Changes in hemocytes of Plutella xylostella after parasitism by Diadegma semiclausum

We examined the changes of hemocytes in the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), due to parasitism by the endoparasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae). Necrosis of prohemocytes in different stages was observed while cell death was absent in the mature hemocytes in the parasitized larvae, which was related to the declined total hemocyte count per microliter (THC). THC in the host hemolymph declined sharply by 12 h post-parasitization and then remained at a low level. When hemocytes of the parasitized larvae were cultured in vitro, encapsulation ability was suppressed coincidently with the inhibited spreading ability; however, such effects were transient. Simultaneously, activation of the prophenoloxidae from the hemocytes was inhibited. Unlike the results of previous studies, the decrease in hemocytes, which was due to the necrosis of the prohemocytes instead of the mature hemocytes in our study, was not responsible for the impaired encapsulation. Our studies suggest that parasitism by D. semiclausum have some effects on hematopoietic regulation and on hemocyte immune reaction of P. xylostella larvae.     

闭弯尾姬蜂与菜蛾盘绒茧蜂寄生菜蛾幼虫时的种间竞争

在室内25℃下,以菜蛾3龄初幼虫作寄主,研究了菜蛾盘绒茧蜂Cotesia plutellae和半闭弯尾姬蜂Diadegma semiclausum的种间竞争。当寄主供2种蜂同时产卵寄生时,2种蜂各自的寄生率与其单独寄生时无显著差异,合计寄生率比一种蜂单独存在时有所提高,但差异不显著。2种蜂均能产卵寄生已被另一种蜂寄生了的寄主幼虫。当寄主被2种蜂寄生的间隔时间很短（少于10 h）时,所育出的蜂绝大部分（80%以上）为绒茧蜂;当寄主先被绒茧蜂寄生,并饲养2天以上再供弯尾姬蜂寄生时,所育出的全为绒茧蜂;当寄主先被弯尾姬蜂寄生,并饲养2天以上再供绒茧蜂寄生时,寄主幼虫绝大部分不能存活,只有少部分能育出寄生蜂,且多为弯尾姬蜂。当2种蜂的幼虫存在于同一寄主体内时,2种蜂的发育均受到另一种蜂的抑制;绒茧蜂1龄幼虫具有物理攻击能力,能将弯尾姬蜂卵或幼虫致死。这些结果表明,菜蛾盘绒茧蜂与半闭弯尾姬蜂在同一寄主中发育时,前者具有明显的竞争优势。     

Parasitism-induced effects on host growth and metabolic efficiency in Plutella xylostella larvae parasitized by Cotesia vestalis or Diadegma semiclausum

The nutritional physiology of the diamondback moth, Plutella xylostella, larvae was examined after parasitization by the solitary endoparasitoids Cotesia vestalis or Diadegma semiclausum. Examinations were performed in two phases, one was examined at the time point of 24 h post‐parasitization, and the other was done at the end of the 4th instar larvae of host. Rates of growth, food consumption, assimilation, excretion, and respiration were calculated as well as approximate digestibility and the rate ratios ECI (percent efficiency of conversion of ingested food to body substance), and ECD (percent efficiency of conversion of digested food to body substance). Parasitization by C. vestalis resulted in significant decrease in the rates of growth, feeding, excretion, assimilation, and respiration, but the final dry rate of respiration at the end of last larval stadium was elevated. The ECI and ECD were also reduced as the result of parasitization, but digestibility was increased. All these parameters in the larvae parasitized by D. semiclausum at 24 h post‐parasitization were also significantly changed compared to the control; however, these differences were quantitatively, but not qualitatively before pupation, similar to those resulted from parasitization by C. vestalis. In spite of the similarities of the parasitism‐induced effects caused by these endoparasitoids, the final metabolic rate, that is, the rate of intake of nutrients required to compensate for metabolism, was much lower in the larvae parasitized by C. vestalis than that of the larvae parasitized by D. semiclausum. All of the results discussed here will contribute toward explaining the different ways these two wasps regulate the parasitoid‐host relationship.     

Interspecific competition between Diadegma semiclausum Hellen (Hym., Ichneumonidae) and Cotesia plutellae (Kurdjumov) (Hym., Braconidae) in parasitizing Plutella xylostella (L.) (Lep., Plutellidea)

Abstract:  Interspecific competition between Diadegma semiclausum and Cotesia plutellae was investigated at 25°C in the laboratory, by exposing the third instar larvae of the diamondback moth, Plutella xylostella to both species together, either species alone or by exposing the host larvae already parasitized by one species, at different intervals, to the other. When host larvae were exposed simultaneously to two species in one arena, parasitism rates of the host by each species were not reduced by the presence of the other species; joint parasitism rate by two species was not significantly higher than that by either parasitoid alone. Both parasitoids could lay eggs into the host larvae which had previously been parasitized by the other species, leading to the occurrence of multiparasitized hosts. When host larvae were parasitized first by D. semiclausum and then being followed within 1–2 h by exposing to C. plutellae , or vice versa, ensuing parasitoid cocoons from the multiparasitized host larvae were nearly all C. plutellae . When host larvae were parasitized initially by C. plutellae and then being followed by D. semiclausum two or more days later, all parasitoids ensued from the multiparasitized hosts were C. plutellae . In contrast, when host larvae were parasitized initially by D. semiclausum and then being followed by C. plutellae two or more days later, most host larvae could not survive to prepupae and most of the ensuing parasitoid adults from the surviving hosts were D. semiclausum . Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that development of both parasitoids in multiparasitized hosts were somewhat arrested, and that the first instar larvae of C. plutellae could initiate a physical attack on the larvae of D. semiclausum and remove the latter.     

Diadegma insulare development is altered by Plutella xylostella reared on water‐stressed host plants

Natural enemies of herbivores function in a multitrophic context, and their performance is directly or indirectly influenced by herbivores and their host plants. Very little is known about tritrophic interactions between host plants, pests and their parasitoids, particularly when the host plants are under any stress. Herbivores and their natural enemies’ response to plants under stress are diverse and variable. Therefore, in this study we investigated how diamondback moth, Plutella xylostella (L.), reared on water‐stressed host plants (Brassica napus L. and Sinapis alba L.) influenced the development of its larval parasitoid, Diadegma insulare (Cresson). No significant differences were observed in development of P. xylostella when reared on water‐stressed host plants. However, all results indicated that water stress had a strong effect on developmental parameters of D. insulare. Development of D. insulare was delayed when the parasitoid fed on P. xylostella, reared on stressed host plants. Egg to adult development of D. insulare was faster on non‐stressed B. napus than non‐stressed S. alba followed by stressed B. napus and S. alba. Female parasitoids were heavier on non‐stressed host plants than stressed counterparts. Furthermore, the parasitoid lived significantly longer on stressed B. napus. However, body size was not affected by water treatment. Most host plant parameters measured were significantly lower for water‐stressed than non‐stressed treatments. Results suggest that development of this important and effective P. xylostella parasitoid was influenced by both water stress and host plant species.     

Trade‐off between thermal tolerance and insecticide resistance in Plutella xylostella

Fitness costs associated with resistance to insecticides have been well documented, usually at normal temperature conditions, in many insect species. In this study, using chlorpyrifos‐resistant homozygote (R_R) and chlorpyrifos‐susceptible homozygote (S_S) of resistance ace1 allele of Plutella xylostella (DBM), we confirmed firstly that high temperature experience in pupal stage influenced phenotype of wing venation in insecticide‐resistant and insecticide‐susceptible Plutella xylostella, and S_S DBM showed significantly higher thermal tolerance and lower damages of wing veins under heat stress than R_R DBM. As compared to S_S DBM, R_R DBM displayed significantly lower AChE sensitivity to chlorpyrifos, higher basal GSTs activity and P450 production at 25°C, but higher inhibitions on the enzyme activities and P450 production as well as reduced resistance to chlorpyrifos under heat stress. Furthermore, R_R DBM displayed significantly higher basal expressions of hsp69s, hsp72s, hsp20, hsp90, Apaf‐1, and caspase‐7 at 25°C, but lower induced expressions of hsps and higher induced expressions of Apaf‐1, caspase‐9, and caspase‐7 under heat stress. These results suggest that fitness costs of chlorpyrifos resistance in DBM may partly attribute to excess consumption of energy caused by over production of detoxification enzymes and hsps when the proteins are less demanded at conducive environments but reduced expressions when they are highly demanded by the insects to combat environmental stresses, or to excess expressions of apoptotic genes under heat stress, which results in higher apoptosis. The evolutionary and ecological implications of these findings at global warming are discussed.     

Insecticidal and antifeedant effects of two alkaloids from Cynanchum komarovii against larvae of Plutella xylostella L

A bioassay‐guided fractionation of Cynanchum komarovii crude alkaloid extract led to the isolation of two alkaloids. The isolated alkaloids were identified as 7‐demethoxytylophorine (1) and 6‐hydroxyl‐2,3‐dimethoxy phenanthroindolizidine (2) based on the comparison of their spectroscopic characteristics with the literature data. Insecticidal, antifeedant and growth inhibitory effects of these two alkaloids against the 3rd instar larvae of Plutella xylostella L. (Lepidoptera: Plutellidae) were examined. The results showed that alkaloid 1 was more toxic than alkaloid 2 against the 3rd instar larvae of Plutella xylostella L., but both alkaloids were less toxic than the total alkaloid fraction. For antifeedant activity, alkaloid 1 showed AFC₅₀ of 1.82 mg/ml at 24 h after treatment, alkaloid 2 showed 3.89 mg/ml, while total alkaloids showed 1.56 mg/ml. In dipping toxicity test, alkaloids 1 and 2 produced 93.3% and 63.3% mortality at 72 h after treatment, respectively, while total alkaloids produced 96.7% mortality. The LC₅₀ values for alkaloids 1, 2 and the total alkaloids were 3.54, 9.21 and 2.63 mg/ml, respectively. The development of larvae was also inhibited, and the growth inhibition rates at the concentration of 15.00 mg/ml were 92.8%, 78.2% and 98.6% for alkaloids 1, 2 and total alkaloids, respectively, at 72 h after treatment. Compared with antifeedant and dipping effect, the alkaloids 1, 2 and total alkaloid fraction revealed weak feeding toxicity, and their corrected mortality rates at the concentration of 15.00 mg/ml were 60.0%, 40.0% and 63.3% at 7 days after treatment. The LC₅₀ values for alkaloids 1, 2 and total alkaloids were 12.58, 32.37 and 8.88 mg/ml, respectively, at 7 days after treatment.     

Geographical variation of Plutella xylostella (Lepidoptera: Plutellidae) populations revealed by mitochondrial COI gene in China

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most serious pests for cruciferous vegetable growers worldwide. To determine the relations of local and regional populations, we performed a mitochondrial COI gene analysis of eight P. xylostella populations from different locations in or around the Qinling Mountains and two other populations, one from Beijing and the other from Guangdong. The mtDNA divergences among the 10 populations were high, and 32 haplotypes were detected in 149 adults. The mean haplotype divergence was 1.7% (range 0.04–4.1%). Haplotype diversity in the 10 populations varied from 0.571 (AK) to 0.885 (HZ), and the nucleotide diversity varied from 0.00286 (AK) to 0.0117 (HZ). The results also did not show significant correlation between genetic and geographical distance. Also, the effective number of migrants between populations (Nm) ranged from 1.43 to infinite, suggesting that population exchange and gene flow among the P. xylostella populations occurred. However, principal component analysis (PCA) showed that the TB and TC populations were differentiated from other populations, indicating possible across‐mountain barrier to migration and gene flow.     

半闭弯尾姬蜂寄生及其毒液对小菜蛾幼虫血细胞吞噬作用的影响

半闭弯尾姬蜂Diadegma semiclausum是小菜蛾Plutella xylostella的优势内寄生蜂, 拥有毒液、多分DNA病毒（PDV）等寄生因子,能有效调控寄主幼虫的营养生理和免疫系统, 但其毒液在这过程中的功能不明。本文利用SDS-PAGE方法分析了半闭弯尾姬蜂毒液的蛋白组分,利用寄主幼虫血细胞体外原代培养的方法,研究了小菜蛾幼虫血细胞噬菌能力在半闭弯尾姬蜂寄生后的变化情况。结果表明：半闭弯尾姬蜂毒液蛋白分子量主要集中在35~220 kDa之间,少数小于15 kDa,但分子量处于35~70 kDa之间的蛋白含量较高,与其他寄生蜂毒液蛋白相似。半闭弯尾姬蜂毒液单独对寄主小菜蛾幼虫功能血细胞（浆血细胞和颗粒血细胞）的延展能力和吞噬功能不产生破坏作用。但半闭弯尾姬蜂寄生后短时间内,寄主功能血细胞的延展受到抑制,然而功能血细胞仍然能识别外源异物, 却无法进一步吞噬外源物; 寄生后24 h,功能血细胞的延展力恢复,颗粒血细胞的吞噬作用可顺利完成。本研究证明了半闭弯尾姬蜂寄生能暂时性地抑制颗粒血细胞的延展性从而影响其噬菌过程。     

Characterization of a myrosinase cDNA from Brassica parachinensis and its defense role against Plutella xylostella after suppression

Abstract In Brassicaceae, myrosinase catalyzes the hydrolysis of glucosinolate and plays an important role in anti‐herbivore defense. We have cloned and characterized the full‐length complementary DNA of myrosinase gene from Brassica parachinensis that exhibits high sequence identity with myrosinase genes from other Brassica species. To investigate the role of this myrosinase in defense against the diamondback moth (Plutella xylostella), we constructed an RNA‐interference (RNAi) cassette expressing a double‐stranded RNA that targeted myrosinase and transfected it into B. parachinensis. Myrosinase was suppressed in the resulting transgenic plants. Diamondback moth larvae feeding on transgenic plants had lower larval and pupal weights, longer pupal duration, and lower fecundity than those feeding on non‐transgenic plants, suggesting that the diamondback moth has adapted to the glucosinolate‐myrosinase defensive system. Therefore, the suppression of myrosinase is a potential approach for controlling the diamondback moth.     

Effects of three different cultivars of cruciferous plants on the age‐stage,two‐sex life table traits of Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Plutella xylostella is an important pest of cruciferous crops worldwide. However, information regarding the age‐stage, two‐sex life parameters of P. xylostella, which is vital for designing more effective control methods, is currently lacking. The present study reports age‐stage, two‐sex life table parameters for P. xylostella on napa cabbage (Brassica oleracea var. napa), white cabbage (B. oleracea var. capitata), and cauliflower (B. oleracea var. botrytis) under laboratory conditions at 25 ± 2°C, 50–60% relative humidity, and a 16‐h light : 8‐h dark photoperiod. The time for development from an egg to a male or female adult P. xylostella on white cabbage (mean [± SE] 41.15 ± 0.54 and 39.50 ± 0.54 days, respectively) was significantly longer than that on cauliflower and napa cabbage. Furthermore, P. xylostella fecundity on cauliflower (261.90 ± 4.53 eggs female) was significantly highest than on napa cabbage and white cabbage. Intrinsic rate of increase (r) and finite rate of increase (λ) were highest on cauliflower 0.182 day^?1 and 1.199 day^?1 respectively as comparison to napa cabbage and white cabbage. The highest gross reproductive rate (GRR) and net reproductive rates (R₀) of P. xylostella 65.87 and 52.58 respectively on cauliflower then those of other hosts. The findings of the present study indicate that cauliflower is the most suitable cultivar (host) for the development of P. xylostella. Based on these findings, crops like cauliflower can be used as trap crops when napa cabbage and white cabbage are the main crops.     

Plant‐mediated interactions between two herbivores differentially affect a subsequently arriving third herbivore in populations of wild cabbage

• Plants are part of biodiverse communities and frequently suffer from attack by multiple herbivorous insects. Plant responses to these herbivores are specific for insect feeding guilds: aphids and caterpillars induce different plant phenotypes. Moreover, plants respond differentially to single or dual herbivory, which may cascade into a chain of interactions in terms of resistance to other community members. Whether differential responses to single or dual herbivory have consequences for plant resistance to yet a third herbivore is unknown.
• We assessed the effects of single or dual herbivory by Brevicoryne brassicae aphids and/or Plutella xylostella caterpillars on resistance of plants from three natural populations of wild cabbage to feeding by caterpillars of Mamestra brassicae. We measured plant gene expression and phytohormone concentrations to illustrate mechanisms involved in induced responses.
• Performance of both B. brassicae and P. xylostella was reduced when feeding simultaneously with the other herbivore, compared to feeding alone. Gene expression and phytohormone concentrations in plants exposed to dual herbivory were different from those found in plants exposed to herbivory by either insect alone. Plants previously induced by both P. xylostella and B. brassicae negatively affected growth of the subsequently arriving M. brassicae. Furthermore, induced responses varied between wild cabbage populations.
• Feeding by multiple herbivores differentially activates plant defences, which has plant‐mediated negative consequences for a subsequently arriving herbivore. Plant population‐specific responses suggest that plant populations adapt to the specific communities of insect herbivores. Our study contributes to the understanding of plant defence plasticity in response to multiple insect attacks.

     

Herbivore‐induced plants do not affect oviposition but do affect fitness of subsequent herbivores on canola

The diamondback moth (DBM), Plutella xylostella (L.) (Lepidoptera: Plutellidae), is oligophagous on plants in the Brassicaceae, and is considered one of the most significant insect pests of canola (Brassica napus L.), a major oilseed crop grown in the Prairie Provinces of Canada. The bertha armyworm (BAW), Mamestra configurata Walker (Lepidoptera: Noctuidae), is a generalist herbivore that preferentially feeds on canola plants. In the canola growing season in the Prairie Provinces of Canada, DBM feeding occurs prior to BAW herbivory. In this study, we test the effect of DBM herbivory on subsequent host use by BAW. Oviposition by female BAW was not influenced by previous DBM‐herbivory or mechanical damage of canola plants. Bertha armyworm larvae were deterred from feeding on canola previously damaged by DBM and larvae developed into lighter pupae when reared on DBM‐damaged plants. Bertha armyworm pupae that developed from larvae fed on mechanically damaged plants had similar pupal weights to those fed undamaged plants. Adult BAW reared on canola with previous DBM feeding damage had marginally smaller wings than moths reared on canola treated differently. The combination of these results suggests that herbivory by the brassicaceous specialist, DBM, negatively influences host use and larval performance by the generalist, BAW, on canola.     

室内条件下小菜蛾在五种花椰菜栽培种上的生物学和种群统计(英文)

【目的】小菜蛾Plutella xylostella (L.)是全球十字花科植物上最重要的害虫。由于施药成本的增加以及对环境的破坏性危害,抗性栽培种成为控制小菜蛾的理想选择。本研究中,鉴于对花椰菜不同栽培种的抗感性缺乏充分的了解,我们评价了几个常见栽培种的抗性以及不同植物栽培种对害虫种群增长潜力的影响。【方法】在25±2℃, RH 65%±5% 和光周期16L∶8D的室内条件下,研究了小菜蛾P. xylostella在5种花椰菜栽培种（Smilla, White cloud, Buris, Galiblanka 和Tokita）上的生命表参数。【结果】不小菜蛾幼期发育历期变化范围从Smilla上的13.44 d至Buris上的15.88 d。在Buris上观察到最高的生殖力。在Smilla上饲养的小菜蛾种群内禀增长率（0.27±0.02）和有限增长率（1.32±0.13）最高,而倍增时间最短（2.50 d）。【结论】因此,与其他栽培种相比,在伊朗南部Smilla更适合小菜蛾存活和繁殖,在条件合适和天敌缺乏时该害虫的种群能快速增长。     

Australian native flowering plants enhance the longevity of three parasitoids of brassica pests

Floral resources from native plants that are adapted to the local environment could be more advantageous than the use of nonnative plants. In Australia, there is a dearth of information on the benefits of native plants to natural enemies and their selectivity against pests. Accordingly, we examined the longevity of the parasitoids Diaeretiella rapae (McIntosh) and Cotesia glomerata (L.) (both Hymenoptera: Braconidae), and Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) exposed to flowering shoots from Australian native plants which was compared with the nonnative buckwheat (Fagopyrum esculentum), often used in conservation biological control. Longevity of parasitoids was significantly enhanced by the Australian natives Westringia fruticosa, Mentha satureioides, Callistemon citrinus, Leptospermum cv. ‘Rudolph’, Grevillea cv. ‘Bronze Rambler’, Myoporum parvifolium, Lotus australis, and nonnative F. esculentum. The highest mean survival by native plant species was 3.4× higher for D. rapae with Leptospermum sp. and 4.3× higher for D. semiclausum with M. parvifolium. For C. glomerata, Grevillea sp. increased longevity by 6.9× compared with water only. Longevity of Plutella xylostella (L.) (Lepidoptera: Plutellidae), a major crop pest, was enhanced by all plants against which it was screened except Acacia baileyana, a species that had no effect on parasitoid longevity. Several Australian native plant species that benefit parasitoids were identified. None of the plant species provided a selective benefit to the parasitoid D. semiclausum compared with its host P. xylostella; however, the benefit of M. parvifolium and Grevillea sp. on the longevity of D. semiclausum was relatively higher compared with the pest. These results suggest the need for field studies to determine whether native Australian plants increase P. xylostella impact in nearby brassica crops.     

Temperature‐sensitive fitness cost of insecticide resistance in Chinese populations of the diamondback moth Plutella xylostella

Alleles conferring a higher adaptive value in one environment may have a detrimental impact on fitness in another environment. Alleles conferring resistance to pesticides and drugs provide textbook examples of this trade‐off as, in addition to conferring resistance to these molecules, they frequently decrease fitness in pesticide/drug‐free environments. We show here that resistance to chlorpyrifos, an organophosphate (OP), in Chinese populations of the diamondback moth, Plutella xylostella, is conferred by two mutations of ace1 – the gene encoding the acetylcholinesterase enzyme targeted by OPs – affecting the amino acid sequence of the corresponding protein. These mutations were always linked, consistent with the segregation of a single resistance allele, ace1R, carrying both mutations, in the populations studied. We monitored the frequency of ace1R (by genotyping more than 20 000 adults) and the level of resistance (through bioassays on more than 50 000 individuals) over several generations. We found that the ace1R resistance allele was costly in the absence of insecticide and that this cost was likely recessive. This fitness costs involved a decrease in fecundity: females from resistant strains laid 20% fewer eggs, on average, than females from susceptible strains. Finally, we found that the fitness costs associated with the ace1R allele were greater at high temperatures. At least two life history traits were involved: longevity and fecundity. The relative longevity of resistant individuals was affected only at high temperatures and the relative fecundity of resistant females – which was already affected at temperatures optimal for development – decreased further at high temperatures. The implications of these findings for resistance management are discussed.     

Diamondback moth egg susceptibility to rainfall: effects of host plant and oviposition behavior

Oviposition patterns of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), differ between common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae) host plants. This study shows that the moth prefers to oviposit on adaxial rather than abaxial leaf surfaces and petioles of both host plants. More eggs were laid in leaf veins than on leaf laminas of both host plants, especially in Chinese cabbage, where 94.6% of eggs were laid in veins. On Chinese cabbage, very few eggs were laid in clusters (≥2 eggs), whereas on common cabbage approximately 30% of eggs were laid in groups of 2 or more eggs. Removal of wax from common cabbage leaves dramatically increased the number of eggs laid singly on the leaf lamina of treated plants, suggesting that leaf waxes affect how eggs are distributed by ovipositing DBM. Eggs were most susceptible to removal by rainfall from the plant surface immediately (<1 h) after oviposition and when close to hatching (>72h old) whereas they were least susceptible 24 h after oviposition. Eggs laid on common cabbage plants were more susceptible to simulated rainfall than eggs laid on Chinese cabbage plants. On common cabbage plants, egg susceptibility to rainfall on different plant parts ranked adaxial leaf surfaces>petioles = abaxial leaf surfaces>stem, but there was no difference in egg susceptibility to rainfall on the various plant parts of Chinese cabbage. Furthermore, on common cabbage plants, eggs laid on both adaxial and abaxial leaf surfaces were afforded significant protection from the effects of rainfall by leaves higher in the plant canopy. On common cabbage plants, oviposition patterns reduce the potential impact of rainfall on eggs, possibly reducing the effect of this important abiotic mortality factor in the field.     

Biological and Integrated Control of Plutella xylostella (Lep., Yponomeutidae) and Crocidolomia pavonana (Lep., Pyralidae) in Brassica Crops in Papua New Guinea

The major constraint to the production of good quality cabbage in Papua New Guinea (PNG) is posed by a complex of insect pests which includes the Diamondback Moth Plutella xylostella (L.) as the most prominent species. In order to evaluate the prospects of a classical control approach economically important major pests and their natural enemies were surveyed in three cabbage growing areas with distinct climatic regimes at low-, mid- and high-elevation. In the PNG highlands (Goroka and Tambul area, Western Highlands Province) the release and successful establishment of the P. xylostella -specific parasitoid Diadegma semiclausum (Hellen) reduced crop losses remarkably since 1995. Favourable circumstances, such as continuous brassica cultivation and low status of associated lepidopteran pests, particularly at Tambul (2400 m above sea level) with an almost temperate climate, were supportive for this approach. In the arid PNG lowlands (Laloki area, Central Province) the introduced P.xylostella -parasitoid Cotesia plutellae (Kurdjumov) exerted 80% parasitism in an experimental site, although a lasting establishment was not achieved in that location. Among several indigenous P. xylostella parasitoids Brachymeria phya (Walker) was a ubiquitous species but did not reduce the pest status of its host. Natural enemies of associated lepidoptera such as Crocidolomia pavonana (Zeller), Spodoptera litura (F.), Helicoverpa armigera (Hübner) and Hellula undalis (F.) were economically insignificant. Thus, insecticidal control, preferably selective, was still a requirement. In comparison to Bacillus thuringiensis -products (Delfin &#174; and Thuricide &#174; ) and the synthetic insect growth regulator Chlorfluazuron (Atabron &#174; ), best results were achieved in field trials with the commercial neem formulation NeemAzal &#174; ( Azadirachta indica A. Juss.) and an aqueous neem seed kernel extract from seeds of PNG grown trees. Besides its high efficacy against lepidopterous pests, neem also controlled the false mustard aphid Lipaphis erysimi (Kalt.), being of economic importance in the arid PNG lowlands. The prospects of integrating C. plutellae into a reduced insecticide spraying program as well as alternative cultural control measures are discussed.     

小菜蛾卵作为赤眼蜂中间寄主的寄生适合度分析

【目的】寻求快速扩繁赤眼蜂种群的寄主,试以繁殖速率较高的小菜蛾为中间寄主,评价不同赤眼蜂种类对小菜蛾卵的寄生适合度并筛选出适合的蜂种。【方法】通过构建稻螟赤眼蜂Trichogramma japonicum Ashmead(简称T.j)、螟黄赤眼蜂T chilonis Ishi(简称T.c)和斑螟分索赤眼蜂Trichogrammatoidea hypsipylae Nagaraja(简称T.h)3种赤眼蜂在小菜蛾Plutella xylostella L.卵上繁殖的实验种群生命表,分析比较其各自的生命表参数,以了解不同蜂种对小菜蛾卵的寄生适合度。【结果】在小菜蛾卵上繁殖的稻螟赤眼蜂的净生殖力R_0、内禀增长率r_m、周限增长率λ与平均世代历期T分别为4.66、0.1633、1.1809、9.2532;斑螟分索赤眼蜂的上述4项参数分别为9.10、0.2177、1.2432、10.1432;螟黄赤眼蜂对小菜蛾卵的寄生能力较差,内禀增长率r_m为0.0338,且其后代性比偏雄,雌雄性比为1♀:6.2(?),以至不能正常传代。斑螟分索赤眼蜂的平均每雌寄生卵数为15.4粒,显著高于稻螟赤眼蜂的10.0粒与螟黄赤眼蜂的8.9粒。【结论】在室内人工培育的小菜蛾卵上繁殖的稻螟赤眼蜂与斑螟分索赤眼蜂对小菜蛾卵的寄生能力较强,尤其是斑螟分索赤眼蜂的内禀增长率r_m与小菜蛾的相近,适合以小菜蛾卵作为中间寄主扩大繁殖,稻螟赤眼蜂次之,而螟黄赤眼蜂并不适合以小菜蛾卵作为中间寄主。