Influence of instar and commodity on insecticidal effect of two diatomaceous earth formulations against larvae of Ephestia kuehniella (Lepidoptera: Pyralidae)

Laboratory experiments were carried out to evaluate the insecticidal effect of two diatomaceous earth (DE) formulations, SilicoSec and PyriSec, against larvae of Ephestia kuehniella Zeller (Lepidoptera: Pyralidae). Three instars were tested: first, third and fifth. The test was conducted in six commodities: barley Hordeum vulgare (L.) (Gramminae), rye Secale cereale L. (Gramminae), wheat Triticum sp. (Gramminae), wheat + 10% cracked wheat, wheat + 30% cracked wheat, and wheat flour. Quantities of these commodities were treated with the DEs at three dose rates: 250, 500, and 1000 ppm. Mortality of the exposed larvae on the DE-treated commodities was measured after 7 d of exposure. For both Des, mortality increased with dose, but this increase was lower when dose was increased from 500 to 1,000 ppm. The type of the commodity significantly affected DE effectiveness. Both DEs were equally effective on barley, rye, and wheat, whereas the presence of cracked wheat reduced larval mortality. In addition, significantly fewer larvae were dead on treated flour compared with the other five commodities. The increase of larval age significantly affected DE effectiveness. First instars were very susceptible to both DEs, and mortality with 1,000 ppm exceeded 86%. In contrast, fifth instar were the least susceptible to DEs, because mortality with 1000 ppm was < 22%.     

Developmental response of the brown-winged green bug, Plautia stali (Heteroptera: Pentatomidae), to food shortage

To study developmental response of the brown-winged green bug, Plautia stali Scott, to food shortage we reared nymphs under restricted feeding conditions produced by shortening the feeding period after molt or withholding food from second to fifth instars. For second instars, molting rates were significantly reduced as the feeding period was shortened. Shortening the feeding periods for third to fifth instars also reduced molting rates, but less so; some nymphs were able to complete their developments even if no food was given to any of the instars. Compared with controls for which feeding was not restricted, nymphs that successfully reached the next instar had reduced postmolt body size as a result of restricted feeding for all instars except the fifth (2-day feeding for second instar, and 1-day feeding for third and fourth instars), whereas instar duration was unchanged or only slightly prolonged for all instars. These results suggest that only nymphs with nutritional accumulation over a specific threshold in each instar can progress to the next instar, and that, particularly for second to fourth instars, nymphs develop on schedule without prolonging instar durations to compensate for reduced growth under conditions of food shortage.     

Laboratory studies of the biology and food requirements ofMacrorhaphis acuta [Hemiptera: Pentatomidae)

Macrorhaphis acuta were bred in the laboratory (25°C) and fed on larvae ofAscotis selenaria reciprocaria. The incubation period was 8.4 days and the mean hatch was 94.4%. There were 5 nymphal instars which occupied 3.3, 5.0, 5.6, 6.6 and 12.0 days, respectively, from the lst to the 5th. Each nymph consumed an average of 22.8 host larvae to complete development. Adults had a mean longevity of 74.9 days and each consumed an average of 67.5 host larvae. Significant reduction was noted in pupation of 5th instar host larvae sucked by adult predators for periods ranging from 4 to 10 mn. The food requirements of 3rd, 4th, and 5th instar nymphs fed on 3rd instar host larvae were also investigated. The conversion ratio varied with the weight of food consumed during the instar and later instars were more efficient than earlier ones. Predatory value did not vary significantly with successive instars.     

Larval and adult seed consumption affected by the degree of food specialization in Amara (Coleoptera: Carabidae)

Many carabid beetles (Coleoptera: Carabidae) are known to feed on plant seeds, but the level of specialization on this food differs. This is the first study in which seed consumption is assessed for all larval instars and adults of ground beetles. Three species of Amara with syntopic occurrence, Amara aenea (DeGeer), Amara familiaris (Duftschmid) and Amara similata (Gyllenhal), were examined. Larvae of all three instars and adults were fed seeds of Stellaria media (L.) Vill., Capsella bursa‐pastoris (L.) Med. and Taraxacum officinale Wick. ex Wigg. in a laboratory no‐choice experiment. In general, larvae, particularly the first instar, showed greater differences in seed consumption than the adults, although the latter showed similar but less marked pattern. Amara aenea consumed all offered seed diets in all life stages. All three larval instars of granivorous A. familiaris almost exclusively fed on seeds of S. media and the adults also ate significantly more of this than other seeds. Amara similata consumed mostly seeds of C. bursa‐pastoris in the first instar and adult stages, whereas the larvae of the later instars seemed to be unspecialized on particular seed diet. Differences in seed‐specific consumption between larval instars in granivorous carabids are reported for the first time. The results provide further support for the parallel evolution of various degrees of granivory in the genus Amara, which may ultimately facilitate species coexistence. The daily seed consumption by the larvae was comparable or (in case of the third instar) even higher than that by the adults. Hence, we suggest that larvae may be the important consumers of seed in the field and should not be forgotten when seed predation is assessed.     

A simple linear relationship and definition of a unit for proteinase activity

A mathematical transformation involving the $\text{3}\text{2}$ power of the number of milligrams of soluble nitrogen released from the substrate makes possible the expression of proteolytic activity in terms of the quantity of enzyme required to cause a given change in the substrate. The relationship is linear for several different enzymes including papain, patent flour, malted barley, malted wheat flour, and several fungal preparations acting on either Bacto-hemoglobin or gluten substrate.One unit of proteinase activity is defined as that activity contained by a quantity of enzyme-active material which gives an increase in soluble nitrogen in a 10-ml. aliquot from the filtrate corresponding to the intersection of the straight line with the transformed value representing 1 ml. of 0.0714 N alkali.This method of expressing proteolytic activity greatly simplifies the expression of proteolytic activity and has been found convenient for analytical purposes as well as for comparing activities of different enzymes acting on the same substrate.     

Colorado potato beetle (Coleoptera: Chrysomelidae) feeding, development, and survival to adulthood after continuous exposure to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field

Colorado potato beetle, Leptinotarsa decemlineata (Say), feeding, development, and survival to adulthood were examined after continuously exposing large larvae to Bacillus thuringiensis subsp. tenebrionis-treated potato foliage from the field. In laboratory assays, the overall consumption and the length of period to become prepupae were determined for larvae, which began as 3rd and 4th instars, that were offered potato leaf disks with naturally declining levels of B. thuringiensis residue. In small-cage field experiments, survival to adulthood and the period to adult emergence for beetles confined to potato plants treated with B. thuringiensis beginning as 3rd and 4th instars also were examined. Third instars remaining on plants after a B. thuringiensis application were unlikely to feed and 4th instars consumed only approximately 50% as much foliage as those fed untreated foliage. Many late instars subjected to B. thuringiensis-treated foliage failed to survive to adulthood; 58-83% of these beetles died during the larval stage. Reduced feeding and poor survival of late instars suggest that counts of large larvae after application do not provide a complete picture of the efficacy of the B. thuringiensis treatment. Late instar Colorado potato beetles that were exposed continually to naturally declining levels of B. thuringiensis-treated potato foliage took an average of 1.8-4.5 d longer to become prepupae and 4-8 d longer to emerge as adults compared with those provided with untreated foliage. Delayed emergence of adults that fed on B. thuringiensis-treated potatoes as late instars indicated that development was prolonged in these insects because of ingestion of a sublethal dose of B. thuringiensis.     

Social and nonsocial stimuli and juvenile hormone titer in a male burying beetle, Nicrophorus orbicollis

We investigated the interaction of social and nonsocial stimuli on juvenile hormone (JH) titer in male burying beetles (Nicrophorus orbicollis). The initial JH response to discovery of a carcass was substantial (10-15-fold increase over controls) and rapid (<1h), and occurred whether or not a female was present. By 3h after discovery, JH titers were declining, the decline being more pronounced when a female was not present. We also tested the effect of larval stimulation on JH titer in care-giving males by removing a male's brood and replacing it with a brood of first or third instar larvae. Males initially providing care for begging first instar larvae continued to maintain high titers of JH when the replacement broods were first but not third instars. Males caring for third instar larvae (normally low JH titers) maintained low levels of JH regardless of the developmental stage of the replacement brood. This suggests that once males begin to care for nutritionally independent third instar larvae, JH titers remain low regardless of subsequent larval stimulation. Burying beetles are socially and hormonally complex organisms in which stimuli from a breeding resource, mating partners, rivals and young interact to alter the JH profile of breeding adults.     

A strain of Serratia marcescens pathogenic for larvae of Lymantria dispar: Infectivity and mechanisms of pathogenicity

The ED₅₀ of a strain of Serratia marcescens for microinjected instar III and IV gypsy moth larvae was 7.5 and 14.5 viable cells, respectively. Percentage and rate of mortality were found to be highly variable among replicates of the same instar and between instars in free-feeding bioassays. Mortality in second instar larvae occurred before ecdysis, whereas practically no mortality occurred in third and fourth instars until the molting period. Neither Boivin endotoxin preparations nor culture filtrates were toxic to instar III larvae when administered per os or by microinjection. Histological evidence indicated that the microorganism invaded the hemocoel of healthy or predisposed insects through the gut wall. The rapid multiplication of the bacterium in the hemocoel of infected insects, followed by death in the absence of extensive tissue damage, indicated mortality was due to a septicemia. The histological and biological evidence presented indicated that the microorganism would be less than effective if utilized as a conventional microbial insecticide.     

Susceptibility of last instar red flour beetles and confused flour beetles (Coleoptera: Tenebrionidae) to hydroprene.

Last instar larvae of the red flour beetle, Tribolium castaneum (Herbst), and the confused flour beetle, Tribolium confusum Jacquelin du Val, were either exposed for 8-144 h on concrete treated with 1.9 x 10(-3) mg(AI)/per cm2 hydroprene, or continually exposed on concrete treated with 9.8 x 10(-4) to 1.9 x 10(-3) mg[AI]/per cm2 hydroprene. In both tests, larvae were exposed and held at 27 or 32 degrees C and 40, 57, or 75% RH. When larvae were exposed with no food to hydroprene for different time intervals, then transferred to untreated concrete containing flour, consistent effects were produced only at 144 h. At this exposure interval, the percentage of beetles arrested in the larval stage after 3-4 wk was generally greater at 75% RH compared with 40 and 57% RH, but there were no differences between species or temperature. The percentages of dead adult red flour beetles and live adults with morphological deformities were also greatest at 75% RH, and defects were more prevalent in red flour beetles than in confused flour beetles. When larvae were continually exposed to different concentrations of hydroprene on concrete that contained flour, the percentage of arrested larvae, dead adults, and live adults of both species generally increased with concentration. There were more deleterious effects at 75% RH compared with either 40 or 57% RH, and effects were more pronounced in the red flour beetle compared with the confused flour beetle. In both experiments, temperature effects were variable and inconclusive. Results indicate that continual exposure of last instar red flour beetle and confused flour beetle to hydroprene can limit population development, but exposure intervals of >6 d may be required for maximum effectiveness.     

Instar Susceptibility of Simulium vittatum (Diptera: Simuliidae) to the Entomogenous Nematode Neoaplectana carpocapsae

Laboratory bioassays showed that the susceptibility of Simulium vittatum to Neoaplectana carpocapsae increased with successive larval instars. First, second, and third instar larvae were resistant to infection, while seventh instars were highly susceptible. Significant differences in intra-instar susceptibility were also evident, as mortality ranged from 58% for the smallest seventh instar larvae to 97% for the largest. Dissections revealed that the basis for the resistance of early instars was physical exclusion of the comparatively large nematodes. The principle factor regulating the susceptibility of mid and late instars was injury to nematodes caused by larval mouthparts during ingestion. Differences in intra-instar susceptibility were similarly related to nematode injury.     

Relationship between population growth of the red flour beetle Tribolium castaneum and protein and carbohydrate content in flour and starch

The effects of eight diets (atta flour, wheat flour, self-rising flour, rice flour, custard powder, corn flour, tapioca starch, and potato starch) on the development of the red flour beetle, Tribolium castaneum (Herbst), reared at 29-31 degrees C and 66-70% RH were assessed. Five pairs of male and female T. castaneum were reared on the respective diets for 28 d before the experimental setup was dismantled and adult counts were recorded. In another experiment, the insects were allowed to mate and oviposit in each flour or starch type over a period of 7 d before being removed. The counting of pupae and adult emergence began on the day of emergence and was continued on a daily basis until day 140. Proximate analysis was performed for chemical composition of each diet, and the numbers of new adults that developed were found to be positively correlated (r2 = 0.97; P < 0.05) with the protein content and negatively correlated (r2 = 0.93; P < 0.05) with the carbohydrate content. For T. castaneum, the suitable diets were ranked as follows: atta flour > wheat flour > self-rising flour > rice flour > custard powder > corn flour > tapioca starch > potato starch. T. castaneum larval development to the pupal and adult stages developed significantly faster in atta flour (P < 0.05) than in the other diets, and the greatest number of progeny was produced from beetles reared on atta flour. Fewer adults emerged from wheat flour, self-rising flour, and rice flour, and no new emergences were recorded for the remaining diets. Developmental rate was much slower in beetles reared on diets in which a low number in progeny was produced. These data illustrate that different diets can influence the sustainability of these insects and affect their development and growth.     

External morphology of the two cypridiform ascothoracid-larva instars of Dendrogaster: The evolutionary significance of the two-step metamorphosis and comparison of lattice organs between larvae and adult males (Crustacea, Thecostraca, Ascothoracida)

We describe the external morphology of the two cypridiform larval instars (first and second ascothoracid-larvae, or “a-cyprids”) of the ascothoracidan genus Dendrogaster. Ascothoracid-larvae of five species were studied with light and scanning electron microscopy, including both ascothoracid-larval instars in Dendrogaster orientalis Wagin. The first and second instars of the ascothoracid-larvae differ in almost all external features. The carapace of instar 1 has a smooth surface and lacks pores, setae, and lattice organs, while instar 2 has all these structures. The antennules of the first instar have only a rudimentary armament, the labrum does not encircle the maxillae, thoracopods 2-3 are not armed with a plumose coxal seta, and the abdomen is four-segmented (versus five-segmented in instar 2). Thus, the first ascothoracid-larva of Dendrogaster represents a transitional, generally brooded stage between the naupliar stages and the dispersive and fully functional second ascothoracid-larva that accomplishes settlement. The presence of two instars of ascothoracid-larvae (a-cyprids) in members of the order Dendrogastrida differs from the single cypridiform instar found in the Cirripedia (cyprid) and Facetotecta (y-cyprid), and we discuss the evolutionary significance of these ontogenies. We found lattice organs in both the second ascothoracid-larvae and in adult males of Dendrogaster. We could not observe both ascothoracid-larvae and males in any single species, but our data suggests that the lattice organs change significantly at the molt between these two instars. The lattice organs of second ascothoracid-larvae have no distinct keel and are situated in wide, shallow pits, whereas they have the ground pattern “crest-in-a-trough” morphology in adult males of two additional species examined for comparison. The positions of the terminal pores of lattice organs 1 and 2 also seem to change during maturation. These findings show that comparative data on lattice organ morphology for phylogenetic purposes must derive from strictly homologous instars, viz., the second ascothoracid-larva (a-cyprid) of the Ascothoracida, the y-cyprid of the Facetotecta, and the cyprid of Cirripedia. The ascothoracid-larvae of Dendrogaster and those of the family Ascothoracidae have four pairs of lattice organs, which suggests that this genus and family form a monophylum, to the exclusion of Ulophysema, which then brings into question the monophyly of the Dendrogastridae. Ulophysema is currently placed in the Dendrogastridae, but its second ascothoracid-larva has lattice organs of different and more plesiomorphic number and morphology. We briefly review lattice organ morphology across the Thecostraca. These organs are normally considered structures of the cypridiform larva and their presence in adult (males) Ascothoracida is unique in the Thecostraca. The continued morphological modification of these sensory structures in males compared to ascothoracid-larvae may suggest that they originated in adult thecostracans, but have come to be functional in the cypridiform larvae as well.     

Performance of Microplitis tuberculifer (Hymenoptera: Braconidae) parasitizing Mythimna separata (Lepidoptera: Noctuidae) in different larval instars

The solitary parasitoid Microplitis tuberculifer (Wesmael) is an important biological control agent of various lepidopteran pests in Asia. We examined the preference of M. tuberculifer for different instars of its common host, Mythimna separata (Walker), host instar effects on parasitoid development, and the consequences of parasitism in different stages for growth and consumption of host larvae. The wasp successfully parasitized the first four larval instars of M. separata, but not the fifth, which appeared to be behaviorally resistant. First and second instars were parasitized at higher rates compared to thirds and fourths in no-choice situations, ostensibly due to longer handling times for the latter, but second instars were most preferred in a choice test that presented all stages simultaneously. Although later instar hosts yielded heavier cocoons, the fastest parasitoid development was obtained in second instars. Lower sex ratios were obtained from first instars as females appeared to lay a smaller proportion of fertilized eggs in small hosts. Both weight gain and food consumption of parasitized larvae were reduced significantly within 24 h of parasitism, regardless of the stage parasitized, and final body weights were less than 10% those of unparasitized larvae. Thus, M. tuberculifer has good potential as a biological control agent of M. separata, successfully parasitizing the first four larval instars and dramatically reducing plant consumption by the host in all cases.     

Instar determination for sugarcane internode borer Chilo sacchariphagus indicus (Kapur) (Lepidoptera: Crambidae)

Internode borer (INB), Chilo sacchariphagus indicus has been a serious threat to sugarcane cultivation for more than six decades. We have determined the number of instars for INB through frequency distribution analysis of cast head capsule widths. This is the first report, which proves that the INB of sugarcane passes through five larval instars to attain its pupal stage. The number of instars determined by kernel density estimation was in corroboration with the number of instars observed in the laboratory. The mean Dyar’s ratios for both the instar-wise observed data on head capsule widths and the theoretical data derived from the frequency distribution analysis were one and the same (1.46). Linear regression (R² > 0.998) between the instar numbers and their corresponding mean head capsule widths reaffirmed that no instar has been overlooked. Further, the theoretical misclassification probabilities of 0.16–1.97% indicates that the chance of misidentifying an INB instar into its preceding or succeeding one is very remote. Since the determination of the exact number of instars in a pest species is a pre-requisite for developing appropriate management strategies, the outcome of this study holds great promise in managing the most notorious Crambid borer of sugarcane.     

The dependence of development and fecundity of Samea multiplicalis on early larval nitrogen intake

Larvae of the moth Samea multiplicalis (Lepidoptera: Pyralidae), developed more rapidly when their food plant, Salvinia molesta was richer in nitrogen. Larvae that fed on plants with less than 1.35% nitrogen during their first instar completed the larval stage in 18.0–24.2 days, after passing through six instars. In contrast, larvae that had fed on food richer in nitrogen during their first instar completed the larval stage in 14.1–17.4 days, and passed through five instars. Experience of nitrogen in later instars had little additional effect on total larval development time. Oöcyte complements of 1-day old adult females was correlated with the mean food nitrogen content over the larval period. Food nitrogen content experienced by larvae in earlier instars was as important as that in the final instars, in determining number of mature oöcytes, which suggests early conditioning of the nitrogen use effciencies of later instars.     

Life history and population biology of the giant ostracod Leuroleberis zealandica (Baird, 1850) (Myodocopida)

A population of this large myodocopid ostracod was studied over 2 yr by random core-sampling of the medium sand bottom at Kaikoura, New Zealand. Leuroleberis zealandica (Baird) passes through seven instars, it is sexually mature only in the final instar and sexes were distinguishable from instar IV. Males and females were equally abundant except in the final instar when the morphologically distinct males were rarely found. The population consists of three cohorts at any one time and each cohort appears to split into fast- and slow-growing individuals during the sixth instar resulting in life times of 1.8–2.0 and 2.7–3.1 yr, respectively. Females produce only one brood of 37 eggs on average per life time that are carried throughout the 5–6 month development period during which there is no loss of embryos. Recruitment is discrete with most broods released in midsummer when the population density may exceed 350·0.1 m^?2. A second lesser recruitment may occur in early spring in some years. Hatched juveniles released from the female grow rapidly to instar IV within 6 months and, although size increments at each moult are proportionally similar, intermoult periods tend to increase with size with some variation according to seasonal growth rates. Instar life tables constructed from instar density data showed a large difference in the frequency of embryos initiating each cohort, very different mortalities at recruitment between cohorts, and that the mortality rates between instars I and VI of different cohorts appear to be independent of density. The biology of Leuroleberis is compared with the few published accounts of myodocopid biology. In addition, several aspects of the biology of myodocopids are reviewed. These include numbers of instars in different taxa, within-instar sexual size disparities, numbers of broods per female life time, egg and brood sizes in relation to adult female size in various taxa, and the question of post-adult moulting.     

短尾秀体溞的发育与生长

短尾秀体溞(Diaphanosoma brachyurum)是东湖6—9月的优势种群。作者在实验室恒温条件下,观察了它的发育与生长。这种溢的卵与胚胎发育时间随温度升高而缩短。卵与胚胎发育时间(D)与温度(T)间的迥归方程为: logD=2.0195-1.3784logT 短尾秀体溞的生长速度随龄数而变化,一般可分为3个时期:幼龄为高速生长期,成龄前期为中速生长期,后期则为缓慢生长期。在25℃时有4个幼龄,10个成龄;而在30、35℃时有3个幼龄,12或11个成龄。幼龄的脱皮频率远大于成龄。每个成龄期的平均龄期约为幼龄期的2倍以上,而同卵与胚胎发育的时间基本相等。龄期、寿命与温度呈反比。在25,30,35℃温度下,累计产卵数分别为65.63,69.09,51.77个。产卵率以25℃为最高(1.3421),30℃为其次(1.2856),35℃为最低(1.1488)。       

The auditory system in larvae of the migratory locust

ABSTRACT. The course and projection areas of the tympanal receptor fibres in the thoracic ventral cord were revealed by iontophoresis in the last three larval instars. There were no significant differences between the arrangement in larvae and that in adults. The threshold curves of the auditory organ of the last three instars were measured by recording summed potentials in the tympanal nerve. In the frequency range tested (1–20 kHz), larvae and adults differed only in sensitivity. More detailed information was obtained by single-cell recordings from receptor neurones in the tympanal nerve of last instar larvae. No differences could be shown between the threshold curves, or the suprathreshold activity, of low frequency receptors of last instars and adults. However, the high frequency receptors of the last instars are far less sensitive in the frequency range above 12 kHz. This seems to depend on the different mechanical properties of the tympanum in larvae. The response patterns of some typical ventralcord neurones (G-, K-, B-type) were identified by extracellular single-cell recordings in last instar larvae. Convergence of auditory and vibratory inputs onto the G-neurone and the B-neurone (as is known to exist in the adult) was found in larvae in the final and penultimate instars to be causing similar response patterns.