Biology in the Chemical Industry

Scientific Approaches to the Problem of Insecticide Resistance, 1920s–1960s

Introduction: The Unseen Arms Race

In the mid-20th century, as synthetic insecticides revolutionized agriculture and public health, scientists encountered a baffling phenomenon: the very pests they were trying to eradicate were beginning to survive. This was not a case of ineffective chemicals, but rather the dawn of a new evolutionary reality. Insecticide resistance had emerged as a formidable problem, forcing a profound shift in the chemical industry's approach.

What began as a purely chemical problem—developing more potent formulas—soon demanded a deep dive into the complex world of biology.

This is the story of how biologists, working within the chemical industry, helped decode this evolutionary puzzle and forever changed our approach to pest control ¹ .

Chemical Industry

Initially focused on developing more potent formulas

Insect Pests

Developing resistance through evolutionary processes

Biology

Provided the key to understanding resistance mechanisms

The Chemical Dawn and a Biological Reckoning

The post-war era saw an explosion in the use of synthetic organic insecticides. DDT, developed by the Geigy company, was hailed as a miracle weapon, with its broad-spectrum efficacy and persistence ¹ ³ . For a time, it seemed chemical ingenuity had won the war against insect pests.

Production Boom

Production of insecticides like lead arsenate and calcium arsenate skyrocketed to meet demand, with one manufacturer's output of calcium arsenate exploding from 50,000 pounds to over 10 million pounds annually in just a few years following its introduction ⁶ .

Control Failures

By the 1950s and 1960s, reports of control failures became increasingly common. The initial industry response was often to attribute failures to ineffective application or external factors ¹ .

The Evolutionary Perspective

Resistance is a classic example of evolution by natural selection. In any large population of insects, a few individuals may possess random genetic mutations that allow them to survive exposure to an insecticide. When the insecticide is applied, it kills the susceptible individuals, leaving the resistant ones to reproduce and pass on their protective traits.

Evolution of Insecticide Resistance

95% Susceptible

5% Resistant

Initial Population

Insecticide Application

20% Susceptible

80% Resistant

After Multiple Generations

With each generation, the proportion of resistant insects in the population grows, eventually rendering the chemical ineffective ³ . This biological fact forced the industry to accept that chemical control alone was insufficient to overcome an insect population's ability to adapt ¹ .

A Closer Look: Coad's Calcium Arsenate Experiment

The struggle against the cotton boll weevil in the early 20th century provides a perfect case study of the interplay between chemical and biological thinking. The boll weevil, a devastating pest, was known to feed through deep punctures in cotton plants, avoiding poisons that remained on the surface. Early attempts to use Paris green and other arsenicals were largely futile ⁶ . The breakthrough came not from a new chemical, but from a novel biological insight.

The Methodology: Thinking Like a Weevil

In the 1910s, USDA entomologist Bert Raymond Coad developed and tested a new approach based on the insect's behavior ⁶ . His methodology was as follows:

Observation of Behavior

Coad noted that the boll weevil had a habit of drinking from dew or other moisture on the surface of cotton plants.

Hypothesis

He theorized that this behavior could be exploited to poison the insect by contaminating the water it drank, rather than relying on it eating a poisoned part of the plant.

Chemical Selection

After testing various compounds, Coad found that calcium arsenate was more poisonous to the weevil than other arsenicals.

Application Innovation

He recommended that farmers dust their cotton crops at night, when the plants were moist with dew. The calcium arsenate would dissolve in the dew, creating a toxic solution that the weevils would consume.

Results, Analysis, and Impact

Large-scale experiments in Louisiana, Arkansas, and Mississippi in 1917 and 1918 were highly successful. This combination of a specific insecticide and a biologically-informed application technique proved effective in controlling the catastrophic damage caused by the boll weevil ⁶ .

Cotton field affected by boll weevil damage

The success of Coad's method had immediate and far-reaching consequences, cementing the role of insecticides as the primary tool for pest control for decades.

Table 1: Efficacy of Calcium Arsenate Against Boll Weevils

Experimental Factor	Observation & Result
Target Pest	Cotton Boll Weevil
Key Insect Behavior	Drinking dew from plant surfaces
Effective Insecticide	Calcium Arsenate
Critical Application Timing	Night-time (when dew forms)
Mechanism of Action	Poisoning via drinking, not feeding
Outcome	Effective control of previously resistant weevil populations

Table 2: Impact of the New Insecticide Strategy on the Market

Aspect of Industry	Pre-1918 (Before Coad's Experiment)	Early 1920s (After Adoption)
Calcium Arsenate Manufacturers	1 manufacturer	25 manufacturers
Annual Production	~50,000 pounds	Over 10 million pounds
Application Technology	Ground-based dusting	Aerial crop-dusting (e.g., 500,000 acres treated by one company in 1927)
Industry Status	Niche product	Major agricultural chemical

The Scientist's Toolkit: Key Research Reagents and Materials

To study resistance, biologists in industry labs relied on a suite of tools and reagents. These allowed them to move from field observation to controlled experimentation, unraveling the physiological and genetic mechanisms at play.

Table 3: Essential Research Tools for Studying Insecticide Resistance

Tool or Reagent	Function in Resistance Research
Insect Rearing Supplies	Maintaining stable, genetically defined populations of pest insects in the laboratory for bioassays.
Bioassay Equipment	Exposing insects to precise doses of insecticides to measure survival rates and determine lethal concentrations.
Chemical Solvents & Buffers	Preparing accurate solutions and reagents for experiments; maintaining stable pH during biochemical tests ⁴ ⁸ .
Enzyme Assay Kits	Detecting and measuring the activity of metabolic enzymes (e.g., esterases, cytochrome P450s) that can break down insecticides.
Analytical Reagents	Using high-purity chemicals in techniques like chromatography and spectroscopy to identify insecticide residues and metabolites .

Laboratory Analysis

Advanced chemical and biochemical techniques to understand resistance mechanisms

Bioassays

Testing insecticide efficacy on controlled insect populations

Genetic Studies

Identifying the genetic basis of resistance traits

The Legacy: From Chemical Solutions to Integrated Management

The work of biologists in the 1950s and 60s laid the groundwork for a more sustainable approach. The realization that resistance was an inevitable evolutionary response led to a fundamental shift in strategy. It became clear that the goal was not to eliminate a pest entirely, but to manage its population in a way that delayed resistance for as long as possible ¹ ³ .

Rotation

Using insecticides with different modes of action in sequence to avoid continuously selecting for the same resistance trait.

Mixtures

Applying two or more insecticides with different targets simultaneously to reduce selection pressure.

Moderation

Using insecticides only when necessary, and at the minimum effective dose to preserve susceptibility.

Insecticide Resistance Action Committee (IRAC)

This new philosophy culminated in the formation of the Insecticide Resistance Action Committee (IRAC) in 1984. This cross-industry consortium of technical experts was created to provide a coordinated, biological-minded response to resistance on a global scale, a direct legacy of the lessons learned in the preceding decades ³ .

Conclusion: A Lesson in Humility and Integration

The history of tackling insecticide resistance from the 1920s to the 1960s is more than a technical story; it is a lesson in scientific humility. The chemical industry's initial belief in a purely chemical solution was challenged by the relentless force of evolution.

This forced a collaboration between chemistry and biology, leading to a more profound and durable understanding of our relationship with the natural world.

The problem of resistance persists today, but the foundational work of these early industrial biologists ensures that we now fight this ongoing evolutionary battle with a much deeper appreciation for the biology of our adversaries.

Key Insight

Resistance is not a chemical problem but a biological one, rooted in evolutionary processes.

Lasting Impact

The integration of biological thinking transformed pest management from chemical warfare to sustainable population control.