Study of the susceptibility of Sechium edule do fruit flies (Diptera:Tephritidae) in laboratory conditions

Background. #Sechium edule# (chayote) is a cucurbit largely cultivated under arbour in Reunion Island but its production strongly declined in recent years. Farmers attributed the yield losses to fruit flies (Tephritidae, Dacini) (#Bactrocera cucurbitae#, #Dacus ciliatus# and #Dacus demmerezi#). However, observations of chayote fruits taken on arbour and on the ground showed limited damage due to Cucurbit flies. The aim of this study was to assess the susceptibility of S. edule to four fruit flies species (#B .cucurbitae#, #D .ciliatus#, #D .demmerezi#, and #C .rosa#), particularly in studying (i) the growth of eggs laid naturally in fruit by gravid females, and (ii) the growth of larvae artificially deposited in fruit. Methods. Two types of experiments were conducted in 2009 and three types of fruit were compared: #S. edule# (young fruit <10cm and mature fruit >10cm) and #C. pepo# as a control. In the first trial, for each species of flies, fruit (#S. edule# and #C. pepo#) were individually exposed to cohorts including gravid females and the number of pupae obtained and adult flies emerged from each fruit were then counted after two weeks. In a second trial, pieces of fruit were artificially infested by L1 larvae of the four species, and their survival rate was measured during six days. Results. Growth of the four species of flies was better in #C. pepo# than in #S. edule#, especially for #B. cucurbitae# (615 pupae in #C. pepo# versus 0 pupae in #S. edule#) and #D. demmerezi# (445 versus 250 pupae). The mean number of #B. cucurbitae# pupae released from each fruit of #C. pepo# were no significantly different (p>0.05) to #D. demmerezi#. Complete development (eggs to emerged flies) on #S. edule# was observed only for D. demmerezi and D. ciliatus. Nevertheless, D. demmerezi had a better development on S. edule than D. ciliatus, besides its growth was superior in young fruit. Conclusions. These results lead us to learn more about the development of fruit flies in S. edule. The low levels of infestation observed and the difficulties of development for the larvae allowed us to suggest that fruit flies might not be the only cause of damage and yield losses in chayote crop. These results are essential to provide guidelines and to adapt the fruit flies management scheme to the particular case of S. edule crop. (Texte intégral

Agroecological pest management against cucurbit flies (Diptera : Tephritidae) : A case study on la Réunion with large scale farming

Background. Tephritid flies are major economic pests for crop production worldwide. On La Réunion, three species (#Bactrocera cucurbitae#, #Dacus ciliatus# and #D. demmerezi#) cause high yield losses for cucurbits growers. Up to now, control exclusively relied on agrochemistry. Since 2009, CIRAD initiated a three years cooperative program of agro-ecological management of vegetables flies (GAMOUR). This areawide research and extension program gathers twelve local or national organisms specialised in agricultural support. It aims to bring a sustainable methodology to suppress pest populations. i.e. to develop and implement technical innovations that are both economically viable and environmentally friendly. Methods. We designed a technical package based on the existing foreign experiences, and particularly the experience of researchers in Hawaii, with monitoring, sanitation, bait sprays on border crops, male annihilation by mass trapping, conservative biocontrol and agroecological engineering. In pilot areas, vegetables growers were then requested to conduct an initial survey of agricultural practices. They were afterwards proposed the package in September 2009. Since that, the ecological, social and economical impacts were assessed by a weekly monitoring of flies population and a survey of agricultural practices. Results. GAMOUR is currently running in three pilot areas on La Réunion (Salazie, Entre-Deux and Petite Ile), with 27 farmers cumulating about 50 ha of vegetable crops (25% of cucurbits). For most of them, the usual method of protection against flies was purely chemical, with a mean of 1 to 3 insecticide cover sprays per week. Moreover, as the technical package is compatible with organic farming as well, four organic farms were included as pilot sites in Bras-Panon, Etang-Salé, Colimaçons, and Boucan-Canot. After one year, in all three pilot areas, curative treatments based on classical pesticides have been almost totally stopped. Meanwhile, the growers declared minimal yield losses, with a maximum of 20-25% of production, which is similar or less than the damage they used to experience during the same season with chemical practices. A detailed economic evaluation is currently in progress to compare the financial outputs of classical and GAMOUR methods, but the growers already declared their satisfaction about the savings in pesticides costs, the decrease of working time and a significant increase in production. Conclusion. These results demonstrate that an agroecological management approach may be an efficient and sustainable alternative pest control method on La Réunion. One of the main issues of GAMOUR is to support the proper application of the package in pilot areas, in order to stimulate the further extension of the program beyond these areas. Such an approach is part of a global perspective on the evolution of farming practices and a first step to agroecological and sustainable agriculture on La Réunion. (Texte intégral

Impact of fruit flies (Diptera:Tephritidae) on Chayote (Sechium edule) in Reunion Island

Background. Chayote is a popular vegetable in Reunion Island. Traditionally and extensively cultivated for its leaves, it is nowadays usually intensively cultivated under treillises for the production of fruit. A high number of fruit fallen on the ground result in a significant loss in production. Farmers attribute this to three fruit fly species (Bactrocera cucurbitae, Dacus ciliatus and Dacus demmerezi) which roost in the trellises. This situation provokes major insecticide applications in the chayote trellises to combat fruit flies. The present study aimed therefore at evaluating the real incidence of fruit flies in chayote cultivation. Methods. The experiments were conducted in 2008 and 2009 and observations in trellised crops were performed in different sites on the island. In 2008, hundreds of fruit were collected at a single site to study the susceptible stage of the chayote fruit while the development of samples of 20 recently blemished fruit and 20 unblemished fruit was regularly followed in the field. In addition, 120 blemished fruit were collected in 2008 in two sites 20 fruit were weekly collected at a site in 2009 and the emergence of adult flies was measured in the Cirad laboratory over 15 days. In addition, bird nets were placed under the trellis of three fields in 2009 to collect fallen fruit and the number of blemishes and the infestation of the fruit gathered were examined. In the lab, eight chayote fruit were exposed to gravid females per fly species and dissected. Results. In situ, fruit smaller than 6 cm length appeared to be unaffected by female blemishes. Two to four weeks after blemishes under the trellis, the blemished fruit did not show any morphological difference compared to unblemished fruit. This observation was strengthened by the results of emergence tests: only one of 120 blemished fruit collected in 2008 and only five fruit collected from 219 fruit harvested in the crop in 2009 showed emergence of flies. D. ciliatus appeared to be the only species able to emerge not only from these infested fruit collected in the field but also from the fruit exposed to gravid females in the lab. A defence reaction of the fruit to eggs or L1 larvae of B. cucurbitae and D. demmerezi was also observed by dissecting infested fruit in the lab. Finally, other field observations showed that only 13 of 197 fruit fallen from the trellis were infested by larvae, meaning that 93 % of fruit fell for other reasons. Conclusion. This study provides first results on the real incidence of fruit flies in chayote crops in Reunion Island. Although fly adults roost in chayote trellis, these pests are not responsible for the significant production losses recorded by the farmers. This suggests that the chemical protection used against fruit flies in chayote trellis is not appropriate, especially when one considers the secondary negative effects of the chemical treatments. A physiological shedding caused by an overloaded production of fruit under this type of intensive cultivation under trellis could be the main cause of the fruit fall and this requires further research. (Texte intégral

L'augmentorium, un outil de protection agroécologique des cultures. Conception et évaluation en milieu paysan de l'Ile de la Réunion

À La Réunion, la protection des cultures contre les mouches des fruits et des légumes (Diptera, Tephritidae) a pris un virage agroécologique. Dans cette démarche, les mesures prophylactiques reposent sur l'utilisation d'un augmentorium. Il s'agit d'une structure ressemblant à une tente fermée dans laquelle on dépose régulièrement les fruits infestés ramassés au champ. L'augmentorium empêche ainsi la ré-infestation de l'agroécosystème par une nouvelle génération d'adultes de mouches qui émergent dans l'augmentorium, alors qu'un filet à la maille adaptée, placé sur le toit de l'augmentorium, permet de relâcher dans la nature les parasitoïdes des mouches. L'objectif de l'étude est de mettre au point et d'évaluer la technique de l'augmentorium adaptée au contexte de La Réunion. En premier lieu, une enquête montre que, dès qu'elle est correctement présentée et expliquée, la technique de l'augmentorium reçoit un très bon accueil, non seulement de la part des agriculteurs produisant des légumes, mais aussi de la part des particuliers possédant des arbres fruitiers dans leur jardin. Les deux types d'augmentorium qui ont été conçus en concertation avec des agriculteurs, puis fabriqués localement, se révèlent faciles d'emploi et adaptés à la diversité des situations de production. Plusieurs dizaines d'agriculteurs utilisent l'augmentorium depuis 2009 : ils considèrent cette technique simple, efficace, respectueuse de l'environnement et peu consommatrice en coÛt et en temps. À terme, l'utilisation de ce type de technique peut être envisagée aussi bien en ville qu'à la campagne, reliant ainsi protection agroécologique des cultures et écologie urbaine. (Résumé d'auteur

Species diversity within a community of the cucurbit fruit flies Bactrocera cucurbitae, Dacus ciliatus and Dacus demmerezi roosting in corn borders near cucurbit production areas of Reunion Island

In order to better control fruit flies (Diptera: Tephritidae) attacking Cucurbitaceae on Reunion Island (21o6 S/ 55o36 E), biological characteristics (seasonal fluctuation, relative abundance, sex ratio) of communities roosting in corn borders were investigated. The study was conducted in austral summer across a range of altitudes (750-1150 m) corresponding to the main areas of cucurbit cropping. Living adults were recorded roosting on corn planted within or around cucurbit fields. Results showed a high variability in seasonal fluctuation of populations according to local conditions. Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae) was the least abundant species (27%) compared to Dacus ciliatus Loew (36%) and Dacus demmerezi Bezzi (37%). Relative abundance of B. cucurbitae was lowest (< 18%) in high altitude sites (above 1000 m), where D. demmerezi was the most prevalent species (> 56%). Dacus ciliatus showed variable relative abundance (from 18 to 51%) depending on the experimental design (varying in location and in year). Sex ratio was also very variable from one species to another and from one experimental design to another. (Résumé d'auteur

Performance of augmentorium as a sanitation technique against fruit flies (Diptera: tephritidae) in Reunion Island

Background. Tephritid fruit flies cause severe damage to fruit and vegetable crops in Reunion Island. Instead of the curative approach to reduce existing populations, the first step proposed for their management is sanitation. This method is based on an original technique firstly developed by USDA in Hawaii utilizing a tent-like structure called an "augmentorium" which aims to sequester adult flies emerging from infested fruit while allowing the parasitoids to escape, via a net placed at the top of the structure. This study focused on the performance and the efficiency of the augmentorium prototype recently tested in Reunion Island and particularly (i) the number of adult flies that can potentially be sequestered in an augmentorium in the field; (ii) the efficiency of the net mesh for fly sequestration and parasitoid escape; (iii) the feasibility of producing compost with infested fruit collected in the field. Method. The potential number of flies that could be sequestered was estimated by measuring in the lab the emergence of several species of flies from infested fruit collected in the field from 2005 to 2009 in different sites of the island. Emergence of adult flies was measured for six species of flies: (i) Bactrocera cucurbitae, Dacus ciliatus and D. demmerezi attacking three species of Cucurbits (pumpkin: Cucurbita maxima; cucumber: Cucumis sativus and courgette: Cucurbita pepo); (ii) Bactrocera zonata, Ceratitis rosa and C. capitata attacking one species of fruit (mango: Mangifera indica). The sequestration of three of these fly species (B. cucurbitae, B. zonata and C. capitata) and the escape of two of their parasitoids (Psyttalia fletcheri and Fopius arisanus) were assessed in the Cirad laboratory in Saint-Pierre in 2008. Preliminary tests on the feasibility of producing compost were then conducted in Saint-Pierre in 2009, mixing courgette and other components. Results. Collections of infested fruits showed the following means of emerged adults per kg of fruit: 76 for mango (B. zonata, C. rosa, C. capitata); 217 for cucumber, 340 for pumpkin and 594 for courgette (B. cucurbitae, D. ciliatus, D. demmerezi). The efficiency of the mesh chosen for the prototype of augmentorium (hole area 1.96 mm²) proved to be perfectly effective in the lab with 100% of sequestration of adult flies. In the same way, 100% of the parasitoids were able to escape from the mesh if they choose to do so. In addition, we showed that a ratio of 50:30:20 of courgette, sugar cane stem and chicken litter respectively was well adapted to produce compost. Conclusion. These results confirm the relevance and the efficiency of the augmentorium in an agroecological crop protection. As a sanitation technique against fruit flies, the augmentorium sequesters on average several hundreds of adult flies per kg of infested fruit. As a biological control method, it may contribute to increase parasitoid populations which are often low because of the previous and significant pesticide pressure. The augmentorium can also be considered as a useful tool to produce compost in the context of sustainable agriculture. The technique of sanitation using the augmentorium is now well accepted by farmers in pilot areas in Reunion Island. (Texte intégral

Cage study of spinosad-based bait efficacy on Bactrocera cucurbitae, Dacus ciliatus, and Dacus demmerezi (Diptera: Tephritidae) in Reunion Island

On Reunion Island, Bactrocera cucurbitae (Coquillett), Dacus ciliatus (Loew), and Dacus demmerezi (Bezzi) cause severe damage to Cucurbit crops. The aim of the study was to test in field cages the effectiveness of Synéis-appât (Dow AgroSciences), a spinosad-based bait (0.02% of spinosad) on both attraction and mortality of young adults (6-9 d old) of these three species. The effects of gender were also evaluated for all species whereas the effects of protein deprivation were tested with B. cucurbitae only. For the first 15 min after application, significantly more B. cucurbitae adults (21.7 ± 1.8%) were attracted to the bait than D. demmerezi (7.6 ± 2.4%) and D. ciliatus (2.7 ± 1.4%); the subsequent response (30-75 min after bait application) of D. demmerezi was statistically similar to that recorded for B. cucurbitae; whereas the response of D. ciliatus to the bait was consistently significantly lower. Adult mortality was significantly higher for B. cucurbitae (94.6 ± 0.7%) than for D. demmerezi (85.7 ± 2.1%), and was significantly higher for the latter than for D. ciliatus (60.4 ± 4.4%). Sex had no significant effect on the mortality rate for each species. The efficiency of the bait was the same for B. cucurbitae adults regardless whether or not the diet included proteins. Overall, Synéisappât appears to be more effective against B. cucurbitae and B. demmerezi than against D. ciliatus. In Reunion Island, this bait could constitute a useful component in the framework of Integrated Pest Management. (Résumé d'auteur