Impacts of hippodamia variegata (col.: coccinellidae) predation and aphidius colemani (hym.: braconidae) parasitism on myzus persicae nicotianae (hem.: aphididae)

Abstract

The tobacco aphid (Myzus persicae nicotianae) is a cosmopolitan pest and one of the major pests of tobacco. Due to its damaging potential, particularly as a vector of virus diseases, management of M. persicae nicotianae relies heavily on chemical control. However, due to insecticide resistance development and ever-stringent regulations on plant protection products in external markets in the First World, it is now clear that an integrated pest management approach which encourages natural enemy activity is needed. This study evaluated the effectiveness of two of the most commonly found tobacco aphid natural enemies in the country, the ladybird beetle, Hippodamia variegata (Coleoptera: Coccinellidae) and the parasitoid, Aphidius colemani (Hymenoptera: Braconidae) as biological control agents of the tobacco aphid. The biology of H. variegata and its aphid predation rates, A. colemani parasitism rate, intraguild predation of the parasitoid by the ladybird, and the effects of some common aphicide sprays on the ladybird were studied. The egg and larval-pupal periods of H. variegata were 2.6 and 12-17 days, respectively. Hippodamia variegata 1st instar larvae could not survive on tobacco leaves due to impeded movement by sticky exudates from leaf trichomes making them less effective in controlling the tobacco aphid. Adult ladybrids, however, proved to be the most effective. A female ladybird had a daily predation rate of 30.2 aphids compared to the male which consumed 5.5 aphids per day. The adult male + female and adult female + 3rd instar larva combinations were equally capable of suppressing tobacco aphid populations as was the female alone. Aphidius colemani developmental period ranged from 12 to 15 days with a mean percent adult emergence of 48.3% and a sex ratio of 1:0.9 (male: female). Adult female lifespan averaged 1.8 days with daily parasitism rate of 10.8 aphids on day 1 and 5 aphids on day 2. Ladybird predation of A. colemani-parasitized aphids occurred during the early stages of parasitoid development but significantly decreased with time after parasitization. Aphicides used for tobacco aphid control vi differed in their effects on H. variegata. Dimethoate 40 EC caused the highest ladybird mortality (100% on both larvae and adults) followed by Acephate 75 SP (52% adult mortality and 22% larval mortality). Acetamiprid applied at 15 g/100 litres did not induce any ladybird mortality. From the findings of this research, it was concluded that H. variegata and A. colemani are efficient biological control agents of M. persicae nicotianae, both individually and in combination and it is recommended that they be conserved in tobacco fields. Thus, selective aphicides like acetamiprid should be used ahead of broad spectrum ones in tobacco production.