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Development of Ephestia kuehniella (Zeller), Plodia interpunctella (Hübner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on kernels and wholemeal flours of Fagopyrum esculentum (Moench) and Triticum aestivum L.
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J. stored Prod. Res. Vol. 34, No. 4, pp. 269±276, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0022-474X(98)00008-3 0022-474X/98 $19.00 + 0.00
Development of Ephestia kuehniella (Zeller), Plodia interpunctella (HuÈbner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on Kernels and Wholemeal Flours of Fagopyrum esculentum (Moench) and Triticum aestivum L. D. P. LOCATELLI* and L. LIMONTA Istituto di Entomologia agraria, UniversitaÁ degli Studi, Via Celoria 2, 20133 Milano, Italy (Accepted 25 February 1998)
AbstractÐThree stored product moth pests, Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were reared on the following ®ve foods: whole buckwheat with pericarp, decorticated buckwheat, wheat var. ``Centauro'' (kernels), wholemeal wheat ¯our and whole buckwheat ¯our. Results showed that achenes of buckwheat with pericarp are a poor food for the development of these species. A low rate of survival to adulthood for E. kuehniella and P. interpunctella was recorded, with a considerable extension of post-embryonic development. Although the mandibles of larvae are strong, they have trouble in breaking the ®brous buckwheat pericarp. It was observed that when the seed was decorticated there was a higher percentage of adults emerged. The emergence of E. kuehniella began, according to the food given, 34±42 days after the eggs were laid. The susceptibility index (s.i.) of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The ®rst P. interpunctella adults were found after 29 days on wheat and after 56 days on buckwheat with pericarp. The shortest mean period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp at 81 days. The highest susceptibility index was on kernels (s.i. 12.8), the lowest one was on buckwheat with pericarp (s.i. 2.3). C. cephalonica began to emerge, according to the food given, after 40±55 days. In this case, fewer adults were recorded from buckwheat with pericarp, but no signi®cant dierences among the means of emerged adults on wheat, wholemeal wheat ¯our and whole buckwheat ¯our were observed. The longest mean period of development was recorded on wholemeal wheat ¯our (72 days) while the shortest was on wheat kernels (58 days). The highest value for the susceptibility index was obtained for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5). # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐEphestia kuehniella, Plodia interpunctella, Corcyra cephalonica, Fagopyrum esculentum, Triticum aestivum, development
*Author for correspondence. 269
270
D. P. Locatelli and L. Limonta
INTRODUCTION
Buckwheat (Fagopyrum esculentum Moench), of the Chenopodiaceae family, was an important crop in some countries for many years. In recent times its use has declined, but its wholemeal ¯our is still used in traditional cooking in the mountain areas of northern Italy. Studies show that whole buckwheat has lower susceptibility to attack by insects after harvesting than other cereals. The presence of a resistant pericarp obstructs both the laying of the eggs and the emergence of grain weevil adults (Sitophilus spp.) (Strachov-Koltchin, 1915; Bako et al., 1915; Locatelli and Antignati, 1993). Candura (1943, 1950) showed that the Angoumois grain moth, Sitotroga cerealella Olivier, a common pest of cereal kernels, can infest buckwheat. The silvanid beetle Oryzaephilus surinamensis (L.) also develops well on whole buckwheat ¯our (Ciesielska, 1966). In this paper the susceptibility of buckwheat to attack by Ephestia kuehniella (Zeller), Plodia interpunctella (HuÈbner) and Corcyra cephalonica (Stainton) was compared to the susceptibility of wheat (Triticum aestivum L.). MATERIALS AND METHODS
The tests were carried out using the following ®ve foods: whole buckwheat, decorticated buckwheat, wheat variety ``Centauro'' (kernels), wholemeal wheat ¯our and whole buckwheat ¯our. wheat kernel wholemeal wheat ¯our (no germ) buckwheat with pericarp buckwheat without pericarp
moisture 12 13.4 14 13.3
protein 12.5 11.5 10 13.1
fat 2.6 1.5 2 2.5
ashes 1.8 1.5 2.2 1.9
Before starting the tests, all the foods were placed in a freezer at a temperature of ÿ208C for 45 days in order to eliminate the possible presence of arthropods. Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were bred at the Istituto di Entomologia Agraria, UniversitaÁ degli Studi, Milan. The eggs were collected from Petri dishes placed under special plexiglass cylinders containing 100 adults of mixed sex. Each cylinder was 15 cm in diameter and 40 cm high, the base was ®tted with an 18 mesh metal net through which the eggs could fall. The cylinders were kept in an incubator at 262 18C and at 702 5% r.h., and with 12 h of light alternating with 12 h of darkness. Tests were carried out on eggs laid 6±24 h previously, preserved in environmental conditions identical to those provided for the laying of the eggs. Before the tests the eggs were observed with a stereomicroscope in order to eliminate those showing evident deformations. The tests were carried out by placing 200 g of food in polystyrene containers (diameter 120 mm, height 65 mm). A small plate containing 100 eggs of the test species was placed in the middle of each container. Such containers, closed with gauze (120 meshes) to provide ventilation, were placed in an incubator at 26 218C and 702 5% relative humidity for 5 days. The unhatched eggs were then counted with a binocular microscope. The containers were returned to the incubator until the end of post-embryonic development. At emergence, ®rst generation adults were counted daily and removed. Adult emergence data were corrected for variations in percentage hatch of eggs in order to compare results for the four replicates of the growth of the three species on the ®ve diets. The data were based on 100 hatched eggs. The developmental period was counted from the time the eggs were laid to the time when 50% of the total adults emerged. Based on the percentage of adult emergence and on the period of development, the susceptibility index* (s.i.) (Dobie, 1974) was determined according to the method of Howe (1971). A further parameter in the evaluation of the developmental ability of *Susceptibility index gives an indication of the possible rate of reproduction on the dierent food media (Howell and Games, 1974; Zar, 1984).
Development of moths on wheat and buckwheat
271
the three species on the dierent substrata is the synchronisation of emergence (Baker, 1988). This is represented by the slope of the cumulative adult emergence curve. Cumulative emergence was seen to ®t a linear regression with probit transformed data. Means were compared by Duncan's multiple range test (P < 0.05). The statistical evaluation did not show signi®cant dierences among means on original and angular transformed data. The program SPSS for Windows1 version 5.01 was used for the probit analysis. RESULTS
In Figs 1±3 the mean number of emerged adults on the dierent diets is reported for each species. The dierences in development of the three moths on the ®ve diets are considered in Tables 1±3. The beginning of adult emergence of E. kuehniella occurred 34±42 days after the eggs were laid according to the food given. The mean number of adults on the dierent foods was higher than 80 except on buckwheat with pericarp (25 individuals). The susceptibility index of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The ®rst P. interpunctella adults were observed on wheat after 29 days, while on buckwheat with pericarp after 56 days; intermediate values were recorded for the other foods. The mean
Fig. 1. Cumulative mean number of adults of Ephestia kuehniella which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
Fig. 2. Cumulative mean number of adults of Plodia interpunctella which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
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Fig. 3. Cumulative mean number of adults of Corcyra cephalonica which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
Table 1. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Ephestia kuehniella. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat-¯our Wheat var. ``Centauro'' kernels Wholemeal wheat-¯our
Mean of adults emerged* 2SD 2522.7 9021.8 8626.8
a b a b
8425.9 9323.4
a
Mean development period* (days)2SD
c
562 6.0 472 0.82 492 0.87
b
a
522 0.79 432 0.13
c d b c b
d
s.i.* 2SD 5.82 0.75 9.72 0.21 9.12 0.28
b b c
8.62 0.26 10.62 0.10
d
c
a
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
Table 2. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Plodia interpunctella. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
Mean of adults emerged* 2SD 7.5 24.4 882 4.7 612 7.7
d
a
802 3.7 732 1.6
c b b
Mean development period* (days)2SD 8121.5 4420.19 5822.5 3420.47 6920.53
a c b
s.i.*2SD 2.32 0.70 10.32 0.15 7.02 0.29
d e
12.82 0.24 6.22 0.08
b
e c
a
d
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
Table 3. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Corcyra cephalonica. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro' kernels Wholemeal wheat ¯our
Mean of adults emerged *2 SD 1622.0 6128.1 7224.4
a
7224.0 81212.6
a a
b
c
Mean development period* (days)2SD 62 22.8 67 24.8 64 21.2 58 23.0 72 21.7
a
s.i.*2 SD
c d b b c
4.52 0.18 6.12 0.42 6.72 0.19
d
7.42 0.45 6.12 0.36
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
b a
c
c
d
Development of moths on wheat and buckwheat
273
Table 4. Regression parameters of the probit line: slope and observed signi®cance level of w2 statistic (P) for Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica on dierent foods Diets
Ephestia kuehniella
Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
slope 0.07 0.16 0.14 0.11 0.25
P 0.90 0.02 <0.01 0.37 <0.01
Plodia interpunctella slope 0.07 0.31 0.13 0.48 0.09
P 0.99 0.07 0.17 0.08 0.99
Corcyra cephalonica slope 0.14 0.08 0.07 0.09 0.11
P 0.92 0.50 0.44 0.96 0.88
number of emerged adults ranged from 7.5 for buckwheat with pericarp to 80 for wheat and 88 for buckwheat without pericarp. The shortest period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp (81 days). Therefore the highest value of susceptibility index was recorded on wheat kernels (s.i. 12.8), the lowest one on buckwheat with pericarp (s.i. 2.3). For C. cephalonica emergence started after 40±55 days according to the foods given. As for the other species, a lower number of adults was obtained from buckwheat with pericarp (16 individuals). No signi®cant dierences occurred among the mean numbers of adults which emerged on wheat, wholemeal wheat and whole buckwheat ¯ours. The longest mean period of development was on wholemeal wheat ¯our (72 days) while the shortest was on wheat kernels (58 days). The highest value of susceptibility index was for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5). The slopes of the ®tted lines show dierences in the synchronisation of emergence (Table 4). For C. cephalonica this parameter was not signi®cantly dierent among the substrates (slope 0.07±0.14) while dierences were recorded for the other two species (slope 0.07±0.48 and 0.07± 0.25 for P. interpunctella and E. kuehniella respectively). The synchronisation of emergence of E. kuehniella was greater if bred on wheat meal (slope 0.25) and lower on buckwheat with pericarp (slope 0.07). Also in the case of P. interpunctella the lowest value was recorded on buckwheat with pericarp (slope 0.07) while the highest was on wheat (slope 0.48). The relationship among the three parameters of development considered here (total number of adults, average period of development and slope of the probit line) for the three species can be analysed. In Fig. 4 the relationship between the mean development period and the probit line slope is recorded. The mean period of development was inversely related to the probit line slope for P. interpunctella (R2=0.98) and E. kuehniella (R2=0.99), while no relationships for C. cephalonica were recorded. For the latter species the probit line slope has a limited range of variability compared with that of other species.
Fig. 4. Relationship between mean development period and slope of the probit regression for Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica on the ®ve diets.
274
D. P. Locatelli and L. Limonta
Table 5. Mean number of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) on dierent foods, treating Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica cumulatively Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
Mean of adult emerged* 2SD 16 28.8 80216 73213 79 26.1 82210
Mean development period* (days)2 SD a a a a
b
662 13 532 13 5727.5 482 12 612 16
a a a a a
s.i. *2SD 4.2 21.8 8.7 22.3 7.6 21.3 9.6 22.8 7.6 22.6
b a a b a a b
*Means within a column followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
It can thus be concluded that the development of C. cephalonica on the foods considered shows no dierences for synchronisation of emergence and average period of development, while such dierences are apparent for E. kuehniella and P. interpunctella. Buckwheat with pericarp signi®cantly depressed the emergence to adulthood of all species (P < 0.05) (Table 5). The mean number of adults emerged out of 100 hatched eggs was 16 compared with 70±80 adults on other diets. The mean period of development of the three species on the dierent foods (minimum value 48 days for wheat and maximum value 66 days for buckwheat with pericarp) did not show a signi®cant dierence (P > 0.05). However, for the susceptibility index, signi®cant dierences were apparent for the considered diets (P < 0.05). Three groups can be observed: the ®rst one with the highest susceptibility index formed by buckwheat without pericarp and by wheat (mean index 9), the second one formed by the two meals with equal mean values (mean index 7.6), the third one represented by buckwheat with pericarp (mean index 4.2).
DISCUSSION
The results demonstrate that buckwheat achenes with pericarp are not the most suitable substratum for the development of E. kuehniella, P. interpunctella and C. cephalonica. In fact, a low percentage of adult emergence was recorded for all the species, in particular E. kuehniella and P. interpunctella, and the post-embryonic development stage was signi®cantly extended. Although the mandibles of larvae are strong, they have diculty in breaking the pericarp of Fagopyrum esculentum. This is because the high quantity of ®bre makes the pericarp more resistant. Many studies point out that larvae can develop more easily on crushed seeds rather than on whole ones as the pericarp oers a barrier to attack by larvae. This has been observed for P. interpunctella and Cadra cautella (Walker) (LeCato, 1976), E. kuehniella (Kunike, 1938) and C. cephalonica (Mbata, 1989; Sharma et al., 1978; Osman, 1986). If buckwheat is decorticated then a high percentage of adults emerge and buckwheat in fact has a similar nutritional content to wheat. P. interpunctella requires a high content of vitamins, polyunsaturated fatty acids and steroids in the diet (Richardson, 1926; Fraenkel and Blewett, 1943a,b; MoreÂre, 1971); wheat kernels have a susceptibility index which is higher than that of wholemeal wheat ¯our; wheat contains group B vitamins in the germ which is removed during the milling process. It has been widely observed that P. interpunctella bred on re®ned ¯ours has a long period of development and that very few emerge as adults compared to those bred on whole wheat kernels and wholemeal wheat ¯our (Altindag and Ugur, 1992; Williams, 1964). This is con®rmed by data comparing whole buckwheat ¯our and wheat ¯our. In fact in the case of buckwheat ¯our the germ is not removed during the milling process as happens with wheat, as it is located centrally. In contrast E. kuehniella has fewer nutritional needs, prefers ground cereals and can also develop on re®ned ¯ours (Jacob and Cox, 1977; Stein and Parra, 1987). Like El-Buzz et al. (1978) and Kamel et al. (1981) we observed that the highest proportion of larvae of C. cephalonica becoming adults occurred on wheat and wholemeal wheat ¯our; but,
Development of moths on wheat and buckwheat
275
unlike these authors, we found that on wholemeal wheat ¯our, larvae needed several days longer to complete development. Trematerra (1983) observed that the biological cycle of C. cephalonica is much more rapid on ground products like corn maize ¯ours, barley malt and wheat bran, while the development takes longer on rice kernels, ¯our and corn maize with lower percentages of emergence. On the contrary in these tests we observed that the highest susceptibility index for C. cephalonica occurred on wheat. It is, however, well-known that dierent populations of this species can show diering abilities to develop on dierent diets (Cox et al., 1981).
REFERENCES Altindag N. and Ugur A. (1992) Investigations on the development of Plodia interpunctella (Hbn.) (Lep., Piralidae) on various foods. In Proceedings of the Second Turkish National Congress of Entomology. Ege Universitesi, Izmir, Turkey, pp. 21±28. Baker J. E. (1988) Development of four strains of Sitophilus oryzae (L.) (Coleoptera: Curculionidae) on barley, corn (maize), rice and wheat. Journal of Stored Products Research 24, 193±198. Bako N. J., Gussev M. A. and Miroshnikov L. A. (1915) The biology of Calandra granaria L. Journal of Applied Entomology 1, 99±101. Candura G. S. (1943) Italy. Further damage caused by the Indian meal moth (Plodia interpunctella) and the Angoumois grain moth (Sitotroga cerealella). International Bulletin of Plant Protection 17, 19±20. Candura G. S. (1950) Reperti sulla Sitotroga cerealella Oliv. nell'Italia settentrionale e su altre tignole dei viveri. Bollettino di Zoologia Agraria e Bachicoltura 16, 99±146. Ciesielska Z. (1966) Research on the ecology of Oryzaephilus surinamensis L. (Coleoptera, Cucujidae). Ekologia Polska 14, 439±489. Cox P. D., Crawford L. A., Gjestrud G., Bell C. H. and Bowley C. R. (1981) The in¯uence of temperature and humidity on the life-cycle of Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae). Bulletin of Entomological Research 71, 171±181. Dobie P. (1974) The laboratory assessment of the inherent susceptibility of maize varieties to post-harvest infestation by Sitophilus zeamais Motsch. (Coleoptera: Curculionidae). Journal of Stored Products Research 10, 183±197. El-Buzz H. K., Kamel A. H., El-Nahal A. K. and El-Borollossy N. F. (1978) The eect of diet on the biology of Corcyra cephalonica Staint. (Galleriidae: Lepidoptera). Bulletin SocieÂte Entomologique d'EÂgypte 59, 225±232. Fraenkel G. and Blewett M. (1943a) The natural foods and food requirements of several species of stored products insects. Transactions of the Royal Entomological Society of London 93, 457±489. Fraenkel G. and Blewett M. (1943b) Vitamins of the B group required by insects. Nature, London 151, 703±704. Fraenkel G. and Blewett M. (1946) Linoleic acid, vitamin E and other fat-soluble substances in the nutrition of certain insects, Ephestia kuehniella, E. elutella, E. cautella and Plodia interpunctella (Lep.). Journal of Experimental Biology 22, 172±190. Howe R. W. (1971) A parameter for expressing the suitability of an environment for insect development. Journal of Stored Products Research 7, 63±65. Howell J. F. and Games P. A. (1974) The eects of variance heterogeneity on simultaneous multiple-comparison procedures with equal samples size. British Journal of Mathematical and Statistical Psychology 27, 72±81. Jacob T. A. and Cox P. D. (1977) The in¯uence of temperature and humidity on the life-cycle of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Journal of Stored Products Research 13, 107±118. Kamel A. H., Ali N. A. and El-Bishlawy H. N. (1981) Eect of ¯our constituents on certain biological aspects of the rice moth, Corcyra cephalonica Staint. Bulletin SocieÂte Entomologique d'EÂgypte 61, 137±142. Kunike G. (1938) Die Feststellung des NaÈhrwertes verschiedener Stoe durch Frassversuche mit VortsschaÈdlingen. Anzeiger SchaÈdlingskunde 14, 101±105. LeCato G. L. (1976) Yield, development and weight of Cadra cautella (Walker) and Plodia interpunctella (HuÈbner) on twenty-one diets derived from natural products. Journal of Stored Products Research 12, 43±47. Locatelli D. P. and Antignati E. (1993) SuscettibilitaÁ degli acheni di Fagopyrum esculentum Moench agli attacchi di Sitophilus granarius (L.), S. oryzae (L.) e S. zeamais Motsch. Tecnica Molitoria 44, 1047±1051. Mbata G. N. (1989) Studies on some aspects of the biology of Corcyra cephalonica (Stainton) (Galleriidae). Journal of Stored Products Research 25, 181±186. MoreÂre G. L. (1971) Le caroteÂne: substance indispensable pour la nutrition de Plodia interpunctella HuÈbner. Comte Rendu de l'AcadeÂmie des Sciences 272, 2229±2231. Osman N. (1986) Development of the rice moth, Corcyra cephalonica (St.) on dierent grains. Pertanika 9, 155±159. Richardson C. H. (1926) A physiological study of the growth of the Mediterranean ¯our moth (Ephestia kuehniella Zeller) in wheat ¯our. Journal of Agricultural Research 32, 895±929. Sharma G. K., Jain K. L. and Pareek B. L. (1978) Host preference and host-biology relations of Corcyra cephalonica and Ephestia cautella. Entomon 3, 37±40. Stein C. P. and Parra J. R. P. (1987) Aspectos bioloÂgicos de Anagasta kuehniella (Zeller, 1979) criada em 2 substratos alimentares. Anales de Sociedad Entomologica do Brasil 16, 173±185.
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Stratchov-Koltchin A. L. (1915) Calandra granaria L. Memoirs of the Voronezh Station for the Control of Pests of Plants 1, 1±74. Trematerra P. (1983) Biologia e preferenze alimentari di Corcyra cephalonica (Stainton) (Lepidoptera, Galleriidae). Industrie Alimentari 34, 540±548. Williams G. C. (1964) The life-history of the Indian meal-moth, Plodia interpunctella (HuÈbner) (Lep. Phycitidae) in a warehouse in Britain and on dierent foods. Annals of Applied Biology 53, 459±475. Zar J. H. (1984) Biostatistical Analysis. Prentice Hall Inc., Englewood Clis, New Jersey.
J. stored Prod. Res. Vol. 34, No. 4, pp. 269±276, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain S0022-474X(98)00008-3 0022-474X/98 $19.00 + 0.00
Development of Ephestia kuehniella (Zeller), Plodia interpunctella (HuÈbner) and Corcyra cephalonica (Stainton) (Lepidoptera: Pyralidae) on Kernels and Wholemeal Flours of Fagopyrum esculentum (Moench) and Triticum aestivum L. D. P. LOCATELLI* and L. LIMONTA Istituto di Entomologia agraria, UniversitaÁ degli Studi, Via Celoria 2, 20133 Milano, Italy (Accepted 25 February 1998)
AbstractÐThree stored product moth pests, Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were reared on the following ®ve foods: whole buckwheat with pericarp, decorticated buckwheat, wheat var. ``Centauro'' (kernels), wholemeal wheat ¯our and whole buckwheat ¯our. Results showed that achenes of buckwheat with pericarp are a poor food for the development of these species. A low rate of survival to adulthood for E. kuehniella and P. interpunctella was recorded, with a considerable extension of post-embryonic development. Although the mandibles of larvae are strong, they have trouble in breaking the ®brous buckwheat pericarp. It was observed that when the seed was decorticated there was a higher percentage of adults emerged. The emergence of E. kuehniella began, according to the food given, 34±42 days after the eggs were laid. The susceptibility index (s.i.) of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The ®rst P. interpunctella adults were found after 29 days on wheat and after 56 days on buckwheat with pericarp. The shortest mean period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp at 81 days. The highest susceptibility index was on kernels (s.i. 12.8), the lowest one was on buckwheat with pericarp (s.i. 2.3). C. cephalonica began to emerge, according to the food given, after 40±55 days. In this case, fewer adults were recorded from buckwheat with pericarp, but no signi®cant dierences among the means of emerged adults on wheat, wholemeal wheat ¯our and whole buckwheat ¯our were observed. The longest mean period of development was recorded on wholemeal wheat ¯our (72 days) while the shortest was on wheat kernels (58 days). The highest value for the susceptibility index was obtained for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5). # 1998 Elsevier Science Ltd. All rights reserved Key wordsÐEphestia kuehniella, Plodia interpunctella, Corcyra cephalonica, Fagopyrum esculentum, Triticum aestivum, development
*Author for correspondence. 269
270
D. P. Locatelli and L. Limonta
INTRODUCTION
Buckwheat (Fagopyrum esculentum Moench), of the Chenopodiaceae family, was an important crop in some countries for many years. In recent times its use has declined, but its wholemeal ¯our is still used in traditional cooking in the mountain areas of northern Italy. Studies show that whole buckwheat has lower susceptibility to attack by insects after harvesting than other cereals. The presence of a resistant pericarp obstructs both the laying of the eggs and the emergence of grain weevil adults (Sitophilus spp.) (Strachov-Koltchin, 1915; Bako et al., 1915; Locatelli and Antignati, 1993). Candura (1943, 1950) showed that the Angoumois grain moth, Sitotroga cerealella Olivier, a common pest of cereal kernels, can infest buckwheat. The silvanid beetle Oryzaephilus surinamensis (L.) also develops well on whole buckwheat ¯our (Ciesielska, 1966). In this paper the susceptibility of buckwheat to attack by Ephestia kuehniella (Zeller), Plodia interpunctella (HuÈbner) and Corcyra cephalonica (Stainton) was compared to the susceptibility of wheat (Triticum aestivum L.). MATERIALS AND METHODS
The tests were carried out using the following ®ve foods: whole buckwheat, decorticated buckwheat, wheat variety ``Centauro'' (kernels), wholemeal wheat ¯our and whole buckwheat ¯our. wheat kernel wholemeal wheat ¯our (no germ) buckwheat with pericarp buckwheat without pericarp
moisture 12 13.4 14 13.3
protein 12.5 11.5 10 13.1
fat 2.6 1.5 2 2.5
ashes 1.8 1.5 2.2 1.9
Before starting the tests, all the foods were placed in a freezer at a temperature of ÿ208C for 45 days in order to eliminate the possible presence of arthropods. Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica were bred at the Istituto di Entomologia Agraria, UniversitaÁ degli Studi, Milan. The eggs were collected from Petri dishes placed under special plexiglass cylinders containing 100 adults of mixed sex. Each cylinder was 15 cm in diameter and 40 cm high, the base was ®tted with an 18 mesh metal net through which the eggs could fall. The cylinders were kept in an incubator at 262 18C and at 702 5% r.h., and with 12 h of light alternating with 12 h of darkness. Tests were carried out on eggs laid 6±24 h previously, preserved in environmental conditions identical to those provided for the laying of the eggs. Before the tests the eggs were observed with a stereomicroscope in order to eliminate those showing evident deformations. The tests were carried out by placing 200 g of food in polystyrene containers (diameter 120 mm, height 65 mm). A small plate containing 100 eggs of the test species was placed in the middle of each container. Such containers, closed with gauze (120 meshes) to provide ventilation, were placed in an incubator at 26 218C and 702 5% relative humidity for 5 days. The unhatched eggs were then counted with a binocular microscope. The containers were returned to the incubator until the end of post-embryonic development. At emergence, ®rst generation adults were counted daily and removed. Adult emergence data were corrected for variations in percentage hatch of eggs in order to compare results for the four replicates of the growth of the three species on the ®ve diets. The data were based on 100 hatched eggs. The developmental period was counted from the time the eggs were laid to the time when 50% of the total adults emerged. Based on the percentage of adult emergence and on the period of development, the susceptibility index* (s.i.) (Dobie, 1974) was determined according to the method of Howe (1971). A further parameter in the evaluation of the developmental ability of *Susceptibility index gives an indication of the possible rate of reproduction on the dierent food media (Howell and Games, 1974; Zar, 1984).
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the three species on the dierent substrata is the synchronisation of emergence (Baker, 1988). This is represented by the slope of the cumulative adult emergence curve. Cumulative emergence was seen to ®t a linear regression with probit transformed data. Means were compared by Duncan's multiple range test (P < 0.05). The statistical evaluation did not show signi®cant dierences among means on original and angular transformed data. The program SPSS for Windows1 version 5.01 was used for the probit analysis. RESULTS
In Figs 1±3 the mean number of emerged adults on the dierent diets is reported for each species. The dierences in development of the three moths on the ®ve diets are considered in Tables 1±3. The beginning of adult emergence of E. kuehniella occurred 34±42 days after the eggs were laid according to the food given. The mean number of adults on the dierent foods was higher than 80 except on buckwheat with pericarp (25 individuals). The susceptibility index of achenes without pericarp (s.i. 9.7) was higher than that observed on wheat (s.i. 8.6). The ®rst P. interpunctella adults were observed on wheat after 29 days, while on buckwheat with pericarp after 56 days; intermediate values were recorded for the other foods. The mean
Fig. 1. Cumulative mean number of adults of Ephestia kuehniella which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
Fig. 2. Cumulative mean number of adults of Plodia interpunctella which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
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Fig. 3. Cumulative mean number of adults of Corcyra cephalonica which emerged from dierent diets. Each point is the mean of four replicates for 100 eggs diet combination.
Table 1. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Ephestia kuehniella. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat-¯our Wheat var. ``Centauro'' kernels Wholemeal wheat-¯our
Mean of adults emerged* 2SD 2522.7 9021.8 8626.8
a b a b
8425.9 9323.4
a
Mean development period* (days)2SD
c
562 6.0 472 0.82 492 0.87
b
a
522 0.79 432 0.13
c d b c b
d
s.i.* 2SD 5.82 0.75 9.72 0.21 9.12 0.28
b b c
8.62 0.26 10.62 0.10
d
c
a
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
Table 2. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Plodia interpunctella. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
Mean of adults emerged* 2SD 7.5 24.4 882 4.7 612 7.7
d
a
802 3.7 732 1.6
c b b
Mean development period* (days)2SD 8121.5 4420.19 5822.5 3420.47 6920.53
a c b
s.i.*2SD 2.32 0.70 10.32 0.15 7.02 0.29
d e
12.82 0.24 6.22 0.08
b
e c
a
d
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
Table 3. Mean of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) for Corcyra cephalonica. Each datum is the mean of four replicates (2SD) Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro' kernels Wholemeal wheat ¯our
Mean of adults emerged *2 SD 1622.0 6128.1 7224.4
a
7224.0 81212.6
a a
b
c
Mean development period* (days)2SD 62 22.8 67 24.8 64 21.2 58 23.0 72 21.7
a
s.i.*2 SD
c d b b c
4.52 0.18 6.12 0.42 6.72 0.19
d
7.42 0.45 6.12 0.36
*Means followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
b a
c
c
d
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Table 4. Regression parameters of the probit line: slope and observed signi®cance level of w2 statistic (P) for Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica on dierent foods Diets
Ephestia kuehniella
Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
slope 0.07 0.16 0.14 0.11 0.25
P 0.90 0.02 <0.01 0.37 <0.01
Plodia interpunctella slope 0.07 0.31 0.13 0.48 0.09
P 0.99 0.07 0.17 0.08 0.99
Corcyra cephalonica slope 0.14 0.08 0.07 0.09 0.11
P 0.92 0.50 0.44 0.96 0.88
number of emerged adults ranged from 7.5 for buckwheat with pericarp to 80 for wheat and 88 for buckwheat without pericarp. The shortest period of development occurred on wheat (34 days) while the longest was on buckwheat with pericarp (81 days). Therefore the highest value of susceptibility index was recorded on wheat kernels (s.i. 12.8), the lowest one on buckwheat with pericarp (s.i. 2.3). For C. cephalonica emergence started after 40±55 days according to the foods given. As for the other species, a lower number of adults was obtained from buckwheat with pericarp (16 individuals). No signi®cant dierences occurred among the mean numbers of adults which emerged on wheat, wholemeal wheat and whole buckwheat ¯ours. The longest mean period of development was on wholemeal wheat ¯our (72 days) while the shortest was on wheat kernels (58 days). The highest value of susceptibility index was for wheat kernels (s.i. 7.4) and the lowest one for buckwheat with pericarp (s.i. 4.5). The slopes of the ®tted lines show dierences in the synchronisation of emergence (Table 4). For C. cephalonica this parameter was not signi®cantly dierent among the substrates (slope 0.07±0.14) while dierences were recorded for the other two species (slope 0.07±0.48 and 0.07± 0.25 for P. interpunctella and E. kuehniella respectively). The synchronisation of emergence of E. kuehniella was greater if bred on wheat meal (slope 0.25) and lower on buckwheat with pericarp (slope 0.07). Also in the case of P. interpunctella the lowest value was recorded on buckwheat with pericarp (slope 0.07) while the highest was on wheat (slope 0.48). The relationship among the three parameters of development considered here (total number of adults, average period of development and slope of the probit line) for the three species can be analysed. In Fig. 4 the relationship between the mean development period and the probit line slope is recorded. The mean period of development was inversely related to the probit line slope for P. interpunctella (R2=0.98) and E. kuehniella (R2=0.99), while no relationships for C. cephalonica were recorded. For the latter species the probit line slope has a limited range of variability compared with that of other species.
Fig. 4. Relationship between mean development period and slope of the probit regression for Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica on the ®ve diets.
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Table 5. Mean number of emerged adults corrected for 100 hatched eggs (Mean of adults emerged), time needed to attain 50% of adult emergence (Mean development period) and susceptibility index (s.i.) on dierent foods, treating Ephestia kuehniella, Plodia interpunctella and Corcyra cephalonica cumulatively Diets Buckwheat with pericarp Buckwheat without pericarp Whole buckwheat ¯our Wheat var. ``Centauro'' kernels Wholemeal wheat ¯our
Mean of adult emerged* 2SD 16 28.8 80216 73213 79 26.1 82210
Mean development period* (days)2 SD a a a a
b
662 13 532 13 5727.5 482 12 612 16
a a a a a
s.i. *2SD 4.2 21.8 8.7 22.3 7.6 21.3 9.6 22.8 7.6 22.6
b a a b a a b
*Means within a column followed by the same letter are not signi®cantly dierent (P > 0.05, ANOVA, Duncan's test).
It can thus be concluded that the development of C. cephalonica on the foods considered shows no dierences for synchronisation of emergence and average period of development, while such dierences are apparent for E. kuehniella and P. interpunctella. Buckwheat with pericarp signi®cantly depressed the emergence to adulthood of all species (P < 0.05) (Table 5). The mean number of adults emerged out of 100 hatched eggs was 16 compared with 70±80 adults on other diets. The mean period of development of the three species on the dierent foods (minimum value 48 days for wheat and maximum value 66 days for buckwheat with pericarp) did not show a signi®cant dierence (P > 0.05). However, for the susceptibility index, signi®cant dierences were apparent for the considered diets (P < 0.05). Three groups can be observed: the ®rst one with the highest susceptibility index formed by buckwheat without pericarp and by wheat (mean index 9), the second one formed by the two meals with equal mean values (mean index 7.6), the third one represented by buckwheat with pericarp (mean index 4.2).
DISCUSSION
The results demonstrate that buckwheat achenes with pericarp are not the most suitable substratum for the development of E. kuehniella, P. interpunctella and C. cephalonica. In fact, a low percentage of adult emergence was recorded for all the species, in particular E. kuehniella and P. interpunctella, and the post-embryonic development stage was signi®cantly extended. Although the mandibles of larvae are strong, they have diculty in breaking the pericarp of Fagopyrum esculentum. This is because the high quantity of ®bre makes the pericarp more resistant. Many studies point out that larvae can develop more easily on crushed seeds rather than on whole ones as the pericarp oers a barrier to attack by larvae. This has been observed for P. interpunctella and Cadra cautella (Walker) (LeCato, 1976), E. kuehniella (Kunike, 1938) and C. cephalonica (Mbata, 1989; Sharma et al., 1978; Osman, 1986). If buckwheat is decorticated then a high percentage of adults emerge and buckwheat in fact has a similar nutritional content to wheat. P. interpunctella requires a high content of vitamins, polyunsaturated fatty acids and steroids in the diet (Richardson, 1926; Fraenkel and Blewett, 1943a,b; MoreÂre, 1971); wheat kernels have a susceptibility index which is higher than that of wholemeal wheat ¯our; wheat contains group B vitamins in the germ which is removed during the milling process. It has been widely observed that P. interpunctella bred on re®ned ¯ours has a long period of development and that very few emerge as adults compared to those bred on whole wheat kernels and wholemeal wheat ¯our (Altindag and Ugur, 1992; Williams, 1964). This is con®rmed by data comparing whole buckwheat ¯our and wheat ¯our. In fact in the case of buckwheat ¯our the germ is not removed during the milling process as happens with wheat, as it is located centrally. In contrast E. kuehniella has fewer nutritional needs, prefers ground cereals and can also develop on re®ned ¯ours (Jacob and Cox, 1977; Stein and Parra, 1987). Like El-Buzz et al. (1978) and Kamel et al. (1981) we observed that the highest proportion of larvae of C. cephalonica becoming adults occurred on wheat and wholemeal wheat ¯our; but,
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275
unlike these authors, we found that on wholemeal wheat ¯our, larvae needed several days longer to complete development. Trematerra (1983) observed that the biological cycle of C. cephalonica is much more rapid on ground products like corn maize ¯ours, barley malt and wheat bran, while the development takes longer on rice kernels, ¯our and corn maize with lower percentages of emergence. On the contrary in these tests we observed that the highest susceptibility index for C. cephalonica occurred on wheat. It is, however, well-known that dierent populations of this species can show diering abilities to develop on dierent diets (Cox et al., 1981).
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Stratchov-Koltchin A. L. (1915) Calandra granaria L. Memoirs of the Voronezh Station for the Control of Pests of Plants 1, 1±74. Trematerra P. (1983) Biologia e preferenze alimentari di Corcyra cephalonica (Stainton) (Lepidoptera, Galleriidae). Industrie Alimentari 34, 540±548. Williams G. C. (1964) The life-history of the Indian meal-moth, Plodia interpunctella (HuÈbner) (Lep. Phycitidae) in a warehouse in Britain and on dierent foods. Annals of Applied Biology 53, 459±475. Zar J. H. (1984) Biostatistical Analysis. Prentice Hall Inc., Englewood Clis, New Jersey.