Some stem-boring larvae eat any other larvae they encounter. If this occurs with a biological control agent it may be necessary to ensure that larvae occupy separate plant stems during rearing. Only one larva of the cerambycid Nupserha vexator survives in a multi-stemmed Xanthium strumarium plant after larvae from the branches enter the main stem. In mass rearing this can be largely avoided by growing host plants so densely so that only single-stemmed plants are available for the insects.

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