Pseudonapomyza spicata

Pseudonapomyza spicata (Malloch, 1914)

This species is very similar to Pseudonapomyza spinosa, the only reliable adult difference is the shape of the male genitalia.

Posterior spiracles of larva with 3-5 bulbs, On the segments lie characteristic rows of long spines. However, spines or setae on the segments are variable, sometimes inconspicuous or even absent.
The mines are located in the leaf-blade. The young mines appear silvery whereas the mines of the mature larva become green. This is, because the older larva consumes nearly the whole leaf tissue between the epidermis instead of only one cell layer. The frass is scattered as distinct pellets at the sides of the mine (El-Sherif et al., 1978).

The life history of the species on maize was studied by El-Sherif et al., 1978. According to these authors, the total development of larva and pupa lasts only 12-15 days. The larva hatches 1-3 days after oviposition, the three larval instars complete their development in 2-3 days, pupariation takes place in the soil. The adult fly emerges after a pupation time of 5-11 days. In the laboratory the longevity of the adult flies varied between 1-3 days. The authors (El-Sherif et al., 1978) did not mention whether the adults were supplied with food during the experiment.
In Egypt several subsequent generations throughout the season were observed. The infestation of maize was low at the beginning of the season and increases considerably until August. Spencer stated that in Egypt occur Ps. spicata and Ps. spinosa sympatrically, hence, the preceding results might contain data from both species.
The larva forms narrow leaf mines, particularly at the tip of the leaves in young plants. Further details about the mines are mentioned in the section about the immature stages.

Zea mays L. (maize, corn), Triticum aestivum L. (wheat), Hordeum vulgare L. (barley), Panicum miliaceum L. (millet), Saccharum officinarum L. (sugar cane), Sorghum vulgare (sorghum), Echinochloa colonum Link. (jungle rice), Panicum crus-galli L. (barnyard grass), Panicum dactylon L. (Bermuda grass), Panicum repens L. and other wild grasses.

Pacific: Guam, Hawaii, Bonin, Palau, Iwo Jima, Yap, Marshall Is.; Iraq, Israel, Egypt, Sudan (Spencer, 1973), Japan (K. Ohno, Japan, personal communication).

The species was considered as serious pest of maize (Swezey, 1946, Hammad, 1956, Spencer, 1973, El-Sherif et al., 1978). It is not yet clear, if the main damage is actually caused by Ps. spicata or rather by the closely related species Pseudonapomyza spinosa. Further taxonomical research is necessary.