Abstract:
The oviposition behaviour of Maruca testul ali s on host plant (cowpea), non-host plant s (cotton and sunhemp), and artificial substrates (filter , butter, crepe, and aluminium foil papers) was observed in laboratory and field. These studies were carried out with the aim of gathe ring data on oviposition behaviour patterns e s pecia l ly on how the ovipositing female inter acts with host pla nts, non- host plants as well as potential artificial oviposition substrates. It was also intended to generate information about the sensory structures involved in this biological activity. Oviposition activities commenced two hours after lights-off increasing to a peak, four hours later. Gravid moths laid eggs on all the plant substrates tested and the preferences were as follows : cowpea > cotton > sunhernp. Among the artificial substrates examined, crepe paper evoked the best oviposition response in choice and non-choice experiments. These results suggest that physical text ur e (mechanical stimuli ) of the oviposition substrate can influence choice of oviposition site in M. testulalis. During the oviposition process, a gravid female displayed several behavioural manoeuvres which included antennae waving, feeding, flight, walking , abdomen bending, pulsating of the terminal abdominal segments, wing twitching, ovipositor tip dragging, and searching with ovipositor tip before egg deposition. These events occurred in various sequences. The deposition of eggs at any one position was immediately followed by flight. The ovipositing moth always chose a new area. Three bouts of oviposition were observed within the six hours observation periods . Most of these activities occurred in the early part of the dark period. Females were generally quiescent in the latter part of the dark period . The pattern of egg distribution within the experimental cages and on the leaf was contagious with a negative binomial distribution. The eggs were laid singly or in loose clusters (2-16 eggs per cluster). The antennae and especially the ovipositor are the main parts of the body involved in locating the site for egg deposition. Light and electron microscopy studies revealed that these structures i.e the antennae and ovipositor are equipped with various types of sensilla. Five main sensilla types including sensil la trichodea, basiconica and coeloconica were found on the female antennae while two main types of sensilla (trichoid chemo mechano-sensilla} were found on the ovipositor tip. Host plant odour, texture of oviposition substrates and components in the plant extracts were found to influence oviposition response of M. testulalis . Cowpea extracts evoked better oviposition responses than cotton and sunhernp extracts. These studies have c reated a basis for further investigations on M. testulalis oviposition behaviour .