Sheltered Lives

What do leaf miners, wood borers, shoot borers, and internal fruit feeders all have in common? They all have lifestyles which allow them to be sheltered inside their food sources for part of their life cycles. This certainly allows for easy access to their food and also helps to protect them from the extremes of weather. In some cases, this sheltered lifestyle may also help them avoid predators and parasites. However, no matter how protected the shelter, there is always a predatory or parasitic insect that has found a way to break in. There are many species of wasps that parasitize wood boring larvae; determining where their hosts are feeding is no easy matter but on top of that these parasitoids have amazing ovipositors (egg laying organs) with sheaths that can drill through solid wood to the depth of the borers’ galleries. The parasitoids of leaf miners don’t need such penetrating egg laying equipment, just the ability to find their hosts. Oriental fruit moth larvae are often parasitized during the first and second generation by parasitoids of the genus Macrocentrus, but those that escape parasitism early in the year leave offspring that bore into fruit, escaping the relatively short ovipositors of Macrocentrus spp. Insects have been at this deadly game of hide and seek for at least 100 million years.

Growers of fruit, do not, for the most part, have the same kinds of tools that allow them to pursue pests with sheltered lives. There are a few insecticides for fruit with some measure of systemic activity (often limited to translocation through the leaf surface) but many available insecticides work only by contact or through ingestion by the target pest. The window of opportunity for contact or ingestion is often very narrow for pests with a sheltered lifestyle. Many of the more persistent insecticides, which in the past permitted a wide open window of opportunity for treatment, are being lost. Restrictions on the use of older pesticides and “re-evaluations” (usually meaning “loss”) of persistent products may mean that the sheltered pests are regaining an advantage.

There are some simple steps to ensure that sheltered pests (and other pests) do not gain the upper hand in orchards. The most important step in this context is a cornerstone of integrated pest management (IPM) – monitoring. Knowing when pests are active and identifying that narrow window of opportunity for control of pests with sheltered lives is the key to timely application of products or management strategies. This knowledge can best be gained by contracting with qualified crop consultants to regularly and rigorously monitor orchards. Monitoring puts the advantage back on the growers side by giving them the opportunity to act when the pests are most vulnerable. Most pests are site-specific, meaning that monitoring individual orchards gives you the very best information with which to work. Whether you institute a monitoring program yourself or have a crop consultant do the monitoring, the effort will pay dividends in orchard health, crop quality, and management of pests – including those with sheltered lives.