Parasitoid Diadegma Semiclausum Research Articles

Percentage Attacks of Plutella xylostella and Parasitization of the Parasitoid Diadegma semiclausum on Cabbage in Kintamani District

Cabbage plants are one of the horticultural commodities that many farmers cultivate in Indonesia because they have economic value, because apart from being able to meet domestic needs, cabbage also has the opportunity to become an export commodity. This study aims to determine the percentage of attacks by the cabbage leaf caterpillar Plutella xylostella and the level of parasitization of the parasitoid Diadegma semiclausum in Kintamani District. This research was carried out in Sekaan Village and Kedisan Village. The research method uses a survey method. Sampling of cabbage plants in the field was carried out diagonally so that 5 sample points were obtained, 10 plants were observed at each sample point. The research results showed that the percentage of P. xylostella pest attacks in Sekaan Village and Kedisan Village ranged from 12% to 28%. The average population of P. xylostella larvae in Sekaan Village ranges from 0.98 individuals/plant to 1.82 individuals/plant and the highest average population of P. xylostella larvae in Kedisan Village ranges from 0.7 individuals/plant to 1.66 individuals/plant. The level of parasitization of the parasitoid D. semiclausum in Sekaan Village ranges from 32% to 56% and the level of parasitization of the parasitoid D. semiclausum in Kedisan Village ranges from 24% to 48%. The highest peak of parasitization was found in the fourth observation (4 WAP).

Enhanced parasitisation of caterpillars and aphids on field‐grown Brassica oleracea plants upon soil amendment with insect exuviae

Abstract Multitrophic plant–insect interactions are mediated by plant volatiles. The emission of herbivore‐induced plant volatiles is influenced by environmental conditions, such as soil microbes and nutrient composition, with consequences for above‐ground trophic interactions. Here, we investigated whether insect exuviae in the soil alter the plant's volatile blend and attraction of parasitoids in the laboratory and whether this attraction also occurs in the field. We studied the effects of soil amendment with exuviae originating from three insect species, Tenebrio molitor, Acheta domesticus and Hermetia illucens, on the proportion of parasitised Plutella xylostella caterpillars and Brevicoryne brassicae aphids in the field in three consecutive years. In the laboratory, we collected and analysed the volatile blend of amended plants infested with caterpillars or aphids. The attraction of the parasitoids Diadegma semiclausum and Diaeretiella rapae, respectively, towards these volatile blends was assessed in an olfactometer. Our study shows that insect exuviae‐amended soil enhanced the proportion of parasitised herbivores of two species in the field. Relative amounts of several components of the plant volatile blend were affected by soil amendment. Soil amendment with Acheta domesticus or Tenebrio molitor exuviae resulted in an increased attraction of the two parasitoid species in the olfactometer. Soil amendment with insect exuviae altered the plant volatile blend leading to enhanced attraction of parasitoids in laboratory assays. These effects were sustained under the complex and variable biotic and abiotic conditions in the field. Our results underline the importance of belowground processes, such as the decomposition of insect exuviae, on aboveground volatile‐mediated multitrophic interactions. Read the free Plain Language Summary for this article on the Journal blog.

Predicting the impacts of climate change on the biological control of Plutella xylostella by Diadegma semiclausum

Abstract The parasitoid Diadegma semiclausum Hellén (Hymenoptera: Ichneumonidae) has been widely adopted as a biological control agent for Plutella xylostella L. (Lepidoptera: Plutellidae) over the last 80 years. Earlier studies have found differential responses to temperature between the host and its parasitoid and demonstrated the multiple ways in which the parasitoid is more susceptible to elevated temperatures. Using data from experimental studies, the modelling package CLIMEX was used to investigate the suitability of current climates for the host and its parasitoid and the effects on their potential global geographical distributions. The study was then extended to investigate possible changes to these distributions that might result under different climate change scenarios by 2080. The models predict that the global distributions of both the host and parasitoid will be reduced. These changes will not be proportionate and many areas in tropical, sub‐tropical, and temperate regions that are currently suitable for D. semiclausum are predicted to become unsuitable for the parasitoid, whereas retaining suitability for P. xylostella. The seasonal dynamics of both the host and parasitoid are also predicted to be significantly reshaped under climate change. Analysis of associations between annual P. xylostella outbreaks and weather conditions in three provinces in China with field data collected between 1995 and 2017 indicated significant effects of temperature on P. xylostella outbreaks at the beginning of the peak season in warmer provinces where P. xylostella can overwinter; such associations were not found in the colder provinces where it is unable to survive harsh winters.

Differential temperature responses between Plutella xylostella and its specialist endo-larval parasitoid Diadegma semiclausum-Implications for biological control.

Understanding the thermal dynamics of host-parasitoid interactions is crucial to predicting how biological control of pest insects by parasitoids might be affected by geographic location and climate change. We compared performance traits of Plutella xylostella (Lepidoptera: Plutellidae) and its solitary endo-larval parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae), over a wide range of constant rearing temperatures (10-30°C). Parasitoids reared at 30°C experienced reductions in pupation rate, pupal mass, egg load, and adult life span when compared with those reared at lower temperatures. Our analyses of the fate of parasitoids and their hosts and intergenerational population growth at different rearing temperatures show that D. semiclausum and P. xylostella respond differently to temperature, leading to divergent outcomes under different temperature conditions. Some parasitoid larvae could not complete development at 30°C, the temperature at which the host biomass was least and the metabolic demands of the parasitoid could be high, suggesting that parasitoid development might be constrained by lack of host resources at higher temperatures. We discuss the potential mechanisms of parasitoid susceptibility to elevated temperatures, which likely explain the pronounced seasonal dynamics of D. semiclausum in subtropical regions and its failure to establish in lowland tropical regions, where P. xylostella is a serious pest. Similar interactions in other host-parasitoid associations would constrain the efficacy of parasitoids as biological control agents as global temperatures increase.

EKSPLORASI DAN IDENTIFIKASI PARASITOID HAMA Plutella xylostella PADA TANAMAN KUBIS Brassica oleracea

This study aims at exploring and identifying parasitoid Plutella xylostella pest on cabbage plants Brassica oleracea in Nduaria Village and finding out the most dominant parasitoid associated with Plutella xylostella pest. Observation variables used included identification of parasitoid species being parasitic in each stage of Plutella xylostella pest life found in the field, parasitoid species abundance and domination of parasitoid. The result of exploration in three sub-villages of NduariaVillage indicated that there were three species of the parasitoid, namely eggof parasitoid Trichogrammatoidae cojuangcoi, the larva of parasitoid Diadegma semiclausum and Cotesia Plutellae. The dominant parasitoid is Diadegma semiclausumwith the value of 0,11. The most abundance in parasitoid larva Diadegma semiclausum is 5,7%. Damage intensity caused by Plutella xylostella was categorized as medium damage intensity of>25-?50%, and this kept rising along with the age of larva and population as well as supporting environment condition due to Plutella xylostella resistance to the pesticide.

Parameter Biologi dan Demografi Parasitoid Diadegma semiclausum Hellen (Hymenoptera : Ichneumonidae) pada Plutella xylostella L. (Lepidoptera : Plutellidae)

Biological and Demographic Parameters of Parasitoid Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) on Plutella xylostella L. (Lepidoptera: Plutellidae). Diadegma semiclausum Hellen (Hymenoptera: Ichneumonidae) is one of the parasitoid larvae which attacks Plutella xylostella (Lepidoptera: Plutellidae) effectively. This research was aimed to know the biology of parasitoid D. semiclausum in broccoli. The research was carried out in a laboratory by observing the development of parasitoid, fecundity, longevity the males and females as well as parameters demographic of D. semiclausum. The results showed that immature development time of D. semiclausum parasitoid from egg up to adult the imago was 10.65 ± 0.63 days, with the number of fecundity was 22.9 grains. Longevity of male imago of D. semiclausum was 12.10 ± 0.74 days and imago of females 9.80 ± 1.87 days. Parameters demographic of D. semiclausum showed that net reproduction rate (R0) was 22.11 per generation, intrinsic growth rate (r) was 0.18 per day, limited increased rate (?) was 1.16 individuals per day, generation time (T) was 17.50 day.

Effects of Two Cultivated Brassica spp. on the Development and Performance of Diadegma semiclausum (Hymenoptera: Ichneumonidae) and Cotesia vestalis (Hymenoptera: Braconidae) Parasitizing Plutella xylostella (Lepidoptera: Plutellidae) in Kenya.

The diamondback moth (DBM), Plutella xylostella L., is the most destructive pest affecting vegetable production in Kenya and around the world. Parasitoids have shown promising results in lowering the pest populations and damage caused by DBM. However, variations in host plant quality have been reported to have bottom-up effects up to the third and fourth trophic levels. We assessed the effects of two cultivated Brassica varieties (cabbage, Brassica oleracea var. capitata L. cultivar 'Gloria F1' and kale, B. oleracea var. acephala L. cultivar 'Thousand headed') on the development and performance of the specialist pest P. xylostella and two exotic parasitoids Diadegma semiclausum (Hellen) and Cotesia vestalis (Haliday). The exposed larval period of DBM took about 1.5 d longer on kale than cabbage and the total immature development time of both females and males was significantly longer on kale than cabbage. Higher pupal weight and higher fecundity were recorded on DBM fed on kale. Development time of D. semiclausum and C. vestalis was not affected by the host crop as was the parasitism rate of D. semiclausum. Heavier male pupae and larger adults of D. semiclausum, as well as more fecund adults of C. vestalis, were obtained from hosts fed on cabbage. Larger adults of C. vestalis were obtained from herbivores fed on kale. These results show potentially positive effects of host plant allelochemicals that are detrimental to herbivores while promoting parasitoid development and performance, which can be harnessed for the control of DBM.

Biological study of the parasitoid Diadegmasemiclausum (Hellen) on the diamond back moth Plutellaxylostella L. under laboratory conditions

Biological study of the parasitoid Diadegmasemiclausum (Hellen) on the diamond back moth Plutellaxylostella L. under laboratory conditions

Keberhasilan hidup parasitoid Diadegma semiclausum Hellen dan serangga inangnya Plutella xylostella (L.) terhadap aplikasi ekstrak biji srikaya (Annona squamosa L.)

Pengendalian Plutella xylostella L. dapat dilakukan baik secara hayati maupun kimiawi. Pengendalian secara hayati umumnya banyak dilakukan dengan cara memanfaatkan ekstrak tanaman untuk membunuh serangga hama. Penelitian ini bertujuan mengetahui pengaruh ekstrak biji srikaya terhadap kematian dan perkembangan parasitoid Diadegma semiclausum Hellen serta inangnya, P. xylostella. Pengaruh ekstrak biji srikaya terhadap larva P. xylostella instar III awal diuji dengan metode residu pada daun dan metode residu pada permukaan gelas untuk menguji pengaruh kontak ekstrak biji srikaya terhadap kematian imago D. semiclausum. Pengaruh ekstrak biji srikaya terhadap parasitisasi dan perkembangan D. semiclausum pradewasa dilakukan dengan memaparkan larva P. xylostella yang telah terkontaminasi ekstrak biji srikaya pada konsentrasi subletal (LC5 dan LC10) pada imago D. semiclausum. Hasil penelitian menunjukkan ekstrak biji srikaya pada konsentrasi 0,0632–0,1% pada kontaminasi 24 jam berpengaruh terhadap kematian larva P. xylostella dan imago parasitoid D. semiclausum. Imago parasitoid lebih peka terhadap peningkatan konsentrasi ekstrak biji srikaya dibandingkan dengan larva P. xylostella. Hambatan perkembangan P. xylostella oleh ekstrak biji srikaya pada konsentrasi yang digunakan umumnya tidak nyata. Demikian pula, hambatannya terhadap perkembangan parasitoid D. semiclausum dalam inang yang terkontaminasi konsentrasi subletal (LC5 dan LC10) ekstrak biji srikaya umumnya tidak berbeda nyata. Keberadaan ekstrak biji srikaya dalam inang juga tidak berpengaruh nyata terhadap tingkat parasitisasi, panjang kokon, lebar kokon, dan bobot kokon. Oleh karena itu, terdapat peluang memadukan pengendalian P. xylostella secara kimiawi dan hayati.

A plant volatile‐based attractant formulation is not attractive to Diadegma semiclausum (Hymenoptera: Ichneumonidae)

AbstractA synthetic plant volatile‐based attractant has been commercialised for integrated pest management (IPM) of Helicoverpa armigera (Hübner) and H. punctigera (Wallengren) in Australian cotton, corn and beans. This attract‐and‐kill formulation is being tested in Australia in canola as an IPM tool to minimise the amount of insecticide used for the control of diamondback moth (DBM) Plutella xylostella (Linnaeus). DBM is a destructive insect pest of cruciferous crops with a cosmopolitan distribution and has developed resistance to almost every synthetic insecticide applied in the field. However, in brassica crops, naturally occurring parasitoids are often important components of IPM. Therefore, it is essential to investigate how parasitoids deal with plant volatiles released from this formulation and whether this formulation is safe for non‐target insects especially parasitoids. Wind tunnel experiments were conducted to assess the effect of the formulation on larval parasitoid Diadegma semiclausum (Hellén), which is an effective biological control agent of DBM. Our results showed that the formulation was significantly less attractive than either water or untreated leaves. Unfed female D. semiclausum were highly attracted to the honey food source, while after feeding, there was no significant preference among treatments with the exception of significantly less visits to leaves treated with the formulation. Furthermore, the presence of the formulation appears to have reduced the attractiveness of leaves, which were infested with DBM larvae. Our result shows that 2 days after application, female wasps visited leaves treated with the formulation significantly less than untreated healthy leaves, even if DBM larvae were present on the leaves treated with the formulation. We conclude that the formulation is not attractive to D. semiclausum female wasps. The wasps' avoidance of leaves treated with the attractant, even if those leaves were infested with DBM larvae, suggests that the formulation can act as a repellent to the female wasps.

Importance of primary metabolites in canola in mediating interactions between a specialist leaf-feeding insect and its specialist solitary endoparasitoid

The role of primary plant chemistry on trophic interactions is not well studied. We examined the effect of primary plant metabolites, focusing on nitrogen, on several biological indices of second and third trophic level insects in a model tritrophic system, consisting of two strains of the crucifer, Brassicanapus (canola) (SLM046 and RGS003), the specialist insect herbivore Plutella xylostella (L.) (Lepidoptera: Plutellidae), and its specialist koinobiont larval-pupal parasitoid Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae). In particular, we measured relative growth rate of the herbivore in relation to an index for plant quality (nitrogen content of leaf tissues), developmental time of the herbivore (sum of second, third, and fourth larval instars durations), and intrinsic rate of increase (rm) of the herbivore and the parasitoid. Tritrophic studies were conducted on development, survivorship curve analysis, reproductive potential, life history, parasitism, and several other fitness correlates of the parasitoid. The life table parameters of D. semiclausum were determined under laboratory conditions. The intrinsic rate of increase (rm) of the parasitoid was significantly higher on RGS003 than SLM046. In this tritrophic model, the results indicated that the bottom-up direct effect on the herbivore population growth rate was marginally as strong as the direct effect of top-down force due to the parasitoid population growth rate; but it was higher than its indirect counterpoint mediated with the parasitoid population growth rate. Consequently, D. semiclausum performed better on RGS003, which was the most inferior host to P. xylostella in comparison with another plant cultivar and had the lowest content of nitrogen in its leaves.

Effects of mixed cropping on population densities and parasitism rates of the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae)

Effects of mixed cropping and barrier crops on the population density and parasitism of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), were evaluated in field plots of cabbage grown in Bali, Indonesia. The densities of P. xylostella at larval and pupal stages, as well as the overall density at larval plus pupal stages, were significantly lower in cabbage/coriander mixed cropping subplots than in cabbage monoculture subplots. Parasitism of P. xylostella by the larval parasitoid Diadegma semiclausum (Hellen) (Hymenoptera: Ichneumonidae) was not significantly different between the mixed and monocultural cropping systems. These results do not support the so-called enemies hypothesis, but suggest that disruption of the host searching behavior of female moths by neighboring non-host plants is the mechanism behind the associational resistance observed in the coriander mixed cropping system. The inclusion of a Napier grass barrier between mixed crop and monoculture subplots did not affect the influence of mixed cropping on larval and pupal densities. Therefore, Napier grass, which is used locally as a fence for preventing livestock invasion of fields, would not obstruct the pest-reducing effect of coriander/cabbage mixed cropping.

Population dynamics of the diamondback moth Plutella xylostella L. (Lepidoptera: Yponomeutidae) in the Sydney Region of Australia

The population dynamics of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Yponomeutidae) was investigated at three farms on the Western side of the Sydney Basin, Australia, from November 2003 to October 2004. Adult populations were monitored fortnightly by counting the number that was trapped on yellow sticky traps, which peaked around November to December (summer) in all three farms, with virtually no trap catches in the winter months (June-August). The seasonal trend of adult DBM showed a higher number per trap in summer, ranging from 34.5-41.7 compared with the other seasons. Larval and pupal densities were highest in summer (2.0-4.0 and 3.3-5.1 per plant, respectively), while the lowest numbers were recorded in winter. Rainfall had a significant impact on the DBM populations. The activity (numbers and parasitism) of the DBM parasitoid Diadegma semiclausum Héllen (Hymenoptera: Ichneumonidae) was recorded in all three farms, with the population showing a synchrony with that of the DBM. The highest number of parasitoids per trap (36.8-53.8) was recorded in summer compared with the other seasons. Parasitism was highest in the non-sprayed farm (56.3%) in summer compared with 16.4% and 31.5% in the other farms which have been sprayed with insecnticides. Canonical correspondence analysis showed environmental variables accounting for 11.2% of the variability in the insect data, out of which 83.9% was explained along the first canonical axis.© 2010 International Formulae Group. All rights reserved.Keywords: Diamondback moth, Plutella xylostella, Diadegma semiclausum, parasitism, brassica

Natural variation in herbivore-induced volatiles in Arabidopsis thaliana

To study whether natural variation in Arabidopsis thaliana could be used to dissect the genetic basis of responses to herbivory in terms of induced volatile emissions, nine accessions were characterized upon herbivory by biting-chewing Pieris rapae caterpillars or after treatment with the phytohormone jasmonic acid (JA). Analysis of 73 compounds in the headspace showed quantitative differences in the emission rates of several individual compounds among the accessions. Moreover, variation in the emission of volatile compounds after JA treatment was reflected in the behaviour of the parasitoid Diadegma semiclausum when they were offered the headspace volatiles of several combinations of accessions in two-choice experiments. Accessions also differ in transcript levels of genes that are associated with the emission of plant volatiles. The genes BSMT1 and Cyp72A13 could be connected to the emission of methyl salicylate and (E,E)-4,8,12-trimethyltrideca-1,3,7,11-tetraene (TMTT), respectively. Overall, Arabidopsis showed interesting phenotypic variations with respect to the volatile blend emitted in response to herbivory that can be exploited to identify genes and alleles that underlie this important plant trait.

The herbivore-induced plant volatile methyl salicylate negatively affects attraction of the parasitoid Diadegma semiclausum.

The indirect defense mechanisms of plants comprise the production of herbivore-induced plant volatiles that can attract natural enemies of plant attackers. One of the often emitted compounds after herbivory is methyl salicylate (MeSA). Here, we studied the importance of this caterpillar-induced compound in the attraction of the parasitoid wasp Diadegma semiclausum by using a mutant Arabidopsis line. Pieris rapae infested AtBSMT1-KO mutant Arabidopsis plants, compromised in the biosynthesis of MeSA, were more attractive to parasitoids than infested wild-type plants. This suggests that the presence of MeSA has negative effects on parasitoid host-finding behavior when exposed to wild-type production of herbivore-induced Arabidopsis volatiles. Furthermore, in line with this, we recorded a positive correlation between MeSA dose and repellence of D. semiclausum when supplementing the headspace of caterpillar-infested AtBSMT1-KO plants with synthetic MeSA.Electronic supplementary materialThe online version of this article (doi:10.1007/s10886-010-9787-1) contains supplementary material, which is available to authorized users.

Nectar to improve parasitoid fitness in biological control: Does the sucrose:hexose ratio matter?

The consumption of saccharide-rich foods such as floral nectar is crucial for the survival of many adult parasitoid wasps. The importance to parasitoids of nectar quality, with regards to its sucrose:hexose ratio, was investigated. Nectar, an aqueous solution of sugars, amino acids and other compounds, differs between plant species. Nectar composition is dominated by sucrose, glucose and fructose. Previous studies have shown that the ratio of sucrose to hexose (glucose+fructose) sugars can explain nectar associations in a range of flower visiting arthropods. It has been suggested that this ratio may be important in terms of parasitoid fitness. Analysis of floral nectar from fourteen plant species confirmed that the sucrose/hexose ratio significantly differed between species. An opportunity to select floral resources based on this measure of nectar quality arose and highlighted the potential to utilize native flowering plant species in place of the seven most commonly deployed, which are usually not native to the countries in which they are used. Results presented in this paper indicate, however, that the sucrose/hexose ratio is not a significant factor explaining parasitoid longevity. The hymenopteran parasitoids Diadegma semiclausum (Ichneumonidae) and Dolichogenidea tasmanica (Braconidae) were fed 40% w/w sugar solutions, differing in their sugar ratios. Solutions were classified as either sucrose-dominant (ratio >0.99), sucrose-rich (ratio 0.5–0.99), hexose-rich (ratio 0.1–0.499) or hexose-dominant (ratio <0.1). No significant differences in parasitoid longevity were found between the different treatments for either species. This suggests there is not an optimal sucrose/hexose ratio for parasitoid wasps, although a greater number of parasitoid species should ideally be tested to confirm if this is true for the wider parasitoid taxonomic groups. Die Nutzung von saccharidhaltigem Blütennektar trägt entscheidend zum Überleben von vielen erwachsenen parasitoiden Wespen bei. Es wurde die Bedeutung der Nektarqualität, gemessen als Verhältnis von Saccharose zu Hexose, für die Parasitoide untersucht. Nektar ist eine wässerige Lösung von Zuckern, Aminosäuren und anderen Bestandteilen, und unterscheidet sich zwischen den Pflanzenarten. Die Nektarzusammensetzung ist von Saccharose, Glukose und Fruktose dominiert. Vorhergehende Untersuchungen haben gezeigt, dass das Verhältnis von Saccharose zu Hexose (Glukose und Fruktose) die Bindungen an Nektar bei einer Reihe von blütenbesuchenden Arthropodengruppen erklären kann. Es wurde vermutet, dass das Verhältnis in Bezug auf die Fitness der Parasitoiden wichtig sein könnte. Die Analyse des Nektars von vierzehn Pflanzenarten bestätigte, dass sich das Verhältnis von Saccharose:Hexose zwischen den Arten signifikant unterschied. Es ergab sich die Gelegenheit die Blütenressourcen auf der Grundlage dieses Maßes für Nektarqualität auszuwählen und sie beleuchtete die Möglichkeit, einheimische Blütenpflanzenarten anstelle der sieben am häufigsten genutzten Arten zu nutzen, die normalerweise in den Ländern, in denen sie genutzt werden, nicht einheimisch sind. Die in dieser Veröffentlichung präsentierten Ergebnisse zeigen jedoch, dass das Verhältnis von Saccharose:Hexose kein signifikanter Faktor ist, um die Lebensspanne der Parasitoiden zu erklären. Die hymenopteren Parasitoide Diadegma semiclausum (Ichneumonidae) und Dolichogenidea tasmanica (Braconidae) wurden mit 40% w/w Zuckerlösungen gefüttert, die sich in ihren Zuckerverhältnissen unterschieden. Die Lösungen wurden entweder als saccharosedominiert (Verhältnis >0,99), saccharosereich (Verhältnis 0.5–0.99), hexosereich (Verhältnis 0.1–0.499) oder hexosedominiert (Verhältnis <0.1) klassifiziert. Es wurden für keine Art signifikante Unterschiede in der Lebensspanne der Parasitoide zwischen den verschiedenen Varianten gefunden. Dies lässt vermuten, dass es kein optimales Verhältnis Saccharose:Hexose für die parasitoiden Wespen gibt, obwohl eine größere Anzahl parasitoider Arten idealerweise getestet werden sollten, um zu bestätigen, ob dies auch für größere parasitoide taxonomische Gruppen gilt.

POTENTIAL IMPACT OF METARHIZIUM ANISOPLIAE ON THE DIAMONDBACK MOTH (LEPIDOPTERA: PLUTELLIDAE) AND ITS PARASITOID DIADEGMA SEMICLAUSUM (HYMENOPTERA: ICHNEUMONIDAE)

Potential Impact of Metarhizium anisopliae on the Diamondback Moth (Lepidoptera: Plutellidae) and Its Parasitoid Diadegma semiclausum (Hymenoptera: Ichneumonidae). Laboratory studies were conducted to evaluate the effect of the Metarhizium anisopliae against the diamondback moth, Plutella xylostella and its parasitoid, Diadegma semiclausum. A completely randomized design consisted of 5 treatments (4 concentrations of conidial suspension: 5 x 104, 3.5 x 105, 2.5 x 106, 1.2 x 107 conidia/ml and control) was used. The results indicated that the mortality of P. xylostella larvae were significantly induced by the fungal treatments. A significant reduction in pupation and adult emergence of P. xylostella was also detected in all treatments when compared with that in the control. The fungus might also result in a male-biased sex ratio of the surviving P. xylostella. When applied at a concentration of 1.2 x 107 conidia/ml, M. anisopliae might significantly reduce the survival of the parasitoid, D. semiclausum. Thus, despite its potential as a biological control agent against P. xylostella, the entomomogenous fungus M. anisopliae was also detrimental to the larvae parasitoid D. semiclausum.

Predicting the time to colonization of the parasitoid Diadegma semiclausum: The importance of the shape of spatial dispersal kernels for biological control

The time at which natural enemies colonize crop fields is an important determinant of their ability to suppress pest populations. This timing depends on the distance between source and sink habitats in the landscape. Here we estimate the time to colonization of sink habitats from a distant source habitat, using empirical mark-capture data of Diadegma semiclausum in Broccoli. The data originated from experiments conducted at two locations and dispersal was quantified by suction sampling before and after a major disturbance. Three dispersal kernels were fitted to the dispersal data: a normal, a negative exponential, and a square root negative exponential kernel. These kernels are characterized by a thin, intermediate and a fat tail, respectively. The dispersal kernels were included in an integro-difference equation model for parasitoid population redistribution to generate estimates of time to colonization of D. semiclausum in sink habitats at distances between 100 and 2000 m from a source. We show that the three dispersal kernels receive similar support from the data, but can produce a wide range of outcomes. The estimated arrival time of 1% of the D. semiclausum population at a distance 2000 m from the source ranges from 12 days to a length of time greatly exceeding the life span of the parasitoid. The square root negative exponential function, having the thickest tail among the tested functions, gave the fastest spread and colonization in three of the four data sets, but it gave the slowest redistribution in the fourth. In all four data sets, the rate of accumulation at the target increased with the mean dispersal distance of the fitted kernel model, irrespective of the fatness of the tail. This study underscores the importance of selecting a proper dispersal kernel for modelling spread and colonization time of organisms, and of the collection of pertinent data that enable kernel estimation and that can discriminate between different kernel shapes.

Assessing the impact of biological control of Plutella xylostella through the application of Lotka–Volterra model

The Lotka–Volterra model was applied to the population densities of diamondback moth (DBM), Plutella xylostella (L.) and its exotic larval parasitoid Diadegma semiclausum (Hellen) data that was collected earlier by icipe's DBM biological control team. The collections were done for 15 months before the release and 36 months after release of the parasitoid in two areas; in Werugha, Coast Province of Kenya and Tharuni, Central Province of Kenya, respectively. For each area in pre- and post-release periods, we estimated Lotka–Volterra model parameters from the minimization of the loss function between the theoretical and experimental time-series datasets following the Nelder-Mead multidimensional method. The model estimated a reduction in the value of the steady state of DBM population from 4.86 to 2.17 in Werugha and from 6.11 to 3.76 and 3.45 (with and without exclusion of the time before D. semiclausum recovery) in Tharuni when transiting from the pre- and post-release periods, respectively. This change was a consequence of the newly introduced parasitoid, in the areas. The study presented a successful and detailed technique for non-linear model parameters restoration which was demonstrated by the correct mimicking of empirical datasets from the classical biological control with D. semiclausum, in different areas of Kenya. The applied model has measured the parasitoids impact on the DBM biological control through a quantitative estimate of the effectiveness of the newly introduced species D. semiclausum. These equations may therefore be used as tool for decision making in the implementation for such pests’ management system strategy.

Contributions of parasitoids and Bacillus thuringiensis to the management of Diamondback Moth in highland crucifer production in Da Lat, Vietnam

Socioeconomic technical surveys were carried out in the highland crucifer production areas of Da Lat, Vietnam to learn the potential impacts of using the multiple biological control agents Bacillus thuringiensis (Bt) and the parasitoids Diadegma semiclausum (Ds) and Diadromus collaris (Dc) for control of Plutella xylostella (Diamondback Moth, DBM). Ds and Dc were introduced in Vietnam in 1995 and were in widespread use by 2000. Crucifer farmers have access to as many as 16 formulated commercial products of Bt. Based on both biological parameters (parasitoid-DBM abundance) and socioeconomic performance indicators such as yield increase, pesticide cost reduction, and gross margin, the present year-long study revealed that farmers who adopted biological controls to manage DBM were able to lower their production cost by US$133–513/ha, thereby reducing their pest management costs by three times in comparison to those who relied only on the chemical pesticides. Farmers who manage DBM using Bt and practice conservation of parasitoids (Ds and Dc) can ensure sustainable crucifer production in highland production systems, reducing the potential ill effects of chemical use.