Search

Climatic changes, even transient events such as heatwaves, can markedly affect crop-insect interactions. Some insects might be favored or hampered in their development, but less clearcut interactions owing to changes in their needs or in agroecosystem resource availability, including in uncultivated surrounding areas, may mediate insect-crop interactions. In Tanzania, sudden and transient devastation of vegetable fields by crickets — which are usually considered as minor pests — raised this question. In this study, we sought to gain insight into whether sudden increased temperature and alternative food availability could affect the pest status of Gryllidae spp. Feeding damage on cabbage plants was measured under three temperatures in mesocosoms in climatic chambers. Tomato fruits were provided as an alternative food source. We demonstrated that Gryllidae spp. were able to feed on young cabbage, and that the damage level increased with temperature when no alternative food was available. Unexpectedly, the presence of alternative food increases feeding on the young cabbages. This case study highlighted how increased temperature could drive increased pest damage, raising concerns about climatic events that may substantially affect plant production in Africa through the interacting effects with insect herbivory. [ABSTRACT FROM AUTHOR]

Vegetable cultivation in closed tunnels in the Tropics is impeded by high temperatures and poor pollination. This study compared the performance of cucurbits cultivated in open plots, in closed tunnels totally covered with small or large mesh nets (nethouse), and in open tunnels with a plastic film roof (rain shelter) in Tanzania over two seasons. Information was collected on climatic conditions, insect pest populations, vegetative development and yield. Temperatures were significantly higher under the tunnels than in the open plots during the day with few differences between the different tunnels. Insect pest populations were lower under nethouses than in open plots and under rain shelters, especially fruit flies. Higher marketable yields were obtained under nethouses with a small mesh (70.9 and 96.9 t.ha−1) and a large mesh (67.4 and 53.1 t.ha−1) than in open tunnels (12.9 and 9.1 t.ha−1) and in open plots (3.8 and 7.2 t.ha−1). Our results demonstrate that nets, especially with a small mesh size, provide versatile and efficient protection against major insect pests of cucumber, as well as a conducive environment for the development of the crop under local climatic conditions. [ABSTRACT FROM AUTHOR]

The cultivation of vegetables under tunnels is considered a promising alternative to the use of chemicals to manage insect pests. However, higher temperatures under covers hinder their use in warm regions. We investigated the effect of high tunnels covered with plastic film or small or large mesh insect-nets on the performances of tomato plants in Tanzania over two years. Control plants were grown in open field plots. The temperature during the day was 4°C and 15°C higher under the nets and under the plastic than in the open. The total number of insect pests per plant over the season was generally lower under the nets than in open, with the small mesh better than the large mesh. The nets promoted plant growth compared with the open plots, with higher leaf area, plant dry weight, and plant height. Marketable yields were lower in open (2.7 and 10.8 t.ha−1), intermediate under the large mesh (7.9 and 38.4 t.ha−1), and high under the small mesh (16.8 and 50.1 t.ha−1). Higher productivity under the nets was associated with better plant growth and fewer insects than in the open. Contrasting results could be obtained in warmer climates because of the increase in temperatures recorded under tunnels. [ABSTRACT FROM AUTHOR]