Food Safety Focus (59th Issue, June 2011) – Food Safety Platform
Pesticides and Pests
Reported by Ms. Joan YAU, Scientific Officer,
Risk Assessment Section, Centre for Food Safety
What are Pesticides?
In simple term, pesticides are chemicals used for killing pests. Generally speaking, pesticide has been considered as any substance or mixture of substances intended for preventing, destroying, repelling or mitigating pests.
Pesticide means any substance intended for preventing, destroying, attracting, repelling, or controlling any pest including unwanted species of plants or animals during the production, storage, transport, distribution and processing of food, agricultural commodities, or animal feeds or which may be administered to animals for the control of ectoparasites. The term includes substances intended for use as a plant growth regulator, defoliant, desiccant, fruit thinning agent, or sprouting inhibitor and substances applied to crops either before or after harvest to protect the commodity from deterioration during storage and transport. The term normally excludes fertilizers, plant and animal nutrients, food additives and animal drugs.
~ Codex Alimentarius Commission
It is clear from the above comprehensive definition that pesticides are substances used for more than killing pests. However, the ultimate goal of applying these pesticides is similar i.e. increase yields. For example, they can be used as plant growth regulators that are natural or synthetic substances for controlling or modifying plant growth processes, e.g. cytokinins (a group of naturally-occurring plant growth regulators that promote cell division, leaf expansion and retard leaf aging) can be used for promoting fruit growth in apple and pistachio. Sometimes farmers may use fruit thinning agents to reduce the number of young fruits so as to increase fruit size and enhance repeat bloom, e.g. the use of carbaryl in apple.
With reference to their usage, pesticides can be grouped under classes as listed in Table 1. Among these pest organisms, it has been reported that herbicide, followed by insecticide, are the most commonly used pesticides in the USA .
Table 1: Classes of pesticides and their target pests or usage 
What are Considered as Pests?
Pests are usually referred to unwanted organisms that may cover a wide range of plants and animals.
A range of organisms are considered as pests. Some of the non-inviting ones are:
(a) Larva of diamond black moth; (b) Flea beetle; (c) Apple snail; (d) Powdery mildew
[Illustrations by courtesy of the Agriculture, Fisheries and Conservation Department]
Pesticides can be derived from different sources and grouped according to their natures: biopesticides and chemical pesticides. Biopesticides are derived from natural materials such as animals, plants and bacteria. Biopesticides commonly used in crop production include microbial pesticides and biochemical pesticides. Chemical pesticides are synthetic chemicals. Some of them, mainly organochorine (OC) pesticides and organophosphate (OP) pesticides , once have raised many eyebrows.