Larval Emergence Rate Research Articles

Toxicicity and Histological Changes Caused by Insecticides in Spodoptera frugiperda (Lepidoptera: Noctuidae) Eggs

Insecticides typically are used to control Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) larvae in corn crops; however, both eggs and larvae are affected by these applications. The purpose of this study was to evaluate the effects of 9 insecticides commonly used on corn crops in Brazil on ovicide and embryonic development of S. frugiperda. The insecticides were applied with an airbrush to the outer surface of eggs at 72, 96, 120, 144, and 168 h after oviposition. Larval emergence rates then were calculated. Eggs in the control and the alpha-cypermethrin and methomyl + novaluron treatment were evaluated by light microscopy to investigate possible histological changes in the embryos. The insecticides methomyl + novaluron, chlorantraniliprole + lambda-cyhalothrin, and deltamethrin reduced the emergence rate of S. frugiperda larvae. A mixture of alpha-cypermethrin and methomyl + novaluron did not affect the embryonic development of S. frugiperda; however, methomyl + novaluron-treated larvae did not emerge. Therefore, the insecticides methomyl + novaluron, chlorantraniliprole + lambda-cyhalothrin, and deltamethrin have an ovicidal effect and may be recommended for managing S. frugiperda.

Epiphyas postvittana (Lepidoptera: Tortricidae)-Botrytis cinerea (Helotiales: Sclerotiniaceae)-Vitis vinifera (Vitales: Vitaceae) Interaction: The Role of B. cinerea on the Development of E. postvittana in Synthetic Nutritional Media.

Epiphyas postvittana (Walker) (light-brown apple moth) is a polyphagous herbivore of economic significance, which also feeds on Vitis vinifera L. The E. postvittana-V. vinifera interacting system also involves the participation of the fungus Botrytis cinerea Persoon ex Fries. We have been exploring the relationship among E. postvittana-V. vinifera-B. cinerea over the past two years. In this article, we report the preference and performance of the larvae of E. postvittana raised solely on a synthetic diet incorporated with the mycelial material of B. cinerea (Diet B). To characterize the effect of fungus on the development of E. postvittana, another synthetic diet was prepared that included the lyophilized leaf material of V. vinifera (Diet C). When raised on Diets B and C, a decrease in the duration of larval development and an increase in the survival and fecundity rate of E. postvittana occurred. Diet B influenced the pupal mass, but a significant increase occurred when the larvae were fed on Diet C. The larval emergence rate was the greatest in E. postvittana raised on Diet B, followed by those on Diet C. The F(2) generation of the larvae reared on Diet B showed similar effects as F(1) on the life-history performance of the larvae. Diet B enhanced the life-history performance of E. postvittana, although the larvae of E. postvittana showed little preference to Diet B. The greater fertility rate of E. postvittana reared on Diet B suggests the importance of sterols as shown in Lobesia botrana (Denis & Schiffermüller) (Lepidoptera: Tortricidae) and in a few Myrmicinae (Hymenoptera: Formicidae), which serve as precursors to different ecdysteroids that regulate many critical processes through embryonic development.

Effects of Body Size, Diet, and Mating on the Fecundity and Longevity of the Goldspotted Oak Borer (Coleoptera: Buprestidae)

Abstract The goldspotted oak borer, Agrilus auroguttatus Schaeffer (Coleoptera: Buprestidae), is an invasive wood-borer that was recently introduced into southern California from southern Arizona, and has caused the rapid mortality of thousands of native oaks. Biological control of A. auroguttatus is a management strategy of high interest, but is in its early stages, which is due, in part, to a lack of information on the basic biology and life history of this beetle. To address this shortcoming, studies were conducted in quarantine on the realized lifetime fecundity of A. auroguttatus, which was determined by comparing oviposition and larval emergence rates of females subjected to different dietary and mating treatments. Longevity and body size were also recorded for male and female adults under these treatments. Mean A. auroguttatus lifetime oviposition and larval emergence were similar in females that were continuously paired with either one or two males. Virgin females laid significantly fewer eggs and no larval emergence resulted from unfertilized eggs. The number of mates did not affect mean A. auroguttatus adult longevity, but a carbohydrate-enriched diet increased both mean longevity and lifetime oviposition by as much as 46 and 250%, respectively. There was no correlation between adult body size and lifetime oviposition, days to initial oviposition, larval emergence, and adult longevity. However, hind tibia length was marginally correlated with total oviposition period. For mass rearing A. auroguttatus eggs in the laboratory, pairing females with one male and providing adults with a continuous diet of 10% honey-water and oak foliage is recommended.

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

Many lake whitefish stocks in Lake Michigan have experienced substantial declines in growth and condition since the 1990s. Reduced growth and condition could result in reduced quality or quantity of eggs produced by spawning females, which in turn could negatively impact recruitment. We evaluated the potential for reduced recruitment by measuring early life stage density and length, and we discuss the utility of these measures as early indicators of lake whitefish year-class strength. Overall, mean larval density (number per 1000 m 3 ± SE) in Lake Michigan was greater in 2006 (373.7 ± 28.3) than in 2005 (16.6 ± 24.8); whereas, mean length (mm ± SE) of larval lake whitefish was smaller in 2006 (12.87 ± 0.07) than in 2005 (14.38 ± 0.13). The ratio of zooplankton to fish density did not show an expected relationship with larval fish density or length. Rather, variation in larval density was best explained by a multiple-regression model that included larval length, spring wind intensity, and adult stock density as predictor variables. Our results suggest that the density of larval lake whitefish is not directly regulated by temperature or zooplankton density at the time of emergence, but that a potential for density-dependent regulation exists when larval emergence rates are high. We conclude that the observed declines in growth and condition of adult lake whitefish are not resulting in substantial reductions in recruitment.

Curative Activity of Insecticides Against Plum Curculio (Coleoptera: Curculionidae) in Tart Cherries

Tart cherry, Prunus cerasus L. variety Montmorency, fruit were infested with plum curculio, Conotrachelus nenuphar (Herbst) (Coleoptera: Curculionidae), and treated with insecticides to target late instars, neonates, and eggs. The organophosphates azinphos-methyl and phosmet and the neonicotinoid thiamethoxam reduced larval emergence rates by >90% for all life stage targets; after >30 d, few surviving larvae were found inside fruit. Acetamiprid and thiacloprid also had curative activity and yielded >75% reductions in emergence and few surviving larvae in the fruit after >30 d. The juvenile hormone analog pyriproxyfen reduced larval emergence, but 66% of fruit that was treated to target late-instars still had live larvae inside of them after >30 d. Novaluron, chlorantraniliprole, and esfenvalerate had no curative activity. Indoxacarb had limited curative activity, and all targeted life stages had larval emergence. Internal and external residues were analyzed and are discussed in relation to their penetration and curative potential. The curative activity of azinphos-methyl has played an important role in meeting federal standards for infestation-free tart cherries at processing. Regulatory changes are eliminating the use of this compound, and new integrated pest management programs for plum curculio will need to address the loss of azinphos-methyl's curative activity.

Population Regulation of a Leaf-Mining Insect, Cameraria Sp. Nov., at Increased Field Densities

We experimentally induced increased field densities of a leaf-mining insect, Cameraria sp. nov. (Lepidoptera: Gracillaridae), by caging a Quercus nigra (Fagaceae) tree to compare insect mortality and survivorship with that on a control tree. Although densities of the leaf ininer were significantly higher on the caged tree, larval survivorship did not decrease as expected if intraspecific competition is density dependent. Rather, survivorship increased. We attribute the significantly higher larval emergence rates to exclusion of most parasites and predators from the caged tree. We contend that natural enemies of leaf miners, particularly hymenopteran parasites, are instrumental in main- taining leaf-mining populations far below levels at which intraspecific competition would occur.

The effect of moisture supply upon the development and hatching the eggs of Nematodirus battus.

Experiments were carried out to investigate the effect of variations in humidity and osmotic pressure upon the development and hatching of the eggs of Nematodirus battus. It was found that no development or hatching took place unless there was free water available, though humidity effects could enhance the subsequent response of the eggs in water. Larvae were found to be very resistant to prolonged exposure to low humidity. The concentration of the hatching medium showed little effect upon development of eggs, though the rate of larval emergence was reduced as the concentration of the culture medium increased. The relevance of this information is discussed in the context of other requirements of the egg stages during their hatching phase and how this may affect the behaviour of this nematode under field conditions.

Increasing the Rate of Larval Emergence From Cysts in Hatching Tests With Beet Eelworm, Heterodera Schachtii Schmidt

Im Vergleich zur standardisierten Schlupftechnik in Glasern lasst sich eine betrachtliche Steigerung des Larvenschlupfes aus den Cysten von Heterodera schachtii durch Verwendung kleiner aus Polyathylen und Nylon hergestellter Siebe erzielen, in denen die Cysten von allen Seiten aus beluftet werden konnen. Auf diese Weise kann nach zwei Wochen eine Steigerung um das 4-fache erreicht werden. Der Larvenschlupf in Wasser wird auch durch Benutzung von Sieben leicht gesteigert. Die gesamte Schlupfmenge ist jedoch bei beiden Verfahren nicht signifikant unterschiedlich. Die Zugabe fungistatischer und bakteriostatischer Stoffe zum Schlupfmedium fuhrt zu einem weiteren Ansteigen sowohl der Schlupfhohe wie des Gesamtschlupfes. Es ist schwer zu sagen, ob dies einer Unterdruckung O2-liebender Mikroorganismen zuzuschreiben ist oder einem unmittelbar wirkenden Schlupfreiz.

THE STIMULATORY PROPERTIES OF SOME ORGANIC SUBSTANCES ON CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT

Techniques for determining the influence of various substances on the rate of larval emergence from cysts of the beet eelworm are described. There is no significant difference between the rates of larval emergence in glutamic acid, galactinol, inositol and water; the rate of larval emergence in beet diffusate, on the other hand, was significantly higher. Studies of larval emergence in carbohydrates suggest that the cyst population used in the experiments was heterogeneous, consisting of two types of cyst which have different reactions to stimulation at different concentrations. The significance of root exudates in relation to beet eelworm is discussed.

THE EMERGENCE OF LARVAE FROM CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT, IN AQUEOUS SOLUTIONS OF ORGANIC AND INORGANIC SUBSTANCES

The rate of larval emergence from cysts of the beet eelworm in a variety of aqueous solutions containing organic and inorganic substances is significantly higher than the emergence rate in water. It is suggested that differences between larval emergence rates in monoamino‐monocarboxylic amino‐acids may be related to the lipid solubility of these substances and their ability to penetrate the egg membranes. The larval emergence rate in fructose, glucose, sucrose and maltose was significantly higher than that in water, but in raffinose, arabinose and xylose the rate of emergence was no higher than in water. A high rate of larval emergence occurred in sodium chloride, potassium chloride and mercuric chloride, but not in magnesium chloride or calcium chloride. Experiments with several other organic solutions are described. There is an optimum concentration for larval emergence in beet diffusate. The osmotic pressure of the diffusate when maximum emergence occurred was 0·48 atm. Measurements of shrinkage of unhatched larvae in various concentrations of urea, sodium chloride and sucrose showed that decreasing rates of emergence at higher concentrations may be due to changes in the unhatched larvae brought about: by an osmotic effect. High concentrations of beet diffusate may have a similar effect.

SOIL AERATION AND THE EMERGENCE OF LARVAE FROM CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHM

Moisture content, pore size, depth and oxygen consumption in the soil, which influence soil aeration, have been studied in relation to larval emergence from cysts of the beet eelworm. Experiments show that the rate of larval emergence increases with aeration. In studies of larval emergence in the field emphasis should be laid on soil structure rather than on a mechanical analysis. Those factors associated with good soil tilth favour high rates of larval emergence.

The Seasonal Emergence of Larvae From Cysts of the Beet Eelworm, Heterodera Schachtii Schmidt *)

Field experiments in 1954 and 1955 showed that there was a high rate of larval emergence from cysts of the beet eelworm during April and May followed by a low emergence rate from June to September. It is shown that low soil moisture content was probably the chief factor inhibiting emergence during the summer months. Larval emergence probably does not occur in soil where the pressure deficiency exceeds 150 cm of water. Recordings of pressure deficiency in 4 soil types during 1955 showed that from June to September the pressure deficiency was mostly above this level. A comparison of larval emergence from cysts within and between soil crumbs was made. At least 50 per cent of the cyst population occurred within crumbs, but the rate of larval emergence from these cysts was very low. It is suggested that when counts of cyst contents in soil are made, a dispersing agent such as Calgon should be used to release cysts enclosed in soil crumbs.

THE INFLUENCE OF SOIL MOISTURE ON THE EMERGENCE OF LARVAE FROM CYSTS OF THE BEET EELWORM, HETERODERA SCHACHTII SCHMIDT

The significance of soil moisture in relation to aeration and larval emergence from cysts of Heterodera schachtii Schmidt is discussed. The rate of larval emergence increased as oxygen concentration increased. A comparison of the moisture characteristics of a mass of cysts and of sand of about the same particle size showed that water was removed from between both the cysts and the sand particles at 12–16 cm. of water‐pressure deficiency. There was an indication that water was removed from between the eggs within the cysts at 100–135 cm‐ of water‐pressure deficiency. The rate of larval emergence showed a gradual decline is suction was increased beyond 20 cm. of water‐pressure deficiency, approaching zero at 175 cm. of water‐pressure deficiency. Results suggest that egg hatch is not directly dependent on pressure deficiency and that the presence of free larvae within the cyst inhibits further egg hatch. A technique is described for measuring larval motility in sand. There is a decline in motility when most of the water has been removed from the sand pore‐spaces. It is suggested that the relatively low rates of larval emergence at high‐pressure deficiencies are due to inhibition of larval migration from the cyst by the surface forces of the water film.

Factors Influencing the Emergence of Larvae from Cysts of the Beet eelworm, Heterodera schachtii Schmidt

Experiments on larval emergence in a series of constant temperatures showed that, of those temperatures tested, 25°C. was the optimum. Results suggest that constant temperatures do not provide optimum conditions for larval emergence and that a higher rate of emergence may occur under fluctuating temperatures. The rate of larval emergence in beet diffusate increased as the initial oxygen concentration increased. Pre-treatment of cysts at low oxygen concentrations reduced the subsequent emergence in diffusate.

Investigations on the Emergence of Larvae from the Cysts of the Potato-root Eelworm, Heterodera rostochiensis.

The foregoing results throw light on the conditions under which hatching tests can be carried out. In the first place, pre-soaking cysts in water for a period of 10 days increases the rate of larval emergence but has no effect on the total number of hatchable larvae. Increase in temperature has a similar effect up to 25°C, but at 80°C. hatching is virtually inhibited. Volume of diffusate per cyst is without effect either on the number of hatchable larvae or on their rate of hatching. Neither was any effect observed from alterations in pH between 8.2 and 8.1. The effect of dilution is more or less linear when dilution is plotted geometrically against cither the number of hatchable larvae or the latter expressed as a proportion of the original cyst contents and subjected to angular transformation. For the effect to be appreciable, dilution must be of a high order. Dilution to a half or a quarter of the original concentration has little appreciable effect. The effect of dilution on the rate of hatching is not obvious and the variations in it resulting from dilution are probably random. Direct sunlight inhibits hatching, diffused daylight is without effect as compared with darkness ; cysts exposed to the action of sunlight and diffusate do not hatch when later removed to the dark. It appears reasonable to assume that this may be due to some lethal effect.