Diurnal flight pattern of Platypus koryoensis (Coleoptera: Platypodinae) in relation to abiotic factors in Korea

The diurnal flight pattern of Platypus koryoensis (Murayama) was examined using sticky traps attached to the trunks of oak trees in central Korea in 2010 and 2011. The flight activities of the beetle were estimated on the basis of 3-h intervals for trap catches from 11:00 to 14:00 on the next day, on June 25–26 and July 1–2, 2010, and on the basis of 2-h intervals for trap catches from 5:00 to 17:00, between June 9 and July 21, 2011 (the peak flight period of the beetle). Over 77% of the beetles were caught from 9:00 to 13:00, with the daily variations in the facing slope. The beetles began to be caught when the air temperature reached around 16 °C, and were the most active when the temperature ranged from 20 to 27 °C. No beetles were caught during rainfall, suggesting that rainfall is one of the factors that hinder beetle flight. The beetles were caught by traps in the east-facing plot earlier than those in the south- and west-facing plots suggesting that the flight behavior of the beetle can be affected by the light. Direction of the beetle flight during the peak of daily flight (from 09:00 to 13:00) was downward along the slope.     

External microstructure of the ambrosia beetle Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae)

Platypus koryoensis is a minute ambrosia beetle found in forests. It can cause significant economic damage to oak trees. Recently in Korea, it has been reported as a major pest of oak trees, because it causes sooty mold of oak by introducing the pathogenic fungus Raffaelea sp. In this paper, we demonstrate the fine structural aspects of the external body of the ambrosia beetle using field emission scanning electron microscopy, as a part of basic research into this pest so that strategies for its control might be developed. This beetle has a sensory system well developed to respond to both visual and chemical stimuli. Both sexes have a pair of faceted compound eyes and a pair of knobbed antennae, but simple eyes are absent. The mouthparts on its distinct snouts are effective devices for penetration and for boring holes. The mouthparts consist of the labrum, a pair of mandibles, a pair of maxillae and the labium. Both the maxillary and the labial palpi have the function of directing the food to the mouth and holding it while the mandibles chew the food. The distal ends of these palpi are flattened and have shovel‐like setae. The thorax has a particularly hard exoskeleton and hard elytra, including powerful muscles that operate both the wings and the legs. The legs are multi‐segmented and have a strong femur and tibia, including one pair of claws on the end of each tarsal segment. Characteristically, both male and female beetles have mycangial cavities for storing spores and other microorganisms, but only females have three pairs of large depressions on their dorsal thorax.     

Attack pattern of Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae) in relation to crown dieback of Mongolian oak in Korea

The ambrosia beetle, Platypus koryoensis (Murayama), vectors the Korean oak wilt (KOW) pathogen, Raffaelea quercus-mongolicae K.H. Kim, Y.J. Choi, & H.D. Shin, in Korea, which is highly lethal to Mongolian oak, Quercus mongolica Fisch., and is considered a major threat to forest ecosystem health. We characterized the attack pattern of P. koryoensis along the lower trunk of 240 Mongolian oaks in relation to tree decline symptoms on Mt. Uam in Gyeonggi-Do Province, Korea during June-July 2009. For each tree, we recorded diameter at breast height (dbh) (DBH) and P. koryoensis entrance hole density at two heights along the lower trunk (near groundline and at 1.5 m above groundline) and on opposite sides (downslope side and upslope side). Trees were assigned to one of three dieback classes: 1) apparently healthy, no or practically no wilted foliage, and no obvious platypodine frass near the base of the tree; 2) no or only partial wilting with obvious frass near the base of the tree; and 3) apparently recently killed by KOW with all foliage wilted and mostly retained with obvious frass near the base of the tree. As dieback class increased from 1 to 3, P. koryoensis entrance hole density increased at all four trunk locations. Attack density was highest on the downslope side of the trunk near groundline, and principal component analysis indicated that this trunk location was the best indicator of tree dieback. In addition, DBH tended to increase with dieback class suggesting that larger trees were infested first.     

Attractant effect of citral on Platypus koryoensis (Coleoptera: Curculionidae)

An environmentally friendly control strategy for the ambrosia beetle Platypus koryoensis (Murayama), a vector of oak wilt disease, was investigated using the citral as a pheromone component. To develop an effective attractant trap, a semi‐field experiment (Yeoju) and a field experiment (Gunpo) were performed. Different ratios of four different attractant mixtures (ethanol 100 %, ethanol + citral (90:10, 95:5), ethanol + citral + hexane extract of Quercus mongolica (90:5:5)) were investigated to determine their effects on P. koryoensis. The 95:5 mixture of ethanol + citral had the greatest attractant effect on P. koryoensis. However, other ambrosia beetle species did not exhibit a specific response to citral. Our findings indicate that the pheromone citral was effective at attracting P. koryoensis and that certain concentrations of citral could be used to develop an effective and environmentally friendly control agent.     

Density related plasticity in stand-level spatial distribution of the ambrosia beetle, Platypus koryoensis (Coleoptera: Curculionidae)

We tested the hypothesis that the population density of ambrosia beetles at the stand level influences the spatial distribution of infested trees. We evaluated the spatial distribution of the ambrosia beetle, Platypus koryoensis (Murayama) in three oak forest stands that varied in beetle population density using a multi-year trapping survey. We used these data to inform a clustering analysis based on aggregation indices using the SADIE software. Four important findings emerged: (1) the spatial distribution pattern of P. koryoensis at the stand level changed as the population density of the beetle varied; (2) at low population densities, beetle distribution was contagious at the stand level; (3) as beetle population densities increased, the spatial distribution of infested trees became random, potentially due to beetle avoidance of mass attacked trees; and (4) at high beetle population densities, the spatial distribution of infested trees became contagious, possibly due to temporal changes in location of the attack epicenter within the stand. Our results support the hypothesis that beetle population density has consequences for the spatial distribution of infested trees at the within-stand scale. We conclude that the spatial distribution of infested trees is flexible in response to beetle population density, suggesting that beetle attack behaviors are mediated by one or more density-dependent effects.     

Effects of leaf conditions and flight activity on the behaviour of Platypus quercivorus (Murayama) (Coleoptera: Platypodidae)

The important role of semiochemicals in the interactions between plants and insects has been extensively investigated. The volatiles produced by oak trees are thought to attract the ambrosia beetle Platypus quercivorus (Murayama), which causes wilt disease in Quercus trees, resulting in widespread damage. In the present study, we hypothesized that (a) P. quercivorus is attracted to the leaf volatiles emitted by host trees and (b) the response of P. quercivorus to leaf volatiles is affected by flight. An experiment was performed to survey the preferences of both sexes of P. quercivorus for the leaf volatiles of Quercus crispula Blume at various stages of leaf deterioration, represented by different number of days after cutting. Additionally, the effect of flight on both sexes was evaluated by testing the beetle flight on a flight mill. The results showed that P. quercivorus was attracted to the volatiles emitted from fresh leaves and was not attracted to those emitted from dry leaves. This suggests that leaf volatiles from healthy hosts are primary attractants for P. quercivorus. Further, males exhibited increased olfactory responses to leaf volatiles as their flight duration increased, whereas the opposite pattern was observed in females. These results suggest that the different ecological roles of the sexes contribute to differences in olfactory responses.     

Mycangia of the ambrosia beetle, Austroplatypus incompertus (Schedl) (Coleoptera: Curculionidae: Platypodinae)

Abstract  Ambrosia beetles have an obligate relationship with the ambrosia fungi that they feed on. This requires that the beetles have means to transport those fungi when they colonise new hosts. Some ambrosia beetles have special structures called mycangia to transport fungi in. This paper describes the mycangia of the ambrosia beetle Austroplatypus incompertus and illustrates how the mycangical hairs are probably used by the beetle to acquire fungal spores for transport. The mycangia and probable method of fungal acquisition of this species are compared with those of other ambrosia beetles.     

Microstructure of the prothoracic mycangia in the ambrosia beetle Platypus koryoensis (Coleoptera: Curculionidae: Platypodinae)

Platypus koryoensis (Murayama) (Coleoptera: Curculionidae: Platypodinae) is a minute ambrosia beetle that can cause significant damage to live oak trees (Quercus mongolica) along with its symbiotic pathogenic fungus (Raffaelea sp.). Although both sexes of the beetle have a number of cuticular depressions for carrying microorganisms, only the females have mycangia that are typical in size on the pronotum. The mycangial cavities are filled with a mass of amorphous substances including yeast-like spores. In addition, mycangial cavities are equipped with cuticular pores which release substances to support symbiotic microorganisms during storage. Small depressions of both sexes can be subdivided into two clusters according to their relative sizes and locations. Although they have a typical cuticular peg (basiconic sensillum), they also share a common morphological characteristic with the typical mycangium of female: a round outlet and an invaginated reservoir containing a mass of secretory substances. Accordingly, our fine structural data suggest that both the female mycangia and the clusters of small cuticular depressions in both sexes also have a mycangial function in common regardless of their relative size and location.     

Phototactic behavior of the ambrosia beetle <Emphasis Type="Italic">Platypus quercivorus</Emphasis> (Murayama) (Coleoptera: Platypodidae) before and after flight

The ambrosia beetle Platypus quercivorus (Coleoptera: Platypodidae) is a vector of the pathogenic fungi, Raffaelea quercivora (Ophiostomatales: Ophiostomataceae), which causes Japanese oak wilt disease. Previous studies have shown that the beetle displays positive phototactic behavior; however, the adaptive significance of this behavior remains unclear. We postulated that positive phototaxis is necessary to allow the beetle to fly skyward immediately after emergence from a tree, and that this taxis changes following a certain period of flight. The present study aimed to clarify the changes in phototactic behavior of P. quercivorus before and after flight by using individual beetles emerging from the trunk of a Quercus crispula (Fagales: Fagaceae) tree that was attacked in 2014. The response of 60 beetles to light was tested ten times each, before and after flight in a flight mill. A generalized linear mixed model was constructed to predict the probability of positive phototaxis of P. quercivorus before and after flight. A best-fit model showed that the probability of positive phototaxis was lower after flight than before. The results suggest that positive phototaxis of P. quercivorus is decreased after flight.     

Identification of volatile emissions from Platypus mutatus (=sulcatus) (Coleoptera: Platypodidae) and their behavioral activity

We report here the identification and behavioral activity of volatile compounds emitted by male Platypus mutatus (=sulcatus) Chapuis while boring galleries in living poplar, Populus deltoides Marshall, trees. Headspace analysis using solid phase microextraction techniques showed the presence of 6-methyl-5-hepten-2-ol (sulcatol) and 6-methyl-5-hepten-2-one (sulcatone). Only one enantiomer of sulcatol, retusol, was found to be part of the volatile emission. Behavioral assays showed that females are more attracted than males to galleries with boring males inside. Both sulcatol and sulcatone elicited electroantennographic responses by female P. mutatus. Furthermore, behavioral bioassays showed that both sulcatol and sulcatone elicit behaviorally attractive responses by females. These results suggest that male P. mutatus releases a sex pheromone composed mainly of retusol and sulcatone.     

Investigating the abundance and flight period of bark beetles (Coleoptera: Curculionidae: Scolytinae) over elevational gradients in Sitka spruce forests

1. A warming climate, as predicted under current climate change projections, is likely to influence the population dynamics of many forest insect species. Numerous bark beetle species in both Europe and North America have already responded to a warming climate by significantly expanding their geographical ranges.
2. The aim of the current study was to investigate how populations of bark beetles within stands of Sitka spruce, a widely planted non-native commercial plantation tree species in the U.K., were likely to respond to a warming climate. Experimental plots were established in stands of Sitka spruce over elevational gradients in two commercial forest plantations, and the abundance and emergence times of key bark beetle species were assessed over a 3-year period using flight interception traps. The air temperature difference between the lowest and highest experimental plot in each forest was consistently >1°C throughout the 3-year period.
3. In general, the abundance of the most dominant bark beetle species (e.g. Trypodendron, Dryocoetes, Hylastes spp.) was higher, and emergence times tended to be earlier in the year at the lower elevation plots, where temperatures were higher, although not all bark beetle species responded in the same manner.
4. The results of the study indicated that, under the projected future climate warming scenarios, monoculture Sitka spruce stands at low elevations may potentially be more vulnerable to significant outbreak events from existing or invasive bark beetle species. Hence, consideration of establishing more resilient forests of Sitka spruce by diversifying the species composition and structure of Sitka spruce stands is discussed.

     

Laboratory evaluation of flight performance of the plum curculio (Coleoptera: Curculionidae)

Flight performance of laboratory-reared adults of the plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), was investigated under controlled conditions by using a flight mill system. Across all insects tested (n=198), median values of total distance traveled, total flight time, and maximum uninterrupted flight time were 122.7 m day(-1), 23.5 min day(-1), and 2.0 min, respectively. The latter result indicates that flight occurred primarily in short bursts. Although females had a significantly higher body mass than males, there were no significant differences in flight performance between the two sexes. Flight during the first 24-h test period (especially the first 6 h) was dominated by escape behavior, i.e., elevated levels of activity presumably associated with attempts by the insects to regain freedom of movement; during the second 24 h, flight activity was very limited throughout the late morning and afternoon, increased around sunset, and remained high during the night. All flight performance variables decreased linearly and significantly with insect age over the age range tested (2-16 d after emergence). Nutritional status also had a significant effect, whereby insects that had been provided with apples as a food source for 2 d after emergence showed considerably improved flight performance compared with those that had been given no food or only water during the same period. There was no significant effect of mating status on flight performance of male or female insects.     

Efficiency of flight interception traps for adult Colorado potato beetles (Coleoptera: Chrysomelidae)

Interception traps have been used to monitor and sample Colorado potato beetle, Leptinotarsa decemlineata (Say), populations in flight, but the efficiency of these traps was unknown. The efficiency of interception window traps is limited because flying adults avoid the traps and may bounce off the trap without being collected. All trap types tested were avoided in flight chamber tests, including those constructed of transparent Plexiglas or yellow wood boards. A larger screen trap and a harp trap designed to reduce detection were also avoided by the beetles in flight. None of the traps provide a direct estimate of the number of adults randomly flying in the trap area. The highest level of efficiency for window traps was obtained with the yellow trap, which caught 16% of the expected flying population. Harp and screen traps without frames intercepted 60-62% of the expected flying population. The presence of a frame did not increase significantly the avoidance of the screen and harp traps by beetles in flight. Recommendations are made to maintain or increase the efficiency of some traps.     

Low beta diversity of ambrosia beetles (Coleoptera: Curculionidae: Scolytinae and Platypodinae) in lowland rainforests of Papua New Guinea

We assessed the effect of geographical distance on insect species turnover in a situation where other major environmental factors, including host plant species, altitude, and climate, were constant. We sampled ambrosia beetles (Coleoptera, Curculionidae: Scolytinae and Platypodinae) from four tree species: Artocarpus altilis , Ficus nodosa , Leea indica and Nauclea orientalis , at three sites forming a 1000 km transect in lowland rainforests of northern Papua New Guinea. A standardized volume of wood from trunk, branches and twigs was sampled for ambrosia beetles from three individuals of the four tree species at each site. Each tree was killed standing and left exposed to beetle colonization for 20 days prior to sampling. We obtained 12 751 individuals from 84 morphospecies of ambrosia beetles. We surveyed most of the local species richness at each site, predicted by Chao 2 species richness estimates. The similarity of ambrosia beetle communities, estimated by Chao-Sorensen index, was not correlated with their geographical distance. Likelihood analysis and Q-mode analysis using Monte Carlo-generated null distribution of beetles among sites supported the hypothesis that the assemblages of ambrosia beetles at different sites are drawn from the same species pool, regardless of their geographical distance. Tree part (trunk, branch, or twig) was more important predictor of the composition of ambrosia beetle communities than was the host species or geographical location. All three variables, however, explained only a small portion of variability in ambrosia assemblages. The distribution of ambrosia beetles among tree parts, tree species and study sites was mostly random, suggesting limited importance of host specificity or dispersal limitation.     

Energy use by the mountain pine beetle (Coleoptera: Curculionidae: Scolytinae) for dispersal by flight

The mountain pine beetle Dendroctonus ponderosae Hopkins is a major native pest of Pinus Linnaeus (Pinaceae) in western North America. Host colonization by the mountain pine beetle is associated with an obligatory dispersal phase, during which beetles fly in search of a suitable host. Mountain pine beetles use stored energy from feeding in the natal habitat to power flight before host colonization and brood production. Lipids fuel mountain pine beetle flight, although it is not known whether other energy sources are also used during flight. In the present study, we compare the level of energy substrates, proteins, carbohydrates and lipids of individual mountain pine beetles flown on flight mills with unflown control beetles. We use a colorimetric method to measure the entire metabolite content of each individual beetle. The present study reveals that mountain pine beetles are composed of more protein and lipid than carbohydrate. Both female and male mountain pine beetles use lipids and carbohydrates as energy sources during flight. There is variation between sexes, however, in the energy substrates used for flight. Male mountain pine beetles use protein, in addition to lipids and carbohydrates, to fuel flight, whereas protein content is not different between flown and control females.     

温度对花绒寄甲飞行能力的影响

为了了解花绒寄甲的飞行行为以及评估其飞行能力,本研究采用飞行磨吊飞技术,测定了不同性别的花绒寄甲成虫在15℃、20℃、25℃、30℃和35℃条件下的飞行距离、飞行持续时间以及平均飞行速度的差异。研究结果表明,花绒寄甲是一种飞行能力很强的昆虫,24 h内最远能飞行22 km,飞行持续时间可达11 h,飞行平均速度在0.43～0.55 m/s之间。总体上雌性花绒寄甲飞行距离和飞行时间均随温度升高而增加,但温度对飞行速度的影响不显著。生物防治生产实践中,花绒寄甲适宜的释放温度在25℃到35℃之间。     

取食和交配对苹小吉丁飞行能力的影响

【目的】苹小吉丁Agrilus mali是一种严重危害苹果树的钻蛀性害虫。本研究旨在明确苹小吉丁的飞行扩散能力及对其飞行能力产生影响的关键因子。【方法】以SUN-FL型智能飞行磨系统对苹小吉丁不同日龄雌雄成虫的飞行能力进行了测定,同时评价了取食和交配情况对其飞行能力的影响。【结果】苹小吉丁飞行能力均随日龄的增加先增强后逐渐降低,初羽化的成虫飞行能力最低,11日龄成虫的飞行能力最强。雌成虫飞行能力强于雄成虫。在24 h内雌雄成虫的最长飞行距离分别为0.4165和0.3559 km;最长飞行时间分别为0.4582和0.4873 h;最大飞行速度分别为2.4639和1.8561 km/h。取食的3日龄雌成虫的平均飞行距离和平均飞行时间分别为0.047 km和0.048 h,雄成虫的分别为0.044 km和0.042 h;而未取食的雌成虫平均飞行距离和平均飞行时间仅分别为0.016 km和0.013 h,雄成虫的仅分别为0.013 km和0.012 h。交配对飞行能力的影响存在性别差异,已交配雌成虫的飞行能力要强于未交配雌成虫的,而已交配雄成虫的飞行能力却低于未交配雄成虫的。【结论】日龄对苹小吉丁成虫的飞行能力影响作用显著。取食显著提高苹小吉丁雌雄成虫的飞行能力,交配显著提高雌成虫飞行能力。     

Investigations of the oogenesis-flight syndrome inAnthonomus grandis (Coleoptera: Curculionidae) using tethered flight tests

This paper investigates the relationship between oogenesis and flight duration and the use of tethered flight as an indicator of tendency to migrate inAnthonomus grandis grandis Boheman (Coleoptera: Curculionidae), the boll weevil. When boll weevils were flown to exhaustion in tethered flight tests, many flew between 2 and 3 h, with several flying more than 4 h. To test the validity of the tethered flight test as an indicator of tendency to migrate, comparisons of mean flight duration were made between boll weevils trapped in pheromone traps far from any cultivated cotton and those trapped at the edge of heavily infested, flowering cotton fields. There was a significant difference in mean flight time between the two groups, supporting the assumption that long-duration tethered flight in the laboratory reflects the tendency to make long-distance flights in the field. Groups of weevils of different ages were killed after flight testing, and the degree of ovarian development and fat body status were determined and related to duration of tethered flight. Insects with undeveloped or partially developed ovaries were the most likely to make long flights. Weevils with ovaries bearing chorionated eggs made very few long flights. Flight duration was positively correlated with degree of fat body development. In contrast, there were no significant differences in the degree of ovarian development with fat body status. We conclude from these experiments thatA. grandis grandis is capable of long-distance flight, that this species displays some behavioral and physiological characteristics typical of many insect migrants including an oogenesis-flight syndrome, and that a tethered flight test is an appropriate means of measuring migratory tendency in this species.