Difficulties in managing Helicoverpa larvae
The Helicoverpa larva is major crop pest worldwide, but yet it is difficult to control such pest due to the following reasons:
1. As mentioned earlier, both H. armigera and H. punctigera have broader host range. By planting host plants that are susceptible to both species will help to build up their populations. Hence, crops must be carefully selected to avoid attracting adults Helicoverpa spp.
2. All Helicoverpa spp. have high fecundity. Zalucki et al. (1986) quoted that females may lay approximately up to 1400 eggs. In their experiment entitled ‘Comparative life history and fecundity of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) on different soybean varieties’, Naseri et al. (2009) observed that the highest and lowest daily fecundity were 118.92 and 37.88 eggs, respectively in DPX and 356, respectively. This suggests that the high fecundity of Helicoverpa spp. is one of the factors causing difficulties in controlling their populations.
3. Once the larger larvae develop, larvae will make their way into the fruits of host plants. Once these larvae enter the fruits, it is difficult to kill the larvae which are now inside the fruits by spraying insecticides and it is rather time consuming to select the damaged fruits manually.
4. Helicoverpa moths are known to have the ability to fly long distances (Dobson et al. 2002). With their well-developed strong wings, they are capable of migrating greater range in search of food sources and mating during unfavourable conditions.
5. The presence of pupal diapause. In some cases, pupal diapause can be as long as 2 months in unfavourable temperature (Hackett & Gatehouse 1982). Difficulty in controlling the populations occurs when there are overlapping populations, whereby the pupae emerge into adults and incoming adults migrate into the same area. Thus, this makes management more challenging.
6. H. armigera has been able to establish resistance against major classes of chemical insecticides, especially against pyrethroid. McCaffery (1998) reported that H. armigera in Australia, New Zealand, Indonesia, China, India, Pakistan, Africa and Turkey. It was reported that H. punctigera seemed to develop fenvalerate resistance in Australia (Gunning et al. 1997, McCaffery 1998). Insecticide resistance management strategies have been implemented in all of these countries, including Israel, so as to prevent more development of resistance in Helicoverpa species.
1. As mentioned earlier, both H. armigera and H. punctigera have broader host range. By planting host plants that are susceptible to both species will help to build up their populations. Hence, crops must be carefully selected to avoid attracting adults Helicoverpa spp.
2. All Helicoverpa spp. have high fecundity. Zalucki et al. (1986) quoted that females may lay approximately up to 1400 eggs. In their experiment entitled ‘Comparative life history and fecundity of Helicoverpa armigera (Hubner) (Lepidoptera: Noctuidae) on different soybean varieties’, Naseri et al. (2009) observed that the highest and lowest daily fecundity were 118.92 and 37.88 eggs, respectively in DPX and 356, respectively. This suggests that the high fecundity of Helicoverpa spp. is one of the factors causing difficulties in controlling their populations.
3. Once the larger larvae develop, larvae will make their way into the fruits of host plants. Once these larvae enter the fruits, it is difficult to kill the larvae which are now inside the fruits by spraying insecticides and it is rather time consuming to select the damaged fruits manually.
4. Helicoverpa moths are known to have the ability to fly long distances (Dobson et al. 2002). With their well-developed strong wings, they are capable of migrating greater range in search of food sources and mating during unfavourable conditions.
5. The presence of pupal diapause. In some cases, pupal diapause can be as long as 2 months in unfavourable temperature (Hackett & Gatehouse 1982). Difficulty in controlling the populations occurs when there are overlapping populations, whereby the pupae emerge into adults and incoming adults migrate into the same area. Thus, this makes management more challenging.
6. H. armigera has been able to establish resistance against major classes of chemical insecticides, especially against pyrethroid. McCaffery (1998) reported that H. armigera in Australia, New Zealand, Indonesia, China, India, Pakistan, Africa and Turkey. It was reported that H. punctigera seemed to develop fenvalerate resistance in Australia (Gunning et al. 1997, McCaffery 1998). Insecticide resistance management strategies have been implemented in all of these countries, including Israel, so as to prevent more development of resistance in Helicoverpa species.