Diadegma semiclausum is an important parasitoid wasp and widely used in the biological control of the diamondback moth, Plutella xylostella, one of the most destructive pests of cruciferous plants. Insect olfactory system is critical in guiding behaviors including feeding, mating, and oviposition, in which odorant binding proteins (OBPs) and odorant receptors (ORs) are two key components. However, limited attention has been paid to D. semiclausum olfactory genes. In this study, a transcriptome sequencing was performed on the RNA samples extracted from D. semiclausum male and female adult antennae. A total of 17 putative OBP and 67 OR genes were annotated and further compared to OBPs and ORs from P. xylostella, and other hemipteran parasitoid species. The expression patterns of D. semiclausum OBPs between male and female antennae were examined using reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR. Six OBPs (DsemOBP 6, 7, 8, 9, 10, and 14) demonstrated significantly higher expression levels in females than in males, which may assist in female D. semiclausum host-seeking and oviposition behaviors. This study advances our understanding of the olfactory system of D. semiclausum at the molecular level and paves the way for future functional studies aiming at increasing the efficacy to control P. xylostella by using D. semiclausum.

In Senegal, damage caused by insect pests is a major obstacle to seasonal stability and an increase in cabbage production. Little is known about the spatial and temporal distribution of cabbage pests, which makes the design of management recommendations to small-scale farmers challenging. The objectives of this study were to: (i) evaluate the status of insect pests observed in cabbage farmers’ fields; (ii) give information on the spatial and temporal distribution of key pests and (iii) assess the effect of temperature, insecticide applications, and host crop abundance on their incidence. A total of 116 cabbage fields were monitored for insect pests and related damage over four crop cycles, from October 2012 to May 2014, in the main vegetable producing area of Senegal (Niayes). The diamondback moth Plutella xylostella (L.) was by far the most important pest present in all the fields and with high levels of incidence (37.1% infested plants), particularly in the latter part of the dry season in the South of Niayes (50% infested plants). The cabbage webworm Hellula undalis (F.) was mainly observed in the early dry season in the south of Niayes, with an incidence of up to 12.5% infested plants. More surprising was the detection of the tomato fruit worm Helicoverpa armigera (Hübner), with damage of up to 9.4% of cabbage heads. The incidence of sucking pests such as whiteflies Bemisia tabaci (Gennadius), or aphids (including Lipaphis pseudobrassicae (Davis, 1914), Myzus persicae (Sulzer) or Brevicoryne brassicae (L.)) was generally low. The incidence of P. xylostella increased significantly with the number of insecticide applications, indicating that control deployed by growers was ineffective. The incidence of H. undalis did not depend on the number of insecticide applications, but significantly increased with host crop abundance and decreased with temperature. This study is a first step towards developing alternative pest management strategies in the framework of sustainable vegetable production systems.

The population density of the diamondback moth (DBM), Plutella xylostella (L.), the species diversity of its predators, parasitism on eggs, larvae and pupae, and associated yield of canola were evaluated in experimental plots where spring canola was grown either as a monoculture or strip-intercropped with annual alfalfa in the ratio of 3C:3A, 6C:3A and 9C:3A over a 2-year period. The egg density was significantly higher in monoculture than in intercrops. The highest and lowest densities of larvae and pupae of DBM were recorded in monoculture (2.9–3.2 larvae per plant and 1.14–1.20 pupae per plant) and intercrop 3C:3A (0.7–0.6 larvae per plant and 0.34–0.29 pupae per plant), respectively. Shannon diversity index (H') for species composition of the predators of DBM immature stages was lower in monoculture than in intercrops, and was similar amongst the three intercrops. Moreover, the percent parasitism for eggs, larvae and pupae was higher in intercrops than in monoculture. The dry seed weight loss was higher in monocrop (37.6–40.1%) compared to 3C:3A (7.9–8.6%), 6C:3A (19.5–21.4%) and 9C:3A (21.6–25.4%). Our results indicate that intercropping canola with annual alfalfa, especially in the ratio 3C:3A, can increase the species diversity, parasitism rates of DBM immature stages, and enhance the yield of canola. The implications of these findings, in relation to integrated pest management (IPM) in canola cropping systems, are discussed.

The diamondback moth, Plutella xylostella (L.) is the major insect pest of cabbage crops in Togo and Benin. For control, farmers very often resort to spraying chemical insecticides at high dosages with frequent applications. Bioassays were carried out on three populations of P. xylostella, two from Togo (Kara and Dapaong) and one from Benin (Cotonou), to assess their level of susceptibility to currently used insecticides. A reference strain of P. xylostella from Matuu in Kenya was used as a control. In the laboratory, three insecticide representatives of different chemical families (deltamethrin, chlorpyrifos ethyl and spinosad) were assayed against third instar larvae of P. xylostella. Results revealed that P. xylostella populations from Dapaong, Kara and Cotonou were more resistant to deltamethrin (13 to 59-fold at LC50 level, 149 to 1772-fold at LC90 level) and chlorpyrifos ethyl (5 to 15-fold at LC50 level, 9 to 885-fold at LC90 level) than the reference strain. Spinosad was more toxic to P. xylostella populations than the other insecticides with LC50 and LC90 values less than 1 µg/ml and 15 µg/ml, respectively. However, the population from Cotonou appeared significantly more resistant to spinosad compared to the reference strain. These results are discussed in the light of developing an integrated pest management strategy for reducing the selection pressure of spinosad.

Plutella xylostella (L.) is the most important pest of Brassicaceae worldwide, with a recent estimate of US$ 4–5 billion expenditure for the control of this insect. A case of very high resistance of this pest to chlorantraniliprole was recently associated with reduced efficacy in a Brazilian field of Brassica spp. Although diamide resistance has been characterized, the fitness of insects due to such resistance has yet to be examined. Therefore, in this study, biological parameters were assessed in both susceptible and resistant strains of P. xylostella subjected to sublethal chlorantraniliprole concentrations. The field strain showed high resistance to chlorantraniliprole (RR50=27,793-fold), although resistance rapidly decreased in the first generations, showing instability. The exposure of susceptible and resistant larvae to their respective LC1, LC10, and LC25 values led to an increased duration of the larval and pupae phases and reduced weight in both strains; however, no significant differences in pupal viability across the treatments were observed. The resistant insects presented significantly lower larval weight and fecundity and higher larval and pupal periods, hatchability, and male longevity when not exposed to chlorantraniliprole, suggesting a fitness cost associated with resistance. In addition, resistant females showed a significantly higher egg-laying period and longevity at LC25, whereas the males lived longer at LC1. Chlorantraniliprole negatively impacted the biological parameters of both strains tested, although these effects were more relevant to the resistant insects. Resistant P. xylostella showed negative and positive biological trade-offs when compared with the susceptible individuals in both the absence and presence of chlorantraniliprole. Despite the important role that these trade-offs may play in the evolution of resistance to chlorantraniliprole, practical applications still depend on such information as the dominance of fitness costs and resistance.

Temperature is considered to be an important abiotic factor influencing insect reproduction. Despite the importance of Plutella xylostella L. (Lepidoptera: Plutellidae) as a pest of brassicaceous crops worldwide, the effects of temperature on its reproduction are not well understood. We evaluated the effect of constant temperatures ranging from 10 to 32.5°C on the reproduction of P. xylostella and developed an oviposition model for the species. The model combined temperature-dependent parameters of total fecundity, age-specific oviposition rate and age-specific survival. Additionally, we modelled population growth as a function of temperature. The estimated parameters allowed us to discuss the possible consequences of global warming on P. xylostella distribution. Temperature affected the length of pre-oviposition after adult emergence, oviposition period, longevity, total fecundity and egg viability. The model predicted that both daily egg production and length of oviposition period decreased at temperatures below 15°C and above 25°C. Population growth increased linearly with temperature in a range from 10°C to 25°C; however, the model predicted a reduction in population growth at temperatures above 28.6°C. Data suggested that temperature plays a critical role in P. xylostella reproduction, and subtle differences in average temperature could have an impact on its population growth. This is especially important in the context of global climate change, which in turn could alter the distribution and abundance of the pest in some regions of the world.

An investigation of the diversity and distribution of wild crucifer species and their importance for cultivated crucifers was conducted during 2005 and 2006 in the highland and mid-altitude semi-arid areas of Kenya. Thirteen species of wild crucifers in nine genera were recorded: Raphanus raphanistrum, Erucastrum arabicum, Sisymbrium officinale, Crambe kilimandscharica, Capsella bursa-pastoris, Rorippa nudiuscula, Ro. micrantha, Ro. microphylla, Lepidium bonariense, Coronopus didymus, Brassica rapa, B. juncea and an unidentified Brassica species. Highland areas had significantly higher species diversity and species richness than mid-altitude semi-arid areas. Species richness, diversity and evenness varied with season and location. Raphanus raphanistrum was the dominant non-cultivated species in the highlands followed by E. arabicum, which was also present and dominant in the semi-arid study sites. Diamondback moth (DBM) was recorded from ten wild crucifer species and R. raphanistrum and E. arabicum were the preferred host plant species. Overall, four larval, one larval-pupal and one pupal parasitoid of DBM were recorded: Diadegma semiclausum, D. mollipla, Apanteles sp., Cotesia plutellae, Oomyzus sokolowskii and Brachymeria species, respectively. Diadegma semiclausum was the most dominant species on all crucifers. We conclude that wild crucifers act as alternative hosts for DBM and provide refugia for DBM parasitoids, which risk local extinction through pesticide application or competition from introduced exotic parasitoid species. The wild crucifers also act as recolonization sites for DBM parasitoids.

The development, survival and reproductive potential of diamondback moth Plutella xylostella (Linnaeus) were studied at 25 ± 1 °C in the laboratory in response to two cultivated Brassica oleracea cultivars (cabbage B. oleracea var. capitata and kale B. oleracea var. acephala) and four wild crucifer species Erucastrum arabicum, Raphanus raphanistrum, Rorippa nudiuscula and Rorippa micrantha. Rorippa micrantha was the most preferred species in oviposition choice tests, while cabbage and kale were least preferred. First instar larval mining period differed significantly between plant species with the longest period recorded on cabbage (3.0 days) and the shortest on R. micrantha (0.4 days). Pupal weight was significantly lower for larvae reared on R. nudiuscula, while those of the others were similar. The developmental period from first instar to adult was the shortest on R. micrantha (14.1 days) and the longest on R. raphanistrum (15.6 days). Survival to adult was not statistically affected by the host plant species. Adult longevity ranged between 18.2 days on R. raphanistrum and 24.7 days on R. nudiuscula. The females were significantly heavier than the males on all plant species. However, males lived longer than females. Moths reared on R. nudiuscula recorded the highest fecundity (326 eggs), while moths reared on cabbage had the lowest fecundity (262 eggs). Kale and R. nudiuscula recorded the longest generation time of 31.7 days, while E. arabicum had the highest net reproductive rate (126.4 eggs per day). The highest intrinsic rate of increase was calculated for R. micrantha (0.179) and the lowest for kale (0.147). This study shows the suitability of wild crucifers as hosts for P. xylostella and indicates that they may play a major role as reservoir for the pest during the absence of cultivated host plants.

Diamondback moth (DBM), Plutella xylostella, is known for causing damage to Brassica crops and developing resistance to chemical and biological pesticides; it has become one of the most difficult pests to manage in many regions around the world. The only way to reduce reliance on pesticides is to maximize the role of natural control agents for integrated pest management programs and be able to incorporate the mortality from control agents into pest control decision-making. More than 90 hymenopterous parasitoids are associated with DBM worldwide; among them, Diadegma semiclausum, is a major endoparasitoid of P. xylostella. To optimize parasitism of pests in pest control decision-making, it is necessary to develop rapid and simple methods for distinguishing parasitized from non-parasitized larvae in the field. Here we report on a number of diagnostic tools to identify parasitized larvae. One is based on differential melanization reactions in hemolymph due to immune suppression in parasitized larvae. The lack of coagulation reactions in hemolymph provides a simple initial test, where squashing a non-parasitized larva onto nitrocellulose membrane traps chlorophyll-containing gut content on the membrane leaving a green dot of clotted gut material. However, in immune-suppressed parasitized larvae, the gut content was washed away in absence of coagulation reactions and the membrane lacks a green dot. This tool alone or combined with others, allows quick detection of parasitized caterpillars in the field. We further showed that the antibody MAb 9A5 can be used to detect D. semiclausum parasitized larvae of DBM in Western blots.

Host shifts in herbivorous insects are thought to sometimes provide enemy-free space on the novel host plant. A population of the diamondback moth Plutella xylostella (Linnaeus), an oligophagous pest on crucifers, recently shifted to sugar snap- and snowpeas (Pisum sativum) in Kenya, resulting in heavy damage to these crops. The impact of this host shift on the interaction with Diadegma mollipla (Holmgren), one of the most frequent parasitoid species attacking P. xylostella in this area, was investigated. Parasitism rates and development of two strains of D. mollipla, one reared from a cabbage-feeding strain of P. xylostella and the second from the new pea-feeding strain, changed based on the host-plant that P. xylostella fed upon, with both parasitoid strains more effective on the novel host plant. Parasitism by the cabbage-D. mollipla strain on P. xylostella infesting peas was four times higher than on P. xylostella infesting cabbage when a single plant species was present. However, when both crops were offered together, the level of parasitism dropped to the level seen when cabbage was offered alone. Diadegma mollipla developed on both hosts, but cabbage-D. mollipla had a longer total development time. Pupae of cabbage-feeding P. xylostella were significantly heavier than pupae of pea-feeding P. xylostella and parasitism had no influence on these differences. Diadegma mollipla preferred to parasitize the pea-feeding P. xylostella. Thus, the host shift by P. xylostella to a novel host plant did not necessarily provide enemy-free space, with the parasitoid species tested. The implications of these findings for the host–parasitoid relationship are discussed.

Shade-dried, powdered drupes of Melia azedarach L. were selected from three states in India, each representing a different geographical region, viz. Rajasthan (arid), Punjab (open plains), and Himachal Pradesh (hilly). Drupes were extracted in chloroform: methanol (9:1) and evaluated against second instar larvae of Plutella xylostella (Linnaeus) using a ‘leaf-disc dip’ bioassay. The ecotype from the arid region of Rajasthan yielded the lowest LC50 (1.47%), followed by that from the open plains of Punjab (1.79%) and the hilly areas of Himachal Pradesh, which yielded the maximum LC50 (2.29%). The survivors demonstrated various types of sublethal effects such as prolongation of larval period (7.0–7.8 days compared to 6.3–6.5 days in the control), reduction in pupal weight (36.0–38.4 mg/10 pupae in comparison to 54.4–56.0 mg in the control), deformation of pupae (up to 69.7%) and inhibition of adult emergence (up to 92%). A highly pronounced curtailment of fecundity (up to 10.4 against 73.2 in the control), significant reduction in oviposition period of the adults (up to 3.5 days compared to 7.4 days in the control) and longevity (5.5–7.8 days against 8.9–10.3 days in the control), were also recorded. The extracts produced from trees in the arid region of Rajasthan caused both lethal and sublethal effects following treatment of the second instar larvae of P. xylostella. Only 1.0% normal adults survived at the end of the study compared to 3.5 and 5.5% adult survival in the extracts from the open plains and hilly area ecotypes, respectively. An understanding of the bases of these variations in the toxicity of the crude extracts from the M. azedarach ecotypes growing in different climate conditions may open up the possibility of propagation and genetic improvement of the desired traits in the future.

Release of transgenic insect-resistant crops creates the potential not only for the insect pest to evolve resistance but for the escape of transgenes that may confer novel or enhanced fitness-related traits through hybridization with their wild relatives. The differential response of diamondback moth (Plutella xylostella) populations in eastern and western Canada to Bt-producing (GT) Brassica napus and the potential for enhanced fitness of GT B. napus and weedy GT Brassica rapa × B. napus hybrid populations (F1, BC1, BC2) were studied. Comparative bioassays using neonates and 4th instars showed that GT B. napus and GT B. rapa × B. napus hybrids are lethal to larvae from both populations. No measurable plant fitness advantage (reproductive dry weight) was observed for GT B. napus (crop) and GT B. rapa × B. napus hybrid populations at low insect pressure (1 larva per leaf). At high insect densities (>10 larvae per leaf), vegetative plant weight was not significantly different for GT B. napusand non-GT B. napus, whereas reproductive plant weight and proportion of reproductive material were significantly higher in GT B. napus. Establishment of the Bt trait in wild B. rapa populations may also increase its competitive advantage under high insect pressure.

The efficacy of neem kernel cake powder water extract (NKCP-WE) and Dipel 2x (Bacillus thuringiensis var. kurstaki) in controlling the diamondback moth (DBM), Plutella xylostella Linn. (Lepidoptera: Yponomeutidae), on cabbage was evaluated in screenhouse experiments. All concentrations of NKCP-WE tested were larvicidal and plants treated with 25 and 50 g/l NKCP-WE retained larvicidal activity for up to 2 weeks after application. The efficacy of 25 and 50 g/1 NKCP-WE and 0.5 g/1 Dipel 2x was compared by observing DBM development on the treated plants and yields of those plants. Dipel 2x-treated plants had less DBM larval infestation than the neem-treated plants but the latter treatment gave better yield. The implications of these observations are discussed.

Lufenuron, N–[2, 5–dichloro–4–(1, 1, 2, 3, 3, 3– hexafluoropropoxy) –phenylaminocarbonyl]–2, 6–difluorobenzamide, a novel acylurea insect growth regulator, exerted significant sublethal effects in larvae, pupae and adults of the diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae). Second, third and fourth instars were treated at their respective LCM using a standard 'leaf–disc dip' method of bioassay. Sizes and weights of pupae from the treated lots were significantly reduced but larval and pupal durations remained unaffected. All the pupae formed from larvae treated as fourth instars were deformed and produced no adults. Only 38 and 14% of adults emerged from the pupae formed following treatment at the second and third instar, respectively, as compared to 88–92% adult emergence in the controls. Apart from significant reduction in body length, some adults from the treatments had fringed and twisted wings which prevented normal flight. IGR treatment also resulted in pronounced reduction in fecundity (up to 10.2 eggs per female in comparison with 135.8 per female in the control) and oviposition periods (up to 3.2 days in comparison to 7.8 days in the control). Field trials to investigate the management of P. xylostella using lufenuron are recommended.

The effectiveness of aqueous neem leaf and seed extracts for the control of the diamondback moth (DBM), Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) on cabbage was evaluated in field tests at Chokwe, Mozambique and compared with parallel dimethoate + cypermethrin treatments. All the neem treatments recorded significantly higher yield of marketable heads of cabbage and significantly better control of diamondback moth than the commonly used mixture of pyrethroids or the untreated control. The neem seed extracts provided the best control of DBM. The possibility of using neem extracts as part of an integrated pest management system for DBM control in smallholder farms is discussed.

In on-farm studies of sustainable agriculture, farmers often have been classified as sustainable according to their organizational affiliation; self identification; or use or non-use of a particular production practice or input, usually synthetic chemicals. Because this is a great oversimplification, researchers recently have been incorporating several dimensions of sustainability into a composite measure. Typically this is a relative measure of sustainability, with scores assigned by comparing individual farmers' practices to those used by all farmers. In contrast, in the farmer sustainability index (FSI) presented here, practices are scored according to their inherent sustainability. We report on the development of an FSI in a case study involving 33 production practices used by 85 cabbage farmers in Malaysia. We describe its underlying principles, the procedure and rationale for scoring each sustainability item, and the result of combining the constituent items into a composite index.