Cotesia Plutellae Kurdjumov Research Articles

Safety of selected botanical and synthetic insecticides against braconid parasitoids of vegetable ecosystems

Insecticides are unavoidable in pest management programmes especially when the pest crosses economic threshold level (ETL). In this context, some of the insecticides and botanicals that are used in vegetable ecosystem were test verified for their relative safety against the commonly encountered parasitoids viz., Bracon brevicornis Wesmael, Chelonus blackburni Cameron and Cotesia plutellae Kurdjumov. Toxicity effects of five insecticides viz ., Acephate 75SP, Chlorpyriphos 20EC, Cypermethrin 10EC, Profenofos 50EC, Quinalphos 25EC and NSKE 5 per cent against B. brevicornis, C. blackburni and Hexane extracts of Lantana camara var. aculeate tested against C. plutellae were evaluated under laboratory conditions. Amongst insecticides tested, Profenofos 50EC was found to be most toxic with LC 50 value of 22.27 and 16.280 ppm; Chlorpyriphos 20EC was the least toxic with the highest LC 50 value of 198.53 and 314.255 ppm and NSKE 5 per cent had no effect against B. brevicornis and C. blackburni , respectively. C. plutellae pupae were treated with hexane extracts of L. camara resulted of 66.67 and 76.67 per cent with reduction of adult emergence at 8 and 10 per cent, respectively. While, C. plutellae adults were found to be safe at all concentrations except 8 and 10 per cent and its contact toxicity of 63.33 and 96.67 per cent adult mortality recorded within 24h by dry film method. The results suggest that the Chlorpyriphos 20EC and botanical extracts can very well integrate in the management of vegetable insect pests.

Effect of Sensitization on the Orientation Response of Cotesia plutellae Females towards the Odour of Cruciferous Host Plant and Host Larval Body Extracts

The importance of odour learning in host habitat and host selection is well demonstrated in many insects. In this present study using Cotesia plutellae Kurdjumov as a model, we examined the capacity of naive C. plutellae females to learn and orient towards the odour of cruciferous host plant, host larval body extracts of Plutella xylostella (L.), larvae reared on different host plants in a 'Y' tube olfactometer by repeated exposure. The acquired capability to recognize an odour by repeated exposures (sensitization) to a particular odour produced a strong decline in orientation time of wasps to the odour source. The decline in orientation time at 5 th exposure level was at least 55% and 36%, respectively, for virgin and gravid females to HPLE odours in relation to first exposure level. Whereas the HLBE odours elicited 49% and 51% decline in orientation time, respectively in virgin and gravid females compared to 1 st exposure level. Briefly, the gravid females oriented much faster toward larval body odours compared to host plant odours; while, virgin females were more attracted and rapidly oriented to host plant odours compared to larval body odours, signifying some synomonal/kairomonal substances are involved in influencing the orientation. The rapid orientation response observed for various infochemical extracts demonstrate that C. plutellae upon sensitization can respond to the chemical signals of most preferred odour in a host plant-herbivore complex associated with cruciferous crop ecosystem.

Insecticide susceptibility of surviving Cotesia plutellae (Hym: Braconidae) and Diaeretiella rapae (M'Intosh) (Hym: Aphidiidae) as affected by sublethal insecticide dosages on host insects

The effects of sublethal dosages of insecticides applied to Plutella xylostella L. (Lepidoptera: Yponomeutidae) and Lipaphis erysimi Kaltenbach (Homoptera: Aphidiidae) on the insecticide susceptibility of the surviving endoparasitoids, Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) and Diaeretiella rapae (M'Intosh) (Hymenoptera: Aphidiidae), were studied in Shangjie, Minhou, China. The susceptibility to methamidophos and the sensitivity of acetylcholinesterase (AChE) to methamidophos and dichlorvos in the adults of host insects were substantially lower than those in the two parasitoids. The host insects were treated with sublethal dosages of methamidophos in P. xylostella and of methamidophos and avermectin in L. erysimi. The cocoon formation in the two parasitoids decreased significantly, from 35.0% (control) to 13.0% (with methamidophos treatment) for C. plutellae; from 20.6% (control) to 9.0% (with methamidophos treatment) and from 24.3% (control) to 16.7% (with avermectin treatment) for D. rapae. The susceptibility to methamidophos of the resultant emerging adults of the two parasitoids was found to be significantly lower than that of the control when the parasitoids were left in contact with the same dosages of methamidophos. The average AChE activity inhibition by methamidophos and dichlorvos in 34-60 adults of the two parasitoids that emerged from the treatments (15.1% and 31.8% respectively for C. plutellae, and 21.1% and 26.9% for D. rapae) was also significantly lower than those of the controls (55.4% and 48.3% respectively for C. plutellae, and 42.9% and 51.7% for D. rapae). The bimolecular rate constant (k(i)) values of AChE to methamidophos and dichlorvos in the adults of parasitoids without the insecticide treatment were 1.78 and 1.56 times as high as those that emerged from the host insects treated with methamidophos for C. plutellae, and 1.91 and 1.66 times as high as those in the case of D. rapae. It is suggested that there is a difference in AChE sensitivity to insecticides between the resultant emerging parasitoids with and without insecticide pretreatment. Furthermore, the introduction of the insecticides to the host insects could be an important factor in the insecticide resistance development of the endoparasitoids. The natural selectivity would favour the parasitoids that had developed an insensitivity to the insecticide(s).

Biological Control of Crucifer Crop Pests and Participatory IPM in Thailand

Larvae of the diamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Ypeunomutidae) and other crucifer pests cause severe economic damage to cabbage, Brassica oleracea L. var. capitata (Brassicaceae) and related vegetables in Thailand and elsewhere in Southeast Asia. Overuse of pesticides is a serious problem in most vegetable growing areas of the country. Six species of parasitoids were reared from DBM larvae and pupae collected in northern Thailand in 1989–90 and 2003–04. The larval parasitoid Cotesiaplutellae Kurdjumov (Braconidae) appears to be the most important parasitoid of DBM in Thailand; other native or naturalized parasitoids may play supplementary roles. These natural enemies can and should be conserved in well thought out, participatory IPM programs. Field experiments comparing local farmer practice (weekly sprays of synthetic pyrethroid insecticides) to a simple IPM protocol using Bt and neem demonstrated superior control and higher yields of undamaged cabbage from the IPM treatment. This information on DBM parasitoids and other natural enemies of crucifer pests has been developed into a poster and other extension materials currently used in national “training of trainer” (for vegetable IPM) programs throughout Thailand. Farmer-centered IPM programs focused on conservation of local DBM parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.

Hymenopteran Parasitoids of Diamondback Moth (Lepidoptera: Ypeunomutidae) in Northern Thailand

Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Ypeunomutidae), cause severe economic damage to cabbage, Brassica oleracea L. variety capitata (Brassicaceae) and related vegetables in Thailand. Overuse of broad-spectrum insecticides for diamondback moth control is a serious problem and has obscured the contributions of indigenous parasitoids. Our objectives were to identify indigenous diamondback moth parasitoids in northern Thailand and to assess their potential for natural control. Six parasitoid species were reared from diamondback moth larvae and pupae collected in 1990 and in 2003-2004. These included the larval parasitoid Cotesia plutellae Kurdjumov (Braconidae), a larval-pupal parasitoid Macromalon orientale Kerrich (Ichneumonidae), and pupal parasitoids Diadromus collaris Gravenhorst (Ichneumonidae) and Brachymeria excarinata Gahan (Chalcididae). Single specimens of Isotima sp. Forster (Ichneumonidae) and Brachymeria lasus Walker (Chalcididae) also were reared from diamondback moth hosts. C. plutellae was the dominant larval parasitoid and was often reared from host larvae collected from fields sprayed regularly with insecticides; parasitism ranged from 14 to 78%. Average parasitism by M. orientale was only 0.5-6%. Parasitism of host pupae by D. collaris ranged from 9 to 31%, whereas B. excarinata pupal parasitism ranged from 9 to 25%. An integrated pest management (IPM) protocol using simple presence-absence sampling for lepidopterous larvae and the exclusive use of Bacillus thuringiensis (Bt) or neem resulted in the highest yields of undamaged cabbage compared with a control or weekly sprays of cypermethrin (local farmer practice). IPM programs focused on conservation of local diamondback moth parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.

Hymenopteran Parasitoids of Diamondback Moth (Lepidoptera: Ypeunomutidae) in Northern Thailand

Larvae of the diamondback moth, Plutella xylostella (L.) (Lepidoptera: Ypeunomutidae), cause severe economic damage to cabbage, Brassica oleracea L. variety capitata (Brassicaceae) and related vegetables in Thailand. Overuse of broad-spectrum insecticides for diamondback moth control is a serious problem and has obscured the contributions of indigenous parasitoids. Our objectives were to identify indigenous diamondback moth parasitoids in northern Thailand and to assess their potential for natural control. Six parasitoid species were reared from diamondback moth larvae and pupae collected in 1990 and in 2003–2004. These included the larval parasitoid Cotesia plutellae Kurdjumov (Braconidae), a larval-pupal parasitoid Macromalon orientale Kerrich (Ichneumonidae), and pupal parasitoids Diadromus collaris Gravenhorst (Ichneumonidae) and Brachymeria excarinata Gahan (Chalcididae). Single specimens of Isotima sp. Förster (Ichneumonidae) and Brachymeria lasus Walker (Chalcididae) also were reared from diamondback moth hosts. C. plutellae was the dominant larval parasitoid and was often reared from host larvae collected from fields sprayed regularly with insecticides; parasitism ranged from 14 to 78%. Average parasitism by M. orientale was only 0.5–6%. Parasitism of host pupae by D. collaris ranged from 9 to 31%, whereas B. excarinata pupal parasitism ranged from 9 to 25%. An integrated pest management (IPM) protocol using simple presence-absence sampling for lepidopterous larvae and the exclusive use of Bacillus thuringiensis (Bt) or neem resulted in the highest yields of undamaged cabbage compared with a control or weekly sprays of cypermethrin (local farmer practice). IPM programs focused on conservation of local diamondback moth parasitoids and on greater implementation of biological control will help alleviate growing public concerns regarding the effects of pesticides on vegetable growers and consumers.

Seasonal Changes of Methamidophos Susceptibility and Biochemical Properties in <I>Plutella xylostella</I> (Lepidoptera: Yponomeutidae) and Its Parasitoid <I>Cotesia plutellae</I> (Hymenoptera: Braconidae)

Methamidophos resistance and acetylcholinesterase (AChE) insensitivity to methamidophos, dichlorvos, and carbofuran were determined in the field populations of Plutella xylostella (L.) (Lepidoptera: Yponomeutidae) and its parasitoid Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) collected from the corresponding hosts between October 1998 and December 2003 in Fuzhou and Minhou, Fijian, China. Resistance levels to methamidophos and AChE insensitivity to the three insecticides in the two species of insects were high during autumn and spring and low during summer. Resistance to methamidophos was 15.3- and 12.6-fold higher in resistant F0 parents of P. xylostella and C. plutellae than in their susceptible F11 progeny, respectively. The bimolecular rate constant (k(i)) values of AChE to methamidophos, dichlorvos, and carbofuran were 4.6-, 6.3-, and 7.7-fold higher in F11 progeny of P. xylostella, and 3.7-, 4.5-, and 3.7-fold higher in F11 progeny of C. plutellae than those in their F0 parents, respectively. Compared with susceptible F11 progeny, the resistance ratios for methamidophos were 4.2-29.8 and 3.8-13.1 in 21 field populations of P. xylostella and C. plutellae, respectively. The k(i) values of AChE to methamidophos, dichlorvos, and carbofuran were 2.0-21.6-, 3.6-9.5-, and 2.6-9.2-fold higher in F11 progeny of P. xylostella, and 1.8-7.6-, 1.9-4.6-, and 2.2-7.6-fold higher in F11 progeny of C. plutellae than those in 21 field populations, respectively. Significant correlative variations of methamidophos resistance as well as significant correlative variations of k(i) values of AChE to insecticides between the two species of insects also were found in space and time. The k(i) values of AChE to insecticides in C. plutellae were far higher than those in P. xylostella. There were no obvious differences in the Km and Vmax of AChE between F0 parents and F11 progeny of P. xylostella and C. plutellae, respectively. But carboxylesterase activity was 1.6-fold higher in F0 parents of C. plutellae than in F11 progeny, and glutathione S-transferase activity was 1.5-fold higher in F0 parents of P. xylostella than in F11 progeny. The results suggested that the AChE insensitivity to insecticides might play the most important role in methamidophos resistance in the two species of insects. From these results, a spatial and temporal correlative evolution of methamidophos resistance and insensitive AChE was found to exist between P. xylostella and C. plutellae.

Host resistance to an insecticide favors selection of resistance in the parasitoid, Cotesia plutellae (Hymenoptera: Braconidae)

Abstract Laboratory selection was conducted for fenvalerate resistance in two colonies of the parasitoid, Cotesia plutellae Kurdjumov, each reared on a different colony of its host, Plutella xylostella (L.), with different level of resistance to the insecticide. In the selection regime the insecticide was applied to the host larvae that harbored the parasitoid larvae. Compared with the unselected parasitoid colony, the parasitoid colony selected with the susceptible hosts acquired 4.5-fold resistance after 14 selection cycles, while the colony selected with the more resistant hosts acquired 13.6-fold resistance after 13 selection cycles. These results demonstrate that parasitoid larvae could be exposed to insecticide selection via the hosts, selection with more resistant hosts could accelerate development of resistance in the parasitoid, and resistance genes selected during larval development could be expressed at the adult stage. This information can help improve selection procedures for insecticide resistance in parasitoids.

Seasonal abundance of the parasitoid complex associated with the diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae) in Hangzhou, China.

An investigation of insect parasitoids of the diamondback moth, Plutella xylostella (Linnaeus), in brassica vegetable crops in the suburbs of Hangzhou was conducted during five periods from 1989 to 1997. Eight species of primary parasitoids were recorded: Trichogramma chilonis Ishii, Cotesia plutellae Kurdjumov, Microplitis sp., Oomyzus sokolowskii Kurdjumov, Diadromus collaris (Gravenhorst), Itoplectis naranyae (Ashmead), Exochus sp. and Brachymeria excarinata Gahan. Seven species of hyperparasitoids were also collected. Rates of parasitism of eggs of P. xylostella were usually very low. However, rates of parasitism of larvae and pupae were substantial and showed two peaks each year, around June-July and September-November respectively. Rates of parasitism during peaks were usually 10-60% and reached over 80% on a few occasions. Cotesia plutellae, O. sokolowskii and D. collaris were the major larval, larval-pupal and pupal parasitoids respectively. In the field, C. plutellae was active throughout the year. Oomyzus sokolowskii was active from May to October, entered a quiescent pupal stage in October-November to overwinter and did not emerge until next April-May. Diadromus collaris was recorded from April to July and October. Rates of parasitism of P. xylostella in radish and mustard fields were usually higher than those in cabbage and Chinese cabbage fields in the same locality. Negative correlations of parasitism rates between C. plutellae and O. sokolowskii indicate a competitive relationship for host larvae between these two larval parasitoids.

Simulation of Integration ofBacillus thuringiensisand the ParasitoidCotesia plutellae(Hymenoptera: Braconidae) for Control of Susceptible and Resistant Diamondback Moth (Lepidoptera: Plutellidae)

We used computer simulations to better understand how to combine the microbial insecticide Bacillus thuringiensis Berliner and the parasitoid Cotesia plutellae Kurdjumov to control diamondback moth, Plutella xylostella (L.). The simulations incorporated potential for the evolution of moth resistance to Bacillus thuringiensis with Bacillus thuringiensis -parasitoid-pest interactions. We considered the effects of pest immigration, pesticide refuge, and pesticide dose on diamondback moth control and resistance development by diamondback moth. Four major conclusions were drawn. First, C. plutellae and B. thuringiensis could be used effectively to control diamondback moth. Second, the use of parasitoids such as C. plutellae could slow the evolution of pesticide resistance by decreasing the number of generations in which pesticide treatment is required. Third, parasitoids could be complementary to refuges from pesticides, with parasitoids maintaining control of a pest while refuges slow the development of resistance to the pesticide by the pest. Fourth, in conjunction with the use of parasitoids, high dose or low dose strategies have similar consequences on pest density over long periods. However, unless there is substantial immigration of susceptible individuals into the pest population or some type of pesticide refuge, a low dose strategy is better for controlling pests.

Diamondback Moth (Lepidoptera: Plutellidae): Parasitism by Cotesia plutellae (Hymenoptera: Braconidae) in Cabbage

Cotesia plutellae Kurdjumov was evaluated as a potential biological control agent for diamondback moth, Plutella xylostella (Linnaeus), in cabbage in spring 1993 and 1994. The parasitoids were reared in a commercial insectary in Texas, delivered overnight via air express, and released 24-48 h after receipt in cabbage fields in Northeast Florida. In 1993, only adult parasitoids were released, but adults and cocoons were released in 1994. The numbers of C. plutellae released ranged from 456 per ha per wk in 1993 to 1,334 per ha per wk in 1994. Four consecutive releases were made each year beginning in early February. Parasitism of diamondback moth larvae by C. plutellae ranged from 3.6 to 10.9%, and the level of parasitism was related to the total numbers of parasitoids released. C. plutellae parasitoids were complimentary to the naturally occurring parasitoid Diadegma insulare (Cresson), and the combined mean seasonal parasitism of diamondback moth exceeded 34% in some fields. There was no evidence that C. plutellae became established in the general area although > 124,000 parasitoids were released over the 2-year test period.

Independent and Combined Effects of Bacillus thuringiensis and the Parasitoid Cotesia plutellae (Hymenoptera: Braconidae) on Susceptible and Resistant Diamondback Moth (Lepidoptera: Plutellidae)

We evaluated mortality to larvae of diamondback moth, Plutella xylostella (L.), caused by the microbial pathogen Bacillus thuringiensis Berliner and the endoparasitic wasp Cotesia plutellae Kurdjumov, separately and in combination. Each of 3 colonies of diamondback moth (susceptible, moderately resistant, and highly resistant to B. thuringiensis ) received the following 4 treatments: (1) control, (2) B. thuringiensis . only, (3) parasitoids only, and (4) B. thuringiensis plus parasitoids. With increasing colony resistance, the effect of B. thuringiensis Decreased but the effect of parasitoids remained the same. The effect of B. thuringiensis plus parasitoids depended on the susceptibility of the host to B. thuringiensis. For the susceptible colony, highest diamondback moth mortality was caused by B. thuringiensis plus parasitoids. but for the 2 resistant colonies, parasitoids alone caused as much mortality as B. thuringiensis and parasitoids combined. For the susceptible and highly resistant colonies, we also evaluated the effect of varying the time interval between parasitism by C. plutellae and exposure to B. thuringiensis on diamondback moth mortality and C. plutellae survival. For the susceptible colony, diamondback moth mortality and C. plutellae survival did not vary as a function of the time interval between parasitism and exposure to B. thuringiensis. For the resistant colony, delaying B. thuringiensis treatment from 0 to 4 d after parasitism occurred did not affect diamondback moth mortality, but it significantly increased parasitoid survival. Efforts to integrate B. thuringiensis and C. plutellae must consider mortality of immature parasitoids inside of susceptible hosts.

Host-Mediated Competition Between the Pathogen Bacillus thuringiensis and the Parasitoid Cotesia plutellae of the Diamondback Moth (Lepidoptera: Plutellidae)

We evaluated the effects of variation in phenotype of Plutella xylostella (L.), diamondback moth, on within-host interactions between the bacterial pathogen Bacillus thuringiensis Berliner and larvae of the parasitoid wasp, Cotesia plutellae Kurdjumov. The outcome of interactions between the parasitoid and pathogen depended on host phenotype. Host resistance to the pathogen reduced the success of both the parasitoid and the pathogen. In susceptible hosts, the parasitoid did not affect performance of the pathogen, but the pathogen had a significant negative effect on the parasitoid. In moderately resistant hosts, the interaction between the parasitoid and pathogen was symmetrical and competitive; the parasitoid had a significant negative effect on pathogen performance and the pathogen had a significant negative effect on parasitoid performance. Highly resistant hosts were not susceptible to infection by the pathogen, which created a refugium from competition for the parasitoid. The results show that, similar to host-plant-mediated competition between herbivores, host phenotype can influence competitive interactions between parasitoids and pathogens.

Field-based studies with the diamondback moth tritrophic system in Cameron Highlands of Malaysia: Implications for pest management

A brief chronological history of the management of Plutella xylotsella L. in the Cameron Highlands to date is presented, including recent evidence for resistance to selective insecticides (Bacillus thuringiensis-based products and abamectin), and the urgent need for resistance management strategies is discussed. Field studies on parasitism of P. xylostella on two host plant species (Brassica oleracea var. capitata and B. pekinensis) by three key parasitoids (Diadegma semiclausum Helle n, Diadromus collaris Gravenhorst and Cotesia plutellae Kurdjumov) are described and show distinct species-specific trends. In particular, Plutella xylostella outbreaks occurred most commonly on B. pekinensis, a crop which appeared less attractive to D. semiclausum (in terms of searching efficiency, the superior endolarval parasitoid) than to Cotesia plutellae. The possible involvement of induction and genetic (co-evolutionary) mechanisms in the observed species-specific differences is discussed together with suggestions for research which mayassist in the long-term management of P. xylostella .

Studies on the characteristics of parasitism ofPlutella xylostella (Lep.: Plutellidae) by a larval parasiteDiadegma semiclausum (Hym.: Ichneumonidae)

Laboratory experiments were conducted to study the characteristics of parasitism of diamondback moth,Plutella xylostella (L.), a worldwide pest of crucifers, by a larval parasite,Diadegma semiclausum Hellen. Results showed that the greater the host larval density, the lesser was the percentage of larvae parasitized. The area of discovery decreased with increasing parasite density, but k-value remained practically unchanged. Parasitism reduced food consumption in parasitised larvae. No difference was observed in duration of larval instars between the parasitized and healthy larvae. As the frequency of superparasitism increased, the proportion of production of female progeny also increased. Presence of parasite larva within the host larva deterred superparasitism greater than the presence of parasite egg. Presence of larva of eitherD. semiclausum or another larval parasite,Cotesia plutellae Kurdjumov, within host larva deterred multiparasitism by either species greater than the presence of egg of either parasite species.Diadegma semiclausum was much more aggressive thanC. plutellae in parasitisingP. xylostella larvae.

Effect of the acylurea insect growth regulator teflubenzuron on the endo‐larval stages of the hymenopteran parasitoids Cotesia plutellae and Diadegma semiclausum in a susceptible and an acylurea‐resistant strain of Plutella xylostella

AbstractThe toxicity of the acylurea, teflubenzuron, was assessed against larval stages of the hymenopteran parasitoids, Cotesia plutellae Kurdjumov and Diadegma semiclausum Hellén in a susceptible laboratory strain and a teflubenzuron‐resistant field strain of the diamondback moth, Plutella xylostella L. In fourth‐instar hosts (L4), when both parasitoid species were in their final larval instar, teflubenzuron significantly (P < 0.05) reduced emergence of adult D. semiclausum but had no significant (P > 0.05) effect on C. plutellae, although a small proportion of the latter were unable to reproduce. Treatment of L4 hosts with teflubenzuron ( > LD50) had no significant (P > 0.05) effect on the fecundity of surviving females of D. semiclausum. Similar differential toxicity with teflubenzuron was observed in L2 hosts, when parasitoids were at the egg or early larval instar stage. There was no apparent increased effect of teflubenzuron on either species of parasitoid when highly resistant (c. 4000‐fold) L2 hosts (field strain) were treated with concentrations of teflubenzuron two to three orders of magnitude greater than in equivalent experiments with the susceptible host strain. This suggests that host resistance to teflubenzuron confers some protection to both species of parasitoid. Uptake experiments with [14C]teflubenzuron showed that accumulation of radioactivity was much greater in D. semiclausum than in C. plutellae and this may account for the differential toxicity observed. The results are discussed in relation to the field status of these parasitoid species. The influence of insecticide resistance in the host on endo‐larval parasitoids is also considered.