Prodiplosis longifila (Diptera: Cecidomyiidae), evolution as a pest and a method to assess its populations on tomato

Abstract

Since the mid 1980´s, Prodiplosis longifila has become the most important entomological problem for tomato crops in Ecuador. The lack of bioecological knowledge for guiding its rational management has resulted in excessive insecticide usage. Since both the insect and the plant are of neotropical origin, the insect’s recent evolution as a phytosanitary problem raises challenging questions. Population studies including biotic regulatory factors are necessary to answer these questions. One methodological approach consists of estimating the percentage of affected plants, complemented with the number of insects in periodic samples of infested foliage along the crop cycle. The usual method of carrying field samples to the laboratory wrapped in paper towels inside plastic bags was inefficient since many larvae became trapped in the moisture inside the bags or spun their cocoons on the paper towel, making their recovery for rearing to obtain adults and parasitoids time consuming. Thus, taking advantage of the insects’ habit of pupating in the soil, a sample container with sieved soil in the bottom was designed so larvae that completed development could drop to spin their cocoons, which were then easily recovered by sieving. The time economy (5x < time), the number of cocoons obtained from the samples and the adults reared from them (5.0-7.7x>), as well as the higher correlation coefficients (1.2-1.9x>) for cocoons vs. adults and parasitoids reared from containers with soil compared to plastic bags, show the comparative efficacy of this new sampling method.