Effect of a novel photopesticide on some biological aspects of milkweed bug Spilostethus pandurus (Scopoli), with reference to ultrastructural changes in the midgut

Abstract

The Hemipteran bug Spilostethus pandurus is a serious pest infesting plant seeds. Haematoporhyrin (HPF) was successful as a novel trend for S. pandurus control in the field due to its accumulation inside their organs after incubation and exposure to sunlight in the summer season. The survival rate of nymphs decreased with increasing HPF concentration. A concentration of 1× 10-3 M/l HPF increased the mortality of the first nymphal instar by 6.06- and 3.9-fold after 2 and 3 days as compared to the control, it produced the highest mortality that remained nearly constant throughout most of the 16 days of development. All biological parameters were affected, showing increased nymphal mortality, decreased number of deposited eggs by females and decreased percentage of egg hatchability. Light and electron microscopic studies on midgut regions (mg1-mg4) of adults resulting from treated nymphs revealed severe disorganisation and disintegration of cells and the presence of a great number of vacuoles. The basement membrane was detached. The microvilli were destroyed in the apical part and the food discharged. In addition, cell lysis appeared from mg1 to mg4 and many of cell organelles disappeared. The appearance of autophagic lysosomes was evident together with looped, vacuolated or swollen mitochondria. It seems likely that the nuclear membrane was ruptured or detached and clumping of the chromatin occurred. The muscle fibre and trachea were malformed. The obtained results might reflect the potency of HPF as a novel photoinsecticide in milkweed bug control in an integrated pest management (IPM) programme.