Renkang K. Peng

Integrated pest management in mango orchards in the Northern Territory Australia, using the weaver ant, Oecophylla smaragdina , (Hymenoptera: Formicidae) as a key element

Mango is the most important commercial fruit crop in the Northern Territory, Australia. Growers currently rely on insecticides to control insect pests of mango, resulting in environmental and social problems. To reduce dependency on insecticides, a suitable IPM programme is needed. Previous work showed that weaver ants can control the major mango insect pests, but they protect soft scales, damage fruits by their formic acid and annoy operatives during fruit harvest. Further research addressing these constraints showed that certain chemicals can reduce soft scale numbers without seriously affecting weaver ant populations, the isolation of ant colonies reduces fruit damage by formic acid, and water spray reduces the ant activity during harvest. A field experiment with two treatments, weaver ants plus soft chemicals (WPS) and weaver ants plus chemical insecticides (CI), was conducted at Howard Springs in the Northern Territory. In two out of the three years, the yield of first class fruit was 20% higher in WPS than in CI. This was mostly explained by lower insect pest damage, lower incidence of mango scab disease and lower infestation of lenticels in WPS. Trees in WPS produced significantly more fruits than in CI in 2002. Overall, trees in WPS resulted in a profit of A

The weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), an effective biological control agent of the red-banded thrips, Selenothrips rubrocinctus (Thysanoptera: Thripidae) in mango crops in the Northern Territory of Australia

14.50/tree per year, but trees in CI produced only A

The effect of colony isolation of the predacious ant, Oecophylla smaragdina (F.) (Hymenoptera: Formicidae), on protection of cashew plantations from insect pests

8.38/tree per year. During harvest, farmers experienced only minor problems with ant disturbance. An IPM model using weaver ants as a key element is discussed with respect to ‘organic’ production.

Distribution of the green ant, Oecophylla smaragdina (F.) (Hymenoptera: Formicidae), in relation to native vegetation and the insect pests in cashew plantations in Australia

Weaver ants, Oecophylla smaragdina (Fabricius), have been successfully used to control the main insect pests of cashew plantations in northern Australia and Papua New Guinea. The red-banded thrips, Selenothrips rubrocinctus (Giard), is an economically important insect pest of mango, Mangifera indica L., orchards in the Northern Territory. This work was undertaken to evaluate whether weaver ants, which are abundant in mango orchards, have the potential to control the red-banded thrips. Field surveys, field experiments and laboratory trials were carried out in four mango orchards in the Darwin area over four years. In field surveys, the number of shoots damaged by the thrips was significantly lower on trees with abundant weaver ants (2.8%) than with fewer ants (21.1%), or without the ants (30.3%). Trees with abundant weaver ants also produced the highest numbers of flower panicles. Leaf examinations revealed that newly mature leaves on trees with abundant weaver ants had significantly fewer thrips than on trees with fewer or no ants. Field experiments showed that weaver ants were as effective as chemical insecticides in limiting fruit damage by thrips. In laboratory trials, seedlings without weaver ants were heavily damaged, and lost all their leaves within six weeks, while seedlings with weaver ants grew well and lost no leaves. This work suggests that the weaver ant is an effective biological control agent of the red-banded thrips, and the use of weaver ants in mango orchards is discussed.

Effective control of Jarvis's fruit fly, Bactrocera jarvisi (Diptera: Tephritidae), by the weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), in mango orchards in the Northern Territory of Australia

Fierce boundary fights between Oecophylla smaragdina colonies were previously identified as the major factor limiting ant populations and the efficiency of ants as biological control agents. In order to determine the feasibility and effect ofpreventing boundary fights between colonies, experiments with full-, semi- and no-isolation of existing antcolonies in cashew plantations were done in 1996 and 1997. In a related experiment, ant colonies were transplanted from native vegetation to a cashew orchard. Trees with ant colonies which were fully isolated from other colonies were significantly less damaged by the main insect pests and produced significantly higher yield than those with ant colonies which were partly isolated or were not isolated. That was because fighting events between fully isolated ant colonies were eliminated, and the populations of these colonies were high throughout the cashew flowering and fruiting period. Trees in which O. smaragdina colonies were transplanted suffered little damage b...

The control efficacy of the weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), on the mango leafhopper, Idioscopus nitidulus (Hemiptera: Cicadellidea) in mango orchards in the Northern Territory

The effect of native vegetation on the distribution of the green ant, Oecophylla smaragdina, and the main insect pests in cashew, Anacardium occidentale, plantations in tropical northern Australia was studied by field surveys and by observations. O. smaragdina was an efficient predator and the most abundant ant species in cashew plantations. Infestations of the main insect pests in the trees lacking ant nests were significantly higher than in those with ant nests. Although O. smaragdina were abundant on a wider range of native tree species, they preferred Acacia aulacocarpa and Planchonia careya, and they also thrived on cashew trees after dispersing into cashew plantations. In cashew plantations, O. smaragdina preferentially colonized trees with thick canopies irrespective of tree height. Fierce fights between O. smaragdina colonies were a major factor responsible for changes in population sizes, colonization and distribution of O. smaragdina in cashew plantations. The availability of preferred native tr...

The effect of the weaver ant, Oecophylla smaragdina (Hymenoptera: Formicidae), on the mango seed weevil, Sternochetus mangiferae (Coleoptera: Curculionidae), in mango orchards in the Northern Territory of Australia

Abstract Jarviss fruit fly, Bactrocera jarvisi (Tryon), is a major insect pest in mango production in the Northern Territory of Australia. Chemical insecticides, together with farming strategies, are effective in reducing fruit fly damage, but have resulted in increased costs, the reduction of natural enemies and environmental pollution. For organic growers, no effective options are available. Weaver ants, Oecophylla smaragdina (Fabricius), are effective in controlling many insect pests in citrus, cashew and mango orchards. To determine whether weaver ants have the potential to control Jarviss fruit fly, field experiments were conducted from 2001 to 2003 at three orchards in northern Australia. Data from a conventional orchard showed that the treatment with weaver ants plus soft chemicals produced lower levels of rejected fruits (0 – 0.4%) than the treatment with chemical insecticides (0.9 – 4.7%). In organic or insecticide-free orchards, fruits were much less damaged on trees with weaver ants (≤1%) than on trees without the ants (1.5 – 5.1%). Fewer fruit fly puparia were produced from fruits collected in the weaver ant treatment (0 – 0.6 puparia/fruit) than from fruits collected in the insecticide treatment (1.2 – 3.7 puparia/fruit). Green mature fruits produced fewer fruit fly puparia (1.2 puparia/fruit) than ripe fruits (3.7 puparia/fruit). More fruit fly adults were observed in the insecticide treatment (0.8 adult/tree) than in the weaver ant treatment (0.2 adult/tree). This work indicates that weaver ants are efficient biocontrol agents of Jarviss fruit fly.

Control threshold analysis for the tea mosquito bug, Helopeltis pernicialis (Hemiptera: Miridae) and preliminary results concerning the efficiency of control by the green ant, Oecophylla smaragdina (Hymenoptera: Formicidae) in northern Australia

Abstract The mango leafhopper, Idioscopus nitidulus (Walker), is one of the most serious mango insect pests in the Oriental region. It was first detected in Darwin in the Northern Territory in 1997, and it has been one of the major mango insect pests since 1998. Successful control can be achieved by conventional growers with regular sprays of chemical insecticides, but no suitable control methods are available for organic growers. Weaver ants, Oecophylla smaragdina (Fabricius), have been used to control the main insect pests in cashew orchards since 1998. Three series of field experiments and five field surveys were conducted from 2001 to 2003 in the Darwin area to evaluate whether weaver ants, which are usually abundant in non-sprayed mango orchards, have the potential to control the mango leafhopper. In the field experiments, an average 3.2% of floral shoots and 10.9% of foliar shoots were damaged in the weaver ant treatment, which was similar to or better than in the insecticide treatment (6.7% of floral shoots and 29.9% of foliar shoots damaged). In the treatment without weaver ants or insecticides, the average damage was 30% for floral shoots and 53.4% for foliar shoots. In the field surveys, an average of 4.4% floral shoots were damaged on trees with abundant weaver ants, while 17.5% were damaged on trees with fewer weaver ants and 18.6% on trees with other ant species or no ants. This work indicates that weaver ants are efficient biocontrol agents of the mango leafhopper, and that it is important to maintain the ants at high levels for successful control of the leafhopper. Various aspects of using weaver ants in mango orchards are discussed.

Locating queen ant nests in the green ant, Oecophylla smaragdina (Hymenoptera, Formicidae)

Abstract The mango seed weevil, Sternochetus mangiferae (Fabricius), is one of the major mango insect pests in northern Australia. A reasonable level of control can be obtained with insecticide sprays together with orchard sanitation, but the only option available for organic growers is the latter. Weaver ants, Oecophylla smaragdina (Fabricius), are effective in controlling the main insect pests in citrus, cashew and mango orchards. To determine whether weaver ants, which are usually abundant in non-sprayed mango orchards, have the potential to control the mango seed weevil, field experiments together with regular monitoring programmes at six orchards in the Northern Territory of Australia were conducted from 2001 to 2003. Data from two conventional orchards showed that the treatment with weaver ants plus soft chemicals produced lower levels of downgraded fruits (<0.5%) compared to the treatment with chemical insecticides (1.4 – 2.1%). In three organic or insecticide-free orchards, fruits were much less damaged on trees with weaver ants (<1%) than on trees without the ants (2.5 – 15.7%). In the sixth orchard, that had much higher mango seed weevil populations than the others, levels of downgraded fruits were lower on trees with abundant weaver ants than on trees with fewer weaver ants. We conclude that weaver ants are efficient biocontrol agents of the mango seed weevil, and that for successful control of the pest it is important both to maintain the ants at high levels and to destroy excess fruits.

The effect of weaver ants Oecophylla smaragdina on the shoot borer Hypsipyla robusta on African mahoganies in Australia

Helopeltis pernicialis damage to a cashew crop was very serious in each of two years, resulting in no harvest unless the trees were protected either by pesticides or biological control agents. A control threshold was determined by a combination of the net income from increased yield and the frequency of insecticide use. A damage level of 1- 5% achieved the highest net profit. A damage level of 6- 10% resulted in yield that was over 73% of the yield of the 1- 5% damage level, but required one third less pesticide application. Therefore, it appears that 6- 10% damage level can be regarded as a control threshold for H. pernicialis . The pre-flowering flush appeared to be the most appropriate time to carry out the monitoring and spray programme to control H. pernicialis . Preliminary results showed that at the time when H. pernicialis caused serious damage to a tree without O. smaragdina nests, a tree with a constant ant population was only slightly damaged, andthe damage level never exceeded the control thre...