Facts about two spotted mites
Hot conditions
Hot and dusty conditions favour two-spotted mite outbreaks. Mites develop and reproduce faster at higher temperatures.
Actually, temperatures above about 32C are too hot even for mites, but mites live on the undersides of leaves in a micro-climate where temperatures are cooler.
Dry conditions
Mites are susceptible to outbreaks of certain fungal diseases that help keep their populations in check.
Epizootics of fungal disease often cause dramatic reductions in spider mite numbers during rainy periods when humidity is high.
Dry conditions interfere with the development of these fungi and allow spider mite populations to increase.
Dusty conditions
Current thoughts are that dusty conditions favour mite outbreaks because the dust that accumulates on plant leaves interferes with the searching ability of predatory mites and insects that prey on spider mites and help keep their numbers in check.
Very fast life cycle
Spider mites have a very fast life cycle. Under optimum conditions mites can complete a generation in as little as six or seven days.
This means that they can complete many generations in a year, and explains why they quickly develop resistance when repeatedly treated with the same miticide.
Eggs
Eggs are laid on the undersides of the leaves, where they hatch into 6-legged larvae.
These larvae molt into 8-legged nymphs, which quickly develop into adults that are able to mate and reproduce.
Mating—gender determination
Female mites are diploid (have one set of chromosomes). Male mites are haploid (have two sets of chromosomes).
When mated, females avoid the fertilisation of some eggs to produce males. Fertilized eggs produce diploid females.
Unmated, unfertilized females lay eggs that are exclusively haploid males.
Egg laying and hatching (continued next month)
See this article in Tree Fruit April 2015
