Ultrastructure of the galeal sensory complex in adults of the Colorado potato beetle, Leptinotarsa decemlineata

ABSTRACT. The structure of galeal sensilla of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), is described using electron microscopical methods. Previous electro-physiological studies indicate that these sensilla respond to amino acids, sucrose and plant saps. One physiological type is particularly sensitive to L-alanine and gamma amino butyric acid (GABA).
Three morphologically different types of sensilla occur on the galeal tip. The more numerous apical pegs are not distinguishable from one another on the basis of external structure, although they differ physiologically. Five sensory cells are associated with most apical pegs. One apical peg, the α-sensillum, contains only four cells. All apical pegs have one cell with a tubular body. The remaining cells have unbranched dendrites and are associated with a single apical pore.
Apical hairs differ from the apical pegs by having double innervation. Within the hair shaft, a dendritic sheath is lacking and the sensillar sinus extends to the base of the hair. The function of this hair type is not known.
Numerous mechanosensory hairs which surround the other sensilla are singly innervated and contain a tubular body at the level of the outer dendritic segments.     

Characterization and chromosome location of satellite DNA in the leaf beetle Chrysolina americana (Coleoptera, Chrysomelidae)

This paper is the first record of the satellite DNA of the specialized phytophagous genus Chrysolina. The satellite DNA of Chrysolina americana is organized in a tandem repeat of monomers 189 bp long, has a A + T content of 59.6 % and presents direct and inverted internal repeats. Restriction analysis of the total DNA with methylation sensitive enzymes suggests that this repetitive DNA is undermethylated. In situ hybridization with a biotinylated probe of the satellite DNA showed the pericentromeric localization of these sequences in all meiotic bivalents. The presence of this repetitive DNA in other species of the genus was also tested by Southern analysis. The results showed that this satellite DNA sequence is specific to the C. americana genome and has not been found in three other species of Chrysolina with a different choice of host plants than in the former. This revised version was published online in July 2006 with corrections to the Cover Date.     

Endemism patterns in the Italian leaf beetle fauna (Coleoptera,Chrysomelidae)

In this contribution the results of a zoogeographical analysis, carried out on the 123 endemic leaf beetle species (Coleoptera: Chrysomelidae) occurring in Italy and its immediately adjacent regions, are reported. To assess the level of faunistic similarity among the different geographic regions studied, a cluster analysis was performed, based on the endemic component. This was done by calculating the Baroni Urbani & Buser’s similarity index (BUB). Finally, a parsimony analysis of endemicity (PAE) was used to identify the most important areas of endemism in Italy.     

Larva of the leaf beetle Labidostomis longimana (Coleoptera, Chrysomelidae, Clytrinae)

The first- and the last-instar larvae of the leaf-beetle Labidostomis longimana are described in detail for the first time. The last instar larva is morphologically close to L. sibirica larva and differs from it in the absence of a projection in the medial emargination of the labrum, in the presence of 7 spiniform setae on the tibiotarsus ventrally, 11–13 narrow simple setae on the tibiotarsus dorsally, and fine rugae on the larval case.     

Egg cannibalism by larvae and adults of the milkweed leaf beetle (Labidomera clivicollis, Coleoptera: Chrysomelidae)

Abstract.

• 1 Egg cannibalism is a form of infanticide that has been implicated in the evolution of guarding of eggs and immatures in some species of insects. The milkweed leaf beetle, Labidomera clivicollis (Coleoptera: Chrysomelidae), exhibits three types of egg cannibalism in the field: siblicide, cannibalism of eggs by older larvae from earlier hatching egg clutches, and cannibalism of eggs by adult females. Unlike their close relative, L.suterella (Choe, 1989), female L.clivicollis do not guard their eggs or immatures. They move slowly about a patch of milkweeds laying multiple egg clutches.
• 2 First instar and older larvae cannibalized eggs in two geographically separated study populations (subspecies) in Austin, Texas, and Bridgeport, New York, U.S.A. Although adult females of both populations cannibalized eggs in the laboratory, only the Texas subspecies, L.c.rogersii, exhibited such cannibalism in the field.
• 3 In the field, correlates of siblicide varied both temporally (within subspecies) and spatially (between subspecies) in terms of whether they were statistically significant, but trends were all in the same direction. Group size was positively correlated with hatching success and siblicide, but negatively correlated with other types of predation. Siblicide was also positively correlated with egg density in a laboratory study of the Texas subspecies, L.c.rogersii.
• 4 In the laboratory, an average of 15–17% of L.c.clivicollis eggs never developed embryos. Although these were almost always cannibalized, some viable eggs were also eaten and there is no evidence that females increased the proportion of infertile eggs they laid to increase siblicide.
• 5 Field data and laboratory experiments showed that adult female L. c.rogersii cannibalized eggs while males rarely did. Females preferentially ate the eggs of other females over their own eggs in an experiment that removed spatial cues.
• 6 Although the selective context of cannibalism is not demonstrated here, I suggest that females may increase siblicide by increasing egg density and may cannibalize eggs to protect their own eggs from being eaten by second and third instar larvae produced by other females.

     

To the knowledge of the leaf beetle genus Cystocnemis (Coleoptera, Chrysomelidae)

Four subspecies of Cystocnemis discoidea are distinguished; two subspecies are described as new to science based on investigation of intraspecific variation in different parts of the species range, and ssp. gebleri was resurrected from synonymy. The ways of speciation in highland-hollow landscapes are discussed. The alpine subspecies C. discoidea oreas ssp. n. has an altibiome disjunction with the nominotypical subspecies. Similarity of the alpine subspecies of C. discoidea to the species from the subgenus Entomomela was found to be the reason of permanent confusion of representatives of these taxa. The subgenus Entomomela is transferred from the genus Oreomela to the genus Cystocnemis. A key to species and subspecies of the genus Cystocnemis is given.     

Mating behavior of the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Abstract  Circadian mating rhythms, mating frequency, mating duration, and the effect of mating duration on fecundity and fertility in the cabbage beetle, Colaphellus bowringi were investigated in the laboratory. Mating occurred throughout the 24-h cycle but the majority of copulations occurred in the photophase with two apparent peaks, one at 8:00 and another at 16:00. Mating frequency observations for 10 consecutive days indicated that pre-mating period of C. bowringi was about 4 days, and pairs mated an average of 5 times per day and an average of 40 times during the first 10 days. There was a negative correlation between mating frequency and mating duration during the consecutive mating. The mean duration of the first copulation (136.24 ± 4.62 min) was significantly longer than those of the second (57.87 ± 2.03 min), third (53.05 ± 2.05 min) and fourth copulation (30.86 ± 2.98 min). Fecundity showed a slight increase with increasing mating duration but no significant difference among treatments. However, fertility was significantly influenced by the mating duration in this species. Mating of 20-min duration did not produce viable eggs. The mean percentage of fertile eggs with completed mating duration (204.43 ± 18.96 min, 56.75% fertile eggs) was significantly higher than those with 60 min (39.55%) and 30 min (17.91%) mating duration, suggesting that the longer mating duration might be associated with transfer of more sperm that are used to increase the fertility of eggs.     

Ovipositional biology of Viburnum leaf beetle, Pyrrhalta viburni (Coleoptera: Chrysomelidae)

Pyrrhalta viburni Paykull, a new landscape pest in the United States, feeds in both the larval and adult stages on foliage of plants in the genus Viburnum. We measured lifetime oviposition capacity of mated and unmated females reared in the laboratory versus field-collected females, as well as ovipositional response to physical characteristics of the host plant. Both mated and unmated females produced eggs, but at different rates. Field-collected females and mated females reared in the laboratory laid similar numbers of egg masses containing similar numbers of eggs, but unmated females laid approximately one half as many eggs, the result primarily of smaller clutch size. Mated females reared in the laboratory had a preovipositional period of 11.4 +/- 1.7 versus 29 + 11.7 d for unmated females, and unmated females lived significantly longer than mated females. The angle and diameter of stems of V. trilobum, a very susceptible host, both greatly influenced oviposition; females laid most eggs on vertically oriented stems, and those of smallest diameter; when these factors were combined, stem diameter predominated. Females also had a very strong geotactic response, preferring to lay eggs on portions of stems toward gravity, even when stems were at fairly shallow angles.     

Benefits of polyandry in Parthenium beetle,Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae)

The influence of polyandry on the reproductive performance of females and on offspring fitness in Zygogramma bicolorata Pallister was investigated using four experimental treatments, viz. (A) monandrous, limited mating, (B) monandrous, unlimited mating, (C) polyandrous, no-choice limited mating, and (D) polyandrous, mate choice unlimited mating. Polyandrous females had higher reproductive performance than monandrous ones. Monandrous females subjected to unlimited matings had higher egg viability than those subjected to limited matings, but fecundity did not differ significantly. In polyandrous females, the freedom to choose mates did not affect reproductive performance. However, offspring of polyandrous females allowed mate choice developed fastest and had the highest survival at 25, 27, and 30 °C. Thus, polyandry in Z. bicolorata appears to provide both direct (material) and indirect (genetic) benefits resulting in better reproductive performance and increased adaptability of the offspring to counter environmental stresses. The present study not only adds to the knowledge of reproductive biology of Z. bicolorata but it could also be of economic value as it may help in the mass rearing of Z. bicolorata and in the management of Parthenium hysterophorus.     

Spatial distribution of the cereal leaf beetle (Coleoptera: Chrysomelidae) in wheat

A 2-yr study was conducted in wheat fields in South Carolina involving weekly sampling of cereal leaf beetle, Oulema melanopus (L.). In each of the six fields of this study, temporal patterns showed two distinct peaks in March and in May of adult O. melanopus. Populations decreased as wheat plants matured. In 2009, larval populations had one peak in April in between the two adult peaks. The χ(2) statistics for observed and Poisson predicted distributions of O. melanopus indicated nonrandom distribution for adults and larvae. In addition, the values of I(D) were >1 for adults and larvae in both years across sampling dates. These results indicate that the sampling distributions of both adult and larval populations of O. melanopus were aggregated. Slopes of Taylor power's law (b) and patchiness regressions (β) were significantly (P < 0.05) different than one in all cases, except for b in 2008 for adults. Across sampling dates, the distance from field border had a significant effect on adult O. melanopus in both years, but not on larval O. melanopus. Densities of adult O. melanopus were greatest at 0 m (the field edge), and decreased at 5-25 m from the field edge. The inverted distance weighted interpolation method showed considerable levels of spatial variability in densities within fields. High densities along the edge of wheat fields suggests that localized control methods in wheat may be effective in reducing migration of O. melanopus and damage in corn, Zea mays L.     

Cold tolerance and supercooling capacity in overwintering adults of elm leaf beetle Xanthogaleruca luteola (Coleoptera: Chrysomelidae)

Elm leaf beetle, Xanthogaleruca luteola (Muller) is one of the key pests of elm trees all over the world, and survives winter in reproductive diapause in sheltered locations. Seasonal variation of whole body supercooling points (SCPs), LT50 (temperature at which 50% of the test individuals die) and survival rate after exposure to subzero temperatures were determined in field collected adults during October 2008 to May 2009 and October 2009 to May 2010. The SCP of adults decreased significantly from October (median=-13.8°C) to January (median=-20.7°C) in first year, relatively similar results was observed in the second year. The lowest LT50 was observed in overwintering adults collected in January (-16.81°C) in the first year and December (-15.59°C) in the second year. Mortality at -15°C for 24 h was >70% in early autumn in both years whereas it decreased to lower than 45% in early winter, the highest mortality (100%) was observed in adults collected in May in both years. Cold acclimated adults (30 d, 5°C) in November 2008 exhibited significantly higher SCP (-12.21±0.64°C) than nonacclimated adults (-15.57±1.35°C). A 30-d exposure to 5°C caused >20% mortality in November, while <9% mortality was observed in adults collected in December and January 2008. Overwintering adults died upon freezing and the lower lethal temperatures were within the range of SCP, indicating that X. luteola is a freeze intolerant insect.     

Potential resistance of crape myrtle cultivars to flea beetle (Coleoptera: Chrysomelidae) and Japanese beetle (Coleoptera: Scarabaeidae) damage

Field and laboratory studies were conducted to identify potential resistance among crape myrtles, Lagerstroemia spp., to Japanese beetle, Popillia japonica Newman and to flea beetles, Altica spp. Damage ratings revealed variation among cultivars in susceptibility to beetle feeding. Cultivars with Lagerstroemia fauriei Koehne in their parentage exhibited the least amount of damage in choice and no-choice experiments, with few exceptions. The data indicate that both beetle species cause more feeding damage on certain cultivars of Lagerstroemia indica L., such as 'Country Red', 'Twilight', and 'Carolina Beauty' than interspecific cultivars with L. fauriei in their parentage, such as 'Natchez', 'Tonto', and 'Muskogee'. When comparing the effect of parentage on all of the major pests of crape myrtle, L. faurei confers resistance to all pests except crape myrtle aphid. No correlation was found between leaf toughness, leaf color, and leaf nutrients in estimating flea beetle cultivar preference. With this information, growers can more effectively target scouting measures to the most susceptible cultivars. and breeders can select plants that will require the fewest chemical inputs.     

Resistance potential of colorado potato beetle (Coleoptera: Chrysomelidae) to novaluron

Novaluron (Rimon 10 EC), a novel insect growth regulator, could play an important role in future management programs for Colorado potato beetle, Leptinotarsa decemlineata (Say). Studies were conducted to determine the potential of Colorado potato beetle to develop resistance to novaluron before its widespread use in Colorado potato beetle management. Second instars of an imidacloprid-resistant Colorado potato beetle strain exhibited reduced susceptibility (2.5-fold) to novaluron. The toxicity of novaluron to this strain was synergized by S,S,S-tributyl phosphorotrithioate (DEF) but not by piperonyl butoxide (PBO), suggesting that esterase-based detoxification mechanisms were responsible for novaluron resistance. Bioassays with treated potato foliage found that a single low- or medium-rate novaluron application was highly persistent under field conditions, resulting in up to 85% mortality of second instars 5 wk after treatment. Thus, intense selection pressure for novaluron-resistant Colorado potato beetle may continue long after population densities have been reduced below an economic threshold level. In a national survey, the susceptibility of second instars to a novaluron diagnostic dose was determined for 27 different field populations collected from six Canadian provinces in summer 2003. Despite no previous exposure to novaluron, mortalities at the diagnostic dose ranged from 55 to 100%. Although novaluron has several characteristics that should delay resistance development in insect pests, these results highlight the need for judicious use of the compound in management of Colorado potato beetle.     

Diapause induction and clock mechanism in the cabbage beetle, Colaphellus bowringi (Coleoptera: Chrysomelidae)

Photoperiodic control of diapause induction was investigated in the short-day species, Colaphellus bowringi, which enters summer and winter diapause as adult in the soil. Photoperiodic responses at 25 and 28 degrees C revealed a critical night length between 10 and 12 h; night lengths > or =12 h prevented diapause, whereas night lengths <12 h induced summer diapause in different degree. Experiments using non-24-h light-dark cycles showed that the duration of scotophase played an essential role in the determination of diapause. Night-interruption experiments with T=24 h showed that diapause was effectively induced by a 2-h light pulse in most scotophases; whereas day-interruption experiments by a 2-h dark break had a little effect on the incidence of diapause. The experiments of alternating short-night cycles (LD 16:8) and long-night cycles (LD 12:12) during the sensitive larval period showed that the information of short nights as well as long nights could be accumulated. Nanda-Hamner experiments showed three declining peaks of diapause at 24 h circadian intervals. Bünsow experiments showed two very weak peaks for diapause induction, one being 8 h after lights-off, and another 8 h before lights-on, but it did not show peaks of diapause at a 24 h interval. These results suggest that the circadian oscillatory system constitutes a part of the photoperiodic clock of this beetle but plays a limited role in its photoperiodic time measurement.     

Intraspecific mitochondrial DNA variation in the Colorado potato beetle,Leptinotarsa decemlineata (Coleoptera: Chrysomelidae)

Restriction endonuclease analyses of mitochondrial DNA (mtDNA) were used to examine genetic variability and population structure inLeptinotarsa decemlineata (Say). A group of three enzymes, EcoRI, HpaI, and PstI, was used to reveal polymorphism both within and among some of the 10 populations tested, yielding 16 haplotypes in combination. The frequencies of these 16 haplotypes differed significantly across geographic regions, indicating some partitioning of mtDNA haplotypes. Estimates of mtDNA sequence divergence (δ) between haplotypes ranged from 0.016 to 0.135%, suggesting local differentiation of mtDNA in some populations. Analysis of these data suggests that Texas was colonized by more than one mtDNA lineage, most likely originating in Mexico. We hypothesize that a larger founder size for the initial introductions or high levels of variability in the parent population at the edge of the CPB expanding range led to the initial partitioning of haplotypes observed in samples from Texas.     

Desiccation and egg viability of the ragwort flea beetle,Longitarsus flavicornis (Coleoptera: Chrysomelidae)

A study was conducted to investigate the effect of desiccation on the survival of eggs of Longitarsus flavicornis. Eclosion of L. flavicornis eggs in laboratory trials decreased with increasing desiccation time between 0 days (93% hatching) and 42 days (no egg hatching) at 50±2% relative humidity and 23±2°C. Probit analysis indicated that 25, 50 and 99% mortality of L. flavicornis eggs occurred after 5.7, 9.3 and 50.4 days desiccation, respectively. Egg development varied between a minimum of 8 days at 7 days desiccation to a maximum of 15 days at 28 days desiccation. Hatching span did not differ between treatments with all eggs hatching within 12 days of each other. A relative humidity of 88–100% was measured under ragwort rosettes in non-drought field conditions. This would be expected to facilitate successful egg eclosion. However, the occurrence of summer drought could be detrimental to egg survival.     

Host specificity of the ragwort flea beetle Longitarsus jacobaeae (Waterhouse) (Coleoptera:Chrysomelidae)

Abstract

The ragwort flea beetle, Longitarsus jacobaeae, was tested for host specificity against representative species of native New Zealand Senecio. Adult feeding and oviposition tests were carried out under quarantine with and without a choice of host plants. Larval development was assessed using potted plants. It was concluded that L. jacobaeae is highly specific to Senecio jacobaea and that it is extremely unlikely to be damaging to native New Zealand Senecio species.     

Resistance to adult banded cucumber beetle (Coleoptera: Chrysomelidae) in romaine lettuce

Four cultivars of lettuce, Lactuca sativa L., were evaluated for their resistance to the adult banded cucumber beetle, Diabrotica balteata LeConte, under laboratory conditions. When paired with each of the other three cultivars, leaf consumption in all possible combinations of short-term (48 h) two-choice tests among the cultivars was significantly reduced only for 'Valmaine'. However, in a 48-h no-choice situation, beetles fed Valmaine or 'Short Guzmaine' had similarly low leaf consumption, followed by 'Parris White', with the greatest consumption occurring on 'Tall Guzmaine'. In longer term experiments, female beetles fed Valmaine for 10, 13, or 16 d generally had lower survival and the lowest body weights compared with beetles fed any of the other three cultivars. No mature eggs were found in the ovaries of females fed Valmaine, whereas from 14% (Short Guzmaine, day 10) to 100% (Tall Guzmaine, day 13) of females fed the other cultivars produced mature eggs. In a starvation test, most D. balteata of either sex did not survive after 7 d with access only to water. Moreover, starved females did not produce mature eggs. Thus, food consumption by adult D. balteata is very important to their survival and reproductive performance, and it is likely that females fed Valmaine failed to produce mature eggs because they did not consume a sufficient amount of this cultivar. However, because Valmaine-fed beetles maintained their body weight and lived significantly longer than starved beetles, it appears that they can obtain some nourishment from their limited feeding on this cultivar. Overall, these results suggest that Valmaine, and to a lesser extent short Guzmaine (a cultivar produced by crossing Valmaine with two other cultivars), exhibit antixenosis-based resistance against D. balteata.