Oviposition by autumn gum moth (Mnesampela privata) in relation to Eucalyptus globulus defoliation, larval performance and natural enemies

Abstract 1 Eucalyptus globulus Labill. exhibited consistent intraspecific variation in oviposition choice by Mnesampela privata (Guenée) (Lepidoptera: Geometridae) in field surveys of host plants that had been designated, based on the prior season's defoliation levels, as resistant or susceptible to M. privata. At both field sites significantly fewer egg batches were found on resistant compared to susceptible trees. 2 In cage bioassays we demonstrated a significant oviposition preference by M. privata, with over two‐fold greater number of egg batches laid on foliage sprigs from susceptible compared to resistant trees. Despite differences in tree oviposition choice, we found no evidence in the field or the laboratory of adult females adjusting egg batch size in accordance to oviposition preference. 3 Caged larval survival, development times and pupal weight did not vary significantly between resistant and susceptible trees. Similarly, in a laboratory feeding experiment, neonates utilized resistant and susceptible foliage equally. 4 Larval mortality in the field attributed to natural enemies did not vary significantly between resistant and susceptible trees, nor did the percentage of Telenomus sp. parasitism of M. privata eggs within a batch and batches per tree. 5 Failure to associate either larval performance or natural enemy efficacy with the observed intraspecific variation in E. globulus susceptibility to M. privata oviposition indicates that some other unidentified factors drive the evolution of host selection for oviposition.     

人工补充寄主卵对松林内卵蜂种群消长的影响

在不同生境的松林中,人工补充寄主卵都能提高寄生效果。但林地生境不同,寄生率有明显差异。在松阔混交林中补充寄主,其寄生率比对照提高5.5—16.2倍。植被稀疏的纯松林效果较差,补充的寄生率比对照提高3.0倍。 卵蜂种群消长随季节温度而变化,全年以5月中旬至6月下旬和9月中旬至10月中旬为两个寄生高峰。卵蜂种群与松毛虫种群的消长存在较明显的相依关系,卵蜂种群随着松毛虫种群的消长而消长。施药对卵蜂种群有较大影响,施药区比对照区的寄生率约降低一倍。在混交林中填充寄主卵,能促进卵蜂种群世代延续。在逐步改善林地生境的基础上,利用人工补充寄主,可以代替人工繁蜂放蜂。     

寄生3种夜蛾卵的夜蛾黑卵蜂种群增长潜能

夜蛾黑卵蜂是草地贪夜蛾卵期的一种重要寄生性天敌,适宜的寄主是实现其规模化繁育及应用的基础。本文应用实验种群生命表方法,分析、评价了草地贪夜蛾、斜纹夜蛾及甜菜夜蛾这3种夜蛾卵上夜蛾黑卵蜂的生长发育及种群增长潜能。结果表明,夜蛾黑卵蜂在3种夜蛾卵上均能顺利完成幼期发育且出蜂日期较为整齐,羽化当日即为产卵高峰日,羽化后3 d内的寄生卵量占总产卵量的80%以上。子代羽化率介于77.90%～85.56%之间,雌性比率介于0.53～0.59之间。不同寄主繁育的夜蛾黑卵蜂雄蜂后足胫节长度无明显差异,但以甜菜夜蛾卵繁育的雌蜂的后足胫节最长(152.00μm),斜纹夜蛾卵繁育的次之(146.33μm),草地贪夜蛾卵繁育的最短(142.67μm)。以甜菜夜蛾卵繁育的夜蛾黑卵蜂的内禀增长率(r_m)、净生殖力(R₀)及周限增长率(λ)均最高,分别为0.3486、57.94和1.4171,以斜纹夜蛾卵繁育的次之(r_m,0.3091;R₀,49.60;λ,1.3623),而以草地贪夜蛾卵繁育的最小(r_m,...     

Spatial and temporal dynamics of oviposition behavior of bollworm and three of its predators in Bt and non-Bt cotton fields

Host plants exhibiting insect resistance traits have long been known to influence within‐plant distributions of pests and their natural enemies. Sites and timing of egg deposition are particularly important for synchrony of predators and their prey in the field. Temporal and spatial distribution of eggs of the cotton bollworms [Heliothis virescens (F.) and Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae)] and that of the predators Geocoris punctipes (Say) (Heteroptera: Geocoridae), Chrysoperla rufilabris (Burmeister) (Neuroptera: Chrysopidae), and Micromus spec. (Neuroptera: Hemerobiidae) were determined during three cotton seasons, from 2002 to 2004, by collecting and examining plants throughout each season. Comparisons also were made between Bt and non‐Bt cotton to investigate possible changes in oviposition behavior on Bt cotton. The study was conducted in commercial fields with insecticide use to manage pests when economic thresholds were exceeded in both cotton types. Egg densities for predators and bollworms varied among years, but were similar on Bt and non‐Bt cottons. Oviposition of bollworms and G. punctipes correlated spatially within plants, with most eggs laid on structures in the top five nodes of cotton plants and on the three outermost leaves on lateral branches regardless of cotton type. Bollworm oviposition dynamics exhibited two peaks within the season (early July and early August). Eggs of all predators and bollworms collected from the field and incubated in the laboratory had high hatching rates throughout each season (74–100%). Temporal association of predator with bollworm oviposition showed a significant correlation with green lacewings, a delay of 10 days for big‐eyed bugs, and no correlation with brown lacewings. Furthermore, Bt cotton plants exerted no significant effect on temporal or spatial patterns of oviposition of bollworms or the predators, indicating no change in oviposition behavior of bollworm females within plant structures after almost one decade of widespread planting of Bt cotton.     

Seasonal Fluctuations of Noctuid Stemborer Egg Parasitism in Southern Benin with Special Reference to Sesamia calamistis Hampson (Lepidoptera: Noctuidae) and Telenomus spp. (Hymenoptera: Scelionidae) on Maize

Parasitism of noctuid stemborer eggs was assessed in monthly surveys in maize fields in southern Benin, from May 1995 to October 1996, and on alternative hosts, i.e. wild grasses, during the dry season from November 1995 to February 1996. Sesamia calamistis was the most prevalent stemborer species, accounting for 98% of the larvae identified from subsamples reared on ear pieces. Egg batch densities ranged between 0.02-0.15 per plant, with lowest densities found during high rainfall periods. 77% of all egg batches were found to be parasitized The egg parasitoids were the scelionids Telenomus busseolae, T. isis , and the trichogrammatid Lathromeris ovicida , accounting for 55.6, 41.6 and 2.8% of total counts, respectively. Parasitism increased in the course of the cropping season and reached peaks of 92 and 86% during the second growing season of 1995 and 1996, respectively. This coincides with the time when farmers have planted a second crop and during a stage when the plants were most attractive and susceptible to S. calamistis attacks. During the dry season, relatively high parasitism was found on maize and wild grasses in inland valleys, and it was concluded that those habitats play an important role in stabilizing the system for both the pest and its natural enemies. As a result, in the Dahomey Gap, which includes parts of Benin, Togo and Ghana, S. calamistis is usually not of economic importance. Although T. busseolae is ubiquitous in Africa, T. isis was only reported from West Africa, including Cameroon. It is recommended that the geographic range of T. isis should be expanded and include East and Southern Africa, where another host, Busseola fusca , is the most important noctuid stemborer pest on cereals.     

PARASITICAL BEHAVIOR OF TELENOMUS THEOPHXLAE WU ET CHEN*

Abstract The parasitical behavior of Telenomus theophilae can be divided into five successive steps: examining, probing, drilling, ovipositing and marking. The total time for completing this process required 17 min 20 s in average. The time for drilling and oviposition accounts for 86. 5%. The results implied that the females of T. theophilae have a learning process of host recognition at first time of parasitization, and the percentage of superparasitism in the first host egg of Theophila mandarina (70. 6%) is 4. 8 times as that in the fourth host egg (14. 7%).     

Development and survival of Telenomus lobatus, a parasitoid of chrysopid eggs: effect of host species

Telenomus lobatus Johnson & Bin (Hymenoptera: Scelionidae), previously known only from the eggs of a berothid species, emerged from field-collected eggs of the chrysopid Mallada macleodi. In the laboratory, host species differentially influenced development, survival, and size of the parasitoid. Females parasitized between 55 and 65% of the available eggs of Chrysoperla (C. carnea, C. harrisii, and C. rufilabris), and these yielded 98 to 100% adult parasitoids within an average of 13 days. In contrast, eggs of Chrysopa were parasitized less frequently, (C. chi: 50%; C. oculata: 16%; C. quadripunctata: 1.3%) and relatively few (C. chi: 5.6%; C. oculata: 21%) or no (C. quadripunctata) parasitoids survived to adult emergence. Preimaginal development of T. lobatus in eggs of C. chi and C. oculata was approximately two days longer than in eggs of Chrysoperla spp. Although eggs of Meleoma dolicharthra were parasitized infrequently (approx. 16%), they yielded 100% adult parasitoids. Anomalochrysa maclachlani eggs were parasitized at low rates (1.8%) and parasitoid survival was intermediate (40.7%). Among all species, size of the host egg was positively related to the size of the emerging parasitoid adult.

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Résumé T. lobatus Johnson & Bin (Hym. Scelionidae) connu jusqu'ici uniquement comme parasitoïde des ufs de Berothidae, a étè obtenu d'ufs du chrysope, Mallada macleodi récoltés dans la nature. Au laboratoire, l'espèce de l'hôte influe sur le développement, la survie et la taille du parasitoïde. Les femellles ont parasité 55 à 65% des ufs disponibles de Chrysoperla (C. carnea, C. harrisii, C. rufilabris) et ceux-ci ont donné 98 à 100% de parasitoïdes adultes en 13 jours en moyenne. Par contre, les ufs de Chrysopa étaient moins souvent parasités,-C. chi: 50%; C. oculata: 16%; C. quadripunctata: 1,3%-, et relativement peu de parasitoïdes avaient survecu jusqu'à l'émergence,-C. chi: 5,6%; C. oculata: 21%; C. quadripunctata: 0. Le développment préimaginal est approximativement 2 jours plus long dans les ufs de C. chi et C. oculata que dans ceux de Chrysoperla spp. Bien que les ufs de Meleoma dolicharthra aient été peu parasités,-environ 16%-, 100% ont donné des parasitoïdes adultes. Les ufs de Anomalochrysa maclachlani ont été peu parasités,-1,8%-, et le taux de survie a été moyen: 40,7%. Pour toutes les espèces, la taille de l'uf de l'hôte était liée positivement à la taille du parasitoïde obtenu.

     

Geostatistical analysis shows species-specific habitat preferences for parasitoids

Parasitoids are known to inhabit native vegetation on Australian farms but the extent to which they spill-over into nearby crops is not clear. Geostatistical analysis of parasitoid distribution data showed that vegetational preference and spill-over between native vegetation and cotton fields are highly variable, even between congenerics.     

Functional response of Telenomus busseolae (Hym.: Scelionidae) an egg parasitoid of the sugarcane stem borer,Sesamia nonagrioides (Lep.: Noctuidae) at different temperatures

Telenomus busseolae Gahan is the most important egg parasitoid of sugarcane stem borers in Iran. Laboratory experiments were conducted to evaluate the functional response of T. busseolae to egg densities of Sesamia nonagrioides (Lefebvre) under four different temperatures (20, 25, 30 and 35°C). Results of logistic regression revealed a type III functional response for all temperatures tested and type of functional response was not affected by temperature. Roger's random parasite equation was fitted to observed data at 35°C. In the other data sets (collected data under 20, 25 and 30 °C) Roger's equation could not provide meaningful parameters, therefore Holling's disk equation was used to fit the data. The attack rate for T. busseolae varying from 0.001784 to 0.10704, 0.0026 to 0.152, 0.0024 to 0.144 and 0.000866 to 0.05196 per h and estimated handling times were 0.59, 0.50, 0.53 and 0.29 h at 20, 25, 30 and 35°C, respectively. Based on asymptotic 95% confidence intervals, functional response parameters did not differ significantly from 20 to 30°C, which indicates that handling time and attack rate are least affected by the temperature changes. The results suggest a similar performance of T. busseolae against S. nonagrioides eggs at temperatures of 20–30°C. These results show that T. busseolae is well adapted to temperature changes during the sugarcane growing season.