Induced defence reaction in Scots pine following stem attacks by Tomicus piniperda

The induced defence reaction of Scots pine Pinus sylvestris to stem attacks by the common pine shoot beetle, Tomicus piniperda (Col, Scolytidae), was studied by inducing natural attacks on young Scots pine trees of different vigour Pruned trees were more heavily attacked by T piniperda than unpruned ones Vigorous trees successfully contained the attacking beetles within resinous lesions, whereas less vigorous trees failed to defend themselves The content of resin acids increased dramatically in the lesions on all trees, and the resin acid composition differed somewhat between some treatments Starch accumulation in the inner bark of the main stem was lower in pruned trees than in unpruned ones, and starch reserves were depleted in the most heavily attacked trees All but one of the unpruned trees survived the attack, whereas most of the severely pruned ones died following attack by beetles at densities exceeding c 300 egg galleries m⁻²     

Oviposition behaviour and response of Monochamus scutellatus (Coleoptera: Cerambycidae) to conspecific eggs and larvae

• 1 The oviposition behaviour of white‐spotted sawyer beetle Monochamus scutellatus (Say) (Coleoptera: Cerambycidae) females was studied under laboratory and field conditions.
• 2 Females walked over the bark surface and stopped to palpate it with their labial and maxillary palpi. Once a potential oviposition site was located, the female excavated a scar in the bark with her mandibles, deposited an egg and brown plug in the scar and inserted her mandibles again into the scar prior to leaving the area.
• 3 Female M. scutellatus preferred to lay eggs on bolts containing no eggs (control) to those containing eggs from other females, but did not show this preference when provided with control bolts and those containing their own eggs. When females were provided with bolts containing their own eggs and bolts containing eggs from other females, they laid more eggs on bolts containing their own eggs. Females laid more eggs on control bolts than on bolts containing their own larvae or larvae from other females.
• 4 The brown plug in the oviposition scar may provide a protective barrier to the egg, a chemical message that the site is occupied, or both.

     

云南切梢小蠹对云南松树的蛀干危害及致死机理

蛀干危害是云南切梢小蠹致死云南松树的关键环节。通过控制云南切梢小蠹蛀干密度,对云南切梢小蠹在自然条件下蛀干行为与危害进行了首次探讨。结果表明,云南切梢小蠹蛀干密度与云南松存活率呈负相关,蛀干密度直接决定云南松死亡或存活。研究发现,蛀干密度115坑/m2是云南松树的最低致死密度阈值,云南松树在蛀干密度低于26.4坑/m2情况下存活,在26.4-115坑/m2有部分存活,超过115坑/m2以后将被害致死。云南切梢小蠹对树干攻击形成有卵和无卵两类坑道。形成无卵坑道的蛀干攻击可导致树势衰弱,形成有卵坑道的蛀干危害严重破坏了韧皮组织,是导致云南松死亡的直接原因。     

Interactions between the phloem-feeding speciesTomicus piniperda (Col.: Scolytidae) andAcanthocinus aedilis (Col.: Cerambycidae), and the predatorThanasimus formicarius (Col.: Cleridae) with special reference to brood production

Interactions betweenTomicus piniperda (L.) (Col.: Scolytidae),Acanthocinus aedilis (L.) (Col.: Cerambycidae) andThanasimus formicarius (L.) (Col.: Cleridae) were investigated in caged pine bolts. The treatments wereT. piniperda alone,A. aedilis alone,T. piniperda together withA. aedilis, T. piniperda together withT. formicarius and all three species together. T. piniperda offspring production per m² was reduced by 92% when reared withT. formicarius, by 78% when reared withA. aedilis, and by 94% when all three species were reared together, compared withT. piniperda reared alone.A. aedilis had a negative influence on the offspring production ofT. formicarius and vice versa. When both species were present in the same bolt (together withT. piniperda) offspring production was reduced by 74% forA. aedilis and by 42% forT. formicarius compared with their respective production values when each species was present alone with the bark beetle. The new generation ofT. formicarius emerged as larvae from June to August while most of theA. aedilis offspring emerged as adults from September to October, leaving only a few larvae in the bolts to hibernate.A. aedilis only reproduced in a small part of one of the bolts without bark beetles.     

Host and non-host odour signals governing host selection by the pine shoot beetle, Tomicus piniperda and the spruce bark beetle, Hylurgops palliatus (Col., Scolytidae)

Abstract:  Tomicus piniperda and Hylurgops palliatus colonize susceptible host trees by responding to host-specific odour signals as well as by avoiding volatiles emanating from non-host conifers. In the field, the pine shoot beetle, T. piniperda , responded in high numbers to natural odour sources provided by their host tree, Pinus sylvestris , while the non-host conifers Larix decidua , Picea abies , or Pseudotsuga menziesii were significantly less attractive. In contrast, the spruce bark beetle, Hylurgops palliatus , preferentially responded to its main host, P. abies . Furthermore, T. piniperda attacks on P. sylvestris bolts decreased in presence of bark and wood particles from the non-host P. abies , whereas particles from P. menziesii appeared not to affect T. piniperda attacks. Apparently, tree-specific volatiles act at close range as specific signals that lead to the successful discrimination and colonization of the respective host tree species.     

The influence of natural enemies on brood production inIps typographus (Col. scolytidae) with special reference to egg-laying and predation byThanasimus formicarius (Col.: Cleridae)

The predatorThanasimus formicarius (L.) (Coleoptera, Cleridae) and its preyIps typographus (L.) (Coleoptera, Scolytidae) were studied in the laboratory and the field. In the laboratory, 11T. formicarius laid 71–132 eggs (mean=162) during 66–123 days. During this time they ate 66–132I. typographus adults per pair (male +female). The number of eggs laid per female was not correlated with life span or the number ofIps eaten. In the field, predation byT. formicarius larvae and other natural enemies onI. typographus brood was studied in the last year of an outbreak. Caged and uncaged spruce bolts attacked byI. typographus were used, and pairs ofT. formicarius were released in the cages. The treatments were: uncaged bolts, caged bolts withoutT. formicarius, caged bolts with 4T. formicarius pairs, and caged bolts with 8T. formicarius pairs. The productivity ofI. typographus was highest in the caged bolts withoutT. formicarius (mean=4.5 offspring/female) and lowest in the uncaged bolts (mean=0.9 offspring/female). The density ofI. typographus galleries was similar in the different treatments. Hence, the variation in productivity between treatments could not have been due to differences in the levels of intraspecific competition. There was no difference in bark beetle productivity or density ofT. formicarius larvae between bolts with 4 pairs ofT. formicarius and bolts with 8 pairs (mean=2.5 offspring/female). This indicates that some kind of interference occurred betweenT. formicarius individuals (e.g. cannibalism) and that a maximum level of predation was reached. Predation by larvae ofMedetera spp. (Diptera, Dolichopodidae),Thanasimus spp. and other beetles, and parasitism by wasps (Hymenoptera, Pteromalidae) probably caused the low productivity in the uncaged bolts.      

Number of gallery arms of the tree-killing bark beetle Polygraphus proximus (Coleoptera: Curculionidae: Scolytinae)

Polygraphus proximus Blandford (Coleoptera: Curculionidae: Scolytinae) is a non-aggressive monogynous bark beetle that has caused mass mortality in fir (Abies spp.) forests in the last decade. Although gallery structures made by polygynous beetles may influence their reproductive success, the gallery structure and the number of eggs laid by the monogynous tree-killing bark beetle P. proximus has not been investigated in detail in the natural setting of their native range. We, therefore, investigated the length of mother galleries of P. proximus and the number of eggs oviposited by the beetles in relation to gallery systems with different numbers of arms. The number of eggs oviposited in two-armed galleries was significantly greater than that observed in one- and three-armed galleries. Additionally, the length of one- or two-armed galleries with no oviposition was significantly shorter than that in galleries consisting of more than two arms. Our data may suggest that the optimal number of arms in a gallery system (in terms of the number of eggs oviposited) was two.     

Interactions between the predators thanasimus formicarius (Col.: Cleridae) and rhizophagus depressus (Col: Rhizophagidae), and the bark beetle tomicus Piniperda (Col.: Scolytidae)

The occurrences of Thanasimus formicarius (L.) (Cleridae), Rhizophagus depressus (F.) (Rhizophagidae), and Epuraea marseuli Reitter (Nitidulidae) in cut Scots pines, Pinus sylvestris L., attacked by Tomicus piniperda (L.) (Col.: Scolytidae) were recorded in the field, and interactions between the species were studied in caged pine bolts attacked by T. piniperda. T. formicarius eggs and R. depressus adults were abundant in the T. piniperda attacked trees, whereas only a few individuals of E. marseuli were found. T. formicarius and R. depressus, but not E. marseuli, reproduced in the caged bolts. T. piniperda offspring production per unit area of bark was reduced by 41% when reared with R. depressus, by 81% when reared with T. formicarius, and by 89% when all three species were reared together, compared with T. piniperda alone. The interaction between T. formicarius and R. depressus was mutually antagonistic. When both species were present in the same bolt the total number of larvae was reduced by 49% for R. depressus and the number of large larvae (length > 10 mm) was reduced by 35% for T. formicarius compared with their respective production values when each species was present alone with the bark beetle. There was a positive relationship between T. piniperda egg gallery density and the production of R. depressus larvae per m². Larvae of both R. depressus and T. formicarius developed into new adults during the first summer.

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Résumé Interactions entre les prédateursThanasimus formicarius (Col.: Cleridae) etRhizophagus depressus (Col.: Rhizophagidae) et le scolyteTomicus piniperda (Col.: Scolytidae) La présence deThanasimus formicarius (L.) (Cleridae),Rhizophagus depressus (F.) (Rhizophagidae), etEpuraea marseuli Reitter (Nitidulidae) a été étudiée sur le terrain dans des pins sylvestres (Pinus sylvestiris L) abattus, attaqués partomicus piniperda (L.) (Col.: Scolytidae) et les relations entre les espèces ont été étudiées sur des rondins de pin attaqués parT. piniperda et placés sous cage. Le nombre d’∄ufs deT. formicarius et d’adultes deR. depressus était important dans les arbres attaqués parT. piniperda, alors que seuls quelques individus deE. marseuli ont pu être trouvés.T. formicarius etR. depressus, mais pasE. marseuli, se sont reproduits dans les rondins sous cage. La production de descendants deT. piniperda par unité de surface d’écorce était réduite de 41% quand le scolyte était élevé avecR. depressus, de 81% en élevage avecT. formicarius et de 89% quand les trois espèces sont élevées ensemble, par comparaison avecT. piniperda seul. Les interactions entreT. formicarius etR. depressus étaient mutuellement antagonistes. Quand les deux espèces étaient présentes dans le même rondin, le nombre total de larves était réduit de 49% pourR. depressus et le nombre de grosses larves (longueur > 10 mm) était réduit de 35% pourT. formicarius comparé aux valeurs respectives quand chaque espèce était présente isolément avec le scolyte. Il y a une corrélation positive entre la densité de galeries avec des ∄ufs deT. piniperda et la production de larves deR. depressus par m². Les larves deR. depressus et deT. formicarius se sont transformés en adultes l’été suivant.

     

栎旋木柄天牛生殖行为研究

为了阐明栎旋木柄天牛Aphrodisium sauteri Matsushita生殖行为的方式和特点,寻找有效的防治手段,本试验观察了栎旋木柄天牛的生殖行为,并在林间尝试了成虫诱集。结果表明:雌雄成虫之间表现出较强的吸引作用,近距离时雌雄虫可相互吸引,而远距离时雌虫引诱力更强。室内试验中求偶时间会随着成虫的衰弱而增加。成虫交配主要发生于白天。羽化出孔后1～14日龄雌虫和2～13日龄雄虫均可多次交配。成虫一次完整交配平均需时70.12min,交配后保护平均仅用时3.86min。一次完整交配过程中,不同日龄成虫的交配历时、交配间隔历时及交配次数都存在差异,各日龄成虫的交配间隔历时均大于交配历时。交配或产卵经历对雄虫交配行为的影响明显大于雌虫。雌虫产卵前期平均为30.71h。雌虫每产1粒卵平均需时99.58s,并随日龄增长显著加长。每头雌虫平均每日产卵量和总产卵量分别为7.89和26.20粒。雌虫多在白天产卵,用产卵器触探树皮表面寻找合适的产卵部位。卵主要产于树皮裂缝和枝条疤痕内,一般每次产卵1粒,卵表面无覆盖物。     

Flexible oviposition behavior in the golden egg bug (Phyllomorpha laciniata) and its implications for offspring survival

Female golden egg bugs show unique flexibility in their oviposition behavior. Females can lay eggs on plants, where they are leftunattended, or on the back of conspecifics, where they remainuntil hatching. In this article we show that eggs have greatersurvival rates when carried by an adult than when laid on plants.The main causes of egg mortality are predators and a parasitoidwasp. Our results suggest that, although predation pressureis similar, fewer eggs are attacked by parasitoid wasps whencarried by an adult than when laid on plants. In addition,we show that, when given a choice, females prefer to lay eggson the backs of conspecifics than on plants. Thus, female ovipositionchoice is adaptive and minimizes individual offspring mortality.The factors that may maintain such behavioral variation in current populations are discussed.     

Harem size and oviposition behaviour in a polygynous bark beetle

Abstract. 1. Harem polygyny can have fitness benefits and costs on females. In bark beetles of the genus Ips the latter may include within‐harem competition between larvae. However, earlier competition between females for male care and mating opportunities may also influence oviposition behaviour. There has been relatively little investigation into the relationship between harem size and initial egg output. The present study investigated this relationship in the bark beetle Ips grandicollis. 2. The measure of egg output used was the number of eggs in the gallery with the most eggs in each harem. Mean (±SE) harem size of 242 observed harems was 3.25 ± 0.10. A curvilinear relationship was found between egg output and harem size, with females in smaller harems (one to four females) laying more eggs with increased harem size. However, females in larger harems (five to seven females) laid fewer eggs as harem size increased. The optimal harem size (in terms of number of eggs laid) was close to four females. 3. We found no evidence from a behavioural assay that females could preferentially choose unmated males over mated males with harems of two females. Additionally, the distribution of harem sizes suggests that females distribute themselves among males randomly. 4. The results suggest that harem size has effects on female reproduction that extend beyond larval competition and influence patterns of oviposition. The mechanism that determines why egg laying is greatest at intermediate levels is unknown. There is no evidence that smaller harems belong to lower quality males, but females may adjust egg‐laying behaviour in large harems as a result of reduced male attendance or anticipated larval competition.     

Notes on the mating system of Hylesinus varius (F.)(Col., Scolytidae), a putatively bigynous bark beetle

Abstract: Previous research has left confusion about central features of the mating system of the common ash bark beetle Hylesinus varius; in particular, reports conflict as to whether this species is monogynous or bigynous. It was found that females initiated egg tunnel construction; copulation takes place either on the bark in the initial phase of egg tunnel construction, or inside the tunnel system. Observations of one male copulating with several females and of solitary females in galleries with eggs suggested that the males sometimes leave after copulation. In contrast to findings for populations in Slovakia, Norwegian male H. varius were most commonly paired with only one female. Bigynous galleries contained significantly more eggs than monogynous galleries, but bigynous males did not double their reproductive success as found in some other bigynous bark beetles. This suggests that bigynous galleries at first are the work of one female but some males are later joined by a second female.     

Field oviposition rates and egg load dynamics of pollen beetles (Meligethes aeneus Fab.) (Colepotera: Nitidulidae)

Abstract 1 Egg loads from field collected pollen beetles (Meligethes aeneus Fab., Coleoptera: Nitidulidae) were determined by dissecting beetles caught at the beginning and end of the putative daily oviposition period. Field collected beetles were offered Brassica napus (L.) plants in cages for 8 (morning and early afternoon), 16 (overnight), and 24 h to ascertain the number of eggs laid during these time periods. 2 Most eggs were laid in the morning and early afternoon. The proportion of gravid females was higher at the beginning of the oviposition period than at the end. Most females in the morning carried two eggs, whereas one egg was more common in the afternoon. 3 We hypothesized that the number of eggs laid during the oviposition period would be equivalent to the difference between egg loads at the beginning and end of oviposition. This was not the case; differences in egg loads were significantly lower than number of eggs laid. However, the number of eggs laid was equivalent to the egg load at the beginning of the oviposition period, suggesting that eggs available in the morning are laid during the following day. 4 Population estimates of daily oviposition rates, approximately 0.7 eggs per beetle and day, were close to estimates from laboratory studies when the proportion of gravid females was taken into consideration.     

Gallery construction and oviposition of the bark beetle Ips typographus (Coleoptera: Scolytidae) at different breeding densities

Abstract. 1. The bole of a Norway spruce, Picea abies (L.) Karst., was cut in 25 cm sections and infested in the laboratory with 2 or 8 females/dm² of Ips typographus (L.) and an equal number of males.
2. One log of each beetle density was dissected every second day, beginning 2 days after female introduction.
3. The oviposition rate was highest at the beginning of the breeding period for both densities and then declined, especially at the high density. Residence time is a useful approximation for the number of laid eggs in the beginning of the oviposition period or when the density is low.
4. Final gallery length and egg number per gallery were on average significantly smaller at density 8 than at density 2.
5. Linear relationships between total gallery length and number of egg niches were found to be similar for the two densities.
6. An estimate of the egg to adult mortality at different densities was found by using data from a field study that related gallery length to breeding density in attacked living trees, together with published relationships between density and egg niches or emergence of new adults.
7. It was concluded that both decreased oviposition rate and earlier re-emergence at higher densities contribute to a declining oviposition with increasing density. The final offspring production is futher reduced by lower survival due to larval competition as density increases.     

Comparative population genetic study of two oligophagous insects associated with the same hosts

A parallel study of the genetic structure of two oligophagous species associated with the same hosts was conducted to determine the main factors shaping the distribution of genetic diversity. The bark beetle Tomicus piniperda and the pine processionary moth (PPM) Thaumetopoea pityocampa are both associated with the genus Pinus and belong to different guilds (xylophagous vs defoliating species). The PPM is an ectophagous species that feeds on the needles of living trees, whereas T. piniperda is endophagous and bores galleries in the inner bark of weakened trees. Both species were sampled in the main regions of France, and their genetic structure was assessed after genotyping with five microsatellite markers. Populations of the PPM were significantly structured. A pattern of isolation by distance was found when distances were calculated as bypassing the Massif Central, whereas no such pattern could be found with raw geographic distances. On the contrary, most populations of T. piniperda were not differentiated. No effect of host species could be detected in either of the two species. We conclude that the two taxa have contrasting effective dispersal rates per generation, and we hypothesize that this reflects the different selection pressures acting on individual fitness via different strategies of host use.     

Enemies in low places - insects avoid winter mortality and egg parasitism by modulating oviposition height

Oviposition site selection in insects is essential in terms of low egg mortality, high offspring survival and therefore a high reproductive output. Although oviposition height could be a crucial factor for the fitness of overwintering eggs, it has rarely been investigated. In this study the oviposition height of a polyphagous leaf beetle, Galeruca tanaceti Linnaeus in different habitats and at different times of the season was examined and its effect on egg clutch mortality was recorded. The leaf beetle occurs as an occasional pest on several agricultural plants. It deposits its eggs within herbaceous vegetation in autumn. Eggs are exposed to numerous biotic and abiotic mortality factors summarized as egg parasitism and winter mortality. Oviposition height of the leaf beetle was not uniform, but changed significantly with the structure of the habitat and during the season. Mean oviposition height per site (70.2+/-4.9 cm) was significantly higher than mean vegetation height (28.4+/-2.4 cm). Height of plants with egg clutches attached and oviposition height were significantly positively correlated. The results suggest that females try to oviposit as high as possible in the vegetation and on the plants selected. In accordance with this, the probability of egg parasitism and of winter egg clutch mortality significantly declined with increasing oviposition height. A preference of G. tanaceti for oviposition sites high up in the vegetation might therefore have evolved due to selection pressures by parasitoids and winter mortality.     

云南横坑切梢小蠹生物学研究

横坑切梢小蠹Tomicus minor (Hartig)是云南松Pinus yunnanensis Franchet的主要次期性害虫之一。1980年以来,该虫与纵坑切梢小蠹T. piniperda（L.）一起在中国西南部大量发生,导致数十万公顷云南松林受害。本文报道了横坑切梢小蠹在云南地区的生活史、生长、发育、繁殖等生物学特征。横坑切梢小蠹年生活史为一代,前后两代在冬春季有部分重叠。成虫羽化于4月下旬开始陆续,5 月下旬结束。成虫羽化后即飞到树冠上蛀食枝梢,直到11月发育成熟,开始繁殖。在此期间,每头成虫可以蛀食4～6个枝梢。横坑切梢小蠹在云南没有越冬习性。繁殖期从11月至次年3月。成虫主要在已经受到纵坑切梢小蠹危害的树木的中、下部产卵。繁殖期较纵坑切梢小蠹约迟1周。由于横坑切梢小蠹从枝梢到树干对云南松持续危害,对树木的危害性较在其它地区更为严重。横坑切梢小蠹利用受到纵坑切梢小蠹蛀害的树木繁殖产卵,加强了蠹虫对云南松树的危害,加速了受害树木的死亡进程。横坑切梢小蠹的上述生物生态学特征是该虫对云南松造成严重危害的重要原因。从横坑切梢小蠹虫体和虫坑中检测到伴生真菌云南半帚孢Leptographium yunnanensis。横坑切梢小蠹对该菌的带菌率在蛀梢期为11.5%;在蛀干中期约为10%～26%。     

Egg size and composition in an ageing capital breeder – consequences for offspring performance

1. Egg size is often used as a proxy of egg quality although size and composition may vary, e.g. in insects egg size usually decreases as female ages. Whether this decrease in size reflects reduced concentrations of essential nutrients such as lipids and proteins of eggs laid by ageing females, or does reduced size per se explain often observed lower fitness of later laid eggs is poorly explored. 2. Egg properties were compared with fitness parameters of offspring laid on the first and fourth night during the oviposition period of a capital breeding moth, Cleorodes lichenaria (Hufnagel). The study aim was to explore whether decreased egg size is caused by decreased provisioning into later laid eggs measured as egg protein and lipid concentration, and whether it results in lower fitness of later laid offspring. 3. The fresh and dry weight of eggs decreased over the oviposition period, but the protein and lipid concentration remained constant. Survival of larvae was lower among the fourth night laid offspring on a low quality host Parmelia sulcata Taylor compared to a high quality host Ramalina fraxinea (L.) Ach. No differences were observed in egg fertility or hatchability, neonate survival without food and pupal mass between the offspring produced on different nights. 4. Decreased survival of offspring produced later was rather attributable to absolute provisioning (i.e. lower weight of eggs) than relative provisioning (i.e. decreased concentrations of nutrients in eggs). It is argued that lower survival of later laid smaller eggs on low quality diet is likely attributable to physical and chemical characteristics of host lichens and/or physical properties of tiny neonate larvae.     

松墨天牛对寄主树木的产卵选择

在室内采用选择行为方法,研究了松墨天牛Monochamus alternatus对几种松属植物的产卵选择行为。结果表明,松墨天牛对黑松Pinus thunbergii的选择性最强,对马尾松P.massoniana的选择性最弱,二者间差异显著,它们与火炬松P. taeda和湿地松P. elliottii间无明显差异。在黑松和马尾松的被松材线虫危害木与健康木之间,松墨天牛明显选择被害木产卵;具产卵痕枝段和虫粪处理过的枝段,对松墨天牛的产卵有显著抑制作用,松墨天牛明显地选择对照枝段产卵。     

四种材料作为异色瓢虫产卵载体的适合性比较

比较了蚕豆苗叶片、甘蓝叶片、小油菜叶片和纸条作为人工扩繁异色瓢虫Harmoniaaxyridis(Pallas)时产卵载体的适合性。异色瓢虫对这 4种产卵载体有明显的选择性 ,多在蚕豆苗叶片和甘蓝叶片上产卵 ,纸条上次之 ,在小油菜叶片上产卵很少。在产卵载体对单雌产卵量影响方面 ,蚕豆苗叶片、甘蓝叶片和纸条 3者之间的差异不显著 ,且产于这 3种载体上的卵块在 ( 1 0± 1 )℃下冷藏的孵化率没有明显差异。由于纸条不会出现枯萎现象 ,易制成卵卡 ,所以可用作卵商品化时的产卵载体 ,而蚕豆苗叶片和甘蓝叶片可作为保留虫源或繁殖时的产卵载体。