, P ϭ 0.101, male: range (Vaishampayan et al. 1975). ␹2 ϭ 1.8, df ϭ 1, P ϭ 0.180; Fig. 4). When the data of The results from our experiments with a choice females and males were pooled, the response to low between a transmissive wavelengthcue and black in- and high contrast shows a signiÞcant difference when dicate that apple blossom weevils show positive pho- tested in blue and green (␹2 ϭ 7.20, df ϭ 1, P ϭ 0.007). totaxis. The weevils orient toward light when black The higher contrast was preferred in green, whereas serves as a blank in the bioassay design. Female wee- the lower contrast was preferred in the blue range. vils favor UV, green, and blue wavelengthcues when The time after diapause did not inßuence the choice offered versus black, and therefore, have the ability to of achromatic contrast in males and females (green perceive these cues with their visual system. Males low versus high contrast: females: ␹2 ϭ 0.18, df ϭ 2, P ϭ only prefer UV signiÞcantly over black. Nevertheless, 0.913, males: ␹2 ϭ 1.67, df ϭ 2, P ϭ 0.438; blue low this does not exclude the ability of the males to per- versus high contrast: females: ␹2 ϭ 0.76, df ϭ 2, P ϭ ceive green and blue, because they are able to dis- 0.685, males: ␹2 ϭ 2.22, df ϭ 2, P ϭ 0.324). criminate between these two colors when offered against each other in a choice test. Both sexes favor the color blue over green, which proves that the weevils Discussion can distinguishbetween green and blue solely on the Our laboratory results show that apple blossom basis of wavelengthdifferences. weevils orient positively toward transmissive visual During the colonization of apple trees in early stimuli and show preferences between different col- spring, weevils encounter the visual stimuli of sky, 1414 ENVIRONMENTAL ENTOMOLOGY Vol. 33, no. 5 green vegetation, and brown or gray bark of apple conservative trait that does not change during colo- trees. In this period, weevils need to recognize the nization of orchards in spring. Although the physiol- dark apple trees without foliage surrounded by green ogy of the receptors in curculionids, including A. po- vegetation. Indeed, they choose a high contrast sil- morum, remains to be investigated (Briscoe and houette in the green wavelength range. In the blue Chittka 2001), our Þndings support the hypothesis that range, the weevils show phototaxis toward the homo- the weevils have a trichromatic visual system with UV, geneous transmissive cue, and this difference, in re- blue, and green receptors. sponse to achromatic cues in the blue and green range, is signiÞcant when analyzed for both sexes together. The necessity to orient toward other colors than green Acknowledgments during host plant location might lead to the general We thank S. Sto¨ckli and S. Katulic for assistance with preference of blue over green in the visual test arena. experiments and A. Rott, K. Tschudi-Rein, J. R. Miller, and Nevertheless, the choice of the low contrast silhouette two anonymous referees for valuable comments on previous versus high contrast in the blue wavelength range is drafts of the paper. surprising and will require Þeld tests for further in- terpretation. References Cited The more discriminating response of the female sex in the apple blossom weevil in the visual test arena may Briscoe, A. D., and L. Chittka. 2001. The evolution of color reßect a greater visual acuity or a higher visual re- vision in insects. Annu. Rev. Entomol. 46: 471Ð510. sponsiveness in females than in males, possibly be- Butkewich, S. L., and R. J. Prokopy. 1997. Attraction of adult cause of a higher afÞnity for the host plant. Females plum curculio (Coleoptera: Curculionidae) to host-tree odor and visual stimuli in the Þeld. J. Entomol. Sci. 32: 1Ð6. should have an advantage of a more critical choice Chittka, L. 1996. Does bee color vision predate the evolu- because (1) they have to select oviposition sites and tion of ßower color? Naturwissenschaften. 83: 136Ð138. (2) their choice is Þnal because the larvae cannot Ctvrtecka, R., and J. Zdarek. 1992. Reproductive diapause abandon the buds into which the eggs were laid. This and its termination in the apple blossom weevil (Anthono- Þnding coincides with the visual response of the white mus pomorum) (Coleoptera, Curculionidae). Acta pine weevil, Pissodes strobi, to cardboard silhouettes in Entomol. Bohemos. 89: 281Ð286. the laboratory: female weevils select only vertical Duan, J. J., D. C. Weber, B. A. Hirs, and S. Dorn. 1999. A rectangles, whereas males are less critical in their new character for sex differentiation of adults of Anthono- choice (VanderSar and Borden 1977). Similar evi- mus pomorum L. (Col., Curculionidae). J. Appl. Entomol. 123: 319Ð320. dence was found in the Colorado potato beetle, Lep- Hausmann, C., J. Samietz, and S. 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