A Stochastic Model for Oviposition Tactics in the Bean Weevil

In a recent paper, MITCHELL (1975) experimentally investigated the oviposition behavior of weevils on mung beans. In this paper, we develop a stochastic model to study the oviposition tactics of the female weevils on beans.     

Eustenopus villosus (Coleoptera: Curculionidae) Feeding of Herbicide-Resistant Yellow Starthistle (Centaurea solstitialis L.)

A population of yellow starthistle (Centaurea solstitialis L.) near Dayton, Washington developed herbicide resistance in response to repeated applications of picloram and other auxin-type herbicides. Laboratory and field experiments were conducted in 1998 to determine host acceptability and suitability of this herbicide-resistant yellow starthistle population to the biological control weevil Eustenopus villosus (Boheman) (Coleoptera: Curculionidae). In choice and no-choice feeding and oviposition experiments using excised buds, the weevil did not demonstrate a consistent preference for either herbicide-resistant (R) or -susceptible (S) yellow starthistle. When caged on buds of intact plants, the E. villosus feeding rate of 97% did not differ between R and S types. Host plant suitability, measured as larval damage and development to adult weevils, was equivalent in R and S types, with weevils maturing in 46% of the R and in 32% of the S capitula bearing oviposition scars. The number of viable achenes per capitulum was reduced by 87% due to larval feeding, with no difference between R and S types. Observations at the field site where resistance was found revealed oviposition scars on 78% of the late-bud-stage capitula on 23 June 1998 and 73% of the flowering and postflowering capitula on 15 August 1998. Selection for herbicide resistance has not created host incompatibility for E. villosus nor reduced the effectiveness of E. villosus as a biological control agent.     

Leaf scarring by the weevils Neochetina eichhorniae and N. bruchi enhances infection by the fungus Cercospora piaropi on waterhyacinth, Eichhornia crassipes

Additive or synergistic effects among introduced and native insect and plant pathogen agents are necessary to achieve biological control of waterhyacinth (Eichhornia crassipes), a globally damaging aquatic weed. In field plots, plants were infested with waterhyacinth weevils (Neoechetina bruchi and N. eichhorniae) and leaves were scarred by weevil feeding. Subsequent infection by the fungal pathogen Cercospora piaropi caused necrotic lesions to form on leaves. Necrosis development was 7.5- and 10.5-fold greater in plots augmented with both weevils and C. piaropi and weevils alone, respectively, than in plots receiving only C. piaropi. Twenty-four days after weevil infestation, the percentage of laminar area covered by lesions on third-youngest and oldest live leaves was elevated 2.3–2.5-fold in plots augmented with weevils. Scar density and necrosis coverage on young leaf laminae were positively correlated, even though antipathogenic soluble peroxidases were elevated 3-fold in plots augmented with weevils alone or weevils and C. piaropi. Combined weevil and fungal augmentation decreased shoot densities and leaves per plant. In a no-choice bioassay, weevil feeding on oldest but not young leaves was reduced 44 two weeks after C. piaropi inoculation. Protein content and peroxidase activities were elevated 2–6-fold in oldest leaves three weeks after inoculation. Augmentation with both waterhyacinth weevils and C. piaropi led to the development of an additive biological control impact, mediated by one or more direct interactions between these agents, and not plant quality effects.     

Oviposition specificity and behavior of the watermilfoil specialist Euhrychiopsis lecontei

Eurasian watermilfoil (Myriophyllum spicatum L.) is a nuisance aquatic weed, exotic to North America. The freshwater weevil Euhrychiopsis lecontei (Dietz) is a potential control agent of Eurasian watermilfoil and is a fully submersed aquatic specialist herbivore. Its presumed original host is the native northern watermilfoil (Myriophyllum sibiricum Komarov). We conducted a set of oviposition experiments to reveal first and second oviposition preference of Euhrychiopsis lecontei when presented with seven macrophytes. We tested differences between source (lake) populations of weevils, differences in behavior between weevils reared on the exotic Eurasian watermilfoil and the native northern watermilfoil and between weevils in the presence and absence of their preferred hostplant. Oviposition assays confirmed that E. lecontei is a watermilfoil specialist. Out of the 207 females that laid eggs, only three oviposited on a non-watermilfoil plant, Megalodonta beckii. The weevils' degree of specificity was influenced by the watermilfoil species on which they were reared. Weevils reared on Eurasian watermilfoil tended to oviposit on Eurasian watermilfoil, spent more time on Eurasian watermilfoil than on other plants, and spent more time off plants and took longer to oviposit when Eurasian watermilfoil was removed. Weevils reared on northern watermilfoil did not exhibit a preference for either watermilfoil species in oviposition or in time allocation, although they oviposited on and spent significantly more time on watermilfoils than on other species. Rearing of the two populations on their complementary watermilfoil hostplant resulted in responses typical of the rearing plant, not the original host. These results show that although both weevil populations are watermilfoil specialists, Eurasian-reared weevils prefer Eurasian watermilfoil in general host attraction and oviposition, whereas northern-reared weevils do not. The results support the contention that E. lecontei may be a good biocontrol agent for Eurasian watermilfoil because of its high specificity. The results also suggest that the current host range expansion of the weevil to Eurasian watermilfoil has the potential to become a host shift due to the increased specificity. Herbivory in freshwater systems is not well studied, and the E. lecontei-M. spicatum relationship is a rare example of submersed freshwater specialist herbivore-host-plant interactions.     

Flooding influences ovipositional and feeding behavior of the rice water weevil (Coleoptera: Curculionidae)

The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is the most destructive insect pest of rice in the United States. As part of an effort to develop strategies to manage this pest, the ovipositional and feeding habits of L. oryzophilus on rice plants subjected to different flooding treatments were characterized in greenhouse studies. Presence and depth of flood had a direct influence on the ovipositional behavior of weevils in no-choice studies. More eggs were found in flooded plants than in unflooded plants. Moreover, plants flooded to a depth of 5.1 cm received more eggs than plants flooded to depths of 1.3 or 10.2 cm. Presence and depth of flood influenced both the proportion of females that oviposited in plants and the number of eggs laid by those females that did oviposit. In choice studies, female weevils showed a marked ovipositional preference for plants flooded to a depth of 10.2 cm over unflooded plants and plants flooded to a depth of 1.3 cm. In separate choice experiments, adult rice water weevils fed more on flooded plants than on unflooded plants. In a third set of experiments, flooded plants were taller and had higher concentrations of 10 of 13 plant nutrients than unflooded plants. Thus, flooding may influence rice water weevil behavior both directly, by acting as a stimulus for feeding or oviposition, and indirectly, by inducing changes in the suitability of rice plants for feeding or oviposition. These data suggest that it may be possible to manipulate populations of weevils in rice by changing water management practices.     

Host specificity and variation in oviposition behaviour of milkweed stem weevils and implications for species divergence

1. An herbivore's life-history strategy, including optimization of resource use, is constrained by its evolutionary history and ecological factors varying across the landscape. 2. We asked if related and co-distributed herbivore species maintain consistency of host preference and oviposition behaviours along the species' range. We surveyed two putative species of milkweed stem weevils, Rhyssomatus lineaticollis and R. annectens, which co-occur alongside their hosts, Asclepias syriaca and A. incarnata. 3. We confirmed the two species status of weevils, supported by differences in morphology and a bilocus gene phylogeny. Furthermore, we found that species divergence recapitulated the weevils current host plant use. 4. We found oviposition variation within and between species. R. annectens poked the stem haphazardly or girdled it before oviposition. Meanwhile, R. lineaticollis primarily trenched stems in the north, but poked or girdled in the south. Variation in oviposition patterns could be a response to variation in host plant defenses. 5. In nature, weevils strictly oviposited on their respective host plants, while in bioassays, R. lineaticollis exhibited strong preference for A. syriaca and R. annectens fed equally on both host plants. 6. Overall, our results support that milkweed stem weevils are strict specialists but might be undergoing changes in host use. R. lineaticollis specializes on A. syriaca but has two distinct modes of oviposition. Meanwhile R. annectens seems to be more accepting of other hosts. We hypothesize that these weevils might be shifting host use associated with changes in host plant distributions.     

Bud burst and success of the beech weevil, Rhynchaenus fagi: feeding and oviposition

Abstract. 1. Overwintered and starved weevils fed on beech within 5 min of contacting the plant in spring, and oviposition occurred in less than 48 h after feeding.
2. Size of unlaid eggs was significantly reduced when feeding weevils were subsequently starved from beech for 3 days.
3. Date of bud burst did not affect the amounts of feeding or oviposition by weevils.
4. Weevils fed and oviposited preferentially among trees, and the same trees were preferred in two successive years. This preference was independent of bud burst date.     

Prior host feeding experience influences ovipositional but not feeding preference in a polyphagous insect herbivore

Black vine weevils, Otiorhynchus sulcatus (Fabricius) (Coleoptera: Curculionidae), are globally‐distributed polyphagous pests of many horticultural crops. We investigated how adult weevils were affected by host switching and, in particular, how host plant species nutritional and defensive chemistry affected subsequent host plant species selection and oviposition. Adults were fed one of three host plant species, blackcurrant [Ribes nigrum L. (Grossulariaceae)], raspberry [Rubus idaeus L. (Rosaceae)], or strawberry [Fragaria x ananassa Duchesne (Rosaceae)], throughout their pre‐reproductive periods and then subjected to behavioral choice assays with these plants. Foliar chemistry differed significantly among the three host plant species. Compared to raspberry and strawberry foliage, blackcurrant foliage was 13% lower in nitrogen, 3% higher in carbon, and 28% higher in phenolic compounds. Initial host plant species had a significant effect on weevil mortality, with more weevils dying when previously fed blackcurrant (12%) than strawberry (3%) or raspberry (0%) regardless of subsequent host. Initial host plant species also affected oviposition, with weevils laying only ca. two eggs per week when previously fed blackcurrant, compared to those on raspberry or strawberry (ca. 11 and 15 eggs per week, respectively). When given a choice, weevils discriminated among host plant species and tended to oviposit on plants on which they had previously fed, even when the plant was nutritionally inferior for egg production and adult survival. In contrast, feeding behavior was only affected by the current host plant species. Feeding and oviposition were related to leaf chemistry only in blackcurrant, as leaf consumption was negatively correlated with foliar carbon and zinc concentrations, and positively correlated with foliar phosphorus and potassium concentrations.     

微波处理对绿豆象的杀虫效果及对红小豆发芽率的影响

通过设置不同时间和功率的微波对裸露绿豆象Callosobruchus chinensis (L.)成虫、与红小豆混合的成虫、绿豆内幼虫及卵进行处理,以研究微波对绿豆象的杀虫作用及对绿豆象成虫产卵量、幼虫羽化率及卵孵化率等生物学特性的影响。试验结果表明：微波处理裸成虫的死亡率随处理时间及功率增加而升高。成虫在中高火和高火分别处理60 s和50 s以上时间时死亡率过半,为51.21%～99.92%。处理与红小豆混合的成虫死亡率随功率和时间变化趋势同相同处理的裸虫,但相同条件下与红小豆混合的成虫死亡率明显高于相同处理的裸虫。低火至中低火处理60 s、解冻50 s及中火至高火40 s以上时间时成虫死亡都过半,为55.75%～100%,而中火处理70 s、中高火至高火60～70 s可使成虫全部死亡。微波处理具一定后续效应,处理的成虫虽没立刻死亡但随后死亡率仍比对照高。成虫高火处理50 s后的第3天校正死亡率可达87.74%。微波处理还可降低绿豆象成虫产卵量、幼虫羽化率、卵孵化率及红小豆发芽率。成虫、卵和豆内幼虫对微波敏感性依次增高。红小豆在中低火处理60 s、解冻50 s、中火40 s、中高火至高火30 s以上时间时发芽率都低于一半,为0.21%～48.33%。微波对绿豆象杀虫效果显著,但使用时需考虑微波仪器、处理功率和时间、产品用途及含水量等诸多因素的影响并进行优化试验以取得最佳效果。     

Interaction between flight,reproductive development and oviposition in the pine weevil Hylobius abietis

• 1 The development of reproductive and flight capacity of pine weevils Hylobius abietis during the spring and their dispersal to, and subsequent development at, new clearfell oviposition sites comprise key phases in their life cycle in managed forests. At an old clearfell site where autumn‐emerging weevils had overwintered, weevils were trapped as they re‐emerged in the spring and tested for their ability to fly and then dissected to determine the degree of wing muscle and egg development.
• 2 Re‐emerging weevils were most abundant in pine growing at the edge of the clearfell and, over most of the trapping period (April to June), their capacity for flight (proportion flying and wing muscle width) was more advanced than in weevils from the clearfell itself, with a similar trend in the degree of reproductive development (proportion with mature eggs and egg volume).
• 3 In weevils from the clearfell, flight capacity and reproductive development increased concurrently to a peak around mid‐May. In weevils from pine, wing muscles were already well developed at the start of trapping, although few of them flew. Their more advanced development was attributed to the increased opportunities for maturation feeding after emergence in the previous autumn.
• 4 In the spring, weevils reached the canopy of trees for maturation feeding by walking and, to a lesser extent, by flight. Weevils dispersed by flight to oviposition sites in mid‐May when most of them were reproductively mature. After arrival, flight ability and wing muscle size declined rapidly but egg production was maintained until most weevils had stopped flying. When wing muscles reached their minimum size, there was a marked decline in egg size, suggesting that wing muscle breakdown is important in maintaining egg production at oviposition sites. Prospects for further wing muscle and reproductive development are discussed.

     

Phenological analysis of spring colonisation of apple trees by Anthonomus pomorum

Adult apple blossom weevils, Anthonomus pomorum (L.) (Coleoptera: Curculionidae), leave their overwintering sites within and outside orchards to colonise apple trees in early spring. This study was conducted to characterize the temporal pattern of spring colonization of apple trees by overwintered weevils in relation to climatic conditions and apple bud stages, based on multiple mark-release-recapture experiments and field observations of foraging activities of weevils. The process of spring colonization of apple trees by overwintered weevils was related to thermal time totals above 0 °C. The dispersal into orchards initiated when the thermal time totals reached 161±27 (s.d.) degree-days (DD) calculated from January 1, or 117±16 DD from February 1. The daily dispersal speed of individual weevils within orchards was determined primarily by the maximum daily temperature, whereas crawling, feeding, and mating activities of weevils on apple trees were influenced by the mean evening temperature between 18:00 and 22:00 hours. On the other hand, the spring colonization of overwintered weevils was not synchronized with any specific apple bud stage, though the level of female foraging and reproductive activities on apple trees was related to apple bud stages. The overwintered weevils initiated dispersal into orchards over a wide range of bud developmental stages from little silver greenish tip B (51) to the mouse-ear stage C3 (54). These findings are discussed in relation to the ecology and pest management of this insect.     

High oviposition rate ofDasineura marginemtorquens onSalix viminalis genotypes unsuitable for offspring survival

A short history of contact betweenDasineura marginemtorquens and resistant genotypes ofSalix viminalis has previously been suggested as an explanation for a poor correspondence between female oviposition preference and larval performance on certain host types. The discovery of resistant wild willows instigated a quest for an alternative hypothesis. This study presents data from laboratory and field experiments that were designed to detect variability in host preferences of individual members of the midge population. Field tests showed that the oviposition site choices of females followed the same random-natured pattern as choices of females in laboratory situations. Ovipositing females did not distinguish between willow genotypes with very high or very low larval mortality. No differences in post-alighting behavior of midges on the two willow types were discovered. Observations revealed that females usually remained and oviposited on the first plant with which they came into contact, regardless of genotype.     

BCWEEVIL: A simulation model of the joint population dynamics between spruce weevil and Sitka spruce,over the lifetime of a plantation

The spruce terminal weevil Pissodes strobi (Peck) is a major pest in western spruces, attacking trees of all ages beyond the juvenile stage, killing the leader and causing tree distortion. This paper describes a computer simulation model of the joint population dynamics within this tree/pest system, over the lifetime of a plantation, and is combined with the Province of British Columbia's Tree and Stand Simulator (TASS) to drive individual tree growth and stand establishment and development. The model differs from current models of this system, and of other similar systems, in two important ways: (1) it simulates the entire life of a stand, from planting until harvest, and (2) it is based on the underlying biological processes that govern behavior of individual weevils on and in each tree.Each model simulation begins by planting a stand using tree materials from seed or clonal hedge orchards, choosing trees either individually and independently or in groups represented as clones or families. Stand growth and mortality are advanced through a juvenile period, after which weevils appear in the stand. From this time until harvest, the model simulates daily changes in the weevil populations on each tree, tracking mortality, oviposition, and juvenile maturation and emergence, as well as weevil movement from tree to tree. Once a year, the code projects tree mortality and growth, taking into account within-stand competition and damage to leaders caused by weevil attacks. At harvest, the model computes an estimate of the merchantable timber produced by the stand.As illustrations of model output, we present (1) simulated average numbers of adult and juvenile weevils in stands generated using materials from seed orchards, both throughout a single season and also through the years from stand planting until harvest; and (2) the differential effect of weevil damage on two tree genotypes, one resistant and one susceptible, in a stand composed of adjacent clonal blocks. The results of model simulations are in agreement with some of the population dynamics statistics observed in plantations, suggesting that the model reflects biological realism and can be used as a research or management tool.     

Observations on the biology and ecology of Apion vorax (Coleoptera: Apionidae), a vector of broad bean stain and broad bean true mosaic viruses

In spring 1974 and 1975 many adult Apion vorax were found at Rothamsted in woods bordering fields that had been cropped with field beans (Vicia faba) the previous season. The weevils were most common on bramble (Rubus spp.), dog's mercury (Mercurialis perennis) and nettle (Urtica dioica). A decrease in the woodland population in May coincided with the appearance of the weevil on field bean crops in neighbouring areas. In laboratory feeding tests, adult weevils fed more on field bean leaves than on leaves of plants on which they were common in woodlands, and they fed more on field beans in May than at other times of the year. No difference was observed in the feeding of male and female weevils. Many A. vorax were caught on sticky traps in woodlands at Rothamsted in 1975, particularly in April and May, but very few were caught on sticky traps in bean crops. The numbers of A. vorax recorded on the upper foliage of bean crops at Rothamsted in June each year from 1970 to 1980 ranged from 0 to 10 per 10-m row. Eggs, larvae and pupae of A. vorax were found in field bean flowers collected from field crops. The larvae were feeding on the tips of the pistils and stamens. Adult weevils that emerged in mid-June from the flowers of autumn-sown beans mated and produced a second generation when caged on glasshouse-grown plants. Some Apion larvae, possibly A. vorax, were found inside flowers of common vetch (Vicia sativa). The name ‘bean flower weevil’ is considered a suitable common name for A. vorax.     

Host-marking by female pepper weevils, Anthonomus eugenii

Pepper weevils, Anthonomus eugenii Cano (Coleoptera: Curculionidae), feed and oviposit in flower buds and small fruits of plants in the genus Capsicum, as well as several species of Solanum (Solanaceae). Females chew a small hole into the fruit, deposit a single egg within the cavity, and seal the hole with a clear anal secretion that hardens into an ‘oviposition plug’. Female oviposition behavior was studied in a series of small‐arena bioassays to determine whether previous oviposition in Jalapeño pepper fruit deterred subsequent oviposition and to determine what specific cues from an infested fruit influence female behavior. In choice and no‐choice tests, females preferred clean fruit to fruit that had received four eggs 24 h previously (i.e., infested fruit), whether the fruit was infested with conspecific eggs or their own eggs. Further bioassays demonstrated that the presence of female frass, or oviposition plugs alone, in the absence of eggs or any fruit damage, was sufficient to deter oviposition. In addition, females given the choice between an infested fruit with the oviposition plug removed or an unaltered infested fruit preferred the fruit with no plugs, even when eggs, frass, and feeding damage were still present. To determine whether females would avoid infested peppers under more natural conditions, we quantified oviposition on infested and uninfested sentinel pepper fruit within individually caged plants and on clean and infested plants caged together. Females consistently laid more eggs on clean fruit than on infested fruits and moved within and among pepper plants to search for more acceptable oviposition sites. We conclude that oviposition plugs, along with contaminated female, but not male, frass contain a deterrent that, in the absence of any other cue, is enough to alert a female that a patch is occupied.     

Oviposition and feeding behaviour by the vine weevil Otiorhynchus sulcatus on red raspberry: effects of cultivars and plant nutritional status

• 1 The vine weevil Otiorhynchus sulcatus is a major pest of horticultural crops worldwide, with root‐feeding larvae causing most damage. Adult oviposition aboveground may therefore influence levels of damage as the larvae are relatively immobile after oviposition.
• 2 The present study investigated feeding and oviposition behaviour on red raspberry Rubus idaeus using intact plants, ensuring that choices reflected the realistic differences in cultivar appearance and chemical composition. Previous studies investigating vine weevil feeding and oviposition on other crops have used excised plant material, which may inadvertently influence behaviour.
• 3 Adult weevils significantly preferred to feed on particular cultivars in the choice experiment (e.g. Tulameen), although they consumed significantly more foliage (0.22–1.03 cm²/day) on different raspberry cultivars (e.g. Glen Moy, Glen Rosa and a wild accession) in no‐choice situations.
• 4 In choice experiments, weevils tended to avoid laying eggs on some cultivars (e.g. Glen Moy and the wild accession). The number of eggs laid (1.91–4.32 eggs per day) did not, however, differ significantly between the cultivars in a no‐choice situation. Foliar nitrogen and magnesium concentrations were positively, although weakly, correlated with the total number of eggs laid.
• 5 The present study highlights the importance of considering both choice and no‐choice tests when assessing crop susceptibility to attack because weevils may avoid feeding on certain cultivars (e.g. Glen Moy) when given a choice, although this would cause significant damage to such cultivars if they were grown in monoculture (i.e. when there is no alternative).

     

Oviposition behavior ofDrosophila subobscura and its parasitoidAsobara tabida in the laboratory

At 18°C, adultAsobara tabida emerge 21 days after oviposition within the host;Drosophila subobscura emerges 18 days after oviposition. The relatively short pre-oviposition period of adultA. tabida (4 days), compared to that ofD. subobscura (4–8 days) results in the generation times of both host and parasitoid being approximately similar. A yeast source is necessary forD. subobscura females to mature their eggs; female flies will not oviposit on patches without a yeast source. While surface roughness is an important characteristic for maximumD. subobscura oviposition,A. tabida oviposition, and consequent levels of parasitism, is enhanced by coating patches with askin of active yeast. When presented with a multi-patch environment, experienced and inexperienced female wasps showed no significant difference in their level of attack.     

A preliminary histological investigation of gall induction in an unconventional galling system

In an unusual case involving a candidate biological control agent, the histologically complex stem galls of the weevil, Rhinusa pilosa (Coleoptera: Curculionidae) on yellow toadflax (Linaria vulgaris), are rapidly induced during oviposition and reach full size by larval hatch. To investigate gall induction, the oviposition behavior of R. pilosa was described. We experimentally disrupted ovipositing weevils at three key points in the oviposition sequence and compared host-plant tissue responses post disruption, to what occurs during normal gall induction using histological methods. De novo xylem production, intercellular spaces in the cortex, and hyperplasia and hypertrophy of the procambium and pith parenchyma surrounding the egg were some of the tissue- and cellular-level modifications observed only 3?C5?days after normal oviposition. Normal gall development was not observed after any of the oviposition disruption treatments, although some of the cellular and tissue responses resembled those found after undisrupted oviposition. Feeding by the female during oviposition canal formation induced wound meristem and callus tissue formation, but no other modifications consistent with gall formation. When females were disrupted about 20?s into oviposition, a homogenously dense substance was observed, which was suspected to be ovipositional fluid. There was minor stem swelling 10?days later and histologically, periclinal cell divisions, de novo xylem, and pith cells with numerous stained plastids were observed as in normal gall development, thus suggesting that ovipositional fluid plays a role in gall induction.     

Reproductive development and maternal effects in the pine weevil Hylobius abietis

1. In a laboratory study of maturation feeding of female pine weevil Hylobius abietis on current and 1‐year‐old stem bark of transplants of Scots and Corsican pine, Norway and Sitka spruce, Douglas fir, and hybrid larch, the length of the pre‐oviposition period was influenced by the species on which weevils fed. The shortest pre‐oviposition period was on hybrid larch (11.8 days) and the longest on Douglas fir (15.5 days). 2. The species on which weevils fed also affected fecundity but there was evidence of a species–year interaction. Over a period of 36 days, most eggs were laid by weevils feeding on current stem of Norway spruce and Corsican and Scots pine and fewest on current stem of Sitka spruce. 3. Significant maternal effects on egg size were observed both in relation to female size and conifer species. The largest eggs were laid on Corsican pine and the smallest on Douglas fir, with no evidence of a trade‐off between number of eggs laid and their size. 4. There was a positive relationship between egg and larval size and between larval size and survival on logs of four conifer species. Residual resistance mechanisms in the bark of recently cut stumps and larval competition are discussed briefly in relation to the importance of the observed maternal effects on weevil population dynamics.     

共生菌通过氧气浓度调控果蝇产卵偏嗜性

【目的】研究东方醋杆菌(Acetobacter orientalis)和短小乳杆菌(Lactobacillus brevis)通过氧气浓度调控黑腹果蝇(Drosophila melanogaster)产卵的偏嗜性,并研究其对后代存活率和发育历期的生物学意义。【方法】利用双相选择装置解析果蝇产卵行为。利用分光光度仪和pH计测量细菌的OD值与pH值。通过改变果蝇的视觉、味觉和嗅觉感官以检测介导果蝇产卵行为的感觉系统。用后代的发育历期与存活率评价其生物学意义。【结果】果蝇产卵对东方醋杆菌具有趋避性,产卵指数为–0.76,对短小乳杆菌具有趋向性,产卵指数为0.5,并且二者接种比例决定了果蝇的产卵选择。氧气作为一个调节因子,可改变果蝇对东方醋杆菌和短小乳杆菌的产卵偏嗜性。氧气是东方醋杆菌生长必需的条件,有氧培养的OD值为1.3,而无氧培养的OD值为0.4。氧气是短小乳杆菌生长非必需的条件,有氧和无氧培养的OD值均为2.2。破坏嗅觉可严重地影响果蝇对细菌的产卵偏嗜性。东方醋杆菌和短小乳杆菌均促进了果蝇的生长,分别提高存活率1倍和1.5倍,分别缩短果蝇发育历期1 d和2 d。【结论】东方醋杆菌和短小...