Field Populations Of Diamondback Moth Research Articles

Origin, selection, and spread of diamide insecticide resistance allele in field populations of diamondback moth in east and southeast Asia.

The investigation of molecular mechanisms and evolution of resistance to insecticides is an ongoing challenge, as researchers must provide guidance to manage the resistance to achieve sustainable production in agriculture. Predicting, monitoring, and managing insecticide resistance requires information on the origins, selection, and spread of resistance genes. The resistance of Plutella xylostella (L.) against diamide insecticides is becoming an increasingly severe problem in east and southeast Asia. In this study, the evolution of resistance was investigated using a resistance allele [ryanodine receptor (RyR); G4946E mutation] and its flanking regions, as well as mitochondrial cytochrome c oxidase subunit I (mtCOI). The sequences of the flanking region of the G4946E and mtCOI suggested that the G4946E mutation has a key role in resistance. Furthermore, the G4946E mutation has multiple origins, and congenic resistant mutations have spread across east and southeast Asia, despite substantial geographical barriers. In addition, the susceptibility of field populations partially recovered during winter, based on the observed decrease in the G4946E (resistant allele) frequency. Finally, the resistance level indexed by the frequency of the E4946 allele was significantly lower in non-overwintering regions than in overwintering regions. The information of the present study is useful to monitor resistance using molecular markers and to develop strategies to delay the evolution of diamide resistance.

Selection of a Field Population of Diamondback Moth (Lepidoptera: Plutellidae) with Acetamiprid Maintains, but Does Not Increase, Cross-Resistance to Pyrethroids

Bioassays (at generation G2) with a newly collected field population (designated CH4) of Plutella xylostella (L.) (Lepidoptera: Plutellidae) from farms in the Cameron Highlands, Malaysia, indicated resistance to acetamiprid, deltamethrin, lambda-cyhalothrin, and esfenvalerate. At G3, the field-derived population was divided into two subpopulations, one subpopuplation was selected (G3 to Go10) with acetamiprid (aceta-SEL), whereas the second subpopulation was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G,1, indicating that the observed resistance to each insecticide was unstable. For aceta-SEL, bioassays at G,, found that selection with acetamiprid gave a resistance ratio of 409 compared with UNSEL. The LC50 values for deltamethrin, lambda-cyhalothrin, and esfenvalerate to aceta-SEL were similar at both G11 and G2. This suggests that acetamiprid selection maintained the otherwise unstable resistance to these compounds in the aceta-SEL population. Logit regression analysis of F1 reciprocal crosses between aceta-SEL and the susceptible Lab-UK indicated that resistance to acetamiprid was inherited as an autosomal, incompletely recessive (DLC = 0.26) trait. Tests of monogenic inheritance and weight distribution suggested that resistance to acetamiprid was controlled by a single locus.

Selection of a Field Population of Diamondback Moth (Lepidoptera: Plutellidae) with Acetamiprid Maintains, but Does Not Increase, Cross-Resistance to Pyrethroids

Selection of a Field Population of Diamondback Moth (Lepidoptera: Plutellidae) with Acetamiprid Maintains, but Does Not Increase, Cross-Resistance to Pyrethroids

Genetics and evidence for an esterase‐associated mechanism of resistance to indoxacarb in a field population of diamondback moth (Lepidoptera: Plutellidae)

Bioassays (at generation G2) with a newly collected field population (designated CH3) of Plutella xylostella L. from farmers' fields in the Cameron Highlands, Malaysia, indicated resistance ratios of 813-, 79-, 171-, 498- and 1285-fold for indoxacarb, fipronil, spinosad, deltamethrin and Bacillus thuringiensis toxin Cry1Ac respectively compared with a laboratory susceptible population (Lab-UK). At G2 the field-derived population was divided into two subpopulations: one was selected (G2 to G7) with indoxacarb (indoxa-SEL), while the second was left unselected (UNSEL). A significant reduction in the resistance ratio for each compound was observed in UNSEL at G8. For indoxa-SEL, bioassays at G8 found that selection with indoxacarb gave a resistance ratio of 2594 compared with Lab-UK and of 90 compared with UNSEL. The toxicity of fipronil, spinosad and deltamethrin was not significantly different in indoxa-SEL at G8 compared with G2 but was significantly greater than UNSEL at G8. The toxicity of Cry1Ac was significantly reduced in indoxa-SEL at G8 compared with G2 but was also significantly greater than UNSEL at G8. This suggests that indoxacarb selection maintained resistance to these compounds in the indoxa-SEL population. Synergist studies indicated that resistance to indoxacarb in indoxa-SEL was esterase associated. Logit regression analysis of F1 reciprocal crosses between indoxa-SEL and Lab-UK indicated that resistance to indoxacarb was inherited as an autosomal, incompletely recessive (D(LC) = 0.35) trait. Tests of monogenic inheritance suggested that resistance to indoxacarb was controlled by a single locus.

Parasitism of Cotes/a plutellae Alters Morphological and Biochemical Characters of Diamondback Moth, Plutella xylostella

A solitary endoparsitoid, Cotesia plutellae, has been regarded as a major biological regulator to manipulate field population of diamondback moth (DBM), Plutella xylostella. It parasitizes DBM and alters its physiology into a favorable condition for the parasitoid development. This research has been focused on the physiological changes in terms of internal morphology and biochemical changes of the parasitized DBM. The parasitized DBM exhibited significantly hypotrophied structures in Malpighian tubules, fat body, and testes, while it did not show apparent change in the digestive organ structure. The parasitoid represented almost 70% of total body weight of the parasitized DBM. This estimate was well corresponded to the measurements of the major nutrient amounts in the parasitized DBM. This study clearly indicates that the major nutrients obtained by the parasitoid DBM are exploited by the koinobiont parasitoid for its own development.

Local variation in susceptibility of the diamondback moth, Plutella xylostella (Linnaeus) to insecticides and role of detoxification enzymes

The susceptibility of five different field populations of the diamondback moth collected as larvae within 15 km radius of Ottanchathiram and of the IARI 17-65 laboratory strain to Biobit © ( Bacillus thuringiensis var. kurstaki HD-1), cartap, Cry1Ab, fenvalerate, fipronil, flufenoxuron and RH 2485 was studied using cabbage leaf disc feeding bioassays. All field populations were highly tolerant to fenvalerate and flufenoxuron compared with the IARI 17-65 strain. Monocrotophos tolerance in three field populations was about 3.7–4.5-fold higher than in the IARI 17-65 strain. All field populations showed 10–24-fold tolerance to cartap and 120–505-fold tolerance to fipronil compared with the IARI 17-65 strain. Wide variation in susceptibility of the field populations to insecticides appeared to be due to differential usage of these insecticides. Biobit ©, Cry1Ab and RH 2485 were highly toxic to field populations of diamondback moth and could be used as alternate insecticides. An increased rate of detoxifying enzymes—hydrolases, transferases and oxygenases was responsible for imparting resistance in Plutella xylostella larvae to insecticides. These results emphasize a need for developing a location-specific insecticide resistance management.

Prevalence of Nosema bombycis in Malaysian field populations of the diamondback moth, Plutella xylostella

A study on the prevalence of Nosema bombycis infection in field populations of diamondback moth, Plutella xylostella L., was conducted in October 1998 and April 1999. There was a significant difference in the percentage of Nosema infection and mean infection intensity among diamondback moth larvae or pupae sampled from the Cameron Highlands and Serdang-Gombak, each representative of high- and lowland cabbage-growing areas in Malaysia. The percentage of infection on diamondback moth larvae in Cameron Highlands was significantly higher than that in Serdang-Gombak in both sampling periods (seasons). The possible factors causing prevalence of disease infection are discussed.

Parasitism of Diamondback Moth (Lepidoptera: Plutellidae) Larvae by Cotesia plutellae (Hymenoptera: Braconidae) and Diadegma insulare (Hymenoptera: Ichneumonidae) in Cabbage Fields after Inundative Releases of C. plutellae2

Cocoons of Cotesia plutellae (Kurdjumov) were released for nine consecutive wk along the margins of two commercial cabbage (Brassica oleracea var. bravo L.) fields near Bunnell, Flagler Co., FL, in spring 1996. The larval parasitism of diamondback moth, Plutella xylostella (L.), by C. plutellae and by the native parasitoid Diadegma insulare (Cresson) was evaluated in release fields and in nearby cabbage fields using two methods-sentinel collard (Brassica oleracea var. acephala L.) or sentinel cabbage plants and non-sentinel plants. Total parasitism of diamondback moth larvae on sentinel plants in the release and adjacent fields was 35.7%. There were no significant differences in the level of parasitism by C. plutellae among sentinel plant locations within the release fields. In non-release fields, parasitoids spread as far as 1,500 m from the nearest release site during the release period, but parasitism of larvae on sentinel plants decreased as the distance from the release area increased. Parasitism of diamondback moth larvae by D. insulare was 8.3% in C. plutellae release and adjacent fields, but 14.6% in the nearby fields. Sampling of non-sentinel cabbage plants for diamondback moth larvae demonstrated a total of 37.4% larval parasitism by C. plutellae in the release and adjacent fields, similar to that recorded on sentinel plants. However, C. plutellae were detected only as far as 800 m from the release site on non-sentinel cabbage plants, and total parasitism in the dispersal fields also was very low. Diadegma insulare contributed only 1.1% parasitism of larvae sampled from non-sentinel plants in all cabbage fields. Cotesia plutellae was more effective than D. insulare in attacking diamondback moth larvae in this study where field populations of diamondback moth were low (<0.1 larva per cabbage plant).

Field-Evolved Resistance to Bacillus thuringiensis Toxin CryIC in Diamondback Moth (Lepidoptera: Plutellidae)

Previous results have shown that diamondback moth, Plutella xylostella (L.), populations resistant to toxins from Bacillus thuringiensis subsp. kurstaki were susceptible to toxin CryIC. Use of commercial formulations of B. thuringiensis subsp. aizawai that contain CryIC has increased recently. Analysis of two commercial formulations by high pressure liquid chromatography showed that CryIC accounted for 26% of the CryI protein in the B. thuringiensis subsp. aizawai formulation, but did not occur in the B. thuringiensis subsp. kurstaki formulation. CryIAb was the most abundant CryI protein in the commercial formulations of B. thuringiensis subspp. aizawai and kurstaki. We found resistance to CryIC in a field population of diamondback moth from Hawaii that had been treated with B. thuringiensis subsp. aizawai . Leaf residue bioassays showed that, at 5 d after treatment with CryIC, LC50s for colonies derived from this population in 1993 and 1995 were ≈20 times greater than the LC50 for a susceptible laboratory colony. For a nearby population that had not been treated with B. thuringiensis subsp. aizawai , responses to CryIC did not differ significantly from those of the susceptible laboratory colony. Resistance to CryIAb was lower in a CryIC-resistant colony than in a CryIC-susceptible colony that had been selected with B. thuringiensis subsp. kurstaki . These results suggest that the gene(s) conferring resistance to CryIC segregate independently from the gene(s) conferring resistance to CryIAb. In contrast with previous results with colonies derived in 1989, resistance to B. thuringiensis subsp. kurstaki in a colony derived in 1993 from the same field population did not decline when exposure to B. thuringiensis stopped. Thus, stability of resistance is not necessarily a fixed character, even for a specific population and pesticide. Despite substantial resistance to CryIC and B. thuringiensis subsp. kurstaki , resistance to a spore-crystal formulation of B. thuringiensis subsp. aizawaiwas only 2- to 4-fold.

Inheritance of resistance to a Bacillus thuringiensis toxin in a field population of diamondback moth (Plutella xylostella)

AbstractInheritance of resistance to the Bacillus thuringiensis Berl. CryIA(b) crystal protein was studied in Plutella xylostella L. (diamondback moth). A field population 50‐fold more resistant to CryIA(b) than a control susceptible strain was used. Dose‐mortality curves of the resistant population, the susceptible strain and the F1 from the two reciprocal crosses were compared. Resistance transmission to the F1 was dependent on the sex of the resistant progenitor. Sex ratio of the survivors to high doses of CryIA(b) in the F1 of the two reciprocal crosses did not corroborate the preliminary hypothesis of resistance being due to a recessive sex‐linked allele. Since, in a previous work, the loss of CryIA(b) binding capacity of resistant insects had been demonstrated, binding to midgut tissue sections from F1 individuals was also analysed. The presence of binding in all of the F1 preparations showed that, at least, a recessive autosomal allele was responsible for the loss of binding capacity in the resistant population.

Evolution of Resistance to Bacillus thuringiensis

Insecticides derived from the common soil bacterium Bacillus thuringiensis (Bt) are becoming increasingly important for pest management. Insecticidal crystal proteins (also called 8-endotoxins) from Bt are extremely toxic to certain pests, yet cause little or no hann to humans, most beneficial insects, and other nontarget organisms (19, 40). After proteolytic activation in the insect midgut, Bt toxins bind to the brush border membrane of the midgut epithelium and create pores that cause cells to swell and lyse (55). Technical innovations, including expression of Bt toxin genes in transgenic crop plants and transgenic bacteria, should increase the usefulness of Bt (6, 12, 35, 46, 91, 94, 109, 116). At the same time, mounting concerns about environmental hazards and widespread resistance in pest populations are reducing the value of conventional synthetic insecticides. Because Bt had been used commercially for more than two decades without reports of substantial resistance development in open field popu­ lations, some scientists had presumed that evolution of resistance was unlikely (21, 89). However, resistance to Bt was documented recently in field populations of diamondback moth in Hawaii, the continental US, and Asia (36, 42, 92a, 128, 129, 131, 138, 146, 148, 151). These reports confirmed suspicions raised by the results of laboratory selection for resistance to Bt in several major pests (102, 104, 135). Scientists in industry, government, and academia now recognize evolution of resistance to Bt in pests as the greatest threat to the continued success of Bt (18, 44, 58, 59, lOla, 108). To delay or reverse resistance to Bt in pests, we must first understand

Evolution of Resistance to Bacillus Thuringiensis

Insecticides derived from the common soil bacterium Bacillus thuringiensis (Bt) are becoming increasingly important for pest management. Insecticidal crystal proteins (also called 8-endotoxins) from Bt are extremely toxic to certain pests, yet cause little or no hann to humans, most beneficial insects, and other nontarget organisms (19, 40). After proteolytic activation in the insect midgut, Bt toxins bind to the brush border membrane of the midgut epithelium and create pores that cause cells to swell and lyse (55). Technical innovations, including expression of Bt toxin genes in transgenic crop plants and transgenic bacteria, should increase the usefulness of Bt (6, 12, 35, 46, 91, 94, 109, 116). At the same time, mounting concerns about environmental hazards and widespread resistance in pest populations are reducing the value of conventional synthetic insecticides. Because Bt had been used commercially for more than two decades without reports of substantial resistance development in open field popu­ lations, some scientists had presumed that evolution of resistance was unlikely (21, 89). However, resistance to Bt was documented recently in field populations of diamondback moth in Hawaii, the continental US, and Asia (36, 42, 92a, 128, 129, 131, 138, 146, 148, 151). These reports confirmed suspicions raised by the results of laboratory selection for resistance to Bt in several major pests (102, 104, 135). Scientists in industry, government, and academia now recognize evolution of resistance to Bt in pests as the greatest threat to the continued success of Bt (18, 44, 58, 59, lOla, 108). To delay or reverse resistance to Bt in pests, we must first understand

Managing Resistance to Bacillus thuringiensis: Lessons from the Diamondback Moth (Lepidoptera: Plutellidae

Laboratory selection increased resistance to B. thuringiensis in three strains established from a moderately resistant field population of diamondback moth, Plutella xylostella (L.). Five generations of laboratory selection caused 5- to 7-fold increases in LC50, resulting in 150- to 190-fold resistance compared with a susceptible laboratory colony. Nine generations of selection produced 430- to 820-fold resistance. In contrast, five foliar applications of B. thuringiensis in the field did not increase the LC50 of a moderately resistant population. Field-selected resistance to B. thuringiensis declined slowly in the absence of treatments. The rapid response to laboratory selection shows intrapopulation genetic variation in susceptibility to B. thuringiensis and suggests that intense selection may produce much higher levels of resistance to B. thuringiensis than those previously reported from the field. We hypothesize that resistance increased faster in the laboratory than in the field because selection intensity was lower in the field. Because susceptibility was not restored quickly when treatments were discontinued, rotations may not be especially effective for managing resistance to B. thuringiensis in diamondback moth. Field populations of diamondback moth developed resistance to a commercial formulation containing a mixture of B. thuringiensis toxins, an event that raises doubts about the ability of mixtures to retard resistance development. Extensive and intensive exposure of pests to B. thuringiensis toxins through transgenic crop plants or other tactics may cause widespread pest resistance. We urge judicious use of B. thuringiensis to conserve its efficacy.

Field Development of Resistance to Bacillus thuringiensis in Diamondback Moth (Lepidoptera: Plutellidae)

Foliar applications of commercial formulations of the insecticidal spore-crystal protein complex of Bacillus thuringiensis subsp. kurstaki caused development of resistance in field populations of a major lepidopteran pest of vegetables, diamondback moth, Plutella xylostella (L.). Laboratory bioassays of larvae showed that the LC50 and LC95 for a field population of diamondback moth treated repeatedly with B. thuringiensis were 25 to 33 times greater than the respective LC50’s and LC95’s for two susceptible laboratory colonies. Mortality at the field rate of B. thuringiensis was 34-35% in two resistant populations compared with 90-100% in two susceptible laboratory colonies. The results suggest that the potential for resistance development in pest populations is an important consideration for deployment of B. thuringiensis toxin genes in genetically-engineered crop plants and use of B. thuringiensis in related tactics.