Coptotermes formosanus Shiraki and C. gestroi (Wasmann) are the most widely distributed species of the genus and occur sympatrically in the subtropics. Results of two bioassays in the current study showed that C. gestroi was more aggressive than C. formosanus. In the petri-dish bioassays, C. gestroi won most of the agonistic encounters over C. formosanus. In the two-dimensional foraging arena bioassays, over 73% tunnel interceptions observed in the 18 replications were caused by progressing tunnels of C. gestroi encountering the tunnels of C. formosanus. Tunnel interception of the two species resulted in minor agonistic interactions. Both species quickly buried the connected tunnel at multiple locations. Termite cadavers resulting from agonistic behavior appeared to have induced sand deposition that resulted in tunnel blockages and deterred reopening of these blockages. Sealing individual tunnels in response to encounters with other species acts to prevent further agonism and mortality, and on a broad scale, the aggregate of such blocked tunnels may come to define the borders between adjacent colonies.

1. This study investigates how female seed beetles, Callosobruchus maculatus, distribute their eggs on various‐sized seeds when the size of seed was varied during the egg‐laying period.2. Beetles were allowed to lay eggs on one of three arrays of 64 adzuki beans (Vigna angularis). Each array contained four size classes of seed, ranging from small (5.0–5.5 mm diameter) to large (6.5–7.0 mm), but differed in how they were distributed within the environment. In the most heterogeneous condition (the 64‐patch design), the four sizes were interspersed, while in the least heterogeneous condition (the four‐patch design) they were grouped into four separate blocks. Thus, a beetle exploring the 64‐patch design would frequently encounter all four seed sizes, whereas a beetle exploring the four‐patch design would only rarely encounter a change in bean size.3. Beetles experiencing greater seed size heterogeneity were more likely to lay eggs on larger seeds, whereas those in the blocked condition were more likely to oviposit on small seeds. Beetle responses to seed size heterogeneity suggest that the degree of preference for large seeds depends on a female’s recent experience.4. Female beetles exhibited size discrimination throughout their egg‐laying process; however, there was a trade‐off between seed size and egg discrimination (i.e. avoiding those seeds already containing developing eggs) in response to the change in fitness gained from either laying on larger seeds or lower egg‐load seeds during the egg‐laying process.5. Our model provides the first evidence that evolving seed size discrimination ability is adaptive for the seed beetle with egg‐discrimination ability.

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