Reduction In Number Of Larvae Research Articles

A Removal Experiment with Darkling Beetles: Lack of Evidence for Interspecific Competition

A removal experiment tested for interspecific competition among darkling ground bee- tles (Tenebrionidae) in a montane New Mexico meadow. Adult Eleodes obscures were removed from three fenced 0. 1-ha plots from August 1975 through August 1978. This species accounts for >50% of the adult tenebrionid biomass in the community (Wise, in press). Adult E. obscures numbers were rapidly reduced and were kept low throughout the experiment. Removing adults should also have reduced densities of the soil-dwelling larvae, though the extent of any reduction in larval numbers could not be measured directly. Three plots in which E. obscures adults were not removed were controls. Adult population densities of the other species did not increase in response to reducing E. obscures density. Adult size was also measured because increased size at eclosion from the pupa would reflect release from competition among larvae. Removing E. obscures adults produced no consistent evi- dence that competition between larval E. obscures and larvae of the other species was influencing their size at eclosion. Adult size differed more between years than between removal and control plots. The number of E. obscures adults emerging in the removal plots had not declined by 1978. Thus, lack of evidence for larval competition may reflect failure to have reduced substantially densities of E. obscures larvae rather than the absence of competition. However, adult E. obscures densities were substantially reduced, yet the other species showed no evidence of competitive release. Inter- specific competition between adults may not be a major interaction in tenebrionid communities.

Fall Armyworm Control in Whorl-Stage Sorghum, 1979

Abstract Three tests were utilized to evaluate the effectiveness of various materials in controlling fall armyworms in sorghum whorls. The tests were planted in Cecil clay soil by conventional tillage methods on July 17’79. Test 3 was ratooned and fertilized on Sept 7’79. Hybrids planted were Funk’s HW 1762 (Test 1) and Funk’s G522DR (Tests 2 and 3). Treatment dates for the respective tests were Aug 17V9, Aug 29’79, and Sept 28’79. Treatments were applied with compressed-air sprayers calibrated to deliver 60 gal H2O/acre. Control was evaluated 3 and 7 day postapplication by counting larvae in the whorls within a 3-m section of the middle row of each plot. All plots were 6.1 m × 3 rows. All tests incorporated a completely random design with 3 (Tests 1 and 2) or 4 (Test 3) replicates. Some natural reductions in larval numbers occurred at 7 days post-application and were probably due to increasing plant maturity beyond the whorl stage.

Trichinella spiralis: Effects on the host-parasite relationship in mice of BCG (attenuated Mycobacterium bovis)

The effects of BCG (Bacillus Calmette-Guérin, i.e., attenuated Mycobacterium bovis) on the host-parasite relationship in murine trichinosis were examined. A total of 2 × 10 7 colony forming units of BCG given iv 1 week prior to Trichinella spiralis infection delayed the expulsion of adult worms from the gut. The suppression of adult worm elimination was proportional to the dose of BCG given. This finding was associated with a reduction in the degree of partial villous atrophy induced in the small bowel by T. spiralis. Adult female worms were fecund when they were examined 1, 2, and 3 weeks after infection of mice with T. spiralis. Despite the prolongation of fecund adult worms in the gut, there were no significant differences in muscle larval counts 4 and 6 weeks after infection. When newborn larvae were cultivated in vitro and injected iv, there was a significant 25% reduction in larval numbers recovered from the muscles of BCG-treated mice 4 weeks later. The administration of BCG had no effect on the inflammatory reaction around larvae in the muscles 4 and 6 weeks after infection. It is concluded that BCG alters the host-parasite relationship producing retention of adult worms in the gut, reduction in the severity of partial villous atrophy, and increased nonspecific resistance to the systemic larval phase of this parasite.

Strongylus vulgaris infection in the horse.

The work described in this thesis is concerned with studies on various aspects of infection with one of the most common and pathogenic of the equine helminths, Strongylus vulgaris. In order to facilitate these experimental studies, an efficient technique was developed for the production of large numbers of S. vulgaris infective larvae in pure culture; in this, third stage S. vulgaris larvae were obtained by surgically transferring adult worms, collected from horses immediately after slaughter, directly into the caeca of worm-free yearling ponies. Subsequently, various investigations on the life-cycle, pathogenesis, epidemiology and immunity of S. vulgaris infection were carried out. Considerable controversy existed concerning the migratory route taken by developing parasitic larval stages of S. vulgaris in the tissues of the host. In order to elucidate this, worm-free pony foals were infected with a pure culture of infective larvae and killed at intervals over a period of 9 months. The results showed that infective larvae exsheathed and penetrated the intestine within a few days of infection. These larvae then moulted in the sub-mucosa, penetrated small arteries and had migrated within the lumina of the intestinal arteries to the anterior mesenteric site by 14 days after infection; in this predilection site larvae developed from early to late fourth stage. After a period of 3 - 4 months the fourth moult was completed and the young adults returned to the intestine again via the lumina of the arteries. Nodules were formed with the subsequent release of young adults into the intestinal lumen. The pre-patent period was 6-7 months. Studies on the pathogenesis of S. vulgaris infection showed that a distinct clinical syndrome occurred within 3-4 weeks of infection in foals given doses of 750 infective larvae. This syndrome was one of pyrexia, anorexia and colic associated with the presence of fourth stage larvae in the intestine and mesenteric arteries. Examination of tissues taken from foals killed over a period of 9 months demonstrated the sequence of pathological changes. During the course of these studies infected foals showed a marked polymorphonuclear leucocytosis and an eosinophilia together with an increase in the serum globulin levels; the latter appeared to be due mainly to increases in the p -globulin levels. Subsequently using 125I labelled albumin and 51Cr labelled red blood cells it was shown that the rate of albumin catabolism was increased and the red cell survival time reduced in ponies with patent infections. The epidemiology of equine helminthiasis was studied in 2 separate systems of management over 2 years. Basically 2 regimens were employed: one where untreated mares and foals went out in the spring to pastures never previously grazed by horses while in the other, mares, regularly treated with anthelmintics, and their foals grazed contaminated pasture. These systems allowed 2 sources of infection for susceptible foals: where mares were treated, the main source of infection was from overwintered larvae; where infected mares went out to clean pasture infection of the foals could only occur from larvae which developed from eggs passed in the faeces of the mare. The results demonstrated the following points. First, foals going out to grass in the spring can be infected by both overwintered larvae and by eggs passed in the faeces of their dams but the latter is by far the more important source of infection. Secondly, where horses remain untreated throughout the grazing season high levels of third stage strongyle larvae develop on pasture, whereas regular anthelmintic treatment at intervals of 2 - 4 weeks reduces pasture contamination to a minimum. Thirdly, although high levels of infective larvae may occur on pasture grazed by infected animals during the summer and autumn, these levels fall during the winter and by May the following year virtually no third stage larvae can be recovered from these pastures. The results of a series of experiments on the immunity to S. vulgaris infection provided the following Information. First, an age immunity was demonstrated when S-year-old worm-free ponies were infected with S. vulgaris larvae. No clinical signs or gross arterial lesions developed in these animals and no fourth stage larvae were recovered at necropsy. Secondly, a degree of acquired immunity in terms of resistance to reinfection was demonstrated in groups of naturally and experimentally infected animals. Finally, the results of a preliminary vaccination experiment have shown that the arterial lesions are less severe and that there is an 80% reduction in larval numbers in vaccinated foals compared to challenge controls.

The effects of dung beetle activity on the numbers of parasitic gastrointestinal helminth larvae recovered from pasture samples

Studies have been made of the effect of the dung beetle, Onthophagus gazella, on the release of strongyle larvae from cattle faeces onto pasture. A series of faecal pats containing parasitic nematode eggs was placed on pasture, and beetles were added to some pats to give three levels of beetle activity, viz. 100 g, 200-250 g, and 500 g of faeces per pair of beetles. These pats were duplicated on irrigated and non-irrigated pasture. In both cases the numbers of strongyle larvae migrating from pats attacked by dung beetles were significantly less than those migrating from control pats containing no dung beetles. Compared with larval recoveries from control pats, the percentage reduction in numbers of larvae migrating from pats on irrigated pasture was 50% for pats of 100 g faeces per pair of beetles, 48 % for pats of 200-250 g faeces per pair, and 84% for pats of 500 g of faeces per pair. The respective figures for pats on nonirrigated pasture were 76, 86, and 93 % reduction in larval numbers. The results indicated that strongyle larvae migrated from faecal material buried by dung beetles, provided soil moisture was adequate. More larvae were recovered from the pasture surrounding irrigated faecal pats attacked by beetles than from the non-irrigated pats. During warm dry weather, surface faecal debris remaining after beetlc attack appeared to be helminthologically sterile.

Insecticidal Control of the Alfalfa Weevil1 in Northern Utah and Some Resulting Effects on the Weevil Parasite Bathyplectes curculionis2

Since 1962, annual experiments for control of Hypera postica (Gyllenhal) have been conducted in northern Utah. During most of these seasons, the effects on the major parasite, Bathyplectes cuculionis (Thomson), were also evaluated. Only 2 materials, carbofuran and phorate, showed promise when applied at the time alfalfa growth started in the spring. These early-season treatments had little or no effect on the parasite. Many materials controlled weevil larvae when applied during late May about 2 to 3 weeks before the 1st cutting. Carbofuran, methyl parathion, parathion, diazinon, GS-13005 ( O,O -dimethyl phosphorodithioate S-ester with 4- (mercaptomethyl) -2-methoxy ∆2-1,3,4thiadiazolin-5-one), azinphosmethyl, and methoxychlor usually gave 80 and 95% reduction in larval numbers, evaluated just before harvest. All treatments applied before cutting reduced the total adult parasite numbers, but only a few longer residual insecticides lowered the percentage of parasitized larvae. The parasite adults returned quickly in plots treated with the shorter residual materials. No treatments killed the parasitized larvae more readily than the unparasitized. Postharvest treatments applied to the stubble during late June or early July caused alfalfa growth to respond quickly, but the actual control was hard to measure. Carbofuran, Imidan® (O, O-dimethyl S -phthalimidomethyl phosphorodithioate), malathion, parathion, methyl parathion, and GS-13005 were all effective. Damage to the parasites was slight, although there was sometimes significant reduction in numbers following stubble treatments. Imidan, methoxychlor, and trichlorfon were generally less damaging to the parasites than the other insecticides tested. Trichlorfon was the least toxic to the parasites, but was ineffective in weevil control.

Field trials in 1963 on the control of grass grub (Costelytra Zealandica (White)) with insecticides

Abstract Three field trials laid down in 1963 to compare various granular insecticide treatments for control of grass grub (Costelytra zealandica (White)) are described, and results obtained during the season of treatment and that following are presented. The effectiveness of treatments was assessed by larval counts and by pasture growth response. Of the 12 insecticides compared with DDT only the chlorinated hydrocarbons heptachlor (at 2 and 1 lb a.i. per acre) and isobenzan (at 0.5 lb per acre) gave effective results. None of the 10 organophosphates tested produced significant effects except diazinon (at 2 lb a. i. per acre), which produced a temporary reduction in larval numbers during the season of application in one trial. On two of the three sites, DDT produced no detectable effect, either in the season of application or that following. In one case this was shown to be due to the presence of a DDT-resistant strain of grass grub and in the other probably to inadequate penetration into the soil despite plentiful rainfall.

The Incidence and Effect of Egg Cannibalism in First-Instar Coleomegilla maculata lengi (Coleoptera: Coccinellidae)

In field-collected egg masses more than 21% of the eggs were destroyed by first-instar larvae from the same egg mass. Since 39.8% of these were estimated to be nonviable, the effective reduction in number of larvae owing to egg cannibalism by undispersed first-instar larvae was 12.7%. Cannibalistic behavior has been stated to have survival value, since this food supply lengthens the life and increases the chance of finding prey by otherwise nonfed larvae. Laboratory experiments showed that cannibalism lengthens the life span, but results also in larvae which disperse from the egg mass later and are less active than noncannibalistic larvae, so their chances of finding prey are reduced. Cannibalism might still be an advantage under low-prey-density situations were it not for the known fact that this species can maintain itself and mature on substances other than prey. Therefore, this behavior may not be advantageous to the role of larvae as natural control agents.

Problems in assessing insecticidal control of Amnemus species (Coleoptera. Curculionidae) in clover pastures of north coastal New South Wales

Results are presented of 15 experiments made in north coastal districts of New South Wales from 1957 to 1961 with insecticides against the weevils Amnemus quadrituberculatus (Boh.) and A. superciliaris (Pasc.), the larvae of which have been reported as pests attacking the roots of clover (Trifolium repents, T. pratense and T. subterraneum) there. The adults live above ground, and single surface applications of insecticides were made to pastures in the form of dusts, granules or dilutions of emulsifiable concentrates in January, when maximum numbers of weevils were present and before significant oviposition had taken place. Insecticidal control was assessed by soil sampling for larvae in July–August, during the following winter. Pasture cuts were made in an attempt to assess the effect of treatments on the yield of clover.Dieldrin at rates of 2 and 4 lb. per acre gave near eradication of Amnemus for one year, and satisfactory control was obtained with 1 lb. per acre. Aldrin, endosulfan (Thiodan) and BHC were less effective, and limited tests with heptachlor suggested that it was inferior to dieldrin. The scanty results available suggest that dieldrin is effective against Amnemus for only one year, but it is doubtful if annual applications are warranted. Owing to the patchy distribution of clover in the pastures, only one experiment showed an increased yield of clover associated with the reduction in numbers of larvae of Amnemus brought about by the application of 1 lb. dieldrin per acre. Similarly, poor persistence of clover on all plots prevented assessment of any residual effect on yield in the second year.No method was found by which accurate estimates could be made of the density and distribution of adults of Amnemus in pastures to which insecticides were to be applied. Treatments, therefore, were replicated more frequently than was needed statistically in order to ensure that measurable levels of larval infestation were present at sufficient sites.Small plots (500–700 sq. ft.) proved of little value, and this is attributed not only to contamination of control plots but possibly also to the death of weevils that moved from untreated into treated plots. Large plots (13,000–21,000 sq. ft.) gave the most consistent results in assessment of insecticides.Control of Amnemus did not increase the productivity or persistence of clover, and it is concluded that any benefits from control are unlikely to be significant unless other factors, such as competition from grasses, drought, floods, nematodes and diseases of clover, which affected the density and persistence of clover in these experiments, are not limiting.