Crocidolomia pavonana larval foraging: behavior and feeding site preferences on cabbage, Brassica oleracea

Experiments were conducted to determine feeding site preferences of Crocidolomia pavonana (Fabricius) (Lepidoptera: Crambidae) larvae within cabbage plants, Brassica oleracea L. var. capitata cv. Warrior (Brassicaceae), and to determine whether induced plant responses to herbivory affect the behavior of larvae. In the first experiment, intra-plant damage and larval distribution were recorded to account for the spreading pattern of damage and larval feeding behavior on a plant; larvae initially fed on the base of leaves and moved progressively to the bud, leaf tips were avoided. In the second experiment, larval performance (the duration of the first instar, survival to the second instar, and weight of second instars) was assessed when larvae fed on the bud, the base, and the tip of the youngest fully expanded leaf on a plant. Crocidolomia pavonana larvae performed best when they fed on bud leaf tissue and most poorly when they fed on leaf tissue at the base of leaves. In the third experiment, expression of induced resistance was tested on each of the three plant parts using a first-instar bioassay. Negative impacts on larval growth and development were not detected when larvae fed on the bud or base tissue when plants were damaged prior to the assay. However, negative effects were detected in larvae feeding on tip leaf tissue when the base of the leaf was damaged prior to the assay or if the bud tissue was damaged simultaneously with the assay. The findings indicate that resource heterogeneity for C. pavonana within-cabbage plants is determined by both the initial quality of food at a location and by subsequent induced changes as a result of larval feeding; both contribute to the feeding pattern observed in these gregarious larvae.     

中国目水螟属研究及一新种记述（鳞翅目：草螟科：水螟亚科）

目水螟属Nymphicula Snellen 已知24种,分布于古北区、东洋区和澳洲区。中国已知5种。本文记录中国目水螟属7种,其中直缘目水螟Nymphicula saigusai Yoshiyasu 为中国新记录种,凹瓣目水螟Nymphicula concaviuscula, sp. nov. 为1新种。文中提供了新种两性外生殖器特征图及中国已知种检索表。模式标本保存于南开大学生物系。 凹瓣目水螟Nymphicula concaviuscula, 新种 (图1,2) 　　新种与短纹目水螟Nymphicula junctalis (Hampson) 相似,主要区别在新种抱器瓣端部凹陷,雌性交配囊有明显囊突区;该新种也与角目水螟Nymphicula patnalis (Felder et Rogenhofer) 相似,区别在于新种雄性阳茎中部无橄榄形角状器,以及抱器瓣端部凹陷,雌性外生殖器具明显的囊突区。 　　正模 ♂, 贵州梵净山,27.55°N,108.41°E,2002-Ⅵ-02,600 m,王新谱采;副模1♀,同正模;2♂♂2♀♀,贵州梵净山,2001-Ⅶ-03, 1300 m,李后魂、王新谱采。     

Newly Reported Females of Two Species of the Genus Ecpyrrhorrhoe Hübner(Lepidoptera:Crambidae:Pyraustinae)from China

The females of Ecpyrrhorrhoe biaculeiformis Zhang,Li et Wang,2004 and E.ruidispinalis Zhang,Li et Wang,2004 are reported for the first time.Drawings of the genitalia are provided.     

Host color preferences and short-range searching behavior of the egg parasitoid Trichogramma ostriniae

The color of lepidopteran eggs often varies by species or egg condition, and parasitoids that attack lepidopteran eggs could therefore potentially use color to obtain information about host identity or quality. The objective of our study was to determine whether females of the egg parasitoid Trichogramma ostriniae Pang & Chen (Hymenoptera: Trichogrammatidae) showed differential responses to egg color when searching for hosts over short distances and when evaluating the suitability of encountered eggs. We examined the wasps’ host‐selection behavior in a Petri dish arena using white, yellow, green, and black clay beads as egg models presented against a green background (to mimic leaf color). In no‐choice tests, bead color had a significant effect on the proportion of tested wasps that accepted a bead for further examination, on the time it took wasps to find and begin examining a bead, and on the time that wasps spent examining the beads. However, bead color had only a marginally significant effect on the proportion of wasps attempting to drill into a bead with their ovipositors, and no significant effect on the amount of time they spent drilling. The wasps also showed significant color preferences when given a choice between two adjacent beads of different colors. The results of the no‐choice and choice trials taken together indicated a color preference ranking of yellow > white > green > black. The wasps’ higher preference for the yellow and white egg models generally corresponds to the white or yellowish‐white egg color of T. ostriniae's target host, the European corn borer moth, Ostrinia nubilalis Hübner (Lepidoptera: Crambidae). The wasps’ strong rejection of black egg models is likely to be an adaptive response that reflects the fact that eggs that are wholly or partially black are often unsuitable for parasitization due to advanced caterpillar development, damage to the egg, or previous parasitization.     

Encapsulation and hemocyte numbers in three lepidopteran stemborers parasitized by Cotesia flavipes-complex endoparasitoids

Determination of the potential and actual host range of a natural enemy is crucial before its importation and release for biological control. We studied some of the factors that are important in determining the physiological host range of insect parasitoids attacking lepidopteran hosts. Our experimental system consisted of novel host-parasitoid associations, with two New World pyralid stalk borers, Diatraea saccharalis and D. grandiosella; one Old World crambid borer, Ostrinia nubilalis as hosts; and three Old World microgastrine braconids, Cotesia chilonis, C. sesamiae, and C. flavipes as parasitoids. Experiments on the chronology of encapsulation of the parasitoid progeny by host hemocytes indicated that lepidopteran stemborers that are taxonomically, behaviorally and ecologically very similar differ in their ability to encapsulate a parasitoid species. D. saccharalis encapsulated C. flavipes sometimes, whereas D. grandiosella consistently encapsulated C. sesamiae and C. flavipes. C. chilonis was not encapsulated by either Diatraea host. If encapsulation occurred it did not start until four days after parasitization and continued during the following days. O. nubilalis was an unsuitable host for all three parasitoid species; parasitoid eggs were killed within 24 hours of parasitization. O. nubilalis had nearly twice as many hemocytes present in the hemolymph compared to the Diatraea species. In many of the host-parasitoid combinations, there was an initial increase of hemocyte number soon after parasitization, which was not due to mechanical damage at oviposition. There was no correlation between total numbers of hemocytes present in the host hemolymph and the observed encapsulation levels. By understanding the encapsulation response we may be able to make better predictions about the host range of a parasitoid species before its release as a biological control agent.     

Resistance of sugarcane borer to Bacillus thuringiensis Cry1Ab toxin

The sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), strain (F52‐3‐R) was developed from F₃ survivors of a single‐pair mating on commercial Cry1Ab Bacillus thuringiensis (Bt) corn plants in the greenhouse. The susceptibility of a Bt‐susceptible and the F52‐3‐R strain of D. saccharalis to trypsin‐activated Cry1Ab toxin was determined in a laboratory bioassay. Neonate‐stage larvae were fed a meridic diet incorporating Cry1Ab toxin at a concentration range of 0.0625 to 32 µg g^?1. Larval mortality, larval weight, and number of surviving larvae that did not gain significant weight (<0.1 mg per larva) were recorded on the 7th day after inoculation. The F52‐3‐R strain demonstrated a significant level of resistance to the activated Cry1Ab toxin. Larval mortality of the Bt‐susceptible strain increased in response to higher concentrations of Cry1Ab toxin, exceeding 75% at 32 µg g^?1, whereas mortality of the F52‐3‐R strain was below 8% across all Cry1Ab concentrations. Using a measure of practical mortality (larvae either died or gained no weight), the median lethal concentration (LC₅₀) of the F52‐3‐R strain was 102‐fold greater than that of the Bt‐susceptible insects. Larval growth of both Bt‐susceptible and F52‐3‐R strains was inhibited on Cry1Ab‐treated diet, but the inhibition of the F52‐3‐R strain was significantly less than that of the Bt‐susceptible insects. These results confirm that the survival of the F52‐3‐R strain on commercial Bt corn plants was related to Cry1Ab protein resistance and suggest that this strain may have considerable value in studying resistance management strategies for Bt corn.     

Role of volatiles emitted by host and non-host plants in the foraging behaviour of Dentichasmias busseolae, a pupal parasitoid of the spotted stemborer Chilo partellus

The role of volatiles from stemborer host and non‐host plants in the host‐finding process of Dentichasmias busseolae Heinrich (Hymenoptera: Ichneumonidae) a pupal parasitoid of Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) was studied. The non‐host plant, molasses grass (Melinis minutiflora Beauv. (Poaceae)), is reported to produce some volatile compounds known to be attractive to some parasitoid species. The studies were conducted to explore the possibility of intercropping stemborer host plants with molasses grass in order to enhance the foraging activity of D. busseolae in such a diversified agro‐ecosystem. Olfactometric bioassays showed that volatiles from the host plants maize, Zea mays L., and sorghum, Sorghum bicolor (L.) (Poaceae), were attractive to the parasitoid. Infested host plants were the most attractive. Volatiles from molasses grass were repellent to the parasitoid. Further tests showed that volatiles from infested and uninfested host plants alone were preferred over those from infested and uninfested host plants combined with the non‐host plant, molasses grass. In dual choice tests, the parasitoid did not discriminate between volatiles from maize infested by either of the two herbivore species, C. partellus or Busseola fusca Fuller (Lepidoptera: Noctuidae). Volatiles from sorghum infested by C. partellus were preferred over those from C. partellus‐infested maize. The study showed that the pupal parasitoid D. busseolae uses plant volatiles during foraging, with those from the plant–herbivore complex being the most attractive. The fact that volatiles from molasses grass were deterrent to the parasitoid suggested that intercropping maize or sorghum with molasses grass was not likely to enhance the foraging behaviour of D. busseolae. Volatiles from the molasses grass may hinder D. busseolae's host location efficiency.     

Host plant or geographic barrier? Reproductive compatibility among Diatraea saccharalis populations from different host plant species and locations in Argentina

The sugarcane borer, Diatraea saccharalis (Fabricius) (Lepidoptera: Crambidae), is one of the main lepidopteran pests of sugarcane and maize. The association of insects with different environments and/or host plants may occur by adaptation and this can generate host races. Adaptation may produce phenotypic or genotypic variation, which results in the differences in bioecological characteristics such as reproductive compatibility that reduces gene flow among populations. The objective of this study was to determine the reproductive compatibility of three population combinations collected in various geographic locations and from different host plants, thereby determining the influence of geographic distance and/or insect plant association. Interpopulation crosses of D. saccharalis populations from Tucumán (maize and sugarcane) and Jujuy (sugarcane) provided evidence of pre‐zygotic and post‐zygotic incompatibility. The results indicate that gene flow barriers are influenced by the host plant. However, populations from various locations revealed that geographical location is the main factor influencing gene flow among populations of D. saccharalis.     

A single semi‐synthetic diet with improved antimicrobial activity for mass rearing of lepidopteran insect pests of cotton and maize

Helicoverpa armigera (Hübner), Earias vittella (Fabricius), Spodoptera litura (Fabricius), Spodoptera exigua (Hübner) (all Lepidoptera: Noctuidae), Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), and Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) are the major pests of cotton and maize. Mass‐rearing of these insects under controlled conditions is necessary to obtain the numbers needed to conduct bioassays to screen insecticides, proteins, and other compounds, as tools for insect pest management. We present a diet suitable for rearing the six lepidopteran pests (five cotton and one maize pest). We further show that this diet is on par with or superior to the published diet recipes for each of the insect species, which were studied for three generations. We also discuss the advantages of antimicrobials other than formalin for keeping microbial growth under check. A combination of antimicrobial solution and benomyl provided effective control and suppressed the growth of microbes for a longer period than a formalin‐containing diet. A common diet for six pests provide opportunities for automation of diet preparation in addition to improved throughput and consistency in the process, while eliminating diet‐batch related errors.     

Effectiveness in the field of Bt rice lines against target pests under various cultural regimes

China has a long history of rice cultivation, incorporating several cultural practices known to influence damage by insect pests. Transgenic Bt rice expresses lepidopteran‐specific insecticidal proteins that primarily target lepidopteran insect pests. However, the effectiveness of Bt rice against target insect pests under different cultural regimes has not been evaluated. In this study, the effectiveness of Bt rice lines against rice leaffolder, Cnaphalocrocis medinalis (Guenée) (Lepidoptera: Pyralidae), and striped stem borer, Chilo suppressalis Walker (Lepidoptera: Crambidae), was evaluated under various transplanting densities, crop establishment methods, and planting times. The results showed that Bt rice lines (T2A‐1 and T1C‐19, containing Cry2A and Cry1C, respectively) could prevent damage by these target pests under a range of cultural practices. Injury by C. medinalis or C. suppressalis on rice did not differ with the rice lines under various transplanting densities. Direct‐seeded non‐Bt rice MH63 suffered heavier injury by C. medinalis and C. suppressalis than it did with transplanting, whereas injury to the two Bt rice lines did not differ with planting methods. Planting time significantly affected injury by C. medinalis or C. suppressalis on non‐Bt rice, whereas injury to Bt rice lines did not differ with planting time. These results suggest that transplanting density, planting method, and planting time did not significantly affect the resistance of two Bt rice lines, due to their high insecticidal activity against target insects.