Egg allocation by Bracon hylobii Ratz., the principal parasitoid of the large pine weevil (Hylobius abietis L.), and implications for host suppression

1 The braconid parasitoid Bracon hylobii Ratz. is one of the few specialist natural enemies of the large pine weevil, Hylobius abietis L., a destructive pest of conifer transplants. An assessment of its role as an agent of biological control requires a detailed knowledge of the allocation of its reproductive effort. 2 Parasitoid females were continuously observed in laboratory culture with individually reared host larvae in bark discs. The outcome of sequential parasitoid–host encounters was recorded by subsequent examination of hosts and by rearing all parasitoids. 3 Parasitoids avoided ovipositing on host larvae < 100 mg fresh weight, even though such larvae represented sufficient biomass for complete parasitoid development. All larger larvae were vulnerable to attack, which leaves a window of vulnerability for parasitoids of about 90% of weevil larval life. 4 Parasitoids presented with a range of host sizes showed no preference above 100 mg for the size of host first attacked, but allocated more eggs and a greater total handling time to larger hosts. 5 Most eggs were deposited on the first host attacked, with progressively fewer allocated to subsequent hosts. However, oviposition experience did not affect the time spent on the next host. 6 From these results it is anticipated that when weevil larval size is reduced by less favourable feeding substrates, fewer parasitoid eggs will be allocated to each but more host larvae will ultimately be attacked. 7 Generation time, host finding, oviposition rate, clutch size, life expectancy and diapause induction are strongly affected by temperature. Life expectancy is substantially shorter for parasitoids deprived of non‐host food supplement. At 15 and 20 °C the number of hosts attacked and the number of eggs deposited decreased with female age. 8 Bracon hylobii is inevitably poorly synchronized with a variable life‐cycle host; it is egg‐limited and can enter diapause at a relatively high field temperature. None of these characteristics suggest that it could stabilize the abundance of its host below an economically acceptable threshold density. However, the reproductive potential of the parasitoid suggests that it could make a significant contribution to larval mortality and suppress adult recruitment, thus complementing other control strategies.     

Induction of adult diapause and of low and high reproductive states in a parasitoid wasp,Ooencyrtus nezarae, by photoperiod and temperature

Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) was reared on eggs ofRiptortus clavatus (Thunberg) (Heteroptera: Alydidae) at various temperatures under long-day (L16:D8) or short-day (L10:D14) conditions. There was no diapause during egg, larval or pupal stages under any set of conditions examined. However, at 15°C under short-day conditions, vitellogenesis was arrested in all adult females and they entered diapause. At 15°C under long-day conditions, or at 20°C under short-day conditions, some adult females entered diapause. Under the latter set of conditions, the adult females laid eggs but they laid fewer eggs than under long-day conditions, Even at 25°C, under short-day conditions, adult females laid fewer eggs than under long-day conditions, and this low rate of oviposition was attributed to the retarded development of ovaries. Diapause adults reared at 15°C were more resistant to low temperature than nondiapause adults reared at 25°C.     

Diapause termination in the spotted stem borer, Chilo partellus (Lepidoptera: Pyralidae) in the laboratory

The effect of temperature, photoperiod, artificial diet and water on the termination of diapause by larvae of the stem borer, Chilo partellus (Lepidoptera: Pyralidae), was studied in the laboratory. Termination of diapause as indicated by pupation was affected mainly by a combination of high temperature and a long day photoperiod. Total darkness did not prevent termination of diapause and pupation occurred also in larvae which were never exposed to water. Long days accelerated pupation, but, under 16 h daylength, termination of diapause was faster than under constant illumination. Provision of artificial diet had no effect or slowed down pupation but water decreased the time to pupation. Under 28°C, 16 h daylength and availability of water, C. partellus diapausing larvae terminated diapause and pupated in about 9 days.     

Phenotypic plasticity and geographical variation in the pre-reproductive period of Autographa gamma (Lepidoptera: Noctuidae) and its implications for migration in this species

Abstract.

• 1 Adults of the noctuid moth Autographa gamma undertake seasonal migrations into areas where they are unable to breed continuously. Individuals migrate into Britain each spring, and offspring of these migrants probably return in autumn to over-wintering areas in North Africa and the Middle East. However, the existence of these return migrations has been questioned.
• 2 Insects usually migrate during the adults' pre-reproductive period (PRP). The length of this period is therefore an index of migratory potential since individuals with longer PRPs have more time to express their potential for flight and to travel further before becoming sexually mature.
• 3 Offspring of insects from Morocco, Britain and Germany showed that, under both long and short photoperiods, PRP increased with latitude over the range 34–53°N. There were significant genotype—environment interactions in the effect of photoperiod on length of PRP.
• 4 However, PRPs of offspring from insects collected in Sweden were no different under a long photoperiod from those of offspring collected further south, and were significantly shorter under a short photoperiod than those of insects from Morocco.
• 5 With the exception of Swedish moths, offspring from insects collected at higher latitudes had longer PRPs and, therefore, the potential to travel further during migrations. The ability of some individuals to respond to environmental cues signalling habitat deterioration will further increase their potential to return to over-wintering areas further south.

     

亚洲玉米螟滞育幼虫的一些生理特征(英文)

对亚洲玉米螟,Ostrinia furnacalis(Guenee)(Lepidoptera:Pyralidae),末龄滞育幼虫的生理生化指标进行了研究。确定了血淋巴滞育关联蛋白的分子量,微量呼吸仪测定了幼虫的呼吸量。同时,对体内水分含量,幼虫对水的耐受性,以及雄性精巢的大小亦进行了分析和观察。发现相应于非滞育幼虫,滞育幼虫有如下特点:1.滞育幼虫的血淋巴中具有一种滞育关联蛋白,它的两个亚肽的分子量分别为72000和840000道尔顿。2.雄性生殖器官发育不完全。3.体内水分含量占体重的比率较低,相对应干重较高。4.在室温下对浸水窒息的耐受性高。5.幼虫呼吸微弱,氧的消耗较小。     

蜕皮激素在银盾革蜱生殖滞育中的作用(英文)

用高效液相色谱法和放射免疫测定法测定了银盾革蜱滞育雌虫的合神经节、血淋巴、卵巢和整体中蜕皮激素的含量,并与正常发育的雌虫做比较。结果表明,滞育雌虫血淋巴和卵巢中蜕皮激素的含量在饱血后前10天与正常发育雌虫基本上相同。饱血10天以后,滞育雌虫蜕皮激素的含量下降,较正常发育雌虫少得多。蜕皮激素的缺乏影响了卵母细胞的发育。为阐明蜕皮激素对滞育雌虫的影响,在不同时间向银盾革蜱滞育雌虫体内注入不同剂量的β-蜕皮素。刚饱血者注入大剂量(1.375和10000ng/蜱)的β-蜕皮素引起雌虫死亡。饱血后20—30天,注入一定剂量(50,70,100ng/蜱)的β-蜕皮素可以促进卵黄形成,并解除了雌虫的生殖滞育,但其所产的卵量明显少于正常发育的雌虫。应用外源蜕皮激素解除硬蜱雌虫的生殖滞育现象尚属首次报道。     

The arrest of embryogenesis at gastrula stage in the diapausing silkwormBombyx mori is related to the synthesis of protein P61

Summary Two-dimensional protein gels are used to assess systematically changes in protein synthesis in diapausing and non-diapausing early embryos ofBombyx mori throughout natural breakage of diapause by chilling and after artificial prevention of diapause by HCl+ heat-shock treatment. A set of proteins, the heat-shock protein (hsp) 70 family previously described, was synthesized in diapausing and non-diapausing development at the early germ-anlage stage; by contrast, protein 61 (P61; 61 kDa) was synthesized only in the diapausing gastrula stage. The synthesis of P61 decreased during days at 5°C. Thereafter, we observed the synthesis of the hsp 70 family at 5°C. After the artificial prevention of diapause, P61 synthesis was not induced at the gastrula stage, whereas the hsp 70 family was enhanced in the 6 h following the preventive treatment. P61 was only synthesized after treatments were ineffective in preventing diapause and in inducing hsp 70. Thus, P61 can be described as a diapause arrest-associated protein.     

Photoperiodic control of adult diapause in the predacious mite, Amblyseius potentillae: repeated diapause induction and termination

ABSTRACT. Photoperiodic control of facultative reproductive diapause was examined in females of the phytoseiid mite, Amblyseius potentillae (Garman). Full diapause was induced by rearing the mites from egg to adult under short-day photoperiods. Egg-laying females, however, which had experienced a long-day photoperiodic regime during pre-imaginal development, could still be induced to enter diapause when they were transferred to a short-day regime. Diapause development proceeded slowly under a short-day photoperiod, but was accelerated under long days. During diapause development under short days the photoperiodic sensitivity of the females diminished gradually and ultimately disappeared completely. However, after completion of diapause, sensitivity to photo-period reappeared. A second diapause could be induced in post-diapause females under short-day photoperiods and completed again under long-day photoperiods. These results show that A. potentillae remains sensitive to diapause-inducing and diapause-averting daylengths during the adult stage and that a second diapause may be induced after completion of the first one.     

Factors limiting the distribution ofDigitaria adscendens andEleusine indica on coastal sand dunes in Japan

Fate ofDigitaria adscendens andEleusine indica seedlings under field conditions and their responses to salt spray, drought and nutrients were experimentally investigated in order to evaluate the possible mechanisms controlling the different distributions of the two species in coastal sand dune areas. Salt spray produced no apparent positive effect on the growth or survival of both species. Seeds of each species germinated well in the field, although 80% ofE. indica seedlings died during a summer drought and surviving seedlings neither grew nor bore fruit. The mortality ofD. adscendens seedlings due to the drought was less than 10% and the survivors mostly bore fruit by the end of the growth season. No major difference in the sublethal water saturation deficit was noticed between the two species. However,D. adscendens individuals extended their roots into the deep sandy soil to a much greater extent in water-stressed conditions than in well watered conditions, whereasE. indica showed no such behavior. Additional watering in a dune environment did not help the growth ofE. indica seedlings, but additional nutrients had a markedly stimulatory effect.D. adscendens maintained its growth and fruition with much smaller amounts of nutrients thanE. indica. Soil nitrogen content at a site whereE. indica andD. adscendens were distributed sympatrically was higher than that at a site where onlyD. adscendens was present. Based on these findings, it is proposed thatE. indica seedlings are unable to become established because of their lower resistance to summer drought and the poor nutrient conditions present in a coastal rear sand dune habitat. Dedicated to Prof. emeritus Toshiro Saeki for his fruitful career in plant ecology.