Effects of water stress, nitrogen stress and certain sensory stimuli on infestation and damage by Chilo partellus (Swinhoe) to maize

Foliar, stalk and dead heart damage caused by Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae) to several maize genotypes (Inbred A, MBR 8637, Poza Rica 7832, ER-29SVR, Across 7844, Bulk CG 4141, MMV 600 and ICZ2-CM) subjected to water stress were significantly lower than those observed when plants were grown in the absence of water stress. Resistance of maize genotypes to C. partellus was distinguished clearly when there was no water stress to the plants. Resistance/susceptibility of maize genotypes Inbred A, MMV 400, MBR 8637 and Poza Rica 7832 to C. partellus was the same at 0, 60, 90 and 120 kg of N per hectare. At each nitrogen level, the genotypes MMV 400, MBR 8637 and Poza Rica 7832 suffered significantly lower damage than the susceptible Inbred A. The humidity stimuli from maize plants and the olfactory/hygro stimuli from the plants infested with larvae were the most important factors affecting host plant selection by ovipositing C. partellus females.     

Plant-odour-specific receptor neurones on the antennae of female and male Spodoptera littoralis

Abstract. Receptor neurones with high selectivity and sensitivity to plant odours were found within short sensilla trichodea on the antenna of both female and male Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) by using single-sensillum recording techniques. In 112 sensilla from females and forty-one from males, twenty-four different receptor neurone types were characterized according to their specificity. Altogether, twenty-six plant and three sex pheromone compounds were tested. Receptor neurones responding with high specificity to flower odours, green leaf volatiles, oviposition deterrents and other general host plant odours were identified. In twenty-one receptor neurone types, responses were elicited by one or several plant compounds, and in three types responses were elicited by sex pheromone compounds. The majority of the receptor neurones responded to only one or two of the tested compounds. In general, only one of the two receptor neurones in a sensillum responded to any of the compounds tested. An exception was a receptor neurone responding to plant odours (green leaf volatiles) and another receptor neurone responding to a sex pheromone compound ([Z]-7-dodecenyl (acetate), which occurred in the same sensillum. The majority of the receptor neurones displayed a high sensitivity to plant odours. No morphological difference was identified the different sensillum types.     

Responses of the stem borer larval endoparasitoid Cotesia flavipes (Hymenoptera: Braconidae) to plant derived synomones: Laboratory and field cage experiments

Laboratory and field cage experiments investigated the response of females of the stem borer larval endoparasitoid Cotesia flavipes to two synthetic synomone components, the terpenoid (E)-β-farnesene and the green leaf volatile, (Z)-3-hexenyl acetate, both compounds identified previously in headspace volatiles of maize plants damaged by stem borer (Chilo partellus). In dose response tests performed in a Y-tube olfactometer, parasitoids were significantly more attracted to the arms bearing 10 or 15 µg of (Z)-3-hexenyl acetate and (E)-β-farnesene than to the control arm. (E)-β-Farnesene was as attractive as the essential oil from the plant Hemizygia petiolata (Lamiaceae) rich in the same compound (80% relative amount). The plant essential oil elicited responses from females of the parasitoid comparable to those elicited by two positive controls, stem borer larval frass and adult parasitoid diet (20% honey solution), tested in the laboratory assays. In field cage trapping experiments, captures in traps baited with the terpenoid, the plant essential oil, (Z)-3-hexenyl acetate and the control of 20% honey solution, were not significantly different relative to captures in unbaited traps. Addition of the green leaf volatile (Z)-3-hexenyl acetate to the plant essential oil to yield a 1:1 two-component blend captured significantly more female parasitoids than traps baited with either of the two components alone. The results show that blends of green leaf volatiles and sesquiterpenoids may have potential in monitoring C. flavipes populations in the field.     

Electrophysiological response to herbivore-induced host plant volatiles in the moth Spodoptera littoralis

In cotton, Gossypium hirsutum (Malvacae), the volatiles emitted from the plant change in response to herbivory. Ovipositing females of the Egyptian cotton leaf worm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) can discriminate between cotton plants subjected to larval feeding and undamaged plants during oviposition. In this study we investigate whether females of this moth can detect the herbivore-induced cotton volatiles. The response of female S. littoralis antennae to volatiles collected from cotton plants subjected to larval feeding was studied using GC-EAD (coupled gas chromatography electroantennographic-detection). By GC-EAD, responses to over 10 different cotton volatiles were observed. Using single sensillum technique the responses of short sensilla trichodea on the antennae of S. littoralis females to 19 cotton volatiles and 12 general plant volatiles were investigated. Responses to these volatiles were recorded from 108 receptor neurones. Several neurones activated by herbivore-induced cotton volatiles were recorded. For example, a neurone type responding to two homoterpenes [(E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene and (E)-4,8-dimethyl-1,3,7-nonatriene] and (E,E)-α-farnesene was frequently found. We also observed sensitive neurones responding specifically to the herbivore-induced volatiles (+/–)-linalool and indole. In general, a stimulus load of less than 1 ng was needed to activate these neurones. In addition, specific neurones were found for constitutive cotton volatiles released in connection with damage to the plant. An abundant neurone type responded to β-caryophyllene and α-humulene. Another neurone type responded specifically to the non-induced cotton volatile (Z)-jasmone. These results show that females of S. littoralis have receptor neurones that would make it possible to discriminate between damaged and undamaged plants using volatile signals.     

The analysis of flight paths of male Egyptian cotton leafworm moths, Spodoptera littoralis, to a sex pheromone source in the field

ABSTRACT. The flight of male Spodoptera littoralis (Boisd.) (Noctuidae) towards a pheromone source was recorded during the early part of the night using a cine camera and an image intensifier. The cine films were analysed frame by frame to produce flight tracks from which it was possible to calculate the mean advance rate of moths towards the pheromone source and their projected ground speed, for a series of positions downwind of the source. As wind speed was measured the moth's air speed was also estimated. The moths compensated for changes in wind speed by varying their air speed, hence maintaining a ground speed independent of wind speed. The ground speed itself was found to decrease as moths flew closer to the pheromone source.     

Large-scale releases of Trichogramma ostriniae to suppress Ostrinia nubilalis in commercially grown processing and fresh market sweet corn

Abstract:  We evaluated the egg parasitoid Trichogramma ostriniae (Pang et Chen) (Hym.: Trichogrammatidae) for control of European corn borer [Lep.:Crambidae: Ostrinia nubilalis (Hübner)] in fields of commercial processing sweet corn in New York in 2002 and 2003. We made inoculative releases of 75 000 T. ostriniae /ha when corn was at mid-whorl and regional O. nubilalis activity had begun. Each release field was paired with a similar non-release control. The incidence of egg mass parasitism, number of stalk tunnels, incidence of ear damage and effect on insecticide spray decisions were evaluated. Parasitism of cumulative number of O. nubilalis egg masses was 51.3 ± 7.2% and 43.5 ± 5.7% (mean ± SEM) in release fields in 2002 and 2003 respectively. The incidence of ear damage by O. nubilalis was not affected by T. ostriniae in either year of the study. There was no difference in stalk damage between release fields and control fields in either 2002 or 2003. However, individual comparisons between paired release and control fields showed reduced stalk tunnelling in 10 of 19 fields, but ear damage was reduced in only two of 19 fields. Neither the number of actual insecticide sprays nor the number of decisions to spray based on sequential sampling were affected significantly by releasing T. ostriniae . In a separate but related study, where releases were conducted in commercial fresh market sweet corn and used higher rates of release, T. ostriniae had no effect on the number of insecticidal sprays. In an additional experiment using small plots of sweet corn, ear damage was similar whether plots were treated with T. Ostriniae or with insecticide. Additional research should focus on improving the timing, frequency and rate of releases.     

Identification of Mythmna separata-induced maize volatile synomones that attract the parasitoid Campoletis chlorideae

Abstract:  Campoletis chlorideae Uchida (Hym., Ichneumonidae) is an important solitary koinobiont larval endoparasitoid of many noctuid species including Mythmna separata (Lep., Noctuidae). In the present study, maize volatiles induced by feeding damage of M. separata were found to be attractive to C. chlorideae in a Y-tube olfactometer. Eleven compounds were released in significant amounts from M. separata -infested maize seedlings, of which five compounds, ( Z )-3-hexen-1-ol, ( Z )-3-hexenyl acetate, ( E )-2-hexenal, linalool and phenylethyl acetate were chosen for electrophysiological and behavioural tests. All five compounds elicited electroantennogram responses in C. chlorideae . However, only pure ( Z )-3-hexenyl acetate and linalool were attractive to the parasitoid in the Y-tube. Interestingly, linalool was also attractive to starved parasitoids over a range of doses tested. These results suggested that ( Z )-3-hexenyl acetate and linalool may be key infochemicals in the host-foraging behaviour of C. chlorideae , and linalool may act as a food-source signal for the parasitoid.     

Influence of genotype and texture on zein content in endosperm of maize grains

The effect of genotypes and texture on the content of proteins in maize grains was examined by assessing absolute amounts of six protein fractions in the whole endosperms of four wild‐type lines with high protein content and four quality protein maize (QPM) varieties and for hand‐dissected hard and soft endosperm regions from eight other lines. As previously reported for six wild‐type lines and their opaque‐2(o2) versions, zeins were predominant for all genetic backgrounds and all types of endosperms. From these data and others the amounts of zeins and true proteins (crude proteins free of non‐protein nitrogen) in developing and mature endosperms of wild‐type lines were correlated. The data points for zeins from hard endosperms lay between the regression line and the upper limit of confidence area. Those for zeins from soft endosperms were located at the lower part of confidence area and on a level with the points corresponding to the most immature endosperms. Furthermore, some data points for zeins from o2 and QPM samples lay near the lower limit while the others were outside the confidence area. This suggested an initial zein accumulation dependent on the genotype at a low relative rate, followed by an accumulation at higher rate. The conditions used for isolating and quantitating zeins are discussed.