Effect of a turnip rape <Emphasis Type="Italic">(Brassica rapa)</Emphasis> trap crop on stem-mining pests and their parasitoids in winter oilseed rape <Emphasis Type="Italic">(Brassica napus)</Emphasis>

Concerns about the negative effects of chemical control of oilseed rape (Brassica napus L.) pests on non-target species, human safety, and development of insecticide resistance, require alternative control strategies such as the use of trap crops and biocontrol to be developed. Psylliodes chrysocephala(L.) (Coleoptera: Chrysomelidae) (cabbage stem flea beetle) and Ceutorhynchus pallidactylus (Marsh.) (Coleoptera: Curculionidae) (cabbage stem weevil) are two major stem-mining pests of oilseed rape. This study investigated the phenology of these pests and their main parasitoids in the UK, the potential use of turnip rape (Brassica rapa L.) as a trap crop to reduce oilseed rape infestation, and the effects of insecticide treatment on pest incidence and larval parasitism. Water trap samples, plant dissections and pest larval dissections were done to determine: the incidence of adult pests and their parasitoids, the level of plant infestation by the pests and percentage larval parasitism, respectively. The turnip rape trap crop borders reduced P. chrysocephalabut not C. pallidactylus infestation of oilseed rape plots. Treatment of the trap crop with insecticide had little effect on either pest or parasitoid incidence in the oilseed rape. TersilochusmicrogasterSzép. andT. obscurator Aub. (Hymenoptera: Ichneumonidae) were the main larval parasitoids of P. chrysocephalaand C. pallidactylus, respectively. Tersilochus microgasteris reported for the first time in the UK. The implications for integrated pest management are discussed.     

Incidence,Spread and Mechanisms of Pyrethroid Resistance in European Populations of the Cabbage Stem Flea Beetle,Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae)

Background

Cabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae) is a major early season pest of oilseed rape throughout Europe. Pyrethroids have been used for controlling this pest by foliar application, but in recent years control failures have occurred, particularly in Germany due to the evolution of knock-down resistance (kdr). The purpose of this study was to investigate the incidence and spread of pyrethroid resistance in CSFB collected in Germany, Denmark and the United Kingdom during 2014. The level of pyrethroid resistance was measured in adult vial tests and linked to the presence of kdr genotypes.

Results

Although kdr (L1014F) genotypes are present in all three countries, marked differences in pyrethroid efficacy were found in adult vial tests. Whereas Danish CSFB samples were in general susceptible to recommended label rates, those collected in the UK mostly resist such rates to some extent. Moderately resistant and susceptible samples were found in Germany. Interestingly, some of the resistant samples from the UK did not carry the kdr allele, which is in contrast to German CSFB. Pre-treatment with PBO, prior to exposure to λ-cyhalothrin suggested involvement of metabolic resistance in UK samples.

Conclusion

Danish samples were mostly susceptible with very low resistance ratios, while most other samples showed reduced sensitivity in varying degrees. Likewise, there was a clear difference in the presence of the kdr mutation between the three countries. In the UK, the presence of kdr genotypes did not always correlate well with resistant phenotypes. This appears to be primarily conferred by a yet undisclosed, metabolic-based mechanism. Nevertheless our survey disclosed an alarming trend concerning the incidence and spread of CSFB resistance to pyrethroids, which is likely to have negative impacts on oilseed production in affected regions due to the lack of alternative modes of action for resistance management purposes.     

Warm springs reduce parasitism of the cereal leaf beetle through phenological mismatch

Variation in weather among years may affect biological control of insect pests by influencing how well matched in phenology specialist parasitoids are with their pest hosts. A 10‐year study in western North America (Utah) revealed greater change with warm versus cool springs in the life cycle timing of the cereal leaf beetle (CLB), Oulema melanopus (L.), than of its principal enemy, the parasitoid wasp Tetrastichus julis (Walker). The beetle laid eggs, and larval populations developed in crop fields earlier on a calendar‐day basis, but nonetheless after more degree‐days had accumulated, in warmer than in cooler springs. The phenology of parasitism by wasps, in contrast, varied little among springs in relation to accumulated degree‐days. Consequently, in warmer springs, larval phenology of the CLB was delayed relative to adult parasitoid activity, and parasitism was reduced. Presently, a significant degree of biological control of the CLB results from parasitism by T. julis. By promoting phenological mismatch between host and parasitoid, however, a warming climate could weaken this biological control of the insect pest.     

The influence of glucosinolates and sugars on feeding by the cabbage stem flea beetle,Psylliodes chrysocephala

Agar was used as an artificial substrate to investigate the feeding behaviour of the cabbage stem flea beetle,Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of winter oilseed rape (Brassica napus) in Europe. Both glucosinolates and sugars stimulated feeding when added to agar. The amount of feeding that occurred was affected by the type and concentration of glucosinolate and surgar and also by combinations of components. Although glucosinolates were potent feeding stimulants forP. chrysocephala, they were not a prerequisite for feeding, nor does it seem likely that glucosinolate profiles are used by this species to discriminate amongst cruciferous plants at the gustatory level.     

Performance of cabbage stem flea beetle larvae (Psylliodes chrysocephala) in brassicaceous plants and the effect of glucosinolate profiles

The cabbage stem flea beetle (CSFB), Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), is one of the most important pests in European winter oilseed rape production. Adult beetles feed on young leaves whereas larvae mine within the petioles and stems. Larval infestation can cause significant crop damage. In this study, the host quality for CSFB of four oilseed rape (Brassica napus L.) cultivars and seven other brassicaceous species with different glucosinolate (GSL) profiles was assessed under controlled conditions. Larval instar weights and mortality were measured after 14 and 21 days of feeding in the petioles of test plants. To study the impact of GSL on the performance of larvae, the GSL contents in petioles from non-infested and infested plants were analysed before, and 21 days after, the start of larval infestation. Larval performance was not significantly different between the four cultivars of oilseed rape, but differed considerably among the other brassicaceous species tested. In comparison to the weight of larvae in the standard B. napus cv. Robust, the larval weight was higher in turnip rape (Brassica rapa L. var. silvestris) and significantly reduced in white mustard (Sinapis alba L.), oil radish (Raphanus sativa L. var. oleiformis), and cabbage (Brassica oleracea L. convar. capitata var. alba). The duration of larval development increased in white mustard and oilseed radish. The GSL profiles of the petioles showed little difference between non-infested and infested plants of oilseed rape whereas the content of aliphatic GSL increased in the infested turnip rape plants. In contrast, the aliphatic and benzenic GSL decreased in infested Indian rape (B. rapa subsp. dichotoma Roxb.). Larval weight was not correlated with the total GSL content of plants, neither before infestation nor 21 days after. Larval weight was positively correlated with progoitrin and 4-hydroxyglucobrassicin. White mustard, which provides inferior host quality for larval development, has the potential to introduce insect resistance into high-yielding oilseed rape cultivars in breeding programmes.     

A behavioural study to help clarify how undersowing with clover affects host-plant selection by pest insects of brassica crops

Laboratory and field-cage tests were done to determine how undersowing brassica plants (Brassica oleraceae L. and B. rapa L.) (Cruciferae) with subterranean clover (Trifolium subterraneum L.) (Papilionaceae) affected host-plant selection by eight pest insect species of brassica crops. The pest species tested were Pieris rapae (Lepidoptera: Pieridae) (the small white butterfly), Pieris brassicae (Lepidoptera: Pieridae) (the large white butterfly), Delia radicum (Diptera: Anthomyiidae) (the cabbage root fly), Phaedon cochleariae (Coleoptera: Chrysomelidae) (the mustard beetle), Plutella xylostella (Lepidoptera: Yponomeutidae) (the diamond-back moth), Evergestis forficalis (Lepidoptera: Pyralidae) (the garden-pebble moth), Mamestra brassicae (Lepidoptera: Noctuidae) (the cabbage moth) and Brevicoryne brassicae (Hemiptera: Aphididae) (the cabbage aphid). In all tests, except two in which the brassica plants were about three times as high as the clover background, 39%–100% fewer of the pest insect stage monitored were found on host plants presented in clover than on those presented in bare soil. Contrary to claims supporting the ‘enemies hypothesis’, differences in colonization alone appeared sufficient to account for the lower numbers of insects found when host plants are undersown with clover. To be effective in reducing plant colonization, the clover must cover 50%, and preferably more, of the vertical profile of the crop plants. As clover used as an undersown crop often has to be cut to make it less competitive with the main brassica crop, temporal aspects of the condition of the clover during critical periods of pest activity need to be recorded carefully before concluding that undersowing does not produce the effect desired against certain pest species under field conditions. The effective clover barrier is like any other treatment, if it is not present at the appropriate time it cannot be expected to reduce pest insect numbers.     

Effects of intercropping white cabbage with clovers on pest infestation and yield

During two consecutive years the effects of intercropping fresh market white cabbage with two species of clover on pest populations and yield were studied. White cabbage cv. Minicole was intercropped withTrifolium repens (white clover) andTrifolium subterraneum (subterranean clover) as compared to the monocrop. During the season observations were made on pest population developments, especially ofMamestra brassicae L. (cabbage moth),Brevicoryne brassicae L. (cabbage aphid),Delia brassicae L. (cabbage root fly), and evaluation of caterpillar feeding injury. At harvest the yield in quantity and quality was determined to be able to assess the gross financial result. Intercropping effects in terms of suppression of oviposition and larval populations of various pests were found. Although no pesticides were used and competition reduced the weight, the quality of the intercropped cabbages lead to a better financial result compared to the monocropped cabbage crop. The results are discussed in the perspective of the practical implications in the context of IPM.     

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.     

Evidence for parasitoid‐induced premature mortality in the Argentine stem weevil

The Argentine stem weevil Listronotus bonariensis Kuschel (Coleoptera: Curculionidae) is an exotic pest of New Zealand ryegrass and the adult‐stage is parasitized by the introduced solitary endoparasitoid Microctonus hyperodae Loan (Hymenoptera: Braconidae: Euphorinae). This biological control agent is effective, although, under both laboratory and field conditions, an unexplained source of premature mortality in the weevils is observed after exposure to M. hyperodae. This premature mortality may be affected to varying degrees by the length of time of parasitoid exposure, the physiological conditions of the host, and the host to parasitoid ratios, although it occurs naturally without any physical interruption to the parasitoid ovipositional process. In the present study, the premature mortality reported in earlier studies is confirmed and it is conjectured to be the result of injection of parasitoid venom without an egg. Moreover, the lack of premature mortality resulting from longer exposure periods indicates that there might be a curative effect resulting from subsequent oviposition; the egg reverses the toxic effect induced by the injection of venom only. As discussed, this phenomenon may not be restricted to the L. bonariensis/M. hyperodae system and, accordingly, there are evolutionary, biosecurity and general pest management questions to be considered.     

Effects of Bt transgenic rice line on stripe stem borer,Chilo suppressalis and its consequences on egg parasitoid,Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae) in the laboratory

Interactions among Chilo suppressalis (Walker), its larval parasitoid Trichogramma brassicae Bezdenko and insect-resistant transgenic rice lines were evaluated under laboratory conditions. The results showed that all neonates and second larvae of stem borer were dead regardless of being fed rotationally or permanently on Bt rice, but 18% and 28% of the third and fourth instar larvae could complete development and turned to adults, respectively, when fed rotationally. In the second year of project, third instar larvae of stem borer were used to evaluate Bt rice impact on T. brassicae. The result showed that emergence rate was lower, the abnormal female rate increased and adult female longevity of the wasp decreased significantly in comparison with the conventional variety. There was no significant difference in gender ratio and parasitism rate under Bt rice treatment in comparison with conventional variety.     

Tri-trophic effects of inter- and intra-population variation in defence chemistry of wild cabbage (<Emphasis Type="Italic">Brassica oleracea</Emphasis>)

The effect of direct chemical defences in plants on the performance of insect herbivores and their natural enemies has received increasing attention over the past 10 years. However, much less is known about the scale at which this variation is generated and maintained, both within and across populations of the same plant species. This study compares growth and development of the large cabbage butterfly, Pieris brassicae, and its gregarious pupal parasitoid, Pteromalus puparum, on three wild populations [Kimmeridge (KIM), Old Harry (OH) and Winspit (WIN)] and two cultivars [Stonehead (ST), and Cyrus (CYR)] of cabbage, Brassica oleracea. The wild populations originate from the coast of Dorset, UK, but grow in close proximity with one another. Insect performance and chemical profiles were made from every plant used in the experiment. Foliar glucosinolates (GS) concentrations were highest in the wild plants in rank order WIN > OH > KIM, with lower levels found in the cultivars. Caterpillar-damaged leaves in the wild cabbages also had higher GS levels than undamaged leaves. Pupal mass in P. brassicae varied significantly among populations of B. oleracea. Moreover, development time in the host and parasitoid were correlated, even though these stages are temporally separated. Parasitoid adult dry mass closely approximated the development of its host. Multivariate statistics revealed a correlation between pupal mass and development time of P. brassicae and foliar GS chemistry, of which levels of neoglucobrassicin appeared to be the most important. Our results show that there is considerable variation in quantitative aspects of defensive chemistry in wild cabbage plants that is maintained at very small spatial scales in nature. Moreover, the performance of the herbivore and its parasitoid were both affected by differences in plant quality.     

A new biological method to control Anobium punctatum,by using the parasitoid wasp Spathius exarator

Biological pest control by means of beneficial organisms is for long part of agriculture and Integrated Pest Management (IPM). A new and efficient strategy to control the most common timber pest species in churches and museums, the furniture beetle Anobium punctatum (De Geer) (Coleoptera: Anobiidae), is based on the parasitoid wasp species Spathius exarator (Linnaeus) (Hymenoptera: Braconidae). Once this braconid wasp detects its host species beneath the surface, it pierces the wood with its ovipositor to lay one single egg onto the beetle larva. After hatching, the wasp larva feeds on the beetle larva thereby killing it. Afterwards, it pupates and emerges through a self-gnawed hole as an adult wasp. The tiny, 0.5-mm-wide exit hole can easily be distinguished from the 1- to 2-mm-wide exit hole of A. punctatum. Laboratory tests revealed that female wasps have an average life span of 85 days and produce a total of 24 offspring, when nutrition is provided. Between 2012 and 2019, braconid wasps were introduced into 54 different A. punctatum infested buildings. Treatment success was monitored by examining exit holes of new beetles and wasps thereby calculating corresponding parasitism rates. After the first year of treatment, parasitism rates were significantly higher with a mean value of 0.15 when compared to untreated objects with a natural parasitism and a mean value of 0.08 (n = 54). Following treatment of three objects over a period of eight years, parasitism rates continuously increased from 0.02 up to 0.31. In a church organ, which was treated during this period, the monitoring revealed a complete suppression of pest activity. These data prove that this biological method of pest control is an efficient, sustainable and non-toxic option to manage the common furniture beetle.     

A prospective model for the phenology of Microctonus hyperodae (Hymenoptera: Braconidae), a potential biological control agent of argentine stem weevil in New Zealand

A predictive phenological model is described for the parasitoid Microctonus hyperodae, introduced to New Zealand as a potential biological control agent against Argentine stem weevil Listronotus bonariensis. The model is based on development/temperature relationships obtained from experiments on the parasitoid in quarantine prior to its release, allowing early predictions of its phenology in different parts of the target pest's New Zealand range. In particular the model was used to predict the number of parasitoid generations each year, the degree of temporal synchrony between parasitoid adults and the susceptible adult pest stage, the order of parasitism and reproduction in the pest's life cycle as a possible basis for a simplified, discrete host/parasitoid population model, and the likely significance of ecotypic differences in development and diapause characteristics of the parasitoid. These applications demonstrate the potential for simple models to help in climate matching of classical biological control agents and estimation of their interaction with pest dynamics, using data obtainable prior to their introduction and release. In addition the model proved useful as a decision aid during the release programme, by indicating the likely effects of unusual weather and the need or otherwise for further parasitoid releases.     

Host searching behavior and potential of an aquatic ichneumonid pupal parasitoid of rice caseworm (Parapoynx stagnalis) in an upland rice paddy agro-ecosystem of the Western Ghats,India

Parapoynx stagnalis (Zeller) (=Nymphula depunctalis (Guenée), is a sporadic rice paddy pest of south and southeast Asian rice paddy fields, and widely known as rice caseworm. A recent outbreak of the pest was observed in the upland rice paddy agro-ecosystem of the central Western Ghats, India. No potential natural enemies of this pest have so far been reported, mainly due to the semi-aquatic behavior of the larvae and pupae. However, an undescribed aquatic ichneumonid wasp species (belonging to a genus near Litochila) is reported as a potentially useful early stage pupal parasitoid of this pest in our study. The host searching behavior and potential of the parasitoid wasp was studied in detail using both field and laboratory experiments. The adult female wasps usually dive into the water in search of the host pupae, remaining under water for a maximum of 90.2s, while searching for rice caseworm pupae. In field and laboratory experiments, we found 73% of the parasitized pupae of P. stagnalis kept under water yielded adult parasitic wasps. However, no parasitoids emerged from parasitized host pupae maintained in dry terrariums. Sex ratio was 2.8:1. The present discovery of the semi-aquatic parasitoid wasp could aid in better management of the rice caseworm population in rice paddy fields.     

Structure and function of adipokinetic hormones of the large white butterfly Pieris brassicae

The large white butterfly Pieris brassicae L. (also called cabbage white) is very common in Europe, Asia and the northern region of Africa, and has also been found in South Africa during approximately the last 20 years. The species is considered a pest insect, with larvae attacking brassicaceous crops. The adult is a strong migratory flyer and new territory can be infested this way. As a first step to investigate methods for combating this pest species, the present study aims to determine the complement of adipokinetic peptides, here generically referred to as adipokinetic hormones (AKHs), which are required to regulate the mobilization of fuels for insect flight. Biological assays, as well as mass spectrometry, reveal information about the presence, structure and function of AKHs in P. brassicae: a methanolic extract of the corpora cardiaca has hypertrehalosaemic activity in cockroaches, does not cause hyperlipaemia in locusts, and has adipokinetic activity in P. brassicae itself. Liquid‐chromatography electrospray ion trap mass spectrometry reveals three peptides that can be associated with the AKH family: the non‐amidated undecapeptide Vanca‐AKH (pELTFTSSWGGK‐OH), the nonapeptide Manse‐AKH (pELTFTSSWG amide) and the novel octapeptide Piebr‐AKH (pELTFSSGW amide). Sequence confirmation of all three assigned structures is obtained from matching mass spectrometry spectra from synthetic and native peptides. Moreover, the synthetic peptides Manse‐AKH and Piebr‐AKH have significant hyperlipaemic (=adipokinetic) activity when injected into newly‐emerged adult cabbage white butterflies. The non‐amidated Vanca‐AKH is, apparently, incompletely processed Manse‐AKH without hormonal activity. Simulated dispersal flight is able to release AKHs, as indicated by the higher concentration of lipids in the haemolymph of adult P. brassicae after activity and rest periods.     

The influence of cultivar and cultivar-aphid odours on the olfactory response of the parasitoid Aphidius colemani

The olfactory response of the parasitoid Aphidius colemani (Viereck) (Hymenoptera: Braconidae) to odours in a tritrophic system involving three cultivars of common cabbage, Brassica oleracea var capitata, characterized by different levels of susceptibility to Myzus persicae (Sulzer) (Hemiptera: Aphididae) was studied in a four‐way olfactometer. Odours influenced A. colemani response in the olfactometer to varying degrees. The magnitude of parasitoid response to odours of uninfested cabbage depended on cultivar, with Derby Day [green‐leaved, susceptible to M. persicae and the crucifer specialist, Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae)] and Minicole (green‐leaved, partially resistant with known antibiosis factors for B. brassicae) preferred over Ruby Ball (red‐leaved with antixenosis factors for M. persicae and B. brassicae). The odour of the cabbage cultivar on which the parasitoid had been reared was preferred over the other cultivars. However, when provided with a choice between odours of infested plants, parasitoids did not show a significant preference for the cultivar on which they were reared. Results from the study show that parasitioids differentiated between odour of the three cultivars in dependence of their rearing history when the plant is uninfested.     

Chemical control of the cabbage stem flea beetle, Psy Modes chrysocephala, on winter oil-seed rape

In East Anglia, from 1974 to 1976, field experiments were carried out on the chemical control of the cabbage stem flea beetle (PsyModes chrysocephala). Carbofuran, 5% granules, proved an outstanding autumn preventive and mid-winter eradicant treatment under both wet and dry conditions, with 1–5-2-24 kg a.i./ha giving virtually 100% control of larvae. Fonofos and phorate granules at 2–24 kg a.i./ha were also effective. AC 92 100 and thiofanox granules were less extensively tested but both gave good control of P. chrysocephala. Several materials showed little or no activity against the pest. The effective preventive granule treatments were all superior to a standard spray of gamma-HCH.     

Parasitisation of Tetrastichus brontispae (Hymenoptera: Eulophidae), a biological control agent of the coconut hispine beetle Brontispa longissima (Coleoptera: Chrysomelidae)

The gregarious endoparasitoids Tetrastichus brontispae Ferrière is one of the important natural enemies of the coconut hispine beetle Brontispa longissima (Gestro), a serious invasive pest on coconut palm plants (Cocos nucifera L.) in Southeast Asia. Development at different temperatures, effect of host and female ages, effect of food and oviposition frequency and superparasitism were investigated in the laboratory. Females were allowed only one attack against one host in all experiments. The wasp developed in a host between 19 and 30°C, whilst no wasp completed its immature development at 16 and 31°C. Host and female ages affected parasitisation. Parasitoid emergence was high on day 0 and day 1 pupal hosts, and younger females produced more offspring than older females. The longevity of the female was affected not only by food supply, but also by oviposition frequency. The female survived longer when oviposition frequency was low. However, the total number of hosts parasitised by the female during her lifetime did not differ at different oviposition frequencies. In superparasitism, although the percentage of adult emergence and body size of offspring decreased with an increasing number of attacks per host, a host parasitised by up to four females could produce parasitoid offspring.     

Observations on the cabbage stem flea beetle, Psylliodes chrysocephala, on winter oil-seed rape in Cambridgeshire

The biology of the cabbage stem flea beetle, Psylliodes chrysocephala (L.) (Coleoptera: Chrysomelidae), on winter oil-seed rape crops was studied in Cambridgeshire from 1974 to 1978, with particular reference to autumn and winter activity. The timing of adult invasion of crops in the autumn and subsequent attack on plants by larvae showed considerable variation from year to year, being influenced mainly by temperature. Also, early-germinating crops tended to be invaded earlier than later-germinating ones. Egg development, which was closely correlated with temperature, required an accumulated sum of 240 day ^oC above 3.2 ^oC (calculated from daily mean temperatures). Monitoring adult activity, and consideration of temperature data, allowed dates of egg hatch to be predicted. The usefulness of this information for accurately timing chemical sprays against the pest is discussed.     

RETRACTED ARTICLE: Foraging of Host-Habitat and Superparasitism in <Emphasis Type="Italic">Cotesia glomerata</Emphasis>: A Gregarious Parasitoid of <Emphasis Type="Italic">Pieris brassicae</Emphasis>

The study investigates differences in the oviposition pattern of a braconid parasitoid, Cotesia glomerata (Linn.) in Pieris brassicae (Linn.) in relation to their use of different cruciferous food plants. The response of P. brassicae to superparasitism and consequences for the parasitoid were examined in order to elucidate the ecological significance of this behaviour. Female parasitoid located various crucifers and searched for host more frequently almost on all the host plants tested i.e. cabbage, cauliflower, Chinese cabbage, broccoli and radish. According to the estimated relative number of female locating hosts, cabbage was the most attractive plant for C. glomerata and total number of eggs laid in host larvae feeding on it was higher than in larvae feeding on other plants. Laboratory experiments demonstrated that superparasitism reduced survivorship of P. brassicae larvae. Superparasitism lengthened parasitoid development and prolonged the feeding period of host larvae. Sex ratio and the body weight of emergent wasps correlated negatively with brood size. Despite a trade-off between maximising brood size and optimising the fitness of individual offspring, two or three ovipositions on P. brassicae larvae resulted in a greater female dry mass than did a single oviposition on the host. Thus, superparasitism might be of adaptive significance under certain circumstances, especially when host density is low and unparasitized hosts are rare in a habitat.