Head Capsule Width Research Articles

Number of Instars of Lissorhoptrus kuscheli (Coleoptera: Curculionidae) from Rice in Venezuela

On the basis of head capsule widths of field-collected larvae, Lissorhoptrus kuscheli O’Brien was found to have 4 instars. The mean head capsule widths are 0.16, 0.23, 0.34, and 0.48 mm for 1st to 4th instars, respectively. L. kuscheli was recovered from ‘Araure 1’ from 3 commercial rice growing areas of Estado Portuguesa, Venezuela. Adult densities were higher in Agua Blanca than in Turen and Durigua, Venezuela. Larval densities suggest 3 generations per year in this area of Venezuela.

Effects of KK-42, an imidazole derivative, on rearing and reproductive performance of Bombyx mori L. during the hot, wet season

Experiments on the effects of KK-42, an anti-juvenile hormone imidazole derivative, on the rearing and reproduction of Bombyx mori L. were carried out in a hot, wet summer in West Bengal, India. A single dose of 3 μg KK-42/larva induced precocious metamorphosis in a bivoltine hybrid (KPGB x P5) race of B. mori when applied topically to freshly moulted (less than 1-h old) fourth instars, and increased their rearing performance over control tetramoulters. However, cocoon and shell weights, shell ratio and filament length were reduced by the anti-JH treatment. Final body weight and head capsule width of the treated fourth instars were significantly higher than those of the controls. Bivoltine trimoulter males also showed good capacity for mating with multivoltine Nistari females. The possibility of obtaining three-way multi-bi hybrid eggs during the wet part of summer in a tropical climate is discussed.

Rapid size-specific changes in the drift of Baetis bicaudatus (Ephemeroptera) caused by alterations in fish odour concentration.

Chemical cues from fish can alter the behaviour of stream invertebrates in experimental tanks but their effect in natural streams has received little attention. By adding brook trout (Salvelinus fontinalis) odour to a trout stream in the Rocky Mountains of Colorado, USA, we tested whether changes in the concentration of chemical cues from visually feeding predatory fish would alter the drift of mayfly nymphs (Ephemeroptera). Stream water was piped from stream-side tanks with (odour) and without (control) three brook trout to two locations in the stream 3.5 m upstream of drift nets at six replicate sites. Five-minute drift samples were collected downstream from odour and control pipes before, during and after the release of water from the tanks into the stream during both the day and night. Almost all drift occurred at night and consisted predominantly of Baetis bicaudatus nymphs. The odour manipulation had no measurable effect on Baetis drift during the day but statistical power was low. During the night, however, the drift of large (>0.65 mm head capsule width, HCW) Baetis nymphs decreased significantly during the odour addition compared to control drift. In contrast, the drift of small nymphs (≤0.65 mm HCW) increased both during and after the odour addition in comparison to control drift. Since the stream contains brook trout (0.04-0.18 m-2), and water from the stream (presumably containing fish odour) altered the behaviour of fishless-stream Baetis nymphs in another experiment, we conclude that the changes in Baetis drift density were a response to an increase in the concentration of fish odour in the stream. Furthermore, we were able to detect the effect within 5 min. of odour addition, indicating that mayfly behavioural response to trout odour was rapid. These results suggest that mayflies can distinguish different concentrations of trout odour in natural streams and that the response is size-specific, according to the relative risk of predation of large and small Baetis.

YIELD OF OCCLUSION BODIES FROM FOREST TENT CATERPILLAR (LEPIDOPTERA: LASIOCAMPIDAE) LARVAE INFECTED WITH A NUCLEAR POLYHEDROSIS VIRUS

The forest tent caterpillar, Malacosoma disstria Hübner (Lepidoptera: Lasiocampidae), is subject to a variety of naturally occurring infectious diseases, including a nuclear polyhedrosis virus (MdNPV) which has been observed to reach epizootic proportions (Stairs 1966; Myers 1993).Because MdNPV is currently available only in limited quantities for small-scale experimentation, production scale-up is vital to it's potential as a biological control agent against the forest tent caterpillar. Viruses replicate only in living cells, therefore it is necessary to produce viral insecticides either in host insect larvae (in vivo) or in susceptible cell cultures (in vitro). Insect cell cultures have not yet been developed so that large-scale production of baculoviruses are feasible (Cunningham 1995), thus in vivo production must be used. To plan for the scale-up of NPV production, it is necessary to establish the yield of occlusion bodies (OBs) from M. disstria larvae. We report here the yield of OBs from four larval instars inoculated with MdNPV, the time to mortality, head capsule widths, and body weights, and recommend larval instars suitable for further research toward commercial-scale production.

Survival, Development, and Oviposition of Resistant Diamondback Moth (Lepidoptera: Plutellidae) on Transgenic Canola Producing a Bacillus thuringiensis Toxin

We measured responses of diamondback moth, plutella xylostella L., to transgenic and nontransgenic canola, Brassica napus L. Transgenic canola expressed a crylAc gene of Bacillus thurngiensis Berliner resulting in 238 ± 29 ng of Cry lAc protein per milligram of total extractable protein in leaves. We tested 2 Hawaiian strains of diamondback moth: NO-QA was resistant to CrylAc and LAB-PS was susceptible. Larval and pupal durations, pupal weights, and adult emergence of the 2 strains were similar on nontransgenic canola, but differed significantly on transgenic canola. Transgenic canola killed all larvae tested from the susceptible strain. In contrast, for the resistant strain, no differences occurred between transgenic and nontransgenic canola in larval survival and head capsule width at day 5, percentage pupation, pupal weight, percentage adult emergence, and extent of defoliation. For both the susceptible and resistant strains of diamondback moth, no differences were detected between transgenic and nontransgenic canola in feeding initiation or oviposition preference. The lack of discrimination between transgenic and nontransgenic canola by neonates and ovipositing females indicates that host choice behavior is independent from susceptibility to CrylAc. Development of resistant diamondback moth on transgenic canola without any adverse effects provides an example of a pest that has completely overcome high levels of a B. thuringiensis toxin expressed by a genetically engineered plant.

Larval growth and development of the stonefly Pteronarcys californica (Insecta: Plecoptera) in the Crowsnest River, Alberta

We used head-capsule width, wing-pad length, larval recruitment, adult emergence, and MULTIFANTM analysis to determine the life history of the stonefly Pteronarcys californica in the Crowsnest River, Alberta. Embryonic development, incorporating an early diapause, accounts for approximately 1 year of the life cycle. Both sexes spend a further 4 years in the larval stage. Female larvae grow faster than males and so achieve a larger size at emergence. Extended larval recruitment leads to variation in the sizes of larvae of the same year class and probably to cohort splitting. There is a high degree of synchrony in adult emergence, perhaps as a result of a summer diapause in antepenultimate-instar larvae. These phenomena (embryonic diapause, extended larval recruitment, different growth rates of the sexes, cohort splitting, and larval diapause) are possibly typical of aquatic insects with long life cycles.

Development of Diaprepes abbreviatus (Coleoptera: Curculionidae) on Artificial and Citrus Root Substrates

Measurement of head capsule widths showed that larvae of D. abbreviatus generally have 10 or 11 instars when reared on artificial diet. The growth ratio for head capsules was j:reater during stadia for the I-5th instars and declined after the 6th. Head capsule widths and larval growth increased steadily for 71 d, at which time, all larvae were 7-10th instar. Larval growth reached a plateau at 114 d during stadia at 9-11th instar and remained unchanged to 188 d. The mean time for development of 1st to 7th instars was less compared with instars >7th. A frequency distribution based on head capsule size for greenhouse- and field-collected larvae fed citrus roots over time had similar stadia peaks to larvae reared on artificial diet in the laboratory. Weight of larvae with head capsule widths >1.0 mm increased slowly within stadia, whereas a greater increase in larval weight was observed for larvae with capsule widths >1.0 mm. Variation in larval weight for each stadium was also greater for larvae with head capsule widths >1.0 mm. Most larval weight gain occurred during stadia at 6-8th instar, suggesting higher food consumption at these developmental stages. Larval weight increased steadily within the initial 71 d but declined slowly thereafter. The mean weight for instars reared on artificial diet was greater than for either greenhouse- or field-collected larvae. The mean weight for larvae fed citrus roots in the greenhouse was smaller than for larvae feeding on roots in the field. On artificial diet, only a few larvae developed to pupae. Approximately 70% of the larvae pupated at the 10th instar, whereas others pupated at the 11th instar. The mean time ± SEM required for larval development to pupae, larvae to adult, and pupae to adult was 153.3 ±28.0 d, 158.3 ± 20.7 d, and 17 ± 3.8 d, respectively. Mean larval weight before pupation was 480.4 ± 102.5 mg, mean pupal weight 378.2 ± 66.1 mg, and mean adult weight 276.0 ± 51.6 mg. Larvae lost 20.3% of their live weight during metamorphosis to pupae and pupae lost 24.7% of their live weight in becoming adults.

Diamondback Moth (Lepidoptera: Plutellidae) Resistance of Brassica napus and B. oleracea Lines with Differing Leaf Characteristics

Canola quality oil produced from oilseed rape, Brassica napus L. (Brassicaceae), is a relatively new crop in the United States and is damaged by a number of insect pests, including the crucifer specialist diamondback moth, Plutella xylostella (L.). Greenhouse tests were performed to evaluate resistance in normal-leafed ('Bingo', 'Cobra', 'Oscar') and glossy-leafed B. napus plants ('glossy Bingo' and plant introductions (PI) 469895, 470055, 470055-2, and 470064) to identify potential resistant sources to diamondback moth. Normal-leafed PI 171538, originally described as B. napus and recently reclassified as B. oleracea, also was evaluated for resistance with B. napus plants and B. oleracea cultivars of broccoli, 'Green Comet', 'Green Valiant', and collard 'Vates'. Plants of Cornell line 92-8611, a broccoli with glossy-leaf type (glossy broccoli), were used as the resistant control in all trials. B. napus entries failed to show feeding nonpreference or antibiosis comparable to that of glossy broccoli, Furthermore, no significant differences were detected between normal and glossy-leafed B. napus lines for most of the parameters tested. Within the tested B. napus entries, PI 470055 exhibited low levels of feeding damage in the restricted-feeding test and some level of antibiosis against diamondback moth. However, B. oleracea entry PI 171538 showed a greater or comparable level of resistance to that of glossy broccoli. Nonpreference for larval feeding and adult oviposition were exhibited by PI 171538. In feeding tests, PI 171538 was less defoliated compared with other B. oleracea entries. Diamondback moth larvae reared on PI 171538 leaves for 5 d had a lower head capsule width compared with larvae reared on other entries. In an oviposition preference test, PI 171538 received 0.9% of eggs as compared with normal-leafed B. napus plants (2.1-4.4%) and glossy broccoli, which received 7.0% of eggs. The experiments indicate that the normal-leafed B. oleracea entry PI 171538 has considerable resistance against diamondback moth. PI171538 is a newly discovered source of resistance and has leaf characteristics that differ from the previously reported diamondback moth-resistant B. oleracea lines.

Greenhouse and field evaluations of transgenic canola against diamondback moth, Plutella xylostella, and corn earworm, Helicoverpa zea

AbstractCanola (Brassica napus L.) cultivars Oscar and Westar, engineered with a Bacillus thuringiensis (Bt) cryIA(c) gene, were evaluated for resistance to lepidopterous pests, diamondback moth, Plutella xylostella L. (Plutellidae) and corn earworm, Helicoverpa zea (Boddie) (Noctuidae) in greenhouse and field conditions. In greenhouse preference assays conducted at vegetative and flowering plant stages, transgenic plants recorded very low levels of damage. A 100% diamondback moth mortality and ≈90% corn earworm mortality were obtained on transgenic plants in greenhouse antibiosis assays. The surviving corn earworm larvae on transgenic plants had reduced head capsule width and body weight. Mortality of diamondback moth and corn earworm were 100% and ≈95%, respectively, at different growth stages (seedling, vegetative, bolting, and flowering) on the transgenic plants in greenhouse tests. In field tests conducted during 1995–1997, plots were artificially infested with neonates of diamondback moth or corn earworm or left for natural infestation. Transgenic plants in all the treatments were highly resistant to diamondback moth and corn earworm larvae and had very low levels of defoliation. Plots infested with diamondback moth larvae had greater damage in both seasons as compared with corn earworm infested plots and plots under natural infestation. After exposure to defoliators, transgenic plants usually had higher final plant stand and produced more pods and seeds than non‐transgenic plants. Diamondback moth injury caused the most pronounced difference in plant stand and pod and seed number between transgenic and non‐transgenic plants. Our results suggest that transgenic canola could be used for effective management of diamondback moth and corn earworm on canola.

Revision of the life history of the High Arctic moth Gynaephora groenlandica (Wocke) (Lepidoptera: Lymantriidae)

Many studies have explored the adaptations of arctic and alpine Gynaephora species (Lepidoptera: Lymantriidae) to their environment, and base-line life-history information is important for the interpretation of such studies. Data and observations on G. groenlandica (Wocke) collected in recent years at Alexandra Fiord, Ellesmere Island, Canada, contradict some of the life-history information previously published for this species from the same site. Detailed analysis of larval head capsule widths and consideration of growth ratios indicate that there are seven rather than six larval instars and that the pattern of development does not deviate significantly from that defined by the Brooks-Dyar rule. Field-rearing of larvae indicates that first-instar larvae overwinter, while field- and laboratory-rearing both indicate that larvae moult once per year, every year. These data and observations greatly shorten and simplify the life history from that previously published and suggest a life cycle of 7 rather than 14 years. This revised life cycle is not presented as an absolute, in recognition of the potential for individual variation, but rather as typical of the developmental pattern of most of the population. As such, it should provide a useful base line for further studies, especially those addressing the influence of predicted climate change in the Arctic.

Selecting a character for identifying larval instars of the lepidopteran stemborers Sesamia calamistis Hampson (Noctuidae) and Eldana saccharina walker (Pyralidae) in maize

In experiments to select a character for identifying larval instars in Sesamia calamistis and Eldana saccharina, body length, body width and head capsule width were measured in populations reared on artificial diet. Seven- instars were found in S. calamistis and 5 in E. saccharina. For both species, body length was determined to be the best characteristic to distinguish instars because it was easy to measure and had the smallest error.

General Program for Determining Instar Distributions from Headcapsule Widths: Example Analysis of Mountain Pine Beetle (Coleoptera: Scolytide) Data

Determining instar distributions from field-collected insect samples is a common problem in insect ecology. We describe a generalized computer program (HCAP) that determines an optimum separation rule based on the distribution of headcapsule widths. The program is initiated through visual interaction with the user to determine starting points for separation rules. HCAP then determines the optimum instar classification rules; estimates of means and standard deviations of headcapsule widths for each instar; estimated number in each instar; and probabilities of misclassification. Application of the program is illustrated by the analysis of 3 data sets of >10,000 observations of headcapsule widths obtained from field collections of larvae of the mountain pine beetle, Dendroctonus ponderosae Hopkins. This analysis resulted in finding significant differences between larvae collected from different hosts (ponderosa pine, Pinus ponderosae Lawson, and lodgepole pine, Pinus contorta Douglas variety latifolia Engelmann) and ecological circumstances (outbreak phase and geographic location). These results indicate that caution must be taken when extrapolating published results to new data or from one ecological situation to another.

Physiological and endocrine changes associated with polydnavirus/venom in the parasitoid–host system Chelonus inanitus-Spodoptera littoralis

As shown earlier, parasitization by the egg–larval parasitoid C. inanitus causes in its host the precocious onset of metamorphosis in the 5th instar followed by developmental arrest in the prepupal stage. Polydnavirus/venom were shown to be responsible for the developmental arrest. We investigated how polydnavirus/venom affect growth of the host larvae and found that head capsule widths were smaller from the 4th to 6th stadium and weights were lower in the 6th stadium in polydnavirus/venom-containing larvae than in non-parasitized larvae. In an attempt to identify endocrine parameters that are modified by polydnavirus/venom and might be responsible for the developmental arrest in the prepupa, we compared juvenile hormones, juvenile hormone esterase and ecdysteroids between non-parasitized and polydnavirus/venom-containing larvae from the 4th instar until pupation or developmental arrest, respectively. Obvious differences became manifest only in the 6th instar at the pupal cell formation stage, i.e. 12 days after entry of polydnavirus/venom into the host egg. Then, prothoracic glands of polydnavirus/venom-containing larvae released less ecdysteroids and ecdysteroid titres were lower than in non-parasitized larvae; this was followed by a delayed, reduced and desynchronized increase in prepupal juvenile hormones and juvenile hormone esterase and a slightly modified metabolism of ecdysone. This indicates that polydnavirus/venom affects the endocrine system of the host only after pupal commitment and that inhibition of prothoracic gland activity is the first detectable effect.

Oviposition, Development, and Host Preference of the Cross-Striped Cabbageworm (Lepidoptera: Pyralidae)

The cross-striped cabbageworm, Evergestis rimosalis (Guenee), is a potentially destructive pest of Brassica crops. Because little is known about its biology, we determined its development on broccoli, Brassica oleracea variety italica Plenck, at 5 temperatures ranging from 15 to 35°C. Development from egg to death of adult was 114.8, 61.2, 47.6, 31.4, and 18.2 d at 15, 20, 25, 30, and 35°C, respectively. Oviposition increased from 7.4 eggs at 15°C to a maximum of 80.9 eggs at 30°C, but decreased to 9.8 eggs per female at 35°C. Eggs were laid in small overlapping masses with number of eggs per mass ranging from 3.7 at 15°C to 17.4 at 30°C. Egg hatch between 20 and 30°C exceeded 90%, but was lower at 15°C (53.8%) and at 35°C (11.2%). There were 4 instars with head capsule widths of 0.34, 0.56, 1.04, and 1.66 mm, respectively. Significant differences were not found in pupa size, adult wing expanse, or body length between sexes. The cross-striped cabbageworm had 4 population density peaks during 1992 and 1993, the 2 in the summer being greater than the 2 in the fall. Host preference field tests with 8 Brassica cultivars showed that Brussels sprouts and collards were the most preferred and cabbage and kale were the least preferred. The population density of a gregarious braconid endoparasitoid of E. rimosalis, Cotesia orobenae Forbes, peaked several weeks after the host.

Biology and Morphology of Chelonus sp. nr. curvimaculatus (Hymenoptera: Braconidae) as a Parasitoid of Pectinophora gossypiella (Lepidoptera: Gelechiidae)

A general description of the life stages of Chelonus sp. nr. curvimaculatus, an egg-larval parasitoid of pink bollworm, Pectinophora gossypiella (Saunders), is presented. Pink bollworms were reared in the laboratory on a wheat germ diet. At 29°C, parasitoid eggs (0.12—0.18 mm) begin to eclose ≈22 h after oviposition. Three instars occur in this species. The 1st instar is endoparasitic and ranged in length from 0.14 mm (neonate) to 1.25 mm (≈9 d old, end of the 1st stadium). The 2nd instar also is endoparasitic and is 1.89–3.04 mm long. This stadium lasts ≈2–3 d. The 3rd instar is an average of 3.82 mm long and is endoparasitic early in its development but becomes ectoparasitic toward the completion of its development. This stadium lasts =3 d. The pupal stage lasts ≈6–7 d. Adult parasitoids begin to emerge ≈21 d after oviposition. Parasitized and unparasitized pink bollworm larvae developed through 4 stadia. Larval head capsule widths, body lengths, and weights of parasitized pink bollworms are significantly smaller than those of unparasitized larvae during the 3rd and 4th stadia. Parasitized 4th-instar pink bollworms have a mean head width of 0.8687 mm, body length of 6.28 mm, and weight of 6.9 mg. Fourth-instar unparasitized pink bollworm measurements were 1.0743 mm, 9.31 mm, and 17.7 mg, respectively.

Occurrence of non-stationary larval moults during diapause in the corn-stalk borer, Sesamia nonagrioides (Lepidoptera: Noctuidae)

Last-instar larvae of the corn stalk borer, Sesamia nonagrioides (Lep.: Noctuidae), enter a facultative diapause under short photoperiods. In this noctuid, diapause development is characterized by the ability of larvae to perform several larval moults (up to seven) before pupation. Surprisingly, these supernumerary moults were not stationary and larval growth did occur as shown by growth in head-capsule width and weight of diapausing larvae. These heavy diapause larvae produced heavier pupae than non-diapausing strains. The number of supernumerary moults varied for insects, although they were reared under the same conditions. Pupal weight of diapause larvae was independent of the number of supernumerary moults performed. Using a radiochemical assay, we show that corpora allata from Sesamia nonagrioides larvae produced juvenile hormone (JH) -III, JH-II and their respective diols and acids. Although corpora allata of day-4 diapause-destined larvae exhibited the same biosynthetic pattern, no labelled products could be detected in the incubation medium containing corpora allata from non-diapausing larvae of the same age. Biosynthetic activity of the corpora allata was detected throughout diapause.

Regression analysis of linear body dimensions vs. dry mass in stream macroinvertebrates

The regression equations for predicting dry mass from linear body dimensions presented in this study allow to calculate biomass of benthic macroinvertebrates from mountain streams of Central Europe. For the description of length-dry mass relationships, the power function y = a . x b or in a few cases the quadratic function y = a + b . x + + c . x 2 proved to be the best models. The relationships between linear body dimensions - e.g. body length (BL) vs. head capsule width (HW) - followed a simple linear model of the type y = a x + b or again a quadratic one. Data of literature imply that the relationships derived from this study should be restricted to carbonate streams.

Incidence of Chironomid Phoretics on Hellgrammites in Streams of Southern Maine

Hellgrammite nymphs (Nigronia serricornis Say) were collected in streams of southern Maine, 1995-1996, to assess the rate of phoresy by midge larvae. The number, location, and identification of phoretic midge larvae (Diptera: Chironomidae) were recorded for each nymph. Nanocladius (Plecopteracoluthus) n. sp. was the only chironomid species identified from hellgrammite hosts. Phoretic midges occurred in three of four populations and were observed on approximately 55% of all individuals examined (n = 108). However, frequency of phoresy ranged from 0 to 86.4%, depending on the stream. Midge phoretics occurred at a mean rate of over 1.5 per host and the number of phoretics was significantly correlated with host head capsule width. The dorsum of the first abdominal segment was the most frequent attachment site for midges. Observed frequency of phoresy in these streams were similar to published rates for chironomid/hellgrammite associations. This is the first documentation of chironomid phoresy on hellgrammites in Maine.

Determination of instar for the window gnat Sylvicola fenestralis (Diptera: Anisopodidae)

The Window Gnat Sylvicola fenestralis is a major nuisance fly inhabiting the biological filters of sewage treatment works. Analysis of measurements of head capsule width, head capsule length and larval body length of 303 laboratory hatched and field collected larvae, established that this species possesses four larval instars. The size range of each instar for the three parameters was determined by plotting cumulative frequency against sample category on probability paper; the inflexion curve method. The growth rate between instars was shown to fit Dyar's rule for all three parameters. The efficacy of many insecticides depends on accurate targeting against the most susceptible stage of the insect life cycle. Hence a more detailed knowledge of the instars of S. fenestralis will allow for the most effective control of this nuisance species.

Studies on the biology of Dinoderus distinctus Lesne (Coleoptera: Bostrychidae)

Some aspects of the biology of Dinoderus distinctus Lesne was studied under laboratory conditions in Port-Harcourt, Nigeria. Whole maize flour was used as food substrate. The mean incubation period of egg was 6.04 ± 0.14 days. The growth ratio of the larval head capsule width. ranged from 1.32 to 1.40. Four larval instars were observed, the prepupal stage lasted for not more than 24 hours and the pupal stage 4-6 days. The period from larva to adult was 26.97 ± 10.9 days. Preoviposition period gave a mean of 24.68 ± 2.14 days. The mean number of eggs laid per female was 162.68 ± 19.36 with the peak of oviposition at the 8th week after adult emergence. The mean longevity of male and female adult on broken maize was 126.04 ± 15.18 days and 137.68 ± 13.54 days respectively.