Impact Of Sublethal Doses Research Articles

Current Insights into Sublethal Effects of Pesticides on Insects.

The effect of pesticides on insects is often discussed in terms of acute and chronic toxicity, but an important and often overlooked aspect is the impact of sublethal doses on insect physiology and behavior. Pesticides can influence various physiological parameters of insects, including the innate immune system, development, and reproduction, through a combination of direct effects on specific exposed tissues and the modification of behaviors that contribute to health and reproductive success. Such behaviors include mobility, feeding, oviposition, navigation, and the ability to detect pheromones. Pesticides also have a profound effect on insect learning and memory. The precise effects depend on many different factors, including the insect species, age, sex, caste, physiological condition, as well as the type and concentration of the active ingredients and the exposure route. More studies are needed to assess the effects of different active ingredients (and combinations thereof) on a wider range of species to understand how sublethal doses of pesticides can contribute to insect decline. This review reflects our current knowledge about sublethal effects of pesticides on insects and advancements in the development of innovative methods to detect them.

Impact of sublethal doses of thiamethoxam and Nosema ceranae inoculation on the hepato-nephrocitic system in young Africanized Apis mellifera

We analyzed the morphological changes on the hepato-nephrocitic system (HNS) of Africanized honey bees exposed to thiamethoxam (TMX) and to Nosema ceranae (NOS) in isolation and co-exposure. We also analyzed the relative amount of hemocytes in TMX and/or Nosema-exposed bees. Newly emerged bees were exposed individually per os to TMX, at doses of 0.0856 ng/bee or 0.00856 ng/bee, or to TMX doses and 60,000 spores of N. ceranae per bee. Eight days after the single exposure, the results showed that TMX was extremely deleterious to the HNS at 0.00856 ng/bee, dramatically inducing morphological changes in HNS cells (trophocytes and oenocytes) and increasing hemocyte number. However, the treatment to TMX at 0.00856 ng/bee with additional NOS inoculation provoked the highest critical damage observed on HNS, collapsing the trophocytes, reducing the surface area of oenocytes, and inducing cell death in pericardial cells. Therefore, a sublethal dose of TMX, applied alone or simultaneously with NOS inoculation, triggered the disruption of the HNS and induced progressive damage on worker bees. The results demonstrated an interaction between biotic and abiotic agents in Africanized bees at individual level, whose impact at the colonial level remains to be assessed under field conditions.

Copper Pollution Increases the Relative Importance of Predation Risk in an Aquatic Food Web.

Although the cascading impact of predators depends critically on the relative role of lethal predation and predation risk, we lack an understanding of how human-caused stressors may shift this balance. Emergent evidence suggests that pollution may increase the importance of predator consumptive effects by weakening the effects of fear perceived by prey. However, this oversimplification ignores the possibility that pollution may also alter predator consumptive effects. In particular, contaminants may impair the consumptive effects of predators by altering density-dependent interactions among prey conspecifics. No study has directly compared predator consumptive and non-consumptive effects in polluted versus non-polluted settings. We addressed this issue by using laboratory mesocosms to examine the impact of sublethal doses of copper on tri-trophic interactions among estuarine predator crabs Cancer productus, carnivorous whelk prey Urosalpinx cinerea, and the basal resource barnacles Balanus glandula. We investigated crab consumptive effects (whelks culled without crab chemical cues), non-consumptive effects (whelks not culled with crab chemical cues), and total effects (whelks culled with crab chemical cues) on whelks in copper polluted and non-polluted waters. Realistic copper concentrations suppressed the effects of simulated crab lethal predation (whelk culling) by removing density-dependent feeding by whelks. Specifically, reductions in conspecific density occurring in elevated copper levels did not trigger the normal increase in whelk consumption rates of barnacles. Weakened effects of fear were only observed at extremely high copper levels, suggesting consumptive effects were more sensitive to pollution. Thus, pollution may shape communities by altering the roles of predators and interactions among prey.

Sublethal impact of paraquat on the life span and parasitic behavior of Diaeretiella rapae M’Intosh

This study focuses on assessing the impact of sublethal doses of paraquat on the survival, the emergence, the life span and the parasitic behavior of Diaeretiella rapae M’Intosh (Hymenoptera: Braconidae). The impact of sublethal doses was measured at room temperature using different densities of the cabbage aphid Brevicoryne brassicae. The results reveal that the field dose of paraquat caused 100% mortality in D. rapae. The percentage emergence of D. rapae decreased from 80.5% in the control group to 71.5% when treated with the lowest concentration of paraquat. Similarly, the life span of parasitoids that emerged from the mummy treated with paraquat also decreased significantly. Oviposition capability and ovipositor thrusting frequency of D. rapae also treated with sublethal dose paraquat decreased significantly along with a shortened patch residence time in the foraging area.

Sub-lethal effects of SpltMNPV infection on developmental stages of Spodoptera litura (Lepidoptera: Noctuidae)

Application of different doses of SpltMNPV on final instars of Spodoptera litura showed dose-related mortality. A significant increase in the time for pupation and progeny mortality as well as reduced fecundity was observed in surviving larvae. Impact of sublethal doses on subsequent generation needs attention in designing baculovirus-based pest management.

Impact of Sublethal Doses of 2,4-D, Simulating Drift, on Tomato Yield

Tomato is considered one of the most sensitive crops regarding 2,4-D drift. In many cases, such susceptibility has led to important restrictions in the use of 2,4-D based products. Field experiments were carried out for two consecutive years in tomato, by applying sublethal doses of 2,4-D (ranging from 0.42 to 13.44 g a.i. ha−1) directly to plants, at different stages of growth, as a simulation of eventual drifts to the crop. The range of rates was based on the assumption of a 0.0625–2.0% drift level of a 1 L ha−1 of the most common formulated herbicides. For this crop, the range of rates between 0.42 and 13.44 g a.i ha−1 applied at the beginning of flowering caused a linear crop reduction. On the other hand, rates ≤13.44 g a.i. ha−1 applied after full development of fourth truss stage or latter had no effect on crop yield or development. For tomato, tolerance to 2,4-D strongly increases with plant age.

FENITROTHION: CARRY-OVER EFFECTS ON THEF1GENERATION OFMANDUCA SEXTA(LEPIDOPTERA: SPHINGIDAE)

In a previous investigation on the effects of sublethal doses of fenitrothion (O,O-dimethyl-O-(3-methyl-4-nitrophenyl)phosphorothioateo)n the tobacco hornworm,Manduca sexta(L.), it was found that the treated larvae developed asynchronously, required more time to reach the pupal stage, and had larger bodyweights than the control larvae (Stewart and Philogène 1983). Regressive moults, faster pupal development, and shorter longevity of the adults were also observed. The impact of sublethal doses of insecticides on subsequent generations of insects has, however, received limited attention. We now present experimental evidence that the progeny of treated insects can also show some of the characteristics described above, an observation that may have significant consequences in the field.