Drift behaviour and microhabitat selection in the preimaginal stages of Simulium chutteri (Diptera Simuliidae)

The aquatic stages of the cattle biting pest, Simulium chutteri Lewis utilize river flow in their dispersal and colonization behaviour. Peaks of drifting activity in S. chutteri larvae occurred in the early morning and late afternoon. It is deduced that female flies scatter eggs onto slow flowing waters upstream of rapids. Larvae hatch from drifting eggs and colonize substrates in slower flowing regions upstream of rapids, while later stage instars move into faster flowing regions within rapids where they complete their development. This microhabitat selection by S. chutteri leads to rapid attainment of large population sizes in suitable sections of river and reduces competition between different stage larvae. In their utilization of a variety of microhabitats the larvae of this species differ from co-existing simuliid species which restrict developmental stages to single habitats.Catastrophic drift was recorded for S. chutteri larvae and could be a mechanism to regulate population size.Drift of simuliid larvae off rapids was not related to benthic population densities in the rapids and was therefore not due to excessive production. It is concluded that larval drift off rapids is related to habitat disturbances associated with water flow fluctuations and the activity of aquatic predators and other animals.The distribution of S. chutteri in the Vaal River is restricted by oviposition requirements of the adult female. Knowledge of drift behaviour and water flow requirements of Simuliidae have been applied to manage the population size of S. chutteri in the Vaal River.     

Protection of potato crop against Phthorimaea operculella (Zeller) infestation using frass extract of two noctuid insect pests under laboratory and storage simulation conditions

The oviposition deterrent effect of water extract of Spodoptera littoralis and Agrotis ipsilon larval frass on Phthorimaea operculella adult females was studied using two types of larval food “Natural host and Semi-artificial diet” under laboratory and storage simulation (semi-field) conditions. Extracted frass of fed larvae on semi-artificial diet showed complete oviposition deterrent effect at treatments with 4th, 5th and 6th instars of S. littoralis, also at treatments with 1st–3rd and 6th instars of A. ipsilon, while the same effect was observed when the larvae fed on castor oil leaves as a natural host only at treatment with frass extract of A. ipsilon 6th instar larvae. Presence of low amounts of phenols and flavonoids in water extract of A. ipsilon larval frass resulted in relatively more effect as oviposition deterrent to fertile adult females on treated oviposition sites, while the opposite effect was obtained in S. littoralis larval frass experiments. At semi-field experiments, the percentage reduction of laid eggs reached 100% after two?days at treatments with frass extracts of 4th and 5th S. littoralis larval instars and A. ipsilon 6th instar larvae fed on semi-artificial diet and/or castor oil leaves. Percentage reduction of laid eggs for untreated sacks reached 93.24 and 48.95% after 2 and 30?days, respectively, when placed between treated sacks, in comparison with the mean number of laid eggs for isolated control.     

The life-history,distribution, and production of Chironomus riparius and Glyptotendipes paripes in a prairie pond

C. riparius and G. paripes exhibited univoltine life-cycles in Stephenson Pond; pupation, emergence and oviposition occurred mainly during May, and both species overwintered as mature fourth instar larvae. The marjority of larval growth for both species took place during the fourth instar stage (August–October), and growth and production were very low during late May to mid July when only young instars were present. Low production occurred during an interval when sestonic chlorophyll a concentration was very low, and the high production period corresponded to the Aphanizomenon bloom (August) and the autumn diatom pulse. None of the growth and production parameters investigated were correlated with temperature at the mud-water interface. Tube structure and behavior of the larvae indicate that G. paripes larvae are filter-feeders, whereas, C. riparius larvae are deposit-feeders.     

Does superparasitism improve host suitability for parasitoid development? A case study in the Microplitis rufiventris-Spodoptera littoralis system

Superparasitism refers to the oviposition behavior of parasitoid females who lay their eggs in an already parasitized host. Recent studies have shown that allocation of additional eggs to an already parasitized host may be beneficial under certain conditions. In the present work, mortality of Microplitis rufiventris wasps was significantly influenced by both host instar of Spodoptera littoralis larvae at parasitism and level of parasitism. In single parasitization, all host instars (first through sixth) were not equally suitable. Percentage of emergence success of wasp larvae was very high in parasitized first through third (highly suitable hosts), fell to 60% in the fourth instar (moderate suitable) and sharply decreased in the penultimate (5th) instars (marginally suitable). Singly parasitized sixth (last) instar hosts produced no wasp larvae (entirely unsuitable), pupated and eclosed to apparently normal adult moths. The scenario was different under superparasitism, whereas supernumerary individuals in the highly suitable hosts were almost always killed as first instars, superparasitization in unsuitable hosts (4th through 6th) had significant increase in number of emergence success of wasp larvae. Also, significantly greater number of parasitoid larvae successfully developed in unsuitable hosts containing three wasp eggs than counterparts containing two wasp eggs. Moreover, the development of surplus wasp larvae was siblicidal in earlier instars and nonsiblicidal gregarious one in the penultimate and last “sixth” instars. It is suggested that the optimal way for M. rufiventris to deal with high quality hosts (early instars) is to lay a single egg, while the optimal way to deal with low quality hosts (late instars) might be to superparasitize these hosts.     

The water velocity preferences of Austrosimulium furiosum and Simulium ornatipes (Diptera: Simuliidae) larvae,and the implications for micro-habitat partitioning

The aquatic larvae of two simuliid species, Austrosimulium furiosum (Skuse) and Simulium ornatipes Skuse, which often occur together in Victorian streams, were shown in laboratory experiments to have preferences for different water velocities: larvae of A. furiosum preferred water velocities of 0.2–0.3 m s^–1, and S. ornatipes preferred water velocities of 0.9–1.3 m s ^–1 . Final instar larvae of both species selected slow water speeds of less than 0.25 m s ^–1 prior to pupation. Flow patterns around a cylinder in a laboratory stream were mapped, and the distribution of A. furiosum larvae within the wake, paired vortices and horseshoe vortex was recorded. Larvae selected areas with suitable water velocities and aligned with the flow, providing flow visualization of micro-current speed and direction. The potential for micro-habitat partitioning is discussed in relation to benthic sampling strategies.     

Factors affecting litter processing by Anisocentropus kirramus (Trichoptera: Calamoceratidae) from an Australian tropical rainforest stream

• 1 Larvae of the caddisfly Anisocentropus kirramus are common leaf shredders in rainforest streams in tropical Queensland. Laboratory experiments were undertaken to examine the effects of (a) differences in leaf species, age and degree of conditioning, (b) leaf preferences, (c) temperature and (d) larval stage on processing of leaf litter by A. kirramus.
• 2 Leaf species (five tested), age (fresh v senescent) and condition (conditioned in stream v unconditioned) each had a significant effect on the amount of leaf material that was processed. For most species, conditioned leaves were processed faster but for one species unconditioned leaves were processed faster. Senescent leaves were processed more rapidly than green leaves in three species but not in the other two. Given a choice of leaf types A. kirramus actively selected leaves that were processed faster; no preference was shown between two different ‘fast’ leaves.
• 3 Processing occurred at all temperatures tested (10, 18 and 25°C), with the processing rate increasing with temperature. Younger instar larvae processed leaves at a greater rate per unit body weight (up to 343% day^?1) than older instars. Final instar (5) larvae were capable of processing some tough leaves that younger instars did not process.
• 4 In rainforest streams, processing of leaves by A. kirramus takes place throughout the year. Its ability to process green leaves is important because of the high input of fresh green leaves into tropical streams, and because of the severe depletion of the supply of conditioned leaves and fine detritus after floods.

     

Biology of Anagrus atomus (Hymenoptera: Mymaridae), an egg parasitoid of the grape leafhopper Arboridia kermanshah (Homoptera: Cicadellidae)

Biology, morphology and oviposition behavior of Anagrus atomus (Linnaeus), an egg parasitoid of the grape leafhopper Arboridia kermanshah Dlabola in Isfahan, Iran, were investigated. Adults were smaller than those so far reported from other regions. Females continuously drummed on plant surfaces with their antennae to search for host eggs. Parasitoid eggs hatched 2–3 days after oviposition, and A. atomus had two larval instars. First instar larvae were sacciform and immobile. Second instar larvae appeared 4 days after oviposition and were very active, and doubled their body length. The prepupal and pupal stages lasted for 1 and 5–6 days, respectively. Adult emergence began 16 days after oviposition, and peaked on day 17.     

Instar sizes,life cycles,and food habits of five Rhyacophila (Trichoptera: Rhyacophilidae) species from the Appalachian Mountains of South Carolina,U.S.A.

The larval head widths at each instar, life cycles, and food habits of late instars were determined for five species of Rhyacophila from two Appalachian mountain streams in South Carolina, U.S.A. Rhyacophila acutiloba Morse & Ross was univoltine with two cohorts, one emerging in the spring and another presumably emerging in early autumn. Rhyacophila fuscula (Walker), R. nigrita Banks, and R. carolina Banks were apparently multicohort, univoltine species with extended flight periods. Rhyacophila minor Banks was univoltine with a spring emergence. All species were predaceous and consumed mainly Plecoptera nymphs and Trichoptera larvae.     

Movement and feeding patterns of Epilachna cucurbitae Richards (Coleoptera:Coccinellidae) on pumpkin and zucchini plants2

The oviposition patterns of adults and the movement and feeding patterns of larvae of Epilachna cucurbitae on two species of cucurbits, Cucurbita maxima cv Queensland Blue and C. pepo cv Blackjack, were studied in the field and laboratory. The physical and nutritional characteristics of host plant leaves of different ages were described. Younger leaves had higher nitrogen contents but were less abundant, smaller and had higher trichome densities than older leaves. The development of first instar larvae was delayed by the leaf hairs on young and mature pumpkin leaves which prevented larvae from reaching the leaf surface to feed First instal larvae developed more quickly on leaves rich in nitrogen. Neither the total developmental time of larvae nor the size of pupae was affected by leafage because larvae on poor quality leaves compensated by eating more. Female beetles oviposited on all but the youngest and oldest leaves of the host plant. The trichomes on young leaves prevented females from attaching eggs to the leaf surface. First instar larvae remained where they hatched, but older larvae were more mobile, Changing feeding sites frequently and moving progressively to younger, more nutritious leaves. Final instar larvae moved onto adjacent vegetation to pupate. The adaptive significance of these patterns is discussed in relation to the nutritional value, hairiness and abundance of host plant leaves of different ages and the physical limitations of different larval instars.     

Mate recognition inCryptomyzus aphids: copulation and insemination

The acceptability of three widely distributed Australian Menispermaceae,Tinospora smilacina Benth.,Sarcopetalum harveyanum F. Muell. andStephania japonica (Thunb.) Miers, as food for larvae of the fruitpiercing moth,Othreis fullonia (Clerck), was examined in three laboratory experiments. When larvae were presented with plant species individually total development times were shortest onT. smilacina and longest onS. japonica, despite relatively similar consumption rates within most instars.T. smilacina elicited greater (P<0.05) relative growth rates thanS. japonica in all instars except the 6th. In the second experiment, when larvae were allowed to select from each of the 3 plants, noS. japonica was chosen by 1 st instars and it represented only 3.7% of food consumed by 2nd instars. Significantly moreT. smilacina was eaten in each instar thanS. japonica, and more thanS. harveyanum except in the 2nd and 4th instars. The final experiment examined the abilities of larvae to switch hosts when forced after the 1st and 3rd instars. After the first or second food change largest average headcapsule widths were associated with feeding onT. smilacina as the most recent food. Feeding by final instars onT. smilacina also resulted in the shortest development time and highest puparial weights. While some larvae survived irrespective of plant sequence 83.3% of the recorded mortality occurred while larvae were exposed toS. japonica, principally during the 1st instar. These experiments lend support to field observations which suggest thatT. smilacina is a major host ofO. fullonia whileS. japonica is notS. harveyanum is probably an important alternate host whenT. smilacina is scarce.     

Dose-dependent influence of Microplitis rufiventris factors on developmental rate and growth of last-instar Spodoptera littoralis larvae

The solitary endoparasitoid, Microplitis rufiventris, attacks and can develop in earlier instars of Spodoptera littoralis larvae with preference to third‐instar larvae. We used the last stadium (sixth instar), a stage which is not naturally parasitized. The newly moulted larvae (0–3 h old) of this stadium were more acceptable for parasitization by the wasp females than the older ones (24 h old). Parasitization by M. rufiventris wasp of last instar S. littoralis larvae leads to dose (no. of eggs + parasitoid factors)‐dependent effects which were more pronounced at 20°C than at 27°C. A single oviposition into a sixth instar host larva resulted in normal development of the host. However, superparasitization increased the proportions of developmentally arrested hosts and number of live wasp larvae. Development of supernumerary individuals of the parasitoid in the host larva leads to dose‐related adverse effects on host growth and development. The present study may provide interesting opportunities for studying the physiological bases of host–parasitoid interactions and parasitoid intra‐specific competition in the biological system considered.     

Cyanide as a feeding stimulant for the southern army worm, Spodoptera eridania

ABSTRACT.

• 1 All instars of Spodoptera eridania larvae grow as well or better when cyanide is present in their diet as when it is absent. Concentrations up to 0.05% stimulate feeding in first to fourth instar larvae. Concentrations from 0.1% to 1.0% stimulate feeding in fifth and sixth instar larvae.
• 2 Three-day-old sixth instar larvae pre-exposed to cyanide are completely resistant to its acutely toxic effects, but previously unexposed larvae suffer reversible symptoms of poisoning when feeding on a diet containing 1.0% KCN.
• 3 A 1.0% dietary KCN exposure during the sixth instar reduces ecdysis to 17% adult emergence and completely inhibits oviposition.
• 4 Cyanide concentrations from 0.5% to 1.0% in the diet, although effecting increased growth rates, induce necrotic lesions in larval mid-gut epithelial cells.
• 5 Thiocyanate, one of the in vivo cyanide metabolites, at 0.5% in the diet reduces pupation to 23%, delays and reduces adult emergence to 20% and inhibits oviposition.
• 6 The preferred host plant of S.eridania is the lima bean, Phaseolus lunatus, probably due to its content of the cyanogenic glycoside linamarin. Dietary valine has no effect on the southern armyworm feeding and growth behaviour (Long & Brattsten, 1982) but dietary cyanide does. The lima bean is known to contain up to 31 ppm cyanide in some varieties.

     

The growth of Bibio johannis (L.) and Dilophus febrilis (L.) (Diptera: Bibionidae) larvae in the field

Bibionid larvae were extracted from soil samples collected from June 1985 to March 1987. Each larva was identified, weighed and measured for maximum head capsule width. Both Bibio johannis and Dilophus febrilis have six larval instars. Bibio johannis grew slowly in late summer and early autumn but rapidly from October to January. Early and late instar larvae of D. febrilis occurred simultaneously and it was concluded that this species was not bivoltine but may exist as two separate cohorts with distinct flight periods.     

Maternal behaviours may explain riffle‐scale variations in some stream insect populations

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Submergence tolerance in immature stages of the stalk-eyed fly Sphyracephala detrahens (Diptera: Diopsidae)

Sphyracephala detrahens (Walker, 1860) (Diptera: Diopsidae) inhabits the riparian zones of streams and rivers. Because of the limited dispersal ability of S. detrahens during egg, larval, and pupal stages, immature individuals are at risk of being submerged by floodwater after heavy rain. In this study, I evaluated the submergence tolerances of immatures of S. detrahens by comparing them to immatures of Drosophila melanogaster, which also feed on rotten fruits but are not restricted to the riparian zone. The results showed that S. detrahens eggs were susceptible to desiccation, but more than 80% of eggs hatched after full submergence. Later instar larvae were more resistant to full submergence than earlier instar larvae. The duration of submergence causing 50% pupation (PD₅₀) in the first, second, and third-instar larvae of S. detrahens were 15.88, 58.46, and 91.74 h, respectively. The PD₅₀ of the third-instar larvae of D. melanogaster was 20.01 h. Third-instar S. detrahens larvae continued to develop in water for a longer duration than D. melanogaster larvae of the same instar. In the pupal stages, late pupae tended to remain afloat longer than early pupae. The duration of submergence causing 50% emergence (ED₅₀) of adults from early and late pupae were 40.70 and 104.74 h, respectively. In the larval and pupal stages, individuals in the later developmental phases tended to be more tolerant to full submergence. The submergence tolerance of the immature stages of S. detrahens may reflect adaptation to an environment with fluctuating water levels.     

Onshore–offshore variations of copepod community in northern South China Sea

Previous studies which have tested the feeding preferences of shredders for fungal species and the food quality of fungi used detritus uniformly colonized by a fungus, which is not the case for decaying leaves in streams. It is not known whether shredders in different development stages exhibit variations in feeding preference and larval performance. This study examined the feeding preferences and the growth of the third and the fifth instars of Pycnopsyche gentilis larvae using fungal-colonized patches and whole leaves, respectively, having different fungal species compositions (Alatospora acuminata, Anguillospora filiformis, Articulospora tetracladia, Tetrachaetum elegans, and all species combined). The aquatic hyphomycetes used were co-dominant on leaves in the stream inhabited by the caddisfly. During 14 d of feeding, the larvae of both instars did not show significant differences in feeding preferences for the patches growing on oak leaves, although the third instar larvae were slightly more selective than the fifth instar larvae. When fed with maple leaves for 18 d, larval growth rates, gross growth efficiencies, and survivorship were not significantly different among the fungal treatments. However, the larval growth of both instars fed with fungal-colonized leaves was always significantly greater than the growth of larvae fed with diets of uncolonized leaves. The third instar larvae grew faster than the fifth instar larvae, but the growth efficiencies of the two instars were similar. These results suggest that P. gentilis larvae exhibit less selectivity in their feeding than other caddisfly shredders that have been examined and that the dominant fungi colonizing leaves in their habitat are similar in palatability and food quality for this shredder. Handling editor: B. Oertli     

Modified Behavior in Baculovirus-Infected Lepidopteran Larvae and Its Impact on the Spatial Distribution of Inoculum

Quantifying the rate of dispersal of target insects when infected with a disease agent will aid the development of biorational pest control programs. The effect of nucleopolyhedrovirus (NPV) infection on the mobility of second and fourth instarMamestra brassicaelarvae was investigated in the laboratory and field. NPV infection altered larval mobility, with the changes in behavior varying with the timecourse of infection. Diseased larvae moved three to five times further than healthy ones during the middle stages of infection. By the 7th day postinfection diseased larvae were less mobile than healthy counterparts. The same pattern of modified behavior was observed in both instars. Fourth instar larvae moved further than second instars under laboratory and field conditions. In the field, infected larvae tended to die on the apex of the cabbage leaves. Bioassay of the leaves showed a linear decrease in inoculum from central to peripheral plants within the plots, which occurred to the same extent for second and fourth instars. Leaves from plots where infected fourth instar larvae had been introduced had higher inoculum density than those from plots with second instars.     

Field experiments on the relationship between drift and henthic densities of aquatic insects in tropical streams (Ivory Coast). III Trichoptera

SUMMARY. 1. Based on in situ gutter trials we related the drift of caddis flies to their benthic densities and to various abiotic factors in streams in the Ivory Coast (West Africa). Members of the families Hydropsychidae, Philopotamidae. Hydroptilidae and Leptoceridae were considered in detail.
2. The drift of larvae peaked at night in both early and late larval instars.
3. Drift of a larval group (a certain instar, species or higher taxon) was more often related to the benthic density of other larval groups than to its own benthic density.
4. Self-regulation of an upper benthic density of a larval group by emigration through drift was not statistically evident.
5. There was no straightforward relationship between drift and abiotic factors.
6. Drift rates differed between taxa as well as between larval instars (size groups) within a taxon. Newly hatched larvae had very high drift rates, whereas the last larval instar usually had the lowest drift rate.
7. We related these results to the violently fluctuating discharge of the streams in the study area and the consequent variability of space for lotic insects.
8. Drift estimates, made at the same time as a monitoring programme on possible side-effects of insecticides (Onchocerciasis Control Programme), failed to reflect benthic densities except in the night drift of Hydropsychidae.     

斜纹夜蛾空间分布图式的研究

斜纹夜蛾幼虫在不同作物上的空间分布特征研究表明：幼虫在低龄阶段高度聚集,聚集的集团是成虫产卵的行为造成。在高龄阶段,聚集度下降,幼虫不断扩散,扩散的原因是密度制约因素引起。在白菜上,幼虫在4龄前为聚集分布,5龄以后为均匀分布,棉花和向日葵上各龄幼虫均为聚集分布。根据种群空间分布图式,导出了数据代换公式。     

Downstream drift of the larvae of Chironomidae (Diptera) in the River Chew,S.W. England

The drift of larval Chironomidae (Diptera) was investigated at two sites on the River Chew, using a pump filtration system with 50 µm mesh-aperture aerial nets, situated on the river bank.Chironomid larvae were found to drift in far greater numbers than previously reported, even in slow-flowing water. First and second instar larvae dominated the drift.Variation in drifting behaviour between taxa was observed, where Orthocladiinae drifted in all instars and Chironominae predominantly as first and second instars. Proportionally different rates of drift were observed between these taxa from the benthos at the two sites.It is suggested that the majority of chironomid drift represents an active dispersal and colonisation mechanism by which population redistribution and habitat selection occurs.