Host location behavior of Cotesia plutellae Kurdjumov (Hymenoptera: Braconidae) in ambient and moderately elevated ozone in field conditions

In field O₃-enrichment experiments increased herbivore densities have been reported, which could be due to negatively affected host location behavior of natural enemies. We addressed the impact of doubling background O₃ on the host location of the parasitoid Cotesia plutellae by conducting 24-h trials in an open-air O₃-fumigation system during two consecutive years. Two circles (radii 1.40 and 4.00 m) of Plutella xylostella-infested potted cabbage plants were placed in the O₃ and ambient plots. Female wasps were released into each plot from the center, and observed 5 times over a 24-h period to assess their host location capability. Thereafter, plants were kept in laboratory conditions until larvae pupation to determine parasitism rates. No significant differences were detected between ambient and O₃-enriched environments either in the number of wasps found in the field, or in the percentages of parasitized larvae. This suggests that moderately elevated O₃ will not affect the behavior of this parasitoid.     

Sex ratio and oviposition responses to host age and the fitness consequences to mother and offspring in the parasitoid wasp Spalangia endius

In the parasitoid wasp Spalangia endius more offspring and a greater proportion of daughters were oviposited in, and emerged from 0-day-old versus 3-day-old hosts. Offspring that developed on the younger hosts (1) were larger at adulthood, (2) developed more quickly, (3) had higher survivorship to adulthood, and (4) were more often able to chew their way out of the host. Sons and daughters did not differ in how host age affected their size, development rate, or survivorship. The greater proportion of daughters from the younger hosts may be adaptive, as described by the host quality model (a variant of the Trivers and Willard hypothesis). It is adaptive if greater size or more rapid development has a more positive effect on a daughter’s than a son’s fitness and the positive effect is large enough to compensate for sons being trapped disproportionately to daughters in the older hosts. Despite greater success at drilling the younger hosts, mothers did not try to drill them sooner or more often. Having previously oviposited on the older rather than the younger hosts had no detrimental effect on the mother’s subsequent longevity or offspring production. Received: 8 March 2000 / Revised: 9 June 2000 / Accepted: 24 June 2000     

Induction of host specificity in larvae of Manduca sexta: chemical dependence controlling host recognition and developmental rate

Summary. The tobacco hornworm, Manduca sexta L. (Lepidoptera: Sphingidae) is a specialist on Solanaceae. This host specificity is induced as the larva feeds on solanaceous foliage, so that solanaceous-reared larvae will refuse to feed on other plants. Experiments were designed to determine the role of dietary constituents on the induction of host specificity and the effects of these on development of M. sexta. Choice assays using leaf discs of cowpea, Vigna sinensis (Fabaceae), were used to monitor the isolation of relevant chemical cues from foliage of potato. An aqueous extract of potato foliage strongly stimulated feeding. This extract was partitioned with n-butanol under alkaline conditions to obtain a highly active butanol extract. Reversed phase flash chromatography with a water-methanol gradient gave an active fraction that was used as a supplement for wheat germ-based artificial diet. Larvae reared on this s-diet became dependent on potato allelochemicals for initiation and continuation of feeding activity. These larvae also developed faster than larvae reared on the control p-diet, but no effect on adult mass was detected. Further flash chromatography of the active fraction under alkaline conditions provided a highly active sub-fraction, and semi-preparative HPLC using gradients of water and acetonitrile resulted in the isolation of a single compound. Bioassays indicated that this compound alone can account for host recognition by solanaceous-reared larvae. The results suggest that the mechanism of induced host specificity in M. sexta involves development of dependence on this compound. Received 21 December 1999; accepted 14 March 2000     

下辽河平原区域地下水典型污染物的筛选

结合潜在危害指数评价方法和加权评分方法,构建了新的地下水中典型污染物的筛选方法,并应用于下辽河平原区域地下水典型污染物的筛选。将急性基准浓度值(CMC)和慢性基准浓度值(CCC)引入潜在危害指数评价中;鉴于潜在危害指数法不考虑化合物的环境浓度,将潜在危害指数法与加权评分法相结合,引进平均浓度、检出频次等影响因素,计算不同污染物加权评分结果;通过聚类分析,筛选出典型污染物。研究表明,下辽河平原区域地下水中筛选出的典型污染物包括:As、NH+4、1,1,2-三氯乙烷、溴二氯甲烷、一氯二溴甲烷、1,1-二氯乙烯、α-六六六、p,p'-滴滴滴、p,p'-滴滴伊、苯并(a)芘。     

Different phagostimulants in potato foliage for Manduca sexta and Leptinotarsa decemlineata

Summary. In the past decades, several studies have focused on the identification of feeding stimulants for specialists that feed on solanaceous plants, especially potato (Solanum tuberosum). In the 1950's, a phagostimulant was isolated from potato and tomato for Manduca sexta and characterised as a glycoside. It was suggested that the phagostimulant for M. sexta and Leptinotarsa decemlineata is identical. We tested whether these insects indeed share the same recognition factor. Previous bioassays for L. decemlineata larvae and adults were found to be unsatisfactory, so a new assay system was developed, using starch and wheat flour-based wafers as a neutral substrate. An aqueous extract of potato foliage that was highly active as a stimulant was fractionated by reverse phase medium pressure liquid chromatography (MPLC). Both insects were stimulated by a MPLC fraction that eluted with 25% methanol in water. Further separation of this and the following fraction (35% methanol, stimulatory for the beetle only) by semi-preparative high performance liquid chromatography (HPLC), using gradients of water and acetonitrile, resulted in the isolation of two distinct fractions that stimulated feeding by L. decemlineata. None of the HPLC fractions was active for M. sexta. However, fractions of the flash chromatography with less polarity (45–75% methanol) had a stimulatory effect only on M. sexta. Thus, the two insects do not use a common feeding stimulant, and for both at least two compounds of different polarity are active. Received 3 July 2000; accepted 24 October 2000     

Learning affects host discrimination behavior in a parasitoid wasp

Learning is generally predicted not to be important in host discrimination by parasitoids, because the stimuli involved are less variable than those used in habitat location. However, Anaphes victus (Hymenoptera: Mymaridae), an egg parasitoid of Listronotus oregonensis (Coleoptera: Curculionidae) apparently learns to associate external pheromones with the presence of a conspecific in a host. In this species, females can reject a parasitized host either after antennal drumming (antennal rejection) or after the insertion of their ovipositor (sting rejection). When they encountered a series of parasitized hosts, females A. victus learned to associate the presence of the external pheromone with the presence of the internal one. Learning lasted less than 4 h and occurred earlier in a series when the female marking the egg and the one detecting that mark were close relatives. This behavior could be adaptive because antennal rejection is faster than sting rejection. Received: 11 March 1997 / Accepted after revision: 30 August 1997     

Cuckoo growth performance in parasitized and unused hosts: not only host size matters

The quality and quantity of food delivered to young are among the major determinants of fitness. A parental provisioning capacity is known to increase with body size. Therefore, brood parasitism provides an opportunity to test the effects of varying provisioning abilities of different-sized hosts on parasitic chick growth and fledging success. Knowledge of growth patterns of common cuckoo, Cuculus canorus, chicks in nests of common hosts is very poor. Moreover, no study to date has focused on any currently unused hosts (i.e., suitable cuckoo host species in which parasitism is currently rare or absent). Here, I compare the growth performance of cuckoo chicks in nests of a common host (the reed warbler, Acrocephalus scirpaceus) and two unparasitized hosts (the song thrush, Turdus philomelos, and the blackbird, Turdus merula). Parasitic chicks were sole occupants of the observed nests, thus eliminating the confounding effect of competition with host chicks. Experiments revealed striking differences in parasitic chick growth in the two closely related Turdus hosts. Cuckoo chicks cross-fostered to song thrush nests grew much quicker and attained much higher mass at fledging than those in nests of their common reed warbler host. Alternatively, parasitic chicks in blackbird nests grew poorly and did not survive until fledging. I discuss these observations with respect to host selection by parasitic cuckoos.     

Test of the adaptiveness of sex ratio manipulation in a parasitoid wasp

In behavioral ecology it is generally assumed that behavior is adaptive. This assumption is tested here for sex ratio manipulation in response to host size in the parasitoid wasp Spalangia cameroni. Females produce a greater proportion of daughters on larger hosts. If this behavior is adaptive, it is not through a positive effect of host size on the fitness of daughters, as theory suggests and as found for other species. Females that developed on larger hosts were not more successful at drilling into hosts, were not more successful at interspecific competition for hosts, and did not have greater dispersal ability as measured by wing loading (weight/area of wing and thorax). The possibility that S. cameroni's sex ratio manipulation may be adaptive through a negative effect of host size on the fitness of sons cannot be ruled out. Relative to males from larger hosts, males from smaller hosts had lower wing loading and thus potentially greater dispersal ability. The actual effect of wing loading on fitness remains to be tested.     

Chemical basis for differential acceptance of two sympatric rutaceous plants by ovipositing females of a swallowtail butterfly, Papilio polytes (Lepidoptera, Papilionidae)

Summary. In the natural habitat of Papilio polytes, a Rutaceae feeder utilizing Toddalia asiatica as a major host plant, some other rutaceous plants such as Murraya paniculata (abundant) and Glycosmis citrifolia (relatively rare) occur sympatrically as potential hosts. Whereas G. citrifolia is occasionally infested in the field, M. paniculata remains entirely unexploited by the butterfly. We thus examined the phytochemical mechanisms that can explain the differential acceptance of the two plants by ovipositing females of P. polytes. The foliage of G. citrifolia was found to readily induce oviposition and females deposited eggs in response to a methanolic extract of the plant. Stimulatory activity-directed fractionation of the extract revealed the presence of two characteristic compounds, trans-4-hydroxy-N-methylproline and 2-C-methylerythronic acid, known to serve as oviposition stimulants for the butterfly. In addition, larvae performed as well or better onG. citrifolia as on T. asiatica. Similar examination of the inhibitory chemical constituents of M. paniculata led to the isolation of an oviposition deterrent. The compound, identified as trigonelline (N-methylpyridine- 3-carboxylic acid), exhibited moderate oviposition deterrency to females. These results combined with our previous data are in agreement with the observed differential utilization of the two plants by P. polytes in the field.     

废塑料-环氧化橡胶制造橡塑型道路反光标志带的研究

借助环氧化天然橡胶（ＥＮＲ）分子链上环氧基团的二次反应，同废旧聚氯乙烯（ＰＶＣ）、聚苯乙烯（ＰＳ）等塑炼、压延成像塑型道路反光标志带（ＰＺ－ＭＳ），其抗拉强度等性能比Ｚ１－２型道路反光标志带（Ｚ－ＭＳ）好，同时治理了白色污染。