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Effect of malathion on larval competition in house fly (Diptera: Muscidae) populations
Abstract:
We studied the competitive abilities of 2 strains of house flies, Musca domestica L., A14/WHO, a strain heterozygous for resistance gene(s), and bwb, a susceptible strain, at 4 densities 450, 900, 1,800, and 3,600 eggs per 100 g of medium in pure and mixed cultures in the absence and presence of malathion. Both genotypes exhibited lower survival, lower mean adult weight, and longer developmental time as the density increased in an environment free of insecticide. There was a relative advantage of A14/WHO strain when mixed with bwb at densities > 450/100 g. At high densities, bwb in mixed culture was at a disadvantage relative to its performance in pure culture. In an environment with insecticide only the males of the A14/WHO strain survived. During these experiments, we observed a parabolic relationship between the egg density and the number of emerging adults in control experiments without malathion treatment. When cultures were treated with malathion, however, this relationship became linear and number of emerging adults increased with egg density. Malathion treatment reduced the intensity of larval competition at high densities by killing part of the population, thereby increasing yield. Malathion treatment also caused the emergence of much heavier flies.
Insights
House fly (Musca domestica L.) competition varied by strain and density. Malathion insecticide reduced larval competition, increasing adult yield and weight, but only males of the resistant strain survived insecticide exposure.
Area of Science:
- Entomology
- Population Genetics
- Pest Management
Background:
- Understanding insect population dynamics is crucial for effective pest control.
- House flies (Musca domestica L.) exhibit complex competitive interactions influenced by genetic resistance and environmental factors.
- Larval competition significantly impacts insect development and survival rates.
Purpose of the Study:
- To investigate the competitive abilities of insecticide-resistant and susceptible house fly strains.
- To determine the effects of larval density and malathion exposure on house fly population dynamics.
- To analyze the interplay between genetic resistance, density-dependent competition, and insecticide efficacy.
Main Methods:
- Comparative study of two house fly strains (A14/WHO - resistant, bwb - susceptible) under varying densities (450-3,600 eggs/100g).
- Experiments conducted in pure and mixed cultures, with and without malathion treatment.
- Evaluation of survival rates, adult weight, developmental time, and adult emergence.
Main Results:
- Increased density negatively impacted survival, weight, and development in insecticide-free environments for both strains.
- The resistant A14/WHO strain showed a competitive advantage over the susceptible bwb strain at densities above 450 eggs/100g.
- Malathion treatment linearized the density-yield relationship, increasing adult emergence and weight by reducing competition, but only resistant males survived.
- A parabolic relationship between egg density and adult emergence was observed without malathion, becoming linear with malathion treatment.
Conclusions:
- Larval competition intensifies with density, affecting house fly fitness.
- Insecticide resistance confers a significant competitive advantage under certain conditions.
- Malathion acts as a density-dependent mortality factor, altering population dynamics and potentially favoring resistant genotypes.
- Malathion application can enhance adult fly yield by mitigating intraspecific competition, with implications for pest management strategies.