Effect of temperature and host tree on cold hardiness of hemlock looper eggs along a latitudinal gradient

The hemlock looper, Lambdina fiscellaria, is an economically important insect pest of Canadian forests which overwinters as eggs. Although the hemlock looper causes extensive damages, no information on the mechanisms related to its cold tolerance is known. The objective of this study was to determine the effect of temperature and exposure duration on hemlock looper winter survival but also to identify seasonal supercooling capacity and cryoprotectant levels of three populations along a latitudinal gradient. As host plant may contribute to offspring overwintering success, cold tolerance of hemlock looper eggs from parents whose larvae were fed on three different tree species was also measured. Mean supercooling point (SCP) of hemlock looper eggs was lower than −30 °C from October through the following spring with values being as low as −47 °C in February. Trehalose was the most abundant sugar found in hemlock looper eggs with a peak concentration of 0.3 μg mg⁻¹ DW⁻¹. Glycerol, a polyol, was more often absent in eggs of the different populations and tree species tested in the study. When exposed to different temperature regimes for various periods of time, significant mortality of hemlock looper eggs occurred at higher temperatures than the mean SCP. Thus, hemlock looper could be considered as a chill tolerant species. No clear pattern of population and host plant effects on SCP and cryoprotectants was detected in this study. However, when exposed to different winter temperatures and exposure duration, hemlock looper from higher latitudes survived better (survival rates ranging between 0 and 89% at −20 °C) than those from lower latitudes (survival rates ranging between 0 and 56% at −20 °C). Our results may contribute to a better understanding of hemlock looper winter biology and thus facilitate predictions of outbreaks and range expansion.     

Effect of simulated fall heat waves on cold hardiness and winter survival of hemlock looper,Lambdina fiscellaria (Lepidoptera: Geometridae)

The hemlock looper (Lambdina fiscellaria) is an important pest of eastern Canadian forests. The ongoing climate warming could modify the seasonal ecology of this univoltine species that lays eggs at the end of summer and overwinters at this stage. Indeed, the increase in frequency and intensity of extreme climatic events such as fall heat waves could interfere with the winter metabolism of the hemlock looper. Moreover, the host plant quality, which influences the quantity of insect energetic reserves, the geographic origin of populations and the conditions prevailing during the cold acclimation period, could cause various responses of this pest to climate warming. The main objective of this study is to determine the impact of these factors on hemlock looper winter biology. In October 2010, hemlock looper eggs initially collected from two geographic areas in the province of Québec, and from parents reared on two host plants, were exposed to fall heat waves of different intensities during 5 consecutive days. Supercooling points and cryoprotectant levels were measured on eggs on four different dates in 2010–2011 and survival rate was measured in April 2011. Our results show that hemlock looper eggs have a very low supercooling point and high levels of trehalose, glucose and mannitol in September and November. However, there is no clear relationship between the concentration of these compounds and the decrease in supercooling points. Contents in trehalose, glucose and mannitol were significantly influenced by fall heat waves and by the origin of the population. Winter survival of eggs from the temperate population was negatively affected by strong heat waves while the boreal population was not affected. This study suggests that the metabolism and winter survival of temperate hemlock looper populations in Québec will be more affected by fall heat waves that will increase in frequency due to climate change, than boreal populations.     

Short‐term influence of partial cutting on hemlock looper (Lepidoptera: Geometridae) parasitism

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Comparison of trapping for eggs, females, and males of the naval orangeworm (Lepidoptera: Pyralidae) in almonds

The navel orangeworm is the primary insect pest of almonds in California, and egg traps are the primary means of monitoring this pest. A previous study found that the current use of 2-4 traps per 64 ha block usually is not sufficient to provide management information specifically for that block. In this study, we compare data from large grids of egg traps in varied commercial almond orchards with trapping data for females and males, with the objective of finding a more cost-effective monitoring program using currently available attractants. The proportion of egg traps with eggs was highly correlated with mean eggs per egg trap, and with females and males trapped simultaneously at the same location. Almond variety and the type of bait used had little impact on the relationship between the proportion of egg traps with eggs and the number of eggs per traps. Traps in orchards with more unharvested (mummy) almonds had more eggs, suggesting that navel orangeworm abundance affected traps more than competition from mummies. Laboratory experiments comparing age-specific oviposition in two-choice and no-choice situations found that younger, more fecund females laid a greater proportion of eggs on the preferred substrate in a two-choice situation, but that age-specific fecundity was not different between substrates in no-choice tests. These findings indicate that the proportion of egg traps with eggs provides a more stable indication of navel orangeworm phenology than mean eggs per trap. We suggest that similar information could be obtained in a more cost-effective manner with female trapping.     

Widespread inbreeding and unexpected geographic patterns of genetic variation in eastern hemlock (Tsuga canadensis), an imperiled North American conifer

Eastern hemlock (Tsuga canadensis [L.] Carr.) is an ecologically important tree species experiencing severe mortality across much of its eastern North American distribution, caused by infestation of the exotic hemlock woolly adelgid (Adelges tsugae Annand). To guide gene conservation strategies for this imperiled conifer, we conducted a range-wide genetic variation study for eastern hemlock, amplifying 13 highly polymorphic nuclear microsatellite loci in 1,180 trees across 60 populations. The results demonstrate that eastern hemlock exhibits moderate inbreeding, possibly a signature of a prehistoric decline associated with a widespread insect outbreak. Contrary to expectations, populations in formerly glaciated regions are not less genetically diverse than in the putative southern refugial region. As expected, peripheral disjunct populations are less genetically diverse than main-range populations, but some are highly genetically differentiated or contain unique alleles. Spatially explicit Bayesian clustering analyses suggest that three or four Pleistocene glacial refuges may have existed in the Southeastern United States, with a main post-glacial movement into the Northeast and the Great Lakes region. Efforts to conserve eastern hemlock genetic material should emphasize the capture of broad adaptability that occurs across the geographic range of the species, as well as genetic variability within regions with the highest allelic richness and heterozygosity, such as the Southern Appalachians and New England, and within disjunct populations that are genetically distinct. Much genetic variation exists in areas both infested and uninfested by the adelgid.     

Abundance and aggregation egg of Aedes aegypti L. and Aedes albopictus (Skuse) (Diptera: Culicidae) in the north and northwest of the State of Paraná, Brazil

The abundance and aggregation of eggs of Aedes aegypti L. and Aedes albopictus Skuse was evaluated in the municipalities of Cambé, Ibipor?, Jacarezinho, Maringá and Paranavaí, in the State of Paraná, Brazil by means of oviposition traps. Of the 225 installed traps, 100 were registered as positive for eggs; 4140 eggs were collected, thus demonstrating an highly aggregate distribution. Both species were registered in Cambé, Jacarezinho, Maringá and Paranavaí. Ae. albopictus was generally less abundant and was not present in Ibipor? nor in the oviposition traps of a second collection of Maringá. The relation between sexes for Ae. aegypti was approximately 1:1. In the comparison of the number of adults collected between the two species, a negative correlation was obtained in the samples of Maringá and Cambé, what was attributed the seasonality of these populations. The coexistence of these species indicates that both are under pressure by the control programs, therefore specific evaluations are necessary.     

Web orientation and prey resources for web-building spiders in eastern hemlock

We examined the arthropod community on eastern hemlock, Tsuga canadensis (L.) Carr, in the context of its role in providing potential prey items for hemlock-associated web-weaving spiders. Using sticky traps simulating spider webs, we evaluated what prey items are available to web-weaving spiders in eastern hemlock based on web orientation (horizontal versus vertical) and cardinal direction. We found that the overwhelming majority (>70%) of prey items available to spiders in hemlock canopies were Diptera. Psocoptera, Hymenoptera, and Hemiptera comprised most of the remaining potential prey. A significant direction × orientation interaction, and greater trap capture in some direction-orientation combinations, suggests that spiders might locate their webs in eastern hemlock canopies for thermoregulatory purposes, ultimately optimizing prey capture. We also evaluated these findings in the context of hemlock infestation by the invasive hemlock woolly adelgid, Adelges tsugae Annand. The adelgid is a sedentary insect with a mobile crawler stage that provides a readily available, easily obtained food source for predators in hemlock canopies. However, an abundance of alternative prey will affect within canopy spider distribution and the potential intensity with which spiders consume these prey. Understanding the response of spiders to potential prey availability is essential to understanding the trophic interactions involving these predators and their potential for influencing herbivore populations.     

Spatial distribution pattern of oviposition in the mosquito Aedes aegypti in relation to urbanization in Buenos Aires: southern fringe bionomics of an introduced vector

The distribution of Aedes aegypti (L) (Diptera: Culicidae) oviposition in Buenos Aires City is spatially heterogeneous. Oviposition activity was monitored for a year with a grid of 279 traps at 850-m intervals that were serviced weekly. Geostatistics were used for the spatial analysis and generalized linear regression to model oviposition as a function of demographic and environmental variables. The proportion of weeks infested and the total number of eggs showed spatial continuity and were higher in areas that had higher densities of houses and were closer to industrial sites; they were lower in areas with higher human populations or higher densities of flats. When all sites were considered, the spatial structure showed a strong trend, but after regression, the residuals presented lower spatial dependence. When only infested sites were considered, the oviposition variables were spatially autocorrelated and the regression residuals showed little or no spatial dependence. The spatial pattern of Ae. aegypti oviposition in a highly urbanized city such as Buenos Aires seems to be related to the urbanization gradient. These urban environments might present different resource availability or continuity between patches of resources.     

Assessment of entomological indicators of Aedes aegypti (L.) from adult and egg collections in S?o Paulo, Brazil

We compared the presence and mean number of eggs from oviposition traps with the mean number of Aedes aegypti females captured by manual aspirators and by MosquiTRAPs to determine the sensitivity of each method and to standardize each indicator. The collections of adults and eggs were performed over 23 weeks in six neighborhoods of Mirassol, state of S?o Paulo, Brazil. A better assessment of indicators required larger number of MosquiTRAPs, but to quantify the number of females per house, one trap was sufficient. The sensitivities of MosquiTRAPs and manual aspirations to detect the presence of A. aegypti females were similar, but were lower compared to oviposition traps. The correlation coefficients between the number of females captured by MosquiTRAPs and manual aspirations and the number of eggs from oviposition traps were low, which may be a consequence of each method showing different stages of the mosquito life cycle.     

A kairomone based attract-and-kill system effective against alfalfa looper (Lepidoptera: Noctuidae)

A chemical lure derived from flowers that are visited by moths attracts male and female alfalfa loopers, Autographa californica (Speyer) (Lepidoptera: Noctuidae). This feeding attractant is dispensed from polypropylene bottles that provide controlled release for several weeks. A killing station was tested in the laboratory, in a screenhouse, and in the field in combination with this lure as an "attract-and-kill" system. Starved alfalfa looper adults (moths) were strongly attracted to the attract-and-kill station in a flight tunnel, and 90.9% of female moths and 87.6% of male moths that contacted the station died. In commercial fields of alfalfa hay, female moths captured in monitoring traps were reduced by 80-93% in plots receiving 125 attract-and-kill stations per hectare. In screenhouse trials using two attract-and-kill stations per screenhouse, oviposition on potted lettuce plants by starved female alfalfa looper moths was reduced by 98.5%. Moths were less likely to be attracted to lures when provided sugar before flight tunnel assays, and oviposition by fed moths was much less affected by attract-and-kill stations in screenhouse trials, compared with starved moths. This method has potential as a means to manage alfalfa looper populations in vegetable and other agricultural crops. However, consideration must be given to competing food and odor sources in the field.     

Too close for comfort: effect of trap spacing distance and pattern on statistical inference of behavioral choice tests in the field

Behavioral choice tests provide a powerful and commonly used technique for evaluating the biological activity of chemical signals. Despite the widespread application of this approach, relatively few studies have evaluated a key assumption, that is, relative independence among treatments. Previous work has demonstrated that both the number of choices and their physical arrangement can affect the results of choice tests with leaf‐feeding insects in laboratory assays. Here, we consider another spatial component, the distance between treatments, in a field assay, using a bark beetle as our model. We used three geometries of trap arrangements, two spacing levels, and both ‘low activity’ lures and a ‘high activity’ lure in our behavioral assays. We found that proximity to an attractive treatment generated unexpectedly high trap catches at relatively non‐attractive treatments, even in the presence of a uniform treatment effect and relatively constant insect population size. Increases in traps baited with ‘low activity’ lures proximate to a highly attractive treatment ranged from 4 to 7× the catch observed in configurations with traps spaced wider apart. Moreover, even in the absence of ‘high activity’ lures, a lure catching less than one insect per day on average could obscure the effect of a control trap at proximate spacing. In our example, a spacing distance of 15 m appears to provide independence among traps used to sample the bark beetle Ips pini (Say) (Coleoptera: Curculionidae: Scolytinae), but 3 m does not. Our broader intent is to provide a useful approach to the design and evaluation of behavioral choice experiments in the field.     

Niche overlap and interspecific association between Chilo partellus and Chilo orichalcociliellus on the Kenya coast

The use of felt traps to estimate oviposition by the cabbage root fly, Delia radicum (L.), and turnip root fly, Delia floralis (Fall.), was compared with soil sampling at seven localities between 1992 and 1994 in Denmark and Norway. In all, 281 comparisons were made, based on 6800 samples. In 4.6% of these comparisons no eggs were found by either method. In 16% of the comparisons, 2.0±0.41 (±S.E.) eggs were found per soil sample and no eggs were found in felt traps, whereas in 0.7% of the comparisons 0.10±0.03 eggs were found per felt trap and no eggs in soil samples. When eggs were found using both methods, the ratio between soil sampling and felt traps varied from 13.1±3.2 when the egg laying rate was very low to 1.8±0.2 at high egg laying rates. Regression analysis showed significant correlation between felt trap catches and soil sampling (P<0.001), whereas locality did not influence felt trap efficiency (P=0.096). The influence of the physical conditions of felt traps, i.e., whether they were clean and dry, were analysed in a single year. Tentative action thresholds for control measures against cabbage root flies and turnip root flies were developed for cauliflower, Brassica oleracea, convar. botrytis (L.) Alef., var. botrytis, based on data from the literature and the present results.     

Efficiency of Malaise traps and colored pan traps for collecting flower visiting insects from three forested ecosystems

Pan and Malaise traps have been used widely to sample insect abundance and diversity, but no studies have compared their performance for sampling pollinators in forested ecosystems. Malaise trap design and color of pan traps are important parameters that influence insect pollinator catches. We compared pan trap (blue, yellow, white, and red) and Malaise trap catches from forests in three physiographic provinces (Piedmont, Coastal Plain, and Blue Ridge) of the southeastern United States. Similarities in trap performance between sites were observed with blue pan traps being most effective overall. Our results showed that various pollinator groups preferred certain pan trap colors and that adding color to Malaise traps influenced insect pollinator catches. However, pan traps generally caught more pollinators than Malaise traps. Because of their low cost and simplicity, using several colors of pan traps is an effective way to sample relative abundance and species richness of flower-visiting insects.     

An Efficient Pit-light Trap to Study Beetle Diversity

A new, highly efficient pit-light trap is described and results of experiments on its efficacy that were carried out in various types of forests are presented. The Luminoc® insect trap is made of two parts: a 1-L collection container inserted into the ground and an upper container which houses a 6-V lantern battery and a circuit for electronic control of a 1.8-W miniature fluorescent tube. A cover is fixed under the upper container to prevent rainwater from entering the collection container. The pit-light trap caught significantly more specimens, species and families of Coleoptera than passive pitfall traps. Many species of common families, such as Carabidae, Cantharidae, Curculionidae, Elateridae, Pyrochroidae, Scarabaeidae, Silphidae and Tenebrionidae were mainly caught in pit-light traps. Several species of uncommon families such as Byrrhidae, Melandryidae, Scraptiidae, Stenotrachelidae and Throscidae were caught only in pit-light traps. The light source increases the sampling area of a trap to include many micro-habitats, which makes pit-light traps more efficient tools that provide less variable results than the passive pitfall traps. The use of only three pit-light traps allows the capture of three times more 'abundant and common' species than any number of passive pitfall traps could provide. Thus, the pit-light trap allows an easier and more accurate characterization of Coleoptera communities than the passive pitfall trap. Because of its high efficacy, the pit-light trap should be considered as a standard tool to study, monitor and inventory beetle diversity.     

Responses of ovipositing moths to host plant deprivation: life history aspects and implications for intercropping

1. When considering intercropping as a strategy to reduce pest oviposition, knowledge about the insect’s oviposition behaviour is very important. Physiological effects on the insect because of difficulties in finding a suitable oviposition site may also be important. 2. In the present study, the effects that delays in access to host plants have on lifetime fecundity on diamondback moth and leek moth were examined. The ability to postpone egg laying, fecundity and lifetime oviposition are discussed in relation to intercrop/cover crop as a strategy to reduce oviposition on crop plants. 3. When faced with host plant deprivation, the diamondback moth is relatively more dependent upon host plant stimuli for the onset of egg production. By contrast, leek moth is able to postpone egg production for a longer time. There even appeared to be a tendency for leek moth females to extend their lifetime when faced with host plant deprivation. 4. We conclude that leek moths have the ability to postpone production of eggs and lay them later in life when finally encountering host plants after a period of host plant deprivation. Therefore, the use of intercropping as a strategy to reduce oviposition is questionable. For such an insect, use of a trap crop might be a better option because the female will lay her eggs in the trap crop and not get the opportunity to lay them later in life when finally encountering crop plants.     

Uraba lugens (Lepidoptera: Nolidae) in New Zealand: pheromone trapping for delimitation and phenology

A synthetic sex pheromone trapping survey of the leaf skeletonizer Uraba lugens Walker (Lepidoptera: Nolidae) demonstrated the unexpectedly widespread distribution of the insect across > 40,000 ha of urban Auckland, New Zealand. A survey of eucalyptus trees planted in parks and other public areas showed a significant spatial correlation between trap catch and breeding populations, validating the trap survey results. Traps in trees showing damage had four-fold higher catches than traps placed in undamaged or nonhost trees, and < 1% of damaged trees with traps failed to catch adult moths. Damage by larval feeding was correlated with male trap catch in the previous generation, offering good prospects for a pest management decision support system, provided that an economic threshold is developed. Catches increased by 3.4-fold in the same georeferenced trapping grid between November and December 2003 and between March and April 2004 across two generations, over the summer. A vertical transect showed that catches increased with height up to the top trap at 13 m (60% of mean tree height). Options for managing the insect will need to overcome the high rate of increase, the rate of spread, and the vertical distribution of the insect on tall eucalyptus trees.     

Geographic biotype and host-associated local adaptation in a polyphagous species, Lambdina fiscellaria (Lepidoptera: Geometridae) feeding on balsam fir on Anticosti Island, Canada

The debate about mechanisms underlying the evolution of host specialization by herbivorous insects remains open. Natural selection may act locally and lead to different patterns of geographic variation in life history traits of polyphagous herbivores. The hypothesis of genetically-based trade-offs in offspring performance on different hosts has been proposed but this has rarely been demonstrated. Under laboratory conditions, the biological performance of two populations of the hemlock looper Lambdina fiscellaria (Guenée), a highly polyphagous lepidopteran, was compared when reared on three different tree host species: balsam fir, eastern hemlock and sugar maple. One population originated from Anticosti Island, Québec, Canada, where the insect has evolved without having access to two of the three tree species tested, the other being from the mainland where all tree species are present. When reared on balsam fir foliage, which was naturally available to each population, larvae from Anticosti Island underwent four instars compared with five for the mainland population, indicating the existence of geographic biotypes in L. fiscellaria. When reared on the foliage of non-naturally available host trees, larvae from Anticosti Island had a higher incidence of supernumerary instars. This is a unique example where local adaptation to environmental conditions of an insect herbivore is expressed through a differential number of larval instars. Moreover, the Anticosti Island population showed a higher growth related index on the host available to both populations indicating that a fitness trade-off was the evolutionary process underlying the local adaptation of this population on balsam fir.     

Evaluation of an oviposition‐stimulating kairomone for the yellow fever mosquito,Aedes aegypti,in Recife,Brazil

A synthetic mixture of an oviposition‐stimulating kairomone for the yellow fever mosquito, Aedes aegypti, comprising of 83% tetradecanoic acid, 16% nonanoic acid and 1% tetradecanoic acid methyl ester (NTT, in short) was tested in a dengue endemic area in Recife, Brazil. Gravid female mosquitoes confined to a cage under semi‐field conditions deposited significantly higher numbers of eggs in traps baited with NTT at doses ranging from 0.6 to 600 ng/μl than in control (water) traps. When tested in homes, egg‐laying in traps baited with 60 ng NTT/μl (final concentration in trap, ≈3.33 ng/ml) and in control traps was not significantly different, but egg deposited in traps with lower dosage (6 ng NTT/μl; final concentration in trap, ≈0.33 ng/ml) was significantly higher than in control traps. In subsequent trials, the numbers of eggs laid in traps baited with 0.6 ng NTT/μl (final concentration in trap, ≈0.033 ng/ml) were not significantly different from the numbers deposited in trap loaded with 6 ng NTT/μl. Egg‐laying was significantly higher in these treatments than in control traps.     

A novel,easy method for estimating pheromone trap attraction range: application to the pine sawyer beetle Monochamus galloprovincialis

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The influence of potential stressors on oviposition site selection and subsequent growth,survival and emergence of the non‐biting midge (Chironomus tepperi)

Theory predicts that animals should prefer habitats where their fitness is maximized but some mistakenly select habitats where their fitness is compromised, that is, ecological traps. Understanding why this happens requires knowledge of the habitat selection cues animals use, the habitats they prefer and why, and the fitness costs of habitat selection decisions. We conducted experiments with a freshwater insect, the non‐biting midge Chironomus tepperi to ask: (a) whether females respond to potential oviposition cues, (b) to explore whether oviposition is adaptive in relation to metal pollution and conductivity, and (c) whether individuals raised in poor quality sites are more likely to breed in similarly poor locations. We found the following: (a) females responded to some cues, especially conductivity and conspecifics, (b) females preferred sites with higher concentrations of bioavailable metals but suffered no consequences to egg/larval survival, (c) females showed some avoidance of high conductivities, but they still laid eggs resulting in reduced egg hatching, larval survival, and adult emergence, and (d) preferences were independent of natal environment. Our results show that C. tepperi is susceptible to ecological traps, depending on life stage and the relative differences in conductivities among potential oviposition sites. Our results highlight that (a) the fitness outcomes of habitat selection need to be assessed across the life cycle and (b) the relative differences in preference/suitability of habitats need to be considered in ecological trap research. This information can help determine why habitat preferences and their fitness consequences differ among species, which is critical for determining which species are susceptible to ecological traps.