I think of it this way.

Biocide: This product kills everything. Sodium hypochlorite (bleach) is a biocide. It kills bacteria, insects, people, plants, and everything else that cannot escape.

Pesticide: these products are generally not biocides. They are at least somewhat selective. You can have subclasses like rodenticide, herbicide, insecticide, fungicide, and so forth. Pesticides can be synthetic, derivatives of natural products, or natural products.

Biopesticide: like pesticide but restricted to unmodified natural products. I can envision a time when some company will genetically engineer Bacillus thuringiensis. I am not sure if the resulting bt product would be a biopesticide or a pesticide.

 Dear Dr. Timothy,

Thank you so much for your kind opinion. These terms are so confusing to me as so many recently published journal articles have mentioned commercially available pesticide as biocide. Whereas these terms are also confusing according to European legislation and US EPA. When a research article is focusing on agricultural pest control using commercially available pesticide, I am afraid how we are using the term biocide. Similarly, controversy raised among the term using biocide and biopesticide.

In US, FIFRA (EPA) has a specific definition for pesticide.  It also defines fungus as including bacteria.  Don't think EPA offers specific definition  for "biocide" but uses in ref to antimicrobial pesticides.  EPA does define biopesticide - "Biopesticides include naturally occurring substances that control pests (biochemical pesticides), microorganisms that control pests (microbial pesticides), and pesticidal substances produced by plants containing added genetic material (plant-incorporated protectants) or PIPs". 

In US, all biocides and biopesticides are (regulated as) pesticides except for exempted applications (e.g. preservatives in drugs, cosmetics, foods).

Suggest you look at Biocidal Directive for EU considerations - https://echa.europa.eu/regulations/biocidal-products-regulation

In brief Pesticides those are chemical substances that are synthesized to control certain pests, those include insecticides, fungicides, herbicides insect growth regulator, nematicide, termiticide, molluscicide and rodenticides.

Biocide is a chemically synthesized substance that kill every living thing such as the prohibited methyl bromide gas.The US Environmental Protection Agency (EPA)define it  as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products".

Biopesticides, those are living micro organisims that are collected from the nature and mass reared and can be used to control certain pests, Such as certain entomopathogenic bacteria, fungi, or nematodes. 

Pesticides and biocides are functionally defined - they cam be synthetic or natural.  for example - milky spore (spores of Paenibacillus popilliae) are used to treat for Japanese beetles.  Milky spore is a registered pesticide it could also be considered a biopesticide.

https://www3.epa.gov/pesticides/chem_search/ppls/063191-00016-20110217.pdf.

Not aware EPA regulates "biocides" per se.  Methyl bromide is registered as a pesticide. https://www.epa.gov/pesticide-registration/mbcommoditybuffer  Biocides do not "kill every living thing".  That would be Sterilants that EPA regulates specifically.   Preservatives, disinfectants, insecticides -  do not kill every living thing.

 Biocide is a general term which indicates any kind of substance or product having an antibiotic effect and there I speak of the anti-vital aspect that often leads to the death or at least to the inhibition of the target organism , Whatever its biological nature (from prokaryotes to balenes)....

The term pesticide is a somewhat technically specific term because it distinguishes products intended to eliminate or inhibit, and even repel, organisms harmful to plants or to human or animal health.

Biopesticide was introduced in the phytosanitary dictionaries since the famous reputation of the bacteria Bacillus thuringiensis. But a biopesticide can be either a pesticidal substance with an active substance of natural biological origin (nicotine, avermectin ...) or the microorganism qualified as biological control agent, the case of Viruses and entomopathogenic  or nematoparasites fungi..... etc.

Pesticides, in general, include all the chemicals used to either kill or suppress harmful activities of pests, biocides include chemicals which kill every living thing such as cyanide and biopesticides are the living organisms or their products such as NPV and Bt products for killing/disrupting the harmful activities of the pests.

A BIOCIDE is a synthetic pesticide that can kill every form of life; e.g. insects, bacteria, fungi, viruses, nematodes, plants, etc. The term is usually applied for pesticides with extremely high toxicity and aggressive to the environment, such as, Methyl Bromide, Aldicarb (Themic), etc.

A PESTICIDE is a product (natural or synthetic) that can kills a specific pest, or related group of pests. For instance, Malathion is a pesticide used to control fruit flies pests. 

A BIOPESTICIDE is a naturally derived product, or a non-synthetic product that can kill a specific pest. They include microorganisms or their products (toxins). For instance, Bacillus thruringiensis, Metarhizium anisopliae, Beauveria bassian, etc.

Biocide is substance (compound) that kills living organisms, such as plants, animals, fungi, chromista, bacteria. A biocide can be therefore of synthetic or natural (e.g. copper, sulphur) origin. A pesticide kills pest organisms, however, a pesticide is also a  biocide restricted to kill pest organisms. Pests are organisms causing economic damage or harm to to humans.

To simplify, a Biocide is the superset containing a number of subsets like Pesticide and Biopesticide. While, Biopesticide is a subset of Pesticide. In other words, a Pesticide and a Biopesticide are types of Biocide. Similarly, a Biopesticide is a type of pesticide.

Bio-cide: Life-killer: Any material (irrespective of their source or makeup) capable of killing/controlling biological entity.

Pesti-cide: Pest-killer: Any material (‎irrespective of their source or makeup) capable of killing/controlling Pests (this is however subject to your definition of what a pest is).

‎

Bio-pesticide: Any material, ONLY  with biological source‎, capable of killing/controlling Pests (this is also subject to your definition of what a pest is).‎

Hi Nuruzzaman

Some references 1

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=11&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFghYMAo&url=http%3A%2F%2Fwww.hse.gov.uk%2Fpesticides%2Ftopics%2Fpesticide-approvals%2Fpesticides-registration%2Fapplicant-guide%2Fbiopesticides-home.htm&usg=AOvVaw1RTHwDcdvMI5gyd4_cA11x

2

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFghfMAs&url=http%3A%2F%2Fwww.oecd.org%2Fchemicalsafety%2Fpesticides-biocides%2Fbiological-pesticides.htm&usg=AOvVaw3k7Jc-bAh3cthkIZExwV1Z

3

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFghlMAw&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FBiopesticide&usg=AOvVaw3QUiliCV_pR8ZzxhO9hgX3

4

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFghrMA0&url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3130386%2F&usg=AOvVaw1_LJobZArNcISOxnTSs3ek

5

https://books.google.iq/books?id=M5sXBgAAQBAJ&pg=PA152&lpg=PA152&dq=differences+in+pesticide,+biopesticide+and+biocide&source=bl&ots=JxSUm36c25&sig=nVU569pqWApgdSxtx5L1K44k0uE&hl=en&sa=X&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQ6AEIczAO

6

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFgh1MA8&url=https%3A%2F%2Farchive.epa.gov%2Fpesticides%2Fbiopesticides%2Fweb%2Fpdf%2Fsession-1a-mexico-presentation.pdf&usg=AOvVaw3JvTOkwHKAmkKFkgKg0XJk

7

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQFgh7MBA&url=https%3A%2F%2Fwww.epa.gov%2Fingredients-used-pesticide-products%2Ftypes-pesticide-ingredients&usg=AOvVaw1zPpeE3BjAD2yocOJn9nXx

8

https://books.google.iq/books?id=l5lsBAAAQBAJ&pg=PA94&lpg=PA94&dq=differences+in+pesticide,+biopesticide+and+biocide&source=bl&ots=LEeC7YLs1Y&sig=i80Br-AaGklWDfKIxXqpp33A6iI&hl=en&sa=X&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQ6AEIggEwEQ

9

https://books.google.iq/books?id=4Z_HmFR5CCcC&pg=PA3&lpg=PA3&dq=differences+in+pesticide,+biopesticide+and+biocide&source=bl&ots=VbmP6Nw_lq&sig=LLwfsUueA1B84WZ-FmaeKtIl5vI&hl=en&sa=X&ved=0ahUKEwi1iOWZztfYAhVTxaYKHY8QD0gQ6AEIhQEwEg

10

https://books.google.iq/books?id=4Z_HmFR5CCcC&pg=PA3&lpg=PA3&dq=differences+in+pesticide,+biopesticide+and+biocide&source=bl&ots=VbmP6Nw2hk&sig=79Qbz8doFePdg1z0gxaJssAtFeo&hl=en&sa=X&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChDoAQgmMAA

11

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=12&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCCkwAQ&url=https%3A%2F%2Fwww.productsafetylabs.com%2Fpesticides-agrochemicals-and-biocides%2Fmicrobial-pesticides%2F&usg=AOvVaw11N__3mJ_DOAiqByS_L3Ad

12

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=14&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCDEwAw&url=https%3A%2F%2Fwww.eurofins.com%2Fagroscience-services%2Fspecialised-services%2Fbiopesticides-biological-control%2F&usg=AOvVaw2uTbspn3oTyGaxrTzSoArC

13

https://books.google.iq/books?id=WjnNBQAAQBAJ&pg=PA19&lpg=PA19&dq=differences+in+pesticide,+biopesticide+and+biocide&source=bl&ots=femXNCCDgx&sig=rn8rAyRpss7rxWlCHyhC6Sa5X4E&hl=en&sa=X&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChDoAQg3MAQ

14

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCDkwBQ&url=https%3A%2F%2Fec.europa.eu%2Ffood%2Fplant%2Fpesticides_en&usg=AOvVaw2Jwf9Y0-YObHE8KtM2H5dd

15

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCEAwBg&url=http%3A%2F%2Fwww.llojibwe.org%2Fdrm%2Fgreenteam%2Fpesticides_Article.pdf&usg=AOvVaw3UDsGtBrMqfFOWEdW6qXdb

16

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=18&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCEUwBw&url=https%3A%2F%2Ffytoweb.be%2Ffr%2Fproduits-phytopharmaceutiques%2Fusage%2Fproduits-phytopharmaceutiques%2Fproduit-phytopharmaceutique&usg=AOvVaw1IGWRPtUxflWrIH2XFF1Q9

17

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=19&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCE0wCA&url=http%3A%2F%2Fwww.who.int%2Fceh%2Fcapacity%2FPesticides.pdf&usg=AOvVaw1p5tb1CNmX20N_Li3dXaNX

18

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=20&cad=rja&uact=8&ved=0ahUKEwjt19TCz9fYAhWlDpoKHYeEAW84ChAWCFQwCQ&url=https%3A%2F%2Fwww.huffingtonpost.com%2Fandrew-kimbrell%2Fthey-are-biocides-not-pesticides-_b_7205586.html&usg=AOvVaw0UbyR51PBMIAnYAnIZeU9V

19

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=21&cad=rja&uact=8&ved=0ahUKEwjOqLDq0dfYAhUrD5oKHXx4BFQ4FBAWCCYwAA&url=http%3A%2F%2Fwww.gabconsulting.de%2Fbusiness-areas%2Fbiopesticides.html&usg=AOvVaw3UsCBH8ocrqyiZ5UhxpfZu

20

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=22&cad=rja&uact=8&ved=0ahUKEwjOqLDq0dfYAhUrD5oKHXx4BFQ4FBAWCCwwAQ&url=http%3A%2F%2Fwww.cirs-reach.com%2FChina_Chemical_Regulation%2FFAQ_Pesticide_Registration_China.html&usg=AOvVaw3DGz7Vk22n-oAG5iIEf5y4