Mortality Of Fourth Instar Larvae Research Articles

Interaction between Steinernema feltiae SC125 and Metarhizium anisopliae sensu lato 9236 for control of the Guatemalan potato moth

ABSTRACT The Guatemalan potato moth (Tecia solanivora) is one of the most destructive pests affecting potatoes in Colombia. Our objective was to evaluate the susceptibility of T. solanivora to a combination of entomopathogenic nematodes and entomopathogenic fungi, to study the interactions of these two agents under laboratory conditions. We evaluated the mortality of fourth instar larvae against 200 Infective Juveniles (IJs) per larva of ten strains of entomopathogenic nematodes, and 104–108 conidia per larva of Beauveria bassiana sensu lato Bb9205 and Metarhizium anisopliae sensu lato Ma9236. We found that Steinernema feltiae SC125 caused a mortality rate of 98.2% with an LC50 of 33 IJs/larva. M. anisopliae sensu lato Ma9236 achieved a mortality rate of 88.8% with an LC50 of 6.9 × 105 conidia/larva. We selected these strains for the interaction tests. We determined that the interaction test results were statistically additive regardless of any difference in application times of the entomopathogens and despite the observation of signs of infection in the hosts from both the nematode and the fungus. Despite not having found synergistic interactions between the evaluated control agents, these laboratory tests suggest a possible strategy of combining entomopathogenic nematode and fungi for biological management of the guatemalan moth T. solanivora in potato crops.

Larvicidal activity of essential oils of Haridra and Tulsi against Aedes aegypti and Anopheles larvae

An attempt is made in the present study to analyse the larvicidal activity of Haridra and Tulsi against Aedes and Anopheles larvae. Larval bioassays were carried out at different concentrations 50-500ppm. The larval mortality of fourth instar larvae of A. aegypti and Anopheles after 24h of treatment was observed separately in control, 50, 62.5, 100, 150, 250, 300 and 500 ppm concentrations. Based on the Probit analysis, Significant effect (Estimate adh_conc = 3.069, 95% C.I. [2.082, 4.057], z = 6.093, p<.05) of Haridra oil extract concentration for Aedes (adh_conc) on the Probit response or mortality was observed. The median lethal Concentration, LC50= 166.353, 95% C.I. [134.745, 203.268], 90% Lethal Concentration, LC90 = 435.065, 95% C.I. [328.259, 712.462] were recorded. Statistical analysis revealed that significant effect (Estimate adt_conc = 3.369, 95% C.I. [2.229, 4.509], z = 5.791, p<.05) of Tulsi oil extract on Aedes larvae concentration (adt_conc) on the Probit response or larvae mortality (adt_mort) was observed. The median Lethal Concentration, LC50= 105.051, 95% Confidence Intervals (C.I). [81.451, 127.428], 90% Lethal Concentration, LC90 = 252.242, 95% C.I. [199.229, 376.772] of essential oil of Tulsi oil against Aedes aegypti larvae was recorded. No mortality of Aedes larvae was recorded in the control group. Essential oil of Haridra at different concentrations shows a significant effect (Estimate anh_conc = 2.038, 95% C.I. [1.180, 2.896], z = 4.655, p<.05 against the mortality of Anopheles Larvae on the Probit response or mortality. The median Lethal Concentration, LC50 = 124.823, 95% Confidence interval CI. [84.002, 164.336], 90% Lethal Concentration, LC90 = 530.978, 95% C.I. [349.474, 1333.827] of essential oil of Curcuma longa against Anopheles larvae was recorded. (Estimate ant_conc = 2.257, 95% C.I. [1.135, 3.200], z = 4.694, p<.05) of Tulsi oil - extract on Anopheles Larvae concentration (ant_conc) on the Probit response or mortality (ant mort) was observed. Median Lethal Concentration, LC50 = 339.419, 95% Confidence Interval (C.I.) [259.239, 533.727], 90% Lethal Concentration, LC90 = 1254.519, 95% C.I. [717.77, 4574.12] of essential oil of Tulsi oil against Anopheles larvae. Larvicidal activity of both the plants against Aedes larvae at different concentration was significant. But LC50 and LC90 values of Ocimum sanctum (Tulsi) against mortality of Aedes aegypti were less as compared to Curcuma longa (Haridra). It revealed that Tulsi showed better larvicidal activity against Aedes larvae as compared to Haridra. It was also observed that LC50 and LC90 values of Haridra against Anopheles larvae were less than Tulsi. It revealed that Haridra showed better larvicidal activity against Anopheles larvae as compared to Tulsi.

Potential of chemical insecticides on fourth larvae instar of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae)

Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) is an important pest of Brazilian agriculture, whose management is oriented mainly towards controlling larvae. The objective of the research was to analyze the effect of chemical insecticides on fourth instar larvae of H. armigera. The research was conducted under laboratory conditions, corresponding to the treatments control, zeta-cypermethrin (37.5 mL /500 L); lambda-cyhalothrin (75 mL/ 150 L); chlorpyrifos (1.0 L / 300 L); bifenthrin + carbosulfan (1.0 L / 350 L); and beta-cyfluthrin (60 mL / 250 L). The bioassays were conducted in plastic containers containing an artificial diet. After treatment applications on the food substrate, and subsequent drying, two larvae were inserted per container, the set of four containers being considered a replicate, totaling four replicates per treatment, with mortality evaluations after 24, 48, 96 and 144 h after the applications. The sublethal effect was analyzed by evaluating the average weight of larvae and pupae (g), and emergence of adults (%). The active ingredients chlorpyrifos and bifenthrin + carbosulfan caused 100% mortality of fourth instar larvae of H. armigera from 48 h after the applications. After 96 h of phytosanitary application, lambda-cyhalothrin was responsible for causing mortality above 80%. Regarding the sublethal effect, better results were observed in the lambda-cyhalothrin and beta-cyfluthrin treatments, influencing the average weight of the larvae and the emergence of adults. The active ingredients chlorpyrifos, bifenthrin + carbosulfan and lambda-cyhalothrin are potential insecticides in the management of fourth instar larvae of H. armigera.

Biopesticides offer an environmentally friendly solution for control of pine processionary moth (Thaumetopoea wilkinsoni Tams) larvae and pupae in urban areas

ABSTRACT Within the framework of finding new biological control methods to suppress allergic effects of pine processionary moth (PPM), Thaumetopoea wilkinsoni Tams, less toxic and environmentally friendly, entomopathogenic fungi and essential oils are considered to be an alternative to chemical insecticides. The aim of the present study was to investigate the effects of essential plant oils and two isolates of Metarhizium brunneum (V275 and ARSEF4556) on PPM larvae and pupae under field and controlled laboratory conditions. PPM larvae inside the nest and late instar larvae preparing to pupate were highly susceptible to both strains of M. brunneum, which caused 100% mortality in the laboratory and 45–100% mortality in field trials. The insecticidal effects of essential oils (ginger, eucalyptus and rosemary) on the first, third and fourth instar larvae of PPM were proportional to dosage and life stage of insect. Ginger oil diluted in water was toxic to first instar larvae even at a dose as low as 1% and 3% (v/v). Field trials showed that injection of essential oils into nests of third instar larvae caused significant mortality (87.4%) but <5% mortality of fourth instar larvae. Surface application of all essential oils at a concentration of 5% killed half of the larvae in one day, while 1% concentration caused from 0% to 20% mortality. Only 1% ginger caused 63% mortality at the end of the trial. This study shows that ginger oil and M. brunneum strains ARSEF 4556 and V275 show promise for the control of PPM larvae under field conditions.

Nano-sized Al2O3 reduces acute toxic effects of thiacloprid on the non-biting midge Chironomus riparius.

This study focuses on interactions between nanoparticles and a pesticide. The aim was to investigate how nano-sized aluminum oxide (410 nm) can alter the toxic effects of thiacloprid, even if no sorption between particles and the insecticide takes place. Thus, our study investigated a rather unexplored interaction. We conducted our research with larvae of Chironomus riparius and used thiacloprid as test substance as its toxicity to C. riparius is well described. The used nano-Al2O3 particles where chosen due to their suitable properties. For testing the acute effects of the interaction, we exposed larvae to thiacloprid (0.5, 1.0, 2.0, and 5.0 μg/L) and nano-Al2O3 (300 and 1000 mg/L), either solely or in binary mixtures. While thiacloprid resulted in elevated mortality, nano-Al2O3 solely did not exert any effects. Moreover, we observed an aggregation of nano-Al2O3 within the lumen of the intestinal tract of the larvae. Further results showed a significantly reduced mortality of fourth instar larvae when they were exposed to mixtures of nanoparticles and the pesticide, compared to thiacloprid alone. With increasing nano-Al2O3 concentration, this effect became gradually stronger. Additionally, chemical analyses of internal thiacloprid concentrations implicate reduced uptake of thiacloprid in animals exposed to mixtures. However, as larvae exposed to thiacloprid concentrations > 0.5 μg/L showed severe convulsions, independent of the presence or concentration of nano-Al2O3, we assume that nano-Al2O3 leads to a delay of mortality and does not entirely prevent it. As sorption measurements on pristine or defecated nano-Al2O3 did not reveal any sorptive interaction with thiacloprid, we can exclude sorption-based reduction of thiacloprid bioavailability as a mechanism behind our results. Even though we used test substances which might not co-occur in the environment in the tested concentrations, our study gives evidence for an interaction besides adsorption, which is important to generally understand how nanoparticles might affect biota.

Larvicidal activity and GC–MS analysis of Leucas aspera against Aedes aegypti Anopheles stephensi and Culex quinquefasciatus

The mosquitocidal activity of aqueous, ethanol, methanol, chloroform and petroleum ether plant extracts of Leucas aspera against Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus was analyzed. The larval mortality of fourth instar larvae of Ae. aegypti, An. stephensi and Cx. quinquefasciatus after 24h and 48h of treatment was observed separately in control 30, 40, 50, 100, 150, 200, 250, 300, 350, 400, 450 and 500ppm concentrations. The plant extracts were screened to identify the phytochemical bioactive compounds. Ae. aegypti was found to be most susceptible than the other species. Based on probit analysis the 24h and 48h methanol extracts of L. aspera showed pronounced larvicidal activity when compared with the other extracts. An LC50 and LC90 value of methanol extracts against Cx. quinquefasciatus was found to be 37.649ppm and 27.855ppm (24h), 79.150ppm and 73.284ppm (48h) respectively. LC50 and LC90 values were 35.624ppm and 20.897ppm (24h), 64.260ppm and 60.096ppm (48h) against Ae. aegypti. The 24h and 48h LC50 and LC90 values of ethanol extracts of L. aspera were found to be 40.877ppm and 34.359ppm, 72.903ppm and 67.355ppm against An. stephensi. The extracts of this plant showed potent larvicidal efficacy and can be considered for further investigation.

Effect of a Bt-based product (Vectobar) on esterases and phosphatases from larvae of the mosquito Aedes aegypti

Bacillus thuringiensis (Bt)-based formulations possess potent insecticidal property, and they are being used in insect vector control programs all over the world. In this study, we examined the efficacy of a Bt-based product (Vectobar) on two developmental stages (fourth instar larvae and pupae) of the mosquito Aedes aegypti. Vectobar at a concentration of 0.25ppm was found to inflict 100% mortality of fourth instar larvae of A. aegypti within 24h. By contrast, this Bt-based product tested up to 2ppm was not effective against the pupae of A. aegypti. The systemic effect of Vectobar was further assessed in the fourth instar larvae of A. aegypti by measuring the levels of total proteins and activity of two important marker enzymes: esterases and phosphatases. Exposure of the larvae to Vectobar at a lethal threshold concentration (0.05ppm) significantly decreased the level of total protein (34%) as well as the activities of acetylcholinesterase (36%), α-carboxylesterase (34%) and alkaline phosphatase (49%). On the other hand, 40% increase in the level of acid phosphatase activity was recorded in these larvae. The Vectobar did not affect the level of β-carboxylesterase activity in the larvae of A. aegypti. This investigation clearly demonstrates differential modulation in the activities of esterases and phosphatases in Vectobar exposed larvae of A. aegypti.

Temperature effects on the action of acylurea insecticides against tobacco hornworm (Manduca sexta) larvae

The toxic effects of six acylurea insecticides on larvae of the tobacco hornworm were investigated at each of four environmental temperatures (20, 25, 30 and 35°C). This spans the range of temperatures which the insects can tolerate. For all the acylureas tested, mortality increased with temperature when either newly hatched or fourth-instar larvae were given insecticide in their food. Sub-lethal growth inhibition also became more pronounced at progressively higher environmental temperatures. This temperature dependence of acylurea action was not due to altered uptake of the insecticide, since there was no significant variation with temperature in the amount of [14C]flufenoxuron taken up by fifth-instar larvae when given a single meal containing labelled insecticide. Additionally, mortality of fourth-instar larvae given a single intra-haemocoelic injection of flufenoxuron was significantly greater at higher temperatures, implying that temperature affects a process that occurs after insecticide uptake. The intrinsic ability of acylureas to inhibit chitin synthesis is temperaturesensitive, since flufenoxuron inhibited the incorporation of [14C]N-acetylalucosamine into chitin by proleg epidermis in vitro significantly less well at 20°C than at the higher temperatures tested. However, there was no significant variation between the effectiveness of in-vitro chitin synthesis inhibition at 25, 30 and 35°C. These data show that the effectiveness of acylurea insecticides is subject to strong temperature effects in the range of temperatures likely to be experienced in the field.

The effect of a predatory leech, Nephelopsis obscura, on mortality, growth, and production of chironomid larvae in a small pond.

The effect of a predatory leech, Nephelopsis obscura, on survivorship, growth, and production of chronomid larvae was studied by enclosure experiments carried out in a small pond. The prey population was composed almost entirely of the tubiculous, microphagous chironomid larvae, Chironomus riparius and Glyptotendipes paripes. Nephelopsis significantly reduced chironomid survivorship within the enclosures, and accounted for most of the measured mortality of fourth instar larvae. The cropping by Nephelopsis was not significantly biased toward either prey species. In long-term experiments (66 d) chironomid biomass in enclosures without leeches reached much higher levels than in enclosures containing Nephelopsis. This increase in biomass was due to growth of surviving larvae, rather than recruitment, since emergence and oviposition were not going on during the course of the experiments. The enhanced survivorship of larvae within leech-free enclosures was eventually accompanied by reduced growth and specific production (daily production/biomass) for C. riparius, which made up about 90% of the larval population. Growth and specific production of G. paripes (10% of larval population) was not affected. Short-term experiments (25 d) involving manipulation of densities and species ratio (9:1 CR:GP and 1:9 CR:GP) of larvae revealed that growth of the majority species was strongly influenced by larval density, whereas growth of the minority species was not. The same pattern was observed both in the presence and in the absence of Nephelopsis and was a result of differences in resource utilization between the two species. In the shortterm experiments, growth rates estimated for larvae exposed to leeches were significantly less than those for larvae in leech-free enclosures. This could be due either to size-biased consumption of larvae by Nephelopsis, or possibly a disturbance factor leading to reduced larval food intake and/or increased metabolic costs.

Toxicological Action of DDT on Three Species of Mosquito Larvae

In tests by radiometric methods the amount of DDT picked up and its relation to the mortality of fourth-instar larvae of Anopheles quadrimaculatus Say, Aedes taeniorhynchus (Wide.), and Aedes aegypti (L.) varied with the exposure time and the concentration. Larvae did not excrete DDT except when exposed to concentrations above the minimum LC-100. The toxic action of DDT on quadrimaculatus larvae differed from that on aegypti. Resistance to DDT in a strain of taeniorhynchus was not related to the uptake or the excretion. Live quadrimaculatus larvae absorbed three times as much DDT as dead larvae; however, in a 24-hour test period the surviving larvae had about the same dose as the nonsurvivors.