Head Capsule Width Research Articles

Separation of Cat Flea (Siphonaptera: Pulicidae) Instars by Individual Rearing and Head Width Measurements

Two methods to verify whether head width measurements fit Dyar's rule were evaluated for the separation of instars of the cat flea, Ctenocephalides felis (Bouché). Individual rearing was a reliable method of determining larval instar but was labor-intensive. The mean observed head widths were significantly different for each instar (first instar, 0.164 mm; second instar, 0.201 mm; third instar, 0.260 mm) and showed no sexual dimorphism. Head capsule width increased roughly 25% from instar to instar with geometrically progressing growth in accordance with Dyar's rule. However, head capsule width cannot be used to determine the instar of randomly selected larvae because the measurements overlap broadly between instars.

Temperature‐dependent variation in Anopheles merus larval head capsule width and adult wing length: implications for anopheline taxonomy

Seasonal variations in mosquito larval head capsule width and adult female wing length were investigated in a field population of Anopheles merus Dönitz at Nceswana Lake, Ophansi, within the endemic malaria area of Natal, South Africa. An inverse relationship was detected between each of these morphological characters and seasonal fluctuations in air/water temperatures. Mean head capsule width in all larval instars decreased by 4.8-7.9% in summer, while mean wing length decreased by 19.6%. These changes are discussed in relation to the annual range in mean air temperature in southern Africa and the distribution of An.merus. Implications for the use of such morphological characteristics in existing taxonomic keys are discussed.

Taxus, Control of Black Vine Weevil (BVW) Larvae, Wooster, Ohio, 1989

Abstract Taxus plants, growing in 1 pint (0.47 liter) containers obtained from a nursery in NE Ohio, were used to evaluate conventional insecticides and entomogenous nematodes against BVW larvae. Plants were repotted 27 Jun in 1 gal (3.9 liter) containers with a 3:1 (pine barkipeat) medium mix. Dolomitic lime was added to the mix at 6 lb/cuyd. Plants were fertigated with 200 ppm N, P, K (Peter’s 20-20-20) every Mon, Wed, and Fri. Beginning 7 Aug, water alone was applied via over-head irrigation. BVW eggs were collected from adults held at 22°C and 80%+ RH and a 16 h photoperiod. On 7 Aug, all containers received 75 brown eggs, placed 2.54 cm beneath the surface of the potting medium. An additional 58 brown eggs were placed 16 Aug, as before. Hatchability was 89 and 77 percent, respectively. Treatments were applied 8 Nov when larval head-capsule width averaged 1.63 mm. A nematode stock suspension was made by placing 1 unit of Otinem (50,000,000 nemas) in 10 gallons of water. Nemas were applied volumetrically in 473 ml of water to deliver predetermined numbers of nemas per pot. AgSorb flake (2.4 grams) was added to the finished suspension for each pot of selected treatments. All finished suspensions were mixed thoroughly in a pint jar and poured over the potting medium to achieve even distribution. Other insecticide treatments were applied by mixing the predetermined pot rate in 473 ml of water which was poured over the pot medium, as before. All plants were watered prior to and after application. Plants were then hand watered every Mon, Wed, and Fri. Treatment effects were evaluated 28-29 Nov, when larvae were nearing maturity, by removing the plant and medium from each container and counting the number of larvae and recording their condition. Some pupation was occurring when evaluations were made.

Modification of the Effect of Bacillus thuringiensis on Sunflower Moth (Lepidoptera: Pyralidae) by Dietary Phenols

The sunflower moth, Homoeosoma electellum (Hulst), a major pest of sun- flower (Helianthus annuus L.), is susceptible to Bacillus thurl.ngiensis Berliner, but field control has been inconsistent. Our study was done to determine whether phenolics in damaged sunflower tissue are in a conjugated or free form and whether they influence the toxicity of B. thurl.ngiensis to the sunflower moth. Larvae fed diets containing B. thurl.ngiensis had reduced survival and growth. The LD50of B. thurl.ngiensis was 52 international units of potency per gram of diet. Phenolic acids are general biocides. They were found in sunflower hybrids largely in the free (nonconjugated) form after tissue injury. The phenolics were probably converted from the conjugated form to the free form after release of glycosidases. By themselves and at the doses tested, specific phenolic acids did not affect sunflower moth survival and growth. When cinnamic or p-coumaric acids were combined with B. thurl.n- giensis in artificial diet, growth (measured as width of sunflower moth head capsules) of larvae was reduced compared with that of larvae fed diets containing B. thurl.ngiensis. High phenolic sunflower might increase the effectiveness of B. thuringiensis as an agent for sunflower moth control.

Biotic Indicators of Host Preference by the Bagworm (Lepidoptera: Psychidae)

Mortality, bag length, and larval head capsule width of the bagworm, Thyridopteryx ephemeraeformis (Haworth), were examined in greenhouse tests as indicators of host preference for deciduous and coniferous hosts, both as donor and recipient host. Neonate larvae reared from eggs collected from deciduous and evergreen hosts were placed on selected tree species and allowed to feed for 30 d. Arborvitae ( Thuja occidentalis L.) and black locust ( Robinia pseudoacacia L.) had lower mortalities compared with eastern white pine ( Pinus strobus L.), honeylocust ( Gleditsia triacanthos L.), and American sycamore ( Plantoides occidentalis L.). Original host had no specific effect on mortality. Significantly longer bags and a corresponding higher frequency of older instars were observed when bagworm originated from black locust compared with other hosts. Compared with other sources, larvae obtained from arborvitae consistently produced longer bags on each host species. This is the first demonstration of a significant difference in bagworm development for each of the biotic factors studied, and the first identification of black locust as a superior host for bagworm. The effect of host shape on rate of infestation is discussed.

Impact of fauna on mortality and size of Haematobia spp. (Diptera: Muscidae) in natural dung pads in Australia and South Africa

Two field experiments examined the effect of dung fauna on the breeding success of Haematobia irritans exigua DeMeijere at Rockhampton, Australia, and Haematobia thirouxi potans (Bezzi) at Hluhluwe Game Reserve, Republic of South Africa. Dung pads naturally infested with Haematobia eggs were produced by cattle at Rockhampton and by Cape buffalo at Hluhluwe. Pads were either exposed to, or protected from, all dung fauna for various periods up to four days. The effect of dung fauna on the immature stages of Haematobia spp. was estimated from differences in the numbers and size of flies that emerged from treated and control pads. In the first experiment, pads produced during the morning and afternoon were exposed for one, two or four days on seven different occasions. At Rockhampton, fauna-induced mortality was substantial but did not increase significantly after the pads had been exposed for one day. At Hluhluwe, in pads produced during the morning, fauna-induced mortality rose substantially with duration of exposure; in afternoon pads the increase was not statistically significant. Fly size, indicated by the mean headcapsule width of surviving females, decreased as exposure of pads to dung fauna increased from zero to four days, except in the afternoon pads at Rockhampton. In the second experiment, pads produced in the afternoon were exposed in the field for four days on 16 occasions at Rockhampton, and on 17 at Hluhluwe. Fauna-induced mortality averaged 79% and 84%, respectively. The activities of the dung fauna reduced the headcapsule widths of surviving flies by an average 2% at Rockhampton and by 7% at Hluhluwe, despite similar levels of dung dispersal. The dung fauna associated with the highest mortality of H. irriatans exigua at Rockhampton were Scarabaeinae and Macrocheles spp., while there were no significant associations between fly mortality and particular fauna in the Hluhluwe data.

ROLE OF 2,4-DIHYDROXY-7-METHOXY-1,4-BENZOXAZIN-3-ONE (DIMBOA) IN THE RESISTANCE OF MAIZE TO WESTERN CORN ROOTWORM, DIABROTICA VIRGIFERA VIRGIFERA (LECONTE) (COLEOPTERA: CHRYSOMELIDAE)

Abstract2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), the major hydroxamic acid present in corn root, was studied for its effects on western corn rootworm, Diabrotica virgifera virgifera (LeConte). Exogenously applied DIMBOA caused mortality in western corn rootworm larvae feeding on fresh corn roots. The LC50 (lethal concentration for 50% mortality) value (fiducial limits) was 153 ppm (108–209) and the LC90 value was 917 ppm (560–2297). The deleterious effects of DIMBOA on western corn rootworm larvae possibly are due to both feeding deterrence and toxicity. In a replicated pot trial during two growing seasons, two corn lines developed by Agriculture Canada from CIMMYT collections, ITR 3872 with high DIMBOA content in roots, and NTR-2 Ger. 4042 with low DIMBOA content in roots, were evaluated for resistance to western corn rootworm larvae. The results indicated that the high DIMBOA line (but not the low DIMBOA line) stressed western corn rootworm larvae to produce inferior adults based on the measurement of adult emergence number, adult weight, and adult head-capsule width. The effect of western corn rootworm on both corn lines with different DIMBOA levels was measured based on plant growth parameters including plant height, stem thickness, plant fresh weight, root fresh weight, plant dry weight, and root dry weight. ITR 3872 (high DIMBOA) showed significantly less damage than NTR-2 Ger. 4042 (low DIMBOA) in almost all plant parameters measured. The results suggest that DIMBOA may in some instances contribute to the resistance of corn to western corn rootworm larvae.

Population Dynamics and Seasonal Biology of the Alfalfa Weevil (Coleoptera: Curculionidae) on Alfalfa in Louisiana

The biology of the alfalfa weevil, Hypera postica (Gyllenhal), was studied in Louisiana during 1986 to 1988 on alfalfa, Medicago sativa (L.). Post-estivation migration of adults in the fall occurs during late November and early December. Fall oviposition during December and January resulted in 58 to 81% of alfalfa stems with egg clusters. Egg viability of eggs laid in the fall was estimated at 75%. Alfalfa weevil egg clusters contained an average of 10.9 (1986–1987) to 13.3 (1987–1988) eggs per cluster. The position of egg clusters in the alfalfa canopy, relative to the base of the stem, indicated that 95 and 50% of all clusters were below 40 and 18 cm, respectively. An ovipositional preference was found with eggs generally laid between the upper 30% and lower 80% regions of the alfalfa stem. Alfalfa weevil larvae were first detected in February. Egg eclosion in 1987 was highly synchronized as indicated by larval counts increasing from 4 to 90 per sweep between 3 and 10 February. In 1988, larval emergence gradually increased from 4 February (≦10/sweep) to 3 March (60/sweep). Head capsule widths were 0.15, 0.28, 0.42, and 0.55 mm for first, second, third, and fourth instars, respectively. Corresponding body lengths were 1.4, 2.8, 4.6, and 6.6 mm for first, second, third, and fourth instars, respectively. The marked decline of alfalfa weevils in April is presumably indicative of adult migration from alfalfa to summer estivation sites. Degree-day accumulations are used to describe and predict spring hatch of the alfalfa weevil in Louisiana.

Temperature-Dependent Development and Survival Rates of Culex quinquefasciatus and Aedes aegypti (Diptera: Culicidae)

Development, growth, and survival of Culex quinquefasciatus Say and Aedes aegypti (L.) were determined at six constant temperatures (15, 20, 25, 27, 30, 34 degrees C). The Sharpe & DeMichele four-parameter model with high-temperature inhibition described the temperature-dependent median developmental rates of both mosquito species. In both species, body size generally decreased as temperature increased. Head capsule widths in all instars in both species were significantly greater at 15 than at 30-34 degrees C. Except for the third instar of Ae. aegypti, the larval body lengths in both species were significantly greater at 15 than at 34 degrees C. All instars and pupae of both species and the adults in Cx. quinquefasciatus were significantly heavier at 15 than at 27-34 degrees C. In Cx. quinquefasciatus, survival from eclosion to adult emergence was highest in the range from 20 to 30 degrees C (85-90%) and dropped drastically at 15 (38%) and 34 degrees C (42%). In Ae. aegypti, survival to adult stage was high at 20 (92%) and 27 degrees C (90%) and lowest at 15 degrees C (3%).

Influence of temperature, photoperiod and nutrition on growth and consumption of Chaetopteryx villosa (Trichoptera)

Chaetopteryx villosa Fabr. is uni‐ or semivoltine. The species was reared at 6°C and 10°C (8 h light, 16 h dark = LD 8/16) and at 10°C and 14°C (LD 14/10). Larval instar duration and pupal period decreased with increasing temperature. Instars II‐IV were completed within 2‐5 wk. Vth instar larvae pupated after two to twelve months. Pupal development required between one and three months. At 6°C no specimens pupated. At 10°C, LD 14/10 accelerated the development of instars II, IV, V and pupae. Head capsule widths were different between laboratory and field specimens. Relative consumption rate (RCR) ranged between 3.07 ± 1.12 (instar II, 14°C) and 0.09 ± 0.05 (instar V 6°C) mg mg‐1 d‐1. Growth rate, relative growth rate and efficiency of conversion were calculated. In a field experiment fine particulate versus coarse particulate organic material were tested as food sources. FPOM‐fed specimens were smaller than those fed with FPOM + CPOM. Pupation was initiated earlier in the FPOM fed group and lasted longer than in the other groups.

Early Development of Nymphs and Establishment of Hindgut Symbiosis in Cryptocercus punctulatus (Dictyoptera: Cryptocercidae)

Young families of the wood-feeding cockroach Cryptocercus punctulatus Scudder are described. Brood size immediately following hatch is 36 ± 13 (x ± SD, n = 168) nymphs; the sex ratio is 1:1. The head capsule width and antennal segmentation of the first four instars are described. The protozoan symbiosis of the hindgut paunch appears established by the third stadium. Neonates develop to the third or fourth instar by their first winter.

Head-Capsule Width of Lobesia botrana (Lepidoptera: Tortricidae) Larvae Reared on Three Different Diets

Both sexes of Lobesia botrana (Denis & Schiffermueller) were found to have five instars, as determined by measurements of head-capsule widths of larvae reared in the laboratory on healthy grape berries, berries infected by the fungus Botrytis cinerea , or on an artificial diet. In the first two instars there were no significant differences in widths of head capsules between larvae reared on the different diets. However, differences became more pronounced in later instars and they were significant between the three diets in fifth instars. Larvae fed on infected berries generally had the largest widths. There was no overlapping in head-capsule width between the various instars. The increase in head-capsule widths approximately followed Dyar's rule but is more accurately described by a second-degree polynomial equation.

Characterization of Larval Development in Pseudoplusia includens (Lepidoptera: Noctuidae)

The growth and development of larvae of the soybean looper, Pseudoplusia includens (Walker), were examined, and a staging protocol for the penultimate and ultimate instars was developed. P. includens larvae pupated after five or six stadia. A critical size threshold was associated with the metamorphic instar, and larvae that failed to attain this threshold as a fifth instar molted to a sixth instar before pupating. Larvae that pupated after five or six stadia could be distinguished by the third or fourth stadium on the basis of head capsule width and weight. A number of morphological and behavioral characters were associated with phases of the penultimate and ultimate stadia. For larvae pupating after five stadia, the fourth and fifth instars were staged using these characters in combination with certain time-weight relationships. In the fourth instar, PTTH-ecdysone release sufficient to stimulate apolysis-ecdysis occurred 22–26 h after ecdysis to the stadium. In the fifth instar, PTTH-ecdysone release sufficient to stimulate pupal cutical tanning occurred 72–76 h after ecdysis.

Comparative biology of two phycitid moths, Plodia interpunctella (Hubn.) and Ephestia cautella (Wlk.) on some selected food media

The life cycles of two phycitid moths, Plodia interpunctella (Hubn.) and Ephestia cautella (Wik.) were studied under ambient laboratory conditions on groundnut, maize, sorghum, wheat and standard medium (maize/wheat/glycerol, 8:8:1, w/w). Egg hatchabilities were found to be 98.6 and 91.6% for P. interpunctella and E. cautella respectively. Five larval instars were recorded for each species based on head-capsule width measurements. The growth ratios of the larval head-capsule width ranged from 1.08–1.72 in P. interpunctella: and 1.33–1.57 in E. cautella. These ranges fall within the acceptable range in Dyar’s rule. Mean fecundities ranged from 96.83 ± 0.31 on wheat to 190.87 ± 0.47 on standard medium for P. interpunctella; and 96.83 ± 0.31 on groundnut to 192 ± 1.33 on standard medium for E. cautella. Mean developmental periods of the two moths on the selected food media ranged from 25.65 days on standard medium to 46.11 days in broken wheat for P. interpunctella; and 26.95 days in broken sorghum to 40.14 days in ground maize for E. cautella.

Honeylocust Clonal Effects on Developmental Biology of Mimosa Webworm (Lepidoptera: Plutellidae)

Mimosa webworm, Homadaula anisocentra Meyrick, larvae were reared in the laboratory on five honey locust clones: ‘Imperial,’ ‘Moraine,’ ‘Shademaster,’ ‘Skyline,’ and ‘Sunburst.’ Larvae fed ‘Moraine’ had significantly smaller head capsule widths and pupal weights, longer larval development times, and lower adult fecundity. Fecundity was most affected by the cultivar used for rearing. Adult females reared on ‘Moraine’ foliage produced approximately 44% fewer eggs than did females reared on the other four cultivars. Such reduced fecundity theoretically could affect webworm infestation levels of isolated ‘Moraine’ trees in urban areas. Larval and pupal mortality were unaffected by cultivar. Although we observed statistically significant detrimental effects from feeding on ‘Moraine’ foliage, differences were small and may not be biologically significant.

Morphometry and biomass determination of dominant mayfly larvae (Ephemeroptera) in running waters

Length-mass regressions and length-carbon mass regressions have been developed to estimate biomass from measured length parameters for four different taxa of mayfly larvae; special attention has been focused on practical applicability. Body length, head-capsule width, mesonotum and pronotum width are the most suitable length parameters among seventeen body dimensions considered here; as a rule, a power function y=ax b is qualitatively better than a linear, exponential or square power function. The choice of a regression model depends on the respective body dimension and the measuring range. These length-biomass regressions obtain considerable significance for practical applicability in production biology

Bionomics and Seasonal Abundance of the Banded Sunflower Moth (Lepidoptera: Cochylidae) on Cultivated Sunflower in the Northern Great Plains

The banded sunflower moth, Cochylis hospes Walsingham, is a pest of cultivated sunflower, Helianthus annuus L., in the northern Great Plains. Adults were first detected between 7 and 11 July in each year between 1983 and 1986. Adult population peaks aldo showed little variation among years, appearing on 22-25 July each year. Oviposition on the heads (capitula) occurred when plants were in the early-bud stage through anthesis (R2-6). Sunflower plants were in the early bud stage (R2-3) when larvae were initially found between 14 and 23 July each year. Larvae were present in sunflower heads for 6-10 wk and reached peak abundance in early to mid-August. After eclosion, larvae fed on the inner surface of the head bracts or florets. The entire immature seed may be consumed by the developing larva. Older larvae (third to fifth instars) entered and fed on mature seeds after chewing a hole in the apical end of the hull (pericarp). After consuming the majority of the kernel, larvae moved to a new seed. Mature larvae dropped to the soil and constructed silken cocoons to overwinter. Linear regression analysis of measurements of head capsule width and body length substantiated that the larvae develop through five instars. Seasonal patterns of the life stages of banded sunflower moth were similar, but population densities varied among years. There was one generation per year. Each larva consumed more than six mature sunflower seeds.

The Phenologies of Cotesia-Urabae, Dolichogenidea-Eucalypti (Hymenoptera, Braconidae) and Their Host Uraba-Lugens (Lepidoptera, Noctuidae) in the Adelaide Region

A field study was undertaken to determine the phenologies of the solitary larval endoparasitoids Cotesia urabae and Dolichogenidea eucalypti in relation to that of their bivoltine host Uraba lugens. C. urabae had two generations within both the summer and the winter generation of U. lugens, and D. eucalypti had two generations in the summer but only one generation in the winter. D. eucalypti parasitised a narrower range of host sizes in the field. Both parasitoids attacked recently hatched (typically 1st instar) or 'small hosts' at the beginning at each host generation. In summer D. eucalypti was the first to emerge from hosts, but both D. eucalypti and C. urabae, emerged from hosts which had modes of 0.85-1.05 mm in head capsule width and 0.9-1.5 mg in dry weight (mid hosts). In winter, C. urabae emerged from hosts which had modes of 1.15 mm in head capsule width and 2.7 mg in dry weight (large hosts). Both species in summer, and C. urabae in winter, then proceeded to parasitise hosts of around these sizes to commence second parasitoid generations. In its second generation in summer and its first generation in winter, D. eucalypti typically emerged after most unparasitised hosts had pupated. Both species of parasitoid overwintered within the larval stage of their host. Levels of parasitisation appeared to be low, and dropped between first and second generations within each host generation. It was concluded that C. urabae and D. eucalypti displayed continuity of generations and a high level of synchronisation with U. lugens in the Adelaide region.

Variation in the number of larval instars of the brownheaded leafroller,Ctenopseustis obliquana(Lepidoptera: Tortricidae) at constant laboratory temperatures

Abstract Larvae of a laboratory population of the brownheaded leafroller (BHLR), Ctenopseustis obliquana (Walker) (Lepidoptera: Tortricidae) developed through 5 or 6 larval instars for both sexes when reared on an artificial diet at 20°C, 50–60% RH, and 18 h photoperiod. Comparison of the life cycle of the two developmental groups showed that the 6 instar group had a greater head-capsule width in the final instar, a longer larval developmental period, heavier pupae and female adults, and a higher egg fertility. The lower the total number of instars, the greater the increase in the head capsule widths between instars. Proportions of larvae in the two instar groups were influenced by the rearing and storage temperatures in the egg and first instar stages. Compared to the incidence of 6 instars in larvae reared at 20°C, eggs developed at 10°C produced 19% more 6 instars, and first instar larvae held at 25°C produced 32% more 6 instars.

Taxus, Black Vine Weevil Larvicide Dip Test, Lake CO., OH, 1986

Abstract Balled and burlaped Taxus media 'Wardi' (30-38 cm) were used to evaluate efficacy of selected insecticides as dips against black vine weevil larvae (1.68 mm mean head capsule width). Insecticidal solutions were mixed in half-sections of 208 liter drums to accommodate submersion of root balls of each of 5 plants/treatment. Plants remained in solution for 30 or 60 sec on 28 Apr. Root balls were removed from solution and placed on the rim of the drum for 10 sec to allow drainage back into the drum. Mean number of larvae/plant prior to treatment was 5.3. Treatment effectiveness was evaluated 10 DAT by removing burlap and visually sorting through soil and assessing viability of larvae.