Effects of plant density on the survival rate of cabbage pests

The population density of herbivores depends on the spatial scale as well as the temporal scale. In a small-scale, short-term experiment, the number of individuals entering from the surrounding area will be most influential in determining the herbivore density. In large-scale, long-term experiments, however, the density of herbivores will rather be influenced by the survival rate of individuals inside the field because most of the herbivorous population derives from the parents that developed inside the field. If we want to predict the large-scale long-term density of herbivores, therefore, emphasis should be placed on the estimation of survival rate. To elucidate the effects of plant density on the large-scale long-term abundance of cabbage pests, we examined the survival rates of three lepidopterous pests, the small white butterfly Pieris rapae crucivora Boisduval (Pieridae), the beet semi-looper Autographa nigrisigna (Walker) (Noctuidae), and the diamondback moth Plutella xylostella (Linnaeus) (Yponomeutidae) under two levels of plant spacing (sparse plot, 2 m × 2 m interval; dense plot, 0.5 m × 0.5 m interval). The experiment with four blocks was repeated in two seasons. The number of eggs per plant was larger in the sparse plots than in the dense plots for all species. The survival rate of eggs and larvae, on the contrary, was lower in the sparse plots than in the dense plots. The lower survival rate of eggs in the sparse plots was mainly caused by the density dependency, while the lower survival rate of larvae in the sparse plots was mainly caused by the direct effects of plant density. It was thus suggested that the density of herbivores may become lower in the sparsely planted field in the long run because of the higher mortality of larvae. Received: September 16, 1998 / Accepted: March 22, 1999     

Influence of parental density on the distribution pattern of eggs in the common cabbage butterfly,Pieris rapae crucivora

To investigate the relation between the distribution pattern of eggs and the parental density in the common cabbage butterfly, Pieris rapae crucivora, the countings of egg number per plant were made on both cabbage plants cultivated in the farm and planted in the net house in which the female butterflies were released at various densities. The frequency distribution of eggs fits well to the negative binomial excepting the cases where they agree withPoisson series, and the degree of aggregation expressed as the reciprocal of the parameter, 1/k, tends to decrease as the egg or parental density increases. At the same parental density, however, the distribution of eggs can be described by the negative binomial with a common parameter, k_c, regardless of the difference in the density of laid eggs. In the case where a single female butterfly lays eggs, the spatial pattern of egg distribution is always lean, while its frequencies conform toPoisson or the negative binomial series. This lean changes toward patchy with increasing the parental density. From these results, it is concluded that the degree of aggregation in the distribution of eggs decreases with the increase of the parental density.     

Heritability estimates of life history traits in small white butterflyPieris rapae crucivora

Heritabilities and genetic correlations of life history characters (pupal weight, age-specific fecundities, and egg weight) of small white butterfly Pieris rapae crucivora are estimated by a quantitative genetic method (sib analysis). The results indicate moderate or high heritabilities and a largely negative genetic correaltion in age-specific fecundities.     

Antifeedant Activity toward Larvae of Pieris rapae crucivora of Aromatic Carbonyl Compounds Related to Capillin Isolated from Artemisia capillaris

The antifeedant activity toward larvae of Pieris rapae crucivora of aromatic carbonyl compounds was studied. When an H atom of aldehyde group of aromatic aldehydes was replaced by a CH₃ group, it was observed that arylmethylketones were more active toward larvae than aromatic aldehydes.     

Process generating the ditribution pattern of eggs of the common cabbage butterfly,Pieris rapae crucivora

The process generating the negative binomial in the distribution pattern of eggs of the common cabbage butterfly, Pieris rapae crucivora, was investigated by releasing the female adults in a net house where cabbages were planted. The distribution of butterflies visited and laid an egg or more per plant followed thePoisson series under the uniform light condition, while that of eggs laid per visit conformed to the logarithmic distribution. From these results, it may be concluded that the negative binomial arises from compounding of thePoisson and the logarithmic distribution. The observed frequency of eggs found per plant fitted to the negative binomial with parameter thus computed theoretically. The change in the degree of aggregation with the increase of the parental density was considered in connection with the above results.     

Estimation of the individual number entering each development stage in an insect population

A method for estimating the number entering each development stage from data obtained by regular sampling through one generation of an insect population was described. This method is consisted of the following two procedures: The provisional estimates are calculated on the assumption that each stage has a common mortality in a sampling interval. Then these estimates are corrected on another assumption that the mortality is different in each stage but constant during a stage. The result of testing its validity with two laboratory populations of the common cabbage butterfly, Pieris rapae crucivora, showed the availability of the present method.     

Response of the wasp (<Emphasis Type="Italic">Cotesia glomerata</Emphasis>) to larvae of the large white butterfly (<Emphasis Type="Italic">Pieris brassicae</Emphasis>)

The large white butterfly (Pieris brassicae L) first invaded northernmost Japan from Siberia around 1994, and after a few years, began to expand its range. The wasp, Cotesia glomerata (L) parasitizes larvae of the small white butterfly (Pieris rapae crucivora Boisduval), a usual host in the same geographic area. Some Pieris brassicae larvae in Hokkaido have been parasitized by Cotesia glomerata, but the parasitism rate of Pieris brassicae larvae tends to be lower than that of Pieris rapae. To examine the process of parasitizing Pieris brassicae larvae, we observed how the parasitoid wasp responded to the host larvae on damaged leaves. Cotesia glomerata females tended to avoid Pieris brassicae larvae, and even when female wasps inserted their ovipositors into Pieris brassicae larvae, none laid eggs. The parasitoids obtained from Pieris rapae larvae failed to parasitize Pieris brassicae during the host-acceptance step.     

Effect of patch size and plant density of Paterson"s curse (Echium plantagineum) on the oviposition of a specialist weevil, Mogulones larvatus

This study examines the oviposition response of a specialist weevil (Mogulones larvatus) to patches of its host, the noxious weed Paterson"s curse/salvation Jane (Echium plantagineum). We simultaneously examined the effect of patch size and plant density (and their interaction), on the recorded oviposition patterns. Our results show that oviposition first occurred on the largest patches with the highest number of plants. However, there was no significant effect of patch size or number of plants per patch at the end of the experiment. At this time the level of attack per plant was negatively correlated with plant density. This negative effect of density on the level of oviposition was not mediated by a reduction in plant size at higher densities. The pattern observed may indicate a risk-spreading strategy by females. Received: 15 July 1999 / Accepted: 14 April 2000     

Avoidance of maladaptive,precocious copulation in the cabbage white butterfly,Pieris rapae crucivora

In the cabbage white butterfly, Pieris rapae crucivora, copulation hinders normal expansion and hardening of the wings of newly emerged females. The resulting permanent wing deformation makes it impossible for females to fly and therefore, to find an oviposition site and nectar sources. An attempt was made to clarify whether the newly emerged female butterfly avoids copulation. Observation of wing expansion and hardening reveals that the wings are fully expanded and hard by 20–30 min after emergence. In the field, presentation of females with soft wings to males shows that males will attempt to copulate with these females. However, newly emerged females prevent successful completion of copulation by assuming the mate refusal posture, and thereby avoid a potentially maladaptive copulation. The discussion focusses on the question as to why females and not males avoid early copulation.     

Inhibition of lipoxygenase affects induction of both direct and indirect plant defences against herbivorous insects

Herbivore-induced plant defences influence the behaviour of insects associated with the plant. For biting–chewing herbivores the octadecanoid signal-transduction pathway has been suggested to play a key role in induced plant defence. To test this hypothesis in our plant—herbivore—parasitoid tritrophic system, we used phenidone, an inhibitor of the enzyme lipoxygenase (LOX), that catalyses the initial step in the octadecanoid pathway. Phenidone treatment of Brussels sprouts plants reduced the accumulation of internal signalling compounds in the octadecanoid pathway downstream of the step catalysed by LOX, i.e. 12-oxo-phytodienoic acid (OPDA) and jasmonic acid. The attraction of Cotesia glomerata parasitoids to host-infested plants was significantly reduced by phenidone treatment. The three herbivores investigated, i.e. the specialists Plutella xylostella, Pieris brassicae and Pieris rapae, showed different oviposition preferences for intact and infested plants, and for two species their preference for either intact or infested plants was shown to be LOX dependent. Our results show that phenidone inhibits the LOX-dependent defence response of the plant and that this inhibition can influence the behaviour of members of the associated insect community.     

Geographic expansion of the cabbage butterfly (Pieris rapae) and the evolution of highly UV‐reflecting females

Abstract Reflection of ultraviolet (UV) light by the wings of the female Eurasian cabbage butterfly, Pieris rapae, shows a large geographic variation. The wings of the female of the European subspecies, P. rapae rapae, reflect little UV light, while butterflies of the Asian subspecies, P. rapae crucivora, may reflect it strongly or at only intermediate levels. The geographic region where P. rapae originated remains to be determined. Moreover, it is not clear if females with wings that reflect little UV light are ancestral to females with wings that reflect UV strongly or vice versa. In the present study, we aimed to determine the geographic origin and ancestral UV pattern of cabbage butterflies through mitochondrial DNA (mtDNA) sequence analysis and amplified fragment length polymorphism (AFLP) analysis. The results of these investigations suggest that P. rapae is of European origin and that it has expanded its distribution eastward to Asia. It follows that the ancestral subspecies is the type with UV‐absorbing wings. Lower nucleotide diversities and haplotype network patterns of mtDNA derived from East Asian populations suggest that population expansion from Europe to East Asia probably occurred fairly recently and at a rapid rate.     

Photoreceptor spectral sensitivities of the Small White butterfly <Emphasis Type="Italic">Pieris rapae crucivora</Emphasis> interpreted with optical modeling

The compound eye of the Small White butterfly, Pieris rapae crucivora, has four classes of visual pigments, with peak absorption in the ultraviolet, violet, blue and green, but electrophysiological recordings yielded eight photoreceptors classes: an ultraviolet, violet, blue, double-peaked blue, green, blue-suppressed-green, pale-red and deep-red class. These photoreceptor classes were identified in three types of ommatidia, distinguishable by the different eye shine spectra and fluorescence; the latter only being present in the eyes of males. We present here two slightly different optical models that incorporate the various visual pigments, the light-filtering actions of the fluorescent, pale-red and deep-red screening pigment, located inside or adjacent to the rhabdom, and the reflectance spectrum of the tapetum that abuts the rhabdom proximally. The models serve to explain the photoreceptor spectral sensitivities as well as the eye shine.     

Response of Steinernema carpocapsae Infective Juveniles to the Plasma of Three Insect Species

Exsheathed infective juveniles of Steinernema carpocapsae All strain were attracted to the plasma of three species of insects in agar plate bioassays. Plasma of Pieris rapae crucivora, Spodoptera litura, and Agrotis segetum attracted 88.6%, 80.4%, and 64.4%, respectively, of Steinernema carpocapsae juveniles added to plates. Autoclaved plasma of S. litura larvae attracted more juveniles than saline controls, but less than nonautoclaved plasma. The active agent passed through a 14,000 MW dialysis membrane.     

Differential effects of jasmonic acid treatment of Brassica nigra on the attraction of pollinators, parasitoids, and butterflies

Herbivore-induced plant defences influence the behaviour of herbivores as well as that of their natural enemies. Jasmonic acid is one of the key hormones involved in both these direct and indirect induced defences. Jasmonic acid treatment of plants changes the composition of defence chemicals in the plants, induces volatile emission, and increases the production of extrafloral nectar. However, few studies have addressed the potential influence of induced defences on flower nectar chemistry and pollinator behaviour. These have shown that herbivore damage can affect pollination rates and plant fitness. Here, we have investigated the effect of jasmonic acid treatment on floral nectar production and the attraction of pollinators, as well as the effect on the behaviour of an herbivore and its natural enemy. The study system consisted of black mustard plants, Brassica nigra L. (Brassicaceae), pollinators of Brassica nigra (i.e., honeybees and syrphid flies), a specialist herbivore, Pieris rapae L. (Lepidoptera: Pieridae), and a parasitoid wasp that uses Pieris larvae as hosts, Cotesia glomerata L. (Hymenoptera: Braconidae). We show that different trophic levels are differentially affected by jasmonic acid-induced changes. While the herbivore prefers control leaves over jasmonic acid-treated leaves for oviposition, the parasitoid C. glomerata is more attracted to jasmonic acid-treated plants than to control plants. We did not observe differences in pollinator preference, the rates of flower visitation by honeybees and syrphid flies were similar for control and jasmonic acid-treated plants. Plants treated with jasmonic acid secreted less nectar than control plants and the concentrations of glucose and fructose tended to be lower than in nectar from control plants. Jasmonic acid treatment resulted in a lower nectar production than actual feeding damage by P. rapae caterpillars.     

Genetic variance and covariance patterns of larval development in the small white butterflyPieris rapae crucivora Boisduval

Quantitative genetic theory indicates that genetic covariance patterns among life history characters should have played an important role as genetic constraint in life history evolution. Highly positve (and negative) genetic correlations between larval development time (or larval growth rate) and adult size characters were detected by means of sib analysis for the small white butterfly Pieris rapae crucivora. The genetic associations suggested that evolution of developmental characteristics and adult phenotypic traits were constrained by pleiotropy. The positive genetic correlations between development time and adult body size may be compatible with the trade-off between them, but the negative genetic correlations between larval growth rate and adult body size are not predicted from theories of optimal energy allocation. That phenotypic correlations drastically differed from the genetic correlations indicates limitations of evolutionary inferences based only on phenotypic variation.     

Continuous cell lines from the common white, Pieris rapae crucivora boisduval

Summary Three continuous cell lines, NIAS-PRC-819A, NIAS-PRC-819B, and NIAS-PRC-819C, were established from the pupal ovaries of the common white, Pieris rapae crucivora Boisduval (Insecta, Lepidoptera, Pieridae). The primary culture was initiated as explant cultures with ovariole fragments in MGM-464 medium supplemented with 20% fetal bovine serum at 25° C. About 6 mo after the culture was set up, the first subculture was prepared. Thereafter, cells were subcultured with decreasing passage intervals, resulting in a cell population that multiplied continuously. The karyotypes of these cell lines were similar to each other, and the majority of the cells showed about 100 microchromosomes. The population-doubling times of these cell lines were 3 to 7 d. The cell lines were susceptible to a microsporidia, Nosema bombycis. Immunodiffusion experiments proved that these cell lines derived from the common white and not from other cell lines by contamination.     

Population density effects on fecundity of Hippelates pusio Loew (Diptera: Chloropidae)

Summary A schematic model is constructed illustrating the pathways and mechanisms of adult density effects on birth rate that have been reported to operate in various taxa of insects. With this model as a guide, experimetal data were collected from laboratory populations of Hippelates pusio Loew within the range of 0.15 to 25 flies per cm³ (sex ratio 1:1), which revealed: a) that adult density did not affect oviposition rate via competition for oviposition site, b) the rates of oviposition for virgin and mated females were not significantly different, and c) density did not affect frequency of copulation to a degree detectable in the hatchability of eggs. These data and previous knowledge on the reproductive biology of Hippelates pusio indicate that the birth rate of this species is independent of adult density, within then density range investigated.Paper no. 3651 of the Journal Series of North Carolina State Agricultural Experiment Station. Research partially supported by Training Grant ES 00069 from the National Institute of Environmental Health Sciences.     

In-flight orientation to volatiles from the plant-host complex in Cotesia rubecula (Hym.: Braconidae): increased sensitivity through olfactory experience

Abstract. Plasticity in in-flight orientation to odours from the plant-host complex (PHC: plant infested by the host) was investigated in Cotesia rubecula , a specialist larval parasitoid of Pieris rapae which feeds almost exclusively upon cruciferous plants. A wind tunnel was used to study effects of both concentration of volatile emissions and females' experience. A low proportion of naive wasps located weak odourant sources, i.e. either a single cabbage leaf or a leaf with two first stadium P.rapae larvae. This rate could be elevated by increasing the odour concentration or by providing the wasps with either a previous oviposition experience on the PHC or an exposure to the PHC odour. Previous oviposition on washed larvae (diet-fed, starved and then rinsed with distilled water) in an odourless environment had no effect, which suggested that increased sensitivity to the PHC odour resulted from olfactory experience. The number of mature eggs in a female was affected by oviposition on the PHC or washed larvae but not by exposure to the PHC odour. Therefore the number of mature eggs available was not correlated to the observed differences in orientation behaviour. Possible mechanisms of the behavioural changes described are discussed in the light of the host specificities of C.rubecula and P.rapae.     

The Effect of Repeated Matings on Sperm Numbers in Successive Ejaculates of the Cabbage White Butterfly Pieris rapae (Lepidoptera: Pieridae)

The effect of repeated matings on sperm numbers in successive ejaculates of the cabbage white butterfly, Pieris rapae, was examined. First ejaculates were larger than successive ones, which did not differ among themselves. Moreover, the cumulative mass of previous spermatophores was not correlated with that of the last mating. The number of eupyrene sperm bundles in the ejaculate did not differ between first and successive matings. Multiplying by 256, a male transfers about 11,000 eupyrene sperm at every mating. First ejaculates contained about 46,000 apyrene sperm, whereas successive ejaculates contained higher numbers. The sperm density increased after the first mating, though the spermatophore mass decreased. The significance of change in sperm quantity with mating number is discussed from the viewpoint of male investment.     

Plant‐mediated effects of host plant density on a specialist herbivore of Solanum carolinense

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