D4.3.11 (HL)—Increased insect life cycles
Warmer conditions can shorten insect development, increase annual generations, and intensify outbreaks such as spruce bark beetle attacks on forests.
- Syllabus
- First assessment 2025
- Objective
- D4.3.11
- Level
- HL
Warmer Conditions Can Add Insect Generations
HL onlyMany insects develop faster in warmer conditions within their tolerance range, potentially increasing the number of life cycles per year.
Development rate, survival and winter conditions determine voltinism. More generations can raise herbivory or disease transmission, but heat beyond tolerance can reduce success.
Check temperature range, development threshold, survival and host availability before predicting generation count.; separate driver, mechanism, response and timescale
A pest that formerly produced two generations may produce three in a warmer season, increasing crop exposure. This gives a concrete prediction from the stated climate condition.
Warming does not always help insects; drought, extreme heat and host decline can reverse the effect. Interpret the result within the stated evidence and scenario limits.
HL Timing and Selection
HL onlyHL D4.3 adds timing and evolution. Phenology tracks when seasonal events happen; warming can desynchronize interacting species, shorten insect development, add generations, and change selection pressures so phenotype frequencies shift.
- timing of flowering, migration, breeding, nesting or insect emergence
- interacting species shift timing by different amounts
- warmer temperatures can add generations and attack periods
- milder winters alter selection and phenotype frequencies
HL Phenology and Climate Selection
HL onlyHL climate questions require reasoning from timing to ecological or evolutionary consequence. The answer starts with a seasonal event or life-cycle stage, explains how warming shifts timing or selection pressure, and states the effect on interaction success, number of generations, attack periods, survival, or phenotype frequency.
- Define phenology and identify the seasonal event being shifted.
- Explain timing mismatch or faster development using named examples such as plant-reindeer, great tit-caterpillar, or spruce bark beetles.
- Link climate-altered selection pressure to phenotype frequency change using the tawny owl example.
Concept essentials
- Temperature can control insect development rate and reproductive timing.
- More warm time can allow extra generations or longer attack periods each year.
- Increased insect cycles can amplify damage to forests, crops, or disease-host systems.
ConceptIB Biology HL