Effect of stalk damage on growth and yield of certain maize cultivars by the maize stalk borer Chilo partellus

The effects of different degrees of stem tunneling caused by different levels of artificial infestation by the larvae of Chilo partellus (Swinhoe) on growth and yield of 4 maize cultivars were studied. The susceptible Inbred A suffered much more tunneling than ICZ1-CM, ICZ2-CM and Katumani Composite B. This tunneling influenced significantly the plant growth of all the four cultivars. There was a significant negative correlation between tunneling and yield for the cultivars Inbred A and Katumani Composite B, but such a relationship was not significant for ICZ1-CM and ICZ2-CM. Such differences in the relationships between tunneling and yield among the 4 cultivars are due to different degrees of tunneling caused by C. partellus larvae to the plants of these cultivars.

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Résumé L'étude a porté sur la croissance et la production avec différents niveaux de minage des tiges de 4 cultivars de maïs, lors de divers degrés de contamination artificielle par des chenilles de C. partellus. Le cultivar sensible Inbred A souffre plus des mines de C. partellus que ICZ1-CM, ICZ2-CM et Katumani composite B. Les mines influent significativement sur la croissance des 4 cultivars. Il y a une corrélation négative significative entre le minage des tiges et la production pour les cultivars Inbred A et Katumani composite B, mais la relation n'est pas significative pour ICZ1-CM et ICZ2-CM. Les différences entre le minage des tiges et la récolte des 4 cultivars sont dues aux différents degrés de minage des tiges de ces cultivars par C. partellus.

     

The importance of the behaviour of young larvae in sorghum resistance to Chilo partellus

Management of spotted stem borer, Chilo partellus (Swinhoe) by the use of resistant cultivars is being developed at ICRISAT. Different cultivars show resistance based on several mechanisms, one of which affects the establishment of first instar larvae in the plant whorl. However, it has been found that low establishment is a factor associated with resistance only in some cultivars and not in others. A number of physical and chemical plant factors are associated with preferential establishment of the young larvae in the leaf whorl. Among the physical characteristics, erect leaves and curled leaf bases are involved in larval establishment. Detailed chemical analysis of surface extracts showed that the concentration of one compound in the wax is related to resistance at this stage and assessment of physical and chemical plant characters has been used to predict resistance.

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Résumé L'Institut International de Recherches sur les Cultures en Régions Semi-Arides (ICRISAT) étudie la protection contre C. partellus Swinhoe par l'utilisation de cultivars résistants. Différents cultivars présentent une résistance à différents stades de croissance de la plante, et à différents stades de l'insecte. La résistance du sorgho à C. partellus dépend de plusieurs mécanismes, l'un d'eux conditionnant l'installation des chenilles du premier stade dans le verticille de la plante. Cependant, la lenteur de l'installation d'est un facteur lié à la résistance que chez quelques cultivars. Plusiers facteurs physiques et chimiques sont associés à l'installation préférentielle des jeunes chenilles dans le verticille foliare. Parmi les caractères physiques, le port érigé des feuilles, la présence de poches à leur base et les cires superficielles sont impliqués dans l'installation des chenilles. Une analyse chimique détaillée d'extraits des structures superficielles a montré que la concentration d'une substance, le C32 marqueur de la lignée résistante IS 2205, était 2 fois plus faible que dans les lignées sensibles IS 1151 et CSH 1.

     

Parasites of the spotted stalk borer,Chilo partellus [Lepidoptera: Pyralidae] in South Africa

One egg parasite, 7 larval parasites, 2 pupal parasites and 3 larval hyperparasites were recorded parasitizing the spotted stalk borer,Chilo partellus (Swinhoe) on maize and grain sorghum in South Africa.Trichogrammatoidea lutea Girault [Trichogrammatidae] parasitized eggs ofC. partellus mainly in mid-summer. The larval parasites were active throughout the season with occasional peaks of up to 75% parasitism.Apanteles sesamiae Cameron [Braconidae], proved to be the most abundant larval parasite. It was recorded fromca. 93% of parasitized larvae but its efficiency was reduced by the hyperparasite,Aphanogmus fijiensis (Ferriére) [Ceraphronidae], which reached sometimes up to 100% parasitism on cocoons ofA. sesamiae. The efficiency ofIphiaulax sp. [Braconidae], the 2^nd most abundant larval parasite, was also hindered by the hyperparasite,Eurytoma sp. [Eurytomidae] Pupal parasites were sometimes very abundant reaching up to 100% parasitism without any interference by hyperparasites. The most abundant pupal parasites wereDentichasmias busseolae Heinrich [Ichneumonidae] andPediobius furvus (Gahan) [Eulophidae].      

Increase in cereal stem borer populations through partial elimination of natural enemies

An insecticide exclusion method was used to evaluate the effect of parasitoids on level of infestation by the stem borers, Busseola fusca (Fuller) and Chilo partellus (Swinhoe), in grain sorghum. In field trials conducted at Brits and at Delmas, South Africa, a selective organophosphate insecticide, dimethoate, was applied twice weekly at each site to three subplots whereas three other identical subplots served as controls. Twelve plants were randomly selected from each subplot at weekly intervals and removed from the field. In the laboratory all plants were dissected to record borer infestation. In order to determine parasitism levels egg batches were kept in Petri dishes and all borer larvae and pupae were kept individually in vials until either parasitoids or moths emerged. At Brits ca. 97% of borers were C. partellus and 3% B. fusca, whereas at Delmas 37.5% were C. partellus and 62.5% B. fusca. The most abundant parasitoids of B. fusca were Cotesia sesamiae (Cameron) and Bracon sesamiae Cameron. The dominant parasitoids of C. partellus at both sites were C. sesamiae, Stenobracon spec., Dentichasmias busseolae Henrich and Pediobius furvus (Gahan). No egg parasitoids were found. At both sites, infestation levels in the sprayed plots were significantly higher than in the untreated plots. On the other hand, parasitism levels of borers in the unsprayed plots were significantly higher than in the treated plots. It was concluded that the higher infestation level of sorghum by stem borers in the sprayed plots was because of partial elimination of parasitoids and possibly other natural enemies by the pesticide.     

Mating and oviposition behaviour in the legume pod borer, Maruca testulalis

Experiments were conducted outdoors and in the insect rearing laboratory at the International Institute of Tropical Agriculture (IITA) in Nigeria. Four or five nights pairing duration gave the highest mating percentage and oviposition by the pod borer. Direct observations on adult mating revealed that some males mated more than once. The majority of females mated only once. A one-to-one ratio (with 10 males: 10 females) gave the best results for mating and oviposition. Mating took place between 21.00 h and 05.00 h when temperature ranged between 20–25°C and rh over 80% with peak activity occurring between 02.00 and 03.00 h. Oviposition followed a similar trend to that observed for mating with an equal sex ratio (of 10 or more pairs per cage) giving the highest egg count. The average number of eggs laid was ca. 400 per female. These results show a much higher oviposition potential for Maruca testulalis than has been previously reported. The results are discussed with regard to the rearing of this species under laboratory conditions.

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Accouplement et comportement de ponte de Maruca testulalis

Résumé Tant de l'extérieur qu'au laboratoire (à l'IITA au Nigéria), la durée optimale de maintien des couples de M. testulalis Geyer (Lep. Pyralidae) pour obtenir l'accouplement et la ponte a été de 4 à 5 nuits, toutefois les meilleurs résultats ont été obtenus à l'extérieur. L'observation directe a révélé que contrairement aux femelles, les mâles peuvent copuler plus d'une fois. Le meilleur rapport sexuel pour obtenir l'accouplement et la ponte est 1/1 (10 mâles/10 femelles), suivi de près par un raport avec excédent de mâles. L'accouplement a lieu entre 21 h et 5 h quand la température est entre 20 et 30°C et HR supérieure à 80%; un pic est observé entre 2 et 3 h. La ponte présente la même tendance que l'accouplement, avec une production d'ufs plus élevée pour au moins 10 couples par cage. Le nombre moyen d'ufs par femelle est environ 400. Ces résultats sont supérieurs à ce qui avait été indiqué précédemment. La discussion porte sur les difficultés rencontrées pour élever cette espèce au laboratoire.

     

Duration of diapause in the stem borers, Busseola fusca and Chilo partellus

The duration of diapause in the stem borers Busseola fusca (Fuller) and Chilo partellus (Swinhoe) was studied in South Africa by collecting diapausing larvae from the field throughout winter (April–August). B. fusca larvae emerged as moth around the middle of October regardless of the date of collection and the length of time they were kept in the laboratory under constant 21 °C. C. partellus larvae collected in April–June emerged in November, those collected in July emerged in October, and those collected in August emerged in September. Regardless of the collection date C. partellus started to emerge from diapause earlier and moth emergence lasted up to twice as long as in B. fusca. Under laboratory conditions at 60% RH both borer larvae lost about 50% of their body mass during diapause. When provided with water B. fusca larvae lost about 30% of their body mass and adults emerged 20 days earlier than when kept dry. C. partellus, on the other hand, lost only 13% of their body weight and emerged 34 days earlier. The differences between the two species are discussed in light of different types of diapause; i.e., obligatory diapause in B. fusca and facultative diapause in C. partellus.     

Relations of intraspecific variations in fecundity, clutch size, and oviposition frequency to the body size in three species of stoneflies, Sweltsa sp., Isoperla aizuana, and Stavsolus japonicus

Most stoneflies oviposit several times during their adult stage. In this study, the relations among oviposition frequency, the number of eggs per egg mass, and body size were examined in the chloroperlid stonefly Sweltsa sp. and two perlodid stoneflies, Isoperla aizuana and Stavsolus japonicus. It was found that larger individuals tended to oviposit more frequently than smaller ones, but the relation was significant only in Isoperla aizuana. In Sweltsa sp. and Isoperla aizuana, the number of eggs per egg mass was higher for the less-frequently ovipositing individuals than for those ovipositing more frequently, and the number of eggs per egg mass decreased with successive oviposition events. Stavsolus japonicus showed the same tendency but it was not statistically significant.     

Development, adult size and fecundity of Aphidius sonchi reared in two instars of its aphid host, Hyperomyzus lactucae

Development, adult size and fecundity of the aphid parasite, Aphidius sonchi Marshall (Hymenoptera: Aphidiidae), which began their development in the first and third instar nymphs of Hyperomyzus lactucae (L.) (Homoptera: Aphididae), were studied in the laboratory. Survival and development times were almost identical in the two host instars. However, adult parasites reared in the first instar hosts were smaller and had fewer eggs at emergence than those reared from the third instar.Further analysis showed that the size of an adult parasite, irrespective of host stage at reception of the parasite egg, was largely determined by the size of the host when the parasite was in its destructive feeding phase. Furthermore, within parasites reared from each of the two host instars, the earlier emerging individuals were larger and contained more eggs on emergence. However, the relationships between size, development time and fecundity in the parasites differed significantly between cohorts reared from the two host instars.These results indicate that (1) the suitability of the aphid to the development of the parasite varies as the aphid develops, and (2) several aspects of the parasite biology must be studied to show the relative suitability of the aphids of a given instar.

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Résumé L'étude a porté sur le développement, la fécondité et la taille des adultes d'A. sonchi Marshall (Hym: Aphidiidae) qui commence son développement dans le ler et le 3ème stades larvaires d'H. lactucae (Homopt: Aphididae). La survie et la durée de développement sont presque identiques dans les hôtes des deux stades. Cependant les adultes élevés dans le ler stade de l'hôte étaient plus petits et avaient moins d'oeufs à l'émergence que ceux élevés dans le 3ème stade.Des observations ultérieures ont montré que la taille de l'adulte, indépendamment du stade de l'hôte au moment de la réception de l'oeuf, était fortement déterminée par la taille de l'hôte au moment où la larve du parasite était dans sa phase alimentaire destructrice. De plus, parmi les parasites élevés à partir des hôtes de chacun des deux stades, les premiers émergés étaient plus gros et contenaient plus d'oeufs. Cependant la relation entre taille, durée de développement et fécondité des parasites différait significativement suivant les cohortes élevées à partir des hôtes des deux stades.Ces résultats indiquent (1) que l'adéquation du puceron au développement du parasite change pendant que le puceron se développe et (2) que différents aspects de la biologie du parasite doivent être étudiés pour montrer l'adéquation relative des pucerons d'un stade donné.

     

Antifeedant and insecticidal properties of azadirachtin to the European Corn Borer, Ostrinia nubilalis

Azadirachtin, a triterpenoid substance from the neem tree, Azadirachta indica A. Juss., Meliaceae, was evaluated for its antifeedant and insecticidal properties to the European corn borer Ostrinia nubilalis Hübner. The 50% protective concentration for larval feeding on treated corn disks (PC₅₀) was 3.5 ppm for neonate larvae and 24 ppm for third instar larvae. Azadirachtin severely reduced larval growth at 1 and 10 ppm in a meridic diet and eventually caused 100% mortality at 10 ppm and 90% at 1 ppm. At 0.1 ppm azadirachtin showed no significant effect on larvae but altered the sex ratio in favor of male moths during adult emergence and arrested oviposition of female moths.Nutritional indices for naive and habituated third instar larvae suggested that reduction of growth was due to toxicity as shown by a lowered efficiency of conversion in the azadirachtin treated groups, rather than changes in digestibility. No clear evidence of tolerance was observed in the habituated group. The data suggest that at 10 ppm azadirachtin is an effective botanical insecticide for control of O. nubilalis.

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Résumé On a examiné les propriétés anti-appétantes et insecticides de l'azadirachtine, une substance triterpénoïde provenant d'Azadirachta indica envers la pyrale du maïs Ostrinia nubilalis. La concentration effective pour causer 50% d'inhibition de l'alimentation larvaire (PC₅₀) sur des disques foliaires a été de 3.5 ppm pour les larves de premier stade et de 24 g/8 pour celle de troisième stade. L'azadirachtine a sévèrement réduit la croissance larvaire à des concentrations de 1 et 10 ppm dans une diète méridique et, éventuellement, a causé 100% de mortalité à 10 ppm et 90% à 1 ppm. A 0.1 ppm l'azadirachtine n'a pas eu d'effet significatif sur les larves maïs a modifié l'indice de masculinité en faveur des mâles au moment de l'émergence et a empêché l'oviposition chez les femelles. Les indices nutritionnels pour les larves naïves de troisième âge et celles ayant subi une accoutumance suggèrent que la réduction de croissance est le résultat d'une intoxication comme le démontre une efficacité réduite de transformation chez les groupes traités à l'azadirachtine, plutôt que des changements de digestibilité. Il n'y a pas d'évidence claire de tolérance dans le groupe ayant subi l'accoutumance. Les résultats suggèrent qu'à 10 ppm l'azadirachtine est un insecticide botanique efficace envers O. nubilalis.

     

Onion fly egg distribution in soil: a new sampling method and the effect of two granular insecticides

Tests were carried out in a screenhouse to determine the potential of a microsporidian pathogen,Nosema marucae (Microspora: Nosematidae), for the control of the spotted stalk borer,Chilo partellus (Lepidoptera: Pyralidae), on sorghum. Foliar application of an aqueous suspension ofN. marucae spores on egg batches pasted on the sorghum plants reduced leaf-damage in plants in the protected plots, and increased the proportion of plants with fully- and partially formed heads compared to unsprayed plots. Further, there was less tunnelling and fewer larvae in the sprayed plots. The pathogen also reduced pest infestation and damage to plants when the plots were infested with newly emerged larvae instead of eggs.N. marucae has a potential to controlC. partellus.     

Egg size and egg mass of Daphnia magna: response to food availability

The influence of different food availability on egg size and egg mass in Daphnia magna Straus was studied in long-term experiments using a flow-through system. Daphnia were either kept a constant high or low food levels or subjected to alternating periods of high food and starvation. Some animals were starved continuously after they had deposited their first clutch of eggs. Eggs were measured and weighed and their density (dry mass per volume) was determined. The results support the model of Glazier (1992), which defines a region of reproductive constraint at very low food concentrations and a region of adaptive response as food concentration increase. Egg sizes were largest under continuously low food concentrations (0.1 mg Cl^–1), which indicates that the maximum of Glazier's non-linear response curve is at very low food levels. Eggs produced during starvation were small, probably as a result of reproductive constraints. Egg density was about 0.37 mg dry weight mm^–1 and did not differ between treatments.     

Changes in egg colour, egg weight and oviposition rate with the number of eggs laid by wild females of the small heath butterfly, Coenonympha pamphilus

ABSTRACT. 1. The colour of eggs laid by individual Coenonympha pamphilus (L.) (Lep., Satyridae) females changed over their lifespan. The first laid eggs were green, but after having laid about 100 eggs, females laid only yellow eggs.
2. By following females in the field, or by capturing wild females, and noting the colour of their eggs, it was established that younger females showed higher oviposition rates and laid heavier eggs than older females.
3. Hence, wild C.pamphilus females are unable to sustain a constant egg production by extracting amino acids or any other nutrients from nectar. We hypothesize that this is a general phenomenon in nectar feeding butterflies.
4. The egg colour did not seem to match the colour of the substrate on which the female chose to deposit the egg.     

Effect of bisabolangelone on development ofCydia pomonella larvae and oviposition of the females

The effects of bisabolangelone on the development of codling moth larvae,Cydia pomonella L., and on ovipositional behaviour of the females were studied under laboratory conditions. Entry of the neonate larvae into apples and their development on a semi-synthetic medium were completely inhibited when the larvae were exposed respectively to 10 μg a.i./cm² and 20 μg a.i./ml of this compound. While concentrations of 1.25 to 5.0 μg a.i./ml bisabolangelone in the medium did not significantly affect larval development, exposure of the larvae to a higher rate (10 μg a.i./ml) resulted in 80% mortality during the first week. Nevertheless, the larvae which survived the treatments underwent further development until emergence of the adults. No significant changes in duration of larval or pupal periods were recorded. Oviposition of the females in plastic beakers, whose inner surfaces were partially painted with two concentrations of bisabolangelone (1.25 to 5.0 μg a.i./cm²), was significantly reduced and the eggs were mainly laid on the parts painted with the ethanol solvent alone. When the inner surface of the cups was completely treated (i.e. top, bottom, and side) with similar concentrations of bisabolangelone, a dramatic reduction in oviposition occurred and the eggs were mostly laid on the bottom of the beakers. While this compound did not significantly influence egg hatch, it inhibited the normal upward movement of the adults in the cups and migration of the newly hatched larvae through perforations of the lids.     

Influence of host plants on development, fecundity and egg hatchability of the arctiid moth Diacrisia casignetum

Measurements were made of the differences between sunflower and climbing hempweed leaves for development, fecundity and egg hatchability of Diacrisia casignetum Kollar. Developmental time and weight gains of sunflower-fed larvae were respectively longer and greater than those of hempweed-fed ones. The development time and weight gain, attributable to differences in host plants, were statistically heterogeneous (P<0.05-<0.10). Relative fecundity and egg hatchability of sunflower reared insects were greater than those of hempweed reared ones, and these were also statistically heterogeneous (P<0.1 and <0.05, respectively). Hempweed leaves contained relatively high titres of phenols and low ratios of proteins to phenols. Ovaries were heavier in insects reared on sunflower than on hempweed, whereas the level of phenols incorporated into the ovary was higher in insects fed on hempweed than those on sunflower. The differences in these parameters may be due to variations in nutritional quality of these hosts and incorporation of ingested phenolic materials to ovary and insect biomass.

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Résumé L'étude a porté sur l'évaluation de l'influence des feuilles de tournesol (Helianthus annuus) et de Mikana cordata sur le développement, la fécondité et l'éclosion des oeufs de D. casignetum Kollaz. La durée de développement et le gain de poids sur tournesol étaient plus importants que sur M. cordata. La durée de développement était statistiquement hétérogène (P<0.05), ce qui peut être dû à des différences entre plantes. La fécondité et le taux d'éclosion chez les insectes élevés sur tournesol étaient plus élevés que ceux observés sur M. cordata, dont les résultats étaient aussi hétérogènes (P<0.1 et<0.05 respectivement). Les feuilles de M. cordata contenaient des taux relativement élevés de phénols et des rapports protéines sur phénols bas. Tout ceci suggère que les différences observées sont attribuables à des variations dans la qualité nutritive de ces hôtes et dans l'incorporation à la biomasse de l'insecte de matériaux phénologiques ingérés.

     

Role of photoperiod and temperature in the induction of overwintering pupal diapause in the spotted tentiform leafminer,Phyllonorycter blancardella

The role of photoperiod and temperature in the induction of overwintering diapause inPhyllonorycter blancardella (F.) (Lepidoptera: Gracillariidae) was examined in the laboratory and field using leafminers from commercial apple orchards in Ontario, Canada.P. blancardella exhibited a long-day response to photoperiod: long daylengths resulted in uninterrupted development whereas short daylengths induced diapause. The estimated critical photoperiod for diapause induction was L14.25∶D9.75. The larvae of leafminers destined to enter diapause took ca. 3× longer to complete development than the larvae of non-diapausing leafminers. The development prolonging effect of photoperiod decreased with decreasing daylength. Temperature modified the diapause inducing effect of photoperiod. At L14.25∶D9.75, diapause incidence was similar at 15 and 20°C but was lower at 25°C. Photoperiod also altered the normal relationship between development rate and temperature. At L14.25∶D9.75, the duration of larval development of diapausing leafminers was similar at 15, 20 and 25°C. Temperature alone is unlikely to have a role in the induction of diapause because leafminers exposed to natural late summer and fall temperature regimes and L16∶D8 did not enter diapause.     

Laboratory evaluation of the virulence of Beauveria bassiana isolates to the sorghum shoot borer Chilo partellus Swinhoe (Lepidoptera: Pyralidae) and their characterization by RAPD-PCR

Beauveria bassiana has long been used as a mycopesticide. It has a wide host range; isolates have been reported to differ in host range and virulence to a given insect species. Identification of a molecular marker linked to a virulent phenotype to a target pest would be useful in screening for isolates effective against it. Twenty B. bassiana isolates were tested for their virulence to the second instar larvae of Chilo partellus Swinhoe in laboratory bioassays and their DNA fingerprints were generated by RAPD-PCR. Three arbitrary categories of aggressiveness were chosen; isolates that caused >70%, between 70 and 40% and <40% larval mortality were grouped as highly, medium and less aggressive types, respectively. In the random amplified polymorphic DNA (RAPD) analysis a 30% variability was observed among the isolates; which clustered into three major groups. The groups based on virulence rating did not match with the RAPD clusters. One of the highly aggressive isolates clustered with less aggressive isolates in one cluster and the other grouped along with the medium aggressive isolates in a different cluster. The B. bassiana isolates were classified phenotypically based on the taxonomic order of the original insect host and the climatic zone (tropical/temperate) from which they were isolated. No correlation between the aggressiveness of the isolate and the relatedness of the original insect host to the tested insect was observed; both the highly aggressive isolates were from coleopteran insects. A correlation was found between the RAPD grouping and the phenotypic classification of the isolates. All the lepidopteran isolates grouped into one major cluster, most sub clusters were constituted by isolates from the same climatic zone.     

Covariance of adult size and development time in the parasitoid waspAphidius ervi in relation to the size of its host,Acyrthosiphon pisum

Summary Adult size (in terms of dry weight; DW) and development time (T _p ) of the solitary parasitoidAphidius ervi varied when reared in different nymphal instars of its host, apterous virginoparae of the pea aphid (Acyrthosiphon pisum). Parasitoid DW increased with an increase in the DW of the host at parasitization, from the first to the third aphid instar. Female wasps gained 1.1 times more in DW than their male counterparts in all four host classes, butT _p did not significantly differ between the sexes. Parasitoid DW was consistently more variable thanT _p . The two traits covaried positively with an increase in host size from the first to the third instar, but they varied independently in parasitoids from fourth-instar hosts. The host size (and stage) at the time of parasitization imposes constraints on the growth and development of immatureA. ervi that are reflected in the pattern of covariation between DW andT _p . When growing in aphids below a certain size threshold, parasitoids can maximize fitness by a trade-off between DW andT _p . Consequently, the assumption implicit in host-size models of parasitoid oviposition decisions — that females incur a relatively greater reduction in size (used as an index of fecundity) than males when developing in poor quality hosts — can be falsified.     

Sex pheromone of the female currant borer, Synanthedon tipuliformis: Identification and field evaluation

(E,Z)-2,13-octadecadien-1-ol acetate and (Z)-13-octadecen-1-ol acetate have been identified from the ovipositor extracts of the currant borer, Synanthedon tipuliformis (Clerck), by capillary GC, and the structures were verified by GC-MS. The diene/monoene ratio in the extract was found to be 93:7. Mixtures of these two compounds as well as the diene alone attracted conspecific males in the field.

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Zusammenfassung (E,Z)-2,13-Octadecadienylacetat und (Z)-13-Octadecenylacetat wurden in Ovipositor-Extrakten des Johannisbeerglasflüglers Synanthedon tipuliformis kapillar-gaschromatographisch nachgewiesen. Die Strukturen wurden mittels Gaschromatographisch-Massenspektrometrie bestätigt. Das Verhältnis Dien/Monoen im Extrakt betrug 93:7. Mischungen der beiden Komponenten wie auch (E,Z)-2,13-Octadecadienylacetat allein lockten im Freiland Männchen dieser Glasflüglerart an.

     

The role of glucosinolates and their hydrolysis products in oviposition and host-plant finding by cabbage webworm, Hellula undalis

The cabbage webworm, Hellula undalis (Fabricius) (Lepidoptera: Pyralidae), a tropical pest on crucifers (Brassicaceae), differentiated among host-plant species for oviposition in laboratory and field tests. White mustard, Sinapis alba (L.) var. Selinda, was the preferred host-plant, followed by Brassica juncea (L.) Czern. et. Coss var. Canadian brown mustard, and pak-choi, Brassica campestris L. ssp. chinensis var. Joi Choi, Black Behi and Bai Tsai. Glucosinolates (GS), secondary plant compounds characteristic to the Cruciferae plant family, and their breakdown products were analyzed by using HPLC and GC-MS-techniques. Species differed in GS composition and concentration. Content of GS was highest in S. alba with progressively lower contents detected in B. juncea and B. chinensis. The aromatic GS, 4-hydroxybenzyl-GS and benzyl-GS, were detected in S. alba. In B. juncea the alkenyl GS, allyl-GS, dominated, whereas in varieties of B. chinensis indolyl and alkenyl GS predominated. Oviposition of H. undalis females on the non-host-plant Vigna unguiculata ssp. sesquipedalis (L.) Fruwirth was stimulated by application of GS extracts from the crucifer species; the extract from S. alba was preferred, followed by extracts from B. juncea and B. chinensis. Hydrolysis of GS in the plant extract from B. chinensis causes loss of the oviposition stimulatory effect of the extract. Application of the GS, allyl-GS, and benzyl-GS also stimulated oviposition by H. undalis. Significantly more eggs were laid on leaves treated with the aromatic GS, benzyl-GS, than with the alkenyl GS, allyl-GS. Host-plant odor attracted H. undalis females but not males, in behavioral assays conducted in a Y-tube olfactometer. Low concentrations of the GS hydrolysis product, allyl-isothiocyanate, induced anemotaxis of females, but a high concentration of allyl-isothiocyanate was repellent. Oviposition by H. undalis females was not stimulated by host-plant volatiles. Females laid eggs on inserted traps and the walls of the Y-tube regardless of presence or absence of host-plant odor. The relevance of these results in the context of crucifer-insect interactions is discussed.     

Effect of artificial wetting and rainfall on the larval diapause of a stem borer, Busseola fusca in Western Kenya

Clarification of factors enabling diapause termination was carried out in a stem borer, Busseola fusca. Diapausing larvae very rarely pupated under dry conditions. Water apparently played a significant role in the termination of late diapause. During the late diapause period, larvae in the field were exposed to rains of the short rainy season. This precipitation, however, terminated diapause in only a few larvae, which indicate that termination requires sustained exposure to wet conditions that are not usually met during the short rains.

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Résumé Les causes de la fin de la diapause ont été précisées sur B. fusca. Les chenilles diapausantes se nymphosent très rarement en conditions sèches. L'eau joue apparement un rôle important dans la fin de la dernière phase de la diapause. Dans la nature, les chenilles sont exposées pendant cette période aux plues de la brève saison de pluies. Cependant, ces précipitations n'interrompent la diapause que d'un nombre limité de chenilles, ce qui montre que la fin de la diapause exige une exposition prolongée à des conditions humides que l'on ne rencontre pas généralement pendant la brève saison des pluies.