Antestia bug

Watch for coffee flowers that dry up and drop without setting berries, green berries that blacken, rot and fall early, and beans that come out shrivelled or marked with dark 'zebra' stripes. Shoot tips may die back and throw out a bushy fan of weak little shoots. The final give-away appears at the mill or in the cup — a raw-potato smell and taste.

is a shield-shaped stink bug about the size of a coffee bean (6–8 mm) — dark brown-to-black but boldly marked with a bright cross of white-cream and orange lines and spots across its back, often with a blue-green metallic shine. Squash one and it gives off a foul stink. The young ones (nymphs — the wingless juveniles before they grow wings) are rounder but just as colourful, and the eggs sit in small clusters on the underside of the leaves.

in the heat of the day it hides deep inside the shady, humid middle of the bush, so search in the cool of early morning. Don't confuse it with the plain brown or green shield bugs that also rest on coffee — antestia is the one wearing the bright white-and-orange cross on its back.

start scouting from flowering and right through the green-berry stage — the mid-to-late-season window — because that is exactly when the bug attacks the flowers and developing berries you are trying to protect. Check every 1–2 weeks through this window, and step it up in warm, humid weather (18–28°C) after rain, when the bug is most active.

cover a large "W" across the block so you check all four corners and the middle, not just the row beside the path. Make about 10 stops along the way, and give extra attention to the bushiest, most heavily shaded trees, which is where antestia loves to hide.

hold an old cloth, a tray or an open feed-sack under a branch, then beat or shake the branch sharply and count the bugs that drop onto it. Do a couple of branches per tree. Working in the cool of early morning shakes down more of them, because the bugs are sluggish and sheltering inside the canopy.

if you find 2 or more antestia bugs on a single tree, that is your signal to treat — this is the level tied to bean damage and the potato-taste defect. Below that, keep scouting and lean on prevention rather than spraying.

The bug thrives in dense, humid shade, so prune and de-sucker — cut out the water-shoots and crowding stems — to open the canopy and let light and air through. Keep any shade trees thinned to a moderate level, and hard-prune or grub out the overgrown, neglected bushes that harbour the bug. A well-pruned, airy coffee bush simply loses the humid refuge antestia needs.

Strip off and destroy the blackened, rotting and dropped berries instead of leaving them lying under the trees — that removes both the ruined beans and the bugs feeding on them.

Tiny parasitic wasps — egg parasitoids, wasps that lay their own eggs inside the bug's eggs and kill them before they hatch — plus other predators quietly keep antestia down for free. Blanket spraying wipes them out, so do not spray unless you have reached the threshold: every needless spray sets you back by killing the very insects that were working for you.

A pyrethroid is a fast contact insecticide (it kills the bug on touch, so you must actually hit it). Use it only when you find 2 or more bugs per tree, and aim into the shaded inside of the bush where the bugs shelter. Safety: cover your skin, eyes, nose and mouth; spray in the cool of morning or evening with the wind at your back; keep it off food, drinking water, children and bees (pyrethroids kill bees and your helpful wasps too); and respect the pre-harvest interval — the set number of days you must wait between spraying and picking so no poison is left on the beans (check the label). Wash yourself and your equipment afterwards.

If you must spray more than once, rotate to a different chemical group each time so the bug does not build resistance (stop being killed by one poison). If the bugs keep coming back after spraying, the real cause is almost always a canopy that is still too dense or overgrown neighbouring trees re-infesting yours — fix it with harder pruning, ideally pruned together with your neighbours at the same time. And when it is genuinely too late — berries already rotted or the potato taste already set in — you cannot rescue those beans; sort out and discard the damaged berries at harvest so a handful of tainted beans does not drag down the price of your whole batch, then prune hard to reset the bushes for next season.