Comparing different methods for trapping mated queens of weaver ants (Oecophylla longinoda; Hymenoptera: Formicidae)

The predatory efficiency of African weaver ants Oecophylla longinoda and their utilisation in protein production is a function of ant abundance. Reliable control of insect pests in tropical crops is achieved when ant populations are constantly high. Transplanted populations of weaver ant colonies containing egg-laying queens are more stable than those without. Achieving such stability through collection of colonies established in the wild is usually difficult because of uncertainty in locating the nest containing the egg-laying queen. In this study, we investigated four methods that may be used to collect mated queens that subsequently can be used to stock ant nurseries. The catch efficiencies of (1) leaf traps, (2) paper traps (both types providing a refuge for founding queens), (3) random search for queens and (4) light trapping were compared. Light trapping was the most efficient way to collect queens followed by leaf traps, random search and, last, paper traps. Light trapping and random search, though, required the presence of a person throughout the ant's mating season (several months), whereas this was not required when using leaf and paper traps.     

Using insect traps to increase weaver ant (Oecophylla longinoda) prey capture

Weaver ants (Oecophylla spp.) are managed in plantations to control insect pests and are sometimes harvested as a protein‐rich food source. In both cases, the amount of insect prey caught by the ants is imperative for returns, as more prey leads to more effective biocontrol and to a higher production of ants. Malaise‐like traps placed in trees may catch flying insects without catching ants, as ants may use pheromone trails to navigate in and out of the traps. Thus, ants may increase their prey intake if they are able to extract insects caught in traps. In a mango plantation in Tanzania, we estimated the amount of insects caught by simple traps (cost per trap = 3.9 USD), and whether Oecophylla longinoda was able to collect insects from them. On average, a trap caught 110 insects per month without catching any weaver ants. The number of insects found in traps with ant access was 25% lower than in control traps (ants excluded), showing that ants were able to gather prey from the traps. Ant activity in traps increased over time, showing that prey extraction efficiency may increase as ants customize to the traps. The prey removed from traps by ants constituted 5% of the number of prey items collected by O. longinoda under natural conditions (without traps), potentially increasing to 14% if ants learn to extract all insects. Thus, prey intake may be increased with 5–14% per 3.9 USD invested in traps. These numbers increased to 38 and 78%, respectively, when light was used to attract insects during night time. Combining ant predation with insect trapping is a new approach potentially building increased returns to ant biocontrol and to ant entomophagy.     

Efficacy of African weaver ant,Oecophylla longinoda (Hymenoptera: Formicidae) in reducing losses due to frugivorous fruit flies (Diptera: Tephritidae) in smallholder mango production systems in Eastern Tanzania

Fruit flies (Diptera: Tephritidae) are dipteran insects that cause high losses of fruits and vegetables in the tropical and subtropical regions of the world. As quarantine pests, fruit flies affect export markets because trade regulations hamper export of fruits from areas with occurrence of fruit flies. We compared the effectiveness of Oecophylla longinoda with the insecticide; imidacloprid for the control of Bactrocera dorsalis in a 6-year-old orchard of mango cultivar ‘Apple’. Mango samples at different developmental stages were collected between September and November in 2012 and between November 2013 and January 2014 at a three-week interval between sampling dates. Every fruit was cultured in a separate individual plastic container containing approximately 500?g sieved sterilised sand. Three weeks later, larvae and pupae were sieved from sand and counted. In both years, significantly higher (P?<?.0001) incidences and infestation rates were recorded in the control plots when compared to the trees protected with insecticides and O. longinoda. Incidences and infestation rates did not differ significantly (P?>?.05) between insecticide and weaver ants protected fruits, implying that O. longinoda was as effective as imidacloprid in suppressing the population of fruit flies. Peak fruit fly incidences and infestation rates coincided with the ripening stage of mango fruits. Our results have shown that the incidences and infestation rates on incubated mango fruits were lowest in the O. longinoda and the imidacloprid protected trees. Thus, O. longinoda is an effective bio-control agent that could be exploited to serve as a vital Integrated Pest Management component on mango orchards.     

Temporal abundance of African weaver ant,Oecophylla longinoda (Hymenoptera: Formicidae) under unimodal rainfall pattern in Tanzania

Weaver ants, Oecophylla spp., provide adequate protection to crops against insect pests when their populations are high and stable. A study was conducted in a cashew field in Tanzania from November 2012 to October 2014 to determine temporal abundance of O. longinoda. We determined (i) the number of shoots with O. longinoda in a tree (established fortnightly) monitored at four cardinal points of a tree, using 1 m² wooden quadrats, (ii) the percentage of branches with ant trails per tree per month and (iii) the number of visible ant nests within the tree canopy per month. Furthermore, we assessed the association of weather and phenology with O. longinoda populations. More weaver ant populations were recorded during reproductive and vegetative phases of cashew. We recorded significant positive associations between rainfall and temperature with the number of shoots with O. longinoda (p < .001), as well as relative humidity with the number of nests (p < .001). The percentage of shoots with O. longinoda was significantly associated with cashew growth phases. Rainfall and temperature negatively affected the number of nests. Consideration of cashew phenology and weather parameters can greatly enhance successful weaver ant augmentation strategies.     

Control of mango seed weevils (Sternochetus mangiferae) using the African Weaver Ant (Oecophylla longinoda Latreille) (Hymenoptera: Formicidae)

The mango seed weevil, Sternochetus mangiferae (Fabricius), is among the major threats to mango production in Tanzania. Sternochetus mangiferae is primarily a quarantine pest whose presence inside the fruits restricts access to new foreign markets and leads to rejections of fruits destined for export. Management options for the pest have largely been dependent on field sanitation and application of synthetic insecticides with some success. Thus, more sustainable methods are needed to substitute insecticides, as this may also open up opportunities for organic markets. We conducted field experiments for two fruiting seasons in a mango plantation at Mlandizi, Kibaha district, along the coastal belt of Tanzania to evaluate and compare the effectiveness of the predaceous ant Oecophylla longinoda Latreille with foliar insecticidal sprays of Dudumida (70 WDG Imidacloprid) in controlling S. mangiferae. Mango seed weevil infestation was assessed fortnightly based on infestation marks on developing fruits starting eight weeks after fruit set to early ripening phase. Between 50 and 64 fruits were sampled, well labelled in jute bags, secured and transported to the laboratory at Kibaha Biological Control Unit (KBCU) for incubation at room temperature using rearing transparent containers. Two weeks later, the fruits were dissected and inspected for the presence of S. mangiferae developmental stages. Field and laboratory results indicated that fruits from trees that were occupied by O. longinoda and from those treated with insecticide showed significantly (P < 0.0001) lower incidences and infestation rates by S. mangiferae than from untreated trees. Furthermore, there were no significant differences between the insecticide and the weaver ant treatments. We conclude that in our experiments, O. longinoda is an efficient biological control agent for a long‐term control programme and is comparable to insecticide (Dudumida) in suppressing S. mangiferae and may be used in Tanzanian mango plantations.     

Effect of supplementary feeding of Oecophylla longinoda on their abundance and predatory activities against cashew insect pests

Many studies have shown the efficiency of using weaver ants (Oecophylla species) as natural biocontrol agents against agricultural pests. Supplementary feeding could promote fast growth of this ant's population and discourage them from moving away. However, such artificial feeding might slow down ants search rates and in this way make them less efficient bio-agents. The experiments were conducted for two consecutive seasons at Naliendele Research Station. Cashew trees planted at a spacing of 12 m × 12 m in 2002 were used to investigate whether supplementary feeding could enhance foraging behaviour of Oecophylla longinoda. Fed O. longinoda colonies fed weaver ants (FWA) were supplemented with a 30% sugar solution and approximately 22 g of finely ground fish meat at two-week intervals while the unfed colonies unfed weaver ants (UWA) had access to only naturally occurring food sources. Weaver ant densities and pest damage were monitored fortnightly on newly damaged shoots, panicles and fruits and nut yields assessed after each harvest season. The results revealed that there was a significant difference (P < 0.05) with higher weaver ant densities in the FWA compared to UWA colonies and significantly lower (P < 0.05) pest damage levels were recorded on weaver ant treatments compared to plots without weaver ants. No significant differences (P > 0.05) in yields and mean damage levels were recorded between the two weaver ant treatments. Highest nut yield (4.22 ± 0.30 kg/tree and 5.37 ± 0.27 kg/tree) was recorded in the fed colonies, followed by non-fed colonies (4.20 ± 0.30 kg/tree and 4.88 ± 0.24 kg/tree) and the least (2.66 ± 0.19 kg/tree and 2.99 ± 0.19 kg/tree) was recorded from the untreated controls in 2012/2013 and 2013/2014, respectively. The studies indicated that supplementary feeding could boost weaver ants to higher population levels without reducing their effectiveness as biocontrol agents.     

Avermectins and flea control: structure-activity relationships and the selection of selamectin for development as an endectocide for companion animals

Evaluation of a wide range of avermectin derivatives for flea activity in an in vitro feeding screen using the cat flea, Ctenocephalides felis, revealed a narrow structure-activity relationship (SAR) with activity surprisingly associated with monosaccharides and especially their C-5-oximes. We discovered commercially exploitable flea activity in a single compound, selamectin 33, which also possessed the necessary antiparasitic spectrum and margin of safety for development as a broad-spectrum companion animal endectocide.     

Influence of sodium and calcium ions and membrane potential on glutamate receptor desensitization

1. The effects of Na, Ca and membrane potential on desensitization of postjunctional glutamate receptors on locust muscle were investigated. 2. The kinetics of desensitization were measured ionophoretically. 3. Replacement of Na by equimolar concentrations of the permeant cations Li, NH4 and guanidine and the impermeant cation choline accelerated desensitization onset, increased the steady-state leve of desensitization and reduced the rate of recovery from desensitization. 4. Desensitization onset rates and steady-state levels of desensitization were not significantly altered either by changing the extracellular Ca concentration or by changing the membrane potential of voltage clamped muscle fibres.