In This Section | Notes
on Nut Insects |
| Author: | OMAFRA Staff |
|---|---|
| Creation Date: | 17 May 2006 |
| Last Reviewed: | 17 May 2006 |
Walnut husk maggot (Rhagoletis sp.) is a common pest in Ontario and will infest nut husks of English walnuts, Japanese walnuts and native black walnuts. The adult fly, slightly smaller than a housefly, is light brown in colour. Its wings have a dark cross bar pattern. Husk maggot can be differentiated from other fruit maggot pests by the wing pattern. See Figure 1, Wing Patterns of Walnut Husk Fly Compared to Other Common Fruit Flies. The larvae are a cream colour and grow to 1 cm in length.
Figure 1. Wing Patterns of Walnut Husk Fly Compared to Other Common Fruit Flies
Female adult husk maggot flies lay eggs in the husks
of maturing nuts in late summer and early autumn. The eggs hatch and larvae burrow
into and feed in the husk, which produces black slimy husks that stain the nutshell
black. Larvae may be seen crawling on husks as they move from one nut to another.
Husk maggot overwinter as pupae in the shallow soil and decaying litter under
trees.
Use yellow sticky board traps to monitor when adult husk maggots emerge prior to egg laying. See Suppliers of Pest Monitoring Equipment and Biological Control Agents, on the OMAFRA website.
Husks severely infested with maggot at harvest are very difficult
to remove from the nut, either by hand or by mechanized de-husking machines. This
reduces the crop value. Shell staining makes the nut crop unattractive and undesirable
to growers and consumers. Infested husks may impart off-flavours through the shell
into the nut kernel and spoil -marketability.
The pick up and removal of infested walnuts from the orchard floor as soon as possible after they fall from the trees can achieve some control of husk maggot.
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