The Agapanthus Borer (Neuranethes spodopterodes) is a medium-sized Owlet Moth (Noctuidae). It feeds exclusively on plants within the Agapanthus genus, as well as hybrids. Adults are most abundant during the warmest periods of the year. Mature female moths lay eggs on inflorescences and leaves. Once hatched, caterpillars attack the buds, boring their way through to the stems, ending their journey at the rhizomes. Plants are left moderately to severely damaged, with possible plant death. In the last ten years, they've spread across east coastal regions, now being established in the Western Cape and Gauteng. They are frost intolerant which has prevented populations from becoming established in other South African locations.
A major pest in horticulture.
Has abundant natural enemies, such as parasitic wasps.
Adults: Moths possess short wings, delicately marbled with browns, whites and greys (wingspan: 3.5cm). The posterior end of the wings shows wavy, silver and grey banding. Each wing displays two grey circles, one large and one small (closest to the head). Larvae: They possess 'greasy' or shiny looking skin. The heads are orange and the body grey with black spots (tubercles). They're rounded and grub-like, growing between 1 and 3cm. Pupae: Normally between 1-3cm, are smooth, shiny and brownish-red in colour. Eggs: Red-pink spherical eggs are laid in clusters on the leaves and buds of plants.
Adult moths hide within plant debris and on the ground in the day. Holes in flowerbuds. Burst buds. Insect frass (excrement) visible on leaves or in plant crevices. Brown circular lesions may be visible on the flower buds. Loss of vigour. Red-pink clusters of eggs laid beneath Agapanthus leaves.
By regularly monitoring the high-risk plants in your garden (see below) you might be able to catch these pests before the damage becomes irreversible. If damage has already been done, not to worry, we've put together some tips and tricks that will help prevent another infestation in the following years. Always try to scarify and plough the soil before doing any planting. This will hopefully reveal any pupae or larvae hiding in the soil. Weeds and plant debris should be cleared two weeks to ten days before planting. Plant checks should be undertaken during the nighttime using a torch, or at dawn, this is when caterpillars will be most active. Likewise, inspect beneath the leaves of Agapanthus for clusters of small, circular-shaped pink-red eggs. Wipe them off as and when they're found. A range of insects and animals eat cutworms. Sometimes it's worth waiting for other insects to take care of your pests if the infestation is considered average. Parasitic wasps and flies use these caterpillars to feed their larvae. Likewise, ground beetles, lacewings, praying mantis, ants, and birds will all eat these insects. Before you sow your seeds, let your chickens loose on your veg patch. They will clear the area of grubs, caterpillars or any overwintering pupae. Diluted neem seed and leaf sprayed onto potato in regular intervals is proposed an effective treatment. Installing protective collars, made from plastic cups, bottles, or paper tubes, etc., can help protect the stems of young plants. Sticky substances are another barrier that can be effective at preventing caterpillars from reaching stems. Diatomite earth, sawdust, or crushed eggshells are substances disliked by caterpillars.
Lastly, there is a whole range of chemical products varying in persistence and toxicity, that can be purchased from a local garden centre. Follow label instructions carefully and always double-check if you are feeling unsure. Be sure you're using the correct volumes of product to water, and using the proper nozzle. It's essential to assess whether the plants are worth saving or not because treatments can result in some resistance build-up in the pest population. Assess the time of the year vs damage. Contact insecticides containing natural plant oils can be more environmentally benign than synthetic pesticides. Look out for products containing natural pyrethrums, fatty acids and plant oils. Synthetic pyrethroids that are available for home use include ingredients: deltamethrin, lambda-cyhalothrin and cypermethrin.