A network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests.
PestNet is a network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests. It started in 1999. Anyone with an interest in plant protection is welcome to join. PestNet is free and is moderated, ensuring that messages are confined to plant protection.
September 2016. Attached, a picture of what is thought to be an adult female Helicoverpa armigera, but please let me know otherwise. I believe that the particular adult emerged from the larger larva (late instar) of the two in the other picture. I still cannot distinguish between H. armigera and H. zea.
The host plant is the Hawaiian Super Sweet #9 corn. Larvae collected for rearing on the 11 September 2016 and first adult emerged on the 23 September 2016. The larvae were reared from tomato fruits of the same plot which produce similar adults. Should Zea mays be used as guard crop for solanaceous crops targeted by this particular fruit borer?
There was disagreement here. Another member said that they are both good species, the former ‘Old World’ and the latter ‘New World’ and, as far as I know, the only place where both occur are parts of Brazil and southern South America, where H. armigera is recently introduced.
They used to be considered one species, more than 60 years ago, and were often referred to as the American bollworm; the continuing use of that common name outside the Americas has caused some confusion.
In the Pacific only H. armigera is expected to occur, so any possible new record of H. zea would require urgent investigation based on genitalia dissections and barcoding. However, a priori, your material is likely to be H. armigera.
It is generally accepted that corn and tomato are both preferred hosts for H. armigera and it is unlikely that corn is a useful barrier. Crops become attractive for egg laying at flowering and silking. Minimising damage is based on the fact that small larvae do NOT normally bore into fruit. The small larvae just feed on upper tomato leaves or silks. So, you can control H. armigera by scouting crops and good timing of a larvicide while the larvae are still small, before they move down the plants and bore into fruit or cobs.
Bt sprays are effective on tomato crops, it’s a bit harder to get good control in corn because the small larvae are in the silks. Pheromone trapping or degree day calculation can be used for timing of different generations. New Zealand is fortunate in having an effective biocontrol agent, Cotesia kazak, that kills up to 90% of small larvae before they begin boring into fruit. That’s in tomatoes, unfortunately the parasitoid will not go into corn crops.
On the question of a trap crop, sunflower would be the better choice. At flowering, female moths will be attracted to flowering sunflower and thus oviposit on the latter`s heads. Larvicides can then be used to control these and thus minimise damage to the tomato crop.
The sunflower approach contributed to the suppression of Spodoptera litura infestations in South and SE Asian peanut/groundnut crops. Sunflower plants dotted around the field were preferential oviposition sites that also attracted ladybird predators (not sure if it was the egg masses or the plants themselves!). The plants also acted as perches for insectivorous birds (drongos = king crows) that used the plants as spotting platforms in their search for larger caterpillars that escaped the attention of ladybirds on the peanut plants. It was thought that the birds droppings that landed around the sunflower plants were also the nuclei of nuclear polyhedrosis virus mini-epidemics. Data was not collected which was an omission. Application of a conventional insecticide to the sunflowers would of course have messed up the ladybird-driven IPM protocol.