Sex pheromone components of the cabbage armyworm, Mamestra brassicae: Isolation, identification and field experiments

Glass capillary gaschromatography coupled to a mass spectrometer has shown that in addition to Z-11-hexadecenyl acetate, hexadecyl acetate and Z-11-heptadecenyl acetate are present in pheromone glands of calling virgin females of Mamestra brassicae L. (Lepidoptera: Noctuidae, Hadeninae). Electroantennography revealed positive responses for Z 11–17: Ac and 16: Ac, while behavioural tests were only positive for Z 11–17: Ac.

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Résumé Il a été procédé à l'identification des phéromones par chromatographie en phase gazeuse et par spectrographie de masse. Outre l'acétoxy-1 hexadécène-11Z, on identifié l'acétoxy-heptadécène-11Z et l'acétoxy-1-hexadécane dans les glandes des femelles vierges de M. brassicae. L'antennographie a montré des réactions positives à l'acétoxy-hepta-décène-11Z et à l'acétoxy-1-hexadécane, tandis que seul l'acétoxyhepta-décène-11Z provoque un comportement sexuel des mâles.

     

Calcium magnesium imbalance in clovers: A cause of negative yield response to liming

Three pot experiments, in which causes of negative yield responses to liming were investigated, are reported. The soil used, Waimumu silt loam (Fragiochrept), differed from others that have been reported to show negative yield response to liming, in that it is only moderately weathered and leached, only moderately acid and has previously shown positive yield responses to liming. Deficiencies of Zn and Mg were identified, but limed (pH 6.8) soils still showed a 40% yield depression even where all nutrients were supplied daily. Phosphorus availability was little affected by liming, and despite Mg and Zn addition, yields were depressed at high lime (pH 6.4) and high P while plants showed leaf symptoms of Mg deficiency. Neither plant nor soil analyses indicated low Mg levels but Ca: Mg ratios in soil were 22:1. When a pH range 5.2–6.1 was produced by liming with CaCO₃ and MgCO₃ at ratios between 100:0, and 50:50 on an equivalent basis, negative yield response was eliminated at Ca:Mg of 50:50. There was no evidence that Mg was fixed or rendered unavailable at the higher pH levels. A Ca induced Mg deficiency arising when exchangeable Ca:Mg>20 is suggested as the cause. The role of variable surface charge in converting soils that respond positively to lime to a negative response condition is discussed.     

ReleasingAmblyseius spp. [Acarina: Phytoseiidae] to controlThrips tabaci [Thysanoptera: Thripidae] on cabbage

Two species of predaceous mites,Amblyseius barkeri (Hughes) [=A. mckenziei Schuster & Pritchard] andA. cucumeris (Oudemans) [Acarina: Phytoseiidae] were evaluated as potential biological control agents forThrips tabaci Lindeman [Thysanoptera: Thripidae] on cabbage.A. barkeri colonized cabbage heads in preliminary trials. Field releases of different numbers of mites per plant during 1987 showed thatA. barkeri reduced the number of thrips in cabbage heads at harvest, and the reduction was proportional to the number of mites released, but thrips damage was unaffected. ReleasingA. cucumeris at different times during 1988, but releasing the same number of mites each time, we found that earlier releases resulted in fewer thrips and less damage at harvest; these relationships were not present, however, in plots treated with pyrethroid insecticides. We conclude that inoculative release ofAmblyseius spp. is a potentially useful thrips management strategy, but improvements in release timing and strategy will be required to provide commercially acceptable control.      

Reduction of insect pest attack on sorghum and cowpea by intercropping

Two experiments to establish the relationship between insect suppression by intercropping and grain yield in sorghum and cowpea were conducted under field conditions. Treatments consisted of monocrops and intercrops of sorghum and cowpea and an additional pair of monocultures and mixtures protected by insecticides. Intercropping reduced the numbers of stem borer,Chilo partellus in sorghum and thrips,Megalurothrips sjostedti in cowpea. In the monocropped, unprotected sorghum, yield was reduced by 28% compared to the protected monocrop, while reduction in the unprotected intercropped sorghum was 15% compared to the protected intercrop. Similarly, in the unprotected cowpea, monocrop yield was reduced by 94% and intercrop yield was reduced by 51%. Thus, there are yield advantages under conditions where intercropping reduces insect pest density. Intercropping can form a component of an integrated pest management programme.     

Effects of undersown clover on host-plant selection by Thrips tabaci adults in leek

The suppressive effects of undersown clover on Thrips tabaci Lindeman infestation in leek is known but not the stages in thrips population dynamics that are affected by intercropping and the mechanisms involved. Colonization or settling of adult onion thrips (T. tabaci) in monocropped leek (Allium porrum L.) and in leek intercropped with strawberry clover (Trifolium fragiferum L.) was studied in two potted plant experiments. Potted leek plants with and without undersown clover were placed for a short period (2 and 5 days) in monocropped or intercropped field plots when high thrips infestation was expected. Thrips adults were counted on all leaves and in the shaft during this observation period. Thrips populations were monitored weekly in the field plots throughout the entire growing season.In both potted plant experiments, there were consistently fewer thrips adults on intercropped leek plants than on monocropped plants. The plant growth parameters – number of leaves and stem diameter – were similar in all treatments and thus did not explain differences in thrips adults. Natural enemies were absent on both leek and clover, and thus cannot explain the differences in adult thrips numbers. Furthermore, no adults of T. tabaci were found on the clover in the potted plant experiment and only very few in the field experiment. Thus it was concluded that strawberry clover was not an effective trap crop for thrips.In the second potted plant experiment, clover was removed just before the leek plants were introduced to the field, thus eliminating direct physical, visual and olfactory interference by clover. After the undersown clover was removed, the leek plants harboured only one-third of the number of thrips adults, as compared to the monocropped plants. This study supports the notion that there are subtle links between intercropping and plant quality, and indicates that host-plant quality is an underlying cause of the reduction in adult thrips numbers in leek/clover intercropping.     

The courtship behavior of the cabbage moth,Mamestra brassicae (Lepidoptera: Noctuidae), and the role of male hair-pencils

The courtship behavior of the cabbage moth, Mamestra brassicae(L.), was studied in moving air conditions in a wind tunnel, using video techniques. Quantitative analyses were undertaken to determine the behavioral sequence occurring in the courtship. Comparison of successful and unsuccessful courtship suggested that courtship success was more dependent on the behavior of the female than that of the male. In an attempt to elucidate the function of the male hair-pencils (HPs), courtships involving males without HPs were also studied. HP removal did not affect the overall courtship success rate of males, but detailed analysis showed significant changes infernale behavior during such courtships. HP removal also affected female behavior following pair formation, with females struggling more when paired with males without HPs. Consequently, it is proposed that the HP volatiles act as an arrestant for the female, both during courtship and after pair formation, to increase female acceptance and to prevent premature termination of copulation. Experiments were also conducted to test previous hypotheses for HP function. However, no evidence was found to suggest that the HP volatiles in M. brassicaeact to attract females, affect female calling behavior, or affect the behavior of other males. A further possible function of HPs in defense is discussed.     

Effect of trap background on cabbage root fly landing and capture

Pieces (600 mm × 800 mm) of coloured board, plastic sheeting and woven materials, place beneath water traps prevented the traps from becoming soiled during rainy weather. Such backgrounds are not recommended for use with traps for monitoring populations of the cabbage root fly (Delia radicum L. — Diptera: Anthomyiidae), however, as, instead of increasing trap catch they reduced the numbers of female flies caught by 70%–90%. The main effect was that the visually attractive stimuli from the introduced backgrounds competed with those from the trap. A white background competed with a white trap on a direct fly/unit area basis. Green backgrounds stimulated males to land and the vertical stems of both real and artificial grass induced trivial flights that resulted in greater numbers of males entering traps resting on short grass. Most females were caught over bare soil. To minimize the variation in catch between traps used for monitoring cabbage root fly populations, the background beneath each trap should be similar. For maximum capture, the background should be of grass for male flies and of bare soil for female flies. Care is required if data from traps within mulched crops are used to make pest control decisions, as they will underestimate considerably the numbers of flies in such crops.     

Modified Behavior in Baculovirus-Infected Lepidopteran Larvae and Its Impact on the Spatial Distribution of Inoculum

Quantifying the rate of dispersal of target insects when infected with a disease agent will aid the development of biorational pest control programs. The effect of nucleopolyhedrovirus (NPV) infection on the mobility of second and fourth instarMamestra brassicaelarvae was investigated in the laboratory and field. NPV infection altered larval mobility, with the changes in behavior varying with the timecourse of infection. Diseased larvae moved three to five times further than healthy ones during the middle stages of infection. By the 7th day postinfection diseased larvae were less mobile than healthy counterparts. The same pattern of modified behavior was observed in both instars. Fourth instar larvae moved further than second instars under laboratory and field conditions. In the field, infected larvae tended to die on the apex of the cabbage leaves. Bioassay of the leaves showed a linear decrease in inoculum from central to peripheral plants within the plots, which occurred to the same extent for second and fourth instars. Leaves from plots where infected fourth instar larvae had been introduced had higher inoculum density than those from plots with second instars.     

Effect of beetle size on predation of cabbage root fly eggs by ground beetles

Laboratory studies were done to determine the numbers of cabbage root fly (Delia radicum L.) (Diptera: Anthomyiidae) eggs eaten by sixty species of ground beetles (Coleoptera: Carabidae) collected from a range of habitats. For 35 species that were between 2.7 mm and 10 mm long, there was a linear relationship between the numbers of eggs eaten and beetle length. For each 1 mm increase in length above 2.7 mm, an additional 18 eggs were eaten/beetle/day. Eight further species within the above size range did not eat any fly eggs, as these species are known to be either phytophagous or to feed on moving prey. Large numbers of eggs were eaten by beetles in 13 of the 25 genera tested. Based on size, maximum numbers of eggs were eaten by 7 species of Agonum Bonelli, 5 species of Amara Bonelli and seven species of Bembidion Latreille. Only one of the 6 species of Pterostichus Bonelli tested, P. strenuus (Panz.), ate the expected numbers of eggs, the other species being too large to feed from such small prey items as cabbage root fly eggs. The numbers of beetles larger than 10 mm that ate eggs was highly variable and so 10 mm was considered the upper size limit of carabid predators of cabbage root fly eggs.     

Laboratory studies on aestivation in the cabbage root fly (Delia radicum)

Laboratory experiments at 16°–30°C showed that the cabbage root fly can only be induced into aestivation during the early part of the pupal stage. The relationship between the percentage of pupae entering aestivation (y) and the average daily temperature (T) was the same under both constant and alternating temperatures. The percentage of pupae entering aestivation at a particular temperature was given by y=13T–255. An additional 13% of the pupae entered aestivation for each degree rise between 20° and 27°C. There was no constant period of arrested development following the induction of aestivation. Aestivating pupae started to develop into flies as soon as the temperature fell below 20°C. The reinduction of aestivation occurred more readily than the initial induction. Insect survival was not reduced after a month of aestivation. The effects of aestivation on forecasting the time of the second (summer) generation of flies are discussed.

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Étude au laboratoire de l'estivation de la mouche du Chou (Delia radicum)

Résumé Au laboratoire, à 10°–30°C, l'induction de l'estivation ne peut être obtenue qu'avec des pupes formées depuis peu.Le rapport pourcentage de pupes entrant en estivation (y) température journalière moyenne (T) a été le même, que la température soit constante ou alternée. La relation entre la température et ce pourcentage est donnée par y=13 T–255. Le pourcentage de pupes entrant en estivation a augmenté de 13% pour chaque élévation d'un degré entre 20° et 27°C. L'estivation une fois induite, la période d'arrêt de développement n'est pas constante. Dès que la température est devenue inférieure à 20°C, la formation d'imagos a commencé dans les pupes en estivation. Une nouvelle estivation a été plus facile à provoquer que l'estivation initiale. Le taux de survie des insectes n'avait pas diminué après un mois d'estivation. La discussion examine l'utilisation des conséquences de l'estivation dans la prédiction de la seconde génération d'adultes: génération d'été.

     

Recycling of entomopathogenic nematodes in Delia radicum and in other insects from cruciferous crops

Larvae of Deliaradicum Linnaeus (Diptera: Anthomyiidae) wereexposed to Steinernema feltiae Filipjev(Rhabditida) to study the ability of thenematodes to fulfill their life cycle (recycle)in this host. In addition, the recycling ofSteinernema and Heterorhabditis(Rhabditida) species was studied in larvae ofthe following insects: Meligethes spp.Stephens (Coleoptera: Nitidulidae),Dasyneura brassicae Winnertz (Diptera:Cecidomyidae), Ceutorrhynchus assimilisPaykull, C. pallidactylus Marsham (Coleoptera: Curculionidae) and Mamestrabrassicae Linnaeus (Lepidoptera: Noctuidae).All larval instars of D. radicum werestudied (larvae live and pupate in soil)whereas the final instars of the remaininginsects were studied (larvae only pupate in soil).On average, the following numbers of infectivejuveniles were produced in the different hosts:1,200–1,400 in C. assimilis; 700–1,300 inMeligethes spp. and 47,000 in M.brassicae. In D. radicum, around 400infective juveniles were produced on average inthe smallest larvae and around 3,500 in thelargest larvae. The highest number of nematodesrecorded in a D. radicum larva (thirdinstar) was 9,500 infective juveniles. Thenumber of nematodes produced in D.radicum cadavers was positively related to thesize of the insect host, but large variationwas observed.     

Physical and chemical factors influencing landing and oviposition by the cabbage root fly on host-plant models

Various plant models were used in both choice and no-choice tests in the laboratory to assess landing and oviposition preferences of the cabbage root fly,Delia radicum (L.). The main factor governing the site most suitable for landing was the conspicuousness of the object and not its shape. Oviposition was influenced considerably by the pre-conditioning of the females. Deprived females laid eggs even when denied access to both host plant chemicals and host-plant models. The dominant role of contact chemical stimuli in host acceptance was reconfirmed, but only a combination of physical and chemical stimuli appeared capable of eliciting normal oviposition. The combination of contact chemical stimuli and the presence of a stem on the test model had a synergistic effect on the numbers of eggs laid in both choice and no-choice situations. In choice bioassays, female cabbage root flies distinguished between models of different shapes, heights and sizes. The size and shape of the models appeared to be perceived in part after the flies had landed.     

The effect of colour of the substrate on the landing and oviposition behaviour of the cabbage root fly

Field and laboratory experiments were made in order to understand the relation between the spectral characteristic of a substrate and its attractiveness for Delia radicum (L.) (Diptera: Anthomyiidae) flies to land or oviposit. Landing females preferred substrates with high reflectance of green and particularly of yellow wavelengths, but substrates with a high proportion of the blue and green reflectance simultaneously (light blue and white) were also very attractive. Unattractive substrates had either low reflectance across the whole insect-visible spectrum (dark blue) or increased reflectance only in orange or red region of the spectrum (red) or a large proportion of UV reflectance (aluminium). Landing males were most attracted to the substrates with the highest total reflection. Oviposition attractiveness of a substrate grew with an increase in the proportion of reflectance in the blue and a decrease in the green regions of the spectrum. In addition, the oviposition attractiveness increased with increasing total reflection and contrast with the background, and decreased with a high proportion of UV reflectance.     

Characterization of cell clusters in larval hemolymph of the cabbage armyworm Mamestra brassicae and their role in maintenance of hemocyte populations

Maintenance of hemocyte populations is critical for both development and immune responses. In insects, the maintenance of hemocyte populations is regulated by mitotic division of circulating hemocytes and by discharge from hematopoietic organs. We found cell clusters in the hemolymph of Mamestra brassicae larvae that are composed of small, spherical cells. Microscopic observations revealed that the cells in these clusters are similar to immature or precursor cells present in hematopoietic organs. The results of bromodeoxyuridine (BrdU) incorporation experiments demonstrate that these cells are mitotically active. Furthermore, these cells maintain their immature state and proliferate until late in the last larval instar. The results of in vitro experiments showed that most of the cells changed their morphology to one consistent with plasmatocytes or granulocytes, and that the change was promoted by addition of larval hemolymph to the culture medium, in particular when hemolymph was collected at a prepupal stage. Taken together, our results suggested that cells in clusters may be an additional source of hemocytes during larval development.     

Molecular cloning and functional expression of chitinase-encoding cDNA from the cabbage moth, Mamestra brassicae

Chitinase is a rate-limiting and endo-splitting enzyme involved in the bio-degradation of chitin, an important component of the cuticular exoskeleton and peritrophic matrix in insects. We isolated a cDNA-encoding chitinase from the last larval integument of the cabbage moth, Mamestra brassicae (Lepidoptera; Noctuidae), cloned the ORF cDNA into E. coli to confirm its functionality, and analyzed the deduced amino acid sequence in comparison with previously described lepidopteran chitinases. M. brassicae chitinase expressed in the transformed E. coli cells with the chitinase-encoding cDNA enhanced cell proliferation to about 1.6 times of the untransformed wild type strain in a colloidal chitin-including medium with only a very limited amount of other nutrients. Compared with the wild type strain, the intracellular levels of chitin degradation derivatives, glucosamine and N-acetylglucosamine were about 7.2 and 2.3 times higher, respectively, while the extracellular chitinase activity was about 2.2 times higher in the transformed strain. The ORF of M. brassicae chitinaseencoding cDNA consisted of 1686 nucleotides (562 amino acid residues) except for the stop codon, and its deduced amino acid composition revealed a calculated molecular weight of 62.7 and theoretical pI of 5.3. The ORF was composed of N-terminal leading signal peptide (AA 1-20), catalytic domain (AA 21-392), linker region (AA 393-498), and C-terminal chitin-binding domain (AA 499-562) showing its characteristic structure as a molting fluid chitinase. In phylogenetic analysis, the enzymes from 6 noctuid species were grouped together, separately from a group of 3 bombycid and 1 tortricid enzymes, corresponding to their taxonomic relationships at both the family and genus levels.     

Insect-crop interactions in a diversified cropping system: parasitism by Aleochara bilineata and Trybliographa rapae of the cabbage root fly, Delia radicum, on cabbage in the presence of white clover

Parasitism of the cabbage root fly, Delia radicum (L.) by the staphylinid Aleochara bilineata Gyllenhal and the cynipid Trybliographa rapae Westwood was examined in a cabbage monoculture and a mixed stand of cabbage undersown with white clover. Number of overwintering cabbage root fly pupae per plant was consistently reduced in the mixed stand, and the incidence of plants attacked by cabbage root fly was either reduced or not different in the mixed stand compared to cabbage monoculture. For both parasitoids, the probability of D. radicum attacked plants having at least one parasitized pupa increased with density of cabbage root fly pupae around the plant. For A. bilineata, this positive relation between presence of parasitism and host density was consistently stronger in cabbage monoculture than in cabbage undersown with clover. Location of a host plant by T. rapae was not consistently affected by the presence of clover. D. radicum attacked plants situated in the cabbage and clover mixture were found by T. rapae as easily as in cabbage monoculture. Overall, the total risk of parasitism for a cabbage root fly pupa by A. bilineata was reduced in the mixed stand compared to the cabbage monoculture, whereas the risk of parasitism by T. rapae was not consistently affected by clover. For both parasitoids, intensity of parasitism showed a variable relationship with host density on individual plants attacked by the cabbage root fly. Overall, in spite of consistently lower total density of pupae in the mixed cabbage—clover than in cabbage monoculture, the density of unparasitized pupae was reduced by the presence of non-host plants only in two of the four experiments. The results emphasize the need to include not only herbivore and crop, but also other plant species as well as natural enemies when evaluating management methods.     

Effects of nitrogen and foliar biomass on population parameters of cabbage insects

The effects of different nitrogen (N) fertilization rates (0, 45, 90, and 168 kg N/ha), plant nitrogen concentration, and plant biomass on abundance and population growth of diamondback moth, Plutella xylostella (L.), cabbage looper, Trichoplusia ni (Hübner), cabbage budworm, Hellula phidilealis (Walker), imported cabbageworm, Artogeia rapae (L.), and cross-striped cabbageworm, Evergestis rimosalis (Guenée), were investigated in Homestead and Sanford, Florida in 1987. The effects of these factors on the parasitization of P. xylostella were also examined. In Homestead, abundance of most insect pests and parasitized P. xylostella increased with an increase in the level of N applied and with an increase in plant biomass. Similar results were found in Sanford, although results were not consistently significant. Abundance of most insect pests was significantly positively correlated with plant N concentration. Multiple regression analyses indicated that foliar biomass was significantly more important than N fertilization rate and subsequent plant N concentration at predicting abundance of insect pests and parasitized P. xylostella on cabbage.     

甘蔗—大豆间作对大豆鲜荚产量和农艺性状的影响

为探讨甘蔗-大豆间作模式对大豆鲜荚产量和农艺性状的影响,于2009—2011年连续3年在广州市华南农业大学农场进行大田试验,试验设置2种施氮水平(常规施氮(525kg·hm-2)和减量施氮(300kg·hm-2))和3种种植模式(甘蔗-大豆(1∶1)、甘蔗-大豆(1∶2)、单作大豆)。结果表明:甘蔗-大豆间作(1∶2)模式下,2009年减量施氮水平的大豆鲜荚产量较常规施氮水平提高了33%,2010和2011年不同施氮水平间均无显著差异;甘蔗-大豆间作模式对大豆的单株鲜荚重、多粒荚数和百粒鲜重无显著影响;大豆单株鲜荚重与多粒荚数在不同种植模式下均呈显著相关(P<0.05),在常规施氮间作模式下与大豆单株荚数呈显著相关(P<0.05)。甘蔗-大豆间作没有降低大豆的单株鲜荚产量,也没有对大豆的农艺性状产生负面影响,从增产增收、提高土地生产力来考虑,减量施氮模式下甘蔗-大豆间作具有一定的可行性。     

瓜套棉田烟粉虱与棉蚜种群动态及竞争干扰行为研究

【目的】甜瓜和棉花均是棉蚜及烟粉虱的适宜寄主,瓜套棉种植模式为2种害虫混合危害提供了条件,该模式下哪种害虫具有竞争优势值得探讨。【方法】通过田间定点调查和室内行为学观察,研究了吐鲁番地区瓜套棉种植模式下棉蚜和烟粉虱的发生动态及竞争干扰。【结果】田间观察分别于2011和2012年进行,在瓜套棉种植模式棉花、甜瓜上,棉蚜的发生期较烟粉虱早,但随着烟粉虱田间种群数量增加,对棉蚜产生明显的干扰和竞争作用,8月下旬至9月上旬烟粉虱成为田间优势种群。室内行为观察表明,2种害虫共存状态下均表现出以烟粉虱为优势的竞争作用,主要行为表现为通过触角、足的驱赶行为和进入棉蚜活动区域干扰等。当虫量低于4头·皿~(-1)时,无论棉蚜和烟粉虱哪种昆虫先接入,相互间的影响和干扰都很少。当2种昆虫数量均增加到8头·皿~(-1)时,烟粉虱成虫以触角、足等干扰棉蚜的行为频次显著增多。不同的定殖时间下,无论棉蚜和烟粉虱哪种昆虫先接入,随着定殖时间的延长,烟粉虱通过触角、足以及进入棉蚜活动区域驱逐和干扰棉蚜的行为都呈递减的趋势。【结论】在瓜套棉种植模式下,烟粉虱较棉蚜具有显著的竞争优势。