Statements 1, 2, and 4 are correct: Khapra beetle (Trogoderma granarium) is a destructive primary internal feeder of stored grain (1); only the bristled grubs feed voraciously while adults are harmless and short-lived (2); and larvae crawl into structural cracks entering prolonged facultative diapause resistant to ordinary cleaning (4); statement 3 is completely false because Khapra grubs are exceptionally thermophilic and thrive at temperatures well above 35°C to 44°C.

• 1, 2 and 3 only: Incorrect because statement 3 is false.
• and 2 only: Incomplete; statement 4 is also correct.
• 1, 2 and 4 only: Correct code designating the three true statements.
• All of the above statements: Incorrect due to statement 3.

All three insects - Blow flies (family Calliphoridae), Green bottle flies (Lucilia sericata), and Flesh flies (family Sarcophagidae) - are obligate necrophagous/carrion-feeding dipterans that breed in and consume decaying animal carcasses, playing vital roles in forensic entomology.

• Blow flies: Prominent carrion-feeding necrophagous insects.
• Common Green bottle fly: Metallic calliphorid whose maggots feed on carrion and dead tissue.
• Flesh fly: Sarcophagid flies whose viviparous maggots develop in decaying animal flesh.
• All of the above: All three flies are primary carrion feeders.

The Destructive Insects and Pests Act (DIP Act, Act No. II of 1914) was enacted by the Governor-General of India in Council on 3 February 1914 to regulate and prevent the introduction and spread of destructive exotic insects, fungal pathogens, and pests into British India.

• 1911: Year of Imperial Agricultural Research Institute developments.
• 1913: Year preceding the enactment.
• 1914: The statutory year the Destructive Insects and Pests (DIP) Act was passed.
• 1916: Implementation of initial rules under the Act.