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KUCKES, H., 1956: A bethylid parasite of cone beetles (Hymenoptera: Bethylidae). Pax- Pacific Entomol. 32, 184-185.

- 1958: Observations on two species of pine cone feeding death watch beetles in Cali- fornia (Coleoptera: Anobiidae). Ann. entomol. Soc. Amer. 51, 186-188.

SCHAEFER, C. H., 1962: Life history of Conophthorus radiatae (Coleoptera: Scolytidae) and its principle parasite, Cephalonomia utahensis (Hymenoptera: Bethylidae). Ann. entomol. Soc. Amer. 55, 569-577.

SCHULZE, P., 1919: Eine Bethylide (Hymen.) als Qualgeist des Menschcn in Mazedonien. Sitzungsber. Ges. Nat. Freunde zu Berlin, 375-381.

SINHA, R. N., 1961: Insects and mites associated with hot spots in form stored grain. Canad. Entomol. 93, 609-621.

SOIKA, A. G., 1932: Nota su Scleroderrna domesticum Kief. (Hym. Bethylidae). Boll. Soc. Veneziana di Storia nat. 1, 14-18.

S B M M E , L., 1972: The effects of acclimation and low temperatures on enzyme activities in larvae of Ephestia kuehniella Zell. (Lep., Pyralidae). Entomol. Scand. 3, 12-18.

TAYLOR, J. M., 1964: Studies on Theocolax formiciformis Westw. (Hym., Pteromalidae), a parasitc of Anobium punctatum (Deg.) (Col., Anobiidae). Bull. entomol. Res. 54, 79 7-803.

'I'ICHELER, J. H. G., 1961: An analytical study of the epidemiology of the coffee-berry borer, Stephanoderes hampei Ferr., in the Ivory Coast. Meded. Landb. Hogesch. Wageningen 61, 1-49.

WESTWOOD, J. O., 1839: Trans. entomol. SOC. London 2, 168-169. - 1881: VIII. Observations on the hymenopterous genus Scleroderma, Klug, and some

WINSTON, P. W.; BATES, D. H., 1960: Saturated solutions for the control of humidity in allied groups. Trans. entomol. SOC. London, 117-140.

biological research. Ecology 41, 232-237.

Olfactory and gustatory responses of Trogoderma granarium, Dermestes maculatus and Tribolium custuneum to various

s traig h t-chain fatty acids

By EPHRAIM COHEN~, VLASTA STANIC' and AARON SHULOV~

With 2 figures

Abstract

The olfactory and gustatory responses of Trogoderma granarium, Tribolium castaneum and Dermestes maculatus to various even and odd numbered fatty acids were studied. C5-C8 short-chain fatty acids discouraged aggregation of Khapra beetle adults. Myristic and palmitoleic acids exhibited maximal arrestant activity while oleic acid was the most effective attractant. Other acids displayed mild or no attraction at all. As far as gustatory response is concerned, only valeric acid appeared to be phagostimulatory, whereas short- chain fatty acids C8-Cl3 and the unsaturated linoleic and linolenic acids deterred the insects. Tribolium castaneurn was strongly repelled by short-chain homologs, while the unsaturated acids acted as less efficient repellents. The beetles were induced to aggregate by tridecanoic, pentadecanoic and stearic acids, which however did not stimulate aggrega-

Dept. of Zoology, The George S. Wise Center for Life Sciences, Tel Aviv University,

Dept. of Entomology, The Hebrew University of Jerusalem, Jerusalem, Israel. Tel Aviv, Israel.

2. ang. Ent. 76 (1974), 303-311 @ 1974 Verlag Paul Parey, Hamburg und Berlin ISSN 0044-2240 / AFTM-Coden: ZANEAE

304 E. Cohen, V. Stani i and A. Shulow

tion when tested o i e r a distance. Devmestes maculatus larvae were encouraged to feed on dietary valeric acid, yet were strongly deterred by low and medium chain length fat ty acids (C(j-Ci4). Saturated and unsaturated higher homologs were phagostimulatory except for high dietary levels of linolenic acid. Adults appeared less discriminatory and werc attracted by caproic and also by lauric and myristic acids, in addition to valeric acid. Maximal food deterrent response was induced by dietary pelargonic acid.

1. Introduction

Numerous investigations have been carried out regarding chemosensory effects of lipids, particularly fatty acids, on insects. The flour beetle Tribo- l ium castaneum was induced to aggregate by triglycerides present in high quantities in mycelia of the fungus Nigrospora sphaerica (STARRAT and LOSCHIAVO 1972). Further studies have shown that maximal response was elicited by monounsaturated triglycerides (STARRATT and LOSCHIAVO 1972). The hide beetle Dermestes maculatus is adapted to grow on fat rich food (HINTON 1945) and preferentially consumed a diet containing excessive bacon triglycerides (COHEN, in prep.). Triolein and oleic acid appeared to be effective phagostimulants for the prairie grain wireworm Ctenicera destruc- toy (DAVIS 1968), whereas polyunsaturated linoleic and linolenic acids were attractive to the fire ant Solenopsis saevissima (VINSON et al. 1967). Adults of the khapra beetle Tvogoderma gvanarium were attracted by saponified ethereal extracts of larval faeces, containing various free fatty acids ( S T A N I ~ and SHULOV 1969). It has been suggested that T. granarium faecal pellets might contain an oviposition attractant. The dietary fatty acid fraction of larval faeces, containing palmitic, stearic, oleic and linoleic acids, induced

Gustatory response of T. granarium larvae to straight chain fa t ty acids

Concentration per centP 5.0 10.0 Acid tested Carbon No.'

Valeric Caproic Heptanoic Caprylic Pelargonic Capric Undecanoic Lauric Tridecanoic Myristic Pentadecanoic Palmitic Heptadecanoic Stearic Oleic Linoleic Linolenic Nonadecanoic

5 6 7 8 9

10 11 12 13 14 15 16 17 1s 1 8 : l 1s : 2 1 s : 3 19

0.99 1.06 0.95 0.50 0.39 0.10 0.72 0.47 0.43 0.79 0.75 0.84 0.69 0.97 0.76 0.13 0.26 0.94

1.23 1.08 0.69 0.37 0.11 0.08 0.39 0.21 0.39 0.77 0.77 0.79 0.62 0.87 0.74 0.12 0.12 0.82

Additional numbers indicate degree of unsaturation. - Pasta-rings were dipped in the ethereal solution of fa t ty acids a t the specified concentrations; 40 larvae were introduced to each test chamber and 10 repetitions for each experimental condition were carried out. Numbers represent multiple of the control values.

Response .j T. granarium, D . rnaculatus and T. castaneum to fatty acids 305

and maintained larval diapause and probably plays a significant role in the physiology of T . granarium (IKAN et al. 1970). Experiments carried out by COHEN et al. (1971) revealed that virgin females of the khapra beetle were strongly lured by palmitic, palmitoleic and pentadecanoic acids, which have been previously detected in the insect body lipids. Inferred from the above, higher homologs of straight-chain fatty acids usually serve as attractants or phagostimulants. On the other hand, accumulated information leads to the notion that short-chain compounds are repellent or toxic. Cf;-Cie fatty acids were detrimental to houseflies (LEVINSON and ASCHER 1954; QURAISHI and THORSTEINSON 1965). Toxic effects of dietary capric acid (HOUSE and GRA- HAM 1967) and lauric acid (DADD 1966) were reported for Tribolium con- fusum and Galleria mellonella respectively.

In the present communication we report the olfactory and gustatory re- sponses of three Coleoptera species to Cj-CiH, even - and odd-numbered, straight-chain mono-carboxylic acids. The carnivorous Dermestes maculatus and the non-carnivorous Trogoderma granarium dermestids differ with re- gard to feeding and behavioural habits. We studied the chemosensory in- fluence of n-fatty acids on the above species as well as on the tenebrionid Tribolium castaneum.

3. Material and methods

2.1. Test insects

Trogoderma granarium. The khapra beetle was maintained on ground wheat and kept at 33O C and 40-45 O i o r.h. in darkness. Pupae were removed daily from stock cultures and sex segregated, and emerging females were removed and bioassayed. In the gustatory response experiments, full-grown larvae were directly removed from stock cultures.

Dermestes maculatus. Stock cultures were raised on fishmeal: yeast powder at a ratio of 18:1, supplement with 10°/o wiw casein (NBCo) and bacon. Larvae and females of known supplemented with 10 O i o w/w casein (NBCo) and bacon. Larvae and females of known age were used in the feeding assays.

Tribolium castaneum. The flour beetle was reared on wheat flour containing 5 O i o yeast powder (Marmite); adults of both sexes were removed and bioassayed.

Olfactory response bioassays. C&ig fatty acids were dissolved in diethylether and applied to 4,25 cm filter paper discs (Whatman no. 1). The assay essentially followed the two-choice technique designed by LOSCHIAVO (1965a) and described in detail by LEVINSON and BAR ILAN (1967). Distinction between compounds acting over a distance (i.e. attractants or repellents) and those acting in close contact with the insects arresting their dispersion (arrestants) was achieved by modifying the standard test. In the design called ,,devised" the filter paper circles were attached to the inner side of a petri dish cover by means of two-side adhesive tape. Twenty-five beetles were introduced into each test chamber and each compound was exposed to a total of 500-1000 insects. Average percentage response at the end of the 45-minute period was calculated using the formula given by LEVINSON and BAR ILAN (1967).

2.2. Gustatory response bioassays

2.2.1. Trogoderma granarium Small pasta-rings were coated with various concentrations of fatty acids dissolved in diethylether while controls were dipped in pure solvent. The ether was evaporated and the rings were weighed and placed on the bottom of a petri dish (14 cm diameter), in a two-choice test design i.e. a treated ring was placed opposite to a control one. Forty

306 E . Cohen, V. Stanit and A . Shulov

larvae were introduced into each dish and then kept a t 3 3 ' ~ in darkness for a 24 hr period. Subsequently the rings were reweighed and feeding response was estimated from differences in food consumption between treatment and control.

2.2.2. Dermestes maculatus Glass tubes (4 mm diameter, 20 mm length) were filled with a sysnthetic diet (LEVINSON et al. 1967) mixed with various quantities of the tested compounds and weighed. One opening was sealed with parafilm paper and the tubes were attached to the hotiom of a 9 cm petri dish by a piece of parafilm. The tubes were placed radially a t equal distances with the open side facing the center of the dish. Either 3 medium-size larvae (14-18 mg) or 5-6-day-old females were introduced and allowed to choose among the various diets. After a period of 3-4 days for larvae and 6-8 days for adults, the tubes were reweighed and the rate of food consumption was determined.

3. Results

The data summarized in Fig. l a indicate that the pattern of response of female khapra beetles to the whole range of fatty acids tested in the stand-

A-AduIls Dielary ConsenIration of Compound (%) - 0.5

0 5.0 ILLm 1.0

1.0

c5 ca C8 C I cm ciz Cl. CM 0 1 CI8 I C182 CI8 3

NO OF CARBON ATOMS IN FATTY ACIDS

Fig . 1 . Olfactory response of Trogoderma granarium and Tribolium castaneum to n-fatty acids. 1 mg of acid was applied to each paper disk. Both sexes of T. castaneum and T. gra- narium females were used (See Material and methods for a detailed description). Addi- tional numbers t o carbon numbers indicate the degree of unsaturation of the corre- sponding fat ty acids. Ordinates: + attraction, - repulsion, 20 repetitions for each acid

tested

Response o i T. granari t im, D. macula tus and T. castanetdm t o fa t ty acids 307

-50

ard and “devised” techniques is more or less similar. The short chain homo- logs C:-Cx discouraged aggregation whereas capric, lauric, myristic, penta- decanoic, palmitic, oleic, linoleic and nonadecanoic acids appeared to be attractive. Indifference response was observed for pelargonic, undecanoic, heptadecanoic and linolenic acids. Myristic and palmitoleic acids exhibited maximal arrestant activity while oleic acid displayed considerable attraction to beetles. In the “devised” test a clear repulsion was understandingly obtained with the volatile, short fatty acids such as valeric, caproic, hepta- noic and caprylic acids. Higher homologs with comparatively low vapour pressure exerted little or no effect except for oleic acid. It was rather sur- prising to observe the positive response of the medium-chain-length capric and lauric acids in both assays. (214, Cij and ClG fatty acids seem to be the most potent arrestants, but only pentadecanoic and oleic acids were able to attract over a distance.

It can be realized (Fig lb) that preferential response data obtained by standard and “devised” methods for Tribolium castaneum pointed to the relationship between volatility and extent of response. c5-cll low fatty acids strongly repelled the insects. The unsaturated oleic, linoleic and lino- lenic acids were relatively less effective repellents. Tridecanoic, pentadeca- noic and stearic acids with low vapour pressure exhibited arrestant effects

-

-Standard test technmue ----Devised test technique :::[ 0 Trogoderrna granarium

Fig . 2. Gustatory response of Dermestes maculatus to dietary n-fatty acids. The acids were mixed in the artificial diet at the concentrations specified. Additional numbers to carbon

numbers indicate degree of unsaturation. 40 repetitions for each fatty acid tested

308 E . Coheri, V. Stunii and A. Shulov

but failed to stimulate aggregation over a distance. Gustatory response of larvae Trogoderma granarium is recorded in Table. The insects were deterred by caprylic, pelargonic, capric, undecanoic, lauric and tridecanoic acids. Similar effects were observed with dietary linoleic or linolenic acids. I t is worthy to note that short chain acids such as caproic acid slightly stimulated food consumption and heptanoic acid discouraged feeding to only a small extent. Moreover, valeric acid (C,) increased ingestion when tested at the 10 O / o concentration.

The results presented in Fig. 2 indicate that Dermestes maculatus larvae were strongly discouraged by short chain and medium chain fatty acids (Co-Cii) and stimulated to consume long chain saturated and unsaturated fatty acids (c16-c18), except for linoleiiic acid which apparently was disliked at a high concentration (5 O / O ) . Maximal feeding response was achieved with 5 O/o dietary palmitic and linoleic acids. Attention should be drawn, however, to the phagostiinulatory action of the volatile valeric acid. Certain differen- ces in gustatory response exist between larvae and adults of D. maculatus. Mature stages readily ingested dietary valeric acid, yet, contrary to larvae, adults were induced to feed also by caproic, lauric and myristic acids. Caprylic acid at the highest level and pelargonic acid at all concentrations tested were phagodeterrents, whilst all saturated and unsaturated homologs appeared to enchance food consumption with the exception of linolenic acid. The strongest response was induced by palmitic, stearic, oleic and linoleic acids at elevated levels.

4. Discussion

Increased aggregation of females of T . granarium was induced by certain n-fatty acids. CE-Cle compounds were implicated in maximum positive re- sponse obtained in the standard two-choice test technique. Lauric, myristic, pentadecanoic, palmitic and palmitoleic acids were effective arrestants whereas oleic and pentadecanoic acids exhibited attractant features. The beetles were discouraged by the volatile low homologs which most likely acted over some distance. The above is in good agreement with the observed repulsion by alcohols from n-propyl (C3) to n-decyl (CIO) with no significant activity of n-undecy (Ci,) and n-dodecyl (Cig) (SPANGLER 1965). It has been previously reported that palmitoleic and palmitic acids both were efficient attractants and could be detected in surface cuticular fatty acids of the khapra beetle females (COHEN et al. 1971). Pentadecanoic acid which induced aggregation at high levels, was not found in adult lipids. However it was detected in a minute amount in a thorough extract of larvae (IKAN et al. 1970). The Cts-hydrocarbon, pentadecane, strongly attracted T. granarium larvae (unpubl. data), again pointing to olfactory properties of CiR-CIe com- pounds. Since the quantity required to elicit an assembling response was quite considerable, CeC1e fatty acids were not regarded as pheromones. Cuticular fatty acids might have some role in pheromone solubilization and gradual release, as has been assumed by GOODRICH (1970). Since adult beetles do not feed, only larvae could be assayed as to their gustatory re- sponse to fatty acids. It became evident that, except for valeric acid, none of the compounds stimulated food consumption. Similar to the olfactory pre- ference results, the short acids were inhibitory and discouraged larvae from

Response o/ T. grarzurium, 13. rnucdatus and T. castuneum to f a t t y acitts 309

feeding. Fatty acids of 7 . granarium faeces are composed of palmitic, stearic, oleic and linoleic acids (IKAN et al. 1970). Apart from being associated with induction and maintenance of larval diapause, it was suggested that adults were lured to faecal fatty acids which might serve as oviposition attractants (STANIC and SHULOV 1969). The above acids probably play minor or no role in phagostimulation (Table).

STARRATT and LOSCHIAVO (1 971) have demonstrated that aggregation in the confused flour beetle Tribolium confusum was induced by Nigrospora sphaevica mycelial triglycerides. Maximum response was obtained when the triglyceride major component was oleodipalmitin (STARRATT and LOSCHIAVO 1972), and a previous report (LOSCHIAVO 1965b) revealed intense aggregation and feeding response by palmitic acid. T . gvanarium females were also attracted by triglycerides, such as tristearin and triolein (unpubl. data). In the present report a close species, Tvibolium castaneum aggregated on discs treated with tridecanoic, pentadecanoic, palmitic, stearic and oleic acids and was repelled by CT,-CIY fatty acids. CS-CIJ compounds were phagorepellents to hide beetle larvae, and CN-Cn acids to mature stages. The above trend was also found in T. granavium larvae and adults. Furthermore, short fatty acids heve been reported to be toxic to houseflies (LEVINSON and ASCHER 1954; QURAISHI and THORSTEINSON 1965) as well as to fungi (WYSS et al. 1945). Capric acid ((210) was highly toxic to Tribolium confusum (HOUSE and GRAHAM 1967) and its utilization as pest control has been proposed. Capric acid was an effective food deterrent of T. granarium and D. macula- tus larvae, thus its action is not restricted to the flour beetle only. In addi- tion, lauric acid was toxic to Galleriu mellonella (DADD 1966), whereas dietary lauric and caprylic acids appeared to inhibit the growth rate of D. maculatus larvae (COHEN, in prep.). Low molecular weight fatty acids exert- ed a chemosterilizing effect on hide beetles, whilst higher homologs im- proved oviposition due to their phagostimulatory action (COHEN and LEVIN- SON 1972). Conversion of fatty acids to their methyl esters did not result in altered response of D. maculatus (COHEN, unpubl. information). Valeric acid is phagostimulatory to immature stages of the hide beetle; valeric and caproic acids induced feeding response in adults and in this context it should be recalled that dietary valeric acid stimulated feeding of T. granarium larvae. Thus both dermestids share the same chemosensory response to this volatile acid, which has been previously reported to act as a sex attractant of the sugar beet wireworm Limonius califovnicus (JACOBSON et al. 1968). Except for valeric acid, hide beetle larvae were more discriminatory than adults, being repelled by short-and-medium chain fatty acids. Larvae preferred palmitic acid in the homologous series, whereas lauric acid was stimulatory to adults.

Diverse feeding habits of the two dermestid beetles were reflected in their chemosensory responses. The hide beetles, which are adapted to a lipid-rich environment, exhibited a pronounced positive feeding response when offered dietary long chain fatty acids. On the other hand, the non carnivorous khapra beetles were not stimulated to consume the above dietary acids.

Acknowledgements

The authors wish to thank Mr. YARON TOREN for technical assistance. This communication was supported by Grant No. FG - IS - 250 US. Department of Agriculture.

310 E . Cohen, V. S t a n 2 and A. Shulov

Zusammenfassung

Geruch- und Geschmacksreaktion von Trogoderma granarium, Dermestes maculatus und Tribolium castaneum auj' verschiedene Fettsauren

Es wurden olfaktorische und gustatorische Reaktionen von Trogoderma granarium, Tribo- lium castaneum und Dermestes maculatus auf verschiedene Fettsauren mit gerader und ungerader Kohlenstoffzahl gepruff. C3-CB kurzgliedrige Fettsauren erschwerten die Aggre- gation der Trogoderma-granarium-Kafer. Myristin und Palmitoleinsauren zeigten maximal hemmende (Arrestant) Aktivitat an, wahrend die Oleinsaure der wirksamste Attraktant war. Andere Sauren entfalteten nur geringe oder gar keine Anziehung. Beziiglich gustato- rischer Reaktionen schien nur die Valeriansaure phagostimulatorisch; demgegeniiber wiesen gesattigte kurzgliedrige Fettsauren C8-C13 und die ungesattigten Linolein- und Linolen- sauren die Insekten ab. Tribolium castaneum wurde stark von den kurzgliedrigen Homolo- gen abgewiesen, wahrend ungesattigte Sauren weniger repellent erschienen. Die Kafer wur- den durch Tridecan, Pentadecan und Stearinsauren zur Aggregation veranlafit, welche aber die Aggregation nicht auf kurze Entfernung stimulieren. Dermestes maculatus-Larven wurden durch Fettsauren mit kurzer und mittlerer Kettenlange (CG-CI~) stark abgewiesen. Gesattigte und ungesattigte hohere Homologe waren phagostimulatorisch, ausgenommen bei hoheren diatischen Ebenen der Linolensaure. Erwachsene Insekten zeigten sich weniger wah- lerisch und wurden zusatzlich zu Valerian durch Caprin sowie Laurin und Myristinsaure angezogen. Maximale Nahrungsabweisereaktion wurde bei diatischer Pelargonsaure be- obachtet.

References

COHEN, E.; LEVINSON, Z. H., 1972: The effect of fatty acids on reproduction of the hide- beetle Dermestes maculatus (Dermestidae, Coleoptera). Life Sci. 11, 293-299.

- IKAN, R.; SHULOV, A., 1971 : Response of the female of Trogoderma granarium (Cole- optera, Dermestidae) to cuticular free fatty acids. Ent. exp. & appl. 14, 315-318.

DADD, R. H., 1966: Beeswax in the nutrition of the wax moth, Galleria mellonella (L.). J. Insect Physiol. 12, 1479-1492.

DAVIS, G. R. F., 1968: Phagostimulation and consideration of its role in artificial diets. Bull. ent. SOC. Am. 14, 27-30.

GOODRICH, B. S., 1970: Cuticular lipids of adults and puparia of the Australian sheep blowfly, Lucilia cupprina (Wied.). J. Lipid Res. 11, 1-6.

HINTON, H. E., 1945: A Monograph of Beetles Associated with Stored Products. Vol. 1. London: British Museum.

HOUSE, H. L.; GRAHAM, A. R., 1967: Capric acid blended into foodstuff for control of an insect pest, Tribolium confusum (Coleoptera: Tenebrionidae). Can. Ent. 99, 994-999.

IKAN, R.; S T A N I ~ , V.; COHEN, E.; SHULOV, A., 1970: The function of fatty acids in the diapause of the khapra beetle Trogodermu granarium Everts. Comp. Biochem. Physiol. 37, 205-214.

JACOBSON, M.; LILLY, C. E.; HARDING, C., 1968: Sex attractant of sugar beet wireworm: Identification and biological activity. Science 159, 208-210.

LEVINSON, Z. H.; ASCHER, K. R. S., 1954: Chemicals affecting the pre-imaginal stages of the housefly. IV. The fatty acids. Riv. Parassitol. 15, 111-119.

- BAR ILAN, A. R.; 1967: Function and properties of an assembling scent in the Khapra beetle Trogoderma granarium. Riv. Parassitol. 28, 27-42.

- BARELKOVSKY, J.; BAR ILAN, A. R., 1967: Nutritional effects of vitamin omission and antivitamin administration on development and longevity of the hide beetle Dermestes maculatus Deg. (Coleoptera, Dermestidae). J. Stored Prod. Res. 3, 345-352.

LOSCHIAVO, S. R., 1965a: Methods for studying aggregation and feeding behavior of the confused flour beetle, Triboliurn confusum (Coleoptera: Tenebrionidae). Ann. Ent. SOC. Am. 58, 383-388.

- 1965b: The chemosensory influence of some extracts of Brewer's yeast and cereal products on the feeding behavior of the confused flour beetle, Tribolium confuswn (Coleoptera: Tenebrionidae), Ann. Ent. SOC. Am. 58, 576-588.

QURAISHI, M. S.; THORSTEINSON, A. J., 1965: Toxicity of some straight chain saturated fatty acids t o house fly larvae. J. Econ. Entomol. 58, 400-402.

SPANGLER, H. G., 1965: Reactions of the larvae of the khapra beetle and Trogoderma parabile to certain food substances and organic compounds. J. Econ. Entomol. 58, 2 12-21 8.

Response of T . granari t im, D. macula tus and T . cas taneum to fatty acids 31 1

S T A N I ~ , V.; SHULOV, A., 1969: Olfactory response of Trogodcvma gvanavium adults (Col., Dermest.) to odours of wheat, faeces and some faecal components. J. stored Prod. Res. 5, 299-304.

STARRATT A. N.; LOSCHIAVO, S. R., 1971: Aggregation of the confused flour beetle, Tribol ium confusum, elicited by niycclial constituents of the fungus :'r;igrospora sphae- rica. J. Insect Physiol. 17, 407-414.

- - 1972: Aggregation of the confused flour beetle Tribol ium confusum (Coleoptera: Tenebrionidae), elicited by fungal triglycerides. Can. Entomol. 104, 757-759.

\'INSON, S. B.; THOMPSON, J. L.; GREEN, H. B., 1967: Phagostimulants for the imported fire ant Solenopsis saevissima var. Richteri. J. Insect Physiol. 13, 1729-1736.

WYSS, 0.; LUDWIG, B. J.; JOINER, R. R., 1945: The fungistatic and fungicidal action of fatty acids and related compounds. Arch. Biochem. 7, 415-425.

Plant Breeding Ins t i tu te , T r u m p i n g t o n , C a m b r i d g e

Testing sugar beet for aphid-resistance in the glasshouse: a method and some limiting factors

By H. J. B. LOWE

Abstract

Inherited resistance to aphids has been assessed in vigorous, pot-grown sugar beet with two short, consecutive tests after the seedling stage. The plants were infested with apterous Myzus persicae and Aphis fabae simultaneously, but assessments of resistance to each species were independent. Not only were resistant beet stodrs identified but also individual resistant plants were selected using the same observations.

As the resistance of older plants was not always displayed by seedlings, sugar beet were tested after the area of third and later true leaves equalled the area of earlier leaves. Pot- bound beet were resistant to aphids; and plants had to be tested before this occurred. In winter, artificial lighting in addition to natural light was necessary to keep the sugar beet plants growing well enough to achieve adequate aphid colonisation for the assessment of resistance. Small plants were covered with plastic beakers for about three hours to ensure initial setting of M . persicae.

1. Introduction

When making tests for resistance to aphids in the glasshouse, many factors, including aspects of the environment and qualities of the plants under test, are affected by seasonal variation. These and other factors may also be varied artificially either directly or by adopting different experimental procedures.

Resistance to aphids in sugar beet (Beta vulgaris L.) is strongly influenced by changes in the environment, and is normally expressed as differences in the numbers of aphids found on plants (LOWE and RUSSELL 1969) not as a difference between immune and infested plants. At the Plant Breeding Institute, unsatisfactory tests for resistance have most often been those in which the aphids failed to establish large enough populations to permit positive recognition of resistant plants. A method which both determines the relative

2. ang. Ent. 76 (1974), 311-321 0 1974 Verlag Paul Parey, Hamburg und Berlin ISSN 0044-2240 I ASTM-Coden: ZANEAE